U.S. patent application number 15/622778 was filed with the patent office on 2018-02-01 for three-level chopper apparatus.
The applicant listed for this patent is FUJI ELECTRIC CO., LTD.. Invention is credited to Yasushi ABE, Motoyoshi KUBOUCHI.
Application Number | 20180034362 15/622778 |
Document ID | / |
Family ID | 61010666 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180034362 |
Kind Code |
A1 |
KUBOUCHI; Motoyoshi ; et
al. |
February 1, 2018 |
THREE-LEVEL CHOPPER APPARATUS
Abstract
A three-level chopper apparatus includes a protection switch
circuit that changes a current pathway through which an overvoltage
is applied to a second capacitor or a first capacitor to a current
pathway through which no overvoltage is applied to the second
capacitor or the first capacitor when a first switch or a second
switch has a failure.
Inventors: |
KUBOUCHI; Motoyoshi;
(Matsumoto-shi, JP) ; ABE; Yasushi; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI ELECTRIC CO., LTD. |
Kawasaki-shi |
|
JP |
|
|
Family ID: |
61010666 |
Appl. No.: |
15/622778 |
Filed: |
June 14, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P 27/06 20130101;
H02M 7/483 20130101; H02M 1/14 20130101; H02M 7/537 20130101; H02M
1/36 20130101; H02M 2001/325 20130101; H02M 1/32 20130101; H02M
3/158 20130101 |
International
Class: |
H02M 1/32 20060101
H02M001/32; H02M 1/14 20060101 H02M001/14; H02M 3/158 20060101
H02M003/158 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 2016 |
JP |
2016-150227 |
Claims
1. A three-level chopper apparatus comprising: a direct-current
power supply; a first switch and a second switch; a first diode and
a second diode; a first capacitor and a second capacitor; a
reactor; a connection path; and a protection switch circuit,
wherein the first diode, the first capacitor, the second capacitor,
the second diode, the second switch, and the first switch are
connected in series to each other in this order in a loop, the
direct-current power supply is connected in parallel between a
connection point between the first diode and the first switch and a
connection point between the second switch and the second diode
through the reactor, the connection path connects a connection
point between the first switch and the second switch and a
connection point between the first capacitor and the second
capacitor, and the protection switch circuit is controllable to
change a current pathway through which an overvoltage is applied to
the second capacitor or the first capacitor to a current pathway
through which no overvoltage is applied to the second capacitor or
the first capacitor when the first switch or the second switch has
a failure.
2. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit is a bidirectional protection switch
connected in series to the connection path.
3. The three-level chopper apparatus according to claim 2, wherein
a diode of the bidirectional protection switch includes a silicon
diode.
4. The three-level chopper apparatus according to claim 2, wherein
a diode of the bidirectional protection switch includes a silicon
carbide diode.
5. The three-level chopper apparatus according to claim 2, wherein
a diode of the bidirectional protection switch includes a diode in
which a silicon diode and a silicon carbide diode are connected in
parallel to each other.
6. The three-level chopper apparatus according to claim 2, wherein
the protection switch circuit includes a first resistance connected
in parallel to the bidirectional protection switch.
7. The three-level chopper apparatus according to claim 2, wherein
the protection switch circuit includes a first protection capacitor
connected in parallel to the bidirectional protection switch.
8. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a first protection switch
connected in series between the first switch and the connection
path, a second protection switch connected in series between the
second switch and the connection path, and a second resistance
connected in parallel between a connection point between the first
switch and the first protection switch and a connection point
between the second protection switch and the second switch.
9. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a third protection switch
connected in series between the first switch and the connection
path, a fourth protection switch connected in series between the
second switch and the connection path, and a second protection
capacitor connected in parallel between a connection point between
the first switch and the third protection switch and a connection
point between the fourth protection switch and the second
switch.
10. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a fifth protection switch
connected in series between the first capacitor and the connection
path, a sixth protection switch connected in series between the
second capacitor and the connection path, and a third resistance
connected in parallel between a connection point between the first
capacitor and the fifth protection switch and a connection point
between the sixth protection switch and the second capacitor.
11. The three-level chopper apparatus according to claim 10,
wherein a resistance value Ra satisfies a following formula (1):
Ra.gtoreq.2.times.(2.times.L/C).sup.1/2 where Ra represents a
resistance value of the third resistance, L represents an
inductance of the reactor, and C represents the smaller of a
capacity of the first capacitor and a capacity of the second
capacitor.
12. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a seventh protection switch
connected in series between the first capacitor and the connection
path, an eighth protection switch connected in series between the
second capacitor and the connection path, and a third protection
capacitor connected in parallel between a connection point between
the first capacitor and the seventh protection switch and a
connection point between the eighth protection switch and the
second capacitor.
13. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a ninth protection switch
connected in series to the reactor, and a fourth resistance
connected in parallel to both ends of the ninth protection
switch.
14. The three-level chopper apparatus according to claim 13,
wherein a resistance value Rb satisfies a following formula (2):
Rb.gtoreq.2.times.(2.times.L/C).sup.1/2 where Rb represents a
resistance value of the fourth resistance, L represents an
inductance of the reactor, and C represents the smaller of a
capacity of the first capacitor and a capacity of the second
capacitor.
15. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes: a tenth protection switch
connected in series to the reactor, and a fourth protection
capacitor connected in parallel to both ends of the tenth
protection switch.
16. The three-level chopper apparatus according to claim 1, wherein
the protection switch circuit includes both: a first protection
switch partial circuit connected in series to the first switch, the
second capacitor, the first diode, or the connection path, and a
second protection switch partial circuit connected in series to the
second switch, the first capacitor, the second diode, or the
connection path.
17. The three-level chopper apparatus according to claim 16,
wherein the first protection switch partial circuit includes an
eleventh protection switch, and is connected in series to the first
switch, the first diode, or the connection path.
18. The three-level chopper apparatus according to claim 16,
wherein the first protection switch partial circuit includes: a
twelfth protection switch, and a fifth resistance connected in
parallel to the twelfth protection switch.
19. The three-level chopper apparatus according to claim 18,
wherein the first protection switch partial circuit is connected in
series to the second capacitor, and a resistance value Rc satisfies
a following formula (3): Rc.gtoreq.2.times.(2.times.L/C2).sup.1/2
where Rc represents a resistance value of the fifth resistance, L
represents an inductance of the reactor, and C2 represents a
capacity of the second capacitor.
20. The three-level chopper apparatus according to claim 16,
wherein the first protection switch partial circuit includes: a
thirteenth protection switch, and a fifth protection capacitor
connected in parallel to the thirteenth protection switch.
21. The three-level chopper apparatus according to claim 16,
wherein the second protection switch partial circuit includes a
fourteenth protection switch, and is connected in series to the
second switch, the second diode, or the connection path.
22. The three-level chopper apparatus according to claim 16,
wherein the second protection switch partial circuit includes: a
fifteenth protection switch, and a sixth resistance connected in
parallel to the fifteenth protection switch.
23. The three-level chopper apparatus according to claim 22,
wherein the second protection switch partial circuit is connected
in series to the first capacitor, and a resistance value Rd
satisfies a following formula (4):
Rd.gtoreq.2.times.(2.times.L/C1).sup.1/2 where Rd represents a
resistance value of the sixth resistance, L represents an
inductance of the reactor, and C1 represents a capacity of the
first capacitor.
24. The three-level chopper apparatus according to claim 16,
wherein the second protection switch partial circuit includes: a
sixteenth protection switch, and a sixth protection capacitor
connected in parallel to the sixteenth protection switch.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The priority application number JP2016-150227, Three-Level
Chopper Apparatus, Jul. 29, 2016, Motoyoshi Kubouchi and Yasushi
Abe, upon which this patent application is based, is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to a three-level chopper
apparatus, and more particularly, it relates to a three-level
chopper apparatus including a first capacitor and a second
capacitor connected in series to each other.
Description of the Background Art
[0003] A three-level chopper apparatus including a first capacitor
and a second capacitor connected in series to each other is known
in general, as disclosed in Japanese Patent Laying-Open No.
9-135589.
[0004] Japanese Patent Laying-Open No. 9-135589 discloses a speed
controller for an induction motor that includes a direct-current
power supply, a reactor, first and second switches including
transistors or the like, first and second capacitors connected in
series to each other, and first and second diodes. In this speed
controller, the reactor and the first and second switches are
connected in series to the direct-current power supply. A series
circuit including the first diode and the first capacitor is
connected to both ends of the first switch, and a series circuit
including the second capacitor and the second diode is connected to
both ends of the second switch. This speed controller further
includes a connection path that connects a connection point between
the first switch and the second switch and a connection point
between the first capacitor and the second capacitor.
[0005] The conventional speed controller described in Japanese
Patent Laying-Open No. 9-135589 is provided with a failure detector
that detects the potential (hereinafter referred to as an
intermediate potential) of a point at which the first capacitor and
the second capacitor are connected in series to each other and
detects the failures of the first capacitor and the second
capacitor based on the detected intermediate potential.
Furthermore, when the conventional speed controller has a failure,
the first switch and the second switch of the speed controller are
generally turned off or a semiconductor switch element of an
inverter provided between the speed controller and a load is
generally turned off such that a current to the load (induction
motor) is interrupted. Consequently, the speed controller is
protected. When one (first switch, for example) of the first switch
and the second switch connected in series to each other has a short
circuit failure in the convention speed controller, for example,
the semiconductor switch element of the inverter is turned off such
that the load is separated from the speed controller, and control
for turning off the other (second switch, for example) of the first
switch and the second switch of the speed controller is
performed.
[0006] When one of the first switch and the second switch has a
short circuit failure in the convention speed controller (chopper
apparatus), the semiconductor switch element of the inverter is
turned off such that the load is separated from the speed
controller. When the other of the first switch and the second
switch of the speed controller is turned off, a series resonant
current flows to the reactor connected to the direct-current power
supply and the capacitor corresponding to the other of the first
and second switches through one of the first and second switches,
which has a short circuit failure, and the connection path in this
speed controller. Thus, the capacitor corresponding to the other of
the first and second switches is disadvantageously charged to a
voltage higher than the voltage of the direct-current power supply
so that an overvoltage occurs on the capacitor.
SUMMARY OF THE INVENTION
[0007] The present invention has been proposed in order to solve
the aforementioned problem, and an object of the present invention
is to provide a three-level chopper apparatus capable of inhibiting
the charging voltage of a capacitor from becoming an overvoltage
even when a failure is generated in a switch.
[0008] In order to attain the aforementioned object, a three-level
chopper apparatus according to an aspect of the present invention
includes a direct-current power supply, a first switch and a second
switch, a first diode and a second diode, a first capacitor and a
second capacitor, a reactor, a connection path, and a protection
switch circuit. The first diode, the first capacitor, the second
capacitor, the second diode, the second switch, and the first
switch are connected in series to each other in this order in a
loop, the direct-current power supply is connected in parallel
between a connection point between the first diode and the first
switch and a connection point between the second switch and the
second diode through the reactor, the connection path connects a
connection point between the first switch and the second switch and
a connection point between the first capacitor and the second
capacitor, and the protection switch circuit is controllable to
change a current pathway through which an overvoltage is applied to
the second capacitor or the first capacitor to a current pathway
through which no overvoltage is applied to the second capacitor or
the first capacitor when the first switch or the second switch has
a failure.
[0009] In the three-level chopper apparatus according to this
aspect of the present invention, as hereinabove described, the
protection switch circuit is controllable to change the current
pathway through which an overvoltage is applied to the second
capacitor or the first capacitor to the current pathway through
which no overvoltage is applied to the second capacitor or the
first capacitor when the first switch or the second switch has a
failure. Thus, even when either the first switch or the second
switch has a failure, the current pathway through which an
overvoltage is applied to the second capacitor or the first
capacitor is changed to the current pathway through which no
overvoltage is applied to the second capacitor or the first
capacitor by the protection switch circuit, and hence the charging
voltage of the first capacitor or the second capacitor can be
inhibited from becoming an overvoltage.
[0010] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit is
preferably a bidirectional protection switch connected in series to
the connection path. When the first switch or the second switch has
a failure, the connection path becomes a part of the current
pathway through which an overvoltage is applied to the second
capacitor or the first capacitor. In view of this point, according
to the present invention, the protection switch circuit is
configured as the bidirectional protection switch connected in
series to the connection path, whereby the connection path that is
a part of the current pathway through which an overvoltage is
applied to the first capacitor or the second capacitor can be
easily changed to the connection path that is a part of the current
pathway through which no overvoltage is applied to the first
capacitor or the second capacitor by the bidirectional protection
switch.
[0011] In this case, a diode of the bidirectional protection switch
preferably includes a silicon diode. According to this structure,
the on-voltage is reduced as compared with the case where the diode
of the bidirectional protection switch includes a silicon carbide
diode, for example, and hence an increase in a power loss can be
suppressed.
[0012] In the aforementioned three-level chopper apparatus
including the bidirectional protection switch, a diode of the
bidirectional protection switch preferably includes a silicon
carbide diode. According to this structure, the forward recovery
voltage can be reduced as compared with the case where the diode of
the bidirectional protection switch includes a silicon diode.
Consequently, the forward recovery voltage is reduced, whereby the
voltage ripple (flow ripple) is reduced such that the noise can be
reduced.
[0013] In the aforementioned three-level chopper apparatus
including the bidirectional protection switch, a diode of the
bidirectional protection switch preferably includes a diode in
which a silicon diode and a silicon carbide diode are connected in
parallel to each other. According to this structure, the on-voltage
can be reduced while the forward recovery voltage can be reduced,
and hence the noise can be reduced while an increase in a power
loss is suppressed.
[0014] In the aforementioned three-level chopper apparatus
including the bidirectional protection switch, the protection
switch circuit preferably includes a first resistance connected in
parallel to the bidirectional protection switch. According to this
structure, when the first switch has a short circuit failure and
control for turning off the bidirectional protection switch is
performed, for example, an LC series resonant current flows through
a pathway from the direct-current power supply through the reactor,
the first switch having a short circuit failure, the first
resistance, the second capacitor, and the second diode to the
direct-current power supply. In this case, the first resistance is
included in this pathway, and hence this pathway forms an LCR
series resonant circuit. A resonant current that flows through this
LCR series resonant circuit undergoes damped oscillation.
Consequently, the amount of charges that flows into the second
capacitor is reduced, and hence occurrence of an overvoltage on the
second capacitor can be suppressed. In this description, the term
"turn on a switch" denotes a state where a current is conducted by
the switch, and the term "turn off a switch" denotes a state where
a conduction path is disconnected (the flow of a current is
blocked) by the switch.
[0015] In the aforementioned three-level chopper apparatus
including the bidirectional protection switch, the protection
switch circuit preferably includes a first protection capacitor
connected in parallel to the bidirectional protection switch.
According to this structure, when the first switch has a shirt
circuit failure and control for turning off the bidirectional
protection switch is performed, for example, an LC series resonant
current flows through a pathway from the direct-current power
supply through the reactor, the first switch having a short circuit
failure, the first protection capacitor, the second capacitor, and
the second diode to the direct-current power supply. In this case,
the first protection capacitor and the second capacitor are charged
through this pathway while sharing charges, and hence occurrence of
an overvoltage on the second capacitor can be suppressed as
compared with the case where only the second capacitor is
charged.
[0016] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a first protection switch connected in series between the
first switch and the connection path, a second protection switch
connected in series between the second switch and the connection
path, and a second resistance connected in parallel between a
connection point between the first switch and the first protection
switch and a connection point between the second protection switch
and the second switch. According to this structure, when the first
switch has a short circuit failure and control for turning off the
first protection switch and turning on the second protection switch
is performed, for example, an LC series resonant current flows
through a pathway from the direct-current power supply through the
reactor, the first switch having a short circuit failure, the
second resistance, the second protection switch, the second
capacitor, and the second diode to the direct-current power supply.
In this case, the second resistance is included in this pathway,
and hence this pathway forms an LCR series resonant circuit. A
resonant current that flows through this LCR series resonant
circuit undergoes damped oscillation. Consequently, the amount of
charges that flows into the second capacitor is reduced, and hence
occurrence of an overvoltage on the second capacitor can be further
suppressed.
[0017] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a third protection switch connected in series between the
first switch and the connection path, a fourth protection switch
connected in series between the second switch and the connection
path, and a second protection capacitor connected in parallel
between a connection point between the first switch and the third
protection switch and a connection point between the fourth
protection switch and the second switch. According to this
structure, when the first switch has a short circuit failure and
control for turning off the third protection switch and turning on
the fourth protection switch is performed, for example, an LC
series resonant current flows through a pathway from the
direct-current power supply through the reactor, the first switch
having a short circuit failure, the second protection capacitor,
the fourth protection switch, the second capacitor, and the second
diode to the direct-current power supply. In this case, the second
protection capacitor and the second capacitor are charged through
this pathway while sharing charges, and hence occurrence of an
overvoltage on the second capacitor can be more reliably suppressed
as compared with the case where only the second capacitor is
charged.
[0018] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a fifth protection switch connected in series between the
first capacitor and the connection path, a sixth protection switch
connected in series between the second capacitor and the connection
path, and a third resistance connected in parallel between a
connection point between the first capacitor and the fifth
protection switch and a connection point between the sixth
protection switch and the second capacitor. According to this
structure, when the first switch has a short circuit failure and
control for turning off the second switch, turning on the fifth
protection switch, and turning off the sixth protection switch is
performed, for example, an LCR series resonant circuit is formed in
a pathway from the direct-current power supply, the reactor, the
first switch having a short circuit failure, the fifth protection
switch, the third resistance, the second capacitor, and the second
diode to the direct-current power supply. Consequently, the amount
of charges that flows into the second capacitor is reduced such
that occurrence of an overvoltage on the second capacitor can be
more effectively suppressed.
[0019] In this case, a resistance value Ra preferably satisfies a
following formula (1): Ra.gtoreq.2.times.(2.times.L/C).sup.1/2
where Ra represents a resistance value of the third resistance, L
represents an inductance of the reactor, and C represents the
smaller of a capacity of the first capacitor and a capacity of the
second capacitor. According to this structure, a current that flows
through the LCR series resonant circuit including the third
resistance having the resistance value Ra can be critically damped
or overdamped, and hence occurrence of an overvoltage on the first
capacitor or the second capacitor can be more reliably suppressed
when the first switch or the second switch has a short circuit
failure.
[0020] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a seventh protection switch connected in series between
the first capacitor and the connection path, an eighth protection
switch connected in series between the second capacitor and the
connection path, and a third protection capacitor connected in
parallel between a connection point between the first capacitor and
the seventh protection switch and a connection point between the
eighth protection switch and the second capacitor. According to
this structure, when the first switch has a short circuit failure
and control for turning off the second switch, turning on the
seventh protection switch, and turning off the eighth protection
switch is performed, for example, an LC series resonant current
flows through a pathway from the direct-current power supply
through the reactor, the first switch having a short circuit
failure, the seventh protection switch, the third protection
capacitor, the second capacitor, and the second diode to the
direct-current power supply. In this case, the third protection
capacitor and the second capacitor are charged through this pathway
while sharing charges, and hence occurrence of an overvoltage on
the second capacitor can be suppressed as compared with the case
where only the second capacitor is charged.
[0021] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a ninth protection switch connected in series to the
reactor, and a fourth resistance connected in parallel to both ends
of the ninth protection switch. According to this structure, when
the first switch or the second switch has a short circuit failure,
control for turning off the ninth protection switch is performed,
whereby the fourth resistance can be added in the current pathway.
Consequently, when the first switch or the second switch has a
short circuit failure, the current pathway can be formed as an LCR
series resonant circuit, and hence occurrence of an overvoltage on
the first capacitor or the second capacitor can be suppressed.
[0022] In this case, a resistance value Rb preferably satisfies a
following formula (2): Rb.gtoreq.2.times.(2.times.L/C).sup.1/2
where Rb represents a resistance value of the fourth resistance, L
represents an inductance of the reactor, and C represents the
smaller of a capacity of the first capacitor and a capacity of the
second capacitor. According to this structure, a current that flows
through the LCR series resonant circuit including the fourth
resistance having the resistance value Rb can be critically damped
or overdamped, and hence occurrence of an overvoltage on the first
capacitor or the second capacitor can be more reliably suppressed
when the first switch or the second switch has a short circuit
failure.
[0023] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes a tenth protection switch connected in series to the
reactor, and a fourth protection capacitor connected in parallel to
both ends of the tenth protection switch. According to this
structure, when the first switch or the second switch has a short
circuit failure, control for turning off the tenth protection
switch is performed, whereby the fourth protection capacitor can be
added in the current pathway. In this case, the fourth protection
capacitor and one of the first and second capacitors are charged
through this pathway while sharing charges, and hence occurrence of
an overvoltage on the first capacitor or the second capacitor can
be suppressed as compared with the case where only the first
capacitor or the second capacitor is charged.
[0024] In the aforementioned three-level chopper apparatus
according to this aspect, the protection switch circuit preferably
includes both a first protection switch partial circuit connected
in series to the first switch, the second capacitor, the first
diode, or the connection path, and a second protection switch
partial circuit connected in series to the second switch, the first
capacitor, the second diode, or the connection path. According to
this structure, when the first switch or the second switch has a
short circuit failure, the first protection switch partial circuit
and the second protection switch partial circuit can effectively
change the current pathway through which an overvoltage is applied
to the first capacitor or the second capacitor to the current
pathway through which no overvoltage is applied to the first
capacitor or the second capacitor.
[0025] In this case, the first protection switch partial circuit
preferably includes an eleventh protection switch, and is
preferably connected in series to the first switch, the first
diode, or the connection path. Thus, when the first switch or the
second switch has a short circuit failure, the eleventh protection
switch is turned off such that the current pathway through which an
overvoltage is applied to the first capacitor or the second
capacitor can be changed to the current pathway through which no
overvoltage is applied to the first capacitor or the second
capacitor.
[0026] In the aforementioned three-level chopper apparatus
including the first protection switch partial circuit, the first
protection switch partial circuit preferably includes a twelfth
protection switch, and a fifth resistance connected in parallel to
the twelfth protection switch. According to this structure, when
the first switch or the second switch has a short circuit failure,
control for turning off the twelfth protection switch is performed,
whereby the fifth resistance can be added in the current pathway.
Consequently, when the first switch or the second switch has a
short circuit failure, the current pathway can be formed as an LCR
series resonant circuit including the fifth resistance, and hence
occurrence of an overvoltage on the first capacitor or the second
capacitor can be suppressed.
[0027] In this case, the first protection switch partial circuit is
preferably connected in series to the second capacitor, and a
resistance value Rc preferably satisfies a following formula (3):
Rc.gtoreq.2.times.(2.times.L/C2).sup.1/2 where Rc represents a
resistance value of the fifth resistance, L represents an
inductance of the reactor, and C2 represents a capacity of the
second capacitor. According to this structure, a current that flows
through the LCR series resonant circuit including the fifth
resistance having the resistance value Rc can be critically damped
or overdamped, and hence occurrence of an overvoltage on the first
capacitor or the second capacitor can be more reliably suppressed
when the first switch or the second switch has a short circuit
failure.
[0028] In the aforementioned three-level chopper apparatus
including the first protection switch partial circuit, the first
protection switch partial circuit preferably includes a thirteenth
protection switch, and a fifth protection capacitor connected in
parallel to the thirteenth protection switch. According to this
structure, when the first switch or the second switch has a short
circuit failure, the thirteenth protection switch is turned off,
whereby the fifth protection capacitor and the first capacitor or
the second capacitor are charged through the current pathway while
sharing charges. Therefore, occurrence of an overvoltage on the
first capacitor or the second capacitor can be suppressed as
compared with the case where only the first capacitor or the second
capacitor is charged.
[0029] In the aforementioned three-level chopper apparatus
including the second protection switch partial circuit, the second
protection switch partial circuit preferably includes a fourteenth
protection switch, and is preferably connected in series to the
second switch, the second diode, or the connection path. According
to this structure, occurrence of an overvoltage on the first
capacitor or the second capacitor can be suppressed similarly to
the case where the first protection switch partial circuit includes
the twelfth protection switch.
[0030] In the aforementioned three-level chopper apparatus
including the second protection switch partial circuit, the second
protection switch partial circuit preferably includes a fifteenth
protection switch, and a sixth resistance connected in parallel to
the fifteenth protection switch. According to this structure,
occurrence of an overvoltage on the first capacitor or the second
capacitor can be suppressed similarly to the case where the first
protection switch partial circuit includes the twelfth protection
switch and the fifth resistance.
[0031] In this case, the second protection switch partial circuit
is preferably connected in series to the first capacitor, and a
resistance value Rd preferably satisfies a following formula (4):
Rd.gtoreq.2.times.(2.times.L/C1).sup.1/2 where Rd represents a
resistance value of the sixth resistance, L represents an
inductance of the reactor, and C1 represents a capacity of the
first capacitor. According to this structure, a current that flows
through the LCR series resonant circuit including the sixth
resistance having the resistance value Rd can be critically damped
or overdamped, and hence occurrence of an overvoltage on the first
capacitor or the second capacitor can be more reliably suppressed
when the first switch or the second switch has a short circuit
failure.
[0032] In the aforementioned three-level chopper apparatus
including the second protection switch partial circuit, the second
protection switch partial circuit preferably includes a sixteenth
protection switch, and a sixth protection capacitor connected in
parallel to the sixteenth protection switch. According to this
structure, occurrence of an overvoltage on the first capacitor or
the second capacitor can be suppressed similarly to the case where
the first protection switch partial circuit includes the thirteenth
protection switch and the fifth protection capacitor connected in
parallel to the thirteenth protection switch.
[0033] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a circuit configuration diagram of a three-level
chopper apparatus according to a first embodiment of the present
invention;
[0035] FIG. 2 is a circuit configuration diagram of a three-level
chopper apparatus according to a modification of the first
embodiment of the present invention;
[0036] FIG. 3 is a circuit configuration diagram of a three-level
chopper apparatus according to second, third, and fourth
embodiments of the present invention;
[0037] FIG. 4 is a circuit configuration diagram of a three-level
chopper apparatus according to a modification of the second
embodiment, the third embodiment, and the fourth embodiment of the
present invention;
[0038] FIG. 5 is a circuit configuration diagram of a three-level
chopper apparatus according to a fifth embodiment of the present
invention;
[0039] FIG. 6 is a circuit configuration diagram of a three-level
chopper apparatus according to a sixth embodiment of the present
invention;
[0040] FIG. 7 is a circuit configuration diagram of a three-level
chopper apparatus according to a seventh embodiment of the present
invention;
[0041] FIG. 8 is a circuit configuration diagram of a three-level
chopper apparatus according to an eighth embodiment of the present
invention;
[0042] FIG. 9 is a circuit configuration diagram of a three-level
chopper apparatus according to a ninth embodiment of the present
invention;
[0043] FIG. 10 is a circuit configuration diagram of a three-level
chopper apparatus according to a tenth embodiment of the present
invention;
[0044] FIG. 11 is a circuit configuration diagram of a three-level
chopper apparatus according to an eleventh embodiment of the
present invention;
[0045] FIG. 12 is a circuit configuration diagram of a three-level
chopper apparatus according to a twelfth embodiment of the present
invention;
[0046] FIG. 13 is a circuit configuration diagram of a three-level
chopper apparatus according to a thirteenth embodiment of the
present invention;
[0047] FIG. 14 is a circuit configuration diagram of a three-level
chopper apparatus according to a fourteenth embodiment of the
present invention;
[0048] FIG. 15 is a circuit configuration diagram of a three-level
chopper apparatus according to a fifteenth embodiment of the
present invention;
[0049] FIG. 16 is a circuit configuration diagram of a three-level
chopper apparatus according to a sixteenth embodiment of the
present invention;
[0050] FIG. 17 is a circuit configuration diagram of a three-level
chopper apparatus according to a seventeenth embodiment of the
present invention;
[0051] FIG. 18 is a circuit configuration diagram of a three-level
chopper apparatus according to an eighteenth embodiment of the
present invention;
[0052] FIG. 19 is a circuit configuration diagram of a three-level
chopper apparatus according to a nineteenth embodiment of the
present invention; and
[0053] FIG. 20 is an example of the circuit configuration of a
three-level chopper apparatus according to an embodiment obtained
by combining the sixth embodiment and the ninth embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0054] Embodiments of the present invention are hereinafter
described with reference to the drawings.
First Embodiment
[0055] The structure of a three-level chopper apparatus 100
according to a first embodiment is now described.
[0056] (Structure of Three-Level Chopper Apparatus According to
First Embodiment)
[0057] This three-level chopper apparatus 100 according to the
first embodiment converts the voltage VE of a direct-current power
supply 8 into direct-current voltages of three levels and outputs
the direct-current voltages from a high potential output terminal
Po, an intermediate potential output terminal Mo, and a low
potential output terminal No, as shown in FIG. 1. The three-level
chopper apparatus 100 is configured as a power converter used in
the industrial field, the railway field, the power generation
field, etc.
[0058] According to the first embodiment, the three-level chopper
apparatus 100 includes the direct-current power supply 8, switches
101 and 102, diodes 103 and 104, capacitors 401 and 402, a chopper
reactor 701 (hereinafter referred to as a "reactor 701"), a
connection path 13, a protection switch 201, and a control circuit
1a, as shown in FIG. 1. The switches 101 and 102 are examples of a
"first switch" and a "second switch" in the claims, respectively.
The capacitors 401 and 402 are examples of a "first capacitor" and
a "second capacitor" in the claims, respectively. The diodes 103
and 104 are examples of a "first diode" and a "second diode" in the
claims, respectively. The protection switch 201 is an example of a
"protection switch circuit" in the claims.
[0059] The diode 103, the capacitor 401, the capacitor 402, the
diode 104, the switch 102, and the switch 101 are connected in
series to each other in this order in a loop. The direct-current
power supply 8 is connected in parallel between a connection point
N1 between the diode 103 and the switch 101 and a connection point
N2 between the switch 102 and the diode 104 through the reactor
701.
[0060] The connection path 13 connects a connection point N3
between the switch 101 and the switch 102 and a connection point N4
between the capacitor 401 and the capacitor 402. According to the
first embodiment, the protection switch 201 is controllable to
change a current pathway R1 through which an overvoltage is applied
to the capacitor 402 or the capacitor 401 to a current pathway R2
through which no overvoltage is applied to the capacitor 402 or the
capacitor 401 when the switch 101 or the switch 102 has a failure.
The structure is now described in concrete terms.
[0061] In the three-level chopper apparatus 100, a switch series
circuit 11 is connected between a positive pole P and a negative
pole N of the direct-current power supply 8 through the reactor 701
connected in series. The switch series circuit 11 is formed by
connecting the switches 101 and 102 including semiconductor switch
elements such as transistors in series to each other.
[0062] Although the reactor 701 is connected to only the positive
pole P of the direct-current power supply in FIG. 1, a reactor 702
may be connected to only the negative pole N in the three-level
chopper apparatus 100, as shown in view (a) of FIG. 2.
Alternatively, the reactors 701 and 702 may be connected to both
the positive pole P and the negative pole N, respectively, in the
three-level chopper apparatus 100, as shown in view (b) of FIG. 2.
When the reactors 701 and 702 are connected to both the positive
pole P and the negative pole N of the direct-current power supply
8, respectively, in the three-level chopper apparatus 100, the two
reactors 701 and 702 may be magnetically coupled to each other, as
shown in view (c) of FIG. 2.
[0063] A capacitor series circuit 41 formed by connecting the
capacitors 401 and 402 in series to each other is connected to both
ends of the switch series circuit 11 through the diodes 103 and
104, respectively.
[0064] The protection switch 201 is connected between the
connection point N3 at which the switches 101 and 102 of the switch
series circuit 11 are connected to each other and the connection
point N4 at which the capacitors 401 and 402 of the capacitor
series circuit 41 are connected to each other.
[0065] According to the first embodiment, the protection switch 201
is a bidirectional protection switch connected in series to the
connection path 13. More specifically, the protection switch 201
includes a switch including a mechanical switching contact or a
semiconductor bidirectional switch formed by connecting two
semiconductor switches in anti-parallel or in anti-series to each
other, and is a switch capable of controlling bidirectional current
flow.
[0066] The output terminals Po and No on both ends of the capacitor
series circuit 41 are connected with a load 9 including an inverter
91 and an electric motor 92. The inverter 91 may be a two-level
inverter or a three-level inverter, as shown in FIG. 1.
[0067] The control circuit 1a includes a CPU, a memory, etc., for
example, and can control each part by running a program or the like
stored in the memory. For example, the control circuit 1a is
connected to the switch 101, the switch 102, and the protection
switch 201, and controls turning on and turning off of each switch
by transmitting a control signal to the switch 101, the switch 102,
and the protection switch 201.
[0068] The control circuit 1a serves as a failure detector. For
example, the control circuit 1a includes an unshown voltage
detector, acquires a detection result of the connection point N4
(intermediate potential) at which the capacitor 401 and the
capacitor 402 are connected in series to each other, and performs
control for detecting the failures of the switches 101 and 102
based on the acquired detection result. For example, the control
circuit 1a performs control for determining that the switch 101 or
102 has a short circuit failure when a value of the intermediate
potential exceeds a range set in advance. Alternatively, for
example, the control circuit 1a includes an unshown current
detector, acquires a value of a current that flows through the
connection path 13, and performs control for detecting the failures
of the switches 101 and 102 based on the acquired current
value.
[0069] (Normal Operation of Three-Level Chopper Apparatus)
[0070] The normal operation of the three-level chopper apparatus
100 is now described with reference to FIG. 1. In the three-level
chopper apparatus 100, the control circuit 1a performs control
processing. As shown in FIG. 1, the protection switch 201 is turned
on during the normal operation of the three-level chopper apparatus
100. When both the switches 101 and 102 are first turned on, a
current flows from the direct-current power supply 8 to the reactor
701 through the switches 101 and 102, and energy is accumulated in
the reactor 701.
[0071] Then, the lower-stage switch 102 is turned off. Thus, a
current flows through a pathway from the direct-current power
supply 8 through the reactor 701, the switch 101, the protection
switch 201, the capacitor 402, and the diode 104 to the
direct-current power supply 8. Thus, the capacitor 402 is charged
by the direct-current power supply 8 and with the energy
accumulated in the reactor 701, and hence the capacitor 402 is
charged to a predetermined voltage higher than the voltage VE of
the direct-current power supply 8.
[0072] Then, the switch 102 is turned on, and the upper-stage
switch 101 is turned off in a state where energy is accumulated in
the reactor 701. Thus, a current flows through a pathway from the
direct-current power supply 8 through the reactor 701, the diode
103, the capacitor 401, the protection switch 201, and the switch
102 to the direct-current power supply 8, and the capacitor 401 is
charged to a predetermined voltage higher than the voltage VE of
the direct-current power supply 8 by the direct-current power
supply 8 and with the energy accumulated in the reactor 701.
[0073] This is repeated such that voltages to which the capacitors
401 and 402 are charged are adjusted, and voltages of two levels
can be extracted from the output terminals Po and No to the load 9
or voltages of three levels can be extracted from the output
terminals Po, Mo, and No to the load 9.
[0074] This three-level chopper apparatus 100 can convert a
direct-current voltage also through the following operation.
[0075] Both the switches 101 and 102 are first turned off, whereby
a current flows through a pathway from the direct-current power
supply 8 through the reactor 701, the diode 103, the capacitor 401,
the capacitor 402, and the diode 104 to the direct-current power
supply 8, and the capacitors 401 and 402 are charged.
[0076] Then, the lower-stage switch 102 is turned on. In this
state, the capacitor 401 is charged with a current that flows
through the pathway from the direct-current power supply 8 through
the reactor 701, the diode 103, the capacitor 401, the protection
switch 201, and the switch 102 to the direct-current power supply
8.
[0077] From this state, the switch 102 is turned off while the
upper-stage switch 101 is turned on such that the capacitor 402 is
charged with the current that flows through the pathway from the
direct-current power supply 8 through the reactor 701, the switch
101, the protection switch 201, the capacitor 402, and the diode
104 to the direct-current power supply 8. Control for turning on
and off the switches 101 and 102 is repeated such that the voltages
to which the capacitors 401 and 402 are charged can be adjusted. In
this case, a voltage between Po and
[0078] Mo and a voltage between Mo and No are lower than the
voltage VE of the direct-current power supply 8 whereas a voltage
between Po and No is higher than VE.
[0079] (Operation of Three-Level Chopper Apparatus During
Failure)
[0080] The operation of the three-level chopper apparatus 100
during the partial failure of the switch series circuit 11 is now
described with reference to FIG. 1. In the three-level chopper
apparatus 100, the control circuit 1a performs control processing.
A case where the switch 101 has a short circuit failure and
conducts (fully conducts, for example), for example, is
described.
[0081] When the switch 101 has a short circuit failure and fully
conducts, the switch 102 is turned off and the operation of the
inverter 91 is stopped immediately after the failure, whereby the
load 9 is separated from the three-level chopper apparatus, and the
protection switch 201 is turned off.
[0082] In this state, the protection switch 201 is turned off, and
hence no current flows through the current pathway R1 but an LC
series resonant current created by the reactor 701 and the
capacitors 401 and 402 flows through the current pathway R2 from
the direct-current power supply 8 through the diode 103, the
capacitor 401, the capacitor 402, and the diode 104 to the
direct-current power supply 8. Then, the capacitors 401 and 402 are
charged with this current. Thus, the sum of the charging voltages
of the capacitors 401 and 402 exceeds the voltage VE of the
direct-current power supply 8 by energy accumulated in the reactor
701. However, the two capacitors 401 and 402 share the summed
voltage, and hence the voltage to which the capacitor 402 is
charged is reduced as compared with the case where the protection
switch 201 does not disconnect the connection path 13 (current
pathway R1), and occurrence of an overvoltage on the capacitor 402
is suppressed.
[0083] Even when the diode 103 and the switch 101 each have a short
circuit failure, the protection switch 201 is turned off such that
the connection path 13 is disconnected, and hence both ends of the
capacitor 401 are inhibited from being short-circuited by the diode
103 and the switch 101, each of which has a short circuit failure,
and the connection path 13. Thus, the failure of the capacitor 401
caused by a short-circuit current can be suppressed.
[0084] [Effects of First Embodiment]
[0085] According to the first embodiment, the following effects can
be obtained.
[0086] According to the first embodiment, as hereinabove described,
the protection switch 201 is controllable to change the current
pathway R1 through which an overvoltage is applied to the capacitor
402 to the current pathway R2 through which no overvoltage is
applied to the capacitor 402 when the switch 101 has a failure.
Preferably, the control circuit 1a performs control for turning on
or off the protection switch 201 such that the current pathway R1
through which an overvoltage is applied to the capacitor 401 or the
capacitor 402 is disconnected when the switch 101 has a failure.
Thus, even when the switch 101 has a failure, the current pathway
R1 through which an overvoltage is applied to the capacitor 402 is
changed to the current pathway R2 through which no overvoltage is
applied to the capacitor 402 by the protection switch 201, and
hence the charging voltage of the capacitor 402 can be inhibited
from becoming an overvoltage.
[0087] According to the first embodiment, as hereinabove described,
the protection switch 201 is configured as the bidirectional
protection switch connected in series to the connection path 13.
When the switch 101 or the switch 102 has a failure, the connection
path 13 becomes a part of the current pathway R1 through which an
overvoltage is applied to the capacitor 402 or the capacitor 401.
In view of this point, according to the first embodiment, the
protection switch 201 is configured as the bidirectional protection
switch connected in series to the connection path 13, whereby the
connection path that becomes a part of the current pathway R1
through which an overvoltage is applied to the capacitor 401 or the
capacitor 402 can be easily changed to the current pathway R2
through which no overvoltage is applied to the capacitor 401 or the
capacitor 402 by the bidirectional protection switch.
[0088] In the first embodiment, a case where the switch 101 or both
the switch 101 and the diode 103 have a short circuit failure has
been described, but also when the switch 102 and/or the diode 104
has a short circuit failure, the protection switch 201 is similarly
turned off such that overvoltages on and the failures of the
capacitors 401 and 402 can be suppressed. Also in the following
embodiments, a case where the switch 101 and the diode 103 have a
short circuit failure is described as an example.
Second Embodiment
[0089] A three-level chopper apparatus 200 according to a second
embodiment is now described with reference to FIGS. 3 and 4.
[0090] According to the second embodiment, the three-level chopper
apparatus 200 includes a protection switch 201a that connects an
intermediate point (connection point N3) of a switch series circuit
11 and an intermediate point (connection point N4) of a capacitor
series circuit 41, as shown in FIG. 3.
[0091] According to the second embodiment, the protection switch
201a is configured as a bidirectional protection switch connected
in series to a connection path 13. The protection switch 201a is an
example of a "protection switch circuit" or a "bidirectional
protection switch" in the claims.
[0092] For example, the protection switch 201a includes two IGBTs
(insulated gate bipolar transistors) 301 and 302 connected in
anti-parallel with diodes 303 and 304, respectively, as shown in
FIG. 3. These IGBTs 301 and 302 are connected in anti-series to
each other. In other words, the protection switch 201a is
configured as a bidirectional switch. A control circuit 1b
transmits a control signal to the protection switch 201a to control
the protection switch 201a.
[0093] A bidirectional switch used as the protection switch 201a
may be constructed by connecting the two IGBTs 301 and 302
connected in series with the diodes 303 and 304 in a forward
direction, respectively, in anti-parallel to each other, as shown
in view (a) of FIG. 4. Alternatively, the protection switch 201a
may include MOSFETs (metal-oxide-semiconductor field-effect
transistors) or bipolar transistors instead of the IGBTs 301 and
302.
[0094] According to the second embodiment, the diodes 303 and 304
include silicon diodes, silicon carbide diodes, or diodes in which
silicon diodes and silicon carbide diodes are connected in parallel
to each other.
[0095] When the diodes 303 and 304 include the silicon diodes, the
diodes 303 and 304 specifically include silicon PN junction diodes
(hereinafter referred to as Si-pn diodes) made of a silicon base
material. When the diodes 303 and 304 include the silicon carbide
diodes, the diodes 303 and 304 specifically include SiC--SB
(Schottky barrier) diodes. When the diodes 303 and 304 include the
diodes in which silicon diodes and silicon carbide diodes are
connected in parallel to each other, the diodes 303 and 304
specifically include diodes in which Si-pn diodes and SiC--SB
diodes are connected in parallel to each other. The remaining
structures of the three-level chopper apparatus 200 according to
the second embodiment are similar to those of the three-level
chopper apparatus 100 according to the aforementioned first
embodiment.
[0096] (Normal Operation According to Second Embodiment)
[0097] The normal operation of the three-level chopper apparatus
200 according to the second embodiment is now described with
reference to FIG. 3. In the three-level chopper apparatus 200, the
control circuit 1b performs control processing. In the three-level
chopper apparatus 200, gates of the IGBTs 301 and 302 of the
protection switch 201a are first turned on (an ON signal is applied
from the control circuit 1b to the gates) such that both the IGBTs
301 and 302 are set in an on-state. Then, control for switching on
or off switches 101 and 102 of the switch series circuit 11 is
performed such that a direct-current voltage can be converted,
similarly to the aforementioned first embodiment.
[0098] In this case, the switch 101 is turned on while the switch
102 is turned off such that a capacitor 402 is charged. In this
state, the IGBT 302 of the protection switch 201a becomes forward
biased, and hence it is required that the gate of the IGBT 302 be
turned on to allow a current to flow therein. On the other hand,
the IGBT 301 becoming reversely biased may be turned off or on
since a current flows through the diode 303.
[0099] The switch 101 is turned off while the switch 102 is turned
on such that a capacitor 401 is charged. In this state, the IGBT
301 of the protection switch 201a becomes forward biased, and hence
it is required that the gate of the IGBT 301 be turned on to allow
a current to flow therein. On the other hand, the IGBT 302 becoming
reversely biased may be turned off or on since a current flows
through the diode 304.
[0100] In a mode (period) in which both the switches 101 and 102
are turned on or off, no current flows through the protection
switch 201a. In this period, the gates of the two IGBTs 301 and 302
of the protection switch 201a are turned on. Thus, in the period in
which no current flows through the protection switch 201a during
the normal operation of the three-level chopper apparatus 200, the
gates of the two IGBTs 301 and 302 of the protection switch 201a
are turned off such that accumulation of charges in the gates of
the IGBTs 301 and 302 of the protection switch 201a can be
suppressed. When the gates of the IGBTs 301 and 302 are turned off
after the elapse of an appropriate period of time from switching on
or off the switches 101 and 102, accumulation of charges in the
gates can be suppressed while influence on chopper operation is
limited.
[0101] When the diodes 303 and 304 include the silicon diodes, a
current momentarily commutates and a reverse bias is applied to the
diodes 303 and 304 if a current that flows through the diodes 303
and 304 is interrupted by switching the switches 101 and 102 during
the above normal operation. However, the reverse bias is several
volts substantially equal to the saturation voltages of the IGBTs
301 and 302, and no bias is applied in a steady state in which the
transient response is finished. In this case, almost no reverse
recovery loss is generated in the three-level chopper apparatus 200
according to the second embodiment.
[0102] When the diodes 303 and 304 include the silicon carbide
diodes, the forward recovery voltage can be reduced during the
above normal operation as compared with the case where the Si-pn
diodes are used. Thus, the voltage ripple (flow ripple) is reduced
such that the noise can be reduced.
[0103] (Operation During Failure According to Second
Embodiment)
[0104] The operation of the three-level chopper apparatus 200
during the partial failure of the switch series circuit 11 is now
described with reference to FIG. 3. In the three-level chopper
apparatus 200, the control circuit 1b performs control processing.
A case where the switch 101 has a short circuit failure and fully
conducts, for example, is described.
[0105] According to the second embodiment, when the switch 101 of
the switch series circuit 11 has a short circuit failure, the gates
of the IGBTs 301 and 302 are turned off such that the protection
switch 201a is turned off. Thus, the connection path 13 is
disconnected, and charging of the capacitor 402 with an LC series
resonant current created by the capacitor 402 and a reactor 701 can
be suppressed. Thus, overvoltage charging to the capacitor 402 can
be suppressed. At this time, it is particularly necessary to turn
off the gate of the IGBT 302 of the protection switch 201a that
becomes forward biased, but it is safe to turn off both the gates
of the IGBTs 301 and 302.
[0106] [Effects of Second Embodiment]
[0107] According to the second embodiment, the following effects
can be obtained.
[0108] According to the second embodiment, as hereinabove
described, the silicon diodes are provided in the protection switch
201a. Thus, the on-voltage is reduced as compared with the case
where the silicon carbide diodes are provided in the protection
switch 201a, and hence an increase in a power loss can be
suppressed.
[0109] According to the second embodiment, as hereinabove
described, the silicon carbide diodes are provided in the
protection switch 201a. Thus, the forward recovery voltage can be
reduced as compared with the case where the silicon diodes are
provided in the protection switch 201a. Consequently, the forward
recovery voltage is reduced in the three-level chopper apparatus
200, whereby the voltage ripple (flow ripple) is reduced such that
the noise can be reduced.
[0110] According to the second embodiment, as hereinabove
described, the diodes in which silicon diodes and silicon carbide
diodes are connected in parallel to each other are provided in the
protection switch 201a. Thus, in the three-level chopper apparatus
200, the on-voltage can be reduced while the forward recovery
voltage can be reduced, and hence the noise can be reduced while an
increase in a power loss is suppressed.
[0111] The remaining effects of the three-level chopper apparatus
200 according to the second embodiment are similar to those of the
three-level chopper apparatus 100 according to the aforementioned
first embodiment.
Third Embodiment
[0112] A three-level chopper apparatus 300 according to a third
embodiment is now described with reference to FIG. 3 and view (b)
of FIG. 4.
[0113] According to the third embodiment, the three-level chopper
apparatus 300 includes a protection switch 201b inserted into a
connection path 13 that connects an intermediate point (connection
point N3) of a switch series circuit 11 and an intermediate point
(connection point N4) of a capacitor series circuit 41 and a
control circuit 1c (see FIG. 3), as shown in view (b) of FIG.
4.
[0114] According to the third embodiment, the protection switch
201b is constructed by connecting two reverse blocking IGBTs 305
and 306 in anti-parallel to each other. The control circuit 1c
serves as a short circuit detector. The control circuit 1c detects
the short circuit failure of a switch 101 when the switch 101 has a
short circuit failure, and performs control for turning off a gate
of the reverse blocking IGBT 306 of the protection switch 201b to
disconnect the connection path 13. The remaining structures and
operation of the three-level chopper apparatus 300 according to the
third embodiment are similar to those of the three-level chopper
apparatus 200 according to the aforementioned second
embodiment.
[0115] [Effects of Third Embodiment]
[0116] According to the third embodiment, the following effects can
be obtained.
[0117] According to the third embodiment, as hereinabove described,
the protection switch 201b is constructed by connecting the reverse
blocking IGBTs 305 and 306 in anti-parallel to each other. Thus,
according to the aforementioned second embodiment (the structure in
which the IGBTs and the diodes are provided in anti-parallel), when
the protection switch 201a is turned on, a current must flow
through the two elements, i.e. one of the IGBTs and the other diode
that is not the corresponding diode. On the other hand, the
protection switch 201b according to the third embodiment is
constructed by connecting the two IGBTs 305 and 306 having a
reverse blocking function in anti-parallel to each other, and hence
a current flows through only one element. Thus, a power loss in the
three-level chopper apparatus 300 can be reduced as compared with
the three-level chopper apparatus 200 according to the second
embodiment.
[0118] According to the third embodiment, as hereinabove described,
the control circuit 1c serves as the short circuit detector. In
this short circuit detector, a device (circuit) that detects a
switch element having a short circuit failure is incorporated. When
the switch 101 has a short circuit failure, the control circuit 1c
performs control for turning off the gate of the reverse blocking
IGBT 306 of the protection switch 201b and disconnecting the
connection path 13. Thus, when the switch 101 has a short circuit
failure, the gate of the reverse blocking IGBT 305 becoming
reversely biased is turned on, and hence current leakage can be
further reduced as compared with the gate of the reverse blocking
IGBT 305 is turned off.
[0119] Furthermore, in the three-level chopper apparatus, the
device that detects the switch element having a short circuit
failure is incorporated into the control circuit 1c that serves as
the short circuit detector so as to detect the failed switch
element, whereby when the switch element has a failure, which of
the reverse blocking IGBTs 305 and 306 of the protection switch
201b is turned on and which of the reverse blocking IGBTs 305 and
306 is turned off can be easily controlled. The remaining effects
of the three-level chopper apparatus 300 according to the third
embodiment are similar to those of the three-level chopper
apparatus 200 according to the aforementioned second
embodiment.
Fourth Embodiment
[0120] A three-level chopper apparatus 400 according to a fourth
embodiment is now described with reference to FIG. 3 and view (c)
of FIG. 4.
[0121] According to the fourth embodiment, a protection switch 201c
constructed by connecting MOSFETs 307 and 308 in anti-series to
each other is arranged between an intermediate point (connection
point N3) of a switch series circuit 11 and an intermediate point
(connection point N4) of a capacitor series circuit 41 in the
three-level chopper apparatus 400, as shown in view (c) of FIG. 4.
Also when reverse conducting IGBTs are used instead of the MOSFETs,
the same behavior is exhibited. When the reverse conducting IGBTs
with both the functions of an IGBT and a freewheeling diode are
used in one chip, it is not necessary to connect the diodes 303 and
304 according to the second embodiment, and hence the three-level
chopper apparatus 400 can be downsized.
[0122] The three-level chopper apparatus 400 includes a control
circuit 1d. According to the fourth embodiment, the control circuit
1d controls the MOSFETs 307 and 308 to perform synchronous
rectification during a period in which a current flows through a
connection path 13 in the three-level chopper apparatus 400. The
remaining structures of the three-level chopper apparatus 400
according to the fourth embodiment are similar to those of the
three-level chopper apparatus 100 according to the aforementioned
first embodiment.
[0123] (Operation of Three-Level Chopper Apparatus According to
Fourth Embodiment)
[0124] In the three-level chopper apparatus 400 according to the
fourth embodiment, the control circuit 1d performs control
processing. During the normal operation of the three-level chopper
apparatus 400, gates of both the MOSFETs 307 and 308 of the
protection switch 201c are turned on such that the protection
switch 201c is turned on. In an operation mode (operation period)
in which a current flows through the connection path 13 that
connects the intermediate point (connection point N3) of the switch
series circuit 11 and the intermediate point (connection point N4)
of the capacitor series circuit 41, synchronous rectification is
performed in a state where the gate of the MOSFET 307 or 308 of the
protection switch 201c that becomes forward biased is turned on to
allow a current to flow therein while the gate of the MOSFET 307 or
308 that becomes reversely biased is also turned on such that the
MOSFET 307 or 308 conducts. When the gate of the MOSFET 307 or 308
that becomes reversely biased is turned off, a current flows
through a body diode of the MOSFET 307 or 308, but a power loss is
increased, and hence the gate of the MOSFET 307 or 308 is
preferably turned on.
[0125] In an operation mode (operation period) in which no current
flows through the connection path 13 of the three-level chopper
apparatus, the gates of the MOSFETs 307 and 308 may be turned off
to turn off the protection switch 201c. Also during normal
operation, when the gates of the MOSFETs 307 and 308 of the
protection switch 201c are turned off in a period in which the
operation of the chopper apparatus is not influenced, accumulation
of charges in the gates can be suppressed. When the gates of the
MOSFETs 307 and 308 are turned off, an appropriate period of time
for switching is provided after switching on or off of switches 101
and 102 such that the operation of the three-level chopper
apparatus 400 is not influenced. When the synchronous rectification
function of the MOSFETs 307 and 308 is utilized, the number of
diodes elements can be reduced as compared with the case where
MOSFET modules in which diodes are connected in anti-parallel are
used, and hence the structure of the three-level chopper apparatus
400 can be simplified.
[0126] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus, for
example, the connection path 13 is disconnected by turning off the
gates of the MOSFETs 307 and 308 to turn off the protection switch
201c. At this time, it is particularly necessary to always turn off
the gate of the MOSFET of the protection switch 201c that becomes
forward biased to turn off the protection switch 201c. When the
gates of both the MOSFETs 307 and 308 are tuned off, the control is
facilitated.
[0127] [Effects of Fourth Embodiment]
[0128] According to the fourth embodiment, the following effects
can be obtained.
[0129] According to the fourth embodiment, as hereinabove
described, the protection switch 201c constructed by connecting the
MOSFETs 307 and 308 in anti-series to each other is arranged
between the intermediate point (connection point N3) of the switch
series circuit 11 and the intermediate point (connection point N4)
of the capacitor series circuit 41 in the three-level chopper
apparatus 400. Thus, in a state where the gate of the MOSFET 307 or
308 of the protection switch 201c that becomes forward biased is
turned on to allow a current to flow therein while the gate of the
MOSFET 307 or 308 that becomes reversely biased is also turned on
such that the MOSFET 307 or 308 conducts, synchronous rectification
can be performed, and hence a power loss in the protection switch
201c can be reduced. When the gate of the MOSFET 307 or 308 that
becomes reversely biased is turned off, a current flows through a
body diode of the MOSFET 307 or 308, but a power loss is increased,
and hence the gate of the MOSFET 307 or 308 is preferably turned
on.
[0130] According to the fourth embodiment, as hereinabove
described, the control circuit 1d controls the MOSFETs 307 and 308
to perform synchronous rectification during the period in which a
current flows through the connection path 13 in the three-level
chopper apparatus 400. In general, when the synchronous
rectification function of MOSFETs is utilized and is applied to a
switch element of an inverter or a chopper, it is necessary to
provide a period in which only body diodes of the MOSFETs conduct
by providing a dead time before and after switching not to cause a
short circuit at the time of switching. For application according
to the fourth embodiment, on the other hand, it is not necessary to
provide a dead time for providing a period in which only the body
diodes conduct, and hence control processing is not complicated
even when synchronous rectification is performed. The remaining
effects of the three-level chopper apparatus 400 according to the
thirteenth embodiment are similar to those of the three-level
chopper apparatus 100 according to the aforementioned first
embodiment.
Fifth Embodiment
[0131] A three-level chopper apparatus 500 according to a fifth
embodiment is now described with reference to FIG. 5.
[0132] According to the fifth embodiment, the three-level chopper
apparatus 500 includes a protection switch 201 inserted between an
intermediate point (connection point N3) of a switch series circuit
11 and an intermediate point (connection point N4) of a capacitor
series circuit 41 and a resistance 601 connected in parallel to the
protection switch 201, as shown in FIG. 5.
[0133] According to the fifth embodiment, the three-level chopper
apparatus 500 also includes a control circuit 1e. In the
three-level chopper apparatus 500, the control circuit 1e performs
control for changing a current pathway R11 through which an
overvoltage is applied to a capacitor 401 or a capacitor 402 to
current pathways R12 and R13 through which no overvoltage is
applied to the capacitor 401 or the capacitor 402 when a switch 101
or a switch 102 has a failure. The resistance 601 is an example of
a "first resistance" in the claims.
[0134] The protection switch 201 can be configured as a
bidirectional switch constructed by connecting IGBTs and diodes in
anti-parallel to each other and connecting the IGBTs in anti-series
to each other while connecting the diodes in anti-series to each
other, similarly to the protection switch 201a according to the
aforementioned second embodiment shown in FIG. 3. Similarly to the
second embodiment, Si-pn diodes, SiC--SB diodes, or diodes in which
Si-pn diodes and SiC--SB diodes are connected in parallel to each
other can be used as diodes of this bidirectional switch. The
protection switch 201 can also be constructed like the protection
switch 201b according to the third embodiment or the protection
switch 201c according to the fourth embodiment.
[0135] According to the fifth embodiment, the three-level chopper
apparatus 500 is configured such that a resistance value Re
satisfies the following formula (5) or (6), letting Re be the
resistance value of the resistance 601, L be the inductance of a
reactor 701, and C2 be the capacity of the capacitor 402.
Re=2.times.(2.times.L/C2).sup.1/2 (5)
Re>2.times.(2.times.L/C2).sup.1/2 (6)
[0136] When a reactor provided in a positive circuit or a negative
circuit or a combination reactor constructed by combining those
reactors is used as the reactor 701, the self-inductance of this
reactor or the sum of the self-inductances and the mutual
inductance of those reactors is used as the inductance L. As the
two capacitors 401 and 402 of the capacitor series circuit 41,
capacitors having the same capacity are generally used. When
capacitors having different capacities are used, on the other hand,
the capacity value C of the smaller of the capacity of the
capacitor 401 and the capacity of the capacitor 402 is used to
allow the resistance value Re of the resistance 601 to satisfy the
following formula (7), whereby a formed LCR series resonant circuit
can be critically damped or overdamped even when any of the
switches 101 and 102 has a short circuit failure.
Re.gtoreq.2.times.(2.times.L/C).sup.1/2 (7)
[0137] The remaining structures of the three-level chopper
apparatus 500 according to the fifth embodiment are similar to
those of the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
[0138] (Operation of Three-Level Chopper Apparatus According to
Fifth Embodiment)
[0139] In the three-level chopper apparatus 500 according to the
fifth embodiment, the control circuit 1e performs control
processing. During the normal operation of this three-level chopper
apparatus according to the fifth embodiment, the protection switch
201 is turned on such that no current flows through the resistance
601. When the protection switch 201 is constructed like the
protection switch according to the aforementioned second, third, or
fourth embodiment, the same operation can be obtained.
[0140] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 500,
for example, the control circuit 1e turns off the protection switch
201. In this state, the resistance 601 is inserted between the
intermediate point of the switch series circuit 11 and the
intermediate point of the capacitor series circuit 41.
[0141] In this state, an LC series resonant current flows through
the current pathway R12 from a direct-current power supply 8
through the reactor 701, the switch 101 having a short circuit
failure, the resistance 601, the capacitor 402, and a diode 104 to
the direct-current power supply 8 and the current pathway R13 from
the direct-current power supply 8 through the reactor 701, a diode
103, the capacitor 401, the capacitor 402, and the diode 104 to the
direct-current power supply 8. The capacitors 401 and 402 are
charged with this current.
[0142] When the current from the direct-current power supply 8
starts to be reduced as the charging progresses, the voltage of the
resistance 601 is reduced (a potential difference between both ends
of the resistance 601 is reduced). A potential difference between
both ends of the diode 103 is substantially constant, and hence the
potential difference of the diode 103 becomes larger than that of
the resistance 601 such that a current flows through only the
current pathway R12.
[0143] When the switch 101 has a short circuit failure in an
operating state where the voltages of the capacitors 401 and 402
are lower than the voltage VE of the direct-current power supply 8,
the current that flows through the resistance 601 is reduced before
the voltage of the capacitor 402 reaches VE. When the resistance
value of the resistance 601 is relatively large, the current starts
to be reduced at a relatively early stage, and an increase in the
voltage of the capacitor 401 can be suppressed. When the switch 101
has a short circuit failure in an operating state where the
voltages of the capacitors 401 and 402 are higher than the voltage
VE of the direct-current power supply 8, the current from the
direct-current power supply 8 is reduced without being increased,
and hence the capacitor 402 is charged through only the current
pathway R12.
[0144] At this time, damped oscillation occurs in the LCR series
resonant circuit since the LCR series resonant circuit in the
three-level chopper apparatus 500 includes the resistance 601. A
current is limited by the resistance 601, and hence the amount of
charges that flows into the capacitor 402 is reduced such that
occurrence of an overvoltage on the capacitor 402 can be prevented.
According to the fifth embodiment, when the resistance value Re
satisfies the above formula (5), the LCR series resonant circuit is
critically damped, and oscillation of the resonant circuit is
suppressed. When the resistance value Re satisfies the above
formula (6), the LCR series resonant circuit is overdamped, and
oscillation of the resonant circuit is further suppressed.
[0145] When the LCR series resonant circuit is critically damped or
overdamped, an attained value of the voltage of the capacitor 402
does not exceed the voltage VE of the direct-current power supply 8
but occurrence of an overvoltage on the capacitor 402 is suppressed
if the switch 101 has a short circuit failure in the operating
state where the voltages of the capacitors 401 and 402 are lower
than the voltage VE of the direct-current power supply 8. The
remaining operation of the three-level chopper apparatus 500
according to the fifth embodiment is similar to that of the
three-level chopper apparatus 100 according to the aforementioned
first embodiment.
[0146] [Effects of Fifth Embodiment]
[0147] According to the fifth embodiment, the following effects can
be obtained.
[0148] According to the fifth embodiment, as hereinabove described,
the resistance 601 connected in parallel to the protection switch
201 is provided in the three-level chopper apparatus 500. Thus,
when the switch 101 has a short circuit failure and control for
turning off the protection switch 201 is performed, for example, an
LC series resonant current flows through the current pathway R12.
In this case, the resistance 601 is included in the current pathway
R12, and hence this current pathway R12 forms an LCR series
resonant circuit. A resonant current that flows through this LCR
series resonant circuit undergoes damped oscillation. Consequently,
the amount of charges that flows into the capacitor 402 is reduced,
and hence occurrence of an overvoltage on the capacitor 402 can be
suppressed. The remaining effects of the three-level chopper
apparatus 500 according to the fifth embodiment are similar to
those of the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
Sixth Embodiment
[0149] A three-level chopper apparatus 600 according to a sixth
embodiment is now described with reference to FIG. 6.
[0150] According to the sixth embodiment, in the three-level
chopper apparatus 600, a protection switch 202 is connected in
series to a switch 101 of a switch series circuit 11, and a
protection switch 203 is connected in series to a switch 102 of the
switch series circuit 11, as shown in FIG. 6. The three-level
chopper apparatus 600 includes a control circuit 1f.
[0151] According to the sixth embodiment, the control circuit if
performs control for changing a current pathway R21 through which
an overvoltage is applied to a capacitor 401 or a capacitor 402 to
a current pathway R22 through which no overvoltage is applied to
the capacitor 401 or the capacitor 402 when the switch 101 or the
switch 102 has a failure. The protection switch 202 is an example
of an "eleventh protection switch" or a "first protection switch
partial circuit" in the claims. The protection switch 203 is an
example of a "fourteenth protection switch" or a "second protection
switch partial circuit" in the claims.
[0152] As the protection switches 202 and 203, IGBTs or MOSFETs can
be used independently, and parallel connection of diodes can also
be omitted. According to the sixth embodiment, series connection
order of the switches 101 and 102 and the protection switches 202
and 203 that are main components is not restricted to one shown in
FIG. 6, but the switches 101 and 102 and the protection switches
202 and 203 can be connected in any order. When the switch 101 has
a failure, the protection switch 203 may be turned off instead of
turning off the switch 102. The remaining structures of the
three-level chopper apparatus 600 according to the sixth embodiment
are similar to those of the three-level chopper apparatus 100
according to the aforementioned first embodiment.
[0153] (Operation of Three-Level Chopper Apparatus According to
Sixth Embodiment)
[0154] In the three-level chopper apparatus 600 according to the
sixth embodiment, the control circuit if performs control
processing. When the switch 101 is turned on during the normal
operation of the three-level chopper apparatus 600, the protection
switch 202 connected in series to the switch 101 must be turned on
to perform a chopper operation. When the switch 102 is turned on,
the protection switch 203 connected in series to the switch 102
must be turned on to perform a chopper operation. The switches 101
and 102 are switched on and off similarly to the aforementioned
first embodiment, for example, whereby the normal operation of the
three-level chopper apparatus is enabled.
[0155] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 600,
for example, the switch 102 and the protection switch 202 are
turned off. Thus, the switch series circuit 11 is blocked, and
hence the capacitors 401 and 402 are charged by a direct-current
power supply 8 and with energy accumulated in a reactor 701.
Although at this time, a charging current becomes an LC series
resonant current, the two capacitors 401 and 402 share the charging
voltage and are charged, and hence the voltage of each of the
capacitors is inhibited from becoming an overvoltage.
[0156] [Effects of Sixth Embodiment]
[0157] According to the sixth embodiment, the following effects can
be obtained.
[0158] According to the sixth embodiment, as hereinabove described,
both the protection switch 202 connected in series to the switch
101 of the switch series circuit 11 and the protection switch 203
connected in series to the switch 102 of the switch series circuit
11 are provided in the three-level chopper apparatus 600. Thus,
when the switch 101 or 102 has a short circuit failure, the
protection switches 202 and 203 can effectively change the current
pathway R21 through which an overvoltage is applied to the
capacitor 401 or 402 to the current pathway R22 through which no
overvoltage is applied to the capacitor 401 or 402.
[0159] According to the sixth embodiment, as hereinabove described,
the protection switch 202 is provided in the three-level chopper
apparatus 600. Furthermore, the protection switch 202 is connected
in series to the switch 101 and a connection path 13. Thus, when
the switch 101 has a short circuit failure, the protection switch
202 is turned off such that the current pathway R21 through which
an overvoltage is applied to the capacitor 402 can be changed to
the current pathway R22 through which no overvoltage is applied to
the capacitor 402.
[0160] According to the sixth embodiment, as hereinabove described,
the protection switch 203 is provided in the three-level chopper
apparatus 600. Furthermore, the protection switch 203 is connected
in series to the switch 102 and the connection path 13. Thus,
similarly to the case where the protection switch 202 is provided
in the three-level chopper apparatus 600, application of an
overvoltage to the capacitor 401 can be suppressed.
[0161] In the case where a protection switch 201a is provided in
the connection path 13 as in the aforementioned second embodiment,
two elements including IGBTs or MOSFETs are added in a current flow
pathway when only one of the capacitors 401 and 402 is charged
during normal operation, but according to the sixth embodiment,
only one switch element is added in a current flow pathway, and
hence a conduction loss can be reduced as compared with the
aforementioned second embodiment in which the bidirectional switch
is provided. Thus, the efficiency of the three-level chopper
apparatus 600 can be increased. However, in a mode in which both
the switches 101 and 102 are turned on, no loss is caused by the
protection switch circuit according to the first to fifth
embodiments, but a loss is caused by the two protection switches
according to the sixth embodiment. Thus, the first to fifth
embodiments also have an advantage. The remaining effects of the
three-level chopper apparatus 600 according to the sixth embodiment
are similar to those of the three-level chopper apparatus 100
according to the aforementioned first embodiment.
Seventh Embodiment
[0162] A three-level chopper apparatus 700 according to a seventh
embodiment is now described with reference to FIG. 7.
[0163] According to the seventh embodiment, in the three-level
chopper apparatus 700, resistances 602 and 603 are connected in
parallel to the protection switches 202 and 203 connected in series
to the switches 101 and 102 according to the aforementioned sixth
embodiment, respectively, as shown in FIG. 7. The three-level
chopper apparatus 700 includes a control circuit 1g. The protection
switches 202 and 203 according to the seventh embodiment are
examples of a "twelfth protection switch" and a "fifteenth
protection switch" in the claims, respectively. The resistance 602
is an example of a "fifth resistance" or a "first protection switch
partial circuit" in the claims. The resistance 603 is an example of
a "sixth resistance" or a "second protection switch partial
circuit" in the claims.
[0164] According to the seventh embodiment, the control circuit 1g
can perform control for changing a current pathway R31 through
which an overvoltage is applied to a capacitor 401 or 402 to
current pathways R32 and R33 through which no overvoltage is
applied to the capacitor 401 or 402 when the switch 101 or 102 has
a failure.
[0165] According to the seventh embodiment, the resistance value
Rc1 of this resistance 602 is set to a value shown by the following
formula (8), similarly to the fifth embodiment, whereby a resonant
circuit on the pathway R32 can be critically damped or overdamped.
Thus, when the switch 101 has a short circuit failure in an
operating state where the voltages of the capacitors 401 and 402
are lower than the voltage VE of a direct-current power supply 8,
the charging voltage of the capacitor 402 can be kept to the
voltage VE of the direct-current power supply 8. Consequently,
occurrence of an overvoltage on the capacitor 402 can be
suppressed.
Rc1.gtoreq.2.times.(2.times.L/C2).sup.1/2 (8)
[0166] Similarly, according to the seventh embodiment, the
resistance value Rd1 of the resistance 603 is set to a value that
satisfies the following formula (9), whereby the voltage of the
capacitor 401 can be kept to the voltage VE of the direct-current
power supply 8 when the switch 102 has a short circuit failure.
Rd1.gtoreq.2.times.(2.times.L/C1).sup.1/2 (9)
[0167] Even when a diode 103 and the switch 101 each have a short
circuit failure in the three-level chopper apparatus 700 according
to the seventh embodiment, an overvoltage on the capacitor 402 and
the failure of the capacitor 401 can be suppressed by the
resistance 602, similarly to the aforementioned fifth
embodiment.
[0168] Also according to this seventh embodiment, the switches 101
and 102 and the protection switches 202 and 203 can be connected in
any order. The remaining structures of the three-level chopper
apparatus 700 according to the seventh embodiment are similar to
those of the three-level chopper apparatus 600 according to the
aforementioned sixth embodiment.
[0169] (Operation of Three-Level Chopper Apparatus According to
Seventh Embodiment)
[0170] When the switch 101 has a short circuit failure, the switch
102 and the protection switch 202 are turned off. In this state, an
LC series resonant current flows through the current pathway R32
from the direct-current power supply 8 through a reactor 701, the
switch 101 having a short circuit failure, the resistance 602, the
capacitor 402, and a diode 104 to the direct-current power supply 8
and the current pathway R33 from the direct-current power supply 8
through the reactor 701, the diode 103, the capacitor 401, the
capacitor 402, and the diode 104 to the direct-current power supply
8. The capacitors 401 and 402 are charged with this current.
Similarly to the fifth embodiment, when the current is reduced as
the charging progresses, no current flows through the current
pathway R33, and only an LCR series resonant circuit on the pathway
R32, in which damped oscillation occurs, is formed. Thus, the
amount of charges that flows into the capacitor 402 is reduced by
the resistance 602, and occurrence of an overvoltage on the
capacitor 402 is suppressed.
[0171] [Effects of Seventh Embodiment]
[0172] According to the seventh embodiment, the following effects
can be obtained.
[0173] According to the seventh embodiment, as hereinabove
described, the protection switches 202 and 203, the resistance 602
connected in parallel to the protection switch 202, and the
resistance 603 connected in parallel to the protection switch 203
are provided in the three-level chopper apparatus 700. Thus, when
the switch 101 or 102 has a short circuit failure, control for
turning off the protection switch 202 or 203 is performed, whereby
the resistance 602 or 603 can be added in the current pathway
(current pathway R32, for example). Consequently, when the switch
101 or 102 has a short circuit failure, the current pathway can be
formed as an LCR series resonant circuit including the resistance
602 or 603, and hence occurrence of an overvoltage on the capacitor
401 or 402 can be suppressed.
[0174] According to the seventh embodiment, as hereinabove
described, the resistance value Rc1 of the resistance 602 satisfies
the above formula (8) where Rc1 represents the resistance value of
the resistance 602, L represents the inductance of the reactor 701,
and C2 represents the capacity of the capacitor 402. Furthermore,
the resistance value Rd1 of the resistance 603 satisfies the above
formula (9) where Rd1 represents the resistance value of the
resistance 603, L represents the inductance of the reactor 701, and
C1 represents the capacity of the capacitor 401. Thus, a current
that flows through the LCR series resonant circuit including the
resistance 602 having the resistance value Rc1 or the resistance
603 having the resistance value Rd1 can be critically damped or
overdamped, and hence occurrence of an overvoltage on the capacitor
401 or 402 can be more reliably suppressed when the switch 101 or
102 has a short circuit failure. The remaining effects of the
three-level chopper apparatus 700 according to the seventh
embodiment are similar to those of the three-level chopper
apparatus 600 according to the aforementioned sixth embodiment.
Eighth Embodiment
[0175] A three-level chopper apparatus 800 according to an eighth
embodiment is now described with reference to FIG. 8.
[0176] According to the eighth embodiment, in the three-level
chopper apparatus 800, a resistance 604 is connected in parallel
between a connection point N11 between the switch 101 and the
protection switch 202 according to the aforementioned sixth
embodiment and a connection point N12 between the switch 102 and
the protection switch 202 according to the aforementioned sixth
embodiment, as shown in FIG. 8. The protection switches 202 and 203
according to the eighth embodiment are examples of a "first
protection switch" and a "second protection switch" in the claims,
respectively. The resistance 604 is an example of a "second
resistance" in the claims.
[0177] The protection switches 202 and 203 are configured such that
a current can flow and return to a direct-current power supply 8
therethrough. The protection switches 202 and 203 include MOSFETs,
IGBTs having diodes connected in anti-parallel, reverse conducting
IGBTs, or the like. The three-level chopper apparatus 800 includes
a control circuit 1h.
[0178] The resistance value Ra1 of this resistance 604 is set to a
value that satisfies the following formula (10) or (11), similarly
to the aforementioned fifth embodiment.
Ra1.gtoreq.2.times.(2.times.L/C2).sup.1/2 (10)
Ra1.gtoreq.2.times.(2.times.L/C).sup.1/2 (11)
[0179] In the case where as the protection switches 202 and 203,
switches constructed by connecting diodes in anti-parallel to
switching elements such as IGBTs to allow a current to flow and
return to the direct-current power supply 8 therethrough are used,
freewheeling diodes to be connected conduct only when the switch
101, for example, has a failure and the protection switches 202 and
203 are turned off, and during normal operation, no large reverse
bias is applied, or no reverse recovery loss is generated since the
freewheeling diodes do not conduct. Therefore, inexpensive Si-pn
diodes can be used. When it is necessary to reduce a noise at the
time of commutation during normal operation, SiC--SB diodes, which
are excellent in forward recovery characteristics, are preferably
used as the freewheeling diodes to be connected.
[0180] The remaining structures of the three-level chopper
apparatus 800 according to the eighth embodiment are similar to
those of the three-level chopper apparatus 600 according to the
aforementioned sixth embodiment.
[0181] (Operation of Three-Level Chopper Apparatus According to
Eighth Embodiment)
[0182] The protection switches 202 and 203 according to this eighth
embodiment operate similarly to those according to the
aforementioned seventh embodiment. In other words, during the
normal operation of the three-level chopper apparatus, both the
protection switches 202 and 203 are turned on, and the resistance
604 is short-circuited such that no current flows through the
resistance 604.
[0183] When the switch 101 has a short circuit failure in a switch
series circuit 11 of the three-level chopper apparatus, for
example, the switch 102 and the protection switch 202 are
immediately turned off.
[0184] In this state, an LC series resonant current flows through a
pathway R41 from the direct-current power supply 8 through a
reactor 701, the switch 101 having a short circuit failure, the
resistance 604, the protection switch 203 (through which a current
can flow and return to the direct-current power supply 8), a
capacitor 402, and a diode 104 to the direct-current power supply 8
and a pathway R42 from the direct-current power supply 8 through
the reactor 701, a diode 103, a capacitor 401, the capacitor 402,
and the diode 104 to the direct-current power supply 8. The
capacitors 401 and 402 are charged with this current. Similarly to
the fifth embodiment, when the current is reduced as the charging
progresses, no current flows through the pathway R42, and only an
LCR series resonant circuit on the pathway R41, in which damped
oscillation occurs, is formed. Thus, the amount of charges that
flows into the capacitor 402 is reduced by the resistance 604, and
hence occurrence of an overvoltage on the capacitor 402 can be
suppressed.
[0185] The resistance Ra1 of the resistance 604 is set to a value
that satisfies the following formula (10), whereby the resonant
circuit on the pathway R41 is critically damped or overdamped.
Thus, when the switch 101 has a short circuit failure in an
operating state where the voltages of the capacitors 401 and 402
are lower than the voltage VE of the direct-current power supply 8,
the charging voltage of the capacitor 402 can be kept to the
voltage VE of the direct-current power supply 8, and occurrence of
an overvoltage on the capacitor 402 can be suppressed.
[0186] The capacity value C of the smaller of the capacity of the
capacitor 401 and the capacity of the capacitor 402 is used to
allow the resistance value Ra1 of the resistance 604 to satisfy the
above formula (11), whereby a formed LCR series resonant circuit
can be critically damped or overdamped even when any of the
switches 101 and 102 has a short circuit failure.
[0187] Even when a diode 103 and the switch 101 each have a short
circuit failure, an overvoltage on the capacitor 402 and the
failure of the capacitor 401 can be suppressed by the resistance
604, similarly to the aforementioned fifth embodiment.
[0188] [Effects of Eighth Embodiment]
[0189] According to the eighth embodiment, the following effects
can be obtained.
[0190] According to the eighth embodiment, as hereinabove
described, the protection switch 202 connected in series between
the switch 101 and a connection path 13, the protection switch 203
connected in series between the switch 102 and the connection path
13, and the resistance 604 connected in parallel between the
connection point N11 between the switch 101 and the protection
switch 202 and the connection point N12 between the switch 102 and
the protection switch 202 are provided in the three-level chopper
apparatus 800. Thus, when the switch 101 has a short circuit
failure and control for turning off the protection switch 202 and
turning on the protection switch 203 is performed, for example, an
LC series resonant current flows through the pathway R41 from the
direct-current power supply 8 through the reactor 701, the switch
101 having a short circuit failure, the resistance 604, the
protection switch 203, the capacitor 402, and the diode 104 to the
direct-current power supply 8. In this case, the resistance 604 is
included in the current pathway R41, and hence this current pathway
R41 forms an LCR series resonant circuit. A resonant current that
flows through this LCR series resonant circuit undergoes damped
oscillation. Consequently, the amount of charges that flows into
the capacitor 402 is reduced, and hence occurrence of an
overvoltage on the capacitor 402 can be further suppressed.
[0191] According to the eighth embodiment, as hereinabove
described, the resistance Ra1 of the resistance 604 satisfies the
above formula (10) or (11). Thus, a current that flows through the
LCR series resonant circuit including the resistance 604 having the
resistance value Ra1 can be critically damped or overdamped, and
hence occurrence of an overvoltage on the capacitor 401 or 402 can
be more reliably suppressed when the switch 101 or 102 has a short
circuit failure.
[0192] The remaining effects of the three-level chopper apparatus
800 according to the eighth embodiment are similar to those of the
three-level chopper apparatus 600 according to the aforementioned
sixth embodiment.
Ninth Embodiment
[0193] A three-level chopper apparatus 900 according to a ninth
embodiment is now described with reference to FIG. 9.
[0194] The three-level chopper apparatus 900 according to the ninth
embodiment includes a parallel circuit of a protection switch 204
and a resistance 605 and a parallel circuit of a protection switch
205 and a resistance 606 in a capacitor series circuit 41, as shown
in FIG. 9. The three-level chopper apparatus 900 includes a control
circuit 1i. The remaining structures of the three-level chopper
apparatus 900 according to the ninth embodiment are similar to
those of the three-level chopper apparatus 700 according to the
aforementioned seventh embodiment, for example. Although the
protection switches 204 and 205 are required to be capable of
switching on and off a current that attempts to flow from the side
of a capacitor 401 to the side of a capacitor 402, a current in an
opposite direction is only required to be capable of conducting.
Since the protection switches 204 and 205 are configured such that
a current can flow and return to a direct-current power supply 8
therethrough, flow of a current from the capacitors 401 and 402 to
the side of a load 9 is not prevented. Thus, as the protection
switches 204 and 205, MOSFETs, IGBTs in which diodes are connected
in anti-parallel, or the like can be used. The protection switches
204 and 205 are examples of a "fifteenth protection switch" and a
"twelfth protection switch" in the claims, respectively. The
resistances 605 and 606 are examples of a "sixth resistance" and a
"fifth resistance" in the claims, respectively.
[0195] In the three-level chopper apparatus 900 according to this
ninth embodiment, similarly to another embodiment, control for
switching on and off switches 101 and 102 of a switch series
circuit 11 is performed in a state where the protection switches
204 and 205 of the capacitor series circuit 41 are turned on and
the resistances 605 and 606 are short-circuited during normal
operation such that a direct-current voltage is converted.
[0196] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 900,
for example, the switch 102 and the protection switch 205 are
immediately turned off, and the resistance 606 is arranged in the
charging path of the capacitor 402.
[0197] In this state, an LC series resonant current flows through a
pathway from the direct-current power supply 8 through a reactor
701, the switch 101 having a short circuit failure, the resistance
606, the capacitor 402, and a diode 104 to the direct-current power
supply 8. The capacitor 402 is charged with this current. Thus, the
amount of charges that flows into the capacitor 402 is reduced by
the resistance 606, and hence occurrence of an overvoltage on the
capacitor 402 can be prevented.
[0198] Similarly to the aforementioned seventh embodiment, the
resistance value Rc2 of this resistance 606 is set to a value shown
by the following formula (12), whereby a resonant circuit on the
above pathway can be critically damped or overdamped. Thus, when
the switch 101 has a short circuit failure in an operating state
where the voltages of the capacitors 401 and 402 are lower than the
voltage VE of the direct-current power supply 8, the charging
voltage of the capacitor 402 can be kept to the voltage VE of the
direct-current power supply 8. Consequently, occurrence of an
overvoltage on the capacitor 402 can be suppressed. Similarly, the
resistance value Rd2 of the resistance 605 is set to a value shown
by the following formula (13), whereby when the switch 102 has a
short circuit failure in the operating state where the voltages of
the capacitors 401 and 402 are lower than the voltage VE of the
direct-current power supply 8, the voltage of the capacitor 401 can
be kept to the voltage VE of the direct-current power supply 8.
Rc2.gtoreq.2.times.(2.times.L/C2).sup.1/2 (12)
Rd2.gtoreq.2.times.(2.times.L/C1).sup.1/2 (13)
[0199] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 205 are
turned off such that the resistance 606 is inserted into the
charging path of the capacitor 402. A current flow pathway from the
direct-current power supply 8 becomes the pathway from the
direct-current power supply 8 through the reactor 701, the switch
101 having a short circuit failure, the resistance 606, the
capacitor 402, and the diode 104 to the direct-current power supply
8. This pathway is the same as when only the switch 101 has a
failure, and hence an overvoltage on the capacitor 402 can be
prevented also in this case. Furthermore, the resistance value Rc2
of this resistance 606 is set to the value shown by the above
formula (12), and the resistance value Rd2 of this resistance 605
is set to the value shown by the above formula (13), whereby the
charging voltage of the capacitor 402 can be kept to the voltage VE
of the direct-current power supply 8 when the switch 101 has a
short circuit failure in the operating state where the voltages of
the capacitors 401 and 402 are lower than the voltage VE of the
direct-current power supply 8.
[0200] According to the ninth embodiment, the protection switches
204 and 205 can also be bidirectional switches. In that case, the
structure of the bidirectional switches must be the same as that of
the protection switches 201a, 201b, and 202c according to the
aforementioned second, third, and fourth embodiments. However, when
the capacitors 401 and 402 are not charged during normal operation,
it is necessary to discharge a current to the load, and hence a
turning-off period cannot be provided during normal operation
unlike the aforementioned second, third, and fourth embodiments.
When the protection switches 204 and 205 are configured as the
bidirectional switches, the protection switch 204 is immediately
turned off at the time of the short circuit failure of the diode
103 and the switch 101, whereby the discharging current of the
capacitor 401 is limited by the resistance 605 such that the
failure of the capacitor 401 can be suppressed.
[0201] According to this ninth embodiment, a connection order
between the capacitor 401 and the parallel circuit of the
protection switch 204 and the resistance 605 and a connection order
between the capacitor 402 and the parallel circuit of the
protection switch 205 and the resistance 606 are not restricted,
but these can be connected in any order.
[0202] According to the ninth embodiment, a loss is constantly
caused by the protection switches, but the magnitude of a current
becomes a difference between charging from the direct-current power
supply 8 and discharging to the load 9, and hence the current is
reduced as compared with the case where the protection switch
circuit is placed in another pathway. Thus, the loss is not always
disadvantageous. In the case where as the protection switches 204
and 205, switches constructed by connecting diodes in anti-parallel
to switching elements such as IGBTs to allow a current to flow and
return to the direct-current power supply 8 therethrough are used,
during normal operation, no large reverse bias is applied to
freewheeling diodes to be connected, or no reverse recovery loss is
generated since the freewheeling diodes are connected with the
switching elements. Therefore, inexpensive Si-pn diodes that allow
a further reduction in conduction loss as compared with SiC--SB
diodes are preferably used as the freewheeling diodes to be
connected. When it is necessary to reduce a noise at the time of
commutation during normal operation, SiC--SB diodes, which are
excellent in forward recovery characteristics, may be used as the
freewheeling diodes to be connected. When Si-pn diodes and SiC--SB
diodes connected in parallel to each other are used as the
freewheeling diodes to be connected, a low loss and a low noise can
be achieved.
[0203] [Effects of Ninth Embodiment]
[0204] The effects of the three-level chopper apparatus 900
according to the ninth embodiment are similar to those of the
three-level chopper apparatus 700 according to the aforementioned
seventh embodiment.
Tenth Embodiment
[0205] A three-level chopper apparatus 1000 according to a tenth
embodiment is now described with reference to FIG. 10.
[0206] According to the tenth embodiment, in the three-level
chopper apparatus 1000, instead of the resistances 605 and 606
shown in FIG. 9 according to the aforementioned ninth embodiment, a
resistance 607 is connected (in parallel) between a connection
point N21 between a capacitor 401 and a protection switch 204 and a
connection point N22 between a capacitor 402 and a protection
switch 205, as shown in FIG. 10. The three-level chopper apparatus
1000 includes a control circuit 1j. The remaining structures of the
three-level chopper apparatus 1000 according to the tenth
embodiment are similar to those of the three-level chopper
apparatus 900 according to the aforementioned ninth embodiment. The
protection switches 204 and 205 according to the tenth embodiment
are examples of a "fifth protection switch" and a "sixth protection
switch" in the claims, respectively. The resistance 607 is an
example of a "third resistance" in the claims.
[0207] In this three-level chopper apparatus 1000 according to the
tenth embodiment, similarly to another embodiment, control for
switching on and off switches 101 and 102 of a switch series
circuit 11 is performed in a state where the protection switches
204 and 205 of a capacitor series circuit 41 are turned on and the
resistance 607 is short-circuited during normal operation such that
a direct-current voltage is converted. The protection switches 204
and 205 are configured such that a current can flow and return to a
direct-current power supply 8 therethrough, and hence flow of a
current from the capacitors to the side of a load is not
prevented.
[0208] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1000,
for example, the switch 102 and the protection switch 205 are
immediately turned off such that the resistance 607 is inserted
into the charging path of the capacitor 402.
[0209] In this state, an LCR series resonant current flows through
a pathway from the direct-current power supply 8 through a reactor
701, the switch 101 having a short circuit failure, the protection
switch 204 (through which a current can flow and return to the
direct-current power supply 8), the resistance 607, the capacitor
402, and a diode 104 to the direct-current power supply 8. The
capacitor 402 is charged with this current. Thus, the amount of
charges that flows into the capacitor 402 is reduced by the
resistance 607, and hence occurrence of an overvoltage on the
capacitor 402 can be prevented.
[0210] Similarly to the aforementioned fifth embodiment, the
resistance value Ra2 of this resistance 607 is set to a value shown
by the following formula (14), whereby a resonant circuit on the
above pathway can be critically damped or overdamped. Thus, when
the switch 101 has a short circuit failure in an operating state
where the voltages of the capacitors 401 and 402 are lower than the
voltage VE of the direct-current power supply 8, the charging
voltage of the capacitor 402 can be kept to the voltage VE of the
direct-current power supply 8. Consequently, occurrence of an
overvoltage on the capacitor 402 can be suppressed.
Ra2.gtoreq.2.times.(2.times.L/C2).sup.1/2 (14)
[0211] When the capacity value C of the smaller of the capacity of
the capacitor 401 and the capacity of the capacitor 402 is used to
allow the resistance value Ra2 of the resistance 607 to satisfy the
following formula (15), whereby a formed LCR series resonant
circuit can be critically damped or overdamped even when any of the
switches 101 and 102 has a short circuit failure.
Ra2.gtoreq.2.times.(2.times.L/C).sup.1/2 (15)
[0212] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 205 are
immediately turned off such that the resistance 607 is inserted
into the charging path of the capacitor 402. A current flow pathway
from the direct-current power supply 8 becomes the pathway from the
direct-current power supply 8 through the reactor 701, the switch
101 having a short circuit failure, the protection switch 204
(through which a current can flow and return to the direct-current
power supply 8), the resistance 607, the capacitor 402, and the
diode 104 to the direct-current power supply 8. This pathway is the
same as when only the switch 101 has a failure, and hence an
overvoltage on the capacitor 402 can be prevented also in this
case. Furthermore, the resistance value Ra2 of the resistance 607
is set to the value shown by the formula (14) or (15), whereby the
resonant circuit on the above pathway can be critically damped or
overdamped. Thus, when the switch 101 has a short circuit failure
in the operating state where the voltages of the capacitors 401 and
402 are lower than the voltage VE of the direct-current power
supply 8, the charging voltage of the capacitor 402 can be kept to
the voltage VE of the direct-current power supply 8.
[0213] [Effects of Tenth Embodiment]
[0214] According to the tenth embodiment, the following effects can
be obtained.
[0215] According to the tenth embodiment, as hereinabove described,
the three-level chopper apparatus 1000 includes the protection
switch 204 connected in series between the capacitor 401 and a
connection path 13, the protection switch 205 connected in series
between the capacitor 402 and the connection path 13, and the
resistance 607 connected in parallel between the connection point
N21 between the capacitor 401 and the protection switch 204 and the
connection point N22 between the capacitor 402 and the protection
switch 205. Thus, when the switch 101 has a short circuit failure,
for example, the control circuit 1j performs control for turning
off the switch 102, turning on the protection switch 204, and
turning off the protection switch 205, whereby the LCR series
resonant circuit is formed in the pathway from the direct-current
power supply 8, the reactor 701, the switch 101 having a short
circuit failure, the protection switch 204, the resistance 607, the
capacitor 402, and the diode 104 to the direct-current power supply
8. Consequently, the amount of charges that flows into the
capacitor 402 is reduced such that occurrence of an overvoltage on
the capacitor 402 can be more effectively suppressed.
[0216] According to the tenth embodiment, as hereinabove described,
the resistance Ra2 satisfies the above formula (15) where Ra2
represents the resistance value of the resistance 607, L represents
the inductance of the reactor 701, and C represents the smaller of
the capacity of the capacitor 401 and the capacity of the capacitor
402. Thus, a current that flows through the LCR series resonant
circuit including the resistance 607 having the resistance value
Ra2 can be critically damped or overdamped, and hence occurrence of
an overvoltage on the capacitor 401 or 402 can be more reliably
suppressed when the switch 101 or 102 has a short circuit
failure.
[0217] The remaining effects of the three-level chopper apparatus
1000 according to the tenth embodiment are similar to those of the
three-level chopper apparatus 800 according to the aforementioned
eighth embodiment.
Eleventh Embodiment
[0218] A three-level chopper apparatus 1100 according to an
eleventh embodiment is now described with reference to FIG. 11.
[0219] According to the eleventh embodiment, in the three-level
chopper apparatus 1100, a parallel circuit of a protection switch
206 and a resistance 608 and a parallel circuit of a protection
switch 207 and a resistance 609 are connected in series to diodes
103 and 104, respectively, as shown in FIG. 11. The three-level
chopper apparatus 1100 includes a control circuit 1k. The remaining
structures of the three-level chopper apparatus 1100 according to
the eleventh embodiment are similar to those of the three-level
chopper apparatus 700 according to the aforementioned seventh
embodiment. When the protection switches 206 and 207 are turned on,
it is only required to allow a current to flow in a direction in
which the diodes 103 and 104 conduct. The protection switches 206
and 207 are examples of a "fourteenth protection switch" and a
"twelfth protection switch" in the claims, respectively. The
resistances 608 and 609 are examples of a "sixth resistance" and a
"fifth resistance" in the claims, respectively.
[0220] In this three-level chopper apparatus 1100 according to the
eleventh embodiment, when the diodes 103 and 104 are caused to
conduct during normal operation, the protection switches 206 and
207 are turned on, and the resistances 608 and 609 are
short-circuited. In other words, similarly to another embodiment,
control for switching on and off switches 101 and 102 of a switch
series circuit 11 is performed such that a direct-current voltage
is converted.
[0221] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1100,
for example, the switch 102 and the protection switch 207 are
turned off.
[0222] In this state, an LC series resonant current flows through a
pathway from a direct-current power supply 8 through a reactor 701,
the switch 101 having a short circuit failure, a capacitor 402, the
resistance 609, and the diode 104 to the direct-current power
supply 8. The capacitor 402 is charged with this current. Thus, the
amount of charges that flows into the capacitor 402 is reduced by
the resistance 609 such that occurrence of an overvoltage on the
capacitor 402 can be prevented.
[0223] Similarly to the aforementioned seventh embodiment, the
resistance value Rc3 of this resistance 609 is set to a value shown
by the following formula (16), whereby a resonant circuit on the
above pathway can be critically damped or overdamped. Thus, when
the switch 101 has a short circuit failure in an operating state
where the voltages of capacitors 401 and 402 are lower than the
voltage VE of the direct-current power supply 8, the charging
voltage of the capacitor 402 can be kept to the voltage VE of the
direct-current power supply 8. Consequently, occurrence of an
overvoltage on the capacitor 402 can be suppressed. Similarly, the
resistance value Rd3 of the resistance 608 is set to a value shown
by the following formula (17), whereby when the switch 102 has a
short circuit failure in the operating state where the voltages of
the capacitors 401 and 402 are lower than the voltage VE of the
direct-current power supply 8, the voltage of the capacitor 401 can
be kept to the voltage VE of the direct-current power supply 8.
Rc3.gtoreq.2.times.(2.times.L/C2).sup.1/2 (16)
Rd3.gtoreq.2.times.(2.times.L/C1).sup.1/2 (17)
[0224] Also when the diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 207 are
turned off, whereby a current flow pathway from the direct-current
power supply 8 becomes the pathway from the direct-current power
supply 8 through the reactor 701, the switch 101 having a short
circuit failure, the capacitor 402, the resistance 609, and the
diode 104 to the direct-current power supply 8. This pathway is the
same as when only the switch 101 has a failure, and hence an
overvoltage on the capacitor 402 can be prevented also in this
case. Furthermore, the resistance value Rc3 of the resistance 609
is set to the value shown by the formula (16), whereby the resonant
circuit on the pathway can be critically damped or overdamped, and
the voltage of the capacitor 402 can be kept to the voltage VE of
the direct-current power supply 8 when the diode 103 and the switch
101 each have a short circuit failure in the operating state where
the voltages of the capacitors 401 and 402 are lower than the
voltage VE of the direct-current power supply 8.
[0225] When the protection switch 206 is a switch that is
configured such that a current can flow and return to the
direct-current power supply 8 therethrough, the capacitor 401 is
not discharged through the resistance 608, and hence an effect of
suppressing the failure of the capacitor 401 cannot be obtained. On
the other hand, when the protection switches 206 and 207 are
constructed by connecting semiconductor switches including reverse
blocking IGBTs, diodes and MOSFETs, IGBTs, or the like in series to
each other, a current flows through the resistance 608, and hence
the failure of the capacitor 401 is suppressed. When the protection
switch 206 includes reverse blocking IGBTs, a leakage current is
reduced by turning on gates of the reverse blocking IGBTs. When the
protection switch 206 includes bidirectional switches, the
protection switch 206 is turned off immediately after the failure
of the diode 103, whereby the capacitor 401 can also be discharged
through the resistance 608.
[0226] In the case of the protection switches 206 and 207 that are
configured such that a current can flow and return to the
direct-current power supply 8 therethrough and are constructed by
connecting diodes in anti-parallel to IGBTs or the like, for
example, during normal operation, no large reverse bias is applied
to the protection switches, or no reverse recovery loss is
generated since the diodes do not conduct. Therefore, inexpensive
Si-pn diodes are used as the freewheeling diodes, whereby a loss
can be reduced. When a noise at the time of commutation during
normal operation is reduced, SiC--SB diodes, which are excellent in
forward recovery characteristics, may be used as the freewheeling
diodes. Furthermore, a low loss and a low noise can be achieved by
constructing the freewheeling diodes by connecting Si-pn diodes and
SiC--SB didoes in parallel to each other.
[0227] In the case where a protection switch 201a is provided in a
connection path 13 as in the aforementioned fifth embodiment, for
example, two elements including IGBTs, MOSFETs, or diodes are added
in a current flow pathway when only one of capacitors 401 and 402
is charged during normal operation, unlike the case where no
protection switch circuit is provided. On the other hand, according
to this eleventh embodiment, only one switch element is added in a
current flow pathway when switches that are configured such that a
current can flow and return to the direct-current power supply 8
therethrough or reverse blocking IGBTs are used as the protection
switches 206 and 207, and hence a conduction loss can be reduced as
compared with the aforementioned second and fourth embodiments in
which the protection switches 201a and 202c constructed by
connecting the switches in anti-series to each other are provided.
Thus, the efficiency of the three-level chopper apparatus 1100 can
be increased. In a mode in which both the switches 101 and 102 are
turned off, however, a loss is caused by the two protection
switches according to the eleventh embodiment whereas no loss is
caused by the protection switch circuit according to the
aforementioned first to fifth embodiments.
[0228] According to this eleventh embodiment, a connection order of
the diode 103 and the parallel circuit of the protection switch 206
and the resistance 608 and a connection order of the diode 104 and
the parallel circuit of the protection switch 207 and the
resistance 609 are not restricted, but these can be connected in
any order.
[0229] [Effects of Eleventh Embodiment]
[0230] The effects of the three-level chopper apparatus 1100
according to the eleventh embodiment are similar to those of the
three-level chopper apparatus 700 according to the aforementioned
seventh embodiment.
Twelfth Embodiment
[0231] A three-level chopper apparatus 1200 according to a twelfth
embodiment is now described with reference to FIG. 12.
[0232] According to the twelfth embodiment, in the three-level
chopper apparatus 1200, instead of the protection switches 202 and
203 and the resistances 602 and 603 according to the aforementioned
seventh embodiment, a protection switch 208 connected in parallel
with a resistance 610 is connected in series to a reactor 701, as
shown in FIG. 12. The three-level chopper apparatus 1200 includes a
control circuit 1m. The remaining structures of the three-level
chopper apparatus 1200 according to the twelfth embodiment are
similar to those of the three-level chopper apparatus 700 according
to the aforementioned seventh embodiment. The protection switch 208
is an example of a "ninth protection switch" in the claims. The
resistance 610 is an example of a "fourth resistance" in the
claims.
[0233] In the three-level chopper apparatus 1200 according to this
twelfth embodiment, similarly to another embodiment, control for
switching on and off switches 101 and 102 of a switch series
circuit 11 is performed in a state where the protection switch 208
is turned on and the resistance 610 is short-circuited during
normal operation such that a direct-current voltage is
converted.
[0234] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1200,
for example, the switch 102 and the protection switch 208 are
immediately turned off, and the resistance 610 is inserted into the
charging path of a capacitor 402.
[0235] In this state, an LCR series resonant current flows through
a pathway from a direct-current power supply 8 through the
resistance 610, the reactor 701, the switch 101 having a short
circuit failure, the capacitor 402, and a diode 104 to the
direct-current power supply 8. The capacitor 402 is charged with
this current. Thus, the amount of charges that flows into the
capacitor 402 is reduced by the resistance 610, and hence
occurrence of an overvoltage on the capacitor 402 can be
suppressed.
[0236] Similarly to the aforementioned seventh embodiment, the
resistance value Rb of this resistance 610 is set to a value shown
by the following formula (18), whereby a resonant circuit on the
pathway can be critically damped or overdamped. Thus, when the
switch 101 has a short circuit failure in an operating state where
the voltages of capacitors 401 and 402 are lower than the voltage
VE of the direct-current power supply 8, the charging voltage of
the capacitor 402 can be kept to the voltage VE of the
direct-current power supply 8. Consequently, occurrence of an
overvoltage on the capacitor 402 can be suppressed.
Rb.gtoreq.2.times.(2.times.L/C2).sup.1/2 (18)
[0237] When the capacity value C of the smaller of the capacity of
the capacitor 401 and the capacity of the capacitor 402 is used to
allow the resistance value Rb of the resistance 610 to satisfy the
following formula (19), whereby a formed LCR series resonant
circuit can be critically damped or overdamped even when any of the
switches 101 and 102 has a short circuit failure.
Rb.gtoreq.2.times.(2.times.L/C).sup.1/2 (19)
[0238] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 208 are
immediately turned off such that the resistance 610 is inserted
into the charging path of the capacitor 402. A current flow pathway
from the direct-current power supply 8 becomes the pathway from the
direct-current power supply 8 through the resistance 610, the
reactor 701, the switch 101 having a short circuit failure, the
capacitor 402, and the diode 104 to the direct-current power supply
8. This pathway is the same as when only the switch 101 has a
failure, and hence an overvoltage on the capacitor 402 can be
prevented also in this case. Furthermore, the resistance value Rb
of this resistance 610 is set to the value shown by the above
formula (18) or (19), whereby the resonant circuit on the above
pathway can be critically damped or overdamped. Thus, the charging
voltage of the capacitor 402 can be kept to the voltage VE of the
direct-current power supply 8 when the diode 103 and the switch 101
each have a short circuit failure in the operating state where the
voltages of the capacitors 401 and 402 are lower than the voltage
VE of the direct-current power supply 8.
[0239] A connection order of the protection switch 208, the reactor
701, and the direct-current power supply 8 is not restricted, but
these can be connected in any order.
[0240] [Effects of Twelfth Embodiment]
[0241] According to the twelfth embodiment, the following effects
can be obtained.
[0242] According to the twelfth embodiment, as hereinabove
described, the three-level chopper apparatus 1200 includes the
protection switch 208 connected in series to the reactor 701 and
the resistance 610 connected in parallel to both ends of the
protection switch 208. Thus, when the switch 101 or 102 has a short
circuit failure, the control circuit 1m performs control for
turning off the protection switch 208, whereby the resistance 610
can be added in the current pathway. Consequently, when the switch
101 or 102 has a short circuit failure, the current pathway can be
formed as an LCR series resonant circuit, and hence occurrence of
an overvoltage on the capacitor 401 or 402 can be suppressed.
[0243] According to the twelfth embodiment, as hereinabove
described, the resistance value Rb satisfies the above formula (19)
where Rb represents the resistance value of the resistance 610, L
represents the inductance of the reactor 701, and C represents the
smaller of the capacity of the capacitor 401 and the capacity of
the capacitor 402. Thus, a current that flows through the LCR
series resonant circuit including the resistance 610 having the
resistance value Rb can be critically damped or overdamped, and
hence occurrence of an overvoltage on the capacitor 401 or 402 can
be more reliably suppressed when the switch 101 or 102 has a short
circuit failure.
[0244] The remaining effects of the three-level chopper apparatus
1200 according to the twelfth embodiment are similar to those of
the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
Thirteenth Embodiment
[0245] A three-level chopper apparatus 1300 according to a
thirteenth embodiment is now described with reference to FIG.
13.
[0246] According to the thirteenth embodiment, in the three-level
chopper apparatus 1300, a protection capacitor 501 is connected in
parallel to the protection switch 201 inserted into the connection
path 13 that connects the intermediate point (connection point N3)
of the switch series circuit 11 and the intermediate point
(connection point N4) of the capacitor series circuit 41 in the
three-level chopper apparatus 100 according to the aforementioned
first embodiment, as shown in FIG. 13. The three-level chopper
apparatus 1300 includes a control circuit 1n. The remaining
structures of the three-level chopper apparatus 1300 according to
the thirteenth embodiment are similar to those of the three-level
chopper apparatus 100 according to the aforementioned first
embodiment. The protection capacitor 501 is an example of a "first
protection capacitor" in the claims.
[0247] During the normal operation of the three-level chopper
apparatus according to this thirteenth embodiment, the protection
switch 201 is turned on such that no current flows through the
protection capacitor 501.
[0248] When a switch 101 has a short circuit failure in the switch
series circuit 11 of the three-level chopper apparatus, for
example, the protection switch 201 is turned off, and the
protection capacitor 501 is inserted into the connection path 13
that connects the intermediate point of the switch series circuit
11 and the intermediate point of the capacitor series circuit
41.
[0249] In this state, a capacitor 402 and the protection capacitor
501 are charged through a pathway from a direct-current power
supply 8 through a reactor 701, the switch 101 having a short
circuit failure, the protection capacitor 501, the capacitor 402,
and a diode 104 to the direct-current power supply 8, and
capacitors 401 and 402 start to be charged through a pathway from
the direct-current power supply 8 through the reactor 701, a diode
103, the capacitor 401, the capacitor 402, and the diode 104 to the
direct-current power supply 8 when the voltage of the protection
capacitor 501 reaches the voltage of the capacitor 401.
[0250] Thus, the sum of the charging voltages of the protection
capacitor 501 and the capacitor 402 exceeds the voltage VE of the
direct-current power supply 8. However, the protection capacitor
501 and the capacitor 402 share the summed voltage, and hence the
voltage to which the capacitor 402 is charged is reduced as
compared with the case where the protection switch 201 does not
disconnect the connection path 13, and occurrence of an overvoltage
on the capacitor 402 can be suppressed.
[0251] When the diode 103 and the switch 101 each have a short
circuit failure, the protection switch 201 is turned off.
[0252] In this state, an LC series resonant current flows through a
pathway from the direct-current power supply 8 through the reactor
701, the switch 101 having a short circuit failure, the protection
capacitor 501, the capacitor 402, and the diode 104 to the
direct-current power supply 8 and a pathway from the direct-current
power supply 8 through the reactor 701, the diode 103 having a
short circuit failure, the capacitor 401, the capacitor 402, and
the diode 104 to the direct-current power supply 8. In this case,
the diode 103 has a short circuit failure, and hence the capacitors
401 and 402 and the protection capacitor 501 are charged through
any one of the above pathways after short-circuit discharging of
the capacitor 401 or flow of a current to the protection capacitor
501. Also in this case, the voltage to which the capacitor 402 is
charged is reduced as compared with the case where the protection
switch 201 does not disconnect the connection path 13, and
occurrence of an overvoltage on the capacitor 402 can be
suppressed.
[0253] [Effects of Thirteenth Embodiment]
[0254] According to the thirteenth embodiment, the following
effects can be obtained.
[0255] According to the thirteenth embodiment, as hereinabove
described, the three-level chopper apparatus 1300 includes the
protection capacitor 501 connected in parallel to the protection
switch 201. Thus, when the switch 101 has a shirt circuit failure
and control for turning off the protection switch 201 is performed,
for example, an LC series resonant current flows through the
pathway from the direct-current power supply 8 through the reactor
701, the switch 101 having a short circuit failure, the protection
capacitor 501, the capacitor 402, and the diode 104 to the
direct-current power supply 8. In this case, the protection
capacitor 501 and the capacitor 402 are charged through this
pathway while sharing charges, and hence occurrence of an
overvoltage on the capacitor 402 can be suppressed as compared with
the case where only the capacitor 402 is charged.
[0256] The remaining effects of the three-level chopper apparatus
1300 according to the thirteenth embodiment are similar to those of
the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
Fourteenth Embodiment
[0257] A three-level chopper apparatus 1400 according to a
fourteenth embodiment is now described with reference to FIG.
14.
[0258] According to the fourteenth embodiment, in the three-level
chopper apparatus 1400, protection capacitors 502 and 503 are
connected in parallel to the protection switches 202 and 203
connected in series to the switches 101 and 102, which perform
control for turning on and off the switch series circuit 11
according to the aforementioned sixth embodiment, as shown in FIG.
14. The remaining structures of the three-level chopper apparatus
1400 according to the fourteenth embodiment are similar to those of
the three-level chopper apparatus 600 according to the
aforementioned sixth embodiment. The protection switches 202 and
203 according to the fourteenth embodiment are examples of a
"thirteenth protection switch" and a "sixteenth protection switch"
in the claims, respectively. The protection capacitors 502 and 503
are examples of a "fifth protection capacitor" and a "sixth
protection capacitor" in the claims, respectively.
[0259] The operation of the protection switches 202 and 203 in this
three-level chopper apparatus 1400 according to the fourteenth
embodiment is the same as that of the three-level chopper apparatus
600 according to the sixth embodiment. During normal operation, the
protection switches 202 and 203 are turned on, and the protection
capacitors 502 and 503 are short-circuited such that no current
flows through the protection capacitors 502 and 503.
[0260] When the switch 101 has a short circuit failure, the switch
102 and the protection switch 202 are turned off.
[0261] In this state, an LC series resonant current flows through a
pathway from a direct-current power supply 8 through a reactor 701,
the switch 101 having a short circuit failure, the protection
capacitor 502, a capacitor 402, and a diode 104 to the
direct-current power supply 8, and the capacitor 402 and the
protection capacitor 502 are charged. When the voltage of the
protection capacitor 502 reaches the voltage of a capacitor 401, an
LC series resonant current flows through a pathway from the
direct-current power supply 8 through the reactor 701, a diode 103,
the capacitor 401, the capacitor 402, and the diode 104 to the
direct-current power supply 8, and the capacitors 401 and 402 start
to be charged through this pathway.
[0262] Thus, the sum of the charging voltages of the protection
capacitor 502 and the capacitor 402 exceeds the voltage VE of the
direct-current power supply 8. However, the protection capacitor
502 and the capacitor 402 share the summed voltage, and hence the
voltage to which the capacitor 402 is charged is reduced as
compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 can
be suppressed.
[0263] Also when the diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 202 are
turned off, whereby occurrence of an overvoltage on the capacitor
402 can be suppressed similarly to the thirteenth embodiment.
[0264] Also according to this fourteenth embodiment, a connection
order of the switches 101 and 102 and the protection switches 202
and 203 is not restricted, but these can be connected in any
order.
[0265] [Effects of Fourteenth Embodiment]
[0266] According to the fourteenth embodiment, the following
effects can be obtained.
[0267] According to the fourteenth embodiment, as hereinabove
described, the three-level chopper apparatus 1400 includes the
protection switches 202 and 203 and the protection capacitors 502
and 503 connected in parallel to the protection switches 202 and
203. Thus, when the switch 10 1 has a short circuit failure, the
protection switch 202 is turned off, whereby the protection
capacitor 502 and the capacitor 402 are charged through the current
pathway while sharing charges. When the switch 102 has a short
circuit failure, the protection switch 203 is turned off, whereby
the protection capacitor 503 and the capacitor 401 are charged
through the current pathway while sharing charges. Therefore,
occurrence of an overvoltage on the capacitor 401 or 402 can be
suppressed as compared with the case where only the capacitor 401
or 402 is charged.
[0268] The remaining effects of the three-level chopper apparatus
1400 according to the fourteenth embodiment are similar to those of
the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
Fifteenth Embodiment
[0269] A three-level chopper apparatus 1500 according to a
fifteenth embodiment is now described with reference to FIG.
15.
[0270] According to the fifteenth embodiment, in the three-level
chopper apparatus 1500, a protection capacitor 504 is connected in
parallel between a connection point N11 between a switch 101 and a
protection switch 202 and a connection point N12 between a switch
102 and a protection switch 203, as shown in FIG. 15. The remaining
structures of the three-level chopper apparatus 1500 according to
the fifteenth embodiment are similar to those of the three-level
chopper apparatus 700 according to the aforementioned seventh
embodiment. The protection switches 202 and 203 according to the
fifteenth embodiment are examples of a "third protection switch"
and a "fourth protection switch" in the claims, respectively. The
protection capacitor 504 is an example of a "second protection
capacitor" in the claims.
[0271] The protection switches 202 and 203 according to this
fifteenth embodiment operate similarly to those according to the
aforementioned seventh embodiment. More specifically, during the
normal operation of the three-level chopper apparatus, both the
protection switches 202 and 203 are turned on, and the protection
capacitor 504 is short-circuited such that no current flows through
the protection capacitor 504.
[0272] When the switch 101 has a short circuit failure in a switch
series circuit 11 of the three-level chopper apparatus 1500, for
example, the switch 102 and the protection switch 202 are
immediately turned off.
[0273] In this state, an LC series resonant current flows through a
pathway from a direct-current power supply 8 through a reactor 701,
the switch 101 having a short circuit failure, the protection
capacitor 504, the protection switch 203 (through which a current
can flow and return to the direct-current power supply 8), a
capacitor 402, and a diode 104 to the direct-current power supply
8, and the capacitor 402 and the protection capacitor 504 are
charged. When the voltage of the protection capacitor 504 reaches
the voltage of a capacitor 401, the capacitors 401 and 402 start to
be charged through a pathway from the direct-current power supply
8, the reactor 701, a diode 103, the capacitor 401, the capacitor
402, and the diode 104 to the direct-current power supply 8.
[0274] Thus, when the sum of the charging voltages of the
protection capacitor 504 and the capacitor 402 exceeds the voltage
VE of the direct-current power supply 8. However, the protection
capacitor 504 and the capacitor 402 share the summed voltage, and
hence the voltage to which the capacitor 402 is charged is reduced
as compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 is
suppressed.
[0275] Also when the diode 103 and the switch 101 each have a short
circuit failure, occurrence of an overvoltage on the capacitor 402
is suppressed by the protection capacitor 504 similarly to the
aforementioned thirteenth embodiment.
[0276] [Effects of Fifteenth Embodiment]
[0277] According to the fifteenth embodiment, the following effects
can be obtained.
[0278] According to the fifteenth embodiment, as hereinabove
described, the protection capacitor 504 connected in parallel
between the connection points N11 and N12 is provided in the
three-level chopper apparatus 1500. Thus, when the switch 101 has a
short circuit failure and a control circuit 1h performs control for
turning off the protection switch 202 and turning on the protection
switch 203, for example, an LC series resonant current flows
through the pathway from the direct-current power supply 8 through
the reactor 701, the switch 101 having a short circuit failure, the
protection capacitor 504, the protection switch 203, the capacitor
402, and the diode 104 to the direct-current power supply 8. In
this case, the protection capacitor 504 and the capacitor 402 are
charged through this pathway while sharing charges, and hence
occurrence of an overvoltage on the capacitor 402 can be more
reliably suppressed as compared with the case where only the
capacitor 402 is charged.
[0279] The remaining effects of the three-level chopper apparatus
1500 according to the fifteenth embodiment are similar to those of
the three-level chopper apparatus 700 according to the
aforementioned seventh embodiment.
Sixteenth Embodiment
[0280] A three-level chopper apparatus 1600 according to a
sixteenth embodiment is now described with reference to FIG.
16.
[0281] According to the sixteenth embodiment, the three-level
chopper apparatus 1600 includes a parallel circuit of a protection
switch 204 and a protection capacitor 505 and a parallel circuit of
a protection switch 205 and a protection capacitor 506 in a
capacitor series circuit 41. The remaining structures of the
three-level chopper apparatus 1600 according to the sixteenth
embodiment are similar to those of the three-level chopper
apparatus 900 according to the aforementioned ninth embodiment. The
protection switches 204 and 205 are examples of a "sixteenth
protection switch" and a "thirteenth protection switch" in the
claims, respectively. The protection capacitors 505 and 506 are
examples of a "sixth protection capacitor" and a "fifth protection
capacitor" in the claims, respectively.
[0282] In the three-level chopper apparatus 1600 according to this
sixteenth embodiment, similarly to another embodiment, control for
switching on and off switches 101 and 102 of a switch series
circuit 11 is performed in a state where the protection switches
204 and 205 of the capacitor series circuit 41 are turned on and
the protection capacitors 505 and 506 are short-circuited during
normal operation such that a direct-current voltage is converted.
The protection switches 204 and 205 are configured such that a
current can flow and return to a direct-current power supply 8
therethrough, and hence flow of a current from capacitors to the
side of a load is not prevented.
[0283] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1600,
for example, the switch 102 and the protection switch 205 are
immediately turned off, and the protection capacitor 506 is
inserted into the charging path of a capacitor 402.
[0284] In this state, an LC series resonant current flows through a
pathway from the direct-current power supply 8 through a reactor
701, the switch 101 having a short circuit failure, the protection
capacitor 506, the capacitor 402, and a diode 104 to the
direct-current power supply 8. The protection capacitor 506 and the
capacitor 402 are charged with this current.
[0285] Thus, when the sum of the charging voltages of the
protection capacitor 506 and the capacitor 402 exceeds the voltage
VE of the direct-current power supply 8. However, the protection
capacitor 506 and the capacitor 402 share the summed voltage, and
hence the voltage to which the capacitor 402 is charged is reduced
as compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 is
suppressed.
[0286] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 205 are
immediately turned off such that the protection capacitor 506 is
inserted into the charging path of the capacitor 402. A current
flow pathway from the direct-current power supply 8 becomes the
pathway from the direct-current power supply 8 through the reactor
701, the switch 101 having a short circuit failure, the protection
capacitor 506, the capacitor 402, and the diode 104 to the
direct-current power supply 8. This pathway is the same as when
only the switch 101 has a failure, and hence an overvoltage on the
capacitor 402 can be suppressed also in this case.
[0287] The protection switches 204 and 205 can also be
bidirectional switches. In that case, the structure of the
bidirectional switches and control for turning on and off the
bidirectional switches must be the same as when the protection
switches 204 and 205 are the bidirectional switches in the
aforementioned eighth embodiment.
[0288] According to this sixteenth embodiment, a connection order
between the capacitor 401 and the parallel circuit of the
protection switch 204 and the protection capacitor 505 and a
connection order between the capacitor 402 and the parallel circuit
of the protection switch 205 and the protection capacitor 506 are
not restricted, but these can be connected in any order.
[0289] [Effects of Sixteenth Embodiment]
[0290] The effects of the three-level chopper apparatus 1600
according to the sixteenth embodiment are similar to those of the
three-level chopper apparatus 1400 according to the aforementioned
fourteenth embodiment.
Seventeenth Embodiment
[0291] A three-level chopper apparatus 1700 according to a
seventeenth embodiment is now described with reference to FIG.
17.
[0292] According to the seventeenth embodiment, in the three-level
chopper apparatus 1700, instead of the resistance 607 according to
the aforementioned tenth embodiment, a protection capacitor 507 is
connected, as shown in FIG. 17. The remaining structures of the
three-level chopper apparatus 1700 according to the seventeenth
embodiment are similar to those of the three-level chopper
apparatus 1000 according to the aforementioned tenth embodiment.
Protection switches 204 and 205 according to the seventeenth
embodiment are examples of a "seventh protection switch" and an
"eighth protection switch" in the claims, respectively. The
protection capacitor 507 is an example of a "third protection
capacitor" in the claims.
[0293] In the three-level chopper apparatus 1700 according to this
seventeenth embodiment, the structures of and control for the
protection switches 204 and 205 are similar to those in the
three-level chopper apparatus 1000 according to the tenth
embodiment. More specifically, similarly to another embodiment,
control for switching on and off switches 101 and 102 of a switch
series circuit 11 is performed in a state where the protection
switches 204 and 205 of a capacitor series circuit 41 are turned on
and the protection capacitor 507 is short-circuited during normal
operation such that a direct-current voltage is converted. The
protection switches 204 and 205 are configured such that a current
can flow and return to a direct-current power supply 8
therethrough, and hence flow of a current from capacitors to the
side of a load is not prevented.
[0294] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1700,
for example, the switch 102 and the protection switch 205 are
immediately turned off, and the protection capacitor 507 is
inserted into the charging path of a capacitor 402.
[0295] In this state, an LC series resonant current flows through a
pathway from the direct-current power supply 8 through a reactor
701, the switch 101 having a short circuit failure, the protection
switch 204 (through which a current can flow and return to the
direct-current power supply 8), the protection capacitor 507, the
capacitor 402, and a diode 104 to the direct-current power supply
8. The protection capacitor 507 and the capacitor 402 are charged
with this current.
[0296] Thus, when the sum of the charging voltages of the
protection capacitor 507 and the capacitor 402 exceeds the voltage
VE of the direct-current power supply 8. However, the protection
capacitor 507 and the capacitor 402 share the summed voltage, and
hence the voltage to which the capacitor 402 is charged is reduced
as compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 is
suppressed.
[0297] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 205 are
immediately turned off such that the protection capacitor 507 is
inserted into the charging path of the capacitor 402. A current
flow pathway from the direct-current power supply 8 becomes the
pathway from the direct-current power supply 8 through the reactor
701, the switch 101 having a short circuit failure, the protection
capacitor 507, the capacitor 402, and the diode 104 to the
direct-current power supply 8. This pathway is the same as when
only the switch 101 has a failure, and hence an overvoltage on the
capacitor 402 can be prevented also in this case.
[0298] [Effects of Seventeenth Embodiment]
[0299] According to the seventeenth embodiment, the following
effects can be obtained.
[0300] According to the seventeenth embodiment, as hereinabove
described, the three-level chopper apparatus 1700 includes the
protection switch 204 connected in series between a capacitor 401
and a connection path 13, the protection switch 205 connected in
series between the capacitor 402 and the connection path 13, and
the protection capacitor 507 connected in parallel between a
connection point N21 between the capacitor 401 and the protection
switch 204 and a connection point N22 between the protection switch
205 and the capacitor 402. Thus, when the switch 101 has a short
circuit failure and control for turning off the switch 102, turning
on the protection switch 204, and turning off the protection switch
205 is performed, for example, an LC series resonant current flows
through the pathway from the direct-current power supply 8 through
the reactor 701, the switch 101 having a short circuit failure, the
protection switch 204, the protection capacitor 507, the capacitor
402, and the diode 104 to the direct-current power supply 8. In
this case, the protection capacitor 507 and the capacitor 402 are
charged through this pathway while sharing charges, and hence
occurrence of an overvoltage on the capacitor 402 can be suppressed
as compared with the case where only the capacitor 402 is
charged.
[0301] The remaining effects of the three-level chopper apparatus
1700 according to the seventeenth embodiment are similar to those
of the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
Eighteenth Embodiment
[0302] A three-level chopper apparatus 1800 according to an
eighteenth embodiment is now described with reference to FIG.
18.
[0303] According to the eighteenth embodiment, in the three-level
chopper apparatus 1800, a parallel circuit of a protection switch
206 and a protection capacitor 508 and a parallel circuit of a
protection switch 207 and a protection capacitor 509 are connected
in series to didoes 104 and 104, respectively, as shown in FIG. 18.
The remaining structures of the three-level chopper apparatus 1800
according to the eighteenth embodiment are similar to those of the
three-level chopper apparatus 1100 according to the aforementioned
eleventh embodiment.
[0304] The protection switches 206 and 207 according to the
eighteenth embodiment are examples of a "sixteenth protection
switch" and a "thirteenth protection capacitor" in the claims,
respectively. The protection capacitors 508 and 509 are examples of
a "sixth protection capacitor" and a "fifth protection capacitor"
in the claims, respectively.
[0305] In the three-level chopper apparatus 1800 according to this
eighteenth embodiment, when the diodes 103 and 104 are caused to
conduct during normal operation, the protection switches 206 and
207 are turned on, and the protection capacitors 508 and 509 are
short-circuited. More specifically, similarly to another
embodiment, control for switching on and off switches 101 and 102
of a switch series circuit 11 is performed such that a
direct-current voltage is converted.
[0306] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1800,
for example, the switch 102 and the protection switch 207 are
turned off, and the protection capacitor 509 is inserted into the
charging path of a capacitor 402.
[0307] In this state, an LC series resonant current flows through a
pathway from a direct-current power supply 8 through a reactor 701,
the switch 101 having a short circuit failure, the capacitor 402,
the protection capacitor 509, and the diode 104 to the
direct-current power supply 8. The protection capacitor 509 and the
capacitor 402 are charged with this current.
[0308] Thus, when the sum of the charging voltages of the
protection capacitor 509 and the capacitor 402 exceeds the voltage
VE of the direct-current power supply 8. However, the protection
capacitor 509 and the capacitor 402 share the summed voltage, and
hence the voltage to which the capacitor 402 is charged is reduced
as compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 is
suppressed.
[0309] When the diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 207 are
immediately turned off such that the protection capacitor 509 is
inserted into the charging path of the capacitor 402. A current
flow pathway from the direct-current power supply 8 becomes the
pathway from the direct-current power supply 8 through the reactor
701, the switch 101 having a short circuit failure, the capacitor
402, the protection capacitor 509, and the diode 104 to the
direct-current power supply 8. This pathway is the same as when
only the switch 101 has a failure, and hence an overvoltage on the
capacitor 402 can be prevented also in this case.
[0310] According to this eighteenth embodiment, a connection order
of the diode 103 and the parallel circuit of the protection switch
206 and the protection capacitor 508 and a connection order of the
diode 104 and the parallel circuit of the protection switch 207 and
the protection capacitor 509 are not restricted, but these can be
connected in any order.
[0311] [Effects of Eighteenth Embodiment]
[0312] The effects of the three-level chopper apparatus 1800
according to the eighteenth embodiment are similar to those of the
three-level chopper apparatus 1400 according to the aforementioned
fourteenth embodiment.
Nineteenth Embodiment
[0313] A three-level chopper apparatus 1900 according to a
nineteenth embodiment is now described with reference to FIG.
19.
[0314] According to the nineteenth embodiment, in the three-level
chopper apparatus 1900, instead of the resistance 610 according to
the aforementioned twelfth embodiment, a protection capacitor 510
is connected, as shown in FIG. 19. The remaining structures of the
three-level chopper apparatus 1900 according to the nineteenth
embodiment are similar to those of the three-level chopper
apparatus 1200 according to the aforementioned twelfth embodiment.
A protection switch 208 according to the nineteenth embodiment is
an example of a "tenth protection switch" in the claims. The
protection capacitor 510 is an example of a "fourth protection
capacitor" in the claims.
[0315] In the three-level chopper apparatus 1900 according to this
nineteenth embodiment, similarly to another embodiment, control for
switching on and off switches 101 and 102 of a switch series
circuit 11 is performed in a state where the protection switch 208
is turned on and the protection capacitor 510 is short-circuited
during normal operation such that a direct-current voltage is
converted.
[0316] When the switch 101 has a short circuit failure in the
switch series circuit 11 of the three-level chopper apparatus 1900,
for example, the switch 102 and the protection switch 208 are
immediately turned off, and the protection capacitor 510 is
inserted into the charging path of a capacitor 402.
[0317] In this state, an LC series resonant current flows through a
pathway from a direct-current power supply 8 through the protection
capacitor 510, a reactor 701, the switch 101 having a short circuit
failure, the capacitor 402, and a diode 104 to the direct-current
power supply 8. The protection capacitor 510 and the capacitor 402
are charged with this current.
[0318] Thus, when the sum of the charging voltages of the
protection capacitor 510 and the capacitor 402 exceeds the voltage
VE of the direct-current power supply 8. However, the protection
capacitor 510 and the capacitor 402 share the summed voltage, and
hence the voltage to which the capacitor 402 is charged is reduced
as compared with the case where no protection switch circuit is
provided, and occurrence of an overvoltage on the capacitor 402 is
suppressed.
[0319] When a diode 103 and the switch 101 each have a short
circuit failure, the switch 102 and the protection switch 208 are
immediately turned off such that the protection capacitor 510 is
inserted into the charging path of the capacitor 402. A current
flow pathway from the direct-current power supply 8 becomes the
pathway from the direct-current power supply 8 through the
protection capacitor 510, the reactor 701, the switch 101 having a
short circuit failure, the capacitor 402, and the diode 104 to the
direct-current power supply 8. This pathway is the same as when
only the switch 101 has a failure, and hence an overvoltage on the
capacitor 402 can be suppressed also in this case.
[0320] A connection order of the protection switch 208, the reactor
701, and the direct-current power supply 8 is not restricted, but
these can be connected in any order.
[0321] [Effects of Nineteenth Embodiment]
[0322] According to the nineteenth embodiment, the following
effects can be obtained.
[0323] According to the nineteenth embodiment, as hereinabove
described, the three-level chopper apparatus 1900 includes the
protection switch 208 connected in series to the reactor 701 and
the protection capacitor 510 connected in parallel to both ends of
the protection switch 208. Thus, when the switch 101 or 102 has a
short circuit failure, control for turning off the protection
switch 208 is performed, whereby the protection capacitor 510 can
be added in the current pathway. In this case, the protection
capacitor 510 and one of capacitors 401 and 402 are charged through
this pathway while sharing charges, and hence occurrence of an
overvoltage on the capacitor 401 or 402 can be suppressed as
compared with the case where only the capacitor 401 or 402 is
charged.
[0324] The remaining effects of the three-level chopper apparatus
1900 according to the nineteenth embodiment are similar to those of
the three-level chopper apparatus 100 according to the
aforementioned first embodiment.
[0325] [Modification]
[0326] The embodiments disclosed this time must be considered as
illustrative in all points and not restrictive. The range of the
present invention is shown not by the above description of the
embodiments but by the scope of claims for patent, and all
modifications within the meaning and range equivalent to the scope
of claims for patent are further included.
[0327] For example, while an element other than the protection
switch, the resistance, and the protection capacitor is not
provided in the connection path in each of the aforementioned first
to nineteenth embodiments, the present invention is not restricted
to this. According to the present invention, an element other than
the protection switch, the resistance, and the protection capacitor
may alternatively be provided in the connection path so far as the
protection switches can be controlled to be turned on and off such
that one of the capacitors, the resistance, or the protection
capacitor is inserted into the pathway through which an overvoltage
is applied to the other of the capacitors at the time of
failure.
[0328] For example, the protection switch circuit may alternatively
be configured by properly combining the aforementioned sixth,
seventh, ninth, eleventh, fourteenth, sixteenth, and eighteenth
embodiments. Also in a three-level chopper apparatus 2000 shown in
FIG. 20, in which the sixth embodiment and the ninth embodiment are
combined in a three-level chopper apparatus, when a switch 101 has
a short circuit failure, a protection switch 202 is turned off such
that a capacitor 401 is inserted into a pathway through which a
capacitor 402 is charged, and hence an overvoltage on the capacitor
402 is suppressed. Furthermore, a protection switch 204 is turned
off, whereby a resistance 605 is added in a resonant current flow
pathway such that the current is reduced, and the attained voltage
of the capacitor 402 is further reduced. On the other hand, when a
switch 102 has a short circuit failure, the protection switch 204
is turned off, whereby a current with which the capacitor 401 is
charged is damped by the resistance 605, and an overvoltage on the
capacitor 402 can be suppressed.
* * * * *