U.S. patent application number 12/379392 was filed with the patent office on 2009-09-03 for electric power converter.
This patent application is currently assigned to FUJI ELECTRIC DEVICE TECHNOLOGY CO., LTD.. Invention is credited to Masakazu Gekinozu.
Application Number | 20090219006 12/379392 |
Document ID | / |
Family ID | 41012687 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090219006 |
Kind Code |
A1 |
Gekinozu; Masakazu |
September 3, 2009 |
Electric power converter
Abstract
An electric power converter facilitates performing soft
switching in the two-way electric-power-conversion operation
thereof, and reducing the manufacturing costs thereof and the
losses caused therein, The electric power converter includes a
first switching device; a second switching device; a first series
circuit including capacitor, a diode, the primary winding of
transformer, and a third switching device; a second series circuit
including a capacitor, a fourth switching device, the primary
winding of transformer, and a diode; a third series circuit
including a diode and the secondary winding of transformer; and a
voltage clamping element connected in parallel to the primary
winding of transformer. The first series circuit is connected in
parallel to the first switching device, and the second series
circuit is connected in parallel to second switching device. The
third series circuit is connected between the DC output
terminals.
Inventors: |
Gekinozu; Masakazu;
(Matsumoto-shi, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD, SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
FUJI ELECTRIC DEVICE TECHNOLOGY
CO., LTD.
Tokyo
JP
|
Family ID: |
41012687 |
Appl. No.: |
12/379392 |
Filed: |
February 20, 2009 |
Current U.S.
Class: |
323/304 |
Current CPC
Class: |
H02M 3/1582 20130101;
Y02B 70/1491 20130101; Y02B 70/10 20130101; H02M 2001/342
20130101 |
Class at
Publication: |
323/304 |
International
Class: |
G05F 3/02 20060101
G05F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2008 |
JP |
2008-047706 |
Claims
1. An electric power converter, comprising: a first series circuit
including a reactor and a first switching device, and adapted to be
connected between DC input terminals of a DC power supply; a second
series circuit including a second switching device and an output
capacitor having DC output terminals, and connected in parallel
with the first switching device, a load being adapted to be
connected in parallel with the output capacitor; a transformer
having a primary winding, and a secondary winding connected in
parallel with the output capacitor; a third series circuit
including a first capacitor, a first diode, the primary winding and
a third switching device, and connected in parallel with the first
switching device; a fourth series circuit including a second
capacitor, a fourth switching device, the primary winding and a
second diode, and connected in parallel with the second switching
device; a fifth series circuit including a third diode and the
secondary winding of the transformer, and connected between the DC
output terminals; and a voltage clamping device connected in
parallel with the primary winding of the transformer.
2. An electric power converter, comprising: a plurality of first
series circuits connected in parallel to each other to form
parallel connection points, each of the first series circuits
including a first switching device and a second switching device
connected in series via an internal connection point thereof, and a
first capacitor and a second capacitor connected in parallel to the
first switching device and the second switching device,
respectively; a reactor connected at one side to the internal
connection point of one of the first series circuits and adapted to
be connected at the other side to an AC power supply; an output
capacitor having DC output terminals connected to the parallel
connection points of the first series circuits, a load being
adapted to be connected between the DC output terminals; a
transformer having a primary winding, and a secondary winding; a
first diode having an anode terminal connected to the internal
connection point of said one of the first series circuit and a
cathode terminal; a second diode having an anode terminal connected
to the internal connection point of another of the first series
circuit and a cathode terminal connected to the cathode terminal of
the first diode; a second series circuit including a third
switching device and the primary winding of the transformer, and
connected between the cathode terminals of the first and second
diodes and one of the DC output terminals; a third diode including
a cathode terminal connected to the internal connection point of
said one of first series circuit and an anode terminal; a fourth
diode include a cathode terminal connected to the internal
connection point of said another of the first series circuit and an
anode terminal connected to the anode terminal of the third diode;
a third series circuit including a fourth switching device and the
primary winding of the transformer, and connected between the anode
terminals of the third and fourth diodes and the other of the DC
output terminals; a fourth series circuit including a fifth diode
and the secondary winding of the transformer, and connected between
the DC output terminals; and a voltage clamping device connected in
parallel to the primary winding of the transformer.
3. An electric power converter according to claim 2, comprising two
sets of first series circuits arranged parallel to each other, the
output capacitor being connected between a connecting point of the
first switching devices and a connecting point of the second
switching devices in the two first series circuits.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to an electric power converter
that generates a DC output from a DC power supply or from an AC
power supply. Specifically, the present invention relates to the
soft switching function of an electric power converter capable of
conducting two-way operations.
[0002] The circuit of a conventional electric power converter
capable of conducting two-way operations is disclosed in the
following Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2004-147475. The conventional circuit disclosed in
the Patent Document 1 is shown in FIG. 3A.
[0003] The conventional circuit shown in FIG. 3A is described in
connection with a single-phase AC power supply. The conventional
circuit consists of a rectifier circuit including a diode bridge
circuit having diodes 2 through 5, and a chopper circuit including
reactor 21, diode 6, and switching device 15.
[0004] As switching device 15 is turned on, AC power supply 1 is
short-circuited via the diode bridge circuit and reactor 21, energy
is stored in reactor 21, and an AC input current increases.
[0005] Then, as switching device 15 is turned off, the energy
stored in reactor 21 is fed via diode 6 to capacitor 33 and load
34, which constitute a DC output.
[0006] By controlling the ON and OFF of switching device 15, a
rectified AC voltage (DC voltage) is converted to an arbitrary DC
voltage. A soft switching circuit for the chopper circuit is
configured by capacitor 31, diodes 7, 9, 10, voltage clamping
element 30, transformer 22 and switching device 17.
[0007] FIG. 3B is a wave chart describing the operations of the
circuit shown in FIG. 3A.
[0008] As switching device 17 is turned on, the current that
circulates, during a period t1, from reactor 21 to reactor 21 via
diode 6, capacitor 33, diode bridge circuit 40, and AC power supply
1 gradually changes the current path so as to circulate, due to the
influence of the leakage inductance of transformer 22, from reactor
21 to reactor 21 via diode 7, primary winding 22a of transformer
22, switching device 17, diode bridge circuit 40, and AC power
supply 1. Since the current that flows through switching device 17
increases gradually from zero during the commutation described
above, switching device 17 performs soft switching at the turn-ON
thereof.
[0009] Then, a period t2 starts. During the period t2, the current
flowing through switching device 17 becomes equal to the current
flowing through reactor 21 and diode 6 becomes OFF. Since the
current flowing through diode 6 decreases gradually to zero, the
surge voltage and the reverse recovery losses caused by the reverse
recovery are reduced. At the same time, the electric charge stored
in capacitor 31 (or in the parasitic capacitance of switching
device 15) is discharged via a path connecting capacitor 31, diode
7, primary winding 22a of transformer 22, switching device 17, and
capacitor 31. The electric charge stored in capacitor 31 is
regenerated to the output side via secondary winding 22b of
transformer 22 and diode 10.
[0010] By turning on switching device 15 after the voltage thereof
lowers to zero in a period t3, a difference current, which is the
difference between the current flowing through primary winding 22a
of transformer 22 and the current flowing through reactor 21, flows
through switching device 15. Since the difference current that
flows through switching device 15 initially flows through parasitic
diode 12, the current that flows through switching device 15
increases gradually from a negative value. Therefore, switching
device 15 performs soft switching at the state of the turn-ON
thereof.
[0011] Then, the current that has been circulating from reactor 21
to reactor 21 via diode 7, primary winding 22a of transformer 22,
switching device 17, diode bridge circuit 40, and AC power supply 1
gradually changes so as to circulate from reactor 21 to reactor 21
via switching device 15, diode bridge circuit 40, and AC power
supply 1. At the same time, the energy stored in the leakage
inductance of transformer 22 is fed to the output side via
secondary winding 22b of transformer 22 and diode 10. The current
that flows through switching device 17 decreases gradually to zero.
Since switching device 17 is brought into the OFF-state thereof
after the current that flows through switching device 17 reaches
zero, switching device 17 performs soft switching at the state of
the turn-OFF thereof.
[0012] When switching device 15 is turned off, the voltage of
switching device 15 rises gradually due to the current flowing
through capacitor 31. Therefore, the turn-OFF losses are reduced.
Thus, switching devices 15 and 17 perform soft switching.
[0013] In a period t4, a reset voltage equal to the voltage clamped
by voltage clamping element 30 is caused across primary winding 22a
of transformer 22. A voltage, which is as high as the product of
the reset voltage and the winding ratio of transformer 22, is
generated across secondary winding 22b of transformer 22. The sum
of the DC output voltage and the voltage across secondary winding
22b of transformer 22 is applied to diode 10. By setting the
clamping voltage of voltage clamping element 30 to be low, the
voltage applied to diode 10 is reduced.
[0014] FIG. 4A is a circuit diagram of another conventional
electric power converter disclosed in the Patent Document 1.
[0015] In FIG. 4A, a rectifier circuit is configured by reactor 21,
diodes 2 through 5, and switching devices 15 and 16. Switching
device 15 and capacitor 31 are connected in parallel to diode 3.
Switching device 16 and capacitor 32 are connected in parallel to
diode 5. AC power supply 1 is connected between the series
connection point of diodes 2 and 3 and the series connection point
of diodes 4 and 5 via reactor 21. Capacitor 33 and load 34 are
connected between the DC terminals of the diode bridge circuit.
[0016] The parasitic diode of switching device 15 may be used in
substitution for diode 3. The parasitic diode of switching device
16 may be used in substitution for diode 5. The soft switching
circuit for the rectifier circuit is configured by diodes 7 through
10, switching device 17, transformer 20, and voltage clamping
element 30.
[0017] FIG. 4B is a wave chart describing the operations of the
circuit shown in FIG. 4A.
[0018] As switching device 15 is turned on when the AC power supply
voltage is positive, the AC input current, circulating from AC
power supply 1 to AC power supply 1 via reactor 21, switching
device 15, and diode 5, increases while storing energy in reactor
21. Then, as switching device 15 is turned off, the energy stored
in reactor 21 is fed to the DC output side via a path connecting
reactor 21, diode 2, capacitor 33, diode 5, AC power supply 1 and
reactor 21. Therefore, it is possible to convert an AC power supply
voltage to an arbitrary DC voltage by controlling the ON and OFF of
switching device 15 when the AC power supply voltage is positive.
In the same manner, it is possible to convert an AC power supply
voltage to an arbitrary DC voltage by controlling the ON and OFF of
switching device 16 when the AC power supply voltage is
negative.
[0019] In FIG. 4A, diodes 7 and 8 are disposed in substitution for
diode 7 in FIG. 3A. In FIG. 4A, diode 8 works for diode 7 in FIG.
3A, when the AC power supply voltage is positive. Diode 7 works for
diode 7 in FIG. 3A, when the AC power supply voltage is negative.
Since switching device 15 is turned on and off when the AC power
supply voltage is positive, the electric charge stored in capacitor
31 is regenerated to the DC output side through the operations
similar to the operations conducted in the circuit shown in FIG.
3A. Since a current always flows through diode 5 when the AC power
supply voltage is positive, capacitor 32 stores no electric
charge.
[0020] When the AC power supply voltage is negative, the electric
charge stored in capacitor 32 is regenerated to the load side
through the operations similar to the operations conducted in the
circuit shown in FIG. 3A. Therefore, the circuit shown in FIG. 4A
conducts operations similar to the operations conducted by the
circuit shown in FIG. 3A. Switching devices 15, 16, and 17 and
diodes 2 and 4 conduct soft switching. Since the sum of the DC
output voltage and the secondary winding voltage of transformer 22
is applied to diode 10 in the circuit shown in FIG. 4A in the same
manner as in FIG. 3A, the voltage applied to diode 10 is reduced by
setting the clamping voltage of voltage clamping element 30 to be
low.
[0021] For performing two-way electric power conversion, Patent
Document 2: Japanese Unexamined Patent Application Publication No.
Sho 64 (1989)-064557 discloses a combination of a buck chopper and
a boost chopper. For the boost chopper, a boost chopper including
an auxiliary chopper and disclosed in Patent Document 3: Japanese
Unexamined Patent Application Publication No. Hei 05 (1993)-328714
may be used. However, the boost chopper including an auxiliary
chopper and disclosed in the Patent Document 3 includes many
circuit component parts. Moreover, the boost chopper including an
auxiliary chopper and disclosed in the Patent Document 3 is large
in size and expensive.
[0022] For realizing two-way electric power conversion in the
conventional circuit shown in FIG. 3A, it is necessary to replace
diode 6 by a switching device. For realizing two-way electric power
conversion in the conventional circuit shown in FIG. 4A, it is
necessary to replace diodes 2 and 4 by switching devices. The
replacing switching device or the replacing switching devices can
not perform soft switching.
[0023] In view of the foregoing, it would be desirable to obviate
the problems described above, and to provide a two-way electric
power converter that facilitates conducting soft switching
operations inexpensively with low conversion losses.
[0024] Further objects and advantages of the invention will be
apparent from the following description of the invention.
SUMMARY OF THE INVENTION
[0025] According to the subject matter of a first aspect of the
invention, there is provided an electric power converter
including:
[0026] a first series circuit including a reactor and a first
switching device, the first series circuit being connected between
DC input terminals;
[0027] a second series circuit including a second switching device
and an output capacitor including a terminal working for a DC
output terminal, the second series circuit being connected in
parallel to the first switching device;
[0028] a load connected in parallel to the output capacitor;
[0029] a third series circuit including a first capacitor, a first
diode, a primary winding of a transformer, and a third switching
device, the third series circuit being connected in parallel to the
first switching device;
[0030] a fourth series circuit including a second capacitor, a
fourth switching device, the primary winding of the transformer,
and a second diode, the fourth series circuit being connected in
parallel to the second switching device;
[0031] a fifth series circuit including a third diode and the
secondary winding of the transformer, the fifth series circuit
being connected between the DC output terminals; and
[0032] a voltage clamping means connected in parallel to the
primary winding of the transformer.
[0033] According to the subject matter of a second aspect of the
invention, there is provided an electric power converter
including:
[0034] an AC power supply;
[0035] a first series circuit including a first switching device
and a second switching device connected in series to each other via
an internal connection point, N pieces of the first series circuits
being connected in parallel to each other, said N being a
nonnegative integer equal to or more than 2;
[0036] a reactor connected between the AC power supply and the
internal connection point in the first one of the first series
circuits;
[0037] an output capacitor including a DC output terminal, the DC
output terminals being connected between the parallel connection
points of the N pieces of the first series circuits;
[0038] a load connected between the DC output terminals of the
output capacitor;
[0039] the first series circuit including a first capacitor and a
second capacitor connected in parallel to the first switching
device and the second switching device, respectively;
[0040] a first diode including an anode terminal connected to the
internal connection point of the first series circuit and a cathode
terminal, the cathode terminals of the first diodes being connected
collectively;
[0041] a second series circuit including the primary winding of a
transformer and a third switching device; the second series circuit
being connected between the cathode terminals of the first diodes
and the DC output terminal;
[0042] a second diode including a cathode terminal connected to the
internal connection point of the first series circuit and an anode
terminal, the anode terminals of the second diodes being connected
collectively;
[0043] a third series circuit including the primary winding of the
transformer and a fourth switching device, the third series circuit
being connected between the anode terminals of the second diodes
and the DC output terminal;
[0044] a fourth series circuit including a third diode and the
secondary winding of the transformer, the fourth series circuit
being connected between the DC output terminals; and
[0045] a voltage clamping means connected in parallel to the
primary winding of the transformer.
[0046] The electric power converter according to the invention that
conducts two-way electric power conversion facilitates performing
soft switching with a minimal circuit added thereto and reducing
the losses caused thereby.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1A is a circuit diagram showing the circuit
configuration of an electric power converter according to a first
embodiment of the invention.
[0048] FIG. 1B is a wave chart describing the operations of the
circuit shown in FIG. 1A.
[0049] FIG. 2A is a circuit diagram showing the circuit
configuration of an electric power converter according to a second
embodiment of the invention.
[0050] FIG. 2B is a wave chart describing the operations of the
circuit shown in FIG. 2A.
[0051] FIG. 3A is a circuit diagram of a conventional electric
power converter.
[0052] FIG. 3B is a wave chart describing the operations of the
circuit shown in FIG. 3A.
[0053] FIG. 4A is a circuit diagram of another conventional
electric power converter.
[0054] FIG. 4B is a wave chart describing the operations of the
circuit shown in FIG. 4A.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0055] Now, the invention will be described in detail hereinafter
with reference to the accompanied drawings which illustrate the
preferred embodiments of the invention.
[0056] FIG. 1A is a circuit diagram showing the circuit
configuration of an electric power converter according to a first
embodiment of the invention.
[0057] In the circuit shown in FIG. 1A, DC power supply 51 is
employed in substitution for AC power supply 1 and rectifier
circuit 40. Switching device 18 is connected in parallel to diode
6. DC power supply 51, reactor 21, diodes 6 and 12, and switching
devices 15 and 18 constitute a chopper circuit.
[0058] By turning on and off switching device 15 in the chopper
circuit described above, electric power is fed from the DC power
supply side to the load side. By turning on and off switching
device 18 in the chopper circuit described above, electric power is
regenerated from the load side to the DC power supply side. A soft
switching circuit is configured by diodes 7, 9, 10, 41, and 42;
switching devices 17 and 20; transformer 22; and voltage clamping
element 30.
[0059] For feeding electric power from the DC power supply side to
the load side, switching devices 15 and 17 and diode 6 are made to
conduct soft switching in the same manner as in the circuit shown
in FIG. 3A. The electric power converter according to the first
embodiment is different from the conventional electric power
converters in that the electric power converter according to the
first embodiment makes it possible to conduct soft switching in
regenerating electric power from the load side to the DC power
supply side by adding a few circuit component parts. Now the
regeneration operation conducted by the electric power converter
according to the first embodiment will be described in detail
below.
[0060] By turning on switching device 18 in FIG. 1A, the energy
stored in capacitor 33 is transferred to reactor 21 via switching
device 18 and regenerated to DC power supply 51. Then, as switching
device 18 is turned off, the energy transferred to reactor 21 is
regenerated to DC power supply 51 through a path connecting reactor
21, DC power supply 51, and diode 12. Thus, the energy stored in
the capacitor on the load side is regenerated to the DC power
supply side by controlling the ON and OFF of switching device
18.
[0061] Capacitor 71; diodes 9, 10, 41, and 42; voltage clamping
element 30, transformer 22; and switching device 20 form a soft
switching circuit for the regeneration operation mode that
regenerates electric power from the load side to the DC power
supply side. In the same manner as in FIG. 3A, diodes 9 and 10;
voltage clamping element 30; and transformer 22 are employed also
for configuring a soft switching circuit for the operation mode
that feeds electric power from the DC power supply side to the load
side.
[0062] FIG. 1B is a wave chart describing the operations of the
circuit shown in FIG. 1A.
[0063] As switching device 20 is turned on, the electric charge
stored in capacitor 71 (or in the parasitic capacitance of
switching device 18) is discharged in a period t1 through a path
connecting capacitor 71, switching device 20, the primary winding
of transformer 22, and diode 42. At the same time, the electric
charge stored in capacitor 71 is regenerated to the output side via
the secondary winding of transformer 22 and diode 10. Since the
current flowing through switching device 20 gradually increases due
to the leakage inductance of transformer 22, switching device 20
performs soft switching during the state of the turn-ON
thereof.
[0064] As soon as the current value flowing through switching
device 20 becomes equal to the current value flowing through
reactor 21, a period t2 starts and diode 12 becomes OFF. Since the
current flowing through diode 12 decreases gradually to zero, the
surge voltage caused by the reverse recovery and the reverse
recovery losses are reduced. As switching device 18 is turned on in
a period t3 after the voltage of switching device 18 becomes zero,
a difference current, equal to the difference between the current
flowing through the primary winding of transformer 22 and the
current flowing through reactor 21, flows through switching device
18. Since the difference current that flows through switching
device 18 initially flows through diode 6, the current that flows
through switching device 18 gradually increases from a negative
value. Therefore, switching device 18 performs soft switching
during the state of the turn-ON thereof.
[0065] When switching device 15 is turned off, the voltage of
switching device 15 rises gradually due to the current flowing
through capacitor 31. Therefore, the turn-OFF losses are reduced.
Thus, switching devices 15 and 18 perform soft switching at the
turn-OFF thereof. In a period t4, a reset voltage equal to the
voltage clamped by voltage clamping element 30 is caused across the
primary winding of transformer 22. A voltage, which is as high as
the product of the reset voltage and the winding ratio of
transformer 22, is generated across the secondary winding of
transformer 22. The sum of the DC output voltage and the voltage
across the secondary winding of transformer 22 is applied to diode
10. By setting the clamping voltage of voltage clamping element 30
to be low, the voltage applied to diode 10 is reduced.
[0066] FIG. 2A is a circuit diagram showing the circuit
configuration of an electric power converter according to a second
embodiment of the invention.
[0067] As shown in FIG. 2A, a rectifier circuit is configured by
reactor 21, diodes 2 through 5, and switching devices 15, 16, 18
and 19. Switching device 18 and capacitor 71 are connected in
parallel to diode 2 in a diode bridge circuit configured by diodes
2 through 5. Switching device 15 and capacitor 31 are connected in
parallel to diode 3 in the diode bridge circuit. Switching device
19 and capacitor 72 are connected in parallel to diode 4 in the
diode bridge circuit. Switching device 16 and capacitor 32 are
connected in parallel to diode 5 in the diode bridge circuit. AC
power supply 1 is connected between the series connection point of
diodes 2 and 3 and the series connection point of diodes 4 and 5
via reactor 21. Diodes 2 through 5 may be replaced by the parasitic
diodes of switching devices 15, 16, 18, and 19, respectively.
[0068] Diodes 7 through 10, 13, 41 through 43; switching devices 17
and 20; transformer 22; and voltage clamping element 30 form a soft
switching circuit. In detail, the soft switching circuit is
configured in the following manner. The anode of diode 8 is
connected to the series connection point of diodes 2 and 3. The
anode of diode 7 is connected to the series connection point of
diodes 4 and 5. The cathode of diode 42 is connected to the series
connection point of diodes 2 and 3. The cathode of diode 43 is
connected to the series connection point of diodes 4 and 5. The
cathodes of diodes 7 and 8 and the source terminal of switching
device 20, to which diode 41 is connected in parallel, are
connected to the first terminal of the primary winding in
transformer 22. The anodes of diodes 42 and 43 and the drain
terminal of switching device 17, to which diode 13 is connected in
parallel, are connected to the second terminal of the primary
winding in transformer 22. The drain terminal of switching device
20 is connected to the positive terminal of the DC output. The
source terminal of switching device 17 is connected to the negative
terminal of the DC output. A series circuit of diode 9 and voltage
clamping element 30 is connected in parallel to the primary winding
of transformer 22. A series circuit of diode 10 and the secondary
winding of transformer 22 is connected in parallel to capacitor 33,
that is the DC output. The parasitic diodes of switching devices 17
and 20 may be employed in substitution for diodes 13 and 41 with no
problem.
[0069] In feeding electric power from the AC power supply side to
the load side in the circuit shown in FIG. 2A, soft switching is
performed by switching devices 15 through 17 and diodes 2 and 4 in
the same manner as in the conventional circuit shown in FIG. 4A.
The circuit shown in FIG. 2A is different from the conventional
circuit shown in FIG. 4A in that the circuit shown in FIG. 2A
facilitates performing soft switching even in regenerating electric
power from the load side to the AC power supply side with a few
circuit component parts added thereto.
[0070] As switching devices 16 and 18 are turned on when the AC
power supply voltage is positive in the circuit configuration shown
in FIG. 2A, the energy stored in capacitor 33 is transferred to
reactor 21 through a path connecting capacitor 33, switching device
18, reactor 21, AC power supply 1, and switching device 16 and
regenerated to AC power supply 1. Then, by turning off switching
device 18, the energy transferred to reactor 21 is regenerated to
AC power supply 1 through a path connecting reactor 21, AC power
supply 1, switching device 16 and diode 3.
[0071] As switching devices 19 and 15 are turned on when the AC
power supply voltage is negative in the circuit configuration shown
in FIG. 2A, the energy stored in capacitor 33 is transferred to
reactor 21 through a path connecting capacitor 33, switching device
19, AC power supply 1, reactor 21, and switching device 15 and
regenerated to AC power supply 1. Then, by turning off switching
device 19, the energy transferred to reactor 21 is regenerated to
AC power supply 1 through a path connecting reactor 21, AC power
supply 1, switching device 15 and diode 5. Thus, by controlling the
ON and OFF of switching device 18 or 19, the energy stored on the
load side is regenerated to the AC power supply side.
[0072] Capacitors 71 and 72; diodes 9, 10, 41 through 43; voltage
clamping element 30; transformer 22; and switching device 20 form a
soft switching circuit for the regeneration operation mode that
regenerates electric power from the load side to the AC power
supply side. In the same manner as described with reference to FIG.
4A, diodes 9 and 10; voltage clamping element 30; and transformer
22 are employed also for configuring a soft switching circuit for
the operation mode that feeds electric power from the AC power
supply side to the load side.
[0073] FIG. 2B is a wave chart describing the operations of the
circuit shown in FIG. 2A.
[0074] By turning on switching device 20 when the AC power supply
voltage is positive, the electric charge stored in capacitor 71 (or
in the parasitic capacitance of switching device 18) is discharged
in a period t1 through a path connecting capacitor 71, switching
device 20, the primary winding of transformer 22, and diode 42. At
the same time, the electric charge stored in capacitor 71 is
regenerated to the output side via the secondary winding of
transformer 22 and diode 10. Since the current flowing through
switching device 20 increases gradually from zero due to the
leakage inductance of transformer 22, switching device 20 performs
soft switching at the turn-ON thereof.
[0075] As soon as the current value flowing through switching
device 20 becomes equal to the current value flowing through
reactor 21, a period t2 starts and diode 3 becomes OFF. Since the
current flowing through diode 3 decreases gradually to zero, the
surge voltage caused by the reverse recovery and the reverse
recovery losses are reduced. As switching device 18 is turned on in
a period t3 after the voltage of switching device 18 becomes zero,
a difference current, equal to the difference between the current
flowing through the primary winding of transformer 22 and the
current flowing through reactor 21, flows through switching device
18. Since the difference current that flows through switching
device 18 initially flows through diode 2, the current flowing
through switching device 18 increases gradually from a negative
value. Therefore, switching device 18 performs soft switching at
the turn-ON thereof.
[0076] When switching device 18 is turned off, the voltage of
switching device 18 rises gradually due to the current flowing
through capacitor 71. Therefore, the turn-OFF losses are reduced.
Thus, switching devices 18 and 20 perform soft switching.
[0077] In a period t4, a reset voltage equal to the voltage clamped
by voltage clamping element 30 is caused across the primary winding
of transformer 22. A voltage, which is as high as the product of
the reset voltage and the winding ratio of transformer 22, is
generated across the secondary winding of transformer 22. The sum
of the DC output voltage and the voltage across the secondary
winding of transformer 22 is applied to diode 10. By setting the
clamping voltage of voltage clamping element 30 to be low, the
voltage applied to diode 10 is reduced.
[0078] When the AC power supply voltage is negative, the electric
charges stored in capacitor 72 are regenerated to the load side in
the same manner as described above. Therefore, the rectifier
circuit in FIG. 2A works in the same manner as the rectifier
circuit in FIG. 1A. Switching devices 15 through 20 and diodes 2
through 5 perform soft switching.
[0079] The Disclosure of Japanese Patent Application No.
2008-047706 filed on Feb. 28, 2008 is incorporated in the
application.
[0080] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
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