U.S. patent application number 15/655357 was filed with the patent office on 2018-02-01 for bidirectional insulated dc-dc converter.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. The applicant listed for this patent is KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Nobuo HIRABAYASHI.
Application Number | 20180034360 15/655357 |
Document ID | / |
Family ID | 60951018 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180034360 |
Kind Code |
A1 |
HIRABAYASHI; Nobuo |
February 1, 2018 |
BIDIRECTIONAL INSULATED DC-DC CONVERTER
Abstract
A bidirectional insulated DC-DC converter includes a
transformer, a secondary circuit, and a control circuit. When
electric power is transferred from the secondary side to the
primary side of the transformer, the control circuit measures a
first voltage on a high voltage side of the transformer and a
second voltage on a low voltage side of the transformer in each
cycle time. When the voltage ratio is a reference value or larger,
the control circuit calculates a first period during which the
control circuit turns ON the first switching element and a second
period during which the control circuit turns ON the second
switching element after the first period of the cycle time so that
a period ratio is larger than a reference value and controls the
first switching element and the second switching element based on
the first period and the second period.
Inventors: |
HIRABAYASHI; Nobuo;
(Aichi-ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOYOTA JIDOSHOKKI |
Kariya-shi |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Kariya-shi
JP
|
Family ID: |
60951018 |
Appl. No.: |
15/655357 |
Filed: |
July 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 3/33592 20130101;
Y02B 70/1475 20130101; H02M 3/33584 20130101; H02M 1/088 20130101;
Y02B 70/1491 20130101; Y02B 70/10 20130101; H02M 2001/0048
20130101 |
International
Class: |
H02M 1/088 20060101
H02M001/088; H02M 3/335 20060101 H02M003/335 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2016 |
JP |
2016-147111 |
Claims
1. A bidirectional insulated DC-DC converter comprising; a
transformer having a primary winding and a secondary winding; a
secondary circuit connected to the secondary winding of the
transformer and including a coil, a first switching element, and a
second switching element, wherein a first terminal of the coil and
a first terminal of the first switching element are connected to a
first terminal of the secondary winding of the transformer, wherein
a first terminal of the second switching element is connected to a
second terminal of the secondary winding, and wherein a second
terminal of the first switching element and a second terminal of
the second switching element are connected to each other; and a
control circuit controlling the first switching element and the
second switching element, wherein when electric power is
transferred from the secondary side to the primary side of the
transformer, the control circuit measures a first voltage VH that
denotes a DC voltage of the primary winding on a high voltage side
of the transformer and a second voltage VL that denotes a DC
voltage of the secondary winding on a low voltage side of the
transformer in each cycle time, wherein the control circuit
calculates a voltage ratio n, or VH/VL, and wherein when the
voltage ratio n is a reference value J, or 1/(1+L1/2Lm) or larger,
where L1 denotes inductance of the coil and Lm denotes exciting
inductance of the transformer, the control circuit calculates a
first period during which the control circuit turns ON the first
switching element and a second period during which the control
circuit turns ON the second switching element after the first
period of the cycle time so that a period ratio dn, or the first
period/the second period is larger than a reference value dJ, or
n(1+L1/2Lm)-1 and controls the first switching element and the
second switching element based on the first period and the second
period.
2. The bidirectional insulated DC-DC converter according to claim
1, wherein when the first voltage VH is smaller than a
predetermined voltage, the control circuit calculates a third
period during which the control circuit turns OFF the first
switching element and the second switching element of the cycle
time, and wherein the control circuit turns OFF the first switching
element and the second switching element in the third period after
the second period.
3. The bidirectional insulated DC-DC converter according to claim
1, wherein the bidirectional insulated DC-DC converter is an active
clamp forward converter.
4. A bidirectional insulated DC-DC converter comprising: a
transformer having a primary winding and a secondary winding; a
secondary circuit connected to the secondary winding of the
transformer and including a coil, a first switching element, and a
second switching element; wherein a first terminal of the first
switching element is connected to a first terminal of the secondary
winding of the transformer, wherein a first terminal of the second
switching element is connected to a second terminal of the
secondary winding, wherein a first terminal of the coil is
connected to a third terminal of the secondary winding, or an
intermediate terminal of the secondary winding, and wherein a
second terminal of the first switching element and a second
terminal of the second switching element are connected to each
other; and a control circuit controlling the first switching
element and the second switching element, wherein when electric
power is transferred from the secondary side to the primary side of
the transformer, the control circuit measures a first voltage VH
that denotes a DC voltage of the primary winding on a high voltage
side of the transformer and a second voltage VL that denotes a DC
voltage of the secondary winding on a low voltage side of the
transformer in each cycle time or in half of the cycle time,
wherein the control circuit calculates a voltage ratio n, or VH/VL,
and wherein when the voltage ratio n is a reference value J, or
1/(1+L1/2Lm) or larger, where L1 denotes inductance of the coil and
Lm denotes exciting inductance of the transformer, the control
circuit calculates a first period during which the control circuit
turns ON the first switching element and the second switching
element in a former half period of the cycle time and in a latter
half period of the cycle time and a second period during which the
control circuit turns OFF the first switching element and turns ON
the second switching element after the first period in the former
half period of the cycle time and turns ON the first switching
element and turns OFF the second switching element after the first
period in the latter half period of the cycle time so that a period
ratio dn, or the first period/the second period is larger than a
reference value dJ, or n(1+L1/2Lm)-1 and controls the first
switching element and the second switching element based on the
first period and the second period.
5. The bidirectional insulated DC-DC converter according to claim
4, wherein when the first voltage VH is smaller than a
predetermined voltage, the control circuit calculates a third
period during which the control circuit turns OFF the first
switching element and the second switching element in the former
half period of the cycle time and in the latter half period of the
cycle time, and wherein the control circuit turns OFF the first
switching element and the second switching element in the third
period after the second period.
6. The bidirectional insulated DC-DC converter according to claim
4, wherein the bidirectional insulated DC-DC converter is a
full-bridge converter.
7. The bidirectional insulated DC-DC converter according to claim
4, wherein the bidirectional insulated DC-DC converter is a
half-bridge converter.
8. The bidirectional insulated DC-DC converter according to claim
4, wherein the bidirectional insulated DC-DC converter is a
push-pull converter.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a bidirectional insulated
DC-DC converter.
[0002] In a bidirectional insulated DC-DC converter, electric power
is transferred from a secondary side to a primary side of a
transformer. For example, in precharge operation, the bidirectional
insulated DC-DC converter controls two switching elements which are
provided in a secondary circuit connected to the secondary winding
of the transformer to perform synchronous rectification for
transferring electric power.
[0003] Japanese Patent Application Publication No. 2015-228788
discloses such a bidirectional insulated DC-DC converter.
[0004] There are provided switching elements for synchronous
rectification in the secondary circuit for a transformer of the
bidirectional insulated DC-DC converter. When electric power is
transferred from the secondary side to the primary side of the
transformer, the switching elements are controlled to be turned ON
(closed) and OFF (opened). Depending on the duty of the switching
elements, no electric power may be transferred during a period of a
cycle time, which reduces the efficiency of transferring of
electric power from the secondary side to the primary side of the
transformer.
[0005] The present invention which has been made in light of the
problems mentioned above is directed to providing a bidirectional
insulated DC-DC converter that reduces the period during which no
electric power is transferred for a cycle time during transferring
of electric power from a secondary side to a primary side of a
transformer.
SUMMARY OF THE INVENTION
[0006] In accordance with a first aspect of the present invention,
there is provided a bidirectional insulated DC-DC converter that
includes a transformer having a primary winding and a secondary
winding, a secondary circuit connected to the secondary winding of
the transformer and including a coil, a first switching element,
and a second switching element; wherein a first terminal of the
coil and a first terminal of the first switching element are
connected to a first terminal of the secondary winding of the
transformer, wherein a first terminal of the second switching
element is connected to a second terminal of the secondary winding,
and wherein a second terminal of the first switching element and a
second terminal of the second switching element are connected to
each other, and a control circuit controlling the first switching
element and the second switching element. When electric power is
transferred from the secondary side to the primary side of the
transformer, the control circuit measures a first voltage VH that
denotes a DC voltage of the primary winding on a high voltage side
of the transformer and a second voltage VL that denotes a DC
voltage of the secondary winding on a low voltage side of the
transformer in each cycle time. The control circuit calculates a
voltage ratio n, or VH/VL. When the voltage ratio n is a reference
value J, or 1/(1+L1/2Lm) or larger, where L1 denotes inductance of
the coil and Lm denotes exciting inductance of the transformer, the
control circuit calculates a first period during which the control
circuit turns ON the first switching element and a second period
during which the control circuit turns ON the second switching
element after the first period of the cycle time so that a period
ratio dn, or the first period/the second period is larger than a
reference value dJ, or n(1+L1/2Lm)-1 and controls the first
switching element and the second switching element based on the
first period and the second period.
[0007] In accordance with a second aspect of the present invention,
there is provided a bidirectional insulated DC-DC converter that
includes a transformer having a primary winding and a secondary
winding, a secondary circuit connected to the secondary winding of
the transformer and including a coil, a first switching element,
and a second switching element; wherein a first terminal of the
first switching element is connected to a first terminal of the
secondary winding of the transformer, wherein a first terminal of
the second switching element is connected to a second terminal of
the secondary winding, wherein a first terminal of the coil is
connected to a third terminal of the secondary winding, or an
intermediate terminal of the secondary winding, and wherein a
second terminal of the first switching element and a second
terminal of the second switching element are connected to each
other, and a control circuit controlling the first switching
element and the second switching element. When electric power is
transferred from the secondary side to the primary side of the
transformer, the control circuit measures a first voltage VH that
denotes a DC voltage of the primary winding on a high voltage side
of the transformer and a second voltage VL that denotes a DC
voltage of the secondary winding on a low voltage side of the
transformer in each cycle time or in half of the cycle time. The
control circuit calculates a voltage ratio n, or VH/VL. When the
voltage ratio n is a reference value J, or 1/(1+L1/2Lm) or larger,
where L1 denotes inductance of the coil and Lm denotes exciting
inductance of the transformer, the control circuit calculates a
first period during which the control circuit turns ON the first
switching element and the second switching element in a former half
period of the cycle time and in a latter half period of the cycle
time and a second period during which the control circuit turns OFF
the first switching element and turns ON the second switching
element after the first period in the former half period of the
cycle time and turns ON the first switching element and turns OFF
the second switching element after the first period in the latter
half period of the cycle time so that a period ratio dn, or the
first period/the second period is larger than a reference value dJ,
or n(1+L1/2Lm)-1 and controls the first switching element and the
second switching element based on the first period and the second
period.
[0008] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0010] FIG. 1 is a circuit diagram of a bidirectional insulated
DC-DC converter according to a first embodiment of the present
invention;
[0011] FIG. 2A includes three circuit diagrams A, B, C each showing
coil current and exciting current flowing in the bidirectional
insulated DC-DC converter of FIG. 1 in three different states
thereof during the precharge operation;
[0012] FIG. 2B includes three circuit diagrams D, E, F each showing
coil current and exciting current flowing in the bidirectional
insulated DC-DC converter of FIG. 1 in three different states
thereof during the precharge operation;
[0013] FIG. 3A shows the control signals that control switching
elements of a secondary circuit, the coil current, the exciting
current, and the current that flows in the switching elements in
two different cases, namely case A in which failure in electric
power transfer occurs and case B in which failure in electric power
transfer is avoided in an initial stage of precharge operation of
the bidirectional insulated DC-DC converter of FIG. 1,
respectively;
[0014] FIG. 3B is a diagram showing the control signals that
control switching elements of the secondary circuit, the coil
current, the exciting current, and the current that flows in the
switching elements in a later stage of the precharge operation of
the bidirectional insulated DC-DC converter of FIG. 1;
[0015] FIG. 4 is a circuit diagram of a bidirectional insulated
DC-DC converter according to a second embodiment of the present
invention;
[0016] FIG. 5A is a diagram showing the control signals that
control the switching elements of the secondary circuit, the coil
current, the exciting current, and the current that flows in the
switching elements in an initial stage of precharge operation of
the bidirectional insulated DC-DC converter of FIG. 4;
[0017] FIG. 5B is a diagram showing the control signals that
control the switching elements of the secondary circuit, the coil
current, the exciting current, and the current that flows in the
switching elements in the precharge operation in which failure in
electric power transfer is avoided in a later stage of the
precharge operation of the bidirectional insulated DC-DC converter
of FIG. 4;
[0018] FIG. 6 is a circuit diagram of a bidirectional insulated
DC-DC converter of a half-bridge system as a modification of the
second embodiment of the present invention; and
[0019] FIG. 7 is a circuit diagram of a bidirectional insulated
DC-DC converter of a push-pull system as a modification of the
second embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0020] The following will describe embodiments of the present
invention with reference to the accompanying drawings.
First Embodiment
[0021] Referring to FIG. 1, there is shown a bidirectional
insulated DC-DC converter 1 according to a first embodiment of the
present invention. The bidirectional insulated DC-DC converter 1 is
a forward DC-DC converter of an active-clamp system, including a
primary circuit 2, a transformer 3, a secondary circuit 4, and a
control circuit 5.
[0022] The primary circuit 2 includes a switching element 11, a
switching element 12, a capacitor 13, and a capacitor 14. The
primary circuit 2 is connected in parallel to a high-voltage
battery 6 via a relay 7 and a relay 8 on the high voltage side of
the primary circuit 2 and to a primary winding of the transformer 3
on the low voltage side thereof. The positive terminal (+) of the
high-voltage battery 6 is connected to the first terminal (1) of
the relay 7, The negative terminal (-) of the high-voltage battery
6 is connected to the first terminal (1) of the relay 8. The second
terminal (2) of the relay 7 is connected to the first terminal (1)
of the primary winding of the transformer 3, the second terminal
(2) of the capacitor 13, and the first terminal (1) of the
capacitor 14. The second terminal (2) of the relay 8 is connected
to the second terminal (2) of the switching element 12 and the
second terminal (2) of the capacitor 14. The first terminal (1) of
the switching element 11 is connected to the first terminal (1) of
the capacitor 13. The second terminal (2) of the switching element
11 is connected to the second terminal (2) of the primary winding
of the transformer 3 and the first terminal (1) of the switching
element 12. The third terminal (3) of the relay 7 is connected to
the control terminal P1 of the control circuit 5. The third
terminal (3) of the relay 8 is connected to the control terminal P2
of the control circuit 5. The third terminal (3) of the switching
element 11 is connected to the control terminal P3 of the control
circuit 5. The third terminal (3) of the switching element 12 is
connected to the control terminal P4 of the control circuit 5.
[0023] The secondary circuit 4 includes a switching element 15 (the
first switching element of the present invention), a switching
element 16 (the second switching element of the present invention),
a coil 17, and a capacitor 18. The secondary circuit 4 is connected
in parallel to the secondary winding of the transformer 3 on the
high voltage side of the secondary circuit 4 and to a low-voltage
battery 19 on the low voltage side of the secondary circuit 4. The
first terminal (1) of the switching element 15 is connected to the
first terminal (1) of the secondary winding of the transformer 3
and the first terminal (1) of the coil 17. The first terminal (1)
of the switching element 16 is connected to the second terminal (2)
of the secondary winding of the transformer 3. The second terminal
(2) of the coil 17 is connected to the first terminal (1) of the
capacitor 18 and the positive terminal (+) of the low-voltage
battery 19. The second terminal (2) of the switching element 15 and
the second terminal (2) of the switching element 16 are connected
to the second terminal (2) of the capacitor 18 and the negative
terminal (-) of the low-voltage battery 19. The third terminal (3)
of the switching element 15 is connected to the control terminal P5
of the control circuit 5. The third terminal (3) of the switching
element 16 is connected to the control terminal P6 of the control
circuit 5.
[0024] The control circuit 5 generates signals that control ON
(closed) and OFF (opened) operation of the relays 7, 8 and the
switching elements 11, 12, 15, 16 for controlling charging of the
low-voltage battery 19 by electric power supplied from the
high-voltage battery 6 (i.e. controlling by the active clamp
system) and charging of the capacitor 14 by the voltage of the
low-voltage battery 19 (i.e. precharge controlling by the active
clamp system). The control circuit 5 includes a programmable device
such as a Central Processing Unit (CPU), a multi-core CPU, a Field
Programmable Gate Array (FPGA), or a Programmable Logic Device
(PLD).
[0025] When the control circuit 5 generates signals to turn ON the
relays 7, 8, the high-voltage battery 6 is connected to the
capacitor 14. When the control circuit 5 generates signals to turn
OFF the relays 7, 8, the high-voltage battery 6 is disconnected
from the capacitor 14.
[0026] The switching elements 11, 12, 15, 16 may be provided by a
semiconductor switching device such as a Metal Oxide Semiconductor
Field Effect Transistor (MOSFET) and an Insulated Gate Bipolar
Transistor (IGBT). For example, when the switching device is an
N-channel MOSFET, the first terminals (1) of the switching elements
11, 12, 15, 16 are a drain terminal and the second terminals (2)
are a source terminal and the third terminals (3) are a gate
terminal. It is noted that a control signal SIG1 generated from the
control terminal P5 of the control circuit 5 is a signal for
controlling ON/OFF operation of the switching element 15 and a
control signal SIG2 generated from the control terminal P6 of the
control circuit 5 is a signal for controlling ON/OFF operation of
the switching element 16.
[0027] The following will describe the precharge operation while
referring to FIGS. 2A, 2B, and 3A. FIGS. 2A and 2B are circuit
diagrams showing coil current IL1 and exciting current ILm in the
precharge operation of the bidirectional insulated DC-DC converter
according to the first embodiment. The diagrams in FIG. 3A show
control signals SIG1, SIG2 that control the switching elements 15,
16 of the secondary circuit 4, coil current IL1, exciting current
ILm, and currents 115, 116 that flow in the switching elements 15,
16, respectively, in one case A in which failure in electric power
transfer occurs and in the other case B in which failure in
electric power transfer is avoided in the initial stage of the
precharge operation of the bidirectional insulated DC-DC converter
according to the first embodiment.
[0028] In carrying out the precharge, or transferring electric
power from the secondary side to the primary side of the
transformer 3, the control circuit 5 generates signals to turn OFF
the relays 7, 8 and the sequence of steps S1 to S4, which will be
described later, is repeated for each cycle time T thereby to
control charging of the capacitor 14.
[0029] At step S1, before start of the next cycle time T begins,
the control circuit 5 calculates the period td1 in the cycle time T
during which the switching element 15 is turned ON, the period td2
in the cycle time T during which the switching element 16 is turned
ON after the period tdl, and period td3 in the cycle time T during
which the switching elements 15, 16 are turned OFF after the period
td2.
[0030] At step S2, the control circuit 5 generates signals to turn
ON the switching elements 11, 15 and turn OFF the switching
elements 12, 16. As a result, as shown in the circuit diagram A of
FIG. 2A, the coil current IL1 (dashed line) flows from the positive
terminal of the low-voltage battery 19 through the coil 17 and the
switching element 15 to the negative terminal of the low-voltage
battery 19, so that energy is accumulated in the coil 17. The
exciting current ILm (solid line) flows from the first terminal of
the secondary winding of the transformer 3 through the exciting
inductance Lm to the second terminal of the secondary winding of
the transformer 3. In this case, as shown in the period T1 of the
diagram A of FIG. 3A, the coil current IL1 (dashed line) increases
at a gradient that is determined by VL/L1 and the exciting current
ILm (solid line) decreases at a gradient that is determined by
-(VR/N)/Lm to result in zero ampere. When the electric power is
transferred from the secondary side to the primary side of the
transformer 3, the current 11 (solid line) flows in the arrow
direction. In the above description, VL denotes DC voltage on the
low voltage side of the secondary winding of the transformer 3
corresponding to the second voltage VL of the present invention. L1
denotes the inductance of the coil 17. VR denotes the voltage of
the capacitor 13. N denotes the ratio of the number of turns of the
primary and secondary windings of the transformer 3 and in the
example shown in FIG. 1, the ratio is set at N:1.
[0031] When the exciting current ILm is decreased below zero
ampere, as shown in the circuit diagram B of FIG. 2A, the direction
in which the exciting current ILm flows is reversed. That is, the
exciting current ILm flows from the second terminal of the
secondary winding of the transformer 3 through the exciting
inductance Lm to the first terminal of the transformer 3. As shown
in the period T2 of the diagram A of FIG. 3A, the coil current IL1
continues to increase at a gradient that is determined by VL/L1 and
the exciting current ILm continues to decrease at a gradient that
is determined by -(VR/N)/Lm. As a result, the direction in which
the current 11 flows is reversed from the direction before the
exciting current ILm becomes zero ampere, as shown in the diagram B
of FIG. 2A.
[0032] At step S3, the control circuit 5 generates signals to turn
ON the switching elements 12, 16 and turn OFF the switching
elements 11, 15 during the calculated period td2. In this case, as
shown in the circuit diagram C of FIG. 2A, the coil current IL1
flows from the positive terminal of the low-voltage battery 19
through the coil 17, the secondary winding of the transformer 3,
and the switching element 16 to the negative terminal of the
low-voltage battery 19 in the period T3. The exciting current ILm
flows from the second terminal of the secondary winding of
transformer 3 through the exciting inductance Lm to the first
terminal of the secondary winding of the transformer 3, so that
part of the energy accumulated in the coil 17 is transferred in the
capacitor 14. That is, electric power is transferred from the
secondary side to the primary side of the transformer 3. The
currents 11 12 flow in the arrow directions, so that the capacitor
14 is charged. In this case, as shown in the period T3 in the
diagram A of FIG. 3A, the coil current IL1 increases at a gradient
that is determined by (VL-(VH/N))/L1. The exciting current ILm
increases at a gradient that is determined by (VH/N)/Lm and becomes
zero ampere. In the above description, VH denotes DC voltage on the
high voltage side of the primary winding of the transformer 3
corresponding to the first voltage VH of the present invention.
[0033] When the exciting current ILm becomes zero ampere or higher,
the direction in which the exciting current ILm flows is reversed
as shown in the circuit diagram D of FIG. 2B, and the exciting
current ILm flows from the first terminal of the secondary winding
of the transformer 3 through the exciting inductance Lm to the
second terminal of the secondary winding of the transformer 3. That
is, as shown in the period T4 of the diagram A of FIG. 3A, the coil
current ID continues to increase at a gradient that is determined
by (VL-(VH/N))/L1 and the exciting current ILm continues to
increase at a gradient that is determined by (VH/N)/Lm. Then, the
direction in which the current 11 shown in the circuit diagram D of
FIG. 2B flows is reversed from the direction before the exciting
current ILm becomes zero ampere.
[0034] However, if any time exists in the period td2 that satisfies
the Expression 1, which is shown below, during the processing of
the step S3 using the periods td1 and td2 calculated in the step
S1, failure occurs in transferring electric power from the
secondary side to the primary side of the transformer 3.
n=VH/VL.gtoreq.1/(1+L1/2Lm) Expression 1
[0035] The reason for the above failure is that, when Expression
1is satisfied, the coil current ID and the exciting current ILm
increase at a gradient that is determined by VL/(Lm+L1), as shown
in the period T4* of the diagram A of FIG. 3A, so that the coil
current ID and the exciting current ILm flow in directions opposite
to each other, as shown in the circuit diagram E of FIG. 2B, and
the values of the coil current ILA and the exciting current ILm
become substantially the same (IL1=ILm). As a result, the coil
current IL1 cancels the exciting current ILm, so that no electric
power is transferred from the secondary side to the primary side of
the transformer 3.
[0036] For this reason, by carrying out step S1' instead of the
above-described step S1, the period T4* in which no electric power
is transferred is deleted. At step S1', it is determined whether
Expression 1 is satisfied in each cycle time T. When Expression 1
is satisfied, the period td1' (the first period of the present
invention) and the period td2' (the second period of the present
invention) in which Expression 2 described below is satisfied are
calculated.
td1'/td2'>n(1+L1/2Lm)-1 Expression 2
[0037] That is, if the satisfaction of Expression 1 is determined,
periods td1', td2', and period td3 (the third period of the present
invention) that satisfy Expression 2 are calculated before the next
cycle time T starts. When the next cycle type T starts, the control
circuit 5 uses these periods td1', td2', and td3 in controlling the
switching elements 15, 16. The processing at step S1' and the
precharge operation using the periods td1', td2' will be described
later.
[0038] In the step S4, the control circuit 5 turns ON the switching
element 11 and OFF the switching elements 12, 15, 16 in the
calculated period td3, so that the off-state loss of the switching
elements 15, 16 consumes the energy left in the coil 17. When the
voltage VH is low, or the voltage of the capacitor 14 is lower than
a predetermined voltage on an initial stage of precharge, for
example, when the voltage is zero volt, the product ET on the
positive voltage side of the coil 17 is higher than the product ET
on the negative voltage side of the coil 17. It is noted that the
product ET on the positive voltage side of the coil 17 means the
product of the voltage VL and the length of time during which the
switching element 15 is turned ON and the switching element 16 is
turned OFF and also that the product ET on the negative voltage
side of the coil 17 means the product of the voltage VH/N and the
length of time during which the switching element 15 is turned OFF
and the switching element 16 is turned ON. As a result, the coil
current ILI is increased too large to be controlled. To prevent
such an increase of the coil current IL1, the step S4 is carried
out to suppress the increase of the coil current ID. As shown in
the circuit diagram F of FIG. 2B and also in the period T5 of the
diagram A of FIG. 3A, no coil current ID flows. The exciting
current lLm flows from the first terminal of the secondary winding
of the transformer 3 through the exciting inductance Lm to the
second terminal of the secondary winding of the transformer 3. The
exciting current ILm decreases at a gradient determined by
-(VR/N)/Lm.
[0039] The following will describe the precharge operation in which
electric power transfer failure is prevented. In the step S1', when
electric power is transferred from the secondary side of the
transformer 3 to the primary side of the transformer 3, the control
circuit 5 measures the voltage VH and the voltage VL before the
next cycle time T begins and calculates the voltage ratio n, or
VH/VL.
[0040] Then, the control circuit 5 compares the ratio n with a
reference value J that corresponds to 1/(1+L1/2Lm) (See Expression
1) for each cycle time T before the next cycle time T starts. When
the ratio n is J or larger (n.gtoreq.J), the control circuit 5
calculates the period td1' during which the switching element 15 is
turned ON in the cycle time T, the period td2' during which the
switching element 16 is turned ON after the period td1' in the
cycle time T, and the period td3 during which the switching
elements 15, 16 is turned OFF after the period td2' in the cycle
time T. In the periods tdl' and td2', or the period (T-td3) which
is calculated by subtracting the period td3 from the cycle time T,
Expression 2 is satisfied. That is, the periods td1', td2' are a
period during which the control circuit 5 calculates so that the
period ratio dn determined by td1'/td2' is larger than the
reference value dJ determined by n(1+L1/2Lm)-1(dn>dJ).
[0041] Periods td1', td2', and td3 may be determined from a data
table. For example, based on experimental or simulation data,
periods td1', td2', and td3 are obtained previously in the form of
a data table for each different value of ratio n. The reference
data table of the ratio n and the periods td1', td2', and td3 is
stored in a memory of the control circuit 5. Using the ratio n that
is calculated based on the voltage VH and the voltage VL that are
actually measured and referring to the above data table, the
corresponding periods td1', td2', and td3 may be obtained.
[0042] The reference value J is previously calculated, for example
based on the inductance L1 of the coil 17 and the exciting
inductance Lm of the transformer 3 and stored in the memory of the
control circuit 5. The reference value dJ is previously calculated,
for example based on the ratio n, the inductance L1 of the coil 17
and the exciting inductance Lm of the transformer 3 and stored in
the memory of the control circuit 5.
[0043] When the ratio n is smaller than the reference value J
(n<J), there is no occurrence of a period during which no
electric power is transferred at step S1' and, therefore, the
control circuit 5 may turn ON/OFF the switching elements 15, 16 so
that electric power is effectively transferred.
[0044] When Expression 2 is satisfied, the control circuit 5 turns
ON/OFF the switching elements 15, 16 in the periods td1', td2', and
td3 so that no cancelling of the coil current IL1 by the exciting
current ILm occurs, as shown in the circuit diagram E of FIG. 2B
and the period T4* in the diagram A of FIG. 3A. That is, as shown
in the cycle time T including the periods T1', T2', T3', T4', and
T5 in the diagram B of FIG. 3A, the period T4* during which no
electric power is transferred can be deleted. The deletion of the
period T4* allows the transformer 3 to transfer electric power from
the secondary side to the primary side with an improved
efficiency.
[0045] The following will describe another example of the first
embodiment with reference to FIG. 3B. FIG. 3B is a diagram showing
the control signals SIG1, SIG2 that control the switching elements
15, 16 of the secondary circuit 4, the coil current IL1, the
exciting current ILm, and the currents 115, 116 that flow in the
respective switching elements 15, 16 in a later stage of the
precharge operation of the bidirectional insulated DC-DC converter
1 according to the first embodiment.
[0046] At steps S1 and S1' of the first embodiment, the control
circuit 5 calculates the periods td1', td2' considering the period
td3 (=T5) in which step S4 is carried out. According to the another
example of the first embodiment, when the voltage of the capacitor
14 is increased in a later stage of the precharge, or when the
voltage of the capacitor 14 is increased larger than a
predetermined voltage, the product ET on the positive voltage side
and the product ET on the negative voltage side of the coil 17
approach the same value. Then, the coil current IL1 becomes stable
without increasing, so that the control circuit 5 need not turn OFF
the switching elements 15, 16 to consume the energy left in the
coil 17. As a result, the control circuit 5 need not control to
turn ON/OFF the switching elements 15, 16 considering the period
td3.
[0047] Then, the control circuit 5 compares the ratio n with the
reference value J, or 1/(1+L1/2Lm) (See Expression 1) for each
cycle time T. When the ratio n is at the reference value J or
larger (n.gtoreq.J), the control circuit 5 calculates the period
td1'' (the first period of the present invention) during which the
switching element 15 is turned ON in the cycle time T before the
next cycle time T and the period td2'' (the second period of the
present invention) during which the switching element 16 is turned
ON in the cycle time T after the period td1''. The periods td1''
and td2'' are calculated by the control circuit 5 so that the
period ratio dn', or td1'/td2'' is larger than the reference value
dJ, or n(1+L1/2Lm)-1(dn'>dJ).
[0048] Alternatively, the periods td1'' and td2'' may be determined
from a data table. For example, based on experimental or simulation
data, periods tdl", td2" are obtained previously in the form of a
data table for each different value of ratio n. The reference data
table of the ratio n and the periods td1'', td2'' is stored in a
memory of the control circuit 5. Using the ratio n that is
calculated based on the voltage VH and the voltage VL that are
actually measured and referring to the above data table, the
corresponding periods tdl", td2" may be obtained.
[0049] Thus, in a later stage of the precharge operation when the
voltage of the capacitor 14 is increased, or specifically when the
voltage of the capacitor 14 is larger than a predetermined voltage
and dn'>dJ is satisfied, the control circuit 5 controls ON/OFF
operation of the switching elements 15, 16 during the periods
td1'', td2'' so that the period T5 is deleted. As a result, the
switching loss of the switching elements 15, 16 can be reduced.
When the voltage of the capacitor 14 increases with a progress of
the precharge operation, the period T4* in which no electric power
is transferred can be deleted as seen from the cycle time T
including the periods T1'', T2'', T3'', T4'' shown in FIG. 3B. The
deletion of the period T4* allows the transformer 3 to transfer
electric power from the secondary side to the primary side thereof
with an increased efficiency.
Second Embodiment
[0050] The following will describe a bidirectional insulated DC-DC
converter 41 according to a second embodiment of the present
invention with reference to FIG. 4. The bidirectional insulated
DC-DC converter 41 is a forward DC-DC converter of a full-bridge
system, including a primary circuit 42, a transformer 43, a
secondary circuit 44, and a control circuit 45.
[0051] The primary circuit 42 includes switching elements 46, 47,
48, 49 and a capacitor 50. The primary circuit 42 is connected in
parallel to the high-voltage battery 6 via the relay 7 and the
relay 8 on the high voltage side of the primary circuit 42 and to a
primary winding of the transformer 43 on the low voltage side of
the primary circuit 42. The positive terminal (+) of the
high-voltage battery 6 is connected to the first terminal (1) of
the relay 7. The negative terminal (-) of the high-voltage battery
6 is connected to the first terminal (1) of the relay 8. The second
terminal (2) of the relay 7 is connected to the first terminal (1)
of the switching element 46, the first terminal (1) of the
switching element 48, and the first terminal (1) of the capacitor
50. The second terminal (2) of the relay 8 is connected to the
second terminal (2) of the switching element 47, the second
terminal (2) of the switching element 49, and the second terminal
(2) of the capacitor 50. The first terminal (1) of the first
winding of the transformer 43 is connected to the second terminal
(2) of the switching element 46 and the first terminal (1) of the
switching element 47. The second terminal (2) of the first winding
of the transformer 43 is connected to the second terminal (2) of
the switching element 48 and the first terminal (1) of the
switching element 49. The third terminal (3) of the relay 7 is
connected to a control terminal P41 of the control circuit 45. The
third terminal (3) of the relay 8 is connected to the control
terminal P42 of the control circuit 45. The third terminal (3) of
the switching element 46 is connected to the control terminal P43
of the control circuit 45. The third terminal (3) of the switching
element 47 is connected to the control terminal P44 of the control
circuit 45. The third terminal (3) of the switching element 48 is
connected to the control terminal P45 of the control circuit 45.
The third terminal (3) of the switching element 49 is connected to
the control terminal P46 of the control circuit 45.
[0052] The secondary circuit 44 includes a switching element 51
(the first switching element of the present invention), a switching
element 52 (the second switching element of the present invention),
a coil 53, and a capacitor 54. The secondary circuit 44 is
connected in parallel to the secondary winding of the transformer
43 on the high voltage side of the secondary circuit 44 and to the
low-voltage battery 19 on the low voltage side of the secondary
circuit 44. The first terminal (1) of the switching element 51 is
connected to the first terminal (1) of the secondary winding of the
transformer 43. The first terminal (1) of the switching element 52
is connected to the second terminal (2) of the secondary winding of
the transformer 43. The first terminal (1) of the coil 53 is
connected to the intermediate third terminal (3) of the secondary
winding of the transformer 43. The second terminal (2) of the coil
53 is connected to the first terminal (1) of the capacitor 54 and
the positive terminal (+) of the low-voltage battery 19. The second
terminal (2) of the switching element 51 and the second terminal
(2) of the switching element 52 are connected to the second
terminal (2) of the capacitor 54 and the negative terminal (-) of
the low-voltage battery 19. The third terminal (3) of the switching
element 51 is connected to the control terminal P47 of the control
circuit 45. The third terminal (3) of the switching element 52 is
connected to the control terminal P48 of the control circuit
45.
[0053] The control circuit 45 controls ON/OFF operation of the
relays 7, 8 and the switching elements 46, 47, 48, 49, 51, 52 for
controlling charging of the low-voltage battery 19 by electric
power supplied from the high-voltage battery 6 (i.e. controlling by
full-bridge system) and charging of the capacitor 50 by the voltage
of the low-voltage battery 19 (i.e. precharge controlling by the
full-bridge system). The control circuit 45 includes a programmable
device such as a Central Processing Unit (CPU) and a multi-core
CPU.
[0054] When the control circuit 45 generates signals to turn ON the
relays 7, 8, the high-voltage battery 6 is connected to the
capacitor 50. When the control circuit 45 generates signals to turn
OFF the relays 7, 8, the high-voltage battery 6 is disconnected
from the capacitor 50.
[0055] The switching elements 46, 47, 48, 49, 51, 52 may be
provided by a semiconductor switching device such as a MOSFET and
an IGBT. For example, when the switching device is an N-channel
MOSFET, the first terminals (1) of the switching elements 46, 47,
48, 49, 51, 52 are a drain terminal and the second terminals (2)
are a source terminal and the third terminals (3) are a gate
terminal. It is noted that a control signal SIG3 generated from the
control terminal P47 of the control circuit 45 is a signal for
controlling ON/OFF operation of the switching element 51 and a
control signal SIG4 generated from the control terminal P48 of the
control circuit 45 is a signal for controlling ON/OFF operation of
the switching element 52.
[0056] The following will describe the precharge operation of the
bidirectional insulated DC-DC converter 41 according to the second
embodiment of the present invention referring to FIG. 5A. FIG. 5A
is a diagram showing the control signals SIG3, SIG4 that control
the switching elements 51, 52 of the secondary circuit 44, the coil
current ILA, the exciting current ILm, and the currents I51 and I61
that flow in the respective switching elements 51 and 61 when the
electric power transfer failure is prevented in the initial stage
of the precharge operation of the bidirectional insulated DC-DC
converter 41.
[0057] In carrying out the precharge, or transferring electric
power from the secondary side to the primary side of the
transformer 43, the control circuit 45 generates signals to turn
OFF the relays 7, 8 and a sequence of steps Sll to S17, which will
be described later, is repeated for each cycle time T thereby to
charge the capacitor 50 to a predetermined voltage.
[0058] At step S1, when electric power is transferred from the
secondary side to the primary side of the transformer 3, the
control circuit 45 receives data of the voltage VH and the voltage
VL for each cycle time T or for each half cycle time T/2 before the
next cycle time T or the next half cycle time T/2 starts, and then
calculates the voltage ratio n, or VH/VL.
[0059] If Expression 1 is satisfied, the coil currentIL1 and the
exciting current ILm flow varying at the same gradient in opposite
directions to each other in each cycle time T/2 and at the same
value (or IL1=ILm). Therefore, the coil current IL1 and the
exciting current ILm cancel each other, so that no electric power
is transferred from the secondary side to the primary side of the
transformer 43. The control circuit 45 compares the ratio n with
the reference value J, or 1/(1+L1/2Lm) (See Expression 1) for each
cycle time T or each half cycle time T/2, before the next cycle
time T or the next cycle time T/2 starts. If Expression 1 is
satisfied, the control circuit 5 calculates period tdA (the first
period of the present invention) and period tdB (the second period
of the present invention) during which Expression 3 shown below is
satisfied.
tdA/tdB>n(1+L1/2Lm)-1 Expression 3
[0060] In the period (T/2-tdd) which is obtained by subtracting the
period tdd (the third period of the present invention) from the
cycle time T/2, the control circuit 45 calculates the periods tdA
and tdB according to which the period ratio dnn, or tdA/tdB is
larger than the reference value dJ, or
n(1+L1/2Lm)-1(dnn>dJ).
[0061] Period tdA is the period (tda & tdc) during which the
control circuit 45 turns ON the switching elements 51, 52 in the
former half of the cycle time T (the period for T/2 as counted from
the beginning of the cycle time T) and in the latter period of the
cycle time T (the period for T/2 as counted from the beginning of
the latter half of the cycle time T to the end of the cycle time
T). That is, energy is accumulated in the coil 53 in the period
tdA.
[0062] As shown in FIG. 5A, the control circuit 45 turns ON the
switching element 51 during the period tda in the former half of
the cycle time T and turns ON the switching element 52 during the
period tda in the latter half of the cycle time T. The control
circuit 45 turns ON the switching element 51 during the period tdc
in the latter half of the cycle time T and turns ON the switching
element 52 during the period tdc in the former half of the cycle
time T.
[0063] The control circuit 45 turns OFF the switching element 51
and turns ON the switching element 52 during the period tdB, or the
period (tdb-tdd) in the former half of the cycle time T. The
control circuit 45 turns ON the switching element 51 and turns OFF
the switching element 51 in the period tdB, or the period (tdb-tdd)
in the latter half of the cycle time T. That is, part of the energy
accumulated in the coil 53 is transferred from the secondary side
to the primary side of the transformer 43 and the capacitor 50 is
charged in the period tdB, accordingly. As shown in FIG. 5A, the
control circuit 45 turns OFF the switching element 51 during the
period tdb in the former half of the cycle time T and turns OFF the
switching element 52 during the period tdb in the latter half of
the cycle time T.
[0064] The control circuit 45 turns OFF the switching elements 51,
52 during the period tdd in the former half and latter half of the
cycle time T. That is, as shown in FIG. 5A, the period tdd is a
period during which the off-state loss of the switching elements
51, 52 consumes the energy left in the coil 53.
[0065] At step S12, the control circuit 45 turns On the switching
elements 51, 52 during the period Ta, or the period tdA in the
former half of the cycle time T as shown in FIG. 5A and energy is
accumulated in the coil 53, accordingly.
[0066] At step S13, the control circuit 45 turns OFF the switching
element 51 and turns ON switching element 52 in the periods Tb and
Tc as shown in FIG. 5A, so that the capacitor 50 is charged. In the
period Tc, Expression 3 is satisfied, so that electric power is
transferred from the secondary side to the primary side of the
transformer 43.
[0067] At step S14, the control circuit 45 turns OFF the switching
elements 51, 52 in the period Td, or the period tdd in the former
half of the cycle time T as shown in FIG. 5A, so that the off-state
loss of the switching elements 51, 52 consume the energy left in
the coil 53.
[0068] At step S15, the control circuit 45 turns ON the switching
elements 51, 52 in the period Te, or the period tdA in the latter
half of the cycle time T as shown in FIG. 5A, so that energy in the
coil 53 is accumulated.
[0069] At step S16, the control circuit 45 turns OFF the switching
element 52 and turns ON the switching element 51 in the periods Tf
and Tg as shown in FIG. 5A, so that the capacitor 50 is charged. In
the period Tg, Expression 3 is satisfied, so that electric power is
transferred from the secondary side to the primary side of the
transformer 43.
[0070] At step S17, the control circuit 45 turns OFF the switching
elements 51, 52 in the period Th, or the period tdd in the latter
half of the cycle time T as shown in FIG. 5A, so that the off-state
loss of the switching elements 51, 52 consumes the energy left in
the coil 53.
[0071] Periods tdA, tdB, tdd and periods tda, tdb, tdc may be
determined from a data table. For example, based on experimental or
simulation data, periods tdA, tdB, tdd and periods tda, tdb, tdc
are obtained previously in the form of a data table for each
different ratio n. The reference data table of the ratio n, the
periods tdA, tdB, tdd and the periods tda, tdb, tdc is stored in
the memory of the control circuit 5. Using the ratio n that is
calculated based on the voltage VH and the voltage VL that are
actually measured and referring to the above data table, the
corresponding periods tdA, tdB, tdd and periods tda, tdb, tdc may
be obtained.
[0072] The reference value J is previously calculated, for example
based on the inductance L1 of the coil 53 and the exciting
inductance Lm of the transformer 43 and stored in the memory of the
control circuit 45. The reference value dJ is previously
calculated, for example based on the ratio n, the inductance L1 of
the coil 53, and the exciting inductance Lm of the transformer 43
and stored in the memory of the control circuit 45.
[0073] The control circuit 45 compares the ratio n with the
reference value J for each cycle time T or for each half cycle time
T/2. If the ratio n is smaller than the reference value J (n<J),
the control circuit 45 may turn ON/OFF the switching elements 15,
16 even if Expression 3 is not satisfied, and electric power is
effectively transferred, accordingly.
[0074] When Expression 3 is satisfied, the control circuit 45 may
turn ON/OFF the switching elements 51, 52 in the periods tdA, tdB,
tdd and tda, tdb, tdc so as to prevent the coil current ID and the
exciting current lLm from cancelling each other. That is, as
appreciated from the cycle time T including the periods Ta, Tb, Tc,
Td, Te, Tf, Tg, and Th shown in FIG. 5A, the period during which no
electric power is transferred can be deleted. The reduction of such
period allows the transformer 43 to transfer electric power from
the secondary side to the primary side thereof with an improved
efficiency.
[0075] The following will describe a modified example 1 of the
second embodiment with reference to FIG. 5B. FIG. 5B is a diagram
showing the control signals SIG3, SIG4 that control the switching
elements 51, 52 of the secondary circuit 44, the coil current IL1,
the exciting current ILm, and the respective currents I51, I52 that
flow in the switching elements 51, 52 in the precharge operation in
a case in which failure in electric power transfer is prevented in
an later stage of the precharge operation of the bidirectional
insulated DC-DC converter 41 of the second embodiment.
[0076] In the processing at step S11 in the bidirectional insulated
DC-DC converter 41 according to the second embodiment, the control
circuit 45 calculates the periods tdA, tdB, tdd and tda, tdb, tdc
considering the period tdd (=Td) in which step S4 is carried out.
When the voltage of the capacitor 50 is increased with a progress
of the precharge operation, or when the voltage of the capacitor 50
is increased larger than a predetermined voltage, the product ET on
the positive voltage side of the coil 53 and the product ET on the
negative voltage side of the coil 53 approach the same value, so
that the coil current IL1 becomes stable without being increased.
Therefore, the control circuit 45 need not consume the energy left
in the coil 53 by turning OFF the switching elements 51, 52. As a
result, the control circuit 45 need not control the ON/OFF
operation of the switching elements 15, 16 considering the period
tdd.
[0077] Then, the control circuit 45 compares the ratio n with the
reference value J, or 1/(1+L1/2Lm) (See Expression 1). If the ratio
n is the reference value J or larger (n J), the control circuit 45
calculates the period tdA (the first period of the present
invention) during which the switching elements 51, 52 are turned ON
in the cycle time T or half the cycle time T/2 before the next
cycle time T or next half the cycle time T/2, the period tdB' (the
second period of the present invention) during which the switching
element 52 is turned ON in the cycle time T or half the cycle time
T/2 after the period tdA', and the periods tda', tdb'.
[0078] Periods tdA' and tdB' are such periods that are calculated
by the control circuit 45 and satisfy the condition that the period
ratio dm, or tdA'/tdB', is larger than the reference value dJ, or
n(1+L1 /2Lm)-1) (dnn'>dJ).
[0079] Periods tdA', tdB', da', and tdb' may be determined from a
data table. For example, based on experimental or simulation data,
periods tdA', tdB', tda', and tdb' are obtained previously in form
of a data table for each different value of ratio n. The reference
data table of the ratio n and the periods tdA', tdB', tda', and
tdb' is stored in a memory of the control circuit 45. Using the
ratio n that is calculated based on the voltage VH and the voltage
VL that are actually measured and referring to the above data
table, the corresponding periods tdA', tdB', tda', and tdb' may be
obtained.
[0080] When the voltage of the capacitor 50 is increased with a
progress of the precharge operation, or when the voltage of the
capacitor 50 is increased larger than a predetermined voltage and
dnn'>dJ is satisfied, the control circuit 45 controls the ON/OFF
operation of the switching elements 51, 52 in the periods tdA',
tdB' and the periods tda', tdb' so that the period Td may be
deleted as shown in FIG. 5B and the switching loss of the switching
elements 51, 52 may be reduced, accordingly. Even if the voltage of
the capacitor 50 is increased with a progress of the precharge
operation, the period during which no electric power is transferred
can be deleted, as appreciated from the cycle time T including the
periods Ta', Tb', Tc', Te', Tf', Tg' shown in FIG. 5B. The deletion
of the period during which no electric power is transferred allows
the transformer 43 to transfer the electric power from the
secondary side to the primary side thereof with an improved
efficiency.
[0081] The following will describe a modified example 2 of the
bidirectional insulated DC-DC converter according to the second
embodiment. Controlling of the precharge operation may be applied
to a bidirectional insulated DC-DC converter of a half-bridge
system shown in FIG. 6. FIG. 6 is a circuit diagram of a
bidirectional insulated DC-DC converter 61 of a half-bridge system
as the modified example 2 according to the second embodiment of the
present invention. The bidirectional insulated DC-DC converter 61
includes a primary circuit 62, the transformer 43, the secondary
circuit 44, and a control circuit 63.
[0082] The primary circuit 62 includes a switching element 64, a
switching element 65, a capacitor 66, and a capacitor 67. The
primary circuit 62 is connected in parallel to the high-voltage
battery 6 via the relay 7 and the relay 8 on the high voltage side
of the primary circuit 62 and to a primary winding of the
transformer 43 on the low voltage side of the primary circuit 62.
The positive terminal (+) of the high-voltage battery 6 is
connected to the first terminal (1) of the relay 7, The negative
terminal (-) of the high-voltage battery 6 is connected to the
first terminal (1) of the relay 8. The second terminal (2) of the
relay 7 is connected to the first terminal (1) of the switching
element 64 and the first terminal (1) of the capacitor 66. The
second terminal (2) of the relay 8 is connected to the second
terminal (2) of the switching element 65 and the second terminal
(2) of the capacitor 67. The first terminal (1) of the first
winding of the transformer 43 is connected to the second terminal
(2) of the switching element 64 and the first terminal (1) of the
switching element 65. The second terminal (2) of the first winding
of the transformer 43 is connected to the second terminal (2) of
the capacitor 66 and the first terminal (1) of the capacitor 67.
The third terminal (3) of the relay 7 is connected to a control
terminal P41 of the control circuit 63. The third terminal (3) of
the relay 8 is connected to the control terminal P42 of the control
circuit 63. The third terminal (3) of the switching element 64 is
connected to the control terminal P61 of the control circuit 63.
The third terminal (3) of the switching element 65 is connected to
the control terminal P62 of the control circuit 63.
[0083] The secondary circuit 44 has the same configuration as that
which is shown in FIG. 4 and includes a switching element 51 (the
first switching element of the present invention), a switching
element 52 (the second switching element of the present invention),
a coil 53, and a capacitor 54. The control circuit 63 generates
signals for control the ON/OFF operation of the relays 7, 8 and the
switching elements 64, 65, 51, 52 thereby to control charging of
the low-voltage battery 19 by the electric power supplied from the
high-voltage battery 6 (or controlling by a half-bridge system) and
also charging of the capacitors 66, 67 by the voltage of the
low-voltage battery 19 (or precharge controlling by a half-bridge
system). The control circuit 63 includes a programmable device such
as a CPU and a multi-core CPU.
[0084] The switching elements 64, 65 may be provided by a
semiconductor switching device such as a MOSFET and an IGBT. For
example, when the switching device is an N-channel MOSFET, the
first terminals (1) of the switching elements 64, 65 are a drain
terminal and the second terminals (2) are a source terminal and the
third terminals (3) are a gate terminal.
[0085] In carrying out the precharge operation, or transferring
electric power from the secondary side to the primary side of the
transformer 43, the control circuit 63 generates signals to turn
OFF the relays 7, 8 and thereafter step S11 to step S17 which have
been described earlier are executed for each cycle time T or for
each half the cycle time T/2 so that the capacitors 66, 67 are
charged to a predetermined voltage.
[0086] When Expression 3 is satisfied in the modified example 2
according to the second embodiment, the control circuit 63 turns
ON/OFF the switching elements 51, 52 in the periods tdA, tdB, tdd
and the periods tda, tdb, tdc so that no cancelling of the coil
current IL1 and the exciting current ILm occurs. That is, as
appreciated from the cycle time T including the periods Ta, Tb, Tc,
Td, Te, Tf, Tg, Th shown in FIG. 5A, the period in which no
electric power is transferred can be deleted. The deletion of the
period allows the transformer 43 to transfer electric power from
the secondary side to the primary side with an increased
efficiency.
[0087] When the voltages of the capacitors 66, 67 is increased with
a progress of the precharge operation, or when the voltage of the
capacitor 66, 67 is increased larger than a predetermined voltage
and dnn'>dJ, the control circuit 45 controls the ON/OFF
operation of the switching elements 51, 52 during the periods tdA',
tdB' and the periods tda', tdb' so that the period Td is deleted as
shown in FIG. 5B. As a result, the switching loss of the switching
elements 51, 52 can be reduced. When the voltages of the capacitors
66, 67 is increased with a progress of the precharge operation, the
period during which no electric power is transferred can be deleted
as appreciated from the cycle time T including the periods Ta',
Tb', Tc', Te', Tf', Tg' shown in FIG. 5B. The deletion of such
period allows the transformer 43 to transfer electric power from
the secondary side to the primary side with an improved
efficiency.
[0088] The following will describe a modified example 3 of the
bidirectional insulated DC-DC converter according to the second
embodiment. Controlling of the precharge operation which has been
described with reference to the second embodiment can be applied to
a bidirectional insulated DC-DC converter of a push-pull system
which is shown in FIG. 7. FIG. 7 is a circuit diagram of a
bidirectional insulated DC-DC converter 71 of a push-pull system as
the modified example2according to the second embodiment of the
present invention. The bidirectional insulated DC-DC converter 71
includes a primary circuit 72, a transformer 73, the secondary
circuit 44, and a control circuit 74.
[0089] The primary circuit 72 includes a switching element 75, a
switching element 76, and a capacitor 77. The primary circuit 72 is
connected in parallel to the high-voltage battery 6 via the relay 7
and the relay 8 on the high voltage side of the primary circuit 72
and to a primary winding of the transformer 73 on the low voltage
side of the primary circuit 72. The positive terminal (+) of the
high-voltage battery 6 is connected to the first terminal (1) of
the relay 7. The negative terminal (-) of the high-voltage battery
6 is connected to the first terminal (1) of the relay 8. The second
terminal (2) of the relay 7 is connected to the intermediate
terminal, or the third terminal (3) of the primary winding of the
transformer 73 and the first terminal (1) of the capacitor 77. The
second terminal (2) of the relay 8 is connected to the second
terminal (2) of the switching element 75, the second terminal (2)
of the switching element 76, and the second terminal (2) of the
capacitor 77. The first terminal (1) of the primary winding of the
transformer 73 is connected to the first terminal (1) of the
switching element 76. The second terminal (2) of the primary
winding of the transformer 73 is connected to the first terminal
(1) of the switching element 75. The third terminal (3) of the
relay 7 is connected to a control terminal P41 of the control
circuit 74. The third terminal (3) of the relay 8 is connected to
the control terminal P42 of the control circuit 74. The third
terminal (3) of the switching element 75 is connected to the
control terminal P71 of the control circuit 74. The third terminal
(3) of the switching element 76 is connected to the control
terminal P72 of the control circuit 74.
[0090] The secondary circuit 44 has the same configuration as that
which is shown in FIG. 4 and includes the switching element 51 (the
first switching element of the present invention), the switching
element 52 (the second switching element of the present invention),
the coil 53, and the capacitor 54. The control circuit 74 generates
signals to control the ON/OFF operation of the relays 7, 8 and the
switching elements 75, 76, 51, 52 thereby to control charging of
the low-voltage battery 19 by the electric power supplied from the
high-voltage battery 6 (controlling by a push-pull system) and for
charging the capacitor 77 by the voltage of the low-voltage battery
19 (controlling by a push-pull system). The control circuit 74
includes a programmable device such as a CPU and a multi-core
CPU.
[0091] The switching elements, 76 may be provided by a
semiconductor switching device such as a MOSFET and an IGBT. For
example, when the switching device is an N-channel MOSFET, the
first terminals (1) of the switching elements 75, 76 are a drain
terminal and the second terminals (2) are a source terminal and the
third terminals (3) are a gate terminal.
[0092] In carrying out the precharge operation or transferring
electric power from the secondary side to the primary side of the
transformer 73, the control circuit 74 generates signals to turn
OFF the relays 7, 8, so that step S11 to S17 which has been
described above are repeated for each cycle time T or for each half
the cycle time T/2 to charge the capacitor 77 to a predetermined
voltage.
[0093] When Expression 3 is satisfied in the modified example 3 of
the second embodiment, the control circuit 74 controls the ON/OFF
operation of the switching elements 51, 52 in the periods tdA, tdB,
tdd and the periods tda, tdb, tdc so that no cancelling of the coil
current IL1 and the exciting current ILm occurs. That is, as
appreciated from the cycle time T including the periods Ta, Tb, Tc,
Td, Te, Tf, Tg, Th shown in FIG. 5A, the period during which no
electric power is transferred can be deleted. The deletion of such
period allows the transformer 73 to transfer electric power from
the secondary side to the primary side with an improved
efficiency.
[0094] When the voltage of the capacitor 77 is increased with a
progress of the precharge operation, or when the voltage of the
capacitor 67 is increased larger than a predetermined voltage and
dnn'>dJ, the control circuit 74 controls the ON/OFF operation of
the switching elements 51, 52 during the periods tdA', tdB' and the
periods tda', tdb' so that the period Td is deleted, as shown in
FIG. 5B. As a result, the switching loss of the switching elements
51, 52 can be reduced. When the voltage of the capacitor 77 is
increased with a progress of the precharge operation, the period
during which no electric power is transferred can be deleted as
seen from the cycle time T including the periods Ta', Tb', Tc',
Te', Tf', Tg' shown in FIG. 5B. The deletion of such period allows
the transformer 73 to transfer electric power from the secondary
side to the primary side with an improved efficiency.
[0095] The present invention is not limited to the above
embodiments and may be modified within the scope of the present
invention.
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