Bidirectional isolated DC-DC converter having reduced voltage increase for leakage inductance of transformer
A bidirectional isolated DC-DC converter includes a primary-side inverter; a first DC cut capacitor connected to the AC side of the primary-side inverter; a secondary-side inverter; a second DC cut capacitor connected to the AC side of the secondary-side inverter; a transformer having a primary winding connected to the AC side of the primary-side inverter, and a secondary winding connected to the AC side of the secondary-side inverter; and a control unit that controls switching devices of the primary-side inverter and the secondary-side inverter. The control unit determines an operation of the primary-side inverter and an operation of the secondary-side inverter so as to reduce an increase in voltage to be applied to leakage inductances of the transformer, in accordance with failure states of the switching devices.
1 . A bidirectional isolated DC-DC converter comprising:
a primary-side inverter;
a first DC cut capacitor connected to an AC side of the primary-side inverter;
a secondary-side inverter;
a second DC cut capacitor connected to an AC side of the secondary-side inverter;
a transformer including a primary winding connected to the AC side of the primary-side inverter and a secondary winging connected to the AC side of the secondary-side inverter; and
a controller configured to control switching devices of the primary-side inverter and the secondary-side inverter,
wherein the controller is configured to decide operation of the primary-side inverter and operation of the secondary-side inverter depending on a fault state of the switching devices of the primary-side inverter and the secondary-side inverter, so as to reduce increase in voltage applied to a leakage inductance of the transformer.
2 . The bidirectional isolated DC-DC converter as claimed in claim 1 , wherein the controller includes: a limiter configured to limit a phase difference command value to a value equal to or greater than a lower limit and equal to or less than an upper limit, and output the phase difference command value; a carrier generation section configured to output a carrier signal; a fault operation decision section configured to decide operation of a faulty inverter and operation of a normal inverter depending on a short-circuit fault signal or an open-circuit fault signal, so as to reduce a difference between the primary-side inverter and the secondary-side inverter in output voltage; and a gate signal generation section configured to generate gate signals for the switching devices, based on: the carrier signal and the phase difference command value outputted from the limiter, in case that both of the primary-side inverter and the secondary-side inverter are normal; and the carrier signal, the phase difference command value outputted from the limiter, and the operation of the faulty inverter and the operation of the normal inverter decided by the fault operation decision section, in case that at least one of the primary-side inverter and the secondary-side inverter is faulty.
3 . The bidirectional isolated DC-DC converter as claimed in claim 2 , wherein:
the controller includes a normal operation decision section configured to output an output A and an output B based on the phase difference command value and a ratio of a primary-side DC voltage to a secondary-side DC voltage, wherein: the output A is a phase difference in output voltage between the primary-side inverter and the secondary-side inverter which achieves soft switching under a voltage condition between the primary-side DC voltage and the secondary-side DC voltage; and the output B is selection of full-bridge operation or half-bridge operation for the primary-side inverter and the secondary-side inverter; and
the gate signal generation section is configured to generate the gate signals based on a basis X and a basis Y in case that both of the primary-side inverter and the secondary-side inverter are normal, wherein: the basis X is comparison of the carrier signal with the phase difference that is closest to the phase difference command value among the phase differences satisfying the voltage condition; and the basis Y is the selection of full-bridge operation or half-bridge operation for the primary-side inverter and the secondary-side inverter which is outputted from the normal operation decision section.
4 . The bidirectional isolated DC-DC converter as claimed in claim 3 , wherein the controller includes a gain adjustment section configured to multiply the phase difference command value by a gain based on the selection of full-bridge operation or half-bridge operation for the primary-side inverter and the secondary-side inverter, and output the phase difference command value after the gain multiplication to the limiter.
5 . The bidirectional isolated DC-DC converter as claimed in claim 4 , wherein the gain adjustment section is configured to use values of the gain shown in the following Table 3;
Gain for Respective Operation Modes
TABLE 3
GAIN
INV1
INV2
1
FB OPERATION
FB OPERATION
2
HB OPERATION
FB OPERATION
2
FB OPERATION
HB OPERATION
4
HB OPERATION
HB OPERATION
FB operation: full-bridge operation
HB operation: half-bridge operation
INV1: the primary-side inverter
INV2: secondary-side inverter.
6 . The bidirectional isolated DC-DC converter as claimed in claim 3 , wherein the normal operation decision section is configured to derive the phase difference and the selection of full-bridge operation or half-bridge operation for the primary-side inverter and the secondary-side inverter, based on the following Mathematical Expressions (1) to (6)
[
Mathematical
Expression
1
]
θ
ZVS
>
(
1
-
N
V
out
V
in
)
π
2
CONDITION
VOLTAGE
(
V
in
≥
NV
out
)
(
1
)
[
Mathematical
Expression
2
]
θ
ZVS
>
(
1
-
V
in
NV
out
)
π
2
CONDITION
VOLTAGE
(
V
in
≤
NV
out
)
(
2
)
[
Mathematical
Expression
3
]
θ
ZVS
>
(
1
-
NV
out
2
V
in
)
π
2
CONDITION
VOLTAGE
(
2
V
in
≥
NV
out
)
(
3
)
[
Mathematical
Expression
4
]
θ
ZVS
>
(
1
-
2
V
in
NV
out
)
π
2
CONDITION
VOLTAGE
(
2
V
in
≤
NV
out
)
(
4
)
[
Mathematical
Expression
5
]
θ
ZVS
>
(
1
-
2
NV
out
V
in
)
π
2
CONDITION
VOLTAGE
(
V
in
≥
2
NV
out
)
(
5
)
[
Mathematical
Expression
6
]
θ
ZVS
>
(
1
-
V
in
2
NV
out
)
π
2
CONDITION
VOLTAGE
(
V
in
≥
2
NV
out
)
(
6
)
In case of Mathematical Expression (1) or (2), the primary-side inverter: full-bridge operation, the secondary-side inverter: full-bridge operation, secondary-side inverter: full-bridge operation
In case of Mathematical Expression (3) or (4), the primary-side inverter: full-bridge operation, the secondary-side inverter: half-bridge operation
In case of Mathematical Expression (5) or (6), the primary-side inverter: half-bridge operation, the secondary-side inverter: full-bridge operation
θ.sub.zvs: phase difference N: turns ratio
V.sub.out: the secondary-side DC voltage
V.sub.in: the primary-side DC voltage.
7 . The bidirectional isolated DC-DC converter as claimed in claim 2 , wherein: the switching devices of the primary-side inverter include first and second switching devices connected between a positive terminal and a negative terminal of a primary-side DC power supply and third and fourth switching devices connected between the positive terminal and the negative terminal of the primary-side DC power supply; the switching devices of the secondary-side inverter include fifth and sixth switching devices connected between a positive terminal and a negative terminal of a secondary-side DC power supply and seventh and eighth switching devices connected between the positive terminal and the negative terminal of the secondary-side DC power supply; the primary-side inverter uses a connection point between the first and second switching devices and a connection point between the third and fourth switching devices as AC terminals of the primary-side inverter; the secondary-side inverter uses a connection point between the fifth and sixth switching devices and a connection point between the seventh and eighth switching devices as AC terminals of the secondary-side inverter; and the fault operation decision section is configured to decide the operation of the faulty inverter and the operation of the normal inverter, based on the following Tables 1 and 2;
Operation in Case of Short-circuit Fault
TABLE 1
SHORT-CIRCUIT
FAULT COMPONENT
INV1
INV2
S1 or S5
S1: ON
S5: ON
S2: OFF
S6: OFF
S3: SWITCHING (SW)
S7: SW
S4: SW
S8: SW
S2 or S6
S1: OFF
S5: OFF
S2: ON
S6: ON
S3: SW
S7: SW
S4: SW
S8: SW
S3 or S7
S1: SW
S5: SW
S2: SW
S6: SW
S3: ON
S7: ON
S4: OFF
S8: OFF
S4 or S8
S1: SW
S5: SW
S2: SW
S6: SW
S3: OFF
S7: OFF
S4: ON
S8: ON
Operation in Case of open-Circuit Fault
TABLE 2
OPEN-CIRCUIT FAULT
COMPONENT
INV1
INV2
S1 or S5
S1:OFF
S5:OFF
S2:ON
S6:ON
S3:SW
S7:SW
S4:SW
S8:SW
S2 or S6
S1:ON
S5:ON
S2:OFF
S6:OFF
S3:SW
S7:SW
S4:5W
S8:SW
S3 or S7
S1:SW
S5:SW
S2:SW
S6:SW
S3:OFF
S7:OFF
S4:ON
S8:ON
S4 or S8
S1:SW
S5:SW
S2:SW
S6:SW
S3:ON
S7:ON
S4:OFF
S8:OFF
S1 to S8: first to eighth switching devices
INV1: primary-side inverter
INV2: secondary-side inverter.