JP7373802B2 - power converter - Google Patents

Description

The present invention relates to a power conversion device that converts DC power to DC power of a different voltage.

Power conditioners used in solar power generation systems and V2H (vehicle to home) systems are required to have highly efficient power conversion. A V2H system can charge and discharge between a storage battery mounted on an EV/PHEV and a household power supply/load. For example, an EV/PHEV can be charged with electric power generated by a home solar power generation system. Furthermore, the storage battery installed in an EV/PHEV can be used for peak load shifting or backup purposes in the home. In addition to being highly efficient, DC/DC converters used in V2H systems are required to have a wide voltage range and be of an isolated type. One of the DC/DC converters that meets these requirements is a DAB (Dual Active Bridge) converter.

DAB converters generally have problems with increased losses due to hard switching at low outputs and increased losses due to the flow of reactive currents unrelated to power transmission. As a countermeasure to this problem, a method has been proposed in which the PWM signal input to either leg of a bridge circuit composed of four switching elements is completely turned off and a phase shift is used (for example, Patent Document 1 reference). Although this method can solve these problems, there is a timing when current flows through the anti-parallel diode of the switching element during the dead time, and there is room for efficiency improvement.

International Publication No. 16/125374

The present disclosure has been made in view of these circumstances, and its purpose is to provide a highly efficient isolated DC/DC converter.

In order to solve the above problems, a power conversion device according to an aspect of the present disclosure includes a first leg in which a first switching element and a second switching element are connected in series, and a third switching element and a fourth switching element are connected in series. a first bridge circuit, the first leg and the second leg being connected in parallel to a first direct current section; and a third bridge circuit having a fifth switching element and a sixth switching element connected in series. a second bridge circuit having a fourth leg in which a seventh switching element and an eighth switching element are connected in series, the third leg and the fourth leg being connected in parallel to a second DC section; an isolation transformer connected between the first bridge circuit and the second bridge circuit; a first inductance connected or formed in series between the first bridge circuit and the primary winding of the isolation transformer; The present invention includes a second inductance connected or formed in series between a two-bridge circuit and a secondary winding of the isolation transformer, and a control circuit that controls the first switching element and the eighth switching element. A diode is connected or formed in antiparallel to each of the first switching element and the eighth switching element, and a capacitor is connected or formed in parallel to each of the first switching element and the eighth switching element. When transmitting power by boosting the voltage from the first DC section to the second DC section, the first bridge circuit is configured such that the first DC section and the primary winding of the isolation transformer are connected to each other, except for dead time. conduction, and the second bridge circuit has a first period in which both ends of the secondary winding of the isolation transformer are short-circuited within the second bridge circuit, and the secondary winding of the isolation transformer and the second DC section includes a second period in which the current is conductive. The control circuit controls at least one of the fifth switching element and the eighth switching element to be in an on state during a period of boosting and transmitting power from the first DC section to the second DC section.

According to the present disclosure, a highly efficient isolated DC/DC converter can be realized.

FIG. 1 is a diagram for explaining the configuration of a power conversion device according to an embodiment. FIGS. 2(a) to 2(c) are diagrams for explaining the operation of a comparative example of the power conversion device. FIG. 7 is a diagram showing switching timing 1 of the first switching element to the eighth switching element according to the embodiment (step-down mode). FIGS. 4(a) to 4(d) are diagrams (part 1) for explaining the operation of the embodiment (step-down mode) of the power conversion device. FIGS. 5(a) to 5(d) are diagrams for explaining the operation of the embodiment (step-down mode) of the power conversion device (Part 2). FIGS. 6A and 6B are diagrams for explaining the mechanism of recovery loss generation in a diode. FIG. 7 is a diagram showing switching timing 2 of the first switching element to the eighth switching element according to the embodiment (step-down mode). FIG. 3 is a diagram for explaining the configuration of a power conversion device according to Modification 1. FIG. FIG. 7 is a diagram showing the switching timing of the first switching element to the fourth switching element according to Modification 1 (step-down mode). FIG. 7 is a diagram showing switching timing 1 of the first switching element to the eighth switching element according to the embodiment (boosting mode). FIGS. 11(a) to 11(c) are diagrams (part 1) for explaining the operation of the embodiment (boosting mode) of the power conversion device. FIGS. 12(a) to 12(c) are diagrams for explaining the operation of the embodiment (step-up mode) of the power conversion device (Part 2). FIG. 7 is a diagram showing the switching timing of the first switching element to the eighth switching element according to a comparative example (boosting mode). FIGS. 14A and 14B are diagrams for explaining the state of the secondary side dead time Td'' in a comparative example (step-up mode) of the power conversion device. FIG. 7 is a diagram showing switching timing 2 of the first switching element to the eighth switching element according to the embodiment (boosting mode).

FIG. 1 is a diagram for explaining the configuration of a power conversion device 1 according to an embodiment. The power conversion device 1 is an isolated bidirectional DC/DC converter (DAB converter), converts DC power supplied from a first DC power source E1, and transmits the converted DC power to a second DC power source E2. Further, the power conversion device 1 converts the DC power supplied from the second DC power source E2 and transmits the converted DC power to the first DC power source E1. The power conversion device 1 can step down and transmit power, or step up and transmit power.

The first DC power source E1 is, for example, a storage battery or an electric double layer capacitor mounted on an EV, or a stationary storage battery or an electric double layer capacitor. The second DC power source E2 is, for example, a DC bus connected to a commercial power system via an inverter. Other storage batteries, solar cells, fuel cells, etc. may be connected to the DC bus via another DC/DC converter.

The power converter 1 includes a primary capacitor Ca, a first bridge circuit 11, a first inductance L1, an isolation transformer TR1, a second inductance L2, a second bridge circuit 12, a secondary capacitor Cb, and a control circuit 13.

A primary capacitor Ca is connected in parallel with the first DC power source E1. A secondary capacitor Cb is connected in parallel with the second DC power supply E2. For example, an electrolytic capacitor is used as the primary capacitor Ca and the secondary capacitor Cb. In this specification, the first DC power supply E1 and the primary capacitor Ca are collectively referred to as a first DC section, and the second DC power supply E2 and the secondary capacitor Cb are collectively referred to as a second DC section.

The first bridge circuit 11 includes a first leg in which a first switching element Q1 and a second switching element Q2 are connected in series, and a second leg in which a third switching element Q3 and a fourth switching element Q4 are connected in series, which are connected in parallel. It is a full-bridge circuit configured with The first bridge circuit 11 is connected in parallel with the first DC section, and the midpoint of the first leg and the midpoint of the second leg are connected to both ends of the primary winding n1 of the isolation transformer TR1, respectively. The first bridge circuit 11 can convert the primary side DC voltage supplied from the first DC section into an AC voltage and output it to the primary winding n1 of the isolation transformer TR1. Further, the first bridge circuit 11 can convert the AC voltage supplied from the primary winding n1 of the isolation transformer TR1 into a DC voltage, and output the DC voltage to the first DC section.

The second bridge circuit 12 includes a third leg in which a fifth switching element Q5 and a sixth switching element Q6 are connected in series, and a fourth leg in which a seventh switching element Q7 and an eighth switching element Q8 are connected in series, which are connected in parallel. It is a full-bridge circuit configured with The second bridge circuit 12 is connected in parallel with the second DC section, and the middle point of the third leg and the middle point of the fourth leg are respectively connected to both ends of the secondary winding n2 of the isolation transformer TR1. The second bridge circuit 12 can convert the secondary side DC voltage supplied from the second DC section into an AC voltage and output it to the secondary winding n2 of the isolation transformer TR1. Further, the second bridge circuit 12 can convert the AC voltage supplied from the secondary winding n2 of the isolation transformer TR1 into a DC voltage, and output the DC voltage to the second DC section.

A first diode D1 to an eighth diode D8 are connected or formed in antiparallel to the first switching element Q1 to the eighth switching element Q8, respectively. Furthermore, a first capacitor C1 to an eighth capacitor C8 are connected or formed in parallel to the first switching element Q1 to the eighth switching element Q8, respectively.

For example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used for the first switching element Q1 to the eighth switching element Q8. When an IGBT is used, external diode elements are connected between the emitters and collectors of the first switching element Q1 to the eighth switching element Q8 as the first diode D1 to the eighth diode D8, respectively. Alternatively, external capacitors may be connected between the collectors and emitters of the first switching element Q1 and the eighth switching element Q8 as the first capacitor C1 and the eighth capacitor C8, respectively, or the first switching element Q1 and the eighth switching element Q8 may be Parasitic capacitances formed between the collector and emitter of are used as the first capacitor C1 to the eighth capacitor C8. When a MOSFET is used, parasitic diodes formed between the sources and drains of the first switching element Q1 and the eighth switching element Q8 are used as the first diode D1 and the eighth diode D8, or an external diode element is used. are connected as a first diode D1 to an eighth diode D8, respectively. Alternatively, the parasitic capacitances formed between the sources and drains of the first switching element Q1 and the eighth switching element Q8 may be used as the first capacitance C1 and the eighth capacitance C8, or External capacitors are connected between the source and drain of Q8 as a first capacitor C1 to an eighth capacitor C8, respectively.

The capacitance values of the first capacitor C1 to the eighth capacitor C8, which are connected or formed in parallel to the first switching element Q1 to the eighth switching element Q8, respectively, correspond to each other. That is, the emitter-collector or source-drain capacitance values of the first switching element Q1 and the eighth switching element Q8 are substantially equal. Similarly, the resistance values of the first diode D1 to the eighth diode D8, which are connected or formed in antiparallel to the first switching element Q1 to the eighth switching element Q8, respectively, also correspond to each other. In this way, the configurations of the first leg and the fourth leg are all compatible, contributing to reductions in manufacturing costs and circuit area. Furthermore, it can flexibly accommodate any switching pattern.

The isolation transformer TR1 is connected between the AC terminal of the first bridge circuit 11 and the AC terminal of the second bridge circuit 12. The isolation transformer TR1 converts the output voltage of the first bridge circuit 11 connected to the primary winding n1 according to the turns ratio of the primary winding n1 and the secondary winding n2, and converts the output voltage of the first bridge circuit 11 connected to the primary winding n1. The signal is output to the second bridge circuit 12. In addition, the isolation transformer TR1 converts the output voltage of the second bridge circuit 12 connected to the secondary winding n2 according to the turns ratio of the secondary winding n2 and the primary winding n1, and connects it to the primary winding n1. The signal is output to the first bridge circuit 11 where the signal is input.

The first inductance L1 is connected or formed in series between the AC terminal of the first bridge circuit 11 and the primary winding n1 of the isolation transformer TR1. The second inductance L2 is connected or formed in series between the AC terminal of the second bridge circuit 12 and the secondary winding n2 of the isolation transformer TR1. In the example shown in FIG. 1, the first inductance L1 is constituted by a reactor element connected between the midpoint of the first leg of the first bridge circuit 11 and the primary winding n1 of the isolation transformer TR1. The second inductance L2 is composed of a reactor element connected between the midpoint of the third leg of the second bridge circuit 12 and the secondary winding n2 of the isolation transformer TR1.

Note that the first inductance L1 may be configured by the leakage inductance of the primary winding n1 formed between the midpoint of the first leg of the first bridge circuit 11 and the primary winding n1 of the isolation transformer TR1. . The second inductance L2 may be configured by a leakage inductance of a secondary winding n2 formed between the midpoint of the third leg of the second bridge circuit 12 and the secondary winding n2 of the isolation transformer TR1. .

Although not shown in FIG. 1, a first voltage sensor detects the voltage across the first DC section, a first current sensor detects the current flowing through the first DC section, and a first current sensor detects the voltage across the second DC section. Two voltage sensors and a second current sensor that detects the current flowing through the second DC section are provided, and respective detected values are output to the control circuit 13.

The control circuit 13 controls the first switching element Q1 to the eighth switching element Q8 by supplying a drive signal (PWM (Pulse Width Modulation) signal) to the gate terminals of the first switching element Q1 to the eighth switching element Q8. do. The configuration of the control circuit 13 can be realized by cooperation of hardware resources and software resources, or by only hardware resources. Analog elements, microcomputers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

The control circuit 13 executes the following control as basic control. The control circuit 13 determines that when transmitting power from the first DC section to the second DC section (when discharging from the first DC power source E1), the current value (discharge current value) detected by the first current sensor is a current command value. The first switching element Q1 to the eighth switching element Q8 are controlled so that the voltage value detected by the first voltage sensor (discharge voltage value) maintains the voltage command value. Note that the secondary-side current value detected by the second current sensor may be controlled, or the secondary-side voltage value detected by the second voltage sensor may be controlled. In addition, the control circuit 13 determines that when transmitting power from the second DC section to the first DC section (when charging the first DC power source E1), the current value detected by the first current sensor (charging current value) is a current command. The first switching element Q1 to the eighth switching element Q8 are controlled so as to maintain the voltage value or so that the voltage value (charging voltage value) detected by the first voltage sensor maintains the voltage command value. Note that the secondary-side current value detected by the second current sensor may be controlled, or the secondary-side voltage value detected by the second voltage sensor may be controlled.

In this way, the DAB converter has a symmetrical configuration in which the primary side and the secondary side are configured so that power can be transmitted bidirectionally. The operation of the power conversion device 1 will be described below.

(Comparative example)
FIGS. 2(a) to 2(c) are diagrams for explaining the operation of the power conversion device 1 according to a comparative example. In the first state shown in FIG. 2(a), the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4, the sixth switching element Q6, and the seventh switching element Q7, and turns on the second switching element Q2. The third switching element Q3, the fifth switching element Q5, and the eighth switching element Q8 are controlled to be in the off state. In this state, the first DC power source E1 charges the first inductance L1 with power, and the second DC power source E2 charges the second inductance L2 with power.

In the second state shown in FIG. 2(b), the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4, the fifth switching element Q5, and the eighth switching element Q8, and turns on the second switching element Q2. The third switching element Q3, the sixth switching element Q6, and the seventh switching element Q7 are controlled to be in the off state. In this state, the power of the first DC power source E1, the power stored in the first inductance L1, and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the third state (not shown), the control circuit 13 turns on the second switching element Q2, the third switching element Q3, the fifth switching element Q5, and the eighth switching element Q8, and turns on the first switching element Q1 and the fourth switching element Q8. The element Q4, the sixth switching element Q6, and the seventh switching element Q7 are controlled to be in the off state. In this state, the first DC power source E1 charges the first inductance L1 with power, and the second DC power source E2 charges the second inductance L2 with power.

In the fourth state (not shown), the control circuit 13 turns on the second switching element Q2, the third switching element Q3, the sixth switching element Q6, and the seventh switching element Q7, and turns on the first switching element Q1 and the fourth switching element Q3. The element Q4, the fifth switching element Q5, and the eighth switching element Q8 are controlled to be in the off state. In this state, the power of the first DC power source E1, the power stored in the first inductance L1, and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the control according to the comparative example, the second inductance L2 is charged with the power of the second DC power supply E2 in the first state (see FIG. 2A) and the third state (not shown). In the subsequent second state (see FIG. 2(b)) and fourth state (not shown), the power accumulated in the second inductance L2 is discharged to the second DC power source E2. That is, a reactive current unrelated to power transmission flows on the secondary side. The flow of this reactive current causes unnecessary loss.

FIG. 2(c) shows the current flow when the voltage of the first DC power source E1 is significantly lower than the voltage of the second DC power source E2 in the second state shown in FIG. 2(b). . When the voltage of the first DC power source E1 is significantly lower than the voltage of the second DC power source E2, the direction of the current is reversed, and the current flows backward from the second DC power source E2 to the first DC power source E1. In this state, in order to transition to the next state, the first switching element Q1 and the fourth switching element Q4 are turned off, and the second switching element Q2 and the third switching element Q3 are turned on. The third switching element Q3 becomes hard switching, and the first diode D1 of the first switching element Q1 and the fourth diode D4 of the fourth switching element Q4 enter recovery operation, resulting in increased loss.

(Example (step-down mode))
FIG. 3 is a diagram showing switching timing 1 of the first switching element Q1 to the eighth switching element Q8 according to the embodiment (step-down mode). FIGS. 4(a) to 4(d) are diagrams (part 1) for explaining the operation of the embodiment (step-down mode) of the power conversion device 1. FIGS. 5(a) to 5(d) are diagrams for explaining the operation of the embodiment (step-down mode) of the power converter 1 (Part 2).

In the first state shown in FIG. 4(a), the control circuit 13 turns on the first switching element Q1 and the fourth switching element Q4, and turns on the remaining switching elements (the second switching element Q2, the third switching element Q3, and the fourth switching element Q4). 5 switching element Q5, 6th switching element Q6, 7th switching element Q7, and 8th switching element Q8) are controlled to the OFF state (first switching pattern P1 (see FIG. 3)).

In the first state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, since the fifth switching element Q5 to the eighth switching element Q8 on the secondary side are all in the off state, the second bridge circuit 12 is a diode bridge circuit, and the The current is being rectified. In the first state, the first DC power source E1 transmits power to the second DC power source E2 via the fifth diode D5 and the eighth diode D8 while charging the first inductance L1 and the second inductance L2 with power. .

In the second state shown in FIG. 4(b), the control circuit 13 turns on the fourth switching element Q4 and the eighth switching element Q8, and turns on the remaining switching elements (the first switching element Q1, the second switching element Q2, the The third switching element Q3, the fifth switching element Q5, the sixth switching element Q6, and the seventh switching element Q7) are controlled to be in the off state (second switching pattern P2 (see FIG. 3)).

In the second state, both ends of the primary winding n1 of the isolation transformer TR1 are short-circuited within the first bridge circuit 11, and the first inductance L1, isolation transformer TR1, and second inductance L2 are electrically disconnected from the first DC power source E1. be done. Further, the eighth switching element Q8 on the secondary side is in an on state, and rectification is performed via the fifth diode D5 and the eighth switching element Q8. The eighth switching element Q8 performs diode rectification or synchronous rectification. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the eighth diode D8 with the eighth switching element Q8 in the off state. Further, by allowing current to pass through the fifth diode D5 while the fifth switching element Q5 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the second state, the power stored in the first inductance L1 and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the third state shown in FIG. 4(c), the control circuit 13 controls all of the first switching element Q1 to the eighth switching element Q8 to be in the off state (dead time Td (see FIG. 3)). During the dead time Td, if power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power source E1 via the third diode D3 and the second diode D2. Similarly, when power remains in the second inductance L2, current flows from the second inductance L2 to the second DC power supply E2 via the fifth diode D5 and the eighth diode D8.

The fourth state shown in FIG. 4(d) shows a state after the residual power of the first inductance L1 and the second inductance L2 disappears at the dead time Td. When the residual power in the first inductance L1 and the second inductance L2 disappears, no current flows in an ideal state, but in reality, a resonant current flows in the opposite direction. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitor C5 to the eighth capacitor C8, and a resonant current flows. Specifically, a resonant current flows through both the high side path of the second inductance L2, the seventh capacitor C7, and the fifth capacitor C5, and the low side path of the second inductance L2, the eighth capacitor C8, and the sixth capacitor C6. Similarly, on the primary side, resonance occurs between the first inductance L1 and the first capacitor C1 to the fourth capacitor C4, and a resonant current flows. Specifically, a resonant current flows through both a high-side path of the first inductance L1, the first capacitor C1, and the third capacitor C3, and a low-side path of the first inductance L1, the second capacitor C2, and the fourth capacitor C4.

In the fifth state shown in FIG. 5(a), the control circuit 13 turns on the second switching element Q2 and the third switching element Q3, and turns on the remaining switching elements (the first switching element Q1, the fourth switching element Q4, and the third switching element Q3). 5 switching element Q5, 6th switching element Q6, 7th switching element Q7, and 8th switching element Q8) are controlled to the OFF state (third switching pattern P3 (see FIG. 3)).

In the fifth state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, in the fifth state, since the fifth switching element Q5 to the eighth switching element Q8 are all in the off state, the second bridge circuit 12 is a diode bridge circuit, and the seventh diode D7 and the sixth diode D6 are turned off. It is rectified through. In the fifth state, the first DC power source E1 transmits power to the second DC power source E2 via the seventh diode D7 and the sixth diode D6 while charging the first inductance L1 and the second inductance L2 with power. .

In the sixth state shown in FIG. 5(b), the control circuit 13 turns on the third switching element Q3 and the seventh switching element Q7, and turns on the remaining switching elements (the first switching element Q1, the second switching element Q2, the 4 switching element Q4, 5th switching element Q5, 6th switching element Q6, and 8th switching element Q8) are controlled to an OFF state (4th switching pattern P4 (refer to FIG. 3)).

In the sixth state, both ends of the primary winding n1 of the isolation transformer TR1 are short-circuited within the first bridge circuit 11, and the first inductance L1, the isolation transformer TR1, and the second inductance L2 are electrically cut off from the first DC power source E1. be done. Further, the seventh switching element Q7 on the secondary side is in an on state, and rectification is performed via the sixth diode D6 and the seventh switching element Q7. The seventh switching element Q7 performs diode rectification or synchronous rectification. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the seventh diode D7 with the seventh switching element Q7 in an off state. Further, by allowing current to pass through the sixth diode D6 while the sixth switching element Q6 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the sixth state, the power stored in the first inductance L1 and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the seventh state shown in FIG. 5(c), the control circuit 13 controls all of the first switching element Q1 to the eighth switching element Q8 to be in the off state (dead time Td (see FIG. 3)). During the dead time Td, if power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power source E1 via the first diode D1 and the fourth diode D4. Similarly, when power remains in the second inductance L2, current flows from the second inductance L2 to the second DC power supply E2 via the seventh diode D7 and the sixth diode D6.

The eighth state shown in FIG. 5(d) shows a state after the residual power of the first inductance L1 and the second inductance L2 disappears at the dead time Td. When the residual power in the first inductance L1 and the second inductance L2 disappears, no current flows in an ideal state, but in reality, a resonant current flows in the opposite direction. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitor C5 to the eighth capacitor C8, and a resonant current flows. Specifically, a resonant current flows through both a high-side path of the second inductance L2, the fifth capacitor C5, and the seventh capacitor C7, and a low-side path of the second inductance L2, the sixth capacitor C6, and the eighth capacitor C8. Similarly, on the primary side, resonance occurs between the first inductance L1 and the first capacitor C1 to the fourth capacitor C4, and a resonant current flows. Specifically, a resonant current flows through both a high-side path of the first inductance L1, the third capacitor C3, and the first capacitor C1, and a low-side path of the first inductance L1, the fourth capacitor C4, and the second capacitor C2.

Here, the period of the first switching pattern P1 and the third switching pattern P3 is defined as a first period, and the period of the second switching pattern P2 and the fourth switching pattern P4 is defined as a second period. As shown in FIGS. 3, 4(a)-(d), and 5(a)-(d), in this embodiment (step-down mode), the control circuit 13 changes from the second period to the first period. During the switching, a dead time Td is inserted in which all of the first switching element Q1 to the eighth switching element Q8 are turned off. On the other hand, if the dead time Td for turning off all of the first switching element Q1 to the eighth switching element Q8 is not inserted, diode recovery loss occurs.

FIGS. 6A and 6B are diagrams for explaining the mechanism of recovery loss generation in a diode. FIG. 6A shows another switching pattern with a dead time Td between the second switching pattern P2 and the third switching pattern P3.

In this state, when the residual power in the first inductance L1 and the second inductance L2 disappears, no current flows in an ideal state, but in reality, a resonant current flows in the opposite direction. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitor C5 to the eighth capacitor C8, and a resonant current flows. Specifically, a resonant current flows through both the high side path of the second inductance L2, the seventh capacitor C7, and the fifth capacitor C5, and the low side path of the second inductance L2, the eighth capacitor C8, and the sixth capacitor C6. In response to the resonant current on the secondary side, on the primary side, a current flows through the low side path of the first inductance L1, the second switching element Q2, and the fourth diode D4.

When this state transitions to the third switching pattern P3 shown in FIG. 5(a), the third switching element Q3 on the primary side is turned on. When the third switching element Q3 is turned on, a reverse bias voltage is applied to the fourth diode D4 connected to the fourth switching element Q4, and a recovery current flows in the reverse direction. As a result, a through current flows through the third switching element Q3 and the fourth diode D4, increasing loss.

FIG. 6(b) shows another switching pattern with a dead time Td between the fourth switching pattern P4 and the first switching pattern P1. In this state, when the residual power in the first inductance L1 and the second inductance L2 disappears, no current flows in an ideal state, but in reality, a resonant current flows in the opposite direction. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitor C5 to the eighth capacitor C8, and a resonant current flows. Specifically, a resonant current flows through both a high-side path of the second inductance L2, the fifth capacitor C5, and the seventh capacitor C7, and a low-side path of the second inductance L2, the sixth capacitor C6, and the eighth capacitor C8. In response to the resonant current on the secondary side, on the primary side, a current flows through the high side path of the first inductance L1, the third diode D3, and the first switching element Q1.

When this state transitions to the first switching pattern P1 shown in FIG. 4(a), the fourth switching element Q4 on the primary side is turned on. When the fourth switching element Q4 is turned on, a reverse bias voltage is applied to the third diode D3, and a recovery current flows in the reverse direction. As a result, a through current flows through the third diode D3 and the fourth switching element Q4, increasing loss.

On the other hand, in this embodiment, during the transition from the second switching pattern P2 to the third switching pattern P3 and during the transition from the fourth switching pattern P4 to the first switching pattern P1, A dead time Td is inserted in which all eight switching elements Q8 are turned off. Thereby, the current flowing through the fourth diode D4 or the third diode D3 can be suppressed, and the recovery loss of the fourth diode D4 or the third diode D3 can be reduced.

In this embodiment (step-down mode), the control circuit 13 adjusts the duty ratio of the drive signal supplied to the first switching element Q1 and the second switching element Q2, thereby supplying the drive signal from the first DC section to the second DC section. Control the voltage or current of power. The longer the on time of the drive signal supplied to the first switching element Q1 and the second switching element Q2 (the greater the duty ratio), the more the amount of power transmitted from the first DC section to the second DC section increases. The control circuit 13 alternately controls the third switching element Q3 and the fourth switching element Q4 to be in the ON state for half the switching period fsw (excluding dead time Td).

In this way, in this embodiment (step-down mode), power is transmitted from the first DC section to the second DC section using the PWM method. On the other hand, when transmitting power using the phase shift method, it is not possible to provide a period in which the first switching element Q1 to the fourth switching element Q4 on the primary side are all in the OFF state, resulting in the above-mentioned diode recovery loss. cannot be prevented.

When transitioning from the dead time Td to the first switching pattern P1, the control circuit 13 turns on the fourth switching element Q4 in synchronization with turning on the first switching element Q1. That is, the first switching element Q1 and the fourth switching element Q4 are turned on substantially simultaneously.

When transitioning from the first switching pattern P1 to the second switching pattern P2, the control circuit 13 turns on the eighth switching element Q8 in synchronization with turning off the first switching element Q1. That is, the first switching element Q1 is turned off and the eighth switching element Q8 is turned on substantially simultaneously. Thereby, the synchronous rectification period of the eighth switching element Q8 can be maximized, and the loss reduction effect due to the synchronous rectification of the eighth switching element Q8 can be maximized.

When transitioning from the second switching pattern P2 to the dead time Td, the control circuit 13 turns off the eighth switching element Q8 in synchronization with turning off the fourth switching element Q4. That is, the fourth switching element Q4 and the eighth switching element Q8 are turned off substantially simultaneously.

The control circuit 13 controls the first switching element Q1 so that the total time of the on time of the first switching element Q1, the on time of the eighth switching element Q8, and the dead time Td becomes half the switching period fsw. and controls the eighth switching element Q8. The on time of the eighth switching element Q8 adaptively changes depending on the on time of the first switching element Q1.

When transitioning from the dead time Td to the third switching pattern P3, the control circuit 13 turns on the third switching element Q3 in synchronization with turning on the second switching element Q2. That is, the second switching element Q2 and the third switching element Q3 are turned on substantially simultaneously.

When transitioning from the third switching pattern P3 to the fourth switching pattern P4, the control circuit 13 turns on the seventh switching element Q7 in synchronization with turning off the second switching element Q2. That is, the second switching element Q2 is turned off and the seventh switching element Q7 is turned on substantially simultaneously. Thereby, the synchronous rectification period of the seventh switching element Q7 can be maximized, and the loss reduction effect due to the synchronous rectification of the seventh switching element Q7 can be maximized.

When transitioning from the fourth switching pattern P4 to the dead time Td, the control circuit 13 turns off the seventh switching element Q7 in synchronization with turning off the third switching element Q3. That is, the third switching element Q3 and the seventh switching element Q7 are turned off substantially simultaneously.

The control circuit 13 switches the second switching element Q2 so that the total time of the on time of the second switching element Q2, the on time of the seventh switching element Q7, and the dead time Td becomes half the switching period fsw. and controls the seventh switching element Q7. The on time of the seventh switching element Q7 adaptively changes depending on the on time of the second switching element Q2.

In this way, by controlling the first switching element Q1 to the eighth switching element Q8 using the PWM method instead of the phase shift method, it is possible to easily control the period during which the first switching element Q1 to the eighth switching element Q8 are all in the off state. can be generated.

The control circuit 13 synchronizes the period of the first switching pattern P1 and the period of the third switching pattern P3. That is, the period of the first switching pattern P1 and the period of the third switching pattern P3 are controlled to be substantially the same time. Further, the control circuit 13 synchronizes the period of the second switching pattern P2 and the period of the fourth switching pattern P4. That is, the period of the second switching pattern P2 and the period of the fourth switching pattern P4 are controlled to be substantially the same time. As a result, the positive and negative operations become symmetrical, and it is possible to suppress the occurrence of direct current biased magnetism in the transformer.

In the step-down mode control examples shown in FIGS. 3, 4(a)-(d), and 5(a)-(d), the control circuit 13 constantly switches the fifth switching element Q5 and the sixth switching element Q6. Controlled to off state. In this regard, the control circuit 13 may control the seventh switching element Q7 and the eighth switching element Q8 to be in the off state at all times. In this case, in the second switching pattern P2, synchronous rectification is performed by the fifth switching element Q5 instead of the eighth switching element Q8. In the fourth switching pattern P4, synchronous rectification is performed by the sixth switching element Q6 instead of the seventh switching element Q7.

FIG. 7 is a diagram showing switching timing 2 of the first switching element Q1 to the eighth switching element Q8 according to the embodiment (step-down mode). In the switching timing 1 of the first switching element Q1 to the eighth switching element Q8 shown in FIG. 3, an example has been described in which the voltage is stepped down from the first DC section to the second DC section and power is supplied. In this respect, it is also possible to step down the voltage and supply power from the second DC section to the first DC section. In this case, as shown in FIG. 7, the control circuit 13 outputs a drive signal supplied to the first switching element Q1 to the fourth switching element Q4, and a drive signal supplied to the fifth switching element Q5 to the eighth switching element Q8. Just replace it.

As explained above, according to the present embodiment (step-down mode), a state in which the second inductance L2 is charged from the second DC power supply E2 does not occur as in the comparative example (see FIG. 2(a)), so that reactive power is reduced. Can be suppressed. Further, since it is possible to suppress the resonant current from flowing to the anti-parallel diode of the switching element during the dead time, recovery loss of the diode can be reduced. Furthermore, by performing synchronous rectification in the eighth switching element Q8 or the seventh switching element Q7 on the secondary side in states 2 and 5, conduction loss of the diode can be reduced. These can improve the conversion efficiency during step-down operation of the DAB converter.

Further, according to the present embodiment (step-down mode), since a state in which the first DC power supply E1 and the second DC power supply E2 are electrically connected without a diode does not occur, the voltage of the first DC power supply E1 is changed to the voltage of the second DC power supply E2. Even if the voltage decreases significantly with respect to the voltage, the direction of the current will not be reversed, and the current will not flow backward from the second DC power supply E2 to the first DC power supply E1. This makes it possible to prevent hard switching from occurring.

(Modification 1 (step-down mode))
FIG. 8 is a diagram for explaining the configuration of the power conversion device 1 according to the first modification. In the power conversion device 1 according to the first modification, the second bridge circuit 12 includes four bridge-connected diode elements (fifth diode D5-eighth diode D8) instead of the fifth switching element Q5-eighth switching element Q8. ). The power conversion device 1 according to Modification 1 is an isolated unidirectional DC/DC converter that cannot transmit power from the second DC section to the first DC section.

FIG. 9 is a diagram showing switching timings of the first switching element Q1 to the fourth switching element Q4 according to Modification 1 (step-down mode). In modification example 1 (step-down mode), in the first switching pattern P1, the control circuit 13 turns on the first switching element Q1 and the fourth switching element Q4, and turns off the second switching element Q2 and the third switching element Q3. to control. In the second switching pattern P2, the control circuit 13 controls the fourth switching element Q4 to be in the on state, and the first switching element Q1, the second switching element Q2, and the third switching element Q3 to be in the off state. During the dead time Td between the second switching pattern P2 and the third switching pattern P3, the control circuit 13 controls all of the first switching element Q1 to the fourth switching element Q4 to be in the off state.

In the third switching pattern P3, the control circuit 13 controls the second switching element Q2 and the third switching element Q3 to be in the on state, and controls the first switching element Q1 and the fourth switching element Q4 to be in the off state. In the fourth switching pattern P4, the control circuit 13 controls the third switching element Q3 to be in the on state, and controls the first switching element Q1, the second switching element Q2, and the fourth switching element Q4 to be in the off state. During the dead time Td between the fourth switching pattern P4 and the first switching pattern P1, the control circuit 13 controls all of the first switching element Q1 to the fourth switching element Q4 to be in the off state.

According to modification 1 (step-down mode), except that power cannot be transmitted from the secondary side to the primary side and that synchronous rectification using the eighth switching element Q8 or the seventh switching element Q7 on the secondary side cannot be performed, The same effects as in the above embodiment (step-down mode) are achieved.

(Modification 2 (step-down mode))
In modification 2, assuming the configuration of the power conversion device 1 shown in FIG. 1, the control circuit 13 always controls the fifth switching element Q5 to the eighth switching element Q8 to be in the off state.

Specifically, in the second modification (step-down mode), in the first switching pattern P1, the control circuit 13 turns on the first switching element Q1 and the fourth switching element Q4, and turns on the remaining switching elements (second switching element Q2). , the third switching element Q3, the fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8). In the second switching pattern P2, the control circuit 13 turns on the fourth switching element Q4, and the remaining switching elements (first switching element Q1, second switching element Q2, third switching element Q3, fifth switching element Q5, The sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8) are controlled to be in the off state. During the dead time Td between the second switching pattern P2 and the third switching pattern P3, the control circuit 13 controls all of the first switching element Q1 to the eighth switching element Q8 to be in the off state.

In the third switching pattern P3, the control circuit 13 turns on the second switching element Q2 and the third switching element Q3, and turns on the remaining switching elements (first switching element Q1, fourth switching element Q4, fifth switching element Q5, The sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8) are controlled to be in the off state. In the fourth switching pattern P4, the control circuit 13 turns on the third switching element Q3, and the remaining switching elements (first switching element Q1, second switching element Q2, fourth switching element Q4, fifth switching element Q5, The sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8) are controlled to be in the off state. During the dead time Td between the fourth switching pattern P4 and the first switching pattern P1, the control circuit 13 controls all of the first switching element Q1 to the eighth switching element Q8 to be in the off state.

According to modification 2 (pressure reduction mode), the same effects as modification 1 (pressure reduction mode) are achieved. Note that in the second modification (step-down mode), power can also be transmitted from the second DC section to the first DC section.

(Example (boost mode))
FIG. 10 is a diagram showing switching timing 1 of the first switching element Q1 to the eighth switching element Q8 according to the embodiment (boosting mode). FIGS. 11(a) to 11(c) are diagrams (part 1) for explaining the operation of the embodiment (boosting mode) of the power conversion device 1. FIGS. 12A to 12C are diagrams for explaining the operation of the embodiment (boosting mode) of the power conversion device 1 (Part 2).

In the first state shown in FIG. 11(a), the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4, and the sixth switching element Q6, and turns on the second switching element Q2, the third switching element Q3, The fifth switching element Q5, the seventh switching element Q7, and the eighth switching element Q8 are controlled to be in the off state (fifth switching pattern P5 (see FIG. 10)).

In the first state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited within the second bridge circuit 12, and the first inductance L1, the isolation transformer TR1, and the second inductance L2 are electrically cut off from the second DC power supply E2. . In the first state, the first DC power source E1 charges the first inductance L1 and the second inductance L2 with power.

In the second state shown in FIG. 11(b), the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4, and the eighth switching element Q8, and turns on the second switching element Q2, the third switching element Q3, The fifth switching element Q5, the sixth switching element Q6, and the seventh switching element Q7 are controlled to be in the off state (sixth switching pattern P6 (see FIG. 10)).

In the second state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, the eighth switching element Q8 on the secondary side is in an on state, and rectification is performed via the fifth diode D5 and the eighth switching element Q8. The eighth switching element Q8 performs diode rectification or synchronous rectification. In the rectifying state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are electrically connected. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the eighth diode D8 with the eighth switching element Q8 in the off state. Further, by allowing current to pass through the fifth diode D5 while the fifth switching element Q5 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the second state, the power of the first DC power source E1, the power stored in the first inductance L1, and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the third state shown in FIG. 11(c), the control circuit 13 turns on the fifth switching element Q5, the first switching element Q1, the second switching element Q2, the third switching element Q3, the fourth switching element Q4, The sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 are controlled to be in the off state (first primary side dead time Td' (see FIG. 10)).

During the first primary side dead time Td', if power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power source E1 via the third diode D3 and the second diode D2. flows. Further, the fifth switching element Q5 on the secondary side is in an on state, and rectification is performed via the fifth switching element Q5 and the eighth diode D8. The fifth switching element Q5 performs diode rectification or synchronous rectification. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the fifth diode D5 with the fifth switching element Q5 in the off state. Further, when power remains in the second inductance L2, by turning on the fifth switching element Q5, ZVS (zero voltage switching) operation is performed, and switching loss can be reduced. Further, by allowing current to pass through the eighth diode D8 while the eighth switching element Q8 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed.

In the fourth state shown in FIG. 12A, the control circuit 13 turns on the second switching element Q2, the third switching element Q3, and the fifth switching element Q5, and turns on the first switching element Q1, the fourth switching element Q4, The sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 are controlled to be in the off state (seventh switching pattern P7 (see FIG. 10)).

In the fourth state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited within the second bridge circuit 12, and the first inductance L1, the isolation transformer TR1, and the second inductance L2 are electrically cut off from the second DC power supply E2. . In the fourth state, the first DC power supply E1 charges the first inductance L1 and the second inductance L2 with power.

In the fifth state shown in FIG. 12(b), the control circuit 13 turns on the second switching element Q2, the third switching element Q3, and the seventh switching element Q7, and turns on the first switching element Q1, the fourth switching element Q4, The fifth switching element Q5, the sixth switching element Q6, and the eighth switching element Q8 are controlled to be in the off state (eighth switching pattern P8 (see FIG. 10)).

In the fifth state, the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected. Further, the seventh switching element Q7 on the secondary side is in an on state, and rectification is performed via the seventh switching element Q7 and the sixth diode D6. In the rectifying state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are electrically connected. In the rectifying state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are electrically connected. The seventh switching element Q7 performs diode rectification or synchronous rectification. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the seventh diode D7 with the seventh switching element Q7 in an off state. Further, by allowing current to pass through the sixth diode D6 while the sixth switching element Q6 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the fifth state, the power of the first DC power source E1, the power stored in the first inductance L1, and the power stored in the second inductance L2 are transmitted to the second DC power source E2.

In the sixth state shown in FIG. 12(c), the control circuit 13 turns on the sixth switching element Q6, the first switching element Q1, the second switching element Q2, the third switching element Q3, the fourth switching element Q4, The fifth switching element Q5, the seventh switching element Q7, and the eighth switching element Q8 are controlled to be in the off state (second primary side dead time Td' (see FIG. 10)).

During the second primary side dead time Td', if power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power source E1 via the first diode D1 and the fourth diode D4. flows. Further, the sixth switching element Q6 on the secondary side is in an on state, and rectification is performed via the seventh diode D7 and the sixth switching element Q6. The sixth switching element Q6 performs diode rectification or synchronous rectification. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the sixth diode D6 with the sixth switching element Q6 in the off state. Furthermore, when power remains in the second inductance L2, by turning on the sixth switching element Q6, ZVS (zero voltage switching) operation is performed, and switching loss can be reduced. Further, by allowing current to pass through the seventh diode D7 while the seventh switching element Q7 is in an off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed.

Here, the period of the fifth switching pattern P5 and the sixth switching pattern P6 is defined as a third period, and the period of the seventh switching pattern P7 and the eighth switching pattern P8 is defined as a fourth period. As shown in FIGS. 10, 11(a)-(c), and 12(a)-(c), in this embodiment (step-up mode), the control circuit 13 changes from the fourth period to the third period. During the switching, a primary side dead time Td' is inserted in which all of the first switching element Q1 to the fourth switching element Q4 are turned off. The control circuit 13 controls the first switching element Q1 to the fourth switching element Q4 so that the first DC power supply E1 and the primary winding n1 of the isolation transformer TR1 are electrically connected except for the primary side dead time Td'.

On the other hand, the control circuit 13 inserts a secondary side dead time in which all of the fifth switching element Q5 to the eighth switching element Q8 are turned off while switching from the fourth period to the third period. do not have. That is, the control circuit 13 controls at least one of the fifth switching element Q5 to the eighth switching element Q8 to be in the ON state during the period of boosting and transmitting power from the first DC section to the second DC section. .

(Comparative example (boost mode))
FIG. 13 is a diagram showing switching timings of the first switching element Q1 to the eighth switching element Q8 according to a comparative example (boosting mode). In the comparative example (boost mode), on the secondary side, the control circuit 13 always controls the seventh switching element Q7 and the eighth switching element Q8 to the OFF state, and alternately controls the fifth switching element Q5 and the sixth switching element Q6. Control to ON state. In the comparative example (boost mode), diode rectification or synchronous rectification is performed using the fifth switching element Q5 and the sixth switching element Q6. When switching on/off of the fifth switching element Q5 and the sixth switching element Q6, the control circuit 13 controls the secondary side in order to prevent a through current from flowing through the fifth switching element Q5 and the sixth switching element Q6. A dead time Td'' is inserted.

FIGS. 14(a) and 14(b) are diagrams for explaining the state of the secondary side dead time Td'' in a comparative example (step-up mode) of the power converter 1. FIG. 14(a) shows the state of the first secondary side dead time Td'' inserted between the turn-off of the fifth switching element Q5 and the turn-on of the sixth switching element Q6. In this state, the secondary side is rectifying through two diodes, the fifth diode D5 and the eighth diode D8. Since diode rectification has more loss than synchronous rectification, the loss on the secondary side increases compared to the case where the current passes through the fifth switching element Q5 with the fifth switching element Q5 in the on state.

FIG. 14(b) shows the state of the second secondary side dead time Td'' inserted between the turn-off of the sixth switching element Q6 and the turn-on of the fifth switching element Q5. In this state, the secondary side is rectifying through two diodes, the seventh diode D7 and the sixth diode D6. Since diode rectification has more loss than synchronous rectification, the loss on the secondary side increases compared to the case where current passes through the sixth switching element Q6 with the sixth switching element Q6 in the on state.

On the other hand, in the embodiments (boost mode) shown in FIGS. 10, 11(a)-(c), and 12(a)-(c), no secondary side dead time is inserted. A state in which rectification occurs via two diodes on the secondary side does not occur. Therefore, the conversion efficiency is higher than that of the comparative example (boost mode).

In addition, in the comparative example (step-up mode), if the current flowing through the primary winding n1 of the isolation transformer TR1 is small, there is a possibility that the current flowing to the secondary side becomes zero during the secondary side dead time Td''. be. In that case, turning on the fifth switching element Q5 or the sixth switching element Q6 after the secondary side dead time Td'' becomes zero current switching (ZCS).

On the other hand, in the embodiment (step-up mode), even if the current flowing through the primary winding n1 of the isolation transformer TR1 is small, there is no secondary side dead time Td''. At the timing of turn-on of element Q8, the current flowing to the secondary side does not become zero. Therefore, the probability that the turn-on of the seventh switching element Q7 or the eighth switching element Q8 will be zero current switching (ZCS) is low, and it will generally be zero voltage switching (ZVS). Generally, zero voltage switching (ZVS) has less loss than zero current switching (ZCS), so the embodiment (boost mode) can reduce switching loss.

In this embodiment (boost mode), when the control circuit 13 controls the sixth switching element Q6 to be in the on state in the fifth switching pattern P5, the control circuit 13 controls the fifth switching element Q5 to be in the on state in the seventh switching pattern P7. . When short-circuiting both ends of the secondary winding n2 of the isolation transformer TR1 within the second bridge circuit 12, the second bridge In the circuit 12, heat can be prevented from concentrating on the high side or the low side.

The control circuit 13 controls the eighth switching element Q8 to be in the on state in the sixth switching pattern P6, and controls the seventh switching element Q7 to be in the on state in the eighth switching pattern P8. When the secondary side performs a rectifying operation, the seventh switching element Q7 or the eighth switching element Q8 performs synchronous rectification, thereby making it possible to reduce losses on the secondary side.

The control circuit 13 fixes the phase difference between the first leg and the second leg. Specifically, the control circuit 13 controls the phase difference between the first switching element Q1 of the first leg and the fourth switching element Q4 of the second leg, and the second switching element Q2 of the first leg and the third switching element Q2 of the second leg. The phase difference of element Q3 is fixed. For example, the control circuit 13 sets the phase difference between the first leg and the second leg to 0°. In this case, while preventing a through current from flowing between the first switching element Q1 and the second switching element Q2 and between the third switching element Q3 and the fourth switching element Q4, from the first DC section to the second DC section. The maximum power transmission period can be ensured.

On the other hand, in the switching timing according to the comparative example (boost mode) shown in FIG. 13, the phase difference between the first leg and the second leg is not fixed at 0°, so The period for transmitting power to is shorter than that in the embodiment (boost mode). In particular, when the switching frequency is increased, the power transmission efficiency is significantly reduced.

The control circuit 13 controls the voltage or current of the power supplied from the first DC section to the second DC section based on the ratio of the on time and off time of the drive signal supplied to the fifth switching element Q5 or the sixth switching element Q6. do. In this way, in this embodiment (step-up mode), power is transmitted from the first DC section to the second DC section using the PWM method.

The control circuit 13 controls the fifth switching element Q5 so that the total time (not including dead time) of the on time of the fifth switching element Q5 and the on time of the seventh switching element Q7 becomes half the switching period fsw. Q5 and the seventh switching element Q7. Alternatively, the fifth switching element Q5 and the eighth switching element Q5 are connected so that the total time (not including dead time) of the on time of the fifth switching element Q5 and the on time of the eighth switching element Q8 is half the switching period fsw. 8 switching element Q8. Further, the control circuit 13 controls the sixth switching element Q6 so that the total time (not including dead time) of the on time of the sixth switching element Q6 and the on time of the eighth switching element Q8 becomes half the switching period fsw. Controls element Q6 and eighth switching element Q8. Alternatively, the sixth switching element Q6 and the seventh switching element Q7 may be connected so that the total time (not including dead time) of the on time of the sixth switching element Q6 and the on time of the seventh switching element Q7 is half the switching period fsw. 7 switching element Q7.

When transitioning from the sixth switching pattern P6 to the first primary side dead time Td', the control circuit 13 turns on the fifth switching element Q5 in synchronization with the turn-off of the first switching element Q1 and the fourth switching element Q4. let That is, the first switching element Q1 and the fourth switching element Q4 are turned off and the fifth switching element Q5 is turned on substantially simultaneously. By turning on the fifth switching element Q5 earlier than turning on the second switching element Q2 and the third switching element Q3, the fifth switching element Q5 becomes more likely to perform zero voltage switching (ZVS), and efficiency is improved.

When transitioning from the eighth switching pattern P8 to the second primary side dead time Td', the control circuit 13 turns on the sixth switching element Q6 in synchronization with the turn-off of the second switching element Q2 and the third switching element Q3. let That is, the second switching element Q2 and the third switching element Q3 are turned off and the sixth switching element Q6 is turned on substantially simultaneously. By turning on the sixth switching element Q6 earlier than turning on the first switching element Q1 and the fourth switching element Q4, the sixth switching element Q6 becomes more likely to perform zero voltage switching (ZVS), and efficiency is improved.

The control circuit 13 synchronizes the period of the fifth switching pattern P5 and the period of the seventh switching pattern P7. That is, the period of the fifth switching pattern P5 and the period of the seventh switching pattern P7 are controlled to be substantially the same time. Further, the control circuit 13 synchronizes the period of the sixth switching pattern P6 and the period of the eighth switching pattern P8. That is, the period of the sixth switching pattern P6 and the period of the eighth switching pattern P8 are controlled to be substantially the same time. As a result, the positive and negative operations become symmetrical, and it is possible to suppress the occurrence of direct current biased magnetism in the transformer.

In the boost mode control examples shown in FIGS. 10, 11(a)-(c), and 12(a)-(c), the control circuit 13 uses the fifth switching element Q5 and the sixth switching element Q6. A short circuit was made in the second bridge circuit 12, and diode rectification or synchronous rectification was performed using the seventh switching element Q7 and the eighth switching element Q8. In this regard, the roles of the fifth switching element Q5 and the sixth switching element Q6, and the roles of the seventh switching element Q7 and the eighth switching element Q8 may be exchanged. In that case, the switching patterns of the fifth switching element Q5 and the eighth switching element Q8 are exchanged, and the switching patterns of the sixth switching element Q6 and the seventh switching element Q7 are exchanged.

FIG. 15 is a diagram showing switching timing 2 of the first switching element Q1 to the eighth switching element Q8 according to the embodiment (boosting mode). In the switching timing 1 of the first switching element Q1 to the eighth switching element Q8 shown in FIG. 10, an example has been described in which power is boosted and supplied from the first DC section to the second DC section. In this respect, it is also possible to boost the voltage and supply power from the second DC section to the first DC section. In this case, as shown in FIG. 15, the control circuit 13 outputs a drive signal supplied to the first switching element Q1 to the fourth switching element Q4, and a drive signal supplied to the fifth switching element Q5 to the eighth switching element Q8. Just replace it.

As explained above, according to this embodiment (step-up mode), a state in which the second inductance L2 is charged from the second DC power supply E2 does not occur as in the comparative example (see FIG. 2(a)), so that reactive power is reduced. Can be suppressed. Further, in the sixth switching pattern P6 and the eighth switching pattern P8, conduction loss of the diode can be reduced by performing synchronous rectification with the eighth switching element Q8 or the seventh switching element Q7 on the secondary side. Furthermore, by not providing a dead time on the secondary side, it is possible to prevent the fifth switching element Q5 to the eighth switching element Q8 from becoming zero current switching (ZCS), and the fifth switching element Q5 to the eighth switching element Q8 to Switching loss of switching element Q8 can be reduced. These can improve the conversion efficiency during boost operation of the DAB converter.

Further, according to this embodiment (step-up mode), since a state in which the first DC power source E1 and the second DC power source E2 are electrically connected without a diode does not occur, the voltage of the first DC power source E1 is changed to the voltage of the second DC power source E2. Even if the voltage decreases significantly with respect to the voltage, the direction of the current will not be reversed, and the current will not flow backward from the second DC power supply E2 to the first DC power supply E1. This makes it possible to prevent hard switching from occurring.

Note that the fifth switching pattern P5 to the eighth switching pattern P8 may be read as the first switching pattern P1 to the fourth switching pattern P4 in the boost mode. Further, the third period and the fourth period may be read as the first period and the second period of the boost mode.

The present disclosure has been described above based on the embodiments. It will be understood by those skilled in the art that the embodiments are illustrative, and that various modifications are possible to the combinations of each component and each treatment process, and that such modifications are also within the scope of the present disclosure. .

In the above embodiment, an example is assumed in which IGBTs or MOSFETs are used for the first switching element Q1 to the eighth switching element Q8. In this respect, the first switching element Q1 to the eighth switching element Q8 are made of wide bandgap semiconductors using silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond (C), etc. Switching elements may also be used.

Note that the embodiment may be specified by the following items.

[Item 1]
It has a first leg in which a first switching element (Q1) and a second switching element (Q2) are connected in series, and a second leg in which a third switching element (Q3) and a fourth switching element (Q4) are connected in series. a first bridge circuit (11) in which the first leg and the second leg are connected in parallel to a first DC section (E1, Ca);
It has a third leg in which a fifth switching element (Q5) and a sixth switching element (Q6) are connected in series, and a fourth leg in which a seventh switching element (Q7) and an eighth switching element (Q8) are connected in series. a second bridge circuit (12) in which the third leg and the fourth leg are connected in parallel to a second DC section (E2, Cb);
an isolation transformer (TR1) connected between the first bridge circuit (11) and the second bridge circuit (12);
a first inductance (L1) connected or formed in series between the first bridge circuit (11) and the primary winding (n1) of the isolation transformer (TR1);
a second inductance (L2) connected or formed in series between the second bridge circuit (12) and the secondary winding (n2) of the isolation transformer (TR1);
A control circuit (13) that controls the first switching element (Q1) and the eighth switching element (Q8),
Diodes (D1-D8) are connected or formed in antiparallel to each of the first switching element (Q1) and the eighth switching element (Q8),
Capacitors (C1-C8) are connected or formed in parallel to each of the first switching element (Q1) and the eighth switching element (Q8),
When transmitting power by boosting the voltage from the first DC section (E1, Ca) to the second DC section (E2, Cb),
In the first bridge circuit (11), the first DC section (E1, Ca) and the primary winding (n1) of the isolation transformer (TR1) are electrically connected except during dead time,
The second bridge circuit (12) has a first period in which both ends of the secondary winding (n2) of the isolation transformer (TR1) are short-circuited within the second bridge circuit (12), and ) includes a second period in which the secondary winding (n2) of the second DC part (E2, Cb) is electrically connected,
The control circuit (13) includes:
During the period of boosting and transmitting power from the first DC section (E1, Ca) to the second DC section (E2, Cb), the fifth switching element (Q5) - the eighth switching element (Q8) controlling at least one in the on state;
A power conversion device (1) characterized by:
According to this, the period during which synchronous rectification is performed can be lengthened, and high efficiency can be achieved.
[Item 2]
The control circuit (13) includes:
When transmitting power by boosting the voltage from the first DC section (E1, Ca) to the second DC section (E2, Cb),
When the first switching element (Q1) and the fourth switching element (Q4) are in the on state, and the second switching element (Q2) and the third switching element (Q3) are in the off state, the isolation transformer (TR1) a first pattern in which both ends of the secondary winding (n2) are short-circuited within the second bridge circuit (12);
The second bridge circuit ( 12) is the second pattern in the rectified state,
When the second switching element (Q2) and the third switching element (Q3) are in the on state, and the first switching element (Q1) and the fourth switching element (Q4) are in the off state, the isolation transformer (TR1) a third pattern in which both ends of the secondary winding (n2) are short-circuited within the second bridge circuit (12);
When the second switching element (Q2) and the third switching element (Q3) are in the on state, and the first switching element (Q1) and the fourth switching element (Q4) are in the off state, the second bridge circuit ( 12) includes and controls a fourth pattern in a rectified state;
A period of operation in the first pattern and the third pattern corresponds to the first period,
A period of operation in the second pattern and the fourth pattern corresponds to the second period,
The power conversion device (1) according to item 1, characterized in that:
According to this, by not providing dead time when transitioning from the first pattern to the second pattern and from the third pattern to the fourth pattern, synchronous rectification can be performed immediately on the secondary side. , efficiency can be improved. Furthermore, even at low output, the secondary side can operate with zero voltage switching instead of zero current switching, making it possible to reduce loss.
[Item 3]
The control circuit (13) includes:
When the sixth switching element (Q6) is controlled to be in the on state in the first pattern, the fifth switching element (Q5) is controlled to be in the on state in the third pattern;
When the seventh switching element (Q7) is controlled to be in the on state in the first pattern, the eighth switching element (Q8) is controlled to be in the on state in the third pattern.
The power conversion device (1) according to item 2, characterized in that:
According to this, when short-circuiting the secondary side, the upper switching elements (Q5, Q7) and the lower switching elements (Q6, Q8) can be used alternately, and the upper or lower switching elements can be used alternately. Heat concentration can be prevented.
[Item 4]
The control circuit (13) includes:
controlling the eighth switching element (Q8) or the fifth switching element (Q5) to be in an on state in the second pattern;
controlling the seventh switching element (Q7) or the sixth switching element (Q6) to be in an on state in the fourth pattern;
The power conversion device (1) according to item 2 or 3, characterized in that:
According to this, conduction loss of the diode can be reduced by performing synchronous rectification.
[Item 5]
The control circuit (13) includes:
fixing a phase difference between the first leg and the second leg;
The ratio of the on time and off time of the drive signal supplied to the fifth switching element (Q5) or the seventh switching element (Q7) and the sixth switching element (Q6) or the eighth switching element (Q8). , controlling the voltage or current of power supplied from the first DC section (E1, Ca) to the second DC section (E2, Cb);
The power conversion device (1) according to item 3, characterized in that:
According to this, power control can be performed using the PWM method.
[Item 6]
The control circuit (13) includes:
setting a phase difference between the first leg and the second leg to 0°;
The power conversion device (1) according to item 5, characterized in that:
According to this, a sufficient power transmission period can be ensured.
[Item 7]
The control circuit (13) includes:
Turning on the fifth switching element (Q5) or the eighth switching element (Q8) in synchronization with turning off the first switching element (Q1) and the fourth switching element (Q4),
Turning on the sixth switching element (Q6) or the seventh switching element (Q7) in synchronization with turning off the second switching element (Q2) and the third switching element (Q3);
The power conversion device (1) according to any one of items 1 to 6, characterized in that:
According to this, by making the turn-on of the fifth switching element (Q5) or the eighth switching element (Q8) earlier than the turn-on of the second switching element (Q2) and the third switching element (Q3), the fifth switching element (Q5) or the eighth switching element (Q8) can easily perform zero voltage switching, and high efficiency can be achieved. In addition, by making the turn-on of the sixth switching element (Q6) or the seventh switching element (Q7) earlier than the turn-on of the first switching element (Q1) and the fourth switching element (Q4), the sixth switching element (Q6) Alternatively, the seventh switching element (Q7) can easily perform zero voltage switching, and high efficiency can be achieved.
[Item 8]
The control circuit (13) includes:
synchronizing the period of the first pattern and the period of the third pattern;
synchronizing the period of the second pattern and the period of the fourth pattern;
The power conversion device (1) according to any one of items 2 to 4, characterized in that:
According to this, the operation is symmetrical in positive and negative directions, and it is possible to suppress the occurrence of DC biased magnetism.
[Item 9]
The control circuit (13) includes:
When boosting the voltage and transmitting power from the second DC section (E2, Cb) to the first DC section (E1, Ca),
exchanging the drive signal supplied to the first switching element (Q1) - the fourth switching element (Q4) and the drive signal supplied to the fifth switching element (Q5) - the eighth switching element (Q8);
The power conversion device (1) according to any one of items 1 to 8, characterized in that:
According to this, bidirectional operation is possible.

E1 first DC power supply, E2 second DC power supply, 1 power converter, 11 first bridge circuit, 12 second bridge circuit, 13 control circuit, Q1-Q8 switching element, D1-D8 diode, C1-C8 capacitance, L1 1st inductance, L2 2nd inductance, TR1 isolation transformer, n1 primary winding, n2 secondary winding, Ca primary side capacitor, Cb secondary side capacitor.

Claims (9)

It has a first leg in which a first switching element and a second switching element are connected in series, and a second leg in which a third switching element and a fourth switching element are connected in series, and the first leg and the second leg are connected in series. a first bridge circuit connected in parallel to the first DC section;
It has a third leg in which a fifth switching element and a sixth switching element are connected in series, and a fourth leg in which a seventh switching element and an eighth switching element are connected in series, and the third leg and the fourth leg are connected in series. a second bridge circuit connected in parallel to the second DC section;
an isolation transformer connected between the first bridge circuit and the second bridge circuit;
a first inductance connected or formed in series between the first bridge circuit and the primary winding of the isolation transformer;
a second inductance connected or formed in series between the second bridge circuit and the secondary winding of the isolation transformer;
a control circuit that controls the first switching element and the eighth switching element;
A diode is connected or formed in antiparallel to each of the first switching element and the eighth switching element,
A capacitor is connected or formed in parallel to each of the first switching element and the eighth switching element,
When transmitting power by boosting the voltage from the first DC section to the second DC section,
The first bridge circuit is configured such that the first DC section and the primary winding of the isolation transformer are electrically connected except during a dead time;
The second bridge circuit has a first period in which both ends of the secondary winding of the isolation transformer are short-circuited within the second bridge circuit, and a second period in which the secondary winding of the isolation transformer and the second DC section are electrically connected. including a second period;
The control circuit includes:
controlling at least one of the fifth switching element and the eighth switching element to be in an on state during a period of boosting and transmitting power from the first DC section to the second DC section;
A power conversion device characterized by: The control circuit includes:
When transmitting power by boosting the voltage from the first DC section to the second DC section,
The first switching element and the fourth switching element are in the on state, and the second switching element and the third switching element are in the off state, and both ends of the secondary winding of the isolation transformer are in the second bridge circuit. The first pattern in a short circuit state,
a second pattern in which the first switching element and the fourth switching element are in an on state, the second switching element and the third switching element are in an off state, and the second bridge circuit is in a rectifying state;
The second switching element and the third switching element are in the on state, and the first switching element and the fourth switching element are in the off state, and both ends of the secondary winding of the isolation transformer are in the second bridge circuit. 3rd pattern in short circuit state,
The control includes a fourth pattern in which the second switching element and the third switching element are in an on state, the first switching element and the fourth switching element are in an off state, and the second bridge circuit is in a rectifying state. ,
A period of operation in the first pattern and the third pattern corresponds to the first period,
A period of operation in the second pattern and the fourth pattern corresponds to the second period,
The power conversion device according to claim 1, characterized in that: The control circuit includes:
When the sixth switching element is controlled to be in the on state in the first pattern, the fifth switching element is controlled to be in the on state in the third pattern,
when the seventh switching element is controlled to be in the on state in the first pattern, the eighth switching element is controlled to be in the on state in the third pattern;
The power conversion device according to claim 2, characterized in that: The control circuit includes:
controlling the eighth switching element or the fifth switching element to be in an on state in the second pattern;
controlling the seventh switching element or the sixth switching element to be in an on state in the fourth pattern;
The power conversion device according to claim 2 or 3, characterized in that: The control circuit includes:
fixing a phase difference between the first leg and the second leg;
The ratio between the on time and off time of the drive signal supplied to the fifth switching element or the seventh switching element and the sixth switching element or the eighth switching element is determined from the first DC section to the second DC section. control the voltage or current of power supplied to
The power conversion device according to claim 3, characterized in that: The control circuit includes:
setting a phase difference between the first leg and the second leg to 0°;
The power conversion device according to claim 5, characterized in that: The control circuit includes:
Turning on the fifth switching element or the eighth switching element in synchronization with turning off the first switching element and the fourth switching element,
Turning on the sixth switching element or the seventh switching element in synchronization with turning off the second switching element and the third switching element;
The power conversion device according to any one of claims 1 to 6. The control circuit includes:
synchronizing the period of the first pattern and the period of the third pattern;
synchronizing the period of the second pattern and the period of the fourth pattern;
The power conversion device according to any one of claims 2 to 4. The control circuit includes:
When transmitting power by boosting the voltage from the second DC section to the first DC section,
exchanging the drive signal supplied to the first switching element-the fourth switching element and the drive signal supplied to the fifth switching element-the eighth switching element;
The power conversion device according to any one of claims 1 to 8.

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