JP2022049533A - Power converter - Google Patents

Abstract

To realize a highly efficient isolated DC/DC converter with recovery loss reduced.SOLUTION: In a DAB (Dual Active Bridge) converter, when stepping down from a first DC unit to a second DC unit to transmit power, a first bridge circuit 11 includes a first period when a first DC unit and a primary winding n1 of an isolation transformer TR1 conduct and a second period when both ends of a primary winding n1 of the isolation transformer TR1 short-circuits in the first bridge circuit 11. A second bridge circuit 12 includes a rectification period. A control circuit 13 inserts a dead time to turn off a first switching element Q1-an eighth switching element Q8 during switching from the second period to the first period.SELECTED DRAWING: Figure 1

Description

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

Power conditioners used in photovoltaic power generation systems and V2H (Vehicle to Home) systems are required to have highly efficient power conversion. The V2H system can be charged and discharged between the storage battery mounted on the EV / PHEV and the power source / load in the home. For example, the electric power generated by a household photovoltaic power generation system can be charged into an EV / PHEV. Further, the storage battery mounted on the EV / PHEV can be used for peak shift of the load in the home and backup application. In addition to high efficiency, DC / DC converters used in V2H systems are required to have a wide voltage range and isolation. One of the DC / DC converters satisfying these requirements is a DAB (Dual Active Bridge) converter.

DAB converters generally have problems of increasing loss due to hard switching at low output and increasing loss due to the flow of reactive current unrelated to power transmission. As a countermeasure to this problem, a method has been proposed in which a PWM signal input to one of the legs 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 it is possible to solve these problems with this method, sufficient measures have not been taken for the recovery loss due to the resonance current generated during the dead time.

International Publication No. 16/125374

The present disclosure has been made in view of these circumstances, an object of which is to provide a highly efficient isolated DC / DC converter with reduced recovery loss.

In order to solve the above problems, in the power conversion device of the present disclosure, the first leg in which the first switching element and the second switching element are connected in series, and the third switching element and the fourth switching element are connected in series. A first bridge circuit having the second leg and the first leg and the second leg connected in parallel to the first DC unit, and a third switching element and a sixth switching element connected in series. A second bridge circuit having a leg, 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 connected in parallel to a second DC unit, and the above-mentioned 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, and the first. It 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 for controlling the first switching element-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 capacitance is connected or formed in parallel to each of the first switching element and the eighth switching element. When power is transmitted by stepping down from the first DC section to the second DC section, the first bridge circuit has a first one in which the first DC section and the primary winding of the isolated transformer are conductive. It includes a period and a second period in which both ends of the primary winding of the isolated transformer are short-circuited in the first bridge circuit. The second bridge circuit includes a rectification period. The control circuit inserts a dead time for turning off the first switching element-the eighth switching element while switching from the second period to the first period.

According to the present disclosure, it is possible to realize a highly efficient isolated DC / DC converter with reduced recovery loss.

It is a figure for demonstrating the configuration of the power conversion apparatus which concerns on embodiment. 2 (a)-(c) are diagrams for explaining the operation according to the comparative example of the power conversion device. It is a figure which shows the switching timing 1 of the 1st switching element-the 8th switching element which concerns on Example (step-down mode). 4 (a)-(d) are diagrams for explaining the operation according to the embodiment (step-down mode) of the power conversion device (No. 1). 5 (a)-(d) are diagrams for explaining the operation according to the embodiment (step-down mode) of the power conversion device (No. 2). 6 (a)-(b) are diagrams for explaining the mechanism of diode recovery loss generation. It is a figure which shows the switching timing 2 of the 1st switching element-8th switching element which concerns on Example (step-down mode). It is a figure for demonstrating the structure of the power conversion apparatus which concerns on modification 1. FIG. It is a figure which shows the switching timing of the 1st switching element-4th switching element which concerns on modification 1 (step-down mode). It is a figure which shows the switching timing 1 of the 1st switching element-the 8th switching element which concerns on an Example (boosting mode). 11 (a)-(c) are diagrams for explaining the operation according to the embodiment (boost mode) of the power conversion device (No. 1). 12 (a)-(c) are diagrams for explaining the operation according to the embodiment (boost mode) of the power conversion device (No. 2). It is a figure which shows the switching timing of the 1st switching element-the 8th switching element which concerns on a comparative example (boosting mode). 14 (a)-(b) are diagrams for explaining a state of the secondary side dead time Td ″ according to a comparative example (boost mode) of the power conversion device. It is a figure which shows the switching timing 2 of the 1st switching element-the 8th switching element which concerns on an Example (boosting mode).

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

The first DC power supply E1 corresponds to, 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 supply E2 corresponds to, for example, a DC bus connected to a commercial power system via an inverter. Other storage batteries, solar cells, fuel cells, and the like may be connected to the DC bus via another DC / DC converter.

The power conversion device 1 includes a primary side 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 side capacitor Cb, and a control circuit 13.

The primary side capacitor Ca is connected in parallel with the first DC power supply E1. The secondary side capacitor Cb is connected in parallel with the second DC power supply E2. For example, an electrolytic capacitor is used for the primary side capacitor Ca and the secondary side capacitor Cb. In the present specification, the first DC power supply E1 and the primary side capacitor Ca are collectively referred to as a first DC unit, and the second DC power supply E2 and the secondary side capacitor Cb are collectively referred to as a second DC unit.

In the first bridge circuit 11, the first leg in which the first switching element Q1 and the second switching element Q2 are connected in series and the second leg in which the third switching element Q3 and the fourth switching element Q4 are connected in series are connected in parallel. It is a full bridge circuit configured by. The first bridge circuit 11 is connected in parallel with the first DC unit, 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 DC voltage on the primary side supplied from the first DC unit 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 it to the first DC unit.

In the second bridge circuit 12, the third leg in which the fifth switching element Q5 and the sixth switching element Q6 are connected in series and the fourth leg in which the seventh switching element Q7 and the eighth switching element Q8 are connected in series are connected in parallel. It is a full bridge circuit configured by. The second bridge circuit 12 is connected in parallel with the second DC unit, and the midpoint of the third leg and the midpoint of the fourth leg are connected to both ends of the secondary winding n2 of the isolation transformer TR1, respectively. The second bridge circuit 12 can convert the DC voltage on the secondary side 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 it to the second DC unit.

A first diode D1 to an eighth diode D8 are connected or formed in antiparallel to each of the first switching element Q1 and the eighth switching element Q8, respectively. Further, the first capacitance C1 to the eighth capacitance C8 are connected or formed in parallel to the first switching element Q1 to the eighth switching element Q8, respectively.

For the first switching element Q1 to the eighth switching element Q8, for example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used. When an IGBT is used, an external diode element is connected between the emitter and collector of the first switching element Q1 to the eighth switching element Q8 as the first diode D1 to the eighth diode D8, respectively. Further, an external capacitor may be connected between the collector and the emitter of the first switching element Q1-eighth switching element Q8 as the first capacitance C1-8th capacitance C8, or the first switching element Q1-eighth switching element Q8. The parasitic capacitance formed between the collector and the emitter of the above is used as the first capacitance C1 to the eighth capacitance C8. When a MOSFET is used, the parasitic diode formed between the source and drain of the 1st switching element Q1-8th switching element Q8 is used as the 1st diode D1-8th diode D8, or an external diode element is used. Are connected as the first diode D1-the eighth diode D8, respectively. Further, the parasitic capacitance formed between the source and drain of the first switching element Q1-8th switching element Q8 is used as the first capacitance C1-eighth capacitance C8, or the first switching element Q1-eighth switching element. An external capacitor is connected between the source and drain of Q8 as the first capacitance C1 and the eighth capacitance C8, respectively.

The capacitance values of the first capacitance C1 and the eighth capacitance C8 connected or formed in parallel to the first switching element Q1- and the eighth switching element Q8 correspond to each other. That is, the capacitance values between the emitter and collector of the first switching element Q1 and the eighth switching element Q8 or between the source and drain are substantially the same. Similarly, all the resistance values of the first diode D1-8th diode D8 connected or formed in antiparallel to the first switching element Q1-8th switching element Q8 are also supported. As described above, all the configurations of the first leg to the fourth leg correspond to each other, which contributes to the reduction of the manufacturing cost and the circuit area. Moreover, it is possible to flexibly correspond to 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 is connected to the secondary winding n2. It is output to the second bridge circuit 12. Further, 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 to the primary winding n1. It is output to the first bridge circuit 11.

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 composed of 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.

The first inductance L1 may be composed of 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 composed of the leakage inductance of the 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 that detects the voltage across the first DC section, a first current sensor that detects the current flowing through the first DC section, and a second voltage sensor that detects the voltage across the second DC section. A second voltage sensor and a second current sensor for detecting the current flowing through the second DC unit are provided, and their respective detection 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 terminal of the first switching element Q1 to the eighth switching element Q8. do. The configuration of the control circuit 13 can be realized by the cooperation of hardware resources and software resources, or only by hardware resources. Analog devices, 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. In the control circuit 13, when power is transmitted from the first DC section to the second DC section (when discharging from the first DC power supply E1), the current value (discharge current value) detected by the first current sensor is the current command value. The first switching element Q1 to the eighth switching element Q8 are controlled so that the voltage value (discharge voltage value) detected by the first voltage sensor maintains the voltage command value. The current value on the secondary side detected by the second current sensor may be controlled, or the voltage value on the secondary side detected by the second voltage sensor may be controlled. Further, in the control circuit 13, when power is transmitted from the second DC unit to the first DC unit (when charging the first DC power supply E1), the current value (charging current value) detected by the first current sensor is a current command. The first switching element Q1 to the eighth switching element Q8 are controlled so as to maintain the value or so that the voltage value (charging voltage value) detected by the first voltage sensor maintains the voltage command value. The current value on the secondary side detected by the second current sensor may be controlled, or the voltage value on the secondary side detected by the second voltage sensor may be controlled.

As described above, the DAB converter has a symmetrical configuration on the primary side and the secondary side, and can transmit power in both directions. Hereinafter, the operation of the power conversion device 1 will be described.

(Comparative example)
2 (a)-(c) are diagrams for explaining the operation according to the comparative example of the power conversion device 1. In the first state shown in FIG. 2A, 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 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 supply E1 charges the first inductance L1 and the second DC power supply E2 charges the second inductance L2.

In the second state shown in FIG. 2B, 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 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 supply 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 supply 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, the first switching element Q1, and the fourth switching. 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 supply E1 charges the first inductance L1 and the second DC power supply E2 charges the second inductance L2.

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, the first switching element Q1, and the fourth switching. 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 supply 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 supply E2.

In the control according to the comparative example, the power of the second DC power supply E2 is charged to the second inductance L2 in the first state (see FIG. 2A) and the third state (not shown). In the subsequent second state (see FIG. 2B) and the fourth state (not shown), the electric power stored in the second inductance L2 is discharged to the second DC power supply E2. That is, a reactive current that is not related to power transmission is flowing on the secondary side. Wasteful loss is generated by the flow of this reactive current.

FIG. 2C shows the current flow when the voltage of the first DC power supply E1 drops significantly with respect to the voltage of the second DC power supply E2 in the second state shown in FIG. 2B. .. When the voltage of the first DC power supply E1 drops significantly with respect to the voltage of the second DC power supply E2, the direction of the current is reversed, and the current flows back from the second DC power supply E2 to the first DC power supply E1. In this state, when 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 in order to transition to the next state, the second switching element Q2 and the second switching element Q2 and 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 perform recovery operation, and the loss increases.

(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). 4 (a)-(d) are diagrams for explaining the operation according to the embodiment (step-down mode) of the power conversion device 1 (No. 1). 5 (a)-(d) are diagrams for explaining the operation according to the embodiment (step-down mode) of the power conversion device 1 (No. 2).

In the first state shown in FIG. 4A, the control circuit 13 turns on the first switching element Q1 and the fourth switching element Q4, and the remaining switching elements (second switching element Q2, third switching element Q3, first). The 5 switching element Q5, the 6th switching element Q6, the 7th switching element Q7, and the 8th switching element Q8) are controlled to be in 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 conducting. Further, since the fifth switching element Q5- and 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, via the fifth diode D5 and the eighth diode D8. Is rectifying. In the first state, the first DC power supply E1 transmits power to the second DC power supply E2 via the fifth diode D5 and the eighth diode D8 while charging the first inductance L1 and the second inductance L2. ..

In the second state shown in FIG. 4B, the control circuit 13 turns on the fourth switching element Q4 and the eighth switching element Q8, and the remaining switching elements (first switching element Q1, second switching element Q2, first). The 3 switching element Q3, the 5th switching element Q5, the 6th switching element Q6, and the 7th 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 in 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 supply E1. Will be done. Further, the eighth switching element Q8 on the secondary side is in the ON state, and rectification is performed via the fifth diode D5 and the eighth switching element Q8. The eighth switching element Q8 is diode rectified or synchronously rectified. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the eighth diode D8 in the off state of the eighth switching element Q8. Further, when the current passes through the fifth diode D5 in the off state of the fifth switching element Q5, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the second state, the electric power stored in the first inductance L1 and the electric power stored in the second inductance L2 are transmitted to the second DC power supply E2.

In the third state shown in FIG. 4 (c), the control circuit 13 controls all the first switching elements Q1 to the eighth switching element Q8 to the off state (dead time Td (see FIG. 3)). When the electric power remains in the first inductance L1 in the dead time Td, a current flows from the first inductance L1 to the first DC power supply E1 via the third diode D3 and the second diode D2. Similarly, when power remains in the second inductance L2, a 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. 4D shows the state after the residual power of the first inductance L1 and the second inductance L2 is exhausted in the dead time Td. When the residual power of the first inductance L1 and the second inductance L2 disappears, the current does not flow in the ideal state, but in reality, the resonance current flows in the opposite direction to the previous one. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitance C5 to the eighth capacitance C8, and a resonance current flows. Specifically, resonance current flows through both the high-side path of the second inductance L2, the seventh capacitance C7, and the fifth capacitance C5 and the low-side path of the second inductance L2, the eighth capacitance C8, and the sixth capacitance C6. Similarly, on the primary side, resonance occurs between the first inductance L1 and the first capacitance C1 to the fourth capacitance C4, and a resonance current flows. Specifically, resonance current flows through both the high-side path of the first inductance L1, the first capacitance C1, and the third capacitance C3 and the low-side path of the first inductance L1, the second capacitance C2, and the fourth capacitance C4.

In the fifth state shown in FIG. 5A, the control circuit 13 turns on the second switching element Q2 and the third switching element Q3, and the remaining switching elements (first switching element Q1, fourth switching element Q4, first). The 5 switching element Q5, the 6th switching element Q6, the 7th switching element Q7, and the 8th switching element Q8) are controlled to be in 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 conducting. Further, in the fifth state, since all the fifth switching elements Q5- and the eighth switching elements Q8 are 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 used. It is rectifying through. In the fifth state, the first DC power supply E1 transmits power to the second DC power supply E2 via the seventh diode D7 and the sixth diode D6 while charging the first inductance L1 and the second inductance L2. ..

In the sixth state shown in FIG. 5B, the control circuit 13 turns on the third switching element Q3 and the seventh switching element Q7, and the remaining switching elements (first switching element Q1, second switching element Q2, first). 4 The 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 (fourth switching pattern P4 (see FIG. 3)).

In the sixth state, both ends of the primary winding n1 of the isolation transformer TR1 are short-circuited in 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 supply E1. Will be done. Further, the seventh switching element Q7 on the secondary side is in the ON state, and rectification is performed via the sixth diode D6 and the seventh switching element Q7. The seventh switching element Q7 is diode rectified or synchronously rectified. Since the synchronous rectification has a smaller loss than the diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the 7th diode D7 in the off state of the 7th switching element Q7. Further, when the current passes through the sixth diode D6 in the off state of the sixth switching element Q6, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. In the sixth state, the electric power stored in the first inductance L1 and the electric power stored in the second inductance L2 are transmitted to the second DC power supply E2.

In the seventh state shown in FIG. 5 (c), the control circuit 13 controls all the first switching elements Q1 to the eighth switching element Q8 to the off state (dead time Td (see FIG. 3)). When the electric power remains in the first inductance L1 in the dead time Td, a current flows from the first inductance L1 to the first DC power supply E1 via the first diode D1 and the fourth diode D4. Similarly, when power remains in the second inductance L2, a 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. 5D shows the state after the residual power of the first inductance L1 and the second inductance L2 is exhausted in the dead time Td. When the residual power of the first inductance L1 and the second inductance L2 disappears, the current does not flow in the ideal state, but in reality, the resonance current flows in the opposite direction to the previous one. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitance C5 to the eighth capacitance C8, and a resonance current flows. Specifically, resonance current flows through both the high-side path of the second inductance L2, the fifth capacitance C5, and the seventh capacitance C7 and the low-side path of the second inductance L2, the sixth capacitance C6, and the eighth capacitance C8. Similarly, on the primary side, resonance occurs between the first inductance L1 and the first capacitance C1 to the fourth capacitance C4, and a resonance current flows. Specifically, a resonance current flows through both the high-side path of the first inductance L1, the third capacitance C3, and the first capacitance C1 and the low-side path of the first inductance L1, the fourth capacitance C4, and the second capacitance C2.

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

6 (a)-(b) are diagrams for explaining the mechanism of diode recovery loss generation. FIG. 6A shows another switching pattern of the dead time Td between the second switching pattern P2 and the third switching pattern P3.

In this state, when the residual power of the first inductance L1 and the second inductance L2 disappears, the current does not flow in the ideal state, but in reality, the resonance current flows in the opposite direction to the previous one. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitance C5 to the eighth capacitance C8, and a resonance current flows. Specifically, resonance current flows through both the high-side path of the second inductance L2, the seventh capacitance C7, and the fifth capacitance C5 and the low-side path of the second inductance L2, the eighth capacitance C8, and the sixth capacitance C6. On the primary side corresponding to the resonance current on the secondary side, a current flows in the low side path of the first inductance L1, the second switching element Q2, and the fourth diode D4.

When the transition from this state to the third switching pattern P3 shown in FIG. 5A, the third switching element Q3 on the primary side turns 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, and the loss increases.

FIG. 6B shows another switching pattern of the dead time Td between the fourth switching pattern P4 and the first switching pattern P1. In this state, when the residual power of the first inductance L1 and the second inductance L2 disappears, the current does not flow in the ideal state, but in reality, the resonance current flows in the opposite direction to the previous one. On the secondary side, resonance occurs between the second inductance L2 and the fifth capacitance C5 to the eighth capacitance C8, and a resonance current flows. Specifically, resonance current flows through both the high-side path of the second inductance L2, the fifth capacitance C5, and the seventh capacitance C7 and the low-side path of the second inductance L2, the sixth capacitance C6, and the eighth capacitance C8. On the primary side corresponding to the resonance current on the secondary side, a current flows in the high side path of the first inductance L1, the third diode D3, and the first switching element Q1.

When transitioning from this state to the first switching pattern P1 shown in FIG. 4A, the fourth switching element Q4 on the primary side turns 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, and the loss increases.

On the other hand, in this embodiment, the first switching element Q1-first 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. 8 A dead time Td in which all switching elements Q8 are turned off is inserted. As a result, the current flowing through the 4th diode D4 or the 3rd diode D3 can be suppressed, and the recovery loss of the 4th diode D4 or the 3rd diode D3 can be reduced.

In this embodiment (step-down mode), the control circuit 13 supplies power from the first DC unit to the second DC unit by adjusting the duty ratio of the drive signal supplied to the first switching element Q1 and the second switching element Q2. Controls the voltage or current of the power to be used. As the on-time of the drive signal supplied to the first switching element Q1 and the second switching element Q2 becomes longer (the larger the duty ratio), the amount of electric power transmitted from the first DC unit to the second DC unit 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 time of the switching cycle fsw (excluding the dead time Td).

As described above, in this embodiment (step-down mode), power is transmitted from the first DC unit to the second DC unit by the PWM method. On the other hand, in the case of power transmission by the phase shift method, it is not possible to provide a period in which all the first switching elements Q1 to the fourth switching elements Q4 on the primary side are in the off state, and the above-mentioned diode recovery loss occurs. Cannot be prevented.

When the control circuit 13 transitions 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 the turn-on of the first switching element Q1. That is, the first switching element Q1 and the fourth switching element Q4 are turned on substantially at the same time.

When the control circuit 13 transitions 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 the turn-off of the first switching element Q1. That is, the turn-off of the first switching element Q1 and the turn-on of the eighth switching element Q8 are performed substantially at the same time. As a result, the synchronous rectification period of the eighth switching element Q8 can be maximized, and the loss reduction effect of the synchronous rectification of the eighth switching element Q8 can be maximized.

When the control circuit 13 transitions 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 the turnoff of the fourth switching element Q4. That is, the fourth switching element Q4 and the eighth switching element Q8 are turned off substantially at the same time.

The control circuit 13 is 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 is half the time of the switching cycle fsw. And the eighth switching element Q8 are controlled. The on-time of the eighth switching element Q8 changes adaptively according to the on-time of the first switching element Q1.

When the control circuit 13 transitions 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 the turn-on of the second switching element Q2. That is, the second switching element Q2 and the third switching element Q3 are turned on substantially at the same time.

When the control circuit 13 transitions 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 the turn-off of the second switching element Q2. That is, the turn-off of the second switching element Q2 and the turn-on of the seventh switching element Q7 are performed substantially at the same time. As a result, the synchronous rectification period of the 7th switching element Q7 can be maximized, and the loss reduction effect of the synchronous rectification of the 7th switching element Q7 can be maximized.

When the control circuit 13 transitions 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 the turnoff of the third switching element Q3. That is, the third switching element Q3 and the seventh switching element Q7 are turned off substantially at the same time.

In the control circuit 13, the second switching element Q2 has a 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, which is half the time of the switching cycle fsw. And the 7th switching element Q7 are controlled. The on-time of the seventh switching element Q7 changes adaptively according to the on-time of the second switching element Q2.

In this way, by controlling the first switching element Q1-eighth switching element Q8 by the PWM method instead of the phase shift method, it is easy to set the period in which all the first switching elements Q1-eighth switching elements Q8 are off. Can be generated in.

The control circuit 13 synchronizes the period of the first switching pattern P1 with 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 substantially the same time. Further, the control circuit 13 synchronizes the period of the second switching pattern P2 with 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 substantially the same time. As a result, the operation becomes positive and negative symmetrical, and it is possible to suppress the occurrence of DC demagnetization in the transformer.

In the control example of the step-down mode shown in FIGS. 3, 4 (a)-(d) and 5 (a)-(d), the control circuit 13 constantly uses the fifth switching element Q5 and the sixth switching element Q6. Controlled to the off state. In this respect, the control circuit 13 may control the 7th switching element Q7 and the 8th switching element Q8 to be always off. 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 of stepping down from the first DC unit to the second DC unit to supply electric power has been described. In this respect, it is also possible to step down the voltage from the second DC unit to the first DC unit to supply electric power. In this case, as shown in FIG. 7, the control circuit 13 supplies a drive signal supplied to the first switching element Q1-fourth switching element Q4 and a drive signal supplied to the fifth switching element Q5-eighth switching element Q8. You can replace it.

As described above, according to the present embodiment (step-down mode), the state of charging the second inductance L2 from the second DC power supply E2 does not occur as in the comparative example (see FIG. 2A), so that the reactive power is generated. It can be suppressed. Further, since the resonance current can be suppressed from flowing to the antiparallel diode of the switching element during the dead time, the recovery loss of the diode can be reduced. Further, the 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 in the state 2 and the state 5. As a result, the conversion efficiency of the DAB converter during the step-down operation can be improved.

Further, according to the present embodiment (step-down mode), the voltage of the first DC power supply E1 is the voltage of the second DC power supply E2 because the state in which the first DC power supply E1 and the second DC power supply E2 are conductive without passing through the diode does not occur. Even if the voltage drops significantly with respect to the voltage of, the direction of the current does not reverse, and the current does not flow back from the second DC power supply E2 to the first DC power supply E1. This makes it possible to prevent the occurrence of hard switching.

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

FIG. 9 is a diagram showing the switching timing of the first switching element Q1 to the fourth switching element Q4 according to the modification 1 (step-down mode). In the first modification (step-down mode), in the first switching pattern P1, the control circuit 13 turns the first switching element Q1 and the fourth switching element Q4 on, and the second switching element Q2 and the third switching element Q3 off. To control. In the second switching pattern P2, the control circuit 13 controls the fourth switching element Q4 in the on state and the first switching element Q1, the second switching element Q2, and the third switching element Q3 in the off state. In the dead time Td between the second switching pattern P2 and the third switching pattern P3, the control circuit 13 controls all the first switching element Q1 to the fourth switching element Q4 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 in the on state, and the first switching element Q1 and the fourth switching element Q4 in the off state. In the fourth switching pattern P4, the control circuit 13 controls the third switching element Q3 in the on state and the first switching element Q1, the second switching element Q2, and the fourth switching element Q4 in the off state. In the dead time Td between the fourth switching pattern P4 and the first switching pattern P1, the control circuit 13 controls all the first switching elements Q1 to the fourth switching element Q4 in the off state.

According to the first modification (step-down mode), except that power cannot be transmitted from the secondary side to the primary side and synchronous rectification cannot be performed using the 8th switching element Q8 or the 7th switching element Q7 on the secondary side. It has the same effect as that of the above embodiment (step-down mode).

(Modification 2 (step-down mode))
In the second modification, on the premise of the configuration of the power conversion device 1 shown in FIG. 1, the control circuit 13 constantly controls the fifth switching element Q5 to the eighth switching element Q8 in an 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 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) are controlled to the off state. 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. In the dead time Td between the second switching pattern P2 and the third switching pattern P3, the control circuit 13 controls all the first switching element Q1 to the eighth switching element Q8 to 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 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. In the dead time Td between the fourth switching pattern P4 and the first switching pattern P1, the control circuit 13 controls all the first switching elements Q1 to the eighth switching elements Q8 in the off state.

According to the modified example 2 (step-down mode), the same effect as that of the modified example 1 (step-down mode) is obtained. In the second modification (step-down mode), power can be transmitted from the second DC unit to the first DC unit.

(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 (boost mode). 11 (a)-(c) are diagrams for explaining the operation according to the embodiment (boost mode) of the power conversion device 1 (No. 1). 12 (a)-(c) are diagrams for explaining the operation according to the embodiment (boost mode) of the power conversion device 1 (No. 2).

In the first state shown in FIG. 11A, the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4 and the sixth switching element Q6, 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 conducting. Further, both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited in 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 supply E1 charges the first inductance L1 and the second inductance L2 with electric power.

In the second state shown in FIG. 11B, the control circuit 13 turns on the first switching element Q1, the fourth switching element Q4 and the eighth switching element Q8, 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 conducting. Further, the eighth switching element Q8 on the secondary side is in the ON state, and rectification is performed via the fifth diode D5 and the eighth switching element Q8. The eighth switching element Q8 is diode rectified or synchronously rectified. In the rectified state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are conductive. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the eighth diode D8 in the off state of the eighth switching element Q8. Further, when the current passes through the fifth diode D5 in the off state of the fifth switching element Q5, 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 supply 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 supply E2.

In the third state shown in FIG. 11C, 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, and 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)).

In the first primary side dead time Td', when power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power supply E1 via the third diode D3 and the second diode D2. It flows. Further, the fifth switching element Q5 on the secondary side is in the ON state, and rectification is performed via the fifth switching element Q5 and the eighth diode D8. The fifth switching element Q5 is diode rectified or synchronously rectified. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the fifth diode D5 in the off state of the fifth switching element Q5. Further, when the electric power remains in the second inductance L2, the ZVS (zero voltage switching) operation is performed by turning on the fifth switching element Q5, and the switching loss can be reduced. Further, when the current passes through the eighth diode D8 in the off state of the eighth switching element Q8, 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, 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 conducting. Further, both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited in 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 electric power.

In the fifth state shown in FIG. 12B, the control circuit 13 turns on the second switching element Q2, the third switching element Q3, and the seventh switching element Q7, 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 (the 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 conducting. Further, the seventh switching element Q7 on the secondary side is in the ON state, and rectification is performed via the seventh switching element Q7 and the sixth diode D6. In the rectified state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are conductive. In the rectified state, the secondary winding n2 of the isolation transformer TR1 and the second DC power supply E2 are conductive. The seventh switching element Q7 is diode rectified or synchronously rectified. Since the synchronous rectification has a smaller loss than the diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the 7th diode D7 in the off state of the 7th switching element Q7. Further, when the current passes through the sixth diode D6 in the off state of the sixth switching element Q6, 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 supply 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 supply 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, and 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)).

In the second primary side dead time Td', when power remains in the first inductance L1, current flows from the first inductance L1 to the first DC power supply E1 via the first diode D1 and the fourth diode D4. It flows. Further, the sixth switching element Q6 on the secondary side is in the ON state, and rectification is performed via the seventh diode D7 and the sixth switching element Q6. The sixth switching element Q6 is diode rectified or synchronously rectified. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced as compared with the case where the current passes through the sixth diode D6 in the off state of the sixth switching element Q6. Further, when the electric power remains in the second inductance L2, the ZVS (zero voltage switching) operation is performed by turning on the sixth switching element Q6, and the switching loss can be reduced. Further, when the current passes through the seventh diode D7 in the off state of the seventh switching element Q7, 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 the third period, and the period of the seventh switching pattern P7 and the eighth switching pattern P8 is defined as the fourth period. As shown in FIGS. 10, 11 (a)-(c), and 12 (a)-(c), in the present embodiment (boost mode), the control circuit 13 changes from the fourth period to the third period. During the switching, the primary side dead time Td'that turns off all the first switching element Q1 to the fourth switching element Q4 is inserted. 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 conduct with each other except for the primary side dead time Td'.

On the other hand, the control circuit 13 inserts a secondary side dead time that turns off all the fifth switching element Q5 and the eighth switching element Q8 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- and the eighth switching element Q8 to be in the ON state during the period in which the voltage is boosted from the first DC unit to the second DC unit and power is transmitted. ..

(Comparative example (boost mode))
FIG. 13 is a diagram showing the switching timing of the first switching element Q1 to the eighth switching element Q8 according to the comparative example (boost mode). In the comparative example (boost mode), the control circuit 13 controls the 7th switching element Q7 and the 8th switching element Q8 to be always off on the secondary side, and alternately alternates the 5th switching element Q5 and the 6th switching element Q6. Control to the 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. The control circuit 13 is on the secondary side in order to prevent a through current from flowing through the fifth switching element Q5 and the sixth switching element Q6 when the fifth switching element Q5 and the sixth switching element Q6 are switched on / off. The dead time Td'' is inserted.

14 (a)-(b) are diagrams for explaining the state of the secondary side dead time Td ″ according to the comparative example (boost mode) of the power conversion device 1. FIG. 14A shows a 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 rectified via two diodes, the fifth diode D5 and the eighth diode D8. Since diode rectification has a larger loss than synchronous rectification, the loss on the secondary side increases as compared with the case where the current passes through the fifth switching element Q5 in the on state of the fifth switching element Q5.

FIG. 14B shows a 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 rectified via two diodes, the 7th diode D7 and the 6th diode D6. Since diode rectification has a larger loss than synchronous rectification, the loss on the secondary side increases as compared with the case where the current passes through the sixth switching element Q6 in the on state of the sixth switching element Q6.

On the other hand, in the embodiment (boosting mode) shown in FIGS. 10, 11 (a)-(c), and 12 (a)-(c), the secondary side dead time is not inserted. The state of rectifying via the two diodes does not occur on the secondary side. Therefore, the conversion efficiency is higher than that of the comparative example (boost mode).

Further, in the comparative example (boost mode), if the current flowing through the primary winding n1 of the isolation transformer TR1 is small, the current flowing through the secondary side may become zero during the period of the secondary side dead time Td''. be. In that case, the turn-on of 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 (boost mode), even when the current flowing through the primary winding n1 of the isolation transformer TR1 is small, the secondary side dead time Td'' does not exist, so that the seventh switching element Q7 and the eighth switching The current flowing to the secondary side does not become zero at the turn-on timing of the element Q8. Therefore, the probability that the turn-on of the 7th switching element Q7 or the 8th switching element Q8 will be zero current switching (ZCS) is low, and it will be approximately zero voltage switching (ZVS). In general, zero voltage switching (ZVS) has less loss than zero current switching (ZCS), so the embodiment (boosting mode) can reduce the switching loss.

In the present embodiment (boost mode), the control circuit 13 controls the fifth switching element Q5 to the on state by the seventh switching pattern P7 when the sixth switching element Q6 is controlled to the on state by the fifth switching pattern P5. .. When both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited in the second bridge circuit 12, the second bridge is formed by alternately using the fifth switching element Q5 on the high side and the sixth switching element Q6 on the low side. In the circuit 12, it is possible to prevent heat from concentrating on the high side or the low side.

The control circuit 13 controls the eighth switching element Q8 in the on state in the sixth switching pattern P6, and controls the seventh switching element Q7 in the on state in the eighth switching pattern P8. When the secondary side performs rectification operation, the loss on the secondary side can be reduced by synchronously rectifying the seventh switching element Q7 or the eighth switching element Q8.

The control circuit 13 fixes the phase difference between the first leg and the second leg. Specifically, the control circuit 13 includes the phase difference between the first switching element Q1 on the first leg and the fourth switching element Q4 on the second leg, and the second switching element Q2 on the first leg and the third switching on the second leg. The phase difference of the element Q3 is fixed. The control circuit 13 sets, for example, the phase difference between the first leg and the second leg to 0 °. In this case, from the first DC section to the second DC section 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. It is possible to secure the maximum power transmission period.

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 that the first DC section to the second DC section are not fixed. The power transmission period to is shorter than that of the embodiment (boost mode). In particular, when the switching frequency is increased to a high frequency, the power transmission efficiency is greatly reduced.

The control circuit 13 controls the voltage or current of the electric power supplied from the first DC unit to the second DC unit by the ratio of the on time and the off time of the drive signal supplied to the fifth switching element Q5 or the sixth switching element Q6. do. As described above, in this embodiment (boost mode), power is transmitted from the first DC unit to the second DC unit by the PWM method.

The control circuit 13 is a fifth switching element so that the total time (excluding the dead time) of the on time of the fifth switching element Q5 and the on time of the seventh switching element Q7 is half the time of the switching cycle fsw. It controls Q5 and the 7th switching element Q7. Alternatively, the fifth switching element Q5 and the fifth switching element Q5 and the fifth switching element Q5 so that the total time (excluding the 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 time of the switching cycle fsw. 8 Controls the switching element Q8. Further, in the control circuit 13, the sixth switching is performed so that the total time (excluding the dead time) of the on time of the sixth switching element Q6 and the on time of the eighth switching element Q8 is half the time of the switching cycle fsw. The element Q6 and the eighth switching element Q8 are controlled. Alternatively, the sixth switching element Q6 and the sixth switching element Q6 so that the total time (excluding the 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 time of the switching cycle fsw. 7 Controls the switching element Q7.

When the control circuit 13 transitions 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 me. That is, the turn-off of the first switching element Q1 and the fourth switching element Q4 and the turn-on of the fifth switching element Q5 are performed substantially at the same time. By accelerating the turn-on of the fifth switching element Q5 from the turn-on of the second switching element Q2 and the third switching element Q3, the fifth switching element Q5 tends to be in zero voltage switching (ZVS), and the efficiency is improved.

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 when transitioning from the eighth switching pattern P8 to the second primary side dead time Td'. Let me. That is, the turn-off of the second switching element Q2 and the third switching element Q3 and the turn-on of the sixth switching element Q6 are performed substantially at the same time. By accelerating the turn-on of the sixth switching element Q6 from the turn-on of the first switching element Q1 and the fourth switching element Q4, the sixth switching element Q6 is likely to become zero voltage switching (ZVS), and the efficiency is improved.

The control circuit 13 synchronizes the period of the fifth switching pattern P5 with 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 substantially the same time. Further, the control circuit 13 synchronizes the period of the sixth switching pattern P6 with 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 substantially the same time. As a result, the operation becomes positive and negative symmetrical, and it is possible to suppress the occurrence of DC demagnetization in the transformer.

In the boost mode control example 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. The circuit was short-circuited 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 seventh switching element Q7 and the eighth switching element Q8 may be exchanged. In that case, the switching patterns of the 5th switching element Q5 and the 8th switching element Q8 are exchanged, and the switching patterns of the 6th switching element Q6 and the 7th 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 (boost mode). In the switching timing 1 of the first switching element Q1 to the eighth switching element Q8 shown in FIG. 10, an example of boosting the voltage from the first DC unit to the second DC unit to supply electric power has been described. In this respect, it is also possible to boost power from the second DC section to the first DC section. In this case, as shown in FIG. 15, the control circuit 13 supplies a drive signal supplied to the first switching element Q1-fourth switching element Q4 and a drive signal supplied to the fifth switching element Q5-eighth switching element Q8. You can replace it.

As described above, according to the present embodiment (boost mode), the state of charging the second inductance L2 from the second DC power supply E2 does not occur as in the comparative example (see FIG. 2A), so that the reactive power is generated. It can be suppressed. Further, in the sixth switching pattern P6 and the eighth switching pattern P8, the 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. Further, by not providing a dead time on the secondary side, it is possible to suppress the fifth switching element Q5-the eighth switching element Q8 from becoming zero current switching (ZCS), and the fifth switching element Q5-eighth. The switching loss of the switching element Q8 can be reduced. As a result, the conversion efficiency of the DAB converter during the step-up operation can be improved.

Further, according to the present embodiment (boost mode), the voltage of the first DC power supply E1 is the voltage of the second DC power supply E2 because the state in which the first DC power supply E1 and the second DC power supply E2 are conductive without passing through the diode does not occur. Even if the voltage drops significantly with respect to the voltage of, the direction of the current does not reverse, and the current does not flow back from the second DC power supply E2 to the first DC power supply E1. This makes it possible to prevent the occurrence of hard switching.

The present disclosure has been described above based on the embodiments. It is understood by those skilled in the art that the embodiments are exemplary and that various modifications are possible for each of these components and combinations of processing processes, and that such modifications are also within the scope of the present disclosure. ..

In the above embodiment, an example in which an IGBT or MOSFET is used for the first switching element Q1 to the eighth switching element Q8 is assumed. In this regard, the first switching element Q1 to the eighth switching element Q8 are composed of a wide bandgap semiconductor using silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond (C), or the like. Switching elements may be used.

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. Then, the first bridge circuit (11) in which the first leg and the second leg are connected in parallel to the first DC unit (E1, Ca),
It has a third leg in which the fifth switching element (Q5) and the sixth switching element (Q6) are connected in series, and a fourth leg in which the seventh switching element (Q7) and the eighth switching element (Q8) are connected in series. Then, the second bridge circuit (12) in which the third leg and the fourth leg are connected in parallel to the second DC unit (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) for controlling the first switching element (Q1) -the eighth switching element (Q8) is provided.
A diode (D1-D8) is connected or formed in antiparallel to each of the first switching element (Q1) and the eighth switching element (Q8).
A capacitance (C1-C8) is connected or formed in parallel to each of the first switching element (Q1) and the eighth switching element (Q8).
When the power is transmitted by stepping down from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The first bridge circuit (11) includes a first period in which the first DC unit (E1, Ca) and the primary winding (n1) of the isolation transformer (TR1) are conducted, and the isolation transformer (TR1). A second period in which both ends of the primary winding (n1) are short-circuited in the first bridge circuit (11) is included.
The second bridge circuit (12) includes a rectification period.
The control circuit (13) is
During the switching from the second period to the first period, a dead time for turning off the first switching element (Q1) -the eighth switching element (Q8) is inserted.
A power conversion device (1).
According to this, the occurrence of the recovery loss of the diode can be suppressed by inserting the dead time in the all off state.
[Item 2]
The control circuit (13) is
When the power is transmitted by stepping down from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The first pattern, in which the first switching element (Q1) and the fourth switching element (Q4) are in the on state and the remaining switching elements are in the off state.
The fourth switching element (Q4) or the first switching element (Q1) and the fifth switching element (Q5) or the eighth switching element (Q8) are in the ON state, and the remaining switching elements are in the OFF state. 2 patterns,
A third pattern in which the second switching element (Q2) and the third switching element (Q3) are in the on state, and the remaining switching elements are in the off state.
The third switching element (Q3) or the second switching element (Q2) and the sixth switching element (Q6) or the seventh switching element (Q7) are in the ON state, and the remaining switching elements are in the OFF state. Control including 4 patterns,
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device (1) according to item 1, characterized in that.
According to this, the occurrence of the recovery loss of the diode can be suppressed by inserting the dead time in the all off state.
[Item 3]
The control circuit (13) is
The ratio of the on-time and off-time of the drive signal supplied to the first switching element (Q1) or the third switching element (Q3) and the second switching element (Q2) or the fourth switching element (Q4). Controls the voltage or current of the electric power supplied from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The power conversion device (1) according to item 1 or 2, characterized in that.
According to this, the dead time in the all off state can be inserted by controlling by the PWM method.
[Item 4]
The control circuit (13) is
The fourth switching element (Q4) is turned on in synchronization with the turn-on of the first switching element (Q1).
The fifth switching element (Q5) or the eighth switching element (Q8) is turned on in synchronization with the turn-off of the first switching element (Q1) or the fourth switching element (Q4).
The third switching element (Q3) is turned on in synchronization with the turn-on of the second switching element (Q2).
The sixth switching element (Q6) or the seventh switching element (Q7) is turned on in synchronization with the turn-off of the second switching element (Q2) or the third switching element (Q3).
The fifth switching element (Q5) or the eighth switching element (Q8) is turned off in synchronization with the turn-off of the fourth switching element (Q4) or the first switching element (Q1).
The sixth switching element (Q6) or the seventh switching element (Q7) is turned off in synchronization with the turn-off of the third switching element (Q3) or the second switching element (Q2).
The power conversion device (1) according to any one of items 1 to 3, wherein the power conversion device (1) is characterized in that.
According to this, by controlling by the PWM method, the dead time in the all off state can be easily generated.
[Item 5]
The control circuit (13) is
Synchronize the period of the first pattern with the period of the third pattern,
Synchronize the period of the second pattern with the period of the fourth pattern.
The power conversion device (1) according to item 2, characterized in that.
According to this, the operation becomes positive and negative symmetrical, and the generation of DC demagnetization can be suppressed.
[Item 6]
The control circuit (13) is
When the power is transmitted by stepping down from the second DC unit (E2, Cb) to the first DC unit (E1, Ca).
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) are exchanged.
The power conversion device (1) according to any one of items 1 to 5, wherein the power conversion device (1) is characterized in that.
According to this, bidirectional operation becomes possible.
[Item 7]
The control circuit (13) is
The fifth switching element (Q5) -the eighth switching element (Q8) is constantly controlled to be in an off state.
The power conversion device (1) according to item 1, characterized in that.
According to this, the switching operation on the secondary side can be simplified.
[Item 8]
The control circuit (13) is
When the power is transmitted by stepping down from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The first pattern, in which the first switching element (Q1) and the fourth switching element (Q4) are in the on state and the remaining switching elements are in the off state.
A second pattern in which the first switching element (Q1) or the fourth switching element (Q4) is on and the remaining switching elements are off.
A third pattern in which the second switching element (Q2) and the third switching element (Q3) are in the on state, and the remaining switching elements are in the off state.
A fourth pattern in which the second switching element (Q2) or the third switching element (Q3) is in the on state and the remaining switching elements are in the off state is included and controlled.
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device (1) according to item 7, characterized in that.
According to this, the switching operation on the secondary side can be simplified.
[Item 9]
The capacitance values between both ends of the first switching element (Q1) and the eighth switching element (Q8) all correspond to each other.
The power conversion device (1) according to any one of items 1 to 8, wherein the power conversion device (1) is characterized in that.
According to this, the first leg to the fourth leg can have the same configuration, and the manufacturing cost and the circuit area can be reduced. Moreover, it is possible to flexibly correspond to any switching pattern.
[Item 10]
The control circuit (13) is
When boosting the voltage from the first DC unit (E1, Ca) to the second DC unit (E2, Cb) to transmit power.
In the first bridge circuit (11), the primary winding (n1) of the isolation transformer (TR1) is electrically connected to the first DC unit (E1, Ca) except for the dead time.
The second bridge circuit (12) has a third period in which both ends of the secondary winding (n2) of the isolation transformer (TR1) are short-circuited in the second bridge circuit (12), and the isolation transformer (TR1). ) Includes a fourth period in which the secondary winding (n2) and the second DC section (E2, Cb) are conductive.
The control circuit (13) is
During the period of boosting the voltage from the first DC unit (E1, Ca) to the second DC unit (E2, Cb) and transmitting power, the fifth switching element (Q5) -the eighth switching element (Q8). Control at least one on,
The power conversion device (1) according to any one of items 1 to 9, wherein the power conversion device (1) is characterized in that.
According to this, by combining the step-up operation and the step-down operation, it is possible to correspond to a wide voltage range.
[Item 11]
The control circuit (13) is
When boosting the voltage from the first DC unit (E1, Ca) to the second DC unit (E2, Cb) to transmit power.
The isolation transformer (TR1) with the first switching element (Q1) and the fourth switching element (Q4) turned on, and the second switching element (Q2) and the third switching element (Q3) turned off. The fifth pattern in which both ends of the secondary winding (n2) are short-circuited in the second bridge circuit (12).
The second bridge circuit (Q1) with the first switching element (Q1) and the fourth switching element (Q4) turned on, and the second switching element (Q2) and the third switching element (Q3) turned off. 12) is the sixth pattern in the rectified state,
The isolation transformer (TR1) with the second switching element (Q2) and the third switching element (Q3) on, and the first switching element (Q1) and the fourth switching element (Q4) off. 7th pattern in which both ends of the secondary winding (n2) are short-circuited in the second bridge circuit (12).
The second bridge circuit (Q2) with the second switching element (Q2) and the third switching element (Q3) turned on, and the first switching element (Q1) and the fourth switching element (Q4) turned off. 12) is controlled including the eighth pattern of the rectified state.
The period in which the fifth pattern and the seventh pattern operate correspond to the third period.
The period in which the sixth pattern and the eighth pattern operate correspond to the fourth period.
The power conversion device (1) according to item 10, characterized in that.
According to this, by not providing a dead time when transitioning from the 5th pattern to the 6th pattern and when transitioning from the 7th pattern to the 8th pattern, synchronous rectification can be performed immediately on the secondary side. , Efficiency can be improved. Further, even at a low output, it is possible to operate with zero voltage switching instead of zero current switching on the secondary side, and it is possible to reduce the loss.
[Item 12]
The control circuit (13) is
When the sixth switching element (Q6) is controlled to be in the ON state in the fifth pattern, the fifth switching element (Q5) is controlled to be in the ON state in the seventh pattern.
When the 7th switching element (Q7) is controlled to be in the ON state in the 5th pattern, the 8th switching element (Q8) is controlled to be in the ON state in the 7th pattern.
The power conversion device (1) according to item 11, characterized in that.
According to this, when short-circuiting the secondary side, the upper switching element (Q5, Q7) and the lower switching element (Q6, Q8) can be used alternately, and the upper or lower switching element can be used. It is possible to prevent heat from concentrating.
[Item 13]
The control circuit (13) is
In the sixth pattern, the eighth switching element (Q8) or the fifth switching element (Q5) is controlled to be in the ON state.
In the eighth pattern, the seventh switching element (Q7) or the sixth switching element (Q6) is controlled to be in the ON state.
The power conversion device (1) according to item 11 or 12, characterized in that.
According to this, the conduction loss of the diode can be reduced by performing synchronous rectification.
[Item 14]
The control circuit (13) is
The phase difference between the first leg and the second leg is fixed.
The ratio of the on-time to the 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). Controls the voltage or current of the electric power supplied from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The power conversion device (1) according to item 13, characterized in that.
According to this, power control can be performed by the PWM method.
[Item 15]
The control circuit (13) is
The phase difference between the first leg and the second leg is set to 0 °.
The power conversion device (1) according to item 14, characterized in that.
According to this, a sufficient power transmission period can be secured.
[Item 16]
The control circuit (13) is
The fifth switching element (Q5) or the eighth switching element (Q8) is turned on in synchronization with the turn-off of the first switching element (Q1) and the fourth switching element (Q4).
The sixth switching element (Q6) or the seventh switching element (Q7) is turned on in synchronization with the turn-off of the second switching element (Q2) and the third switching element (Q3).
The power conversion device (1) according to any one of items 10 to 15, characterized in that.
According to this, the turn-on of the fifth switching element (Q5) or the eighth switching element (Q8) is accelerated from the turn-on of the second switching element (Q2) and the third switching element (Q3), so that the fifth switching element is turned on. (Q5) or the eighth switching element (Q8) is likely to be subjected to zero voltage switching, and high efficiency can be achieved. Further, by accelerating the turn-on of the 6th switching element (Q6) or the 7th switching element (Q7) from the turn-on of the 1st switching element (Q1) and the 4th switching element (Q4), the 6th switching element (Q6) Alternatively, the 7th switching element (Q7) is likely to be subjected to zero voltage switching, and high efficiency can be achieved.
[Item 17]
The control circuit (13) is
Synchronize the period of the 5th pattern with the period of the 7th pattern.
Synchronize the period of the sixth pattern with the period of the eighth pattern.
The power conversion device (1) according to any one of items 11 to 13, characterized in that.
According to this, the operation becomes positive and negative symmetrical, and the generation of DC demagnetization can be suppressed.
[Item 18]
The control circuit (13) is
When boosting the voltage from the second DC unit (E2, Cb) to the first DC unit (E1, Ca) to transmit power.
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) are exchanged.
The power conversion device (1) according to any one of items 10 to 17, characterized in that.
This makes it possible to realize a highly efficient DC / DC converter capable of buck-boost operation in both directions.
[Item 19]
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. Then, the first bridge circuit (11) in which the first leg and the second leg are connected in parallel to the first DC unit (E1, Ca),
It has a third leg in which a fifth diode (D5) and a sixth diode (D6) are connected in series, and a fourth leg in which a seventh diode (D7) and an eighth diode (D8) are connected in series. A second bridge circuit (12) in which the third leg and the fourth leg are connected in parallel to the second DC unit (E2, Cb), and
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) for controlling the first switching element (Q1) -the fourth switching element (Q4) is provided.
A first diode (D1) -4th diode (D4) is connected or formed in antiparallel to each of the first switching element (Q1) and the fourth switching element (Q4).
Capacities (C1-C4) are connected or formed in parallel to each of the first switching element (Q1) and the fourth switching element (Q4).
The fifth diode (D5) -the eighth diode (D8) is connected in the opposite direction to the second DC unit (E2, Cb).
When the power is transmitted by stepping down from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The first bridge circuit (11) includes a first period in which the first DC unit (E1, Ca) and the primary winding (n1) of the isolation transformer (TR1) are conducted, and the isolation transformer (TR1). A second period in which both ends of the primary winding (n1) are short-circuited in the first bridge circuit (11) is included.
The control circuit (13) is
During the switching from the second period to the first period, a dead time for turning off the first switching element (Q1) -the fourth switching element (Q4) is inserted.
A power conversion device (1).
According to this, during the step-down operation of the unidirectional isolated DC / DC converter, the dead time of the first switching element (Q1) -4th switching element (Q4) in the fully off state is inserted, so that the diode It is possible to suppress the occurrence of recovery loss.
[Item 20]
The control circuit (13) is
When the power is transmitted by stepping down from the first DC unit (E1, Ca) to the second DC unit (E2, Cb).
The first pattern, in which the first switching element (Q1) and the fourth switching element (Q4) are on, and the second switching element (Q2) and the third switching element (Q3) are off.
With the fourth switching element (Q4) or the first switching element (Q1) on, the first switching element (Q1) or the fourth switching element (Q4) and the second switching element (Q2) , The second pattern in which the third switching element (Q3) is off,
A third pattern in which the second switching element (Q2) and the third switching element (Q3) are on, and the first switching element (Q1) and the fourth switching element (Q4) are off.
With the third switching element (Q3) or the second switching element (Q2) on, the first switching element (Q1) and the second switching element (Q2) or the third switching element (Q3) , The fourth pattern in which the fourth switching element (Q4) is off is included and controlled.
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device (1) according to item 19, characterized in that.
According to this, the occurrence of the recovery loss of the diode can be suppressed by inserting the dead time in the completely off state of the first switching element (Q1) -4th switching element (Q4).
[Item 21]
The capacitance values between both ends of the first switching element (Q1) and the fourth switching element (Q4) all correspond to each other.
The power conversion device (1) according to item 19 or 20, characterized in that.
According to this, the first leg and the second leg can have the same configuration, and the manufacturing cost and the circuit area can be reduced.

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

Claims (21)

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. The 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. The 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,
The first switching element-a control circuit for controlling the eighth switching element is provided.
A diode is connected or formed in antiparallel to each of the first switching element and the eighth switching element.
Capacities are connected or formed in parallel to each of the first switching element and the eighth switching element.
When the power is transmitted by stepping down from the first DC section to the second DC section.
In the first bridge circuit, a first period in which the first DC portion and the primary winding of the isolation transformer are conducted, and a second period in which both ends of the primary winding of the isolation transformer are short-circuited in the first bridge circuit. Including the period of
The second bridge circuit includes a rectification period.
The control circuit is
While switching from the second period to the first period, a dead time for turning off the first switching element-the eighth switching element is inserted.
A power conversion device characterized by that. The control circuit is
When the power is transmitted by stepping down from the first DC section to the second DC section.
The first pattern, in which the first switching element and the fourth switching element are in the on state and the remaining switching elements are in the off state.
A second pattern in which the fourth switching element or the first switching element, the fifth switching element or the eighth switching element is on, and the remaining switching elements are off.
A third pattern in which the second switching element and the third switching element are on, and the remaining switching elements are off.
The third pattern or the second switching element and the fourth pattern in which the sixth switching element or the seventh switching element is on and the remaining switching elements are off are included and controlled.
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device according to claim 1. The control circuit is
The ratio of the on time to the off time of the drive signal supplied to the first switching element or the third switching element and the second switching element or the fourth switching element, from the first DC unit to the second DC unit. Controls the voltage or current of the power supplied to
The power conversion device according to claim 1 or 2. The control circuit is
In synchronization with the turn-on of the first switching element, the fourth switching element is turned on.
The fifth switching element or the eighth switching element is turned on in synchronization with the turn-off of the first switching element or the fourth switching element.
In synchronization with the turn-on of the second switching element, the third switching element is turned on.
In synchronization with the turn-off of the second switching element or the third switching element, the sixth switching element or the seventh switching element is turned on.
The fifth switching element or the eighth switching element is turned off in synchronization with the turn-off of the fourth switching element or the first switching element.
The sixth switching element or the seventh switching element is turned off in synchronization with the turn-off of the third switching element or the second switching element.
The power conversion device according to any one of claims 1 to 3, wherein the power conversion device is characterized by the above. The control circuit is
Synchronize the period of the first pattern with the period of the third pattern,
Synchronize the period of the second pattern with the period of the fourth pattern.
The power conversion device according to claim 2. The control circuit is
When the power is transmitted by stepping down from the second DC section to the first DC section.
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 are exchanged.
The power conversion device according to any one of claims 1 to 5, wherein the power conversion device is characterized by the above. The control circuit is
The fifth switching element-controlling the eighth switching element to be in an off state at all times.
The power conversion device according to claim 1. The control circuit is
When the power is transmitted by stepping down from the first DC section to the second DC section.
The first pattern, in which the first switching element and the fourth switching element are in the on state and the remaining switching elements are in the off state.
A second pattern in which the first switching element or the fourth switching element is on and the remaining switching elements are off.
A third pattern in which the second switching element and the third switching element are on, and the remaining switching elements are off.
A fourth pattern in which the second switching element or the third switching element is in the on state and the remaining switching elements are in the off state is included and controlled.
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device according to claim 7. The capacitance values between both ends of the first switching element and the eighth switching element all correspond to each other.
The power conversion device according to any one of claims 1 to 8, wherein the power conversion device is characterized by the above. The control circuit is
When boosting the voltage from the first DC section to the second DC section to transmit power
In the first bridge circuit, except for the dead time, the first DC portion and the primary winding of the isolation transformer are conductive.
In the second bridge circuit, both ends of the secondary winding of the isolation transformer are short-circuited in the second bridge circuit, and the secondary winding of the isolation transformer and the second DC portion are conductive. Including the fourth period
The control circuit is
During the period in which the voltage is boosted from the first DC unit to the second DC unit and power is transmitted, at least one of the fifth switching element and the eighth switching element is controlled to be in the ON state.
The power conversion device according to any one of claims 1 to 9, wherein the power conversion device is characterized by the above. The control circuit is
When boosting the voltage from the first DC section to the second DC section to transmit power
When the first switching element and the fourth switching element are on, and the second switching element and the third switching element are off, both ends of the secondary winding of the isolation transformer are in the second bridge circuit. Fifth pattern in short circuit state,
A sixth pattern in which the first switching element and the fourth switching element are on, the second switching element and the third switching element are off, and the second bridge circuit is in a rectified state.
When the second switching element and the third switching element are on, and the first switching element and the fourth switching element are off, both ends of the secondary winding of the isolation transformer are in the second bridge circuit. 7th pattern in short circuit state,
The second bridge circuit controls including the eighth pattern in which the second switching element and the third switching element are on, the first switching element and the fourth switching element are off, and the second bridge circuit is in a rectified state. ,
The period in which the fifth pattern and the seventh pattern operate correspond to the third period.
The period in which the sixth pattern and the eighth pattern operate correspond to the fourth period.
The power conversion device according to claim 10. The control circuit is
When the sixth switching element is controlled to be in the ON state in the fifth pattern, the fifth switching element is controlled to be in the ON state in the seventh pattern.
When the 7th switching element is controlled to be in the ON state by the 5th pattern, the 8th switching element is controlled to be in the ON state by the 7th pattern.
The power conversion device according to claim 11. The control circuit is
In the sixth pattern, the eighth switching element or the fifth switching element is controlled to be in the ON state.
In the eighth pattern, the seventh switching element or the sixth switching element is controlled to be in the ON state.
The power conversion device according to claim 11 or 12. The control circuit is
The phase difference between the first leg and the second leg is fixed.
The ratio of the on-time to the 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, from the first DC unit to the second DC unit. Controls the voltage or current of the power supplied to
The power conversion device according to claim 13. The control circuit is
The phase difference between the first leg and the second leg is set to 0 °.
The power conversion device according to claim 14. The control circuit is
The fifth switching element or the eighth switching element is turned on in synchronization with the turn-off of the first switching element and the fourth switching element.
The sixth switching element or the seventh switching element is turned on in synchronization with the turn-off of the second switching element and the third switching element.
The power conversion device according to any one of claims 10 to 15, characterized in that. The control circuit is
Synchronize the period of the 5th pattern with the period of the 7th pattern.
Synchronize the period of the sixth pattern with the period of the eighth pattern.
The power conversion device according to any one of claims 11 to 13. The control circuit is
When boosting the voltage from the second DC section to the first DC section to transmit power
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 are exchanged.
The power conversion device according to any one of claims 10 to 17, wherein the power conversion device is characterized. 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. The first bridge circuit connected in parallel to the first DC section,
It has a third leg in which a fifth diode and a sixth diode are connected in series, and a fourth leg in which a seventh diode and an eighth diode are connected in series. The second bridge circuit connected in parallel to
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,
The first switching element-a control circuit for controlling the fourth switching element is provided.
A first diode-a fourth diode is connected or formed in antiparallel to each of the first switching element and the fourth switching element.
Capacities are connected or formed in parallel to each of the first switching element and the fourth switching element.
The fifth diode-the eighth diode is connected in the opposite direction to the second DC portion.
When the power is transmitted by stepping down from the first DC section to the second DC section.
In the first bridge circuit, a first period in which the first DC portion and the primary winding of the isolation transformer are conducted, and a second period in which both ends of the primary winding of the isolation transformer are short-circuited in the first bridge circuit. Including the period of
The control circuit is
While switching from the second period to the first period, a dead time for turning off the first switching element-the fourth switching element is inserted.
A power conversion device characterized by that. The control circuit is
When the power is transmitted by stepping down from the first DC section to the second DC section.
A first pattern in which the first switching element and the fourth switching element are on, and the second switching element and the third switching element are off.
A second pattern in which the fourth switching element or the first switching element is on, the first switching element or the fourth switching element, the second switching element, and the third switching element are off.
A third pattern in which the second switching element and the third switching element are on, and the first switching element and the fourth switching element are off.
A fourth pattern in which the third switching element or the second switching element is on, the first switching element, the second switching element or the third switching element, and the fourth switching element are off. Including and controlling,
The period in which the first pattern and the third pattern operate correspond to the first period.
The period in which the second pattern and the fourth pattern operate correspond to the second period.
The power conversion device according to claim 19. The capacitance values between both ends of the first switching element and the fourth switching element all correspond to each other.
The power conversion device according to claim 19 or 20.

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