Power Conversion Device

Abstract

To stabilize the performance of feedback control regardless of the difference between input and output voltage.SOLUTION: A DAB (Dual Active Bridge) converter includes a first bridge circuit 11, a second bridge circuit 12, and an isolation transformer TR1. A control circuit 13 controls the power and voltage or current of a second DC section by controlling a first switching element Q1 to an eighth switching element Q8. The control circuit 13 dynamically changes the gain of the feedback control in accordance with the difference between the voltage of a first DC section and the voltage of the second DC section.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device that converts DC power into DC power of another voltage. [Background technology]

[0002] Power conditioners used in solar power generation systems and V2H (Vehicle to Home) systems require highly efficient power conversion. V2H systems can charge and discharge power between storage batteries installed in electric vehicles (e.g., EVs and PHEVs) and commercial power grids or household loads. For example, power generated by a home solar power generation system can be charged to the storage battery of an electric vehicle. The storage battery installed in an electric vehicle can also be used for peak shifting or backup purposes for household loads. DC / DC converters used in V2H systems must be highly efficient, isolated, and have a wide voltage range. This is because the voltage of storage batteries installed in electric vehicles varies greatly depending on the vehicle model. One DC / DC converter that meets these requirements is the DAB (Dual Active Bridge) converter.

[0003] In a typical DAB converter, losses increase due to hard switching at low output and the flow of reactive current unrelated to power transmission. In response to these issues, for example, a DAB converter has been proposed that employs a drive method that combines a chopper method and a phase shift method (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO 16 / 125374 Summary of the Invention [Problem to be solved by the invention]

[0005] In a DAB converter, the fluctuation characteristics of the output current relative to the control input (hereinafter referred to as the control output characteristics in this specification) change depending on the difference between the input voltage and the output voltage. In particular, in a DAB converter that uses a chopper method, the control output characteristics change significantly depending on the difference between the input voltage and the output voltage. Large changes in the control output characteristics mean that the performance of the feedback control is unstable, and there are cases where the desired response cannot be obtained.

[0006] The present disclosure has been made in consideration of these circumstances, and its purpose is to provide a power conversion device in which the performance of feedback control is stable regardless of the difference between the input voltage and the output voltage. [Means for solving the problem]

[0007] To solve the above problems, a power conversion device according to an embodiment of the present disclosure includes: a first bridge circuit having 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, the first leg and the second leg being connected in parallel to a first DC section; a second bridge circuit having 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, the third leg and the fourth leg being connected in parallel to a second DC section; an isolation transformer connected between the first bridge circuit and the second bridge circuit; and a control circuit that controls the first switching element to the eighth switching element to control the power, voltage, or current of the second DC section. The control circuit dynamically changes a gain of feedback control according to a voltage difference between the first DC section and the second DC section. [Effects of the Invention]

[0008] According to the present disclosure, the performance of feedback control can be stabilized regardless of the difference between the input voltage and the output voltage. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram for explaining a configuration of a power conversion device according to an embodiment; [Figure 2] 2(a) to 2(c) are diagrams for explaining the operating state of the power conversion device according to Comparative Example 1. FIG. [Figure 3] 3(a) to 3(c) are diagrams for explaining the operating state of the power conversion device according to Comparative Example 2. In FIG. [Figure 4] 4(a) to 4(d) are diagrams illustrating the switching patterns of the first switching element to the eighth switching element according to the second comparative example of the power conversion device. [Figure 5] 5(a) to 5(d) are diagrams for explaining the operating states of the power conversion device according to the embodiment. [Figure 6] 6(a) to 6(c) are diagrams for explaining switching patterns of the first switching element to the eighth switching element according to the embodiment of the power conversion device. [Figure 7] 3 is a diagram for explaining switching among a first operation mode, a second operation mode, and a third operation mode according to an embodiment. FIG. [Figure 8] 10A and 10B are diagrams illustrating specific examples of control output characteristics during a step-down operation of the power conversion device according to the embodiment. [Figure 9] FIG. 1 is a diagram for explaining the basic concept of a loop transfer function. [Figure 10] FIG. 10 is a diagram illustrating an example of a switching table for switching between proportional gain and integral gain of the controller. [Figure 11] FIG. 2 is a diagram illustrating an example of the configuration of a feedback control unit included in a control circuit. [Figure 12] 10 is a flowchart showing the flow of feedback control by the control circuit. [Figure 13] 13(a) to 13(c) are diagrams illustrating switching patterns during reverse transmission of the first switching element to the eighth switching element according to the embodiment of the power conversion device. [Figure 14] 1A and 1B are diagrams illustrating application examples of a power conversion device according to an embodiment. [Figure 15]15(a) to 15(c) are diagrams illustrating switching patterns of the first switching element to the eighth switching element according to a modification of the power conversion device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Fig. 1 is a diagram illustrating the configuration of a power conversion device 1 according to an embodiment. The power conversion device 1 is an isolated bidirectional DC / DC converter (DAB converter) that converts DC power supplied from a first DC power supply E1 and transmits it to a second DC power supply E2. The power conversion device 1 also converts 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 either step down or step up the power for transmission.

[0011] The first DC power source E1 may be, for example, a storage battery or electric double layer capacitor mounted on the electric vehicle, or a stationary storage battery or electric double layer capacitor. The second DC power source E2 may be, for example, a DC bus connected to a commercial power system via an inverter. Other storage batteries, solar cells, fuel cells, etc. may be connected to the DC bus via other DC / DC converters.

[0012] The power conversion device 1 includes a primary side capacitor Ca, a first bridge circuit 11, a first inductance L1, an insulating transformer TR1, a second inductance L2, a second bridge circuit 12, a secondary side capacitor Cb, and a control circuit 13.

[0013] A primary-side capacitor Ca is connected in parallel to the first DC power supply E1. A secondary-side capacitor Cb is connected in parallel to the second DC power supply E2. For example, electrolytic capacitors are used for the primary-side capacitor Ca and the secondary-side capacitor Cb. In this specification, the first DC power supply E1 and the primary-side capacitor Ca are collectively referred to as the first DC unit, and the second DC power supply E2 and the secondary-side capacitor Cb are collectively referred to as the second DC unit.

[0014] The first bridge circuit 11 is a full-bridge circuit configured by connecting 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, in parallel. The first bridge circuit 11 is connected in parallel with the first DC section, and the midpoint of the first leg and the midpoint of the second leg are connected to both ends of the primary winding n1 of the isolation transformer TR1, respectively. The first bridge circuit 11 can convert the primary-side DC voltage supplied from the first DC section into an AC voltage and output it to the primary winding n1 of the isolation transformer TR1. The first bridge circuit 11 can also 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 section.

[0015] The second bridge circuit 12 is a full-bridge circuit configured by connecting a third leg in series, in which a fifth switching element Q5 and a sixth switching element Q6 are connected, and a fourth leg in series, in which a seventh switching element Q7 and an eighth switching element Q8 are connected, in parallel. The second bridge circuit 12 is connected in parallel with the second DC section, 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 secondary-side DC voltage supplied from the second DC section into an AC voltage and output it to the secondary winding n2 of the isolation transformer TR1. The second bridge circuit 12 can also 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 section.

[0016] A first diode D1 to an eighth diode D8 are connected in anti-parallel to or formed with the first switching element Q1 to the eighth switching element Q8, respectively. In addition, a first capacitor C1 to an eighth capacitor C8 are connected in parallel to or formed with the first switching element Q1 to the eighth switching element Q8, respectively.

[0017] The first switching element Q1 through the eighth switching element Q8 can be, for example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). When an IGBT is used for the first switching element Q1 through the eighth switching element Q8, external diodes are connected between the collectors and emitters of the first switching element Q1 through the eighth switching element Q8 as the first diode D1 through the eighth diode D8, respectively. Also, external capacitors are connected between the collectors and emitters of the first switching element Q1 through the eighth switching element Q8 as the first capacitance C1 through the eighth capacitance C8, respectively, or the parasitic capacitances formed between the collectors and emitters of the first switching element Q1 through the eighth switching element Q8 are used as the first capacitance C1 through the eighth capacitance C8.

[0018] When MOSFETs are used for the first switching element Q1 through the eighth switching element Q8, the parasitic diodes formed between the drain and source of the first switching element Q1 through the eighth switching element Q8 are used as the first diode D1 through the eighth diode D8, respectively, or external diodes are connected as the first diode D1 through the eighth diode D8, respectively. Also, the parasitic capacitances formed between the drain and source of the first switching element Q1 through the eighth switching element Q8 are used as the first capacitance C1 through the eighth capacitance C8, or external capacitors are connected between the drain and source of the first switching element Q1 through the eighth switching element Q8, respectively.

[0019] The capacitance values ​​of the first capacitor C1 through the eighth capacitor C8, which are connected in parallel to or formed with the first switching element Q1 through the eighth switching element Q8, respectively, all correspond to each other. That is, the collector-emitter or drain-source capacitance values ​​of the first switching element Q1 through the eighth switching element Q8 are substantially equal. Similarly, the resistance values ​​of the first diode D1 through the eighth diode D8, which are connected in antiparallel to or formed with the first switching element Q1 through the eighth switching element Q8, respectively, also correspond to each other. In this way, the configurations of the first leg through the fourth leg are all compatible, contributing to reduced manufacturing costs and circuit area. Furthermore, any switching pattern can be flexibly accommodated.

[0020] The isolation transformer TR1 is connected between the AC terminals of the first bridge circuit 11 and the AC terminals of the second bridge circuit 12. The isolation transformer TR1 converts the output voltage of the first bridge circuit 11, which is connected to the primary winding n1, in accordance with the turns ratio between the primary winding n1 and the secondary winding n2, and outputs the converted voltage to the second bridge circuit 12, which is connected to the secondary winding n2. The isolation transformer TR1 also converts the output voltage of the second bridge circuit 12, which is connected to the secondary winding n2, in accordance with the turns ratio between the secondary winding n2 and the primary winding n1, and outputs the converted voltage to the first bridge circuit 11, which is connected to the primary winding n1.

[0021] The first inductance L1 is connected or formed in series between the AC terminals 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 terminals 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 formed by a reactor element connected between the midpoint of the first leg of the first bridge circuit 11 and the primary winding n1 of the isolation transformer TR1. The second inductance L2 is formed by 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.

[0022] The first inductance L1 may be formed by the leakage inductance of the primary winding n1 formed between the midpoint of the first leg of the first bridge circuit 11 and the primary winding n1 of the isolation transformer TR1. The second inductance L2 may be formed by 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. Either the first inductance L1 or the second inductance L2 may be omitted.

[0023] A first voltage sensor 21 on the primary side detects the voltage across the first DC section and outputs the detected voltage value to the control circuit 13. A second voltage sensor 22 on the secondary side detects the voltage across the second DC section and outputs the detected voltage value to the control circuit 13. A current sensor 23 on the secondary side detects the current flowing through the second DC section and outputs the detected current value to the control circuit 13. A CT sensor, for example, can be used as the current sensor 23. Although omitted in FIG. 1, a current sensor is also provided on the primary side.

[0024] 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 or base terminal of each of the first switching element Q1 to the eighth switching element Q8. The configuration of the control circuit 13 can be realized by a combination of hardware resources and software resources, or by hardware resources alone. Analog elements, microcontrollers, DSPs, ROMs, RAMs, ASICs, FPGAs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

[0025] Control circuit 13 executes the following control as basic control. When power is transferred from the first DC unit to the second DC unit (when discharging from first DC power supply E1), control circuit 13 controls first switching element Q1 to eighth switching element Q8 so that the current value detected by secondary-side current sensor 23 maintains the current command value. Note that the voltage value detected by first voltage sensor 21 on the primary side, the secondary-side voltage value detected by second voltage sensor 22 on the secondary side, and the current value detected by the primary-side current sensor may be controlled as target values.

[0026] Furthermore, when transferring power from the second DC unit to the first DC unit (when charging the first DC power supply E1), the control circuit 13 controls the first switching element Q1 to the eighth switching element Q8 so that the current value detected by the primary-side current sensor maintains the current command value. Note that the voltage value detected by the primary-side first voltage sensor 21, the secondary-side voltage value detected by the secondary-side second voltage sensor 22, and the current value detected by the secondary-side current sensor 23 may be controlled as target values.

[0027] In this way, the DAB converter has a symmetrical configuration between the primary side and the secondary side, and is capable of transmitting power in both directions. The operation of the power conversion device 1 will now be described.

[0028] (Comparative Example 1) 2(a)-(c) are diagrams illustrating operating states of the power conversion device 1 according to Comparative Example 1. In the first state shown in Fig. 2(a), the control circuit 13 controls the first switching element Q1, the fourth switching element Q4, the sixth switching element Q6, and the seventh switching element Q7 to be on, and the second switching element Q2, the third switching element Q3, the fifth switching element Q5, and the eighth switching element Q8 to be off. In this state, power is charged from the first DC power source E1 to the first inductance L1, and power is charged from the second DC power source E2 to the second inductance L2.

[0029] 2(b), the control circuit 13 controls the first switching element Q1, the fourth switching element Q4, the fifth switching element Q5, and the eighth switching element Q8 to be in the ON state, and the second switching element Q2, the third switching element Q3, the sixth switching element Q6, and the seventh switching element Q7 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.

[0030] In a third state (not shown), the control circuit 13 controls the second switching element Q2, the third switching element Q3, the fifth switching element Q5, and the eighth switching element Q8 to be on, and the first switching element Q1, the fourth switching element Q4, the sixth switching element Q6, and the seventh switching element Q7 to be off. In this state, power is charged from the first DC power supply E1 to the first inductance L1, and power is charged from the second DC power supply E2 to the second inductance L2.

[0031] In a fourth state (not shown), the control circuit 13 controls the second switching element Q2, the third switching element Q3, the sixth switching element Q6, and the seventh switching element Q7 to be in the ON state, and the first switching element Q1, the fourth switching element Q4, the fifth switching element Q5, and the eighth switching element Q8 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.

[0032] In the control according to the comparative example 1, in the first state (see FIG. 2(a)) and the third state (not shown), the power of the second DC power supply E2 is charged to the second inductance L2. In the subsequent second state (see FIG. 2(b)) and the fourth state (not shown), the power stored in the second inductance L2 is discharged to the second DC power supply E2. That is, a reactive current unrelated to power transmission flows on the secondary side. This flow of reactive current causes unnecessary loss.

[0033] 2(c) shows the current flow when the voltage of the first DC power supply E1 drops significantly relative to the voltage of the second DC power supply E2 in the second state shown in FIG. 2(b). When the voltage of the second DC power supply E2 becomes higher than the voltage of the first DC power supply E1, the direction of the current reverses, and 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 to transition to the next state, the second switching element Q2 and the third switching element Q3 enter hard switching mode, and the first diode D1 of the first switching element Q1 and the fourth diode D4 of the fourth switching element Q4 enter recovery mode, resulting in increased loss.

[0034] (Comparative Example 2) 3(a)-(c) are diagrams illustrating the operating state of the power conversion device 1 according to a second comparative example. FIGS. 4(a)-(d) are diagrams illustrating the switching patterns of the first switching element Q1 to the eighth switching element Q8 according to a second comparative example of the power conversion device 1. The second comparative example employs a phase shift method. The duty ratios of the first switching element Q1 to the sixth switching element Q6 are fixed at 50%, and the seventh switching element Q7 and the eighth switching element Q8 are maintained in an all-off state.

[0035] As shown in FIGS. 4(a) and 4(b), in the step-down operation of Comparative Example 2, the phase of the first leg (first switching element Q1 and second switching element Q2) is fixed, and the phase of the second leg (third switching element Q3 and fourth switching element Q4) is variable. By controlling the phase of the second leg, the phase difference θ1 between the first and second legs is controlled. The third leg (fifth switching element Q5 and sixth switching element Q6) is controlled in synchronization with the second leg. When increasing the power transmitted from the primary side to the secondary side, control circuit 13 controls the phase difference θ1 to be smaller (shifting the phase of the second leg to the left). When decreasing the power transmitted from the primary side to the secondary side, control circuit 13 controls the phase difference θ1 to be larger (shifting the phase of the second leg to the right).

[0036] 4(c)-(d), in the boost operation of Comparative Example 2, the phases of the first and second legs are fixed, the phase of the third leg is variable, and the phase difference θ2 between the first and second legs and the third leg is controlled by controlling the phase of the third leg. When increasing the power transmitted from the primary side to the secondary side, the control circuit 13 controls the phase difference θ2 to be larger (shifting the phase of the third leg to the right), and when decreasing the power transmitted from the primary side to the secondary side, the control circuit 13 controls the phase difference θ2 to be smaller (shifting the phase of the third leg to the left).

[0037] 3(a) shows a state in which power is transmitted from the first DC power supply E1 to the second DC power supply E2 (hereinafter referred to as the transmission state). In the transmission state, the second bridge circuit 12 on the secondary side only needs to be in a rectifying state, and both the fifth switching element Q5 and the sixth switching element Q6 constituting the third leg may be controlled to an off state.

[0038] Fig. 3(b) shows a state in which power is transferred from the first inductance L1 and the second inductance L2 to the second DC power supply E2 (hereinafter referred to as a commutation state). Fig. 3(c) shows a state in which power is stored in the first inductance L1 and the second inductance L2 from the first DC power supply E1 (hereinafter referred to as a storage state).

[0039] In step-down operation, the voltage or current of the transmitted power is controlled by the ratio between the transmission state and the commutation state. The higher the commutation state ratio, the lower the voltage or current of the transmitted power is controlled. In step-up operation, the voltage or current of the transmitted power is controlled by the ratio between the transmission state and the storage state. The higher the storage state ratio, the higher the voltage or current of the transmitted power is controlled.

[0040] In Comparative Example 2, the seventh switching element Q7 and the eighth switching element Q8 are maintained in an all-off state, so that current does not flow back from the second DC power supply E2 to the second inductance L2, the first inductance L1, and the first DC power supply E1. That is, no reactive current is generated due to current flowing back from the second DC power supply E2 as shown in Comparative Example 1. Furthermore, even if the voltage of the second DC power supply E2 becomes higher than the voltage of the first DC power supply E1, no current flows back from the second DC power supply E2 to the first DC power supply E1. Therefore, recovery loss due to the first diode D1 and the fourth diode D4 and hard switching of the second switching element Q2 and the third switching element Q3 can be suppressed.

[0041] However, when transitioning from the maximum power switching pattern for buck operation shown in FIG. 4(b) to the minimum power switching pattern for boost operation shown in FIG. 4(c), a dead time Td must be inserted in the third leg. That is, transitioning from the transmission state to the storage state is required to transition from buck operation to boost operation, and a dead time Td must be inserted during this transition. This dead time Td is a period (dead period) during which the transmitted power does not change in response to changes in the control input (changes in the switching waveform). That is, although the control circuit 13 controls the transmitted power to increase, this is a period during which the power does not actually increase. This dead period can easily cause distortion in the output current. In the following, this embodiment proposes a control method for a DAB converter that does not generate a backflow from the second DC power source E2 or a dead period. Note that a dead period also occurs in the PWM method.

[0042] (Example) 5(a)-(d) are diagrams illustrating operating states according to an embodiment of the power conversion device 1. FIGS. 6(a)-(c) are diagrams illustrating switching patterns of the first switching element Q1 to the eighth switching element Q8 according to an embodiment of the power conversion device 1. This embodiment employs a PWM method, and the control circuit 13 controls the voltage or current of the power transmitted from the first DC unit to the second DC unit by controlling the on / off times of each of the first switching element Q1 to the eighth switching element Q8.

[0043] In this embodiment, the voltage or current of the transmitted power is controlled by switching between the transmission state, the commutation state, and the storage state. In the transmission state, the first bridge circuit 11 conducts electricity between the first DC section and the primary winding n1 of the isolation transformer TR1, and the second bridge circuit 12 conducts electricity between the secondary winding n2 of the isolation transformer TR1 and the second DC section.

[0044] The transmission states include a first pattern and a second pattern. In the first pattern, the first switching element Q1 and the fourth switching element Q4 are on, the second switching element Q2 and the third switching element Q3 are off, and the second bridge circuit 12 is in a rectifying state (see FIGS. 5(a)-(b)). The transmission state a shown in FIG. 5(a) is an example in which the secondary side is diode rectified, and the transmission state b shown in FIG. 5(b) is an example in which the secondary side is synchronously rectified. In the second pattern, the second switching element Q2 and the third switching element Q3 are on, the first switching element Q1 and the fourth switching element Q4 are off, and the second bridge circuit 12 is in a rectifying state.

[0045] The commutation state is a state in which both ends of the primary winding n1 of the isolation transformer TR1 are short-circuited within the first bridge circuit 12, and the second bridge circuit 12 conducts the secondary winding n2 of the isolation transformer TR1 to the second DC section. The commutation state includes a third pattern and a fourth pattern. The third pattern is a pattern in which the first switching element Q1 or the fourth switching element Q4 is on, the fourth switching element Q4 or the first switching element Q1, and the second switching element Q2 and the third switching element Q3 are off, and the second bridge circuit 12 is in a rectification state (see FIG. 5(c)). The fourth pattern is a pattern in which the second switching element Q2 or the third switching element Q3 is on, the third switching element Q3 or the second switching element Q2, and the first switching element Q1 and the fourth switching element Q4 are off, and the second bridge circuit 12 is in a rectification state.

[0046] The accumulation state is a state in which the first bridge circuit 11 conducts current between the first DC section and the primary winding n1 of the isolation transformer TR1, and both ends of the secondary winding n2 of the isolation transformer TR1 are short-circuited within the second bridge circuit 12. The accumulation state includes a fifth pattern and a sixth pattern. The fifth pattern is a pattern in which the first switching element Q1, the fourth switching element Q4, and the sixth switching element Q6 or the seventh switching element Q7 are on, and the remaining switching elements are off. The sixth pattern is a pattern in which the second switching element Q2, the third switching element Q3, and the fifth switching element Q5 or the eighth switching element Q8 are on, and the remaining switching elements are off.

[0047] The control circuit 13 synchronizes the periods of the first pattern with the periods of the second pattern. That is, the control circuit 13 controls the periods of the first pattern and the periods of the second pattern to be substantially the same time. The control circuit 13 also synchronizes the periods of the third pattern with the periods of the fourth pattern. That is, the control circuit 13 controls the periods of the third pattern and the periods of the fourth pattern to be substantially the same time. The control circuit 13 also synchronizes the periods of the fifth pattern with the periods of the sixth pattern. That is, the control circuit 13 controls the periods of the fifth pattern and the periods of the sixth pattern to be substantially the same time. These controls result in symmetrical positive and negative operation, making it possible to suppress DC bias magnetism from occurring in the isolation transformer TR1.

[0048] FIG. 6(a) shows the switching pattern of the first operating mode. The first operating mode is a step-down operating mode. In the first operating mode, the duty ratio of one of the first and second legs is fixed at 100% (duty ratio = 1), and the duty ratio of the other leg is variable. In this embodiment, the duty ratio = 100% (duty ratio = 1) is set to (half cycle (Tsw / 2) - dead time Td). In the example shown in FIG. 6(a), the duty ratio of the second leg is fixed at 100%, and the duty ratio of the first leg is variable. As the duty ratio of the first leg increases (the on-time becomes longer), the transmission period becomes longer than the commutation period, and the transmitted power increases. In this way, in step-down operation, the voltage or current of the transmitted power is controlled by primary-side PWM control.

[0049] In the first operating mode, the control circuit 13 turns on the fourth switching element Q4 in synchronization with the turning on of the first switching element Q1. Next, the control circuit 13 turns on the eighth switching element Q8 in synchronization with the turning off of the first switching element Q1. Note that when the duty ratio of the second leg is variable, the fourth switching element Q4 is turned off instead of the first switching element Q1.

[0050] Synchronous rectification is performed by turning on the eighth switching element Q8. Because synchronous rectification has less loss than diode rectification, secondary-side loss is reduced compared to when the eighth switching element Q8 is off and current passes through the eighth diode D8. Furthermore, when the fifth switching element Q5 is off and current passes through the fifth diode D5, it is possible to prevent the direction of current flowing on the secondary side from reversing. Note that the fifth switching element Q5 may be turned on instead of the eighth switching element Q8. Note that when synchronous rectification is not performed, it is not necessary to turn on the eighth switching element Q8 and the fifth switching element Q5.

[0051] Next, the control circuit 13 turns off the eighth switching element Q8 in synchronization with the turning off of the fourth switching element Q4.

[0052] After a dead time Td, the control circuit 13 turns on the third switching element Q3 in synchronization with the turning on of the second switching element Q2. Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with the turning off of the second switching element Q2. Note that if the duty ratio of the second leg is variable, the third switching element Q3 is turned off instead of the second switching element Q2.

[0053] Synchronous rectification is achieved by turning on the seventh switching element Q7. Note that the sixth switching element Q6 may be turned on instead of the seventh switching element Q7. Note that if synchronous rectification is not performed, it is not necessary to turn on the seventh switching element Q7 and the sixth switching element Q6.

[0054] Next, the control circuit 13 turns off the seventh switching element Q7 in synchronization with the turning off of the third switching element Q3, thus completing one cycle.

[0055] Figure 6(b) shows the switching pattern of the second operating mode. This is the boost operating mode. In this mode, the duty ratios of both the first and second legs are fixed at 100%, while the duty ratio of one of the third and fourth legs is variable, with the other leg operating in a complementary manner with the other leg or in a completely off state. In the example shown in Figure 6(b), the transmitted power is controlled by the duty ratio of the third leg. As the duty ratio of the third leg increases (the on-time becomes longer), the accumulation period becomes longer than the transmission period, and the transmitted power increases. In this way, in boost operation, the voltage or current of the transmitted power is controlled by secondary-side PWM control.

[0056] In the second operating mode, the control circuit 13 turns on the fourth switching element Q4 and the sixth switching element Q6 in synchronization with the turning on of the first switching element Q1. Alternatively, the seventh switching element Q7 may be turned on instead of the sixth switching element Q6.

[0057] Next, the control circuit 13 turns on the eighth switching element Q8 in synchronization with the turning off of the sixth switching element Q6. If the seventh switching element Q7 is turned off instead of the sixth switching element Q6, the control circuit 13 turns on the fifth switching element Q5 instead of the eighth switching element Q8. If synchronous rectification is not performed, it is not necessary to turn on the eighth switching element Q8 and the fifth switching element Q5.

[0058] Next, the control circuit 13 turns off the fourth switching element Q4 and the eighth switching element Q8 in synchronization with the turn-off of the first switching element Q1. After a dead time Td, the control circuit 13 turns on the third switching element Q3 and the fifth switching element Q5 in synchronization with the turn-on of the second switching element Q2. Note that the eighth switching element Q8 may be turned on instead of the fifth switching element Q5.

[0059] Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with the turning off of the fifth switching element Q5. If the eighth switching element Q8 is turned off instead of the fifth switching element Q5, the control circuit 13 turns on the sixth switching element Q6 instead of the seventh switching element Q7. If synchronous rectification is not performed, it is not necessary to turn on the seventh switching element Q7 and the sixth switching element Q6.

[0060] Next, the control circuit 13 turns off the third switching element Q3 and the seventh switching element Q7 in synchronization with the turning off of the second switching element Q2, thus completing one cycle.

[0061] FIG. 6(c) shows a switching pattern of the third operating mode. The third operating mode is used when switching from buck operation to boost operation or from boost operation to buck operation. The third operating mode is activated when the duty ratio of the first leg reaches a threshold value α in the buck operating mode. The threshold value α is set, for example, to a value obtained by subtracting the duty ratio corresponding to the dead time from 100%. Note that the threshold value α can be set to any value. The third operating mode is activated when the duty ratio of the third leg reaches a threshold value β in the boost operating mode. The threshold value β is set, for example, to a value obtained by adding the duty ratio corresponding to the dead time to 0%. Note that the threshold value β can be set to any value. In the third operating mode, power control by primary-side PWM control in the first operating mode and power control by secondary-side PWM control in the second operating mode coexist.

[0062] In the third operating mode, the control circuit 13 turns on the fourth switching element Q4 and the sixth switching element Q6 in synchronization with the turning on of the first switching element Q1. Alternatively, the seventh switching element Q7 may be turned on instead of the sixth switching element Q6.

[0063] Next, the control circuit 13 turns on the eighth switching element Q8 in synchronization with the turning off of the sixth switching element Q6. If the seventh switching element Q7 is turned off instead of the sixth switching element Q6, the control circuit 13 turns on the fifth switching element Q5 instead of the eighth switching element Q8. If synchronous rectification is not performed, it is not necessary to turn on the eighth switching element Q8 and the fifth switching element Q5.

[0064] Next, the control circuit 13 turns off the first switching element Q1. If the duty ratio of the second leg is made variable, the control circuit 13 turns off the fourth switching element Q4 instead of the first switching element Q1.

[0065] Next, the control circuit 13 turns off the eighth switching element Q8 in synchronization with the turning off of the fourth switching element Q4. If the duty ratio of the second leg is variable, the control circuit 13 turns off the first switching element Q1 instead of the fourth switching element Q4.

[0066] After a dead time Td, the control circuit 13 turns on the third switching element Q3 and the fifth switching element Q5 in synchronization with the turning on of the second switching element Q2. Note that the eighth switching element Q8 may be turned on instead of the fifth switching element Q5.

[0067] Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with the turning off of the fifth switching element Q5. If the eighth switching element Q8 is turned off instead of the fifth switching element Q5, the control circuit 13 turns on the sixth switching element Q6 instead of the seventh switching element Q7. If synchronous rectification is not performed, it is not necessary to turn on the seventh switching element Q7 and the sixth switching element Q6.

[0068] Next, the control circuit 13 turns off the second switching element Q2. If the duty ratio of the second leg is variable, the control circuit 13 turns off the third switching element Q3 instead of the second switching element Q2.

[0069] Next, the control circuit 13 turns off the seventh switching element Q7 in synchronization with the turning off of the third switching element Q3. If the duty ratio of the second leg is variable, the control circuit 13 turns off the second switching element Q2 instead of the third switching element Q3. This completes one cycle.

[0070] 7 is a diagram for explaining switching among a first operation mode, a second operation mode, and a third operation mode according to an embodiment. In this embodiment, the third operation mode is interposed between the first operation mode (step-down) and the second operation mode (step-up).

[0071] The control circuit 13 calculates a control manipulated variable based on the deviation between a target value of the current or voltage of the controlled object and an actual detected value. For example, the control circuit 13 calculates the control manipulated variable by performing PI compensation on the deviation. The method for calculating the control manipulated variable will be described in detail later. The control circuit 13 switches the operation mode based on the calculated control manipulated variable.

[0072] In the first operation mode, the control circuit 13 PWM controls the first leg, fixes the second leg to a duty ratio of 100%, sets the third leg to an all-off state, and causes the fourth leg to operate complementary to the first leg. When synchronous rectification is not performed, the fourth leg is also set to an all-off state.

[0073] In the second operation mode, the control circuit 13 fixes the duty ratio of the first leg and the second leg to 100%, PWM controls the third leg, and causes the fourth leg to operate complementary to the third leg. When synchronous rectification is not performed, the fourth leg is set to an all-off state.

[0074] In the third operation mode, the control circuit 13 PWM-controls the first leg, fixes the second leg to a duty ratio of 100%, PWM-controls the third leg, and operates the fourth leg in a complementary manner with the third leg. When synchronous rectification is not performed, the fourth leg is set to an all-off state.

[0075] The control circuit 13 switches from the first operation mode to the third operation mode when the duty ratio of the first leg increases to a threshold value α. The control circuit 13 continues the PWM control of the first leg until the duty ratio of the third leg increases to a threshold value β.

[0076] The control circuit 13 switches from the second operation mode to the third operation mode when the duty ratio of the third leg drops to a threshold value β. The control circuit 13 continues PWM control of the third leg until the duty ratio of the first leg drops to a threshold value α.

[0077] In this way, in the first operating mode, the control circuit 13 controls the duty ratio of the first leg to control the voltage or current of the power transmitted from the first DC section to the second DC section. In the second operating mode, the control circuit 13 controls the duty ratio of the third leg to control the voltage or current of the power transmitted from the first DC section to the second DC section. In the third operating mode, the control circuit 13 controls the duty ratios of the first leg and the third leg to control the voltage or current of the power transmitted from the first DC section to the second DC section. In the first operating mode, the control circuit 13 transitions to the third operating mode before the duty ratio of the first leg reaches 1. In the second operating mode, the control circuit 13 transitions to the third operating mode before the duty ratio of the third leg reaches 0.

[0078] FIG. 8 is a diagram showing a specific example of the control output characteristics during step-down operation in the embodiment of the power conversion device 1. The horizontal axis represents the control operation amount (duty), and the vertical axis represents the output current [A]. The larger the voltage difference between the primary side input voltage V1 and the secondary side output voltage V2, the larger the increase in output current with respect to an increase in the control operation amount. In other words, the larger the voltage difference, the higher the sensitivity to the control operation amount. When the voltage difference is small, the output current hardly changes with respect to a change in the control operation amount.

[0079] In a DAB converter, the larger the voltage applied to the first inductance L1 and the second inductance L2, the larger the output current. This relationship is particularly evident in DAB converters using a chopper system such as those shown in the example and comparative example 2. In a step-down chopper system, power is transmitted from the primary side to the secondary side using the voltage difference between the first DC power supply E1 and the second DC power supply E2. The larger the voltage difference, the larger the voltage applied to the first inductance L1 and the second inductance L2, and the larger the output current. Conversely, in a step-up chopper system, the larger the voltage difference between the first DC power supply E1 and the second DC power supply E2, the more energy stored in the first inductance L1 and the second inductance L2 is required for voltage boosting, resulting in a decrease in the output current.

[0080] In this way, the loop transfer function changes depending on the voltage conditions between the primary and secondary sides, and the performance of the feedback control deteriorates. The loop transfer function is a transfer function that shows how the signal input to the controller changes as it goes around the feedback loop. The loop transfer function is used as an index to show whether the feedback system is stable or not.

[0081] 9 is a diagram for explaining the basic concept of the open-loop transfer function. The open-loop transfer function is expressed as C(s)×G(s)×H(s). That is, the open-loop transfer function is determined by the performance of the controller 135, the performance of the converter (in this embodiment, a DAB converter), and the performance of the detector 131. The performance of the detector 131 also includes the performance of the current sensor 23.

[0082] The voltage of storage batteries installed in electric vehicles varies greatly depending on the SOC (State Of Charge) and vehicle model. Therefore, in a V2H converter, the range of the voltage difference between the input voltage and output voltage becomes wide, and G(s) changes significantly depending on the voltage difference. In other words, the open-loop transfer function changes significantly depending on the voltage difference. A large change in the open-loop transfer function indicates that the performance of the feedback control is unstable.

[0083] In this embodiment, in order to stabilize the open-loop transfer function regardless of the voltage difference between the input voltage and the output voltage, the gain of the controller 135 is adaptively switched in accordance with the voltage difference.

[0084] Fig. 10 is a diagram showing an example of a switching table for proportional gain and integral gain of controller 135. Fig. 10 shows an example of a case where controller 135 performs PI control on the deviation between current command value Iref and the current value detected by detector 131. In the example shown in Fig. 10, the voltage difference between the input voltage and the output voltage is divided into 0V to less than 10V, 10V to less than 20V, 20V to less than 30V, 30V to less than 40V, 40V to less than 50V, 50V to less than 70V, 70V to less than 100V, and 100V or more, and a proportional (P) gain and an integral (I) gain are set for each voltage division.

[0085] The proportional gain is set to a smaller value as the voltage difference increases. The integral gain may be set to a fixed value regardless of the voltage range, or may be set to an individual value for each voltage range.

[0086] The designer tunes the proportional gain and integral gain to optimal values ​​based on experiments and simulations. The designer derives the proportional gain and integral gain that allow the current command value Iref and the current value detected by detector 131 to stably match or approximate each other for each voltage range using trial and error, the ultimate sensitivity method, etc. The designer generates a gain switching table for controller 135 for each operating mode. That is, the designer generates gain switching tables for the first operating mode (step-down), the second operating mode (step-up), and the third operating mode (when switching).

[0087] When the controller 135 performs PID control on the deviation between the current command value Iref and the current value detected by the detector 131, a switching table for the proportional (P) gain, integral (I) gain, and differential (D) gain of the controller 135 is generated.

[0088] In this way, by switching the PI gain or PID gain of the controller 135 according to the voltage difference, the open-loop transfer function can be kept constant regardless of the voltage difference. In other words, the performance of the feedback control can be stabilized regardless of the voltage difference.

[0089] 11 is a diagram showing an example of the configuration of a feedback control unit included in control circuit 13. The feedback control unit includes a detector 131, a first subtraction unit 132, a second subtraction unit 133, a control gain determination unit 134, a controller 135, and a PWM generation unit 136. Detector 131 includes an A / D converter. The A / D converter converts the analog output current value Io detected by current sensor 23 into a digital output current value at a predetermined sampling rate.

[0090] A first subtraction unit 132 calculates a deviation err between a current command value Iref to be a target value and an output current value input from the detector 131. A second subtraction unit 133 calculates a voltage difference between an input voltage V1 detected by the first voltage sensor 21 and an output voltage V2 detected by the second voltage sensor 22. A control gain determination unit 134 determines the operation mode of the DAB converter based on the control operation amount duty calculated by the controller 135. The control gain determination unit 134 refers to a gain switching table for the determined operation mode and determines a proportional gain and an integral gain (hereinafter, both are collectively referred to as control gain G) according to the voltage difference.

[0091] The controller 135 calculates the control operation amount duty by performing PI control on the deviation err using the control gain G set by the control gain determination unit 134. The PWM generation unit 136 generates PWM signals for driving the first switching element Q1 to the eighth switching element Q8 based on the calculated control operation amount duty.

[0092] 12 is a flowchart showing the flow of feedback control by the control circuit 13. The control circuit 13 calculates the voltage difference between the input voltage V1 detected by the first voltage sensor 21 and the output voltage V2 detected by the second voltage sensor 22 (S10). The control circuit 13 performs PI control using a control gain G on the deviation err between the current command value Iref and the output current value, and calculates a control operation amount duty for generating a PWM signal (S11). The control gain G is a variable value that changes adaptively according to the voltage difference. Note that a preset default value is used in the initial state.

[0093] The control circuit 13 determines the operation mode of the DAB converter based on the calculated control operation amount duty (S12). For example, as shown in Fig. 7 above, the control circuit 13 determines the operation mode of the DAB converter based on the relationship between the PWM duty ratio corresponding to the control operation amount of the first leg and the threshold value α, or the relationship between the PWM duty ratio corresponding to the control operation amount of the third leg and the threshold value β.

[0094] When the operation mode is the first operation mode (step-down) (step-down in S12), the control circuit 13 refers to the gain switching table for the first operation mode (step-down) and sets the control gain G according to the voltage difference (S13). When the operation mode is the second operation mode (step-up) (step-up in S12), the control circuit 13 refers to the gain switching table for the second operation mode (step-up) and sets the control gain G according to the voltage difference (S14). When the operation mode is the third operation mode (at switching) (at switching in S12), the control circuit 13 refers to the gain switching table for the third operation mode (at switching) and sets the control gain G according to the voltage difference (S15).

[0095] The above-described processing of steps S10 to S15 continues to be executed (N in S16) until the power conversion processing by the DAB converter is completed (Y in S16).

[0096] 13(a)-13(c) are diagrams illustrating the switching patterns of the first switching element Q1 through the eighth switching element Q8 during reverse transmission according to an embodiment of the power conversion device 1. The switching patterns of the first switching element Q1 through the eighth switching element Q8 shown in FIGS. 6(a)-6(c) illustrate an example in which power is transmitted from the first DC unit to the second DC unit. However, it is also possible to transmit power from the second DC unit to the first DC unit. In this case, as shown in FIGS. 13(a)-13(c), the control circuit 13 simply switches the drive signals supplied to the first switching element Q1 through the fourth switching element Q4 and the drive signals supplied to the fifth switching element Q5 through the eighth switching element Q8.

[0097] Fig. 14 is a diagram illustrating an application example of a power conversion device 1 according to an embodiment. In the example illustrated in Fig. 14, the power conversion device 1 according to the embodiment is used in a DC / DC converter 1a in a V2H system 5. The V2H system 5 is a V2H device for connecting an electric vehicle 7 with a receiving point of a commercial power grid 2 in a home or a load 4 in the home. The V2H system 5 and the electric vehicle 7 are connected by a DC charging / discharging cable 6. A gun connector 6a is attached to the tip of the charging / discharging cable 6, and the V2H system 5 and the electric vehicle 7 are connected when the user inserts the gun connector 6a into an inlet of the electric vehicle 7.

[0098] The V2H system 5 includes a DC / DC converter 1a and an inverter 52. One end of the DC / DC converter 1a is connected to the electric vehicle 7 via a charge / discharge cable 6, and the other end of the DC / DC converter 1a is connected to the inverter 52. The DC / DC converter 1a is a bidirectional DC / DC converter for charging and discharging a storage battery mounted on the electric vehicle 7, and uses a power conversion device 1 (DAB converter) according to the embodiment. The storage battery mounted on the electric vehicle 7 is charged and discharged in accordance with, for example, a charge / discharge sequence defined in CHAdeMO.

[0099] The inverter 52 is a bidirectional inverter connected between the DC / DC converter 1a and the distribution board 3. The inverter 52 can convert DC power input from the DC / DC converter 1a into AC power and output the converted AC power to the distribution board 3. The distribution board 3 is connected to the commercial power system 2 and a load 4. The load 4 is a general term for loads within the home. The inverter 52 can convert AC power supplied from the commercial power system 2 via the distribution board 3 into DC power and output the converted DC power to the DC / DC converter 1a.

[0100] It should be noted that a DC / DC converter for a solar cell, a DC / DC converter for a stationary storage battery, or the like may be connected to the DC bus between the DC / DC converter 1a and the inverter 52.

[0101] As described above, according to this embodiment, the performance of the feedback control can be stabilized by adaptively changing the control gain G in accordance with the voltage difference between the input voltage and the output voltage. Even when the control output characteristics change significantly in accordance with the voltage difference between the input voltage and the output voltage, the open-loop transfer function can be kept constant by adjusting the control gain G, and a desired response can be obtained. This embodiment is particularly effective for charging and discharging an on-board storage battery, whose voltage changes significantly depending on the vehicle type and SOC. This embodiment is also effective for a DAB converter that employs a chopper drive system, which experiences significant changes in the control output characteristics.

[0102] Furthermore, by providing a third operating mode, it is possible to smoothly switch between the step-down operation and the step-up operation. Unlike Comparative Example 2, there is no dead period between the step-down operation and the step-up operation, and it is possible to suppress distortion of the output current.

[0103] Furthermore, there is no period in which current flows back from the second DC power supply E2 to the second inductance L2, the first inductance L1, and the first DC power supply E1, and therefore no reactive current is generated due to the backflow of current from the second DC power supply E2. Furthermore, even if the voltage of the second DC power supply E2 becomes higher than the voltage of the first DC power supply E1, no current flows back from the second DC power supply E2 to the first DC power supply E1. Therefore, recovery loss due to the first diode D1 and the fourth diode D4 and hard switching of the second switching element Q2 and the third switching element Q3 can be suppressed.

[0104] Furthermore, according to this embodiment, since control is performed by the PWM method rather than the phase shift method, it is possible to easily generate a dead time during which the first switching element Q1 through the eighth switching element Q8 are all in an off state. This makes it possible to suppress the occurrence of recovery loss in the diodes. As such, according to this embodiment, it is possible to smoothly switch between voltage step-down operation and voltage step-up operation, and to achieve high efficiency.

[0105] The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0106] In the above embodiment, an example was described in which power is controlled by the PWM control method on both the primary side and the secondary side. In the following modified example, an example in which power is controlled by the phase shift method on the primary side and the PWM method on the secondary side will be described.

[0107] 15(a)-(c) are diagrams illustrating switching patterns of the first switching element Q1 to the eighth switching element Q8 according to a modified example of the power conversion device 1. FIG. 15(a) shows a switching pattern in a first operating mode according to the modified example. The first operating mode is a step-down operating mode. In the first operating mode, the phase of one of the first leg and the second leg is fixed, and the phase of the other leg is shifted. In the example shown in FIG. 15(a), the phase of the second leg is fixed, and the phase of the first leg is shifted. As the phase difference between the first leg and the second leg decreases, the transmission period becomes longer than the commutation period, and the transmitted power increases. Note that the commutation period shown in FIG. 15(a) includes two periods: a commutation period a during which the second diode D2 is conducting and performs diode rectification, and a commutation period b during which the second switching element Q2 performs synchronous rectification. In this manner, during step-down operation, the voltage or current of the transmitted power is controlled by primary-side phase shift control. The control on the secondary side is the same as that in the above embodiment shown in FIG. 6(a).

[0108] Figure 15(b) shows the switching pattern of the second operation mode. The second operation mode is an operation mode during voltage boost. The control during voltage boost is the same as the control of the above embodiment shown in Figure 6(b).

[0109] FIG. 15(c) shows a switching pattern of a third operation mode according to a modified example. The third operation mode is an operation mode used when switching from buck operation to boost operation or from boost operation to buck operation. The third operation mode is activated in the first operation mode when the phase difference between the first leg and the second leg is reduced to a phase difference θ corresponding to the dead time. The third operation mode is also activated in the second operation mode when the duty ratio of the third leg reaches a threshold value β. In the third operation mode, power control by primary-side phase shift control in the first operation mode and power control by secondary-side PWM control in the second operation mode coexist.

[0110] In this way, the first operating mode to the third operating mode can also be realized by performing phase shift control on the primary side and PWM control on the secondary side. By performing phase shift control on the primary side, there is no period in which the switching elements Q1 to Q8 are all off in the first operating mode and part of the third operating mode, but synchronous rectification can be performed during the commutation state.

[0111] The adaptive switching control of the control gain G according to the voltage difference between the input voltage and the output voltage according to the present disclosure can also be applied to DAB converters using drive systems other than those described in the above embodiments. For example, it can also be applied to DAB converters using drive systems that do not include the third operating mode (when switching) in the above embodiments. In this case, there is no need to prepare a gain switching table for the third operating mode (when switching). It can also be applied to DAB converters using the drive systems shown in Comparative Example 1, Comparative Example 2, and the above modified example, as well as other drive systems. For drive systems in which the step-down and step-up operating modes are the same, it is sufficient to prepare one type of gain switching table.

[0112] In the above embodiment, it is assumed that the first switching element Q1 to the eighth switching element Q8 are each an IGBT or a MOSFET. However, the first switching element Q1 to the eighth switching element Q8 may be made of a wide bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), or diamond (C).

[0113] The embodiment may be specified by the following items.

[0114] [Item 1] a first bridge circuit (11) having 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, the first leg and the second leg being connected in parallel to a first DC section (E1, Ca); a second bridge circuit (12) including a third leg in which a fifth switching element (Q5) and a sixth switching element (Q6) are connected in series, and a fourth leg in which a seventh switching element (Q7) and an eighth switching element (Q8) are connected in series, the third leg and the fourth leg being connected in parallel to a second DC unit (E2, Cb); an isolation transformer (TR1) connected between the first bridge circuit (11) and the second bridge circuit (12); a control circuit (13) that controls the first switching element (Q1) to the eighth switching element (Q8) to control the power, voltage, or current of the second DC unit (E2, Cb); The power conversion device (1) is characterized in that the control circuit (13) dynamically changes a gain of feedback control according to a difference between a voltage of the first DC section (E1, Ca) and a voltage of the second DC section (E2, Cb). This makes it possible to prevent the open-loop transfer function from changing depending on the difference between the voltage of the first DC section (E1, Ca) and the voltage of the second DC section (E2, Cb), thereby stabilizing the performance of the feedback control. [Item 2] Diodes (D1-D8) are connected or formed in anti-parallel to the first switching element (Q1) to the eighth switching element (Q8), respectively; The control circuit (13) a first operation mode in which the first bridge circuit (11) conducts the first DC section (E1, Ca) and the primary winding (n1) of the isolation transformer (TR1) and the second bridge circuit (12) conducts the secondary winding (n2) of the isolation transformer (TR1) and the second DC section (E2, Cb), and the first operation mode is controlled to include a transmission state in which both ends of the primary winding (n1) are short-circuited within the first bridge circuit (11) and the second bridge circuit (12) conducts the secondary winding (n2) and the second DC section (E2, Cb); a second operation mode in which the first bridge circuit (11) conducts the first DC section (E1, Ca) and the primary winding (n1) and short-circuits both ends of the secondary winding (n2) within the second bridge circuit (12) to include a storage state and the transmission state; The power conversion device (1) according to item 1, comprising: This makes it possible to stabilize the performance of the feedback control of the DAB converter driven by the chopper method. [Item 3] The control circuit (13) a third operating mode controlled to include the transmission state, the storage state, and the commutation state; The power conversion device (1) according to item 2. This allows smooth switching between the first operation mode and the second operation mode. [Item 4] the transmission state includes a first pattern and a second pattern, and the commutation state includes a third pattern and a fourth pattern; The first pattern is a state in which the first switching element (Q1) and the fourth switching element (Q4) are in an on state, the second switching element (Q2) and the third switching element (Q3) are in an off state, and the second bridge circuit (12) is in a rectifying state; the second pattern is a state in which the second switching element (Q2) and the third switching element (Q3) are in an on state, the first switching element (Q1) and the fourth switching element (Q4) are in an off state, and the second bridge circuit (12) is in a rectifying state; the third pattern is a state in which the first switching element (Q1) or the fourth switching element (Q4) is in an on state, the fourth switching element (Q4) or the first switching element (Q1), the second switching element (Q2), and the third switching element (Q3) are in an off state, and the second bridge circuit (12) is in a rectifying state; The fourth pattern is a state in which the second switching element (Q2) or the third switching element (Q3) is in an on state, the third switching element (Q3) or the second switching element (Q2), the first switching element (Q1), and the fourth switching element (Q4) are in an off state, and the second bridge circuit (12) is in a rectifying state. The power conversion device (1) according to item 2. This makes it possible to suppress the reactive current from the second DC section (E2, Cb) during the step-down operation, thereby achieving high efficiency. [Item 5] the accumulation state includes a fifth pattern and a sixth pattern; The fifth pattern is a state in which the first switching element (Q1), the fourth switching element (Q4), and the sixth switching element (Q6) or the seventh switching element (Q7) are in an on state, and the remaining switching elements are in an off state; The sixth pattern is a state in which the second switching element (Q2), the third switching element (Q3), and the fifth switching element (Q5) or the eighth switching element (Q8) are in an on state, and the remaining switching elements are in an off state. The power conversion device (1) according to item 2. This makes it possible to suppress the reactive current from the second DC section (E2, Cb) during the boost operation, thereby achieving high efficiency. [Item 6] The control circuit (13) controls the voltage or current of the power transmitted from the first DC unit (E1, Ca) to the second DC unit (E2, Cb) by controlling the on / off time of each switching element. 6. The power conversion device (1) according to any one of items 1 to 5. According to this, by controlling with the PWM method without using the phase shift method, it is possible to easily generate a dead time in the all-off state and reduce the recovery loss of the diode. [Item 7] The control circuit (13) In the first operation mode, the duty ratio of the first leg or the second leg is controlled, In the second operation mode, the duty ratio of the third leg or the fourth leg is controlled, In the third operation mode, the duty ratio of the first leg or the second leg and the duty ratio of the third leg or the fourth leg are controlled, Controlling the voltage or current of the power transmitted from the first DC unit (E1, Ca) to the second DC unit (E2, Cb); Item 3. The power conversion device (1) according to item 3. According to this, in the third operation mode, by allowing the PWM control of the first operation mode and the PWM control of the second operation mode to coexist, it is possible to smoothly switch between the first operation mode and the second operation mode. [Item 8] The control circuit (13) transitioning to the third operation mode before the duty ratio of the first leg or the second leg reaches 1 in the first operation mode; Item 5. The power conversion device (1) according to item 5. This allows smooth switching from the first operation mode to the second operation mode. [Item 9] The control circuit (13) transitioning to the third operation mode before the duty ratio of the third leg or the fourth leg reaches 0 in the second operation mode; Item 7. The power conversion device (1) according to item 7. This allows smooth switching from the second operation mode to the first operation mode. [Item 10] The control circuit (13) In the first mode of operation, The fourth switching element (Q4) is turned on in synchronization with the turning on of the first switching element (Q1), In synchronization with the turning off of the first switching element (Q1) or the fourth switching element (Q4), the eighth switching element (Q8) or the fifth switching element (Q5) is turned on; In synchronization with the turning off of the fourth switching element (Q4) or the first switching element (Q1), the eighth switching element (Q8) or the fifth switching element (Q5) is turned off; The third switching element (Q3) is turned on in synchronization with the turning on of the second switching element (Q2), In synchronization with the turning off of the second switching element (Q2) or the third switching element (Q3), the seventh switching element (Q7) or the sixth switching element (Q6) is turned on; turning off the seventh switching element (Q7) or the sixth switching element (Q6) in synchronization with the turning off of the third switching element (Q3) or the second switching element (Q2); The power conversion device (1) according to item 2. According to this, by controlling the step-down operation by the PWM method without using the phase shift method, it is possible to easily generate a dead time in the all-off state and reduce the recovery loss of the diode. [Item 11] The control circuit (13) In the second mode of operation, In synchronization with the turning on of the first switching element (Q1), the fourth switching element (Q4), the sixth switching element (Q6), or the seventh switching element (Q7) is turned on; In synchronization with the turning off of the sixth switching element (Q6) or the seventh switching element (Q7), the eighth switching element (Q8) or the fifth switching element (Q5) is turned on; In synchronization with the turning off of the first switching element (Q1), the fourth switching element (Q4), the eighth switching element (Q8) or the fifth switching element (Q5) are turned off; In synchronization with the turning on of the second switching element (Q2), the third switching element (Q3), the fifth switching element (Q5) or the eighth switching element (Q8) are turned on; In synchronization with the turning off of the fifth switching element (Q5) or the eighth switching element (Q8), the seventh switching element (Q7) or the sixth switching element (Q6) is turned on; In synchronization with the turning off of the second switching element (Q2), the third switching element (Q3), and the seventh switching element (Q7) or the sixth switching element (Q6) are turned off. The power conversion device (1) according to item 2. According to this, in the boost operation, by controlling with the PWM method without using the phase shift method, it is possible to easily generate a dead time in the all-off state and reduce the recovery loss of the diode. [Item 12] The control circuit (13) In the third mode of operation, In synchronization with the turning on of the first switching element (Q1), the fourth switching element (Q4), the sixth switching element (Q6), or the seventh switching element (Q7) is turned on; In synchronization with the turning off of the sixth switching element (Q6) or the seventh switching element (Q7), the eighth switching element (Q8) or the fifth switching element (Q5) is turned on; turning off the first switching element (Q1) or the fourth switching element (Q4); turning off the eighth switching element (Q8) or the fifth switching element (Q5) in synchronization with the turning off of the fourth switching element (Q4) or the first switching element (Q1); In synchronization with the turning on of the second switching element (Q2), the third switching element (Q3), the fifth switching element (Q5) or the eighth switching element (Q8) are turned on; In synchronization with the turning off of the fifth switching element (Q5) or the eighth switching element (Q8), the seventh switching element (Q7) or the sixth switching element (Q6) is turned on; turning off the second switching element (Q2) or the third switching element (Q3); turning off the seventh switching element (Q7) or the sixth switching element (Q6) in synchronization with the turning off of the third switching element (Q3) or the second switching element (Q2); Item 3. The power conversion device (1) according to item 3. According to this, when switching between voltage-buck operation and voltage-boost operation, by controlling using the PWM method without using the phase shift method, it is possible to easily generate a dead time in the all-off state and reduce the recovery loss of the diode. [Item 13] The control circuit (13) Synchronizing a period of the first pattern with a period of the second pattern; Synchronizing a period of the third pattern with a period of the fourth pattern; Item 4. The power conversion device (1) according to item 4. This results in a symmetrical operation between positive and negative polarities, making it possible to suppress the occurrence of DC bias magnetism. [Item 14] The control circuit (13) Synchronizing a period of the fifth pattern with a period of the sixth pattern; Item 5. The power conversion device (1) according to item 5. This results in a symmetrical operation between positive and negative polarities, making it possible to suppress the occurrence of DC bias magnetism. [Item 15] The control circuit (13) When transmitting power from the secondary side to the primary side, The drive signals supplied to the first switching element (Q1) through the fourth switching element (Q4) are interchanged with the drive signals supplied to the fifth switching element (Q5) through the eighth switching element (Q8). The power conversion device (1) according to item 1. This makes it possible to realize a DC / DC converter capable of bidirectional transmission. [Item 16] The first DC unit (E1, Ca) includes a storage battery (E1) mounted on the electric vehicle (7). The power conversion device (1) according to item 1. This makes it possible to stabilize the performance of the feedback control even if the voltage changes significantly depending on the vehicle type and SOC. [Explanation of symbols]

[0115] E1 first DC power supply, E2 second DC power supply, 1 power conversion device, 1a DC / DC converter, 11 first bridge circuit, 12 second bridge circuit, 13 control circuit, 21 first voltage sensor, 22 second voltage sensor, 23 current sensor, 131 detector, 132 first subtraction unit, 133 second subtraction unit, 134 control gain determination unit, 135 controller, 136 PWM generation unit, Q1-Q8 switching elements, D1-D8 diodes, C1-C8 capacitance, L1 first inductance, L2 second inductance, TR1 isolation transformer, n1 primary winding, n2 secondary winding, Ca primary side capacitor, Cb secondary side capacitor, 2 commercial power system, 3 distribution board, 4 load, 5 V2H system, 52 inverter, 6 charge / discharge cable, 6a Gun connector, 7 electric car.

Claims

1. a first bridge circuit including 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, the first leg and the second leg being connected in parallel to a first DC section; a second bridge circuit including 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, the third leg and the fourth leg being connected in parallel to a second DC section; an isolation transformer connected between the first bridge circuit and the second bridge circuit; a control circuit that controls the first switching element to the eighth switching element to control the power, voltage, or current of the second DC section, The power conversion device, wherein the control circuit dynamically changes a gain of feedback control in accordance with a difference between the voltage of the first DC section and the voltage of the second DC section.

2. a diode is connected or formed in anti-parallel to each of the first switching element to the eighth switching element, The control circuit a first operation mode in which the inverter is controlled to include a transmission state in which the first bridge circuit conducts the first DC section and a primary winding of the isolation transformer, and the second bridge circuit conducts the secondary winding of the isolation transformer with the second DC section, and a commutation state in which both ends of the primary winding are short-circuited within the first bridge circuit, and the second bridge circuit conducts the secondary winding with the second DC section; a second operation mode in which the first bridge circuit is controlled to include a storage state in which the first DC section and the primary winding are electrically connected and both ends of the secondary winding are short-circuited within the second bridge circuit, and the transmission state; The power conversion device according to claim 1 ,

3. The control circuit a third operating mode controlled to include the transmission state, the storage state, and the commutation state; The power conversion device according to claim 2 .

4. the transmission state includes a first pattern and a second pattern, and the commutation state includes a third pattern and a fourth pattern; the first pattern is a state in which the first switching element and the fourth switching element are in an on state, the second switching element and the third switching element are in an off state, and the second bridge circuit is in a rectifying state; the second pattern is such that the second switching element and the third switching element are in an ON state, the first switching element and the fourth switching element are in an OFF state, and the second bridge circuit is in a rectifying state; the third pattern is a state in which the first switching element or the fourth switching element is in an on state, the fourth switching element or the first switching element, the second switching element, and the third switching element are in an off state, and the second bridge circuit is in a rectifying state; the fourth pattern is a state in which the second switching element or the third switching element is in an on state, the third switching element or the second switching element, the first switching element, and the fourth switching element are in an off state, and the second bridge circuit is in a rectifying state. The power conversion device according to claim 2 .

5. the accumulation state includes a fifth pattern and a sixth pattern, the fifth pattern is a state in which the first switching element, the fourth switching element, and the sixth switching element or the seventh switching element are in an on state, and the remaining switching elements are in an off state; the sixth pattern is such that the second switching element, the third switching element, and the fifth switching element or the eighth switching element are in an on state, and the remaining switching elements are in an off state; The power conversion device according to claim 2 .

6. the control circuit controls the voltage or current of the power transmitted from the first DC unit to the second DC unit by controlling the on / off times of each switching element. The power conversion device according to any one of claims 1 to 5.

7. The control circuit In the first operation mode, the duty ratio of the first leg or the second leg is controlled, In the second operation mode, the duty ratio of the third leg or the fourth leg is controlled, In the third operation mode, a duty ratio of the first leg or the second leg and a duty ratio of the third leg or the fourth leg are controlled, Controlling the voltage or current of the power transmitted from the first DC unit to the second DC unit. The power conversion device according to claim 3 .

8. The control circuit transitioning to the third operation mode before a duty ratio of the first leg or the second leg reaches 1 in the first operation mode; The power conversion device according to claim 7.

9. The control circuit transitioning to the third operation mode before the duty ratio of the third leg or the fourth leg reaches 0 in the second operation mode; The power conversion device according to claim 7.

10. The control circuit In the first mode of operation, turning on the fourth switching element in synchronization with the turning on of the first switching element; turning on the eighth switching element or the fifth switching element in synchronization with the turning off of the first switching element or the fourth switching element; turning off the eighth switching element or the fifth switching element in synchronization with the turning off of the fourth switching element or the first switching element; turning on the third switching element in synchronization with the turning on of the second switching element; turning on the seventh switching element or the sixth switching element in synchronization with the turning off of the second switching element or the third switching element; turning off the seventh switching element or the sixth switching element in synchronization with the turning off of the third switching element or the second switching element; The power conversion device according to claim 2 .

11. The control circuit In the second mode of operation, turning on the fourth switching element, the sixth switching element, or the seventh switching element in synchronization with the turning on of the first switching element; turning on the eighth switching element or the fifth switching element in synchronization with the sixth switching element or the seventh switching element being turned off; turning off the fourth switching element, the eighth switching element, or the fifth switching element in synchronization with the turning off of the first switching element; turning on the third switching element, the fifth switching element, or the eighth switching element in synchronization with the turning on of the second switching element; turning on the seventh switching element or the sixth switching element in synchronization with the turning off of the fifth switching element or the eighth switching element; turning off the third switching element, the seventh switching element, or the sixth switching element in synchronization with the turning off of the second switching element; The power conversion device according to claim 2 .

12. The control circuit In the third mode of operation, turning on the fourth switching element, the sixth switching element, or the seventh switching element in synchronization with the turning on of the first switching element; turning on the eighth switching element or the fifth switching element in synchronization with the sixth switching element or the seventh switching element being turned off; turning off the first switching element or the fourth switching element; turning off the eighth switching element or the fifth switching element in synchronization with the turning off of the fourth switching element or the first switching element; turning on the third switching element, the fifth switching element, or the eighth switching element in synchronization with the turning on of the second switching element; turning on the seventh switching element or the sixth switching element in synchronization with the turning off of the fifth switching element or the eighth switching element; turning off the second switching element or the third switching element; turning off the seventh switching element or the sixth switching element in synchronization with the turning off of the third switching element or the second switching element; The power conversion device according to claim 3 .

13. The control circuit Synchronizing a period of the first pattern with a period of the second pattern; Synchronizing a period of the third pattern with a period of the fourth pattern; The power conversion device according to claim 4.

14. The control circuit Synchronizing the period of the fifth pattern with the period of the sixth pattern; The power conversion device according to claim 5 .

15. The control circuit When transmitting power from the secondary side to the primary side, The drive signals supplied to the first switching element and the fourth switching element are interchanged with the drive signals supplied to the fifth switching element and the eighth switching element. The power conversion device according to claim 1 .

16. The first DC unit includes a storage battery mounted on the electric vehicle. The power conversion device according to claim 1 .

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