JP2024008097A - Power conversion device - Google Patents

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

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

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

In a typical DAB converter, an increase in loss occurs due to hard switching at low output, and an increase in loss due to the flow of reactive current unrelated to power transmission. In response to this, 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).

International Publication No. 16/125374

In a DAB converter, a variation characteristic of an output current with respect to a control operation amount (hereinafter referred to as a control output characteristic in this specification) changes depending on a difference between an input voltage and an output voltage. In particular, in a DAB converter that employs a chopper method, the control output characteristics vary greatly depending on the difference between the input voltage and the output voltage. A large change in control output characteristics means that the performance of feedback control is unstable, and there are cases where a desired response cannot be obtained.

The present disclosure has been made in view of these circumstances, and its purpose is to provide a power conversion device with stable feedback control performance regardless of the difference between input voltage and output voltage.

In order to solve the above problems, a power conversion device according to an aspect of the present disclosure includes a first leg in which a first switching element and a second switching element are connected in series, and a third switching element and a fourth switching element are connected in series. a first bridge circuit, the first leg and the second leg being connected in parallel to a first direct current section; and a third bridge circuit having a fifth switching element and a sixth switching element connected in series. a second bridge circuit having a fourth leg in which a seventh switching element and an eighth switching element are connected in series, the third leg and the fourth leg being connected in parallel to a second DC section; An isolation transformer connected between the first bridge circuit and the second bridge circuit, and the first switching element to the eighth switching element are controlled to control the power, voltage, or current of the second DC section. A control circuit. The control circuit dynamically changes the gain of feedback control according to the difference between the voltage of the first DC section and the voltage of the second DC section.

According to the present disclosure, the performance of feedback control can be stabilized regardless of the difference between input voltage and output voltage.

FIG. 1 is a diagram for explaining the configuration of a power conversion device according to an embodiment. FIGS. 2(a) to 2(c) are diagrams for explaining the operating state of the power conversion device according to Comparative Example 1. FIGS. 3A to 3C are diagrams for explaining the operating state of the power converter according to Comparative Example 2. FIGS. 4A to 4D are diagrams for explaining switching patterns of the first switching element to the eighth switching element according to Comparative Example 2 of the power conversion device. FIGS. 5(a) to 5(d) are diagrams for explaining the operating states of the embodiment of the power conversion device. FIGS. 6A to 6C 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. FIG. 3 is a diagram for explaining switching between a first operation mode, a second operation mode, and a third operation mode according to the embodiment. FIG. 7 is a diagram illustrating a specific example of control output characteristics during voltage step-down operation according to an embodiment of the power conversion device. FIG. 2 is a diagram for explaining the basic concept of a one-loop transfer function. It is a figure which shows an example of the switching table of the proportional gain and integral gain of a controller. FIG. 3 is a diagram showing a configuration example of a feedback control section included in the control circuit. 5 is a flowchart showing the flow of feedback control by the control circuit. FIGS. 13A to 13C are diagrams for explaining switching patterns during reverse direction transmission between the first switching element and the eighth switching element according to the embodiment of the power conversion device. FIG. 2 is a diagram illustrating an application example of a power conversion device according to an embodiment. FIGS. 15A to 15C are diagrams for explaining switching patterns of the first switching element to the eighth switching element according to a modified example of the power conversion device.

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

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

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

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

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

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

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

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

When MOSFETs are used for the first switching element Q1-eighth switching element Q8, parasitic diodes formed between the drains and sources of the first switching element Q1-eighth switching element Q8 are connected to the first diode D1-eighth switching element Q8. They may be used as the diode D8, or external diode elements may be connected as the first diode D1 to the eighth diode D8, respectively. Alternatively, parasitic capacitances formed between the drains and sources of the first switching element Q1 and the eighth switching element Q8 may be used as the first capacitance C1 and the eighth capacitance C8, or External capacitors are connected between the drain and source of Q8 as a first capacitor C1 to an eighth capacitor C8, respectively.

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

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

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

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

The 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 . The 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. The 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. For example, a CT sensor can be used as the current sensor 23. Although not shown in FIG. 1, a current sensor is also provided on the primary side.

The control circuit 13 supplies a drive signal (PWM (Pulse Width Modulation) signal) to the gate terminal or base terminal of the first switching element Q1 to the eighth switching element Q8, thereby controlling the first switching element Q1 to the eighth switching element Q8. Controls Q8. The configuration of the control circuit 13 can be realized by cooperation of hardware resources and software resources, or by only hardware resources. Analog elements, 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.

The control circuit 13 executes the following control as basic control. The control circuit 13 maintains the current value detected by the secondary side current sensor 23 at the current command value when transmitting power from the first DC section to the second DC section (when discharging from the first DC power source E1). The first switching element Q1 to the eighth switching element Q8 are controlled so as to. Note that the voltage value detected by the first voltage sensor 21 on the primary side, the voltage value on the secondary side detected by the second voltage sensor 22 on the secondary side, and the current value detected by the current sensor on the primary side are the targets. It may also be controlled as a value.

Further, the control circuit 13 maintains the current value detected by the primary side current sensor at the current command value when transmitting power from the second DC section to the first DC section (when charging the first DC power source E1). The first switching element Q1 to the eighth switching element Q8 are controlled as follows. Note that the voltage value detected by the first voltage sensor 21 on the primary side, the voltage value on the secondary side detected by the second voltage sensor 22 on the secondary side, and the current value detected by the current sensor 23 on the secondary side may be controlled using the target value.

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

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

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

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

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

In the control according to Comparative Example 1, the second inductance L2 is charged with the power of the second DC power supply E2 in the first state (see FIG. 2A) and the third state (not shown). In the subsequent second state (see FIG. 2(b)) and fourth state (not shown), the power accumulated in the second inductance L2 is discharged to the second DC power source E2. That is, a reactive current unrelated to power transmission flows on the secondary side. The flow of this reactive current causes unnecessary loss.

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

(Comparative example 2)
FIGS. 3A to 3C are diagrams for explaining the operating state of the power conversion device 1 according to Comparative Example 2. FIGS. 4A to 4D are diagrams for explaining switching patterns of the first switching element Q1 to the eighth switching element Q8 according to Comparative Example 2 of the power converter 1. Comparative Example 2 employs a phase shift method. The duty ratio of the first switching element Q1 to the sixth switching element Q6 is fixed at 50%, and the seventh switching element Q7 and the eighth switching element Q8 maintain a completely off state.

As shown in FIGS. 4(a) and 4(b), in the buck 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 Q2) is fixed. By making the phases of Q3 and the fourth switching element Q4 variable and controlling the phase of the second leg, the phase difference θ1 between the first leg and the second leg 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, the control circuit 13 controls so that the phase difference θ1 becomes small (shifts the phase of the second leg to the left), and transmits the power from the primary side to the secondary side. When reducing the power to be used, the phase difference θ1 is controlled to be increased (the phase of the second leg is shifted to the right).

As shown in FIGS. 4(c) to 4(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 of the third leg is controlled. As a result, the phase difference θ2 between the first leg, the second leg, and the third leg is controlled. When increasing the power transmitted from the primary side to the secondary side, the control circuit 13 controls the phase difference θ2 to increase (shifts the phase of the third leg to the right) and transmits the power from the primary side to the secondary side. When reducing the power to be used, the phase difference θ2 is controlled to be small (the phase of the third leg is shifted to the left).

FIG. 3A shows a state in which power is transmitted from the first DC power source E1 to the second DC power source E2 (hereinafter referred to as a transmission state). In addition, 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 forming the third leg may be controlled to be in the off state. .

FIG. 3B shows a state in which power is transmitted from the first inductance L1 and the second inductance L2 to the second DC power source E2 (hereinafter referred to as commutation state). FIG. 3C shows a state in which power is accumulated in the first inductance L1 and the second inductance L2 from the first DC power source E1 (hereinafter referred to as an accumulation state).

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 ratio of commutation states, the lower the voltage or current of the transmitted power is controlled. In boost 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 ratio of the accumulation state, the higher the voltage or current of the transmitted power is controlled.

In Comparative Example 2, current flows backward from the second DC power supply E2 to the second inductance L2, the first inductance L1, and the first DC power supply E1 in order to maintain the seventh switching element Q7 and the eighth switching element Q8 in a completely off state. There's nothing to do. That is, no reactive current is generated due to reverse current flow from the second DC power source E2 as shown in Comparative Example 1. Furthermore, even if the voltage of the second DC power source E2 becomes higher than the voltage of the first DC power source E1, current will not flow backward from the second DC power source E2 to the first DC power source E1. Therefore, recovery loss caused by 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.

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), it is necessary to insert the dead time Td of the third leg. There is. That is, in order to make a transition from a step-down operation to a step-up operation, it is necessary to make a transition from a transmission state to an accumulation state, and it is necessary to insert a dead time Td between the transitions. This dead time Td is a period (dead period) in which the transmitted power does not change in response to a change in the control operation amount (change in the switching waveform). That is, although the control circuit 13 is controlling to increase the transmitted power, there is a period in which the power does not actually increase. This dead period tends to cause distortion in the output current. Hereinafter, in this embodiment, a method of controlling a DAB converter is proposed in which neither a back current from the second DC power supply E2 nor a dead period occurs. Note that the dead period also occurs in the PWM method.

(Example)
FIGS. 5(a) to 5(d) are diagrams for explaining the operating state of the power conversion device 1 according to the embodiment. FIGS. 6A to 6C are diagrams for explaining switching patterns of the first switching element Q1 to the eighth switching element Q8 according to the embodiment of the power conversion device 1. This embodiment employs a PWM method, and the control circuit 13 controls the on/off time of each switching element from the first switching element Q1 to the eighth switching element Q8, thereby controlling Controls the voltage or current of power transmitted to the DC section.

In this embodiment as well, the voltage or current of the transmitted power is controlled by switching the transmission state, commutation state, and accumulation state. In the transmission state, the first bridge circuit 11 conducts the first DC section 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 with the second DC section. It is in a state of

The transmission state includes a first pattern and a second pattern. The first pattern is a pattern in which the first switching element Q1 and the fourth switching element Q4 are in the on state, the second switching element Q2 and the third switching element Q3 are in the off state, and the second bridge circuit 12 is in the rectifying state. (See Figures 5(a)-(b)). A transmission state a shown in FIG. 5A is an example in which the secondary side is diode rectified, and a transmission state b shown in FIG. 5B is an example in which the secondary side is synchronously rectified. The second pattern is a pattern in which the second switching element Q2 and the third switching element Q3 are in the on state, the first switching element Q1 and the fourth switching element Q4 are in the off state, and the second bridge circuit 12 is in the rectifying state. .

In the commutation state, 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 with the second DC section. state. The commutation state includes a third pattern and a fourth pattern. In the third pattern, the first switching element Q1 or the fourth switching element Q4 is in the on state, the fourth switching element Q4 or the first switching element Q1, and the second switching element Q2 and the third switching element Q3 are in the off state, This is a pattern in which the second bridge circuit 12 is in a rectifying state (see FIG. 5(c)). In the fourth pattern, the second switching element Q2 or the third switching element Q3 is in the on state, the third switching element Q3 or the second switching element Q2, and the first switching element Q1 and the fourth switching element Q4 are in the off state, This is a pattern in which the second bridge circuit 12 is in a rectifying state.

In the accumulation state, the first bridge circuit 11 conducts 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 in the second bridge circuit 12. be. 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 in the on state, and the remaining switching elements are in the off state. 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 in the on state, and the remaining switching elements are in the off state.

The control circuit 13 synchronizes the period of the first pattern and the period of the second pattern. That is, the period of the first pattern and the period of the second pattern are controlled to be substantially the same time. Furthermore, the control circuit 13 synchronizes the period of the third pattern and the period of the fourth pattern. That is, the period of the third pattern and the period of the fourth pattern are controlled to be substantially the same time. Further, the control circuit 13 synchronizes the period of the fifth pattern and the period of the sixth pattern. That is, the period of the fifth pattern and the period of the sixth pattern are controlled to be substantially the same time. With these controls, the positive and negative operations are symmetrical, and it is possible to suppress the occurrence of DC biased magnetism in the isolation transformer TR1.

FIG. 6(a) shows the switching pattern of the first operation mode. The first operation mode is a voltage step-down operation mode. In the first operation mode, the duty ratio of one of the first leg and the second leg is fixed at 100% (duty ratio=1), and the duty ratio of the other leg is made variable. In this embodiment, duty ratio=100% (duty ratio=1) is set as (half cycle (Tsw/2)−dead time Td). In the example shown in FIG. 6A, 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 becomes larger (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 transmitted power is controlled by PWM control on the primary side.

In the first operation mode, the control circuit 13 turns on the fourth switching element Q4 in synchronization with turning on 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 made variable, the fourth switching element Q4 is turned off instead of the first switching element Q1.

Synchronous rectification is performed by turning on the eighth switching element Q8. Since synchronous rectification has less loss than diode rectification, the loss on the secondary side is reduced compared to the case where current passes through the eighth diode D8 with the eighth switching element Q8 in the off state. Further, by allowing current to pass through the fifth diode D5 while the fifth switching element Q5 is in the off state, it is possible to prevent the direction of the current flowing to the secondary side from being reversed. Note that the fifth switching element Q5 may be turned on instead of the eighth switching element Q8. Note that if synchronous rectification is not performed, it is not necessary to turn on the eighth switching element Q8 and the fifth switching element Q5.

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

With the dead time Td in between, the control circuit 13 turns on the third switching element Q3 in synchronization with turning on the second switching element Q2. Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with turning off the second switching element Q2. Note that when the duty ratio of the second leg is made variable, the third switching element Q3 is turned off instead of the second switching element Q2.

Synchronous rectification is performed 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, there is no need to turn on the seventh switching element Q7 and the sixth switching element Q6.

Next, the control circuit 13 turns off the seventh switching element Q7 in synchronization with the turning off of the third switching element Q3. One cycle is thus completed.

FIG. 6(b) shows the switching pattern of the second operation mode. The second operation mode is an operation mode during boosting. In the second operation mode, the duty ratio of both the first leg and the second leg is fixed at 100%, the duty ratio of one of the third and fourth legs is variable, and the duty ratio of the other leg is set to 100%. Operate complementary to the leg or turn it completely off. In the example shown in Fig. 6(b), the transmitted power is controlled by the duty ratio of the third leg, and as the duty ratio of the third leg becomes larger (on time becomes longer), the accumulation period becomes shorter than the transmission period. The longer the time, the more power is transmitted. In this way, in the boost operation, the voltage or current of the transmitted power is controlled by PWM control on the secondary side.

In the second operation mode, the control circuit 13 turns on the fourth switching element Q4 and the sixth switching element Q6 in synchronization with turning on the first switching element Q1. Note that the seventh switching element Q7 may be turned on instead of the sixth switching element Q6.

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

Next, the control circuit 13 turns off the fourth switching element Q4 and the eighth switching element Q8 in synchronization with the turning off of the first switching element Q1. With the dead time Td in between, the control circuit 13 turns on the third switching element Q3 and the fifth switching element Q5 in synchronization with turning on the second switching element Q2. Note that the eighth switching element Q8 may be turned on instead of the fifth switching element Q5.

Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with the turning off of the fifth switching element Q5. Note that when the eighth switching element Q8 is turned off instead of the fifth switching element Q5, the sixth switching element Q6 is turned on instead of the seventh switching element Q7. Note that if synchronous rectification is not performed, there is no need to turn on the seventh switching element Q7 and the sixth switching element Q6.

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. One cycle is thus completed.

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

In the third operation mode, the control circuit 13 turns on the fourth switching element Q4 and the sixth switching element Q6 in synchronization with turning on the first switching element Q1. Note that the seventh switching element Q7 may be turned on instead of the sixth switching element Q6.

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

Next, the control circuit 13 turns off the first switching element Q1. Note that when the duty ratio of the second leg is made variable, the fourth switching element Q4 is turned off instead of the first switching element Q1.

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

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

Next, the control circuit 13 turns on the seventh switching element Q7 in synchronization with the turning off of the fifth switching element Q5. Note that when the eighth switching element Q8 is turned off instead of the fifth switching element Q5, the sixth switching element Q6 is turned on instead of the seventh switching element Q7. Note that if synchronous rectification is not performed, there is no need to turn on the seventh switching element Q7 and the sixth switching element Q6.

Next, the control circuit 13 turns off the second switching element Q2. Note that when the duty ratio of the second leg is made variable, the third switching element Q3 is turned off instead of the second switching element Q2.

Next, the control circuit 13 turns off the seventh switching element Q7 in synchronization with the turning off of the third switching element Q3. Note that when the duty ratio of the second leg is made variable, the second switching element Q2 is turned off instead of the third switching element Q3. One cycle is thus completed.

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

The control circuit 13 calculates the control operation amount based on the deviation between the target value of the current or voltage of the controlled object and the actual detected value. For example, the control circuit 13 calculates the control operation amount by PI compensating the deviation. Details of the method for calculating the control operation amount will be described later. The control circuit 13 switches the operation mode based on the calculated control operation amount.

In the first operation mode, the control circuit 13 performs PWM control on the first leg, fixes the second leg at a duty ratio of 100%, puts the third leg in a fully off state, and makes the fourth leg complementary to the first leg. make it work. Note that when synchronous rectification is not performed, the fourth leg is also completely turned off.

In the second operation mode, the control circuit 13 fixes the first leg and the second leg at a duty ratio of 100%, performs PWM control on the third leg, and causes the fourth leg to operate complementary to the third leg. Note that when synchronous rectification is not performed, the fourth leg is completely turned off.

In the third operation mode, the control circuit 13 performs PWM control on the first leg, fixes the second leg at a duty ratio of 100%, performs PWM control on the third leg, and operates the fourth leg in a complementary manner to the third leg. let Note that when synchronous rectification is not performed, the fourth leg is completely turned off.

The control circuit 13 switches from the first operation mode to the third operation mode at the timing when the duty ratio of the first leg rises to the threshold value α. The control circuit 13 continues the PWM control of the first leg until the timing when the duty ratio of the third leg rises to the threshold value β.

The control circuit 13 switches from the second operation mode to the third operation mode at the timing when the duty ratio of the third leg decreases to the threshold value β. The control circuit 13 continues the PWM control of the third leg until the timing when the duty ratio of the first leg decreases to the threshold value α.

In this manner, the control circuit 13 controls the voltage or current of the power transmitted from the first DC section to the second DC section by controlling the duty ratio of the first leg in the first operation mode. Furthermore, in the second operation mode, the control circuit 13 controls the voltage or current of the power transmitted from the first DC section to the second DC section by controlling the duty ratio of the third leg. Further, in the third operation mode, the control circuit 13 controls the voltage or current of the power transmitted from the first DC section to the second DC section by controlling the duty ratio of the first leg and the duty ratio of the third leg. Control. In the first operation mode, the control circuit 13 causes a transition to the third operation mode before the duty ratio of the first leg reaches 1. Furthermore, the control circuit 13 causes a transition to the third operation mode in the second operation mode before the duty ratio of the third leg reaches 0.

FIG. 8 is a diagram showing a specific example of control output characteristics during voltage step-down operation according to the embodiment of the power conversion device 1. The horizontal axis shows the control operation amount (duty), and the vertical axis shows the output current [A]. The larger the voltage difference between the input voltage V1 on the primary side and the output voltage V2 on the secondary side, the larger the amount of increase in the output current with respect to the increase in the control operation amount. That is, 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.

In the 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 noticeable in DAB converters using the chopper method as shown in Example and Comparative Example 2. In the step-down chopper method, power is transmitted from the primary side to the secondary side using the voltage difference between the first DC power source E1 and the second DC power source 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. On the other hand, in the boost chopper method, the larger the voltage difference between the first DC power source E1 and the second DC power source E2, the more energy is required for boosting the energy stored in the first inductance L1 and the second inductance L2. Therefore, the output current decreases.

In this way, the open loop transfer function changes depending on the voltage conditions on the primary side and the secondary side, and the performance of feedback control deteriorates. The open-loop transfer function is a transfer function that represents how the signal input to the controller changes as it passes through the feedback loop. The open loop transfer function is used as an indicator of whether the feedback system is stable.

FIG. 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 converter (DAB converter in this embodiment), and the detector 131. It is assumed that the performance of the detector 131 also includes the performance of the current sensor 23.

The voltage of the storage battery installed in an electric vehicle varies greatly depending on the SOC (State of Charge) and the vehicle model. Therefore, in the V2H converter, the range of the voltage difference between the input voltage and the output voltage becomes wide, and G(s) changes greatly depending on the voltage difference. That is, the open loop transfer function changes greatly depending on the voltage difference. A large change in the open loop transfer function indicates that the performance of the feedback control is not stable.

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 according to the voltage difference.

FIG. 10 is a diagram showing an example of a proportional gain and integral gain switching table of the controller 135. FIG. 10 is an example in which the controller 135 performs PI control on the deviation between the current command value Iref and the current value detected by the detector 131. In the example shown in FIG. 10, the voltage difference between the input voltage and the output voltage is 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 The voltage is divided into less than 100V and 100V or more, and a proportional (P) gain and an integral (I) gain are set for each voltage classification.

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 division, or may be set to an individual value for each voltage division.

Designers tune the proportional gain and integral gain to optimal values based on experiments and simulations. The designer uses trial and error, the limit sensitivity method, etc. for each voltage section to determine the proportional gain and integral gain that will allow the current command value Iref and the current value detected by the detector 131 to continue to stably match or approximate. Derive. The designer generates a gain switching table for the controller 135 for each operating mode. That is, gain switching tables for the first operation mode (step-down), second operation mode (step-up), and third operation mode (when switching) are generated.

Note that 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, the proportional (P) gain, integral (I) gain, and differential (D) gain of the controller 135 are used. A switching table is generated.

By switching the PI gain or PID gain of the controller 135 in accordance with the voltage difference in this manner, the open loop transfer function can be kept constant regardless of the voltage difference. That is, the performance of feedback control can be stabilized regardless of the voltage difference.

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

The first subtractor 132 calculates the deviation err between the current command value Iref to be the target value and the output current value input from the detector 131. The second subtraction unit 133 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. The control gain determining 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 determining unit 134 determines a proportional gain and an integral gain (hereinafter both are collectively referred to as control gain G) according to the voltage difference by referring to the gain switching table of the determined operation mode.

The controller 135 uses the control gain G set by the control gain determining unit 134 to perform PI control on the deviation err to calculate the control operation amount duty. The PWM generation unit 136 generates a PWM signal for driving the first switching element Q1 to the eighth switching element Q8 based on the calculated control operation amount duty.

FIG. 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 the control gain G on the deviation err between the current command value Iref and the output current value, and calculates the control operation amount duty for generating the PWM signal (S11). The control gain G is a variable value that adaptively changes depending on the voltage difference. Note that in the initial state, a preset default value is used.

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 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 and the threshold value corresponding to the control operation amount of the third leg. The operation mode of the DAB converter is determined based on the relationship β.

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 (boost) (boost in S12), the control circuit 13 refers to the gain switching table for the second operation mode (boost) and sets the control gain G according to the voltage difference. (S14). When the operation mode is the third operation mode (when switching) (when switching in S12), the control circuit 13 refers to the gain switching table of the third operation mode (when switching) and sets the control gain according to the voltage difference. G is set (S15).

The processes from step S10 to step S15 described above are continuously executed (N at S16) until the power conversion process by the DAB converter is completed (Y at S16).

FIGS. 13A to 13C are diagrams for explaining switching patterns of the first switching element Q1 to the eighth switching element Q8 in the embodiment of the power converter 1 during reverse direction transmission. In the switching patterns of the first switching element Q1 to the eighth switching element Q8 shown in FIGS. 6(a) to 6(c), an example has been described in which power is transmitted from the first DC section to the second DC section. In this regard, it is also possible to transmit power from the second DC section to the first DC section. In this case, as shown in FIGS. 13(a) to 13(c), the control circuit 13 outputs a drive signal to be supplied to the first switching element Q1 to the fourth switching element Q4, and to the fifth switching element Q5 to the eighth switching element. The drive signal supplied to Q8 may be replaced.

FIG. 14 is a diagram showing an example of application of the power conversion device 1 according to the embodiment. In the example shown in FIG. 14, the power conversion device 1 according to the embodiment is used in the DC/DC converter 1a in the V2H system 5. The V2H system 5 is a V2H device for linking the electric vehicle 7 and a power receiving point of the commercial power system 2 in the house or a load 4 in the house. 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 charge/discharge cable 6, and when the user inserts the gun connector 6a into the inlet of the electric vehicle 7, the V2H system 5 and the electric vehicle 7 are connected.

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 the 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 the power conversion device 1 (DAB converter) according to the embodiment is used. Charging and discharging of the storage battery mounted on the electric vehicle 7 is performed, for example, in accordance with a charging and discharging sequence defined in CHAdeMO.

The inverter 52 is a bidirectional inverter connected between the DC/DC converter 1a and the distribution board 3. The inverter 52 can convert the DC power input from the DC/DC converter 1a into AC power, and can output the converted AC power to the distribution board 3. A commercial power system 2 and a load 4 are connected to the distribution board 3 . Load 4 is a general term for loads in the house. The inverter 52 can convert AC power supplied from the commercial power system 2 via the distribution board 3 into DC power, and can output the converted DC power to the DC/DC converter 1a.

Note that a DC/DC converter for solar cells, a DC/DC converter for stationary storage batteries, etc. may be connected to the DC bus between the DC/DC converter 1a and the inverter 52.

As described above, according to this embodiment, the performance of feedback control can be stabilized by adaptively changing the control gain G according to the voltage difference between the input voltage and the output voltage. Even if the control output characteristics change significantly depending on 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 in-vehicle storage batteries whose voltage varies greatly depending on the vehicle type and SOC. Further, this embodiment is effective for a DAB converter that employs a chopper drive method in which the control output characteristics vary greatly.

Further, by providing the third operation mode, it is possible to smoothly switch between the step-down operation and the step-up operation. Unlike Comparative Example 2, a dead period does not occur between the step-down operation and the step-up operation, and the occurrence of distortion in the output current can be suppressed.

Further, there is no period in which current flows backward from the second DC power supply E2 to the second inductance L2, the first inductance L1, and the first DC power supply E1, and a reactive current due to the current flowing backward from the second DC power supply E2 is generated. Does not occur. Furthermore, even if the voltage of the second DC power source E2 becomes higher than the voltage of the first DC power source E1, current will not flow backward from the second DC power source E2 to the first DC power source E1. Therefore, recovery loss caused by 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.

Further, according to this embodiment, since control is performed using a PWM method instead of a phase shift method, it is possible to easily generate a dead time in which all of the first switching element Q1 to the eighth switching element Q8 are in an off state. This makes it possible to suppress the occurrence of diode recovery loss. As described above, according to this embodiment, it is possible to smoothly switch between the step-down operation and the step-up operation, and it is possible to achieve high efficiency.

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

In the above embodiment, an example was explained in which power is controlled using the PWM control method on both the primary side and the secondary side. In the following modification, an example will be described in which power is controlled on the primary side using a phase shift method and on the secondary side using a PWM method.

FIGS. 15A to 15C are diagrams for explaining switching patterns of the first switching element Q1 to the eighth switching element Q8 according to a modification of the power conversion device 1. FIG. 15(a) shows a switching pattern in a first operation mode according to a modification. The first operation mode is a voltage step-down operation mode. In the first mode of operation, the phase of one of the first and second legs 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 becomes smaller, 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 types: a commutation period a in which the second diode D2 conducts and performs diode rectification, and a commutation period b in which the second switching element Q2 performs synchronous rectification. It will be done. In this way, in step-down operation, the voltage or current of transmitted power is controlled by phase shift control on the primary side. Note that the control on the secondary side is similar to the control in the above embodiment shown in FIG. 6(a).

FIG. 15(b) shows the switching pattern of the second operation mode. The second operation mode is an operation mode during boosting. The control during boosting is the same as the control in the above embodiment shown in FIG. 6(b).

FIG. 15(c) shows a switching pattern of the third operation mode according to the modification. The third operation mode is an operation mode when switching from a step-down operation to a step-up operation or from a step-up operation to a step-down operation. The third operation mode is activated when the phase difference between the first leg and the second leg reduces to a phase difference θ corresponding to the dead time in the first operation mode. Further, in the second operation mode, it is activated when the duty ratio of the third leg reaches the threshold value β. In the third operation mode, power control using phase shift control on the primary side in the first operation mode and power control using PWM control on the secondary side in the second operation mode coexist.

In this way, by performing phase shift control on the primary side and PWM control on the secondary side, it is possible to realize the first operation mode and the third operation mode. By controlling the phase shift on the primary side, there is no period during which the switching elements Q1 to Q8 are completely turned off in the first operation mode and part of the third operation mode, but synchronous rectification occurs during the commutation state. It can be performed.

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 is also applicable to DAB converters using drive methods other than those described in the above embodiments. For example, the present invention can also be applied to a DAB converter of a drive system that does not include the third operation mode (at the time of switching) in the above embodiment. In this case, there is no need to prepare a gain switching table for the third operation mode (when switching). Further, the present invention is also applicable to DAB converters using the drive methods shown in Comparative Example 1, Comparative Example 2, and Variations, as well as other drive methods. In a drive system where the operation mode is the same for step-down and step-up, it is sufficient to prepare one type of gain switching table.

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

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

[Item 1]
It has a first leg in which a first switching element (Q1) and a second switching element (Q2) are connected in series, and a second leg in which a third switching element (Q3) and a fourth switching element (Q4) are connected in series. a first bridge circuit (11) in which the first leg and the second leg are connected in parallel to a first DC section (E1, Ca);
It has a third leg in which a fifth switching element (Q5) and a sixth switching element (Q6) are connected in series, and a fourth leg in which a seventh switching element (Q7) and an eighth switching element (Q8) are connected in series. a second bridge circuit (12) in which the third leg and the fourth leg are connected in parallel to a second DC section (E2, Cb);
an isolation transformer (TR1) connected between the first bridge circuit (11) and the second bridge circuit (12);
A 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 section (E2, Cb). ,
The control circuit (13) dynamically changes the feedback control gain according to the difference between the voltage of the first DC section (E1, Ca) and the voltage of the second DC section (E2, Cb). A power conversion device (1) characterized by:
According to this, the loop transfer function is prevented from changing according to the difference between the voltage of the first DC part (E1, Ca) and the voltage of the second DC part (E2, Cb), and the performance of feedback control is stabilized. can be done.
[Item 2]
Diodes (D1-D8) are connected or formed in antiparallel to each of the first switching element (Q1) and the eighth switching element (Q8),
The control circuit (13) includes:
The first bridge circuit (11) connects the first DC section (E1, Ca) and the primary winding (n1) of the isolation transformer (TR1), and the second bridge circuit (12) connects the first DC section (E1, Ca) to the primary winding (n1) of the isolation transformer (TR1). A transmission state in which the secondary winding (n2) of TR1) is brought into conduction with the second DC section (E2, Cb), and both ends of the primary winding (n1) are short-circuited within the first bridge circuit (11). , a first operation mode in which the second bridge circuit (12) is controlled to include a commutation state in which the secondary winding (n2) is electrically connected to the second DC section (E2, Cb);
The first bridge circuit (11) connects the first DC section (E1, Ca) and the primary winding (n1), and connects both ends of the secondary winding (n2) to the second bridge circuit (12). a second operating mode that is controlled to include an accumulation state in which a short-circuit occurs in the second operating mode; and a second operating mode that includes the transmission state;
The power conversion device (1) according to item 1, having:
According to this, the performance of feedback control of the DAB converter driven by the chopper method can be stabilized.
[Item 3]
The control circuit (13) includes:
further comprising a third operation mode controlled to include the transmission state, the accumulation state, and the commutation state;
The power conversion device (1) according to item 2.
According to this, it is possible to smoothly switch between the first operation mode and the second operation mode.
[Item 4]
The transmission state includes a first pattern and a second pattern, the commutation state includes a third pattern and a fourth pattern,
In the first pattern, the first switching element (Q1) and the fourth switching element (Q4) are in the on state, and the second switching element (Q2) and the third switching element (Q3) are in the off state, the second bridge circuit (12) is in a rectifying state;
In the second pattern, the second switching element (Q2) and the third switching element (Q3) are in the on state, and the first switching element (Q1) and the fourth switching element (Q4) are in the off state, the second bridge circuit (12) is in a rectifying state;
The third pattern is such that when 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 The 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 such that when 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 The 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.
According to this, it is possible to suppress the reactive current from the second DC section (E2, Cb) during the step-down operation, and it is possible to achieve high efficiency.
[Item 5]
The accumulation state includes a fifth pattern and a sixth pattern,
In the fifth pattern, 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 on state. the element is in the off state,
In the sixth pattern, the second switching element (Q2), the third switching element (Q3), 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 on state. the element is in the off state,
The power conversion device (1) according to item 2.
According to this, it is possible to suppress the reactive current from the second DC section (E2, Cb) during the step-up operation, and it is possible to achieve high efficiency.
[Item 6]
The control circuit (13) controls the voltage or voltage of the power transmitted from the first DC section (E1, Ca) to the second DC section (E2, Cb) by controlling the on/off time of each switching element. control the current,
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 a completely off state, and it is possible to reduce the recovery loss of the diode.
[Item 7]
The control circuit (13) includes:
In the first operation mode, by controlling the duty ratio of the first leg or the second leg,
In the second operation mode, by controlling the duty ratio of the third leg or the fourth leg,
In the third operation mode, by controlling the duty ratio of the first leg or the second leg and the duty ratio of the third leg or the fourth leg,
controlling the voltage or current of power transmitted from the first DC section (E1, Ca) to the second DC section (E2, Cb);
The power conversion device (1) according to item 3.
According to this, in the third operation mode, by making the PWM control of the first operation mode and the PWM control of the second operation mode coexist, the difference between the first operation mode and the second operation mode is achieved. You can switch smoothly.
[Item 8]
The control circuit (13) includes:
In the first operation mode, before the duty ratio of the first leg or the second leg reaches 1, transition to the third operation mode.
The power conversion device (1) according to item 5.
According to this, it is possible to smoothly switch from the first operation mode to the second operation mode.
[Item 9]
The control circuit (13) includes:
In the second operation mode, before the duty ratio of the third leg or the fourth leg reaches 0, transition to the third operation mode.
The power conversion device (1) according to item 7.
According to this, it is possible to smoothly switch from the second operation mode to the first operation mode.
[Item 10]
The control circuit (13) includes:
In the first operating mode,
Turning on the fourth switching element (Q4) in synchronization with turning on the first switching element (Q1);
Turning on the eighth switching element (Q8) or the fifth switching element (Q5) in synchronization with 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 turning off the fourth switching element (Q4) or the first switching element (Q1),
Turning on the third switching element (Q3) in synchronization with turning on the second switching element (Q2);
Turning on the seventh switching element (Q7) or the sixth switching element (Q6) in synchronization with 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 turning off 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 using the PWM method without using the phase shift method, it is possible to easily generate a dead time in a completely off state, and it is possible to reduce recovery loss of the diode.
[Item 11]
The control circuit (13) includes:
In the second operating mode,
Turning on the fourth switching element (Q4) and the sixth switching element (Q6) or the seventh switching element (Q7) in synchronization with turning on the first switching element (Q1);
Turning on the eighth switching element (Q8) or the fifth switching element (Q5) in synchronization with turning off the sixth switching element (Q6) or the seventh switching element (Q7),
Turning off the fourth switching element (Q4), the eighth switching element (Q8), or the fifth switching element (Q5) in synchronization with turning off the first switching element (Q1),
Turning on the third switching element (Q3), the fifth switching element (Q5), or the eighth switching element (Q8) in synchronization with turning on the second switching element (Q2),
Turning on the seventh switching element (Q7) or the sixth switching element (Q6) in synchronization with turning off the fifth switching element (Q5) or the eighth switching element (Q8),
Turning off the third switching element (Q3), the seventh switching element (Q7), or the sixth switching element (Q6) in synchronization with turning off the second switching element (Q2);
The power conversion device (1) according to item 2.
According to this, in the step-up operation, by controlling by the PWM method without using the phase shift method, it is possible to easily generate a dead time in a completely off state, and the recovery loss of the diode can be reduced.
[Item 12]
The control circuit (13) includes:
In the third operating mode,
Turning on the fourth switching element (Q4) and the sixth switching element (Q6) or the seventh switching element (Q7) in synchronization with turning on the first switching element (Q1);
Turning on the eighth switching element (Q8) or the fifth switching element (Q5) in synchronization with turning off the sixth switching element (Q6) or the seventh switching element (Q7),
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 turning off the fourth switching element (Q4) or the first switching element (Q1),
Turning on the third switching element (Q3), the fifth switching element (Q5) or the eighth switching element (Q8) in synchronization with turning on the second switching element (Q2),
Turning on the seventh switching element (Q7) or the sixth switching element (Q6) in synchronization with turning off the fifth switching element (Q5) or the eighth switching element (Q8),
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 turning off the third switching element (Q3) or the second switching element (Q2);
The power conversion device (1) according to item 3.
According to this, when switching between buck operation and boost operation, by controlling using the PWM method without using the phase shift method, it is possible to easily generate a dead time in a completely off state, and to reduce recovery loss of the diode. can be reduced.
[Item 13]
The control circuit (13) includes:
synchronizing the period of the first pattern and the period of the second pattern;
synchronizing the period of the third pattern and the period of the fourth pattern;
The power conversion device (1) according to item 4.
According to this, the operation is symmetrical in positive and negative directions, and it is possible to suppress the occurrence of DC biased magnetism.
[Item 14]
The control circuit (13) includes:
synchronizing the period of the fifth pattern and the period of the sixth pattern;
The power conversion device (1) according to item 5.
According to this, the operation is symmetrical in positive and negative directions, and it is possible to suppress the occurrence of DC biased magnetism.
[Item 15]
The control circuit (13) includes:
When transmitting power from the secondary side to the primary side,
exchanging the drive signal supplied to the first switching element (Q1) - the fourth switching element (Q4) and the drive signal supplied to the fifth switching element (Q5) - the eighth switching element (Q8);
The power conversion device (1) according to item 1.
According to this, a DC/DC converter capable of bidirectional transmission can be realized.
[Item 16]
The first DC section (E1, Ca) includes a storage battery (E1) mounted on the electric vehicle (7),
The power conversion device (1) according to item 1.
According to this, even if the voltage changes greatly depending on the vehicle type or SOC, the performance of the feedback control can be stabilized.

E1 first DC power supply, E2 second DC power supply, 1 power converter, 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 section, 133 second subtraction section, 134 control gain determination section, 135 controller, 136 PWM generation section, Q1-Q8 switching element, D1-D8 diode, C1-C8 Capacity, 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 vehicle.

Claims (16)

It has a first leg in which a first switching element and a second switching element are connected in series, and a second leg in which a third switching element and a fourth switching element are connected in series, and the first leg and the second leg are connected in series. a first bridge circuit connected in parallel to the first DC section;
It has a third leg in which a fifth switching element and a sixth switching element are connected in series, and a fourth leg in which a seventh switching element and an eighth switching element are connected in series, and the third leg and the fourth leg are connected in series. a second bridge circuit connected in parallel to the second DC section;
an isolation transformer connected between the first bridge circuit and the second bridge circuit;
a control circuit that controls the first switching element--the eighth switching element to control the power, voltage, or current of the second DC section,
The power conversion device is characterized in that the control circuit dynamically changes the gain of feedback control according to the difference between the voltage of the first DC section and the voltage of the second DC section. A diode is connected or formed in antiparallel to each of the first switching element and the eighth switching element,
The control circuit includes:
a transmission state in which the first bridge circuit conducts the first DC section and the primary winding of the isolation transformer, and the second bridge circuit conducts the secondary winding of the isolation transformer with the second DC section; A first method of controlling such that both ends of the primary winding are short-circuited in the first bridge circuit, and the second bridge circuit includes a commutation state in which the secondary winding is electrically connected to the second DC section. operating mode,
The first bridge circuit is controlled to include an accumulation state in which the first DC section and the primary winding are electrically connected and both ends of the secondary winding are short-circuited in the second bridge circuit, and the transmission state. a second operating mode,
The power conversion device according to claim 1, having: The control circuit includes:
further comprising a third operation mode controlled to include the transmission state, the accumulation state, and the commutation state;
The power conversion device according to claim 2. The transmission state includes a first pattern and a second pattern, the commutation state includes a third pattern and a fourth pattern,
In the first pattern, 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,
In the second pattern, 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,
In the third pattern, the first switching element or the fourth switching element is in an on state, and the fourth switching element or the first switching element, the second switching element, and the third switching element are in an off state. , the second bridge circuit is in a rectifying state,
In the fourth pattern, the second switching element or the third switching element is in an on state, and the third switching element or the second switching element, the first switching element, and the fourth switching element are in an off state. , the second bridge circuit is in a rectifying state;
The power conversion device according to claim 2. The accumulation state includes a fifth pattern and a sixth pattern,
In the fifth pattern, 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,
In the sixth pattern, 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. The control circuit controls the voltage or current of power transmitted from the first DC section to the second DC section by controlling the on/off time of each switching element.
The power conversion device according to any one of claims 1 to 5. The control circuit includes:
In the first operation mode, by controlling the duty ratio of the first leg or the second leg,
In the second operation mode, by controlling the duty ratio of the third leg or the fourth leg,
In the third operation mode, by controlling the duty ratio of the first leg or the second leg and the duty ratio of the third leg or the fourth leg,
controlling the voltage or current of power transmitted from the first DC section to the second DC section;
The power conversion device according to claim 3. The control circuit includes:
In the first operation mode, before the duty ratio of the first leg or the second leg reaches 1, transition to the third operation mode.
The power conversion device according to claim 7. The control circuit includes:
In the second operation mode, before the duty ratio of the third leg or the fourth leg reaches 0, transition to the third operation mode.
The power conversion device according to claim 7. The control circuit includes:
In the first operating mode,
Turning on the fourth switching element in synchronization with turning on the first switching element;
Turning on the eighth switching element or the fifth switching element in synchronization with 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 turning off the fourth switching element or the first switching element,
Turning on the third switching element in synchronization with turning on the second switching element;
Turning on the seventh switching element or the sixth switching element in synchronization with 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 turning off the third switching element or the second switching element;
The power conversion device according to claim 2. The control circuit includes:
In the second operating mode,
Turning on the fourth switching element, the sixth switching element, or the seventh switching element in synchronization with turning on the first switching element,
Turning on the eighth switching element or the fifth switching element in synchronization with turning off the sixth switching element or the seventh switching element,
Turning off the fourth switching element, the eighth switching element, or the fifth switching element in synchronization with turning off the first switching element,
Turning on the third switching element, the fifth switching element, or the eighth switching element in synchronization with turning on the second switching element,
Turning on the seventh switching element or the sixth switching element in synchronization with turning off 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 turning off the second switching element;
The power conversion device according to claim 2. The control circuit includes:
In the third operating mode,
Turning on the fourth switching element, the sixth switching element, or the seventh switching element in synchronization with turning on the first switching element,
Turning on the eighth switching element or the fifth switching element in synchronization with turning off the sixth switching element or the seventh switching element,
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 turning off 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 turning on the second switching element,
Turning on the seventh switching element or the sixth switching element in synchronization with turning off 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 turning off the third switching element or the second switching element;
The power conversion device according to claim 3. The control circuit includes:
synchronizing the period of the first pattern and the period of the second pattern;
synchronizing the period of the third pattern and the period of the fourth pattern;
The power conversion device according to claim 4. The control circuit includes:
synchronizing the period of the fifth pattern and the period of the sixth pattern;
The power conversion device according to claim 5. The control circuit includes:
When transmitting power from the secondary side to the primary side,
exchanging the drive signal supplied to the first switching element-the fourth switching element and the drive signal supplied to the fifth switching element-the eighth switching element;
The power conversion device according to claim 1. The first DC section includes a storage battery mounted on an electric vehicle.
The power conversion device according to claim 1.

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