Power conversion device and control method

Abstract

A power conversion device (1) comprises: a first switch group (10) having a first H switch (Q1) and a first L switch (Q2); a first capacitor (C1); a second switch group (20) having a second H switch (Q3) and a second L switch (Q4); a second capacitor (C2); an inductor (L1) connected between a first node (N1) and a second node (N2); a first BS capacitor (C10); a second BS capacitor (C20); and a control circuit (50). When the voltage of the first BS capacitor (C10) or the second BS capacitor (C20) is equal to or less than a first threshold value in a step-up operation mode or a step-down operation mode or when the step-up operation mode or the step-down operation mode continues for a certain period of time or longer, the control circuit (50) performs switching to a step-up / step-down operation mode in a state in which common mode voltage correction for reducing the respective potentials of both terminals of the inductor (L1) by the same amount is performed.

Description

Power conversion device and control method

[0001] The present disclosure relates to a power conversion device and a control method thereof.

[0002] Patent Document 1 discloses a power supply circuit including two bidirectional choppers configured with half-bridge circuits and two bootstrap circuits (hereinafter also referred to as BS circuits) that supply drive power to the high-side switches of each half-bridge circuit, in which the bootstrap capacitors (hereinafter also referred to as BS capacitors) of the two BS circuits are connected via a switch circuit. In principle, a BS circuit cannot charge the BS capacitor when the high-side switch is always on. In this case, there is a risk that the required gate voltage will not be supplied. Therefore, the power supply circuit described in Patent Document 1 shorts the two BS capacitors with a switch circuit, connecting the two BS capacitors in parallel and charging the BS capacitor with a low voltage. This prevents the required gate voltage from being supplied.

[0003] Japanese Patent Application Laid-Open No. 2020-78203

[0004] However, the technology disclosed in Patent Document 1 requires a switch circuit and a control circuit to drive the switch circuit in order to charge the BS capacitor, which increases the number of components and makes the device larger. Also, if the voltages of two BS capacitors drop simultaneously, the BS capacitors cannot be charged.

[0005] Therefore, the present disclosure provides a power conversion device and the like that can charge a BS capacitor while suppressing an increase in the size of the device.

[0006] A power conversion device according to the present disclosure includes: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; a second bootstrap capacitor for supplying drive power to the second high-side switch; and a control circuit for controlling switching of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch. The control circuit has a first operation mode in which the high-side switch and the low-side switch of one of the first switch group and the second switch group are alternately turned on, and the high-side switch of the other of the first switch group and the second switch group is fixed to an on state and the low-side switch is fixed to an off state, and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on, and the second high-side switch and the second low-side switch are alternately turned on, and when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or longer, the control circuit switches to the second operation mode with a common-mode voltage correction performed to reduce the potentials of both terminals of the inductor by the same amount.

[0007] A control method according to the present disclosure is a control method for a power conversion apparatus, the power conversion apparatus comprising: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; and a second bootstrap capacitor for supplying drive power to the second high-side switch. and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on and the second high-side switch and the second low-side switch are alternately turned on. In the control method, when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold in the first operation mode or when the first operation mode has continued for a certain period of time or longer, the control method switches to the second operation mode after performing common-mode voltage correction to reduce the potentials of both terminals of the inductor by the same amount.

[0008] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0009] According to the power conversion device according to one aspect of the present disclosure, the BS capacitor can be charged while suppressing an increase in the size of the device.

[0010] It is a circuit configuration diagram showing an example of a power conversion device according to an embodiment. It is a table for explaining each operation mode. It is a configuration diagram showing an example of a control circuit according to an embodiment. It is a flowchart showing an example of a control method according to another embodiment.

[0011] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0012] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0013] (Embodiment) Hereinafter, a power conversion device according to an embodiment will be described.

[0014] Fig. 1 is a circuit diagram showing an example of a power conversion device 1 according to an embodiment. In addition to the power conversion device 1, Fig. 1 also shows a load 100, a battery 200, and a switch 300. For example, the power conversion device 1 is mounted on a vehicle or the like, and the switch 300 is normally turned on to supply power from the battery 200, such as a lead-acid battery, to the load 100, such as an auxiliary device of the vehicle. Furthermore, the battery 200 charges capacitors C1 and C2 provided in the power conversion device 1. Then, in the event of a short circuit or other abnormality in the battery 200, the switch 300 is turned off, and power is supplied from the capacitor C2 to the load 100.

[0015] The power conversion device 1 is a power conversion device that converts an input voltage and outputs a desired voltage. The power conversion device 1 is a DC-DC converter that is capable of bidirectional voltage step-up and step-down.

[0016] The power conversion device 1 includes a first switch group 10, a second switch group 20, gate drive circuits 30 and 40, a control circuit 50, capacitors C1 and C2, and an inductor L1. ｃ１, the voltage of the capacitor C2 is the voltage V ｃ２ , the current flowing through the inductor L1 is the current i Ｌ is shown. Ｌ If .gtoreq.0, the current flows from the left to the right of the inductor L1 in FIG. 1, and i Ｌ <0, it is assumed that a current flows from the right to the left of the inductor L1 in FIG.

[0017] The capacitor C1 is connected in parallel with the first switch group 10, and the capacitor C2 is connected in parallel with the second switch group 20. The capacitor C1 is an example of a first capacitor, and the capacitor C2 is an example of a second capacitor. The capacitor C2 is also connected in parallel with the load 100.

[0018] The first switch group 10 includes switches Q1 and Q2 connected in series. The switch Q1 is an example of a first high-side switch, and the switch Q2 is an example of a first low-side switch.

[0019] The switch Q1 is, for example, an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the switch Q1 is connected to one end of the capacitor C1, and the source of the switch Q1 is connected to the drain of the switch Q2. The switch Q2 is, for example, an N-channel MOSFET. The drain of the switch Q2 is connected to the source of the switch Q1, and the source of the switch Q2 is connected to the other end of the capacitor C1.

[0020] The second switch group 20 includes switches Q3 and Q4 connected in series. The switch Q3 is an example of a second high-side switch, and the switch Q4 is an example of a second low-side switch.

[0021] The switch Q3 is, for example, an N-channel MOSFET. The drain of the switch Q3 is connected to one end of the capacitor C2, and the source of the switch Q3 is connected to the drain of the switch Q4. The switch Q4 is, for example, an N-channel MOSFET. The drain of the switch Q4 is connected to the source of the switch Q3, and the source of the switch Q4 is connected to the other end of the capacitor C2.

[0022] 1 shows an anti-parallel diode for each switch, and each anti-parallel diode is connected in parallel to the corresponding switch in the equivalent circuit. Specifically, in the equivalent circuit, the anode of each anti-parallel diode is connected to the source of the corresponding switch, and the cathode is connected to the drain of the corresponding switch. Here, the anti-parallel diode may be configured as a body diode built into the switch.

[0023] The inductor L1 is connected between a node N1 between the switches Q1 and Q2 and a node N2 between the switches Q3 and Q4. The node N1 is an example of a first node, and the node N2 is an example of a second node.

[0024] The gate drive circuit 30 is a circuit for driving the switches Q1 and Q2 in the first switch group 10. The gate drive circuit 30 has gate drivers GD1 and GD2, a capacitor C10, a diode D10, and a power supply Vdd1.

[0025] The gate driver GD1 is connected to the gate of the switch Q1 and drives the switch Q1, and the gate driver GD2 is connected to the gate of the switch Q2 and drives the switch Q2.

[0026] A half-bridge circuit such as the first switch group 10 may use a bootstrap circuit to ensure a drive voltage for the gate driver GD1 of the high-side switch Q1. For example, the gate drive circuit 30 includes a capacitor C10 and a diode D10 as a bootstrap circuit. The capacitor C10 is a bootstrap capacitor for supplying drive power to the switch Q1 and is an example of a first bootstrap capacitor. Because the drive voltage for the gate driver GD1 of the high-side switch Q1 can be ensured by a bootstrap circuit with a simple circuit configuration consisting of the diode D10 and the capacitor C10, costs and size can be reduced.

[0027] One end of capacitor C10 is connected to node N1, and the other end is connected to the power supply terminal of gate driver GD1 and the cathode of diode D10. Diode D10 has an anode connected to power supply Vdd1 and a cathode connected to the power supply terminal of gate driver GD1 and capacitor C10. The drive voltage of gate driver GD2 is supplied from power supply Vdd1.

[0028] Since the capacitor C10 is connected to the power supply terminal of the gate driver GD1, the charging voltage of the capacitor C10 becomes the drive voltage of the gate driver GD1, that is, the voltage for controlling the switch Q1. The capacitor C10 is charged when the switch Q2 is in the on state.

[0029] The gate drive circuit 40 is a circuit for driving the switches Q3 and Q4 in the second switch group 20. The gate drive circuit 40 has gate drivers GD3 and GD4, a capacitor C20, a diode D20, and a power supply Vdd2.

[0030] The gate driver GD3 is connected to the gate of the switch Q3 and drives the switch Q3. The gate driver GD4 is connected to the gate of the switch Q4 and drives the switch Q4.

[0031] A half-bridge circuit such as the second switch group 20 may use a bootstrap circuit to ensure a drive voltage for the gate driver GD3 of the high-side switch Q3. For example, the gate drive circuit 40 includes a capacitor C20 and a diode D20 as a bootstrap circuit. The capacitor C20 is a bootstrap capacitor for supplying drive power to the switch Q3 and is an example of a second bootstrap capacitor. The drive voltage for the gate driver GD3 of the high-side switch Q3 can be ensured by a bootstrap circuit with a simple circuit configuration consisting of the diode D20 and the capacitor C20, thereby reducing costs and size.

[0032] One end of capacitor C20 is connected to node N2, and the other end is connected to the power supply terminal of gate driver GD3 and the cathode of diode D20. Diode D20 has an anode connected to power supply Vdd2 and a cathode connected to the power supply terminal of gate driver GD3 and capacitor C20. The drive voltage for gate driver GD4 is supplied from power supply Vdd2.

[0033] Since the capacitor C20 is connected to the power supply terminal of the gate driver GD3, the charging voltage of the capacitor C20 becomes the drive voltage of the gate driver GD3, that is, the voltage for controlling the switch Q3. The capacitor C20 is charged when the switch Q4 is in the on state.

[0034] The control circuit 50 is a circuit for controlling the switching (specifically, turning on and off) of switches (e.g., switches Q1, Q2, Q3, and Q4) included in the power conversion device 1. The control circuit 50 controls the switching of the switches Q1, Q2, Q3, and Q4 by controlling the gate drivers GD1, GD2, GD3, and GD4. Note that control lines connecting the control circuit 50 to the gate drivers GD1, GD2, GD3, and GD4 are not shown in FIG. 1 .

[0035] The control circuit 50 has a first operation mode and a second operation mode. In the first operation mode, the high-side switch and the low-side switch of one of the first switch group 10 and the second switch group 20 are alternately turned on, and the high-side switch of the other of the first switch group 10 and the second switch group 20 is fixed to the on state and the low-side switch is fixed to the off state. In the second operation mode, the switches Q1 and Q2 are alternately turned on, and the switches Q3 and Q4 are alternately turned on. Specifically, the first operation mode is a boost operation mode in which the power conversion device 1 performs a boost operation or a buck operation mode in which the power conversion device 1 performs a buck operation, and the second operation mode is a buck-boost operation mode in which the power conversion device 1 performs a boost / buck operation. Each operation mode will now be described with reference to FIG. 2 .

[0036] FIG. 2 is a table for explaining each operation mode.

[0037] As shown in FIG. ｃ１ <v ｃ２ When the voltages are equal to or greater than the reference voltage, the control circuit 50 sets the operation mode to the first operation mode, which is the boost operation mode. Specifically, in the boost operation mode, the control circuit 50 alternately turns on the switches Q3 and Q4, fixes the switch Q1 to the on state, and fixes the switch Q2 to the off state. Although the boost operation can be achieved in the buck-boost mode described below, the boost operation mode is used from the viewpoint of reducing losses.

[0038] As shown in FIG. ｃ１ >v ｃ２ When the voltages are equal to or greater than the reference voltage, the control circuit 50 switches to the buck operation mode as the first operation mode. Specifically, in the buck operation mode, the control circuit 50 alternately turns on the switches Q1 and Q2, fixes the switch Q3 to the on state, and fixes the switch Q4 to the off state. Although the buck operation can be realized in the buck-boost mode described later, the boost operation mode is used from the viewpoint of reducing losses.

[0039] As shown in FIG. ｃ１ ≒v ｃ２ For example, if 0.95 × v ｃ１ ≦v ｃ２ ≦1.05×v ｃ１ or 0.95 x v ｃ２ ≦v ｃ１ ≦1.05×v ｃ２ When the voltages V and V are equal to or greater than the voltages V, the control circuit 50 switches to the step-up / step-down operation mode as the second operation mode. Specifically, in the step-up / step-down operation mode, the control circuit 50 alternately turns on the switches Q1 and Q2, and alternately turns on the switches Q3 and Q4. ｃ１ ≒v ｃ２ Since there is a possibility that the step-up operation mode and the step-down operation mode may frequently transition in the case of the MOSFET, the step-up / step-down operation mode is used.

[0040] The BS circuit charges the BS capacitor when the low-side switch is on and supplies power to drive the high-side switch from the BS capacitor when the high-side switch is on. However, due to the principle of the BS circuit, the BS capacitor cannot be charged in the step-up operation mode or step-down operation mode in which the high-side switch is always on. Therefore, in the step-up operation mode, the voltage of the capacitor C10 for driving the switch Q1 of the first switch group 10 drops, and as a result, the gate voltage required to turn on the switch Q1 cannot be supplied. In the step-down operation mode, the voltage of the capacitor C20 for driving the switch Q3 of the second switch group 20 drops, and as a result, the gate voltage required to turn on the switch Q3 cannot be supplied.

[0041] On the other hand, in the step-up / step-down operation mode, the switches Q1 and Q2 are alternately turned on, and the switches Q3 and Q4 are alternately turned on, so that the capacitors C10 and C20 can be charged and power for driving each high-side switch can be continuously supplied. However, because the first switch group 10 and the second switch group 20 each perform switching operations, if the step-up / step-down operation is always performed to prevent a drop in the voltage of the capacitors C10 and C20, switching loss increases.

[0042] Therefore, it is conceivable to temporarily switch from the step-up or step-down operation mode to the step-up / step-down operation mode in order to charge the capacitors C10 and C20. However, simply switching from the step-up or step-down operation mode to the step-up / step-down operation mode starts switching of the low-side switch in the off state, causing fluctuations in the average voltage between both terminals of the inductor L1 (specifically, between the nodes N1 and N2), and subjecting the inductor current to control disturbance.

[0043] Therefore, when the voltage of capacitor C10 or C20 (also referred to as the bootstrap capacitor voltage, or BS capacitor voltage) falls below a first threshold in the first operating mode (specifically, the step-up operating mode or the step-down operating mode) or when the first operating mode continues for a certain period of time or longer, the control circuit 50 performs common-mode voltage correction to reduce the potential of each terminal of inductor L1 by the same amount, and then switches to the second operating mode (specifically, the step-up / step-down operating mode). For example, the switches Q1 and Q3 must be fully turned on to keep their on-resistances or on-voltages below an allowable value, and the first threshold is set according to the minimum voltage required to fully turn on the switches Q1 and Q3. Here, whether the BS capacitor voltage falls below the first threshold may be determined by detecting the BS capacitor voltage and comparing it with the first threshold using a comparator. Furthermore, whether the BS capacitor voltage falls below the first threshold value may be determined by estimating in advance the time it takes for the BS capacitor voltage to fall below the first threshold value after the high-side ON state begins, and then limiting the duration of the first operating mode by the estimated time. The details of this operation of the control circuit 50 will be described with reference to FIG.

[0044] FIG. 3 is a configuration diagram showing an example of the control circuit 50 according to the embodiment.

[0045] The control circuit 50 includes a duty generation unit 51, adders 52 and 53, a PWM control unit 54, and a processing unit 55. The control circuit 50 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs executed by the processor. The duty generation unit 51, adders 52 and 53, the PWM control unit 54, and the processing unit 55 are realized by, for example, a processor that executes programs stored in the memory.

[0046] The duty generation unit 51 generates a voltage command value for setting the output voltages of the first switch group 10 and the second switch group 20 (specifically, the voltages at the nodes N1 and N2) to target voltages. The voltage command value is a command value corresponding to the duty ratio of a switch (e.g., switch Q1) in the first switch group 10 and the duty ratio of a switch (e.g., switch Q3) in the second switch group 20. For example, the duty generation unit 51 generates a voltage command value for setting the output voltages of the first switch group 10 and the second switch group 20 (e.g., switch Q3) to target voltages. ｃ１ , voltage v ｃ２ and current i Ｌ Based on the above, the duty generation unit 51 generates a voltage command value corresponding to the duty ratio of the switch Q1 and a voltage command value corresponding to the duty ratio of the switch Q3. The duty generation unit 51 outputs the voltage command value corresponding to the duty ratio of the switch Q1 to the adder 52, and outputs the voltage command value corresponding to the duty ratio of the switch Q3 to the adder 53. Note that, in the following, an example will be described in which the voltage command values ​​are command values ​​corresponding to the duty ratios of the switch Q1 and the switch Q3 (i.e., command values ​​corresponding to the duty ratios of the respective high-side switches), but this is not limiting. For example, the voltage command values ​​may be command values ​​corresponding to the duty ratios of the switch Q2 and the switch Q4 (i.e., command values ​​corresponding to the duty ratios of the respective low-side switches).

[0047] The adder 52 performs common mode voltage correction on the voltage command value corresponding to the acquired duty ratio of the switch Q1. The adder 53 performs common mode voltage correction on the voltage command value corresponding to the acquired duty ratio of the switch Q3. That is, the control circuit 50 performs common mode voltage correction by correcting the duty ratio of the switch in the first switch group 10 (e.g., the switch Q1) and the duty ratio of the switch in the second switch group 20 (e.g., the switch Q3). The duty ratio of the switch Q1 is corrected by subtracting a correction amount D from the command value corresponding to the duty ratio of the switch Q1. ｃｏｍｐ１ The duty ratio of the switch Q3 is corrected by subtracting a value corresponding to the duty ratio of the switch Q3 from the command value corresponding to the duty ratio of the switch Q3. ｃｏｍｐ２ The voltage command value may be the duty ratio itself, or the correction amount may be subtracted from the voltage command value (duty ratio).

[0048] For example, the control circuit 50 performs common-mode voltage correction under the condition that the voltage fluctuation of the capacitor to be controlled, one of the capacitors C1 and C2, does not exceed a third threshold value. For example, the third threshold value is set according to the maximum allowable voltage fluctuation of the capacitors C1 and C2.

[0049] For example, if the capacitor C1 is the control target (i.e., the voltage v ｃ１ is the feedback target), the correction amount D in the common mode voltage correction ｃｏｍｐ１ and D ｃｏｍｐ２ is calculated as follows:

[0050] First, the control circuit 50 calculates the correction amount D from the allowable voltage fluctuation of the capacitor C1 shown in the following equation 1. ｃｏｍｐ１ The upper limit of Δv is calculated using the following formula 2. ｃ１ is the allowable voltage fluctuation of capacitor C1, and c １ is the capacitance of the capacitor C1, and f ｓｗ is the switching frequency of the switches Q1, Q2, Q3, and Q4. The allowable voltage fluctuation of the capacitor C1 is set depending on the application of the power conversion device 1 (for example, the load 100).

[0051]

[0052]

[0053] Next, the control circuit 50 calculates a correction amount D so that the common mode components of the terminal voltage of the first switch group 10 (specifically, the voltage at the node N1) and the terminal voltage of the second switch group 20 (specifically, the voltage at the node N2) match, as shown in the following equation 3: ｃｏｍｐ２ is calculated as in the following equation 4.

[0054]

[0055]

[0056] For example, if the capacitor C2 is the control target (i.e., the voltage v ｃ２ is the feedback target), the correction amount D in the common mode voltage correction ｃｏｍｐ１ and D ｃｏｍｐ２is calculated as follows:

[0057] First, the control circuit 50 calculates the correction amount D from the allowable voltage fluctuation of the capacitor C2 shown in the following equation 5. ｃｏｍｐ２ The upper limit of Δv is calculated using the following formula 6. ｃ２ is the allowable voltage fluctuation of capacitor C2, and c ２ is the capacitance of the capacitor C2. The allowable voltage fluctuation of the capacitor C2 is set depending on the application of the power conversion device 1 (for example, the load 100).

[0058]

[0059]

[0060] Next, the control circuit 50 calculates a correction amount D so that the common mode components of the terminal voltage of the first switch group 10 (specifically, the voltage at the node N1) and the terminal voltage of the second switch group 20 (specifically, the voltage at the node N2) match, as shown in the following equation 7: ｃｏｍｐ１ is calculated as in the following equation 8.

[0061]

[0062]

[0063] In this way, the control circuit 50 performs common-mode voltage correction by decreasing the amount of correction for the duty ratio of the switch in the switch group to which the capacitor C1 or C2 that is not the control target is connected in accordance with an increase in the voltage of the capacitor that is not the control target. Specifically, the control circuit 50 performs common-mode voltage correction by making the amount of correction for the duty ratio of the switch in the switch group to which the capacitor that is not the control target is connected in inverse proportion to the voltage of the capacitor that is not the control target.

[0064] When the capacitor C1 is the object to be controlled, the control circuit 50 adjusts the duty ratio of the switch Q3 in the second switch group 20 to which the capacitor C2 is connected by a correction amount D ｃｏｍｐ２ , the voltage v of capacitor C2 ｃ２Specifically, the control circuit 50 performs common-mode voltage correction by reducing the duty ratio correction amount D of the switch Q3 in the second switch group 20 to which the capacitor C2 is connected. ｃｏｍｐ２ , the voltage v of capacitor C2 ｃ２ Common mode voltage compensation is performed by making it inversely proportional to

[0065] When the capacitor C2 is the object to be controlled, the control circuit 50 adjusts the duty ratio of the switch Q1 in the first switch group 10 to which the capacitor C1 is connected by a correction amount D ｃｏｍｐ１ , the voltage v of the capacitor C1 ｃ１ Specifically, the control circuit 50 performs common-mode voltage correction by reducing the duty ratio of the switch Q1 in the first switch group 10 connected to the capacitor C1. ｃｏｍｐ１ , the voltage v of the capacitor C1 ｃ１ Common mode voltage compensation is performed by making it inversely proportional to

[0066] More specifically, the control circuit 50 performs common-mode voltage correction by decreasing the correction amount of the duty ratio of the switch in the switch group to which the capacitor C1 or C2 that is not the control target is connected in accordance with an increase in the voltage of the capacitor that is not the control target, and by increasing the correction amount in accordance with an increase in the voltage of the capacitor that is the control target. Specifically, the control circuit 50 performs common-mode voltage correction by making the correction amount of the duty ratio of the switch in the switch group to which the capacitor that is not the control target is connected inversely proportional to the voltage of the capacitor that is not the control target and proportional to the voltage of the capacitor that is the control target.

[0067] When the capacitor C1 is the object to be controlled, the control circuit 50 adjusts the duty ratio of the switch Q3 in the second switch group 20 to which the capacitor C2 is connected by a correction amount D ｃｏｍｐ２ , the voltage v of capacitor C2 ｃ２ and the voltage v of the capacitor C1 ｃ１ Specifically, as shown in the above formula 4, the control circuit 50 performs common-mode voltage correction by increasing the duty ratio correction amount D of the switch Q3 in the second switch group 20 to which the capacitor C2 is connected.ｃｏｍｐ２ , the voltage v of capacitor C2 ｃ２ and the voltage v of the capacitor C1 ｃ１ The common mode voltage is corrected by making it proportional to

[0068] When the capacitor C2 is the object to be controlled, the control circuit 50 adjusts the duty ratio of the switch Q1 in the first switch group 10 to which the capacitor C1 is connected by a correction amount D ｃｏｍｐ１ , the voltage v of the capacitor C1 ｃ１ and the voltage v of the capacitor C2 ｃ２ Specifically, as shown in the above equation 8, the control circuit 50 performs common-mode voltage correction by increasing the duty ratio correction amount D of the switch Q1 in the first switch group 10 to which the capacitor C1 is connected. ｃｏｍｐ１ , the voltage v of the capacitor C1 ｃ１ and the voltage v of the capacitor C2 ｃ２ The common mode voltage is corrected by making it proportional to

[0069] Furthermore, the control circuit 50 reduces the upper limit of the correction amount of the duty ratio of the switch in the switch group to which the controlled capacitor is connected in accordance with an increase in the absolute value of the current flowing through the inductor L1. Specifically, the control circuit 50 makes the upper limit of the correction amount of the duty ratio of the switch in the switch group to which the controlled capacitor is connected in inverse proportion to the absolute value of the current flowing through the inductor L1.

[0070] When the capacitor C1 is the object to be controlled, the control circuit 50 calculates a correction amount D ｃｏｍｐ１ Specifically, as shown in the above equation 2, the control circuit 50 reduces the upper limit of the duty ratio of the switch Q1 in the first switch group 10 connected to the capacitor C1. ｃｏｍｐ１ The upper limit of is inversely proportional to the absolute value of the current flowing through the inductor L1.

[0071] When the capacitor C2 is the object to be controlled, the control circuit 50 calculates a correction amount D ｃｏｍｐ２Specifically, as shown in the above equation 6, the control circuit 50 reduces the upper limit of the duty ratio of the switch Q3 in the second switch group 20 connected to the capacitor C2. ｃｏｍｐ２ The upper limit of is inversely proportional to the absolute value of the current flowing through the inductor L1.

[0072] The fluctuation in the voltage of the controlled capacitor increases as the absolute value of the current flowing through inductor L1 increases. Therefore, as described above, the upper limit of the correction amount for the duty ratio of the switches in the switch group to which the controlled capacitor is connected is reduced in accordance with an increase in the absolute value of the current flowing through inductor L1, specifically, by making it inversely proportional to the absolute value of the current flowing through inductor L1, it is possible to suppress the fluctuation in the voltage of the controlled capacitor.

[0073] For example, the power conversion device 1 may be provided with an ammeter and a voltmeter, and the control circuit 50 may calculate the current i measured by the ammeter. Ｌ and the voltage measured by the voltmeter v ｃ１ and voltage v ｃ２ Alternatively, the control circuit 50 may acquire the current i Ｌ The command value for flowing and the voltage v ｃ１ and voltage v ｃ２ By obtaining the command value for outputting the current i Ｌ and voltage v ｃ１ and voltage v ｃ２ may be obtained.

[0074] The adders 52 and 53 calculate the correction amount D from the voltage command value for the first switch group 10. ｃｏｍｐ１ is subtracted from the voltage command value for the second switch group 20, and the correction amount D ｃｏｍｐ２By subtracting this, the duty ratio of the switch Q1 in the first switch group 10 and the switch Q3 in the second switch group 20 decreases. This allows the potentials of both terminals of inductor L1 to be reduced by the same amount while suppressing fluctuations in the voltage of the capacitor to be controlled. Note that, depending on the variations in the characteristics of each element, it may not be possible to reduce the potentials of both terminals of inductor L1 by exactly the same amount through common-mode voltage correction. For this reason, in this specification, "the same amount" not only means the exact same amount, but also includes the meaning of approximately the same amount. For example, even if the amount of reduction in one potential differs from the amount of reduction in the other potential by ±5%, it is still considered to be the same amount.

[0075] When common mode voltage correction is not performed, the adders 52 and 53 output the acquired voltage command values ​​to the PWM controller 54 as they are.

[0076] The PWM control unit 54 generates a PWM signal for controlling the switching of the switches Q1 and Q2 and the switches Q3 and Q4 based on the voltage command values ​​(e.g., voltage command values ​​that have been subjected to common-mode voltage correction) output from the addition units 52 and 53.

[0077] The processing unit 55 performs processing to reflect the dead time in the PWM signal generated by the PWM control unit 54. The processing unit 55 outputs the PWM signal for the switches Q1 and Q2, in which the dead time is reflected, to the gates of the switches Q1 and Q2 (specifically, gate drivers GD1 and GD2), and outputs the PWM signal for the switches Q3 and Q4, in which the dead time is reflected, to the gates of the switches Q3 and Q4 (specifically, gate drivers GD3 and GD4).

[0078] For example, the control circuit 50 may switch to the second operation mode (specifically, the buck-boost operation mode) when the BS capacitor voltage falls below the first threshold in the first operation mode (specifically, the boost operation mode or the buck operation mode) or when the first operation mode has continued for a certain period of time or longer. Then, when the BS capacitor voltage exceeds the second threshold or when the second operation mode has continued for a certain period of time or longer, the control circuit 50 may switch back to the first operation mode by resetting the correction amount of the common-mode voltage correction to zero. When transitioning to the first operation mode, whether the BS capacitor voltage exceeds the second threshold may be determined by detecting the BS capacitor voltage and comparing it with the first threshold using a comparator. Furthermore, whether the BS capacitor voltage exceeds the second threshold may be determined by estimating in advance the time it takes for the BS capacitor voltage to increase to or exceed the second threshold from the start of the second operation mode and imposing a limit on the duration of the second operation mode by the estimated time. Here, the second threshold may be set to the first threshold. The second threshold value may be set to a value greater than the first threshold value. In this case, chattering during mode transition between the first and second operating modes can be prevented by providing hysteresis.

[0079] In the buck-boost operation mode, the first switch group 10 and the second switch group 20 each perform a switching operation, resulting in increased switching loss. Therefore, if the BS capacitor voltage increases (i.e., the BS capacitor is charged) after switching from the boost or buck operation mode to the buck-boost operation mode, the operation mode is switched back to the boost or buck operation mode. In other words, the operation mode is switched back to the buck-boost operation mode only when the BS capacitor voltage decreases. This reduces loss. Since common-mode voltage correction is performed when switching to the buck-boost operation mode, the correction amount of the common-mode voltage correction is reset to zero when switching from the buck-boost operation mode to the boost or buck operation mode. In other words, the operation mode can be switched to the boost or buck operation mode without common-mode voltage correction.

[0080] In the above description, the first operating mode is transitioned to the second operating mode when the BS capacitor voltage drops to the first threshold. However, the present disclosure is not limited to this. For example, by restricting the duration of the first operating mode, the second operating mode may be transitioned to before the BS capacitor voltage drops to the first threshold. Furthermore, while the second operating mode is transitioned to the first operating mode when the BS capacitor voltage exceeds the second threshold, the transition does not need to occur immediately. For example, by restricting the duration of the second operating mode, the first operating mode may be transitioned to after a certain time. Even in this case, the switching loss is reduced compared to when the device is constantly operating in the second operating mode, and the effect can still be obtained.

[0081] As described above, in the step-up operation mode or the step-down operation mode, the high-side switch is fixed to the on state and the low-side switch is fixed to the off state, which may cause the voltage of the BS capacitor to drop and prevent the supply of the gate voltage required to drive the high-side switch. On the other hand, in the step-up / step-down operation mode, the high-side switch and the low-side switch are alternately turned on, allowing the BS capacitor to be charged. Therefore, by switching to the step-up / step-down operation mode when the BS capacitor voltage drops in the step-up operation mode or the step-down operation mode, the BS capacitor can be charged and the gate voltage required to drive the high-side switch can be supplied. In this way, since a switch circuit for charging the BS capacitor is not required, the BS capacitor can be charged while suppressing an increase in the device size.

[0082] However, simply switching from the step-up or step-down operation mode to the step-up / step-down operation mode causes fluctuations in the average voltage across the inductor L1, resulting in control disturbances to the inductor current. Therefore, the inductor is switched to the step-up / step-down operation mode after common-mode voltage correction is performed to reduce the potentials of both terminals of the inductor L1 by the same amount. This reduces the common-mode voltage while suppressing fluctuations in the average voltage across the terminals of the inductor L1. Therefore, the BS capacitor can be charged while suppressing control disturbances to the inductor current.

[0083] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0084] For example, the present disclosure can be realized not only as the power conversion device 1 but also as a control method including steps (processing) performed by components (for example, the control circuit 50) that make up the power conversion device 1.

[0085] FIG. 4 is a flowchart showing an example of a control method according to another embodiment.

[0086] The control method is a control method for a power conversion apparatus, the power conversion apparatus including: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; and a second bootstrap capacitor for supplying drive power to the second high-side switch, The control method has a first operation mode in which the high-side switch and the low-side switch of the other switch group out of the first switch group and the second switch group are alternately turned on, the high-side switch of the first switch group and the second switch group are fixed to an on state, and the low-side switch is fixed to an off state; and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on, and the second high-side switch and the second low-side switch are alternately turned on. As shown in FIG. 4 , in the first operation mode, when the bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold value or when the first operation mode has continued for a certain period of time or longer, the control method switches to the second operation mode (step S12) after performing common-mode voltage correction to reduce the potentials of both terminals of the inductor by the same amount (step S11).

[0087] Alternatively, the control method may switch to the second operation mode when the bootstrap capacitor voltage becomes equal to or lower than the first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or more, and then switch back to the first operation mode (step S14) by returning the correction amount of the common-mode voltage correction to zero when the bootstrap capacitor voltage exceeds the second threshold value or when the second operation mode has continued for a certain period of time or more.

[0088] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0089] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0090] In the above embodiment, each component included in the power conversion device 1 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0091] Some or all of the functions of the power conversion device 1 according to the above embodiment are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into single chips, or may be integrated into a single chip that includes some or all of the functions. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI.

[0092] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derived technologies, it is natural that each component included in the power conversion device 1 can be integrated using that technology.

[0093] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope that does not deviate from the intent of this disclosure.

[0094] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0095] (Technology 1) A power supply circuit including: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; a second bootstrap capacitor for supplying drive power to the second high-side switch; and a control circuit for controlling switching of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on and the second high-side switch and the second low-side switch are alternately turned on, and when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or longer, the power conversion device switches to the second operation mode with a common-mode voltage correction performed to reduce the potentials of both terminals of the inductor by the same amount.

[0096] In the first operating mode, the high-side switch is fixed to the ON state and the low-side switch is fixed to the OFF state, which may cause the voltage of the BS capacitor to drop and prevent the supply of the gate voltage required to drive the high-side switch. On the other hand, in the second operating mode, the high-side switch and the low-side switch are alternately turned ON, allowing the BS capacitor to be charged. Therefore, by switching to the second operating mode when the BS capacitor voltage drops in the first operating mode, the BS capacitor can be charged and the gate voltage required to drive the high-side switch can be supplied. In this way, a switch circuit for charging the BS capacitor is not required, allowing the BS capacitor to be charged while suppressing an increase in the device size.

[0097] However, simply switching from the first operating mode to the second operating mode would cause the average voltage across the inductor to fluctuate, resulting in control disturbances to the inductor current. Therefore, the second operating mode is switched to after common-mode voltage correction is performed to reduce the potential of both terminals of the inductor by the same amount. This allows the common-mode voltage to be reduced while suppressing fluctuations in the average voltage across the inductor. Therefore, the BS capacitor can be charged while suppressing control disturbances to the inductor current.

[0098] (Technology 2) In the power conversion device according to Technology 1, the control circuit switches to the second operation mode when the bootstrap capacitor voltage becomes equal to or lower than the first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or more, and then switches to the first operation mode by returning the correction amount of the common-mode voltage correction to zero when the bootstrap capacitor voltage exceeds a second threshold value or when the second operation mode has continued for a certain period of time or more.

[0099] In the second operating mode, the first and second switch groups each perform a switching operation, resulting in increased switching loss. Therefore, if the BS capacitor voltage increases after switching from the first operating mode to the second operating mode (i.e., if the BS capacitor is charged), the second operating mode is switched back to the first operating mode. In other words, the first operating mode is switched to the second operating mode only when the BS capacitor voltage decreases. This reduces loss. Because common-mode voltage correction is performed when switching to the second operating mode, the amount of common-mode voltage correction is returned to zero when switching from the second operating mode to the first operating mode. In other words, switching to the first operating mode is possible without common-mode voltage correction.

[0100] (Technology 3) The power conversion device according to Technology 1 or 2, wherein the control circuit performs the common-mode voltage correction by correcting a duty ratio of the switches in the first switch group and a duty ratio of the switches in the second switch group.

[0101] In this way, by correcting the duty ratio of the switches in each switch group, the potentials of both terminals of the inductor can be reduced by the same amount.

[0102] (Technology 4) The control circuit performs the common-mode voltage correction under the condition that the fluctuation in the voltage of the capacitor to be controlled, one of the first capacitor and the second capacitor, does not exceed a third threshold. A power conversion device according to any one of technologies 1 to 3.

[0103] This makes it possible to reduce the potentials of both terminals of the inductor by the same amount while suppressing fluctuations in the voltage of the capacitor to be controlled.

[0104] (Technology 5) The power conversion device according to Technology 4, wherein the control circuit performs the common-mode voltage correction by decreasing a correction amount of a duty ratio of a switch in a switch group to which a capacitor that is not a control target out of the first capacitor and the second capacitor is connected, in accordance with an increase in the voltage of the capacitor that is not a control target.

[0105] In this way, by reducing the amount of correction for the duty ratio of the switches in the switch group to which the capacitors that are not the control target are connected in accordance with the increase in the voltage of the capacitors that are not the control target, it is possible to reduce the potential of each of the terminals of the inductor by the same amount.

[0106] (Technology 6) The power conversion device according to Technology 5, wherein the control circuit performs the common-mode voltage correction by making a correction amount of a duty ratio of a switch in a switch group to which the capacitor that is not the control target is connected in inverse proportion to the voltage of the capacitor that is not the control target.

[0107] In this way, by making the correction amount of the duty ratio of the switches in the switch group to which the capacitor that is not the control target is connected in inverse proportion to the voltage of the capacitor that is not the control target, it is possible to reduce the potential of each of the terminals of the inductor by the same amount.

[0108] (Technology 7) The power conversion device according to Technology 4, wherein the control circuit performs the common-mode voltage correction by decreasing a correction amount of a duty ratio of a switch in a switch group to which a capacitor that is not a control target out of the first capacitor and the second capacitor is connected in accordance with an increase in the voltage of the capacitor that is not a control target, and by increasing the correction amount in accordance with an increase in the voltage of the capacitor that is a control target.

[0109] In this way, by decreasing the correction amount of the duty ratio of the switches in the switch group to which the capacitors that are not the control target are connected in accordance with an increase in the voltage of the capacitors that are not the control target, and by increasing it in accordance with an increase in the voltage of the capacitors that are the control target, it is possible to reduce the potential of each of the terminals of the inductor by the same amount.

[0110] (Technology 8) The power conversion device according to Technology 7, wherein the control circuit performs the common-mode voltage correction by making a correction amount of a duty ratio of a switch in a switch group to which the capacitor not to be controlled is connected inversely proportional to the voltage of the capacitor not to be controlled and proportional to the voltage of the capacitor to be controlled.

[0111] In this way, by making the correction amount of the duty ratio of the switches in the switch group to which the capacitor that is not the controlled object is connected inversely proportional to the voltage of the capacitor that is not the controlled object and proportional to the voltage of the capacitor that is the controlled object, it is possible to reduce the potential of each of the terminals of the inductor by the same amount.

[0112] (Technology 9) A power conversion device according to any one of Techniques 4 to 8, wherein the control circuit reduces an upper limit of a correction amount of a duty ratio of a switch in a group of switches to which the capacitor to be controlled is connected in accordance with an increase in the absolute value of a current flowing through the inductor.

[0113] The voltage fluctuation of the controlled capacitor increases as the absolute value of the current flowing through the inductor increases. Therefore, by decreasing the upper limit of the correction amount for the duty ratio of the switches in the switch group to which the controlled capacitor is connected in accordance with the increase in the absolute value of the current flowing through the inductor, it is possible to suppress the voltage fluctuation of the controlled capacitor.

[0114] (Technology 10) The power conversion device according to Technology 9, wherein the control circuit makes an upper limit of a correction amount of a duty ratio of a switch in a group of switches to which the capacitor to be controlled is connected inversely proportional to an absolute value of a current flowing through the inductor.

[0115] In this way, by making the upper limit of the correction amount for the duty ratio of the switches in the switch group to which the controlled capacitor is connected inversely proportional to the absolute value of the current flowing through the inductor, fluctuations in the voltage of the controlled capacitor can be suppressed.

[0116] (Technology 11) A control method for a power conversion device, the power conversion device comprising: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; and a second bootstrap capacitor for supplying drive power to the second high-side switch, the control method comprising: the control method has a first operation mode in which the high-side switch and the low-side switch of one of the second switch groups are alternately turned on, and the high-side switch of the other of the first switch group and the second switch group is fixed to an on state and the low-side switch is fixed to an off state; and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on, and the second high-side switch and the second low-side switch are alternately turned on, wherein when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold in the first operation mode, the control method switches to the second operation mode after performing common-mode voltage correction to reduce the potentials of both terminals of the inductor by the same amount.

[0117] This makes it possible to provide a control method that can charge the BS capacitor while suppressing an increase in the size of the device.

[0118] The present disclosure can be applied to a power conversion device that steps up or steps down an input voltage and outputs the stepped-up voltage.

[0119] REFERENCE SIGNS LIST 1 Power conversion device 10 First switch group 20 Second switch group 30, 40 Gate drive circuit 50 Control circuit 51 Duty generation unit 52, 53 Addition unit 54 PWM control unit 55 Processing unit 100 Load 200 Battery 300, Q1, Q2, Q3, Q4 Switches C1, C2, C10, C20 Capacitors D10, D20 Diodes GD1, GD2, GD3, GD4 Gate driver L1 Inductor N1, N2 Nodes Vdd1, Vdd2 Power supply

Claims

1. A power supply comprising: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; a second bootstrap capacitor for supplying drive power to the second high-side switch; and a control circuit for controlling switching of the first high-side switch, the first low-side switch, the second high-side switch, and the second low-side switch, a first operation mode in which the high-side switch and the low-side switch of one of the first switch group and the second switch group are alternately turned on, and the high-side switch of the other of the first switch group and the second switch group is fixed to an on state and the low-side switch is fixed to an off state; and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on, and the second high-side switch and the second low-side switch are alternately turned on, and when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or longer, the power conversion device switches to the second operation mode with a common-mode voltage correction performed to reduce the potentials of both terminals of the inductor by the same amount.

2. The power conversion device according to claim 1, wherein the control circuit switches to the second operation mode when the bootstrap capacitor voltage becomes equal to or lower than the first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or more, and then switches to the first operation mode by returning the correction amount of the common-mode voltage correction to zero when the bootstrap capacitor voltage exceeds the second threshold value or when the second operation mode has continued for a certain period of time or more.

3. The power conversion device according to claim 1, wherein the control circuit performs the common-mode voltage correction by correcting a duty ratio of the switches in the first group of switches and a duty ratio of the switches in the second group of switches.

4. The power conversion device according to claim 1, wherein the control circuit performs the common-mode voltage correction under the condition that fluctuations in the voltage of the capacitor to be controlled, one of the first capacitor and the second capacitor, do not exceed a third threshold value.

5. The power conversion device according to claim 4, wherein the control circuit performs the common-mode voltage correction by reducing a correction amount of a duty ratio of a switch in a group of switches to which a capacitor that is not the object of control, of the first capacitor and the second capacitor, is connected, in accordance with an increase in the voltage of the capacitor that is not the object of control.

6. The power conversion device according to claim 5, wherein the control circuit performs the common-mode voltage correction by making the amount of correction of the duty ratio of the switch in the switch group to which the capacitor not to be controlled is connected in inverse proportion to the voltage of the capacitor not to be controlled.

7. The power conversion device according to claim 4, wherein the control circuit performs the common-mode voltage correction by decreasing a correction amount of a duty ratio of a switch in a group of switches to which one of the first capacitor and the second capacitor that is not the controlled capacitor is connected in accordance with an increase in the voltage of the capacitor that is not the controlled capacitor, and by increasing the correction amount in accordance with an increase in the voltage of the capacitor that is the controlled capacitor.

8. The power conversion device according to claim 7, wherein the control circuit performs the common-mode voltage correction by making the amount of correction of the duty ratio of the switch in the group of switches to which the capacitor not to be controlled is connected inversely proportional to the voltage of the capacitor not to be controlled and proportional to the voltage of the capacitor to be controlled.

9. The power conversion device according to any one of claims 4 to 8, wherein the control circuit reduces an upper limit of a correction amount for a duty ratio of a switch in a group of switches to which the controlled capacitor is connected in accordance with an increase in the absolute value of a current flowing through the inductor.

10. The power conversion device according to claim 9, wherein the control circuit sets an upper limit of the correction amount for the duty ratio of the switch in the group of switches to which the capacitor to be controlled is connected to be inversely proportional to the absolute value of the current flowing through the inductor.

11. A control method for a power conversion device, the power conversion device comprising: a first switch group having a first high-side switch and a first low-side switch connected in series; a first capacitor connected in parallel with the first switch group; a second switch group having a second high-side switch and a second low-side switch connected in series; a second capacitor connected in parallel with the second switch group; an inductor connected between a first node between the first high-side switch and the first low-side switch and a second node between the second high-side switch and the second low-side switch; a first bootstrap capacitor for supplying drive power to the first high-side switch; and a second bootstrap capacitor for supplying drive power to the second high-side switch, the control method comprising: a first operation mode in which the high-side switch and the low-side switch of one switch group out of the first switch group and the second switch group are alternately turned on, and the high-side switch of the other switch group out of the first switch group and the second switch group is fixed to an on state and the low-side switch is fixed to an off state; and a second operation mode in which the first high-side switch and the first low-side switch are alternately turned on and the second high-side switch and the second low-side switch are alternately turned on, wherein the control method switches to the second operation mode after performing common-mode voltage correction to reduce the potentials of both terminals of the inductor by the same amount when a bootstrap capacitor voltage of the first bootstrap capacitor or the second bootstrap capacitor becomes equal to or lower than a first threshold value in the first operation mode or when the first operation mode has continued for a certain period of time or longer.

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