Power supply device

Abstract

This enables the creation of a compact, low-loss power supply unit with arbitrarily controllable output current and output voltage. [Solution] The power supply device 100 comprises a group of switch elements 10 having a switch element 11, a switch element 21 connected in series with the low potential side of the switch element 11, and a switch element 31 connected in series with the low potential side of the switch element 21; a reactor 3 with one end connected to a battery 1 and the other end connected between the switch element 21 and the switch element 31; a reactor 4 with one end connected to a battery 2 and the other end connected between the switch element 11 and the switch element 21; a smoothing capacitor 5 connected in parallel with the group of switch elements 10; a capacitor 12 connected in parallel with the switch element 11; and a capacitor 32 connected in parallel with the switch element 31.

Description

Technical Field

[0001] The present invention relates to a power supply device.

Background Art

[0002] Conventionally, there is known a power supply device including a plurality of output circuits capable of arbitrarily switching between series connection and parallel connection to an electrical load by a plurality of switching elements, each output circuit having a reactor and a power supply connected in series, and controlling the operation of each switching element so as to repeatedly and alternately switch between the series connection state and the parallel connection state of the plurality of output circuits, thereby controlling the voltage and current ratio by the plurality of output circuits to arbitrarily set an output balance. (See, for example, Patent Document 1)

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The power supply device described in Patent Document 1 controls the output current and output voltage by operating each switching element in a state where current is flowing to increase or decrease the current of the reactor of each output circuit. Therefore, when the power to be handled is large, there is a problem that the switching loss is large and the device becomes large-sized.

[0005] The present invention has been made in view of the above problems, and its main object is to realize a low-loss and small-sized power supply device capable of arbitrarily controlling an output current and an output voltage.

Means for Solving the Problems

[0006] The power supply device according to the present invention has a first energy storage device and a second energy storage device that each output a predetermined DC voltage, and generates a variable output voltage using the DC voltage output from the first energy storage device and the second energy storage device, and comprises a group of switch elements having a first switch element, a second switch element connected in series with the low potential side of the first switch element, and a third switch element connected in series with the low potential side of the second switch element, a first reactor with one end connected to the first energy storage device and the other end connected between the second switch element and the third switch element, a second reactor with one end connected to the second energy storage device and the other end connected between the first switch element and the second switch element, a smoothing capacitor connected in parallel with the group of switch elements, a first capacitor connected in parallel with the first switch element, and a third capacitor connected in parallel with the third switch element. [Effects of the Invention]

[0007] According to the present invention, a low-loss, compact power supply device can be realized that allows for arbitrary control of output current and output voltage.

[0008] Furthermore, issues, configurations, and effects other than those mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the circuit configuration of a power supply device according to the first embodiment of the present invention. [Figure 2] This figure shows an example of a circuit layout for a group of switching elements. [Figure 3] This diagram shows the switching status of each switch element. [Figure 4] This figure shows an example of the waveform of the power supply when each switch element alternates between state A and state B. [Figure 5] This figure shows an example of the waveform of the power supply when each switch element alternates between state C and state D. [Figure 6] This figure shows an example of a capacitor configuration. [Figure 7] This figure shows the circuit configuration of a power supply device according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0010] (First Embodiment) Figure 1 is a diagram showing the circuit configuration of a power supply device according to the first embodiment of the present invention. The power supply device 100 of this embodiment shown in Figure 1 is used, for example, mounted on a vehicle, and comprises batteries 1 and 2 which are energy storage devices, reactors 3 and 4 connected in series with batteries 1 and 2, respectively, a smoothing capacitor 5 provided on the output side of the power supply device 100, a group of switch elements 10 in which three switch elements 11, 21, and 31 are connected in series, and capacitors 12 and 32 connected in parallel with switch elements 11 and 31, respectively.

[0011] Batteries 1 and 2 each output a predetermined DC voltage. Reactor 3 has one end connected to battery 1 and the other end connected between switch element 21 and switch element 31. Reactor 4 has one end connected to battery 2 and the other end connected between switch element 11 and switch element 21.

[0012] In the switch element group 10, switch elements 11, 21, and 31 are connected in series in this order from the high potential side to the low potential side. That is, switch element 21 is connected in series with the low potential side of switch element 11, and switch element 31 is connected in series with the low potential side of switch element 21. Switch elements 11, 21, and 31 are each constructed using, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and each performs switching operation in response to the gate signal output from a gate drive circuit (not shown). This controls the current flowing from batteries 1 and 2 to reactors 3 and 4, respectively, and allows for arbitrary control of the output current and output voltage of the power supply unit 100. Details of the switching operation of switch elements 11, 21, and 31 will be described later.

[0013] The smoothing capacitor 5 is connected in parallel to the switch element group 10 on the output side of the power supply unit 100, and smooths the output voltage of the power supply unit 100. The output side of the power supply unit 100 is connected to components such as inverters, motors, and other drive system components, as well as ports for connecting to DC-DC converters, onboard chargers, and external fast chargers. These are just examples of components connected to the output side of the power supply unit 100 used in a vehicle; other components may also be connected.

[0014] Figure 2 shows an example of the circuit arrangement of the switch element group 10 in the power supply unit 100. The power supply unit 100 has, for example, circuit boards 41, 42, and 43. A switch element 11 and a capacitor 12 are mounted on circuit board 41, a switch element 21 is mounted on circuit board 42, and a switch element 31 and a capacitor 32 are mounted on circuit board 43. Circuit boards 41 and 42, and circuit boards 42 and 43 are connected to each other by inter-board connection parts 44 and 45, respectively, and the switch elements 11, 21, and 31 are electrically connected to each other via these inter-board connection parts 44 and 45.

[0015] In Figure 2, the switch element 11 and capacitor 12, and the switch element 31 and capacitor 32 are mounted on separate circuit boards 41 and 43, respectively. However, circuit boards 41 and 43 may be integrated so that they are mounted on the same circuit board. Of course, circuit boards 41, 42, and 43 may also be mounted on the same circuit board.

[0016] In FIGS. 1 and 2, for each component of the power supply device 100 excluding the circuit boards 41, 42, 43 and the board-to-board connection parts 44, 45, a circuit code different from the above reference numerals is also noted respectively. Specifically, for the batteries 1, 2, VB1, VB2 are used; for the reactors 3, 4, L1, L2 are used; for the smoothing capacitor 5, Cmain is used; for the switch elements 11, 21, 31, SW1, SW2, SW3 are used; and for the capacitors 12, 32, C1, C3 are used as the circuit codes respectively. In the following, the operation of the power supply device 100 will be described using these circuit codes.

[0017] FIG. 3 is a diagram showing the switching states of the respective switch elements (SW1, SW2, SW3) constituting the switch element group 10. As shown in FIG. 3, each switch element of the switch element group 10 is switched to any one of the states A, B, C, D according to the state of the gate signal input to each. State A is a switching state where SW1 and SW3 are on and SW2 is off; state B is a switching state where SW1 and SW3 are off and SW2 is on. Also, state C is a switching state where SW1 and SW2 are on and SW3 is off; state D is a switching state where SW2 and SW3 are on and SW1 is off. In the power supply device 100, by arbitrarily switching these states A, B, C, D, the direction and magnitude of the current flowing through the reactors L1, L2 can be controlled respectively, and the output current and output voltage can be arbitrarily controlled.

[0018] FIG. 4 is a diagram showing an example of waveforms of the power supply device 100 when each switch element of the switch element group 10 alternately repeats the states A and B in FIG. 2. In FIG. 4, in order from the top, the current I(L1) flowing through L1, the current I(L2) flowing through L2, the current I(SW1) flowing through SW1 and the voltage V(SW1) applied between the drain and source of SW1, the current I(C1) flowing through C1, the current I(SW2) flowing through SW2 and the voltage V(SW2) applied between the drain and source of SW2, the current I(SW3) flowing through SW3 and the voltage V(SW3) applied between the drain and source of SW3, and the current I(C3) flowing through C3 are shown as examples of waveforms corresponding to the passage of time. Note that the voltage waveforms of V(SW1), V(SW2), and V(SW3) are each shown by a dashed line.

[0019] In Fig. 4, when transitioning from state A to state B, SW1 turns off and the voltage V(SW1) rises. At this time, a displacement current (charging side) flows through C1, causing the current I(SW1) of SW1 to fall early, and since the voltage change due to the turn-off of SW1 is mitigated, the turn-off loss of SW1, represented as the product of the current I(SW1) and the voltage V(SW1), can be significantly reduced. Also, SW3 has the same waveform as SW1.

[0020] On the other hand, when transitioning from state A to state B in SW2, the voltage V(SW2) drops, resulting in a synchronous rectification waveform where it turns on after energizing the body diode. Therefore, there is no overlap between the voltage V(SW2) and the current I(SW2) in SW2, and no turn-on loss occurs.

[0021] In Fig. 4, when transitioning from state B to state A, while SW2 turns off and the voltage V(SW2) rises, the voltages V(SW1), V(SW3) of SW1 and SW3 respectively drop. At this time, displacement currents (discharging side) flow through C1 and C3 respectively, causing the current I(SW2) of SW2 to fall early, and since the voltage change due to the turn-off of SW2 is mitigated, the turn-off loss of SW2, represented as the product of the current I(SW2) and the voltage V(SW2), can be significantly reduced.

[0022] On the other hand, when transitioning from state B to state A in SW1 and SW3, the voltages V(SW1), V(SW3) respectively drop, resulting in a synchronous rectification waveform where they turn on after energizing the body diode. Therefore, there is no overlap between the voltage V(SW1) and the current I(SW1), and between the voltage V(SW3) and the current I(SW3) in SW1 and SW3 respectively, and no turn-on loss occurs.

[0023] As described above, in the power supply device 100 of this embodiment, each switch element of the switch element group 10 can be controlled to alternately repeat state A, in which SW1 is turned on, SW2 is turned off, and SW3 is turned on, and state B, in which SW1 is turned off, SW2 is turned on, and SW3 is turned off. This significantly reduces the switching loss of each switch element, and as shown in Figure 4, currents that increase and decrease by alternately switching between positive and negative polarity with a zero-crossing in between flow through L1 and L2, respectively, thereby enabling control of the output current and output voltage.

[0024] Figure 5 shows an example of the waveform of the power supply unit 100 when each switch element in the switch element group 10 alternately repeats state C and state D in Figure 2. Similar to Figure 4, Figure 5 shows, from top to bottom, an example of the waveforms corresponding to the passage of time for the following: current I(L1) flowing through L1, current I(L2) flowing through L2, current I(SW1) flowing through SW1 and the voltage V(SW1) applied between the drain and source of SW1, current I(C1) flowing through C1, current I(SW2) flowing through SW2 and the voltage V(SW2) applied between the drain and source of SW2, current I(SW3) flowing through SW3 and the voltage V(SW3) applied between the drain and source of SW3, and current I(C3) flowing through C3. Note that the voltage waveforms for V(SW1), V(SW2), and V(SW3) are shown as dashed lines.

[0025] In Figure 5, when transitioning from state C to state D, SW1 turns off and the voltage V(SW1) rises, similar to the transition from state A to state B in Figure 4. At this time, a displacement current (charging side) flows through C1, causing the current I(SW1) of SW1 to fall off early, and the voltage change due to the turn-off of SW1 is mitigated. As a result, the turn-off loss of SW1, which is expressed as the product of current I(SW1) and voltage V(SW1), can be significantly reduced.

[0026] On the other hand, in SW3, when transitioning from state C to state D, the voltage V(SW3) drops, the charge stored in C3 is discharged by the displacement current, and then the SW3 body diode is energized, resulting in a synchronous rectified waveform that turns on. Therefore, there is no overlap between the voltage V(SW3) and the current I(SW3) in SW3, and no turn-on loss occurs. Also, since SW2 remains in the ON state, no switching loss occurs.

[0027] In Figure 5, when transitioning from state D to state C, SW3 turns off and the voltage V(SW3) rises. At this time, a displacement current (charging side) flows through C3, causing the current I(SW3) of SW3 to fall off early and mitigating the voltage change due to the turn-off of SW3. As a result, the turn-off loss of SW3, which is expressed as the product of current I(SW3) and voltage V(SW3), can be significantly reduced.

[0028] On the other hand, in SW1, when transitioning from state D to state C, the voltage V(SW1) drops, the charge stored in C1 is discharged by the displacement current, and then the SW1 body diode is energized, resulting in a synchronous rectified waveform when it turns on. Therefore, there is no overlap between the voltage V(SW1) and the current I(SW1) in SW1, and no turn-on loss occurs. Also, since SW2 remains in the ON state, no switching loss occurs.

[0029] As described above, in the power supply device 100 of this embodiment, each switch element of the switch element group 10 can be controlled to alternately repeat state C, in which SW1 is turned on, SW2 is turned on, and SW3 is turned off, and state D, in which SW1 is turned off, SW2 is turned on, and SW3 is turned on. This significantly reduces the switching loss of each switch element, and as shown in Figure 5, currents that increase and decrease by alternately switching between positive and negative polarity with a zero-crossing in between flow through L1 and L2, respectively, thereby enabling control of the output current and output voltage.

[0030] In both Figure 4 and Figure 5, SW1, SW2, and SW3 repeatedly switch in such a way that none of them are turned on simultaneously. That is, at any given moment, at least one of SW1, SW2, or SW3 is switched off. This prevents a short circuit on the output side.

[0031] Furthermore, in order to reduce the turn-off loss of SW1, it is desirable that SW1 and C1 be connected by the shortest possible distance. Therefore, as explained in Figure 2, it is desirable that SW1 and C1 be mounted on the same circuit board 41. Similarly, in order to reduce the turn-off loss of SW3, it is desirable that SW3 and C3 be connected by the shortest possible distance. Therefore, as explained in Figure 2, it is desirable that SW3 and C3 be mounted on the same circuit board 43.

[0032] Furthermore, it is desirable that the capacitances of C1 and C3 be set according to the current immediately before SW1 and SW3 turn off, the drain-source voltage at the time of turn-off, and the turn-off time, respectively. Specifically, for example, if the current immediately before turn-off and the voltage at the time of turn-off are Ioff = 500A and Voff = 800V, respectively, and the turn-off time is toff = 200ns, the charge Q charged to C1 and C3 during the turn-off transient can be calculated using the following equation (1). Q=Ioff×toff / 2=50μC (1)

[0033] The above charge Q is supplied by the turn-off voltage Voff, and the capacitances of C1 and C3 are set so that the current immediately before SW1 and SW3 turn off is absorbed during the turn-off period. In other words, the capacitances of C1 and C3 are set to be greater than or equal to the capacitance C obtained by the following equation (2). C=Q / Voff=50μC / 800V=62.5nF (2)

[0034] In C1 and C3, ceramic capacitors, film capacitors, and the like can be used as means to achieve appropriate capacitance that satisfies the above conditions. However, the usable capacitors are not limited to these, and C1 and C3 may be constructed using other types of capacitors. Furthermore, C1 and C3 may be constructed by connecting multiple capacitor elements in series and / or in parallel with each other.

[0035] Figure 6 shows examples of the configurations of capacitors 12 (C1) and 32 (C3). In Figure 6, (a) shows an example of C1 and C3 composed of one capacitor element 60, (b) shows an example of C1 and C3 composed of two capacitor elements 60 connected in parallel, and (c) shows an example of C1 and C3 composed of four series-connected capacitor elements 60 connected in parallel. Note that C1 and C3 can be configured not only in the configurations of C1 and C3 shown in Figure 6, but also by connecting any number of capacitor elements 60 in series and / or in parallel.

[0036] In addition, various methods can be used to realize C1 and C3 with appropriate capacitances, such as using or adding switch elements with large output capacitance Coss as SW1 and SW3, connecting diodes with large junction capacitance Cj in antiparallel to SW1 and SW3, or using circuit boards 41 and 43 that are adjusted to have large parasitic capacitances.

[0037] In the switch element group 10, before SW1 or SW3 are turned on, there is always a dead time during which both SW1 and SW3 are switched off. If this period is called the dead time period tDT, it is desirable that the dead time period tDT be set to be longer than the time required to discharge the charge of C1 or C3. That is, during the dead time period tDT, the charge stored in C1 or C3 is drawn out by the current I(L1) flowing through L1, and after the drain-source voltage of SW1 or SW3 drops as a result, the body diode of SW1 or SW3 is energized. Therefore, it is necessary to ensure that all the charge stored in C1 or C3 can be drawn out during the dead time period tDT. Specifically, for example, if the capacitance values ​​of C1 and C3 are C = 62.5 nF as expressed in equation (2) above, and the value of the charge Q stored therein is Q = 50 μC as expressed in equation (1) above, the turn-on time required to discharge it is approximately ton = 200 ns. In other words, if the dead time period tDT is 200ns or more, SW1 and SW3 can be soft-switched even when the device is turned on.

[0038] Furthermore, if a capacitor C2 is provided in parallel with SW2 in the switch element group 10, as shown in Figures 4 and 5, there is no particular benefit in reducing switching losses when the currents of L1 and L2 cross to zero. Also, when the operating state is such that the currents of L1 and L2 do not cross to zero, the charge stored in C2 is discharged through the turned-on switch element, leading to an increase in turn-on losses. For this reason, it is preferable not to provide a capacitor C2 connected in parallel with SW2 in the power supply unit 100. In other words, by connecting capacitors C1 and C3 in parallel to only two of the three switch elements SW1, SW2, and SW3 arranged in series in the switch element group 10 (switch element SW1 and switch element SW3), excluding the middle switch element SW2, the most effective configuration for reducing switching losses can be achieved.

[0039] In the power supply unit 100 of this embodiment, the configuration described above makes it possible to avoid increasing the number of parallel switching elements. Therefore, a compact, inexpensive, and highly efficient power supply unit with low losses can be provided.

[0040] According to the first embodiment of the present invention described above, the following effects are achieved.

[0041] (1) The power supply unit 100 has a battery 1 (first energy storage device) and a battery 2 (second energy storage device) which each output a predetermined DC voltage, and generates a variable output voltage using the DC voltages output from battery 1 and battery 2, respectively. The power supply unit 100 includes a group of switch elements 10 having a switch element 11 (SW1), a switch element 21 (SW2) connected in series with the low-potential side of the switch element 11, and a switch element 31 (SW3) connected in series with the low-potential side of the switch element 21; a reactor 3 (L1) with one end connected to the battery 1 and the other end connected between the switch elements 21 and 31; a reactor 4 (L2) with one end connected to the battery 2 and the other end connected between the switch elements 11 and 21; a smoothing capacitor 5 (Cmain) connected in parallel with the group of switch elements 10; a capacitor 12 (C1) connected in parallel with the switch element 11; and a capacitor 32 (C3) connected in parallel with the switch element 31. In this way, a small power supply unit 100 with low loss and the ability to arbitrarily control the output current and output voltage can be realized.

[0042] (2) The switch element 11 and capacitor 12 are mounted on circuit board 41, the switch element 21 is mounted on circuit board 42, and the switch element 31 and capacitor 32 are mounted on circuit board 43. In this way, the switch element group 10, in which the three switch elements 11, 21, and 31 are connected in series, and the capacitors 12 and 32 connected in parallel to the switch elements 11 and 21 can be mounted at high density in the power supply unit 100.

[0043] (3) In the power supply unit 100, the circuit board 41 and the circuit board 43 may be integrated. In this way, the switch element group 10 and the capacitors 12 and 32 can be mounted at a higher density, and the power supply unit 100 can be made smaller.

[0044] (4) Capacitors 12 and 32 may each be composed of multiple capacitor elements connected in series and / or in parallel with each other. In this way, capacitors 12 and 32 with appropriate capacitance can be realized.

[0045] (5) It is desirable that the capacitance of capacitor 12 be set so that the current immediately before the switch element 11 turns off is absorbed during the period when the switch element 11 is turned off. Similarly, it is desirable that the capacitance of capacitor 32 be set so that the current immediately before the switch element 31 turns off is absorbed during the period when the switch element 31 is turned off. In this way, the turn-off losses of the switch elements 11 and 31 can be greatly reduced, thereby realizing a low-loss, compact power supply unit 100.

[0046] (6) Switch elements 11, 21, and 31 each repeatedly perform switching operations so that they are not all turned on at the same time. In this way, a short circuit on the output side is prevented, and the switching operation of each switch element in the switch element group 10 can be controlled.

[0047] (7) The power supply unit 100 has a first switching state (state A) in which the switch element 11 is turned on, the switch element 21 is turned off, and the switch element 31 is turned on, and a second switching state (state B) in which the switch element 11 is turned off, the switch element 21 is turned on, and the switch element 31 is turned off, respectively. Then, as shown in Figure 4, by repeatedly switching between these switching states alternately, the power supply unit 10 controls the switch element group 10 so that currents that alternately increase and decrease in polarity flow through the reactor 3 and reactor 4, respectively. The power supply unit 100 also has a third switching state (state C) in which the switch element 11 is turned on, the switch element 21 is turned on, and the switch element 31 is turned off, and a fourth switching state (state D) in which the switch element 11 is turned off, the switch element 21 is turned on, and the switch element 31 is turned on, respectively. Then, as shown in Figure 5, by repeatedly switching between these states, the switch element group 10 is controlled so that currents that alternately increase and decrease in polarity flow through reactors 3 and 4, respectively. In this way, the output current and output voltage can be arbitrarily adjusted by controlling the switch element group 10.

[0048] (8) The power supply unit 100 has a dead time period tDT between the third switching state and the fourth switching state in which both the switching element 11 and the switching element 31 are switched off. It is desirable that this dead time period tDT be set to be longer than the time required for the charge of capacitor 12 or capacitor 32 to discharge. In this way, all the charge stored in capacitor 12 or capacitor 32 is drawn out during the dead time period tDT, thereby significantly reducing turn-on losses and enabling the realization of a low-loss, compact power supply unit 100.

[0049] (Second embodiment) Figure 7 shows the circuit configuration of a power supply device according to a second embodiment of the present invention. The power supply device 100A of this embodiment shown in Figure 7 differs from the power supply device 100 described in the first embodiment in that the connection to batteries 1 and 2 and the output side is disconnected.

[0050] The power supply unit 100A in Figure 7 discharges the charge of Cmain by repeatedly alternating between the aforementioned states C and D, that is, by repeatedly charging and discharging C1 and C3. This prevents accidents such as electric shock from occurring even if a worker accidentally touches the output side of the power supply unit 100A during maintenance of a vehicle equipped with the power supply unit 100A.

[0051] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0052] 1, 2... Battery 3,4...Reactor 5. Smoothing Capacitor 10... Switch element group 11, 21, 31... Switch elements 12.32 Capacitors 41, 42, 43... Circuit boards 44, 45... Inter-board connection section 60. Capacitor element 100, 100A... Power supply

Claims

1. A power supply device having a first energy storage device and a second energy storage device that each output a predetermined DC voltage, and which generates a variable output voltage using the DC voltage output from the first energy storage device and the second energy storage device, A group of switch elements comprising: a first switch element; a second switch element connected in series with the low potential side of the first switch element; and a third switch element connected in series with the low potential side of the second switch element. A first reactor, with one end connected to the first energy storage device and the other end connected between the second and third switch elements, One end of the second reactor is connected to the second energy storage device, and the other end of the second reactor is connected between the first switch element and the second switch element. A smoothing capacitor connected in parallel to the group of switching elements, A first capacitor connected in parallel to the first switching element, The third switching element is connected in parallel with a third capacitor, power supply.

2. The first switching element and the first capacitor are mounted on the first circuit board. The second switching element is mounted on the second circuit board, The third switching element and the third capacitor are mounted on the third circuit board. The power supply device according to claim 1.

3. The first circuit board and the third circuit board are integrated into one. The power supply device according to claim 2.

4. The first capacitor and the third capacitor are each composed of a plurality of capacitor elements connected in series and / or parallel to one another. The power supply device according to claim 1.

5. The capacitance of the first capacitor is set such that the current immediately before the first switch element turns off is absorbed during the period when the first switch element is turned off. The capacitance of the third capacitor is set so that the current immediately before the third switch element turns off is absorbed during the period when the third switch element is turned off. The power supply device according to claim 1.

6. The first, second, and third switching elements each repeat their switching operations so that they are not all turned on at the same time. The power supply device according to claim 1.

7. A first switching state in which the first switch element is turned on, the second switch element is turned off, and the third switch element is turned on, It has a second switching state in which the first switching element is turned off, the second switching element is turned on, and the third switching element is turned off, The switching element group is controlled such that by repeatedly switching between the first and second switching states, a current that alternately increases and decreases in polarity flows through the first and second reactors, respectively. The power supply device according to claim 6.

8. A third switching state in which the first switching element is turned on, the second switching element is turned on, and the third switching element is turned off, It has a fourth switching state in which the first switching element is turned off, the second switching element is turned on, and the third switching element is turned on, The switching element group is controlled such that the current, which alternates between positive and negative polarity, increases and decreases as it is repeatedly switched between the third and fourth switching states. The power supply device according to claim 6.

9. Between the third switching state and the fourth switching state, there is a dead time period during which both the first and third switching elements are switched to the off state. The dead time period is set to be longer than the time required for the charge of the first capacitor or the third capacitor to discharge. The power supply device according to claim 8.

10. The system includes a disconnection mechanism for disconnecting the first energy storage device and the second energy storage device from the group of switch elements, When the connection between the first and second energy storage devices and the switch element group is released by the disconnection mechanism, the switch element group is controlled to discharge the charge of the smoothing capacitor by alternately repeating the third and fourth switching states. The power supply device according to claim 8.

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