Power supply apparatus
The power supply device addresses high switching losses and size issues by using energy storage devices, switch elements, and capacitors to alternately switch states, resulting in a low-loss, compact design with efficient current and voltage control.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ASTEMO LTD
- Filing Date
- 2025-08-26
- Publication Date
- 2026-05-21
AI Technical Summary
Conventional power supply devices with multiple output circuits face high switching losses and large size when handling large power loads due to the need for controlling output current and voltage, leading to inefficiencies and bulkiness.
A power supply device incorporating a first and second energy storage device, switch elements, reactors, and capacitors configured to alternately switch between different states to control output current and voltage, minimizing switching losses and device size.
The solution achieves a low-loss, compact power supply device capable of arbitrary control over output current and voltage by reducing switching losses and optimizing component arrangement.
Smart Images
Figure JP2025029899_21052026_PF_FP_ABST
Abstract
Description
Power supply device
[0001] The present invention relates to a power supply device.
[0002] Conventionally, there is 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, and each output circuit has a reactor and a power supply connected in series. By 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, a power supply device capable of arbitrarily setting an output balance by controlling the voltage and current ratio by the plurality of output circuits is known. (See, for example, Patent Document 1)
[0003] Japanese Patent Application Laid-Open No. 2014-64416
[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.
[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.
[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.
[0009] This figure shows the circuit configuration of a power supply device according to the first embodiment of the present invention. This figure shows an example of the circuit arrangement of the switch element group. This figure shows the switching state of each switch element. This figure shows an example of the waveform of the power supply device when each switch element alternates between state A and state B. This figure shows an example of the waveform of the power supply device when each switch element alternates between state C and state D. This figure shows an example of the capacitor configuration. This figure shows the circuit configuration of a power supply device according to the second embodiment of the present 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 is connected to battery 1 at one end and to the space between switch element 21 and switch element 31 at the other end. Reactor 4 is connected to battery 2 at one end and to the space between switch element 11 and switch element 21 at the other end.
[0012] In the switch element group 10, the 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. Each of the switch elements 11, 21, and 31 is constructed using, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and performs switching operations in response to gate signals 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. Connected to the output side of the power supply unit 100 are, for example, drive system components such as inverters and motors, as well as connection ports for 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, and other components may be connected as well.
[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 Figures 1 and 2, each component of the power supply unit 100, excluding the circuit boards 41, 42, and 43 and the inter-board connection parts 44 and 45, is given a circuit code separate from the reference numerals mentioned above. Specifically, batteries 1 and 2 are given the circuit codes VB1 and VB2, reactors 3 and 4 are given the codes L1 and L2, smoothing capacitor 5 is given the code Cmain, switching elements 11, 21, and 31 are given the codes SW1, SW2, and SW3, and capacitors 12 and 32 are given the codes C1 and C3. The operation of the power supply unit 100 will be explained below using these circuit codes.
[0017] Figure 3 is a diagram showing the switching states of each switch element (SW1, SW2, SW3) that constitute the switch element group 10. As shown in Figure 3, each switch element of the switch element group 10 is switched to one of states A, B, C, or D depending on the state of the gate signal input to it. State A is when SW1 and SW3 are on and SW2 is off, state B is when SW1 and SW3 are off and SW2 is on, state C is when SW1 and SW2 are on and SW3 is off, and state D is when SW2 and SW3 are on and SW1 is off. The power supply device 100 can arbitrarily control the output current and output voltage by arbitrarily switching between these states A, B, C, and D, thereby controlling the direction and magnitude of the current flowing through reactors L1 and L2, respectively.
[0018] Figure 4 shows an example of the waveform of the power supply unit 100 when each switch element of the switch element group 10 alternately repeats state A and state B in Figure 2. In Figure 4, from top to bottom, examples of the waveforms corresponding to the passage of time are shown for 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. Note that the voltage waveforms of V (SW1), V (SW2), and V (SW3) are shown as dashed lines.
[0019] In Figure 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 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. SW3 also exhibits a waveform similar to that of SW1.
[0020] On the other hand, in SW2, when transitioning from state A to state B, the voltage V(SW2) drops, resulting in a synchronous rectified waveform that 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 Figure 4, when transitioning from state B to state A, SW2 turns off and the voltage V(SW2) rises, while the voltages V(SW1) and V(SW3) of SW1 and SW3 respectively decrease. At this time, displacement currents (discharge side) flow through C1 and C3 respectively, causing the current I(SW2) of SW2 to fall off early and mitigating the voltage change due to the turn-off of SW2. As a result, the turn-off loss of SW2, which is expressed as the product of current I(SW2) and voltage V(SW2), can be significantly reduced.
[0022] On the other hand, in SW1 and SW3, when transitioning from state B to state A, the voltages V(SW1) and V(SW3) respectively decrease, resulting in a synchronous rectified waveform that turns on after energizing the body diode. Therefore, there is no overlap between the voltage V(SW1) and current I(SW1), and between the voltage V(SW3) and current I(SW3) in SW1 and SW3, 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 of 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 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. Note that the voltage waveforms of 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 that 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, where SW1 is turned on, SW2 is turned on, and SW3 is turned off, and state D, where 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 each repeatedly switch in such a way that they are not all 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 are turned 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 capacitances of C1 and C3 are set so that the above charge Q is supplied by the turn-off voltage Voff, and 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 calculated by the following equation (2): C = Q / Voff = 50 μC / 800 V = 62.5 nF ... (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 different 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 capacitor elements 60 connected in series and then 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 increase parasitic capacitance.
[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 for the charge of C1 or C3 to discharge. 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, when 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 will be approximately ton = 200 ns. In other words, if the dead time period tDT is 200 ns or more, SW1 and SW3 can be soft-switched even during turn-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 only to 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 device 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 device 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 device 100 has a battery 1 (first power storage device) and a battery 2 (second power storage device) that respectively output a predetermined DC voltage, and generates a variable output voltage using the DC voltages output from the battery 1 and the battery 2. The power supply device 100 includes a switch element 11 (SW1), a switch element 21 (SW2) connected in series to the low potential side of the switch element 11, and a switch element 31 (SW3) connected in series to the low potential side of the switch element 21, a switch element group 10 having these; a reactor 3 (L1) whose one end is connected to the battery 1 and the other end is connected between the switch element 21 and the switch element 31; a reactor 4 (L2) whose one end is connected to the battery 2 and the other end is connected between the switch element 11 and the switch element 21; a smoothing capacitor 5 (Cmain) connected in parallel to the switch element group 10; a capacitor 12 (C1) connected in parallel to the switch element 11; and a capacitor 32 (C3) connected in parallel to the switch element 31. By doing so, a low-loss and small-sized power supply device 100 capable of arbitrarily controlling the output current and output voltage can be realized.
[0042] (2) The switch element 11 and the capacitor 12 are mounted on the circuit board 41, the switch element 21 is mounted on the circuit board 42, and the switch element 31 and the capacitor 32 are mounted on the circuit board 43. By doing so, the switch element group 10 in which the three switch elements 11, 21, 31 are connected in series and the capacitors 12, 32 connected in parallel to the switch elements 11, 21 can be mounted in the power supply device 100 with high density.
[0043] (3) In the power supply device 100, the circuit board 41 and the circuit board 43 may be integrated. By doing so, the switch element group 10 and the capacitors 12, 32 can be mounted with even higher density, and the size of the power supply device 100 can be reduced.
[0044] (4) The capacitor 12 and the capacitor 32 may each be constituted by a plurality of capacitor elements connected in series and / or in parallel with each other. By doing so, capacitors 12, 32 having appropriate capacitances 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 element 11, switch element 21, and switch element 31 each repeat their 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 of 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. 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 device 100 has a dead time period tDT during which both the switch element 11 and the switch element 31 are switched off between the third switching state and the fourth switching state. And it is desirable that this dead time period tDT is set to be longer than the time required for discharging the charge of the capacitor 12 or the capacitor 32. If it is configured in this way, since all the charges charged in the capacitor 12 or the capacitor 32 can be extracted during the dead time period tDT, the turn-on loss can be significantly reduced, and thus a low-loss and small-sized power supply device 100 can be realized.
[0049] (Second Embodiment) FIG. 7 is a diagram showing a circuit configuration of a power supply device according to a second embodiment of the present invention. The power supply device 100A of the present embodiment shown in FIG. 7 is different from the power supply device 100 described in the first embodiment in that the connections to the batteries 1 and 2 and the output side are disconnected.
[0050] The power supply device 100A in FIG. 7 discharges the charge of Cmain by alternately repeating the above-described states C and D, that is, by repeatedly charging and discharging C1 and C3. Thereby, for example, even when an operator accidentally touches the output side of the power supply device 100A during maintenance of a vehicle on which the power supply device 100A is mounted, it is possible to prevent an accident such as electric shock.
[0051] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
[0052] 1, 2... Batteries 3, 4... Reactors 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 parts 60... Capacitor element 100, 100A... Power supply devices
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 generating a variable output voltage using the DC voltages output from the first energy storage device and the second energy storage device, the power supply device comprising: 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.
2. The power supply device according to claim 1, wherein the first switch element and the first capacitor are mounted on a first circuit board, the second switch element is mounted on a second circuit board, and the third switch element and the third capacitor are mounted on a third circuit board.
3. The power supply device according to claim 2, wherein the first circuit board and the third circuit board are integrated.
4. The power supply device according to claim 1, wherein the first capacitor and the third capacitor are each composed of a plurality of capacitor elements connected in series and / or in parallel with each other.
5. The power supply device according to claim 1, wherein the capacitance of the first capacitor is set so that the current immediately before the first switch element turns off can be absorbed during the period in which the first switch element is turned off, and the capacitance of the third capacitor is set so that the current immediately before the third switch element turns off can be absorbed during the period in which the third switch element is turned off.
6. The power supply device according to claim 1, wherein the first switch element, the second switch element, and the third switch element each repeat their switching operations so that they are not all turned on at the same time.
7. The power supply device according to claim 6, which has a first switching state in which the first switching element is turned on, the second switching element is turned off, and the third switching element is turned on, and 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, and the group of switching elements is controlled such that a current that alternately increases and decreases in polarity flows through the first reactor and the second reactor, respectively, by alternately repeating the first switching state and the second switching state.
8. The power supply device according to claim 6, which has 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, and 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, and the group of switching elements is controlled such that a current that alternately increases and decreases in polarity flows through the first reactor and the second reactor, respectively, by alternately repeating the third switching state and the fourth switching state.
9. The power supply device according to claim 8, wherein there is a dead time period between the third switching state and the fourth switching state during which both the first switching element and the third switching element are switched off, and 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.
10. The power supply device according to claim 8, further comprising a disconnection mechanism for disconnecting the first energy storage device and the second energy storage device from the group of switch elements, wherein when the disconnection mechanism disconnects the first energy storage device and the second energy storage device from the group of switch elements, the group of switch elements is controlled to discharge the charge of the smoothing capacitor by alternately repeating the third switching state and the fourth switching state.