Power supply unit and control method for power supply unit

Abstract

To prevent surge voltages from being applied to each switching element on the second side and to avoid increased costs. [Solution] The power supply device includes a transformer including a first switching element with one end connected to a first terminal, a second switching element with one end connected to the other end of the first switching element, a third switching element with one end connected to the other end of the second switching element, a fourth switching element with one end connected to the other end of the third switching element and the other end connected to a second terminal, a first capacitor and a second capacitor connected between the first terminal and the second terminal, a first winding, and a second winding, a fifth switching element connected to the second winding and the fourth terminal, a sixth switching element connected to the second winding and the fourth terminal, a first switch connected to the fifth switching element and the third terminal, and a second switch connected to the sixth switching element and the third terminal.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a capacitor and a precharge circuit that can suppress inrush current without inserting a resistor in series.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Normally, in a phase-shift full-bridge circuit, when the turns ratio of the transformer is set to the first turns: the second turns = N: 1, when outputting a voltage of ((second-side battery voltage) × N) or higher from the second side to the first side, in addition to boosting by the transformer, it is necessary to boost also by the output inductor. In this case, the surge voltage generated in the output inductor is applied to the switching element on the second side, and the switching element on the second side may be damaged.

[0005] In recent years, the battery voltage of batteries used in electric vehicles has been increased to a high voltage such as 800V or the like. Therefore, since it is necessary to employ high-voltage-resistant components on the first side in the power supply device, the cost may increase.

[0006] An object of the present disclosure is to suppress the application of a surge voltage to each switching element on the second side and an increase in cost.

Means for Solving the Problems

[0007] The power supply device of the present disclosure steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, comprising: a first switching element with one end electrically connected to the first terminal; a second switching element with one end electrically connected to the other end of the first switching element; a third switching element with one end electrically connected to the other end of the second switching element; a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; a first capacitor with one end electrically connected to one end of the first switching element; a second capacitor with one end electrically connected to the other end of the first capacitor and the other end electrically connected to the other end of the fourth switching element; and a first diode whose cathode is electrically connected to the other end of the first switching element and one end of the second switching element, and whose anode is electrically connected to the other end of the first capacitor and one end of the second capacitor. A transformer comprising: a second diode whose cathode is electrically connected to the anode of the first diode and whose anode is electrically connected to the other end of the third switching element and one end of the fourth switching element; a first winding whose one end is electrically connected to the other end of the second switching element and one end of the third switching element and whose other end is electrically connected to the anode of the first diode and the cathode of the second diode; and a second winding which is magnetically coupled to the first winding; and a transformer whose one end is electrically connected to the center tap of the second winding and whose other end is connected to the third An inductor electrically connected to the child, a fifth switching element with one end electrically connected to one end of the second winding and the other end electrically connected to the fourth terminal, a sixth switching element with one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal, a first switch with one end electrically connected to one end of the fifth switching element and one end of the second winding and the other end electrically connected to the other end of the inductor and the third terminal, and one end electrically connected to one end of the sixth switching element and the other end of the second winding,It includes a second switch whose other end is electrically connected to the other end of the inductor and the third terminal.

[0008] The power supply device of the present disclosure further includes a control unit that controls the first to sixth switching elements, and the first and second switches, and when the second voltage is boosted and output between the first and second terminals, the control unit turns on only the third switching element, the fifth switching element and the first switch during the first period, turns on only the first switch during the second period following the first period, turns on only the second switching element, the sixth switching element and the second switch during the third period following the second period, and turns on only the second switch during the fourth period following the third period.

[0009] The power supply device of the present disclosure further includes a third capacitor, one end of which is electrically connected to the cathode of the first diode and the other end of which is electrically connected to the anode of the second diode.

[0010] The control method for a power supply device of the present disclosure comprises: a first switching element with one end electrically connected to a first terminal; a second switching element with one end electrically connected to the other end of the first switching element; a third switching element with one end electrically connected to the other end of the second switching element; a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to a second terminal; a first capacitor with one end electrically connected to one end of the first switching element; a second capacitor with one end electrically connected to the other end of the first capacitor and the other end electrically connected to the other end of the fourth switching element; a first diode with its cathode electrically connected to the other end of the first switching element and one end of the second switching element, and its anode electrically connected to the other end of the first capacitor and one end of the second capacitor; a second diode with its cathode electrically connected to the anode of the first diode, and its anode electrically connected to the other end of the third switching element and one end of the fourth switching element; and the other end of the second switching element and the third switching element A transformer including a first winding electrically connected at one end and electrically connected at the other end to the anode of the first diode and the cathode of the second diode, and a second winding magnetically coupled to the first winding; an inductor with one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal; a fifth switching element with one end electrically connected to one end of the second winding and the other end electrically connected to the fourth terminal; a sixth switching element with one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; and one end of the A control method for a power supply device, comprising: a first switch electrically connected to one end of a 5-switching element and one end of the second winding, with the other end electrically connected to the other end of the inductor and the third terminal; and a second switch electrically connected to one end of a 6-switching element and the other end of the second winding, with the other end electrically connected to the other end of the inductor and the third terminal, wherein in a first period, only the third switching element, the fifth switching element and the first switch are turned on; and in a second period following the first period, only the first switch is turned on.In the third period following the second period, only the second switching element, the sixth switching element, and the second switch are turned on, and in the fourth period following the third period, only the second switch is turned on. [Effects of the Invention]

[0011] According to this disclosure, it is possible to suppress the application of surge voltage to each switching element on the second side and to prevent increased costs. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows an example of the configuration of the power system of an electric vehicle. [Figure 2] Figure 2 shows the configuration of a conventional DC-DC converter. [Figure 3] Figure 3 shows an example configuration of a DC-DC converter according to the embodiment. [Figure 4] Figure 4 is a diagram illustrating the operation sequence of the DC-DC converter according to the embodiment. [Figure 5] Figure 5 is a diagram showing the current path flowing through the DC-DC converter during the first period according to the embodiment. [Figure 6] Figure 6 is a diagram showing the current path flowing through the DC-DC converter during the second period according to the embodiment. [Figure 7] Figure 7 is a diagram showing the current path flowing through the DC-DC converter during the third period according to the embodiment. [Figure 8] Figure 8 is a diagram showing the current path flowing through the DC-DC converter during the fourth period according to the embodiment. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present disclosure is not limited by this embodiment, and in the following embodiments, the same parts are denoted by the same reference numerals to omit redundant descriptions.

[0014] <First Embodiment> (Configuration Example of Power System of Electric Vehicle) FIG. 1 is a diagram showing a configuration example of a power system of an electric vehicle.

[0015] The power system 1 includes a high-voltage battery 2, a resistor 3, contactors 4, 5, and 6, an inverter 7, a motor 9, a DC-DC converter 10, and a low-voltage battery 11. The inverter 7 includes a smoothing capacitor 8 on the input side.

[0016] The DC-DC converter 10 corresponds to an example of the "power supply device" of the present disclosure.

[0017] The high-voltage battery 2 is exemplified by a driving battery, but the present disclosure is not limited thereto. The voltage of the high-voltage battery 2 is arbitrary. The low-voltage battery 11 is exemplified by an auxiliary battery, but the present disclosure is not limited thereto. The voltage of the low-voltage battery 11 is arbitrary.

[0018] At the initial stage (for example, when the electric vehicle is started), the capacitor 8 may not store power (charge). Therefore, the contactors 5 and 6 are turned on, and the capacitor 8 is pre-charged from the high-voltage battery 2 via the resistor 3. After the pre-charge is completed, the contactor 5 is turned off, and the contactor 4 is turned on.

[0019] When charging the low-voltage battery 11, the DC-DC converter 10 steps down the DC voltage of the capacitor 8 and outputs it to the low-voltage battery 11. The low-voltage battery 11 is charged by the DC voltage output from the DC-DC converter 10.

[0020] (Configuration of Conventional Example) Figure 2 shows the configuration of a conventional DC-DC converter. The DC-DC converter 100 is a phase-shifted full-bridge circuit. Currently, phase-shifted full-bridge circuits are the mainstream for power conversion from high-voltage battery 2 to low-voltage battery 11.

[0021] The DC-DC converter 100 has a first terminal 21, a second terminal 22, a third terminal 23, and a fourth terminal 24.

[0022] The first terminal 21 is electrically connected to one end (high potential side) of the capacitor 8. The second terminal 22 is electrically connected to the other end (low potential side) of the capacitor 8. The third terminal 23 is electrically connected to one end (high potential side) of the low-voltage battery 11. The fourth terminal 24 is electrically connected to the other end (low potential side) of the low-voltage battery 11.

[0023] The DC-DC converter 100 steps down the first voltage V1 input between the first terminal 21 and the second terminal 22 and outputs the second voltage V2 from between the third terminal 23 and the fourth terminal 24.

[0024] The DC-DC converter 100 includes a bridge circuit 31a, an inductor Lr, a transformer T, a choke Lo, a transistor Q5, a transistor Q6, a capacitor 51, and a control unit 61.

[0025] The bridge circuit 31a includes transistors Q1 through Q4.

[0026] Transistor Q1 corresponds to an example of the “first switching element” in this disclosure. Transistor Q2 corresponds to an example of the “second switching element” in this disclosure. Transistor Q3 corresponds to an example of the “third switching element” in this disclosure. Transistor Q4 corresponds to an example of the “fourth switching element” in this disclosure.

[0027] In the embodiments, each transistor is a MOSFET, but the disclosure is not limited to this. Each transistor may be a silicon power device, a GaN power device, a SiC power device (e.g., an IGBT (Insulated Gate Bipolar Transistor)), or the like.

[0028] Each transistor has a parasitic diode (body diode) that can actively conduct current, or a diode connected in antiparallel. A parasitic diode is the pn junction between the back gate and the source and drain of a MOSFET.

[0029] The source of transistor Q1 is electrically connected to the drain of transistor Q2. The drain of transistor Q1 is electrically connected to the drain of transistor Q3. The source of transistor Q3 is electrically connected to the drain of transistor Q4. The source of transistor Q2 is electrically connected to the source of transistor Q4.

[0030] The drains of transistor Q1 and Q3 are electrically connected to the first terminal 21. The sources of transistor Q2 and Q4 are electrically connected to the second terminal 22.

[0031] The transformer T includes a first winding 41, a second winding 42, and a core 43. The first winding 41 and the second winding 42 are wound around the core 43.

[0032] The source of transistor Q1 and the drain of transistor Q2 are electrically connected to one end of inductor Lr. The other end of inductor Lr is electrically connected to one end of the first winding 41. The other end of the first winding 41 is electrically connected to the source of transistor Q3 and the drain of transistor Q4.

[0033] The inductor Lr may be a wound component, or it may be the leakage inductance of the first winding 41.

[0034] The second winding 42 is divided into a first part 42a and a second part 42b at the intermediate tap 42c.

[0035] Let the turns ratio between the first winding 41 and the first part 42a of the second winding 42 be N:1. Similarly, let the turns ratio between the first winding 41 and the second part 42b of the second winding 42 be N:1. N can be any value.

[0036] The center tap 42c is electrically connected to one end of the choke Lo. The other end of the choke Lo is electrically connected to one end (high potential side) of the capacitor 51 and to the third terminal 23.

[0037] One end of the first section 42a is electrically connected to the center tap 42c. The other end of the first section 42a is electrically connected to the drain of transistor Q5.

[0038] One end of the second section 42b is electrically connected to the center tap 42c. The other end of the second section 42b is electrically connected to the drain of transistor Q6.

[0039] The sources of transistor Q5 and transistor Q6 are electrically connected to the other end (low-potential side) and fourth terminal 24 of capacitor 51.

[0040] The control unit 61 outputs a drive control signal P1 to the bridge circuit 31a, a drive control signal P2 to the transistor Q5, and a drive control signal P3 to the transistor Q6.

[0041] When the DC-DC converter 100 outputs a step-down voltage from the first side (capacitor 8 side) to the second side (low-voltage battery 11 side) (when charging the low-voltage battery 11), the DC-DC converter 100 uses a capacitor input method because capacitor 8 is connected in parallel with the high-voltage battery 2.

[0042] When the DC-DC converter 100 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the DC-DC converter 100 uses a choke input method because the choke Lo is connected in series with the low-voltage battery 11.

[0043] When the DC-DC converter 100 boosts the output from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), if the target first voltage V1 is less than or equal to N times the second voltage V2, the boost from the winding ratio of the transformer T is sufficient. However, if the target first voltage V1 is greater than N times the second voltage V2, a boost from the choke Lo is required in addition to the transformer T. In that case, when the choke Lo discharges energy, a surge voltage is generated by the choke Lo, and a large surge voltage is applied to transistors Q5 and Q6, potentially stressing them.

[0044] Furthermore, in recent years, the battery voltage of batteries used in electric vehicles has increased to high voltages such as 800V. Therefore, it is necessary to use high-voltage-resistant components for transistors Q1 to Q4, which may increase costs.

[0045] [Embodiment] (Example of a DC-DC converter configuration) An example configuration of a DC-DC converter according to the embodiment will be described using Figure 3. Figure 3 is a diagram showing an example configuration of a DC-DC converter according to the embodiment.

[0046] Compared to the conventional DC-DC converter 100 (see Figure 2), the DC-DC converter 10 further includes capacitors 52, 53, and 54, diode D11, and diode D12 on the first side, and includes a switching circuit 31 instead of a bridge circuit 31a. Furthermore, compared to the conventional DC-DC converter 100, the DC-DC converter 10 further includes a first switch 71 and a second switch 72 on the second side.

[0047] The switching circuit 31 includes transistors Q1 to Q4.

[0048] The drain of transistor Q1 is electrically connected to terminal 21. The source of transistor Q1 is electrically connected to the drain of transistor Q2. The source of transistor Q2 is electrically connected to the drain of transistor Q3. The source of transistor Q3 is electrically connected to the drain of transistor Q4. The source of transistor Q4 is electrically connected to terminal 22.

[0049] One end of capacitor 52 is electrically connected to the first terminal 21 and the drain of transistor Q1. The other end of capacitor 52 is electrically connected to one end of capacitor 53. Capacitor 52 is an example of a "first capacitor". Capacitor 53 is an example of a "second capacitor".

[0050] The other end of capacitor 53 is electrically connected to the second terminal 22 and the source of transistor Q4.

[0051] One end of capacitor 54 is electrically connected to the source of transistor Q1 and the drain of transistor Q2. The other end of capacitor 54 is electrically connected to the source of transistor Q3 and the drain of transistor Q4. Capacitor 54 is an example of a "third capacitor".

[0052] The cathode of diode D11 is electrically connected to one end of capacitor 54, the source of transistor Q1, and the drain of transistor Q2. The anode of diode D11 is electrically connected to the other end of capacitor 52 and one end of capacitor 53. Diode D11 is an example of a "first diode".

[0053] The cathode of diode D12 is electrically connected to the anode of diode D11, the other end of capacitor 52, and one end of capacitor 53. The anode of diode D12 is electrically connected to the source of transistor Q3 and the drain of transistor Q4. Diode D12 is an example of a "second diode".

[0054] The source of transistor Q2 and the drain of transistor Q3 are electrically connected to one end of inductor Lr. The other end of inductor Lr is electrically connected to one end of the first winding 41. The other end of the first winding 41 is electrically connected to the anode of diode D11 and the cathode of diode D12.

[0055] The first switch 71 includes a diode D7 and a transistor Q7. The anode of diode D7 is electrically connected to the other end of the first portion 42a of the second winding 42 and to the drain of transistor Q5. The cathode of diode D7 is electrically connected to the drain of transistor Q7. The source of transistor Q7 is electrically connected to the other end of choke Lo, one end of capacitor 51 and the third terminal 23. Diode D7 is a reverse current protection diode. The first switch 71 may also be a mechanical switch.

[0056] The second switch 72 includes a diode D8 and a transistor Q8. The anode of diode D8 is electrically connected to the other end of the second portion 42b of the second winding 42 and to the drain of transistor Q6. The cathode of diode D8 is electrically connected to the drain of transistor Q8. The source of transistor Q8 is electrically connected to the other end of choke Lo, one end of capacitor 51 and to the third terminal 23. Diode D8 is a reverse current protection diode. The second switch 72 may be a mechanical switch.

[0057] In this embodiment, diode D7 is placed on the second winding 42 side and transistor Q7 is placed on the capacitor 51 side, but the disclosure is not limited thereto. Transistor Q7 may be placed on the second winding 42 side and diode D7 may be placed on the capacitor 51 side. That is, the drain of transistor Q7 may be electrically connected to the other end of the first portion 42a of the second winding 42 and the drain of transistor Q5, the source of transistor Q7 may be electrically connected to the anode of diode D7, and the cathode of diode D7 may be electrically connected to the other end of choke Lo, one end of capacitor 51 and the third terminal 23. The same applies to diode D8 and transistor Q8.

[0058] The control unit 61 controls transistors Q1 through Q8. The control unit 61 controls the on and off states of transistors Q1 through Q4 by outputting a drive control signal P1 to the switching circuit 31. The control unit 61 controls the on and off states of transistor Q5 by outputting a drive control signal P2 to the gate of transistor Q5. The control unit 61 controls the on and off states of transistor Q6 by outputting a drive control signal P3 to the gate of transistor Q6. The control unit 61 controls the on and off states of transistor Q7 by outputting a drive control signal P4 to the gate of transistor Q7. The control unit 61 controls the on and off states of transistor Q8 by outputting a drive control signal P5 to the gate of transistor Q8.

[0059] When the DC-DC converter 10 steps down the voltage output from the first side (capacitor 8 side) to the second side (low-voltage battery 11 side) (to charge the low-voltage battery 11), the control unit 61 controls transistors Q7 and Q8 to the off state. In this case, the DC-DC converter 10 becomes the equivalent circuit of the DC-DC converter 100. In this case, since capacitor 8 is connected in parallel with the high-voltage battery 2, the DC-DC converter 10 becomes a capacitor input type.

[0060] When the DC-DC converter 10 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the choke Lo is connected in series with the low-voltage battery 11, resulting in a choke input configuration. In this case, the DC-DC converter 10, like the DC-DC converter 100, may generate a surge voltage due to the choke Lo. However, the control unit 61 controls transistor Q7 or transistor Q8 to be in the ON state. As a result, the DC-DC converter 10 regenerates the surge voltage to capacitor 51 via the first switch 71 or the second switch 72.

[0061] Therefore, the DC-DC converter 10 can suppress the application of surge voltage to transistor Q5 or transistor Q6, and can suppress stress on transistor Q5 or transistor Q6.

[0062] (Action sequence) The operation sequence of the DC-DC converter according to the embodiment will be explained using Figure 4. Figure 4 is a diagram illustrating the operation sequence of the DC-DC converter according to the embodiment.

[0063] As shown in Figure 4, the operation sequence includes a first period T1, a second period T2, a third period T3, and a fourth period T4. Line 101 represents the operating state of transistor Q1. Line 102 represents the operating state of transistor Q2. Line 103 represents the operating state of transistor Q3. Line 104 represents the operating state of transistor Q4. Line 105 represents the operating state of transistor Q5. Line 106 represents the operating state of transistor Q6. Line 107 represents the operating state of transistor Q7. Line 108 represents the operating state of transistor Q8.

[0064] (Phase 1) The first period T1 starts at timing t1 and ends at timing t2. At timing t1, the control unit 61 controls transistors Q3, Q5, and Q7 to be turned ON.

[0065] Figure 5 is a diagram showing the current path flowing through the DC-DC converter during the first period according to the embodiment.

[0066] Line 201 shows the current path flowing on the second side of the DC-DC converter 10 during the first period T1. As shown by line 201, on the second side, the current flows in the following order: high-potential end of the low-voltage battery 11 → choke Lo → center tap 42c of the second winding 42 → first part 42a of the second winding 42 → transistor Q5 → low-potential end of the low-voltage battery 11.

[0067] Line 202 shows the current path flowing on the first side of the DC-DC converter 10 during the first period T1. As shown by line 202, on the first side, the current flows through the path from one end of the first winding 41 → inductor Lr → transistor Q3 → diode D12 → the other end of the first winding 41.

[0068] During the first period T1, current flows only through the first portion 42a of the second winding 42, generating a unidirectional magnetic field. Since no current flows through the second portion 42b of the second winding 42, no counteracting magnetic field is generated in the opposite direction. Therefore, an induced voltage is generated in the first winding 41. The ratio of this induced voltage in the first winding 41 to the voltage in the first portion 42a of the second winding 42 is N:1. In this way, during the first period T1, the voltage across the capacitor 52 gradually increases and becomes constant at a predetermined threshold.

[0069] (Second period) The second period T2 starts at timing t2 and ends at timing t3. At timing t2, the control unit 61 controls transistors Q3 and Q5 to the OFF state and transistor Q7 to the ON state.

[0070] Figure 6 is a diagram showing the current path flowing through the DC-DC converter during the second period according to the embodiment.

[0071] Line 211 shows the current path flowing on the second side of the DC-DC converter 10 during the second period T2. As shown by line 211, on the second side, the current flows through the path from one end of choke Lo → center tap 42c of the second winding 42 → first part 42a of the second winding 42 → diode D7 → transistor Q7 → the other end of choke Lo.

[0072] Line 212 shows the current path flowing on the first side of the DC-DC converter 10 during the second period T2. As shown by line 212, on the first side, the current flows through the path from one end of the first winding 41 → inductor Lr → parasitic diode D2 of transistor Q2 → parasitic diode D1 of transistor Q1 → capacitor 52 → the other end of the first winding 41. Also on the first side, as shown by line 212, the current flows through the path from one end of the first winding 41 → inductor Lr → parasitic diode D2 of transistor Q2 → capacitor 54 → diode D12 → the other end of the first winding 41. In other words, on the second side, the current splits and flows through two paths.

[0073] During the second period T2, transistor Q7 is controlled to be ON. This suppresses the application of surge voltage to transistor Q5.

[0074] During the second period T2, current flows through capacitors 52 and 54, so capacitors 52 and 54 are charged. During the second period T2, the voltage across capacitor 52 gradually increases. By distributing the voltage between capacitors 52 and 54, the application of a high voltage from transistor Q1 to transistor Q4 is suppressed. This eliminates the need to use high-voltage components from transistor Q1 to transistor Q4, thus suppressing cost increases.

[0075] (Third period) The third period T3 starts at timing t3 and ends at timing t4. At timing t3, the control unit 61 controls transistors Q2, Q6, and Q8 to the ON state and transistor Q7 to the OFF state.

[0076] Figure 7 is a diagram showing the current path flowing through the DC-DC converter during the third period according to the embodiment.

[0077] Line 221 shows the current path flowing on the second side of the DC-DC converter 10 during the third period T3. As shown by line 221, on the second side, the current flows in the following order: high-potential end of the low-voltage battery 11 → choke Lo → center tap 42c of the second winding 42 → second part 42b of the second winding 42 → transistor Q6 → low-potential end of the low-voltage battery 11.

[0078] Line 222 shows the current path flowing on the first side of the DC-DC converter 10 during the third period T3. As shown by line 222, on the first side, the current flows through the path from the other end of the first winding 41 → diode D11 → transistor Q2 → inductor Lr → one end of the first winding 41.

[0079] During the third period T3, current flows only through the second portion 42b of the second winding 42, so an induced voltage is generated in the first winding 41. The ratio of this induced voltage in the first winding 41 to the voltage in the second portion 42b of the second winding 42 is N:1. During the third period T3, the voltage across the capacitor 53 gradually increases and becomes constant at a predetermined threshold.

[0080] (Fourth period) The fourth period T4 starts at timing t4 and ends at timing t5. At timing t4, the control unit 61 controls transistors Q2 and Q6 to the OFF state and transistor Q8 to the ON state.

[0081] Figure 8 is a diagram showing the current path flowing through the DC-DC converter during the fourth period according to the embodiment.

[0082] Line 231 shows the current path flowing on the second side of the DC-DC converter 10 during the fourth period T4. As shown by line 231, on the second side, the current flows through the path from one end of the choke Lo → the center tap 42c of the second winding 42 → the second part 42b of the second winding 42 → the diode D8 → the transistor Q8 → the other end of the choke Lo.

[0083] Line 232 shows the current path flowing on the first side of the DC-DC converter 10 during the fourth period T4. As shown by line 232, on the first side, the current flows through the path from the other end of the first winding 41 → diode D11 → capacitor 54 → parasitic diode D3 of transistor Q3 → inductor Lr → one end of the first winding 41. Also on the first side, as shown by line 232, the current flows through the path from the other end of the first winding 41 → capacitor 53 → parasitic diode D4 of transistor Q4 → parasitic diode D3 of transistor Q3 → inductor Lr → one end of the first winding 41. In other words, on the second side, the current splits and flows through two paths.

[0084] During the fourth period T4, transistor Q8 is turned on. This prevents surge voltage from being applied to transistor Q6.

[0085] During the fourth period T4, current flows through capacitors 53 and 54, so capacitors 53 and 54 are charged. At this time, the voltage across capacitor 53 gradually increases. Because the voltage is divided and charged between capacitors 52 and 54, the application of high voltage from transistor Q1 to transistor Q4 is suppressed. Therefore, it becomes unnecessary to use high-voltage components from transistor Q1 to transistor Q4, thus suppressing an increase in cost.

[0086] While embodiments of the present disclosure have been described above, the present disclosure is not limited by the content of these embodiments. Furthermore, the aforementioned components include those that are readily conceivable to those skilled in the art, those that are substantially identical, and those that fall within the so-called equivalent range. Moreover, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above. [Explanation of Symbols]

[0087] 1 Power system 2 High-voltage battery 3 resistors 4, 5, 6 Contactors 7 Inverter 8, 51, 52, 53, 54 Capacitors 9 Motors 10,100 DC-DC converter 11 Low-voltage battery 21 1st terminal 22 2nd terminal 23 3rd terminal 24 4th terminal 31 Switching Circuits 41. First Winding 42. Second winding 42a Part 1 42b Part 2 42c mid-tap 43 cores 61 Control Unit 71. Switch 1 72 Second switch 101,102,103,104,105,106,107,108,201,202,211,212,221,222,231,232 line D1, D2, D3, D4 Parasitic diodes D7, D8, D11, D12 diodes Lo Chalk Lr Inductor Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 Transistors

Claims

1. A power supply device that steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, A first switching element having one end electrically connected to the first terminal, A second switching element, one end of which is electrically connected to the other end of the first switching element, A third switching element, one end of which is electrically connected to the other end of the second switching element, A fourth switching element, one end of which is electrically connected to the other end of the third switching element and the other end of which is electrically connected to the second terminal, A first capacitor, one end of which is electrically connected to one end of the first switching element, A second capacitor, one end of which is electrically connected to the other end of the first capacitor and the other end of which is electrically connected to the other end of the fourth switching element, A first diode whose cathode is electrically connected to the other end of the first switching element and one end of the second switching element, and whose anode is electrically connected to the other end of the first capacitor and one end of the second capacitor, A second diode whose cathode is electrically connected to the anode of the first diode, and whose anode is electrically connected to the other end of the third switching element and one end of the fourth switching element, A transformer comprising: a first winding, one end of which is electrically connected to the other end of the second switching element and one end of the third switching element, and the other end of which is electrically connected to the anode of the first diode and the cathode of the second diode; and a second winding that is magnetically coupled to the first winding; An inductor having one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal, A fifth switching element, one end of which is electrically connected to one end of the second winding and the other end of which is electrically connected to the fourth terminal, A sixth switching element, one end of which is electrically connected to the other end of the second winding and the other end of which is electrically connected to the fourth terminal, A first switch, one end of which is electrically connected to one end of the fifth switching element and one end of the second winding, and the other end of which is electrically connected to the other end of the inductor and the third terminal, A second switch, one end of which is electrically connected to one end of the sixth switching element and the other end of the second winding, and the other end of which is electrically connected to the other end of the inductor and the third terminal, Power supply unit, including

2. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, When the second voltage is boosted and output between the first terminal and the second terminal, The control unit, During the first period, only the third switching element, the fifth switching element, and the first switch are turned on. In the second period following the first period, only the first switch is turned on. In the third period following the second period, only the second switching element, the sixth switching element, and the second switch are turned on. In the fourth period following the third period, only the second switch is turned on. The power supply device according to claim 1.

3. The third capacitor further includes one end electrically connected to the cathode of the first diode and the other end electrically connected to the anode of the second diode. The power supply device according to claim 1 or 2.

4. A first switching element with one end electrically connected to a first terminal, a second switching element with one end electrically connected to the other end of the first switching element, a third switching element with one end electrically connected to the other end of the second switching element, a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to a second terminal, a first capacitor with one end electrically connected to one end of the first switching element, a second capacitor with one end electrically connected to the other end of the first capacitor and the other end electrically connected to the other end of the fourth switching element, a first diode with its cathode electrically connected to the other end of the first switching element and one end of the second switching element, and its anode electrically connected to the other end of the first capacitor and one end of the second capacitor, a second diode with its cathode electrically connected to the anode of the first diode, and its anode electrically connected to the other end of the third switching element and one end of the fourth switching element, A power supply control method comprising: a transformer including a first winding whose ends are electrically connected to the other end of the second switching element and one end of the third switching element, and whose other ends are electrically connected to the anode of the first diode and the cathode of the second diode, and a second winding which is magnetically coupled to the first winding; an inductor whose one end is electrically connected to the center tap of the second winding and whose other end is electrically connected to a third terminal; a fifth switching element whose one end is electrically connected to one end of the second winding and whose other end is electrically connected to a fourth terminal; a sixth switching element whose one end is electrically connected to the other end of the second winding and whose other end is electrically connected to a fourth terminal; a first switch whose one end is electrically connected to one end of the fifth switching element and one end of the second winding, and whose other end is electrically connected to the other end of the inductor and the third terminal; and a second switch whose one end is electrically connected to one end of the sixth switching element and the other end of the second winding, and whose other end is electrically connected to the other end of the inductor and the third terminal; During the first period, only the third switching element, the fifth switching element, and the first switch are turned on. In the second period following the first period, only the first switch is turned on. In the third period following the second period, only the second switching element, the sixth switching element, and the second switch are turned on. In the fourth period following the third period, only the second switch is turned on. A method for controlling a power supply unit.

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