Power conversion device

Abstract

A power conversion device is provided. The power conversion device includes a primary-side circuit, a first connection line, a second connection line, a first capacitor provided on the first connection line, a second capacitor provided on the second connection line, and a secondary-side circuit that converts AC power input from the primary-side circuit into DC power and outputs the DC power to two output terminals. The secondary-side circuit includes a first branch, a second branch, a first wiring, and a second wiring. The first branch has a first coil and a first diode connected in series with each other. The second branch has a second coil and a second diode connected in series with each other. An anode terminal of the first diode and an anode terminal of the second diode are electrically connected to a negative-side output terminal of the two output terminals. The cathode terminal of the first diode is electrically connected to the first coil. The cathode terminal of the second diode is electrically connected to the second coil.

Description

Technical Field

[0001] The present disclosure relates to a power conversion device. Background Art

[0002] The power conversion device disclosed in Japanese Patent Application Laid-Open No. 2022-67247 includes a primary-side circuit, a secondary-side circuit, a first connection line and a second connection line that connect the primary-side circuit and the secondary-side circuit, a first capacitor provided in the first connection line, a second capacitor provided in the second connection line, a third connection line provided closer to the secondary-side circuit than the first capacitor and the second capacitor and connecting the first connection line and the second connection line, an exciting inductor provided in the third connection line, and a control unit. The primary-side circuit includes a switching element. The switching element performs a switching operation at a predetermined switching frequency, whereby the primary-side circuit converts input power into AC power. The secondary-side circuit converts the AC power input via the first connection line and the second connection line into DC power. The primary-side circuit and the secondary-side circuit are insulated by the first capacitor and the second capacitor. The control unit controls the switching frequency, the duty ratio, or the phase of the switching element. Thereby, the output voltage is controlled. Summary of the Invention

[0003] Sometimes, it is desired to further reduce the output voltage in a power conversion device that insulates the primary-side circuit and the secondary-side circuit using capacitors.

[0004] A power conversion device according to one embodiment of the present disclosure includes: a primary side circuit configured to include a switching element and convert input power into AC power by a switching operation of the switching element and output the AC power; a first connection line and a second connection line; a first capacitor provided on the first connection line; a second capacitor provided on the second connection line; and a secondary side circuit configured to convert the AC power input from the primary side circuit into DC power and output the DC power to two output terminals. The first connection line and the second connection line each include a first end electrically connected to the primary side circuit and a second end electrically connected to the secondary side circuit. The secondary side circuit includes: a first branch having a first coil and a first diode connected in series with each other, and the second end of the first connection line is connected to a connection point between the first coil and the first diode; a second branch having a second coil and a second diode connected in series with each other, and the second end of the second connection line is connected to a connection point between the second coil and the second diode; a first wiring connecting the first coil and the second coil to one of the two output terminals; and a second wiring connecting the first diode and the second diode to the other of the two output terminals. An anode terminal of the first diode and an anode terminal of the second diode are electrically connected to a negative side output terminal of the two output terminals. A cathode terminal of the first diode is electrically connected to the first coil. A cathode terminal of the second diode is electrically connected to the second coil.

[0005] The power conversion device according to other aspects of the present disclosure includes: a primary side circuit configured to include a switching element and convert the input power into AC power by the switching operation of the switching element and output the AC power; a first connection line and a second connection line; a first capacitor provided on the first connection line; a second capacitor provided on the second connection line; and a secondary side circuit configured to convert the AC power input from the primary side circuit into DC power and output the DC power to two output terminals. The first connection line and the second connection line each include a first end electrically connected to the primary side circuit and a second end electrically connected to the secondary side circuit. The secondary side circuit includes: a first branch having a first coil and a first diode connected in series with each other, and the second end of the first connection line is connected to a connection point between the first coil and the first diode; a second branch having a second coil and a second diode connected in series with each other, and the second end of the second connection line is connected to a connection point between the second coil and the second diode; a first wiring connecting the first coil and the second coil to one of the two output terminals; and a second wiring connecting the first diode and the second diode to the other of the two output terminals. The cathode terminals of the first diode and the second diode are electrically connected to the positive-side output terminal of the two output terminals. The anode terminal of the first diode is electrically connected to the first coil. The anode terminal of the second diode is electrically connected to the second coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a circuit diagram of a power conversion device.

[0007] Figure 2 is a circuit diagram of a power conversion device.

[0008] Figure 3 is Figure 1 a circuit diagram of the second converter included in the power conversion device of

[0009] Figure 4 is a timing chart showing the states of the fifth switching element and the sixth switching element, the currents flowing through the fifth switching element and the sixth switching element, the currents flowing through the first coil and the second coil, the voltages across the first capacitor and the second capacitor, and the voltages across the first coil and the second coil.

[0010] Figure 5 is a diagram showing Figure 4 the load current and the non-load current flowing through the second converter of

[0011] Figure 6 is a diagram showing Figure 4Graph of the load current and no-load current flowing through the second converter.

[0012] Figure 7 represents the load current and no-load current flowing through the second converter in Figure 4 Graph of the load current and no-load current flowing through the second converter.

[0013] Figure 8 represents the load current and no-load current flowing through the second converter in Figure 4 Graph of the load current and no-load current flowing through the second converter.

[0014] Figure 9 represents the load current and no-load current flowing through the second converter in Figure 4 Graph of the load current and no-load current flowing through the second converter.

[0015] Figure 10 represents the load current and no-load current flowing through the second converter in Figure 4 Graph of the load current and no-load current flowing through the second converter.

[0016] Figure 11 Graph of the load current and no-load current of the second converter showing a modified example.

[0017] Figure 12 Graph of the load current and no-load current of the second converter showing a modified example.

[0018] Figure 13 Graph of the load current and no-load current of the second converter showing a modified example.

[0019] Figure 14 Graph of the load current and no-load current of the second converter showing a modified example.

[0020] Figure 15 Graph of the load current and no-load current of the second converter showing a modified example.

[0021] Figure 16 Graph of the load current and no-load current of the second converter showing a modified example.

[0022] Figure 17 Graph of the second converter showing a modified example. Detailed implementation

[0023] An embodiment of the power conversion device will be described.

[0024] As Figure 1As shown, the vehicle 10 includes a high-voltage battery 11, a low-voltage battery 12, and a power conversion device 20. The high-voltage battery 11 supplies power to the main machine of the vehicle 10, for example. The main machine is, for example, a driving motor that drives the vehicle 10. The low-voltage battery 12 supplies power to the auxiliary machine of the vehicle 10, for example. The auxiliary machine is an electrical component other than the main machine. The rated voltage of the high-voltage battery 11 is higher than the rated voltage of the low-voltage battery 12. Therefore, in order to charge the high-voltage battery 11, a higher voltage needs to be applied compared to the case of charging the low-voltage battery 12.

[0025] <Power Conversion Device>

[0026] The power conversion device 20 includes two input terminals 21, 22, a first converter 30, two input / output terminals 23, 24, and a capacitor 25. The two input terminals 21, 22 are electrically connected to an external power supply PS. The external power supply PS is an AC power supply. The external power supply PS includes a first terminal T1 and a second terminal T2. The external power supply PS alternately switches the polarity between the first terminal T1 and the second terminal T2 over time. The first terminal T1 of the external power supply PS is electrically connected to the first input terminal 21, which is one of the two input terminals 21, 22. The second terminal T2 of the external power supply PS is electrically connected to the second input terminal 22, which is the other of the two input terminals 21, 22. The power conversion device 20 charges the high-voltage battery 11 and the low-voltage battery 12 by converting the power supplied from the external power supply PS electrically connected to the input terminals 21, 22.

[0027] The first converter 30 converts the power input from the external power supply PS via the input terminals 21, 22. The first converter 30 is a flying capacitor converter. The first converter 30 includes a switching circuit 31, a reactor 32, a flying capacitor 33, a switch 34, a first input / output line L1, and a second input / output line L2.

[0028] The switching circuit 31 includes a first switching element Q1, a second switching element Q2, a third switching element Q3, and a fourth switching element Q4. The switching circuit 31 is formed by connecting the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 in series with each other in this order. The switching elements Q1 to Q4 are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switching elements Q1 to Q4 can also be IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0029] The flying capacitor 33 electrically connects the connection point between the first switching element Q1 and the second switching element Q2 to the connection point between the third switching element Q3 and the fourth switching element Q4.

[0030] The switch 34 is disposed between the first input terminal 21 and the second input terminal 22. The switch 34 connects the first input terminal 21 and the second input terminal 22 by being in a closed state.

[0031] The two input / output terminals 23, 24 are electrically connected to a switching circuit 31. The first input / output line L1 electrically connects the input / output terminal 23, which is one of the two input / output terminals 23, 24, to one end 31A of the switching circuit 31. The second input / output line L2 electrically connects the input / output terminal 24, which is the other of the two input / output terminals 23, 24, to the other end 31B of the switching circuit 31. A first switching element Q1 is connected to the input / output terminal 23 via the first input / output line L1. A fourth switching element Q4 is connected to the input / output terminal 24 via the second input / output line L2.

[0032] The first converter 30 includes a fifth switching element Q5, a sixth switching element Q6, a first input line L3, a second input line L4, a positive line L5, and a negative line L6. The fifth switching element Q5 and the sixth switching element Q6 are connected in series with each other. The fifth switching element Q5 and the sixth switching element Q6 are, for example, MOSFETs. The fifth switching element Q5 and the sixth switching element Q6 may also be IGBTs or GaN-HEMTs.

[0033] The first input line L3 electrically connects the first input terminal 21 to a connection point between the second switching element Q2 and the third switching element Q3. A reactor 32 is disposed on the first input line L3.

[0034] The second input line L4 electrically connects the second input terminal 22 to one of the two input / output terminals 23, 24. Whether the second input line L4 is electrically connected to the input / output terminal 23 or the input / output terminal 24 is switched according to whether the first terminal T1 is positive or the second terminal T2 is positive.

[0035] The positive line L5 electrically connects the second input line L4 and the first input / output line L1. Accordingly, the second input line L4 is electrically connected to the input / output terminal 23 via the positive line L5 and the first input / output line L1.

[0036] The negative line L6 electrically connects the second input line L4 and the second input / output line L2. Accordingly, the second input line L4 is electrically connected to the input / output terminal 24 via the negative line L6 and the second input / output line L2.

[0037] The fifth switching element Q5 is arranged on the positive line L5. The sixth switching element Q6 is arranged on the negative line L6. When the switching elements Q5 and Q6 are MOSFETs, the switching elements Q5 and Q6 are arranged such that the forward direction of the parasitic diode is from the second input / output line L2 toward the first input / output line L1. That is, the anode terminal of the parasitic diode of the switching element Q6 is electrically connected to the second input / output line L2, and the cathode terminal of the parasitic diode of the switching element Q5 is electrically connected to the first input / output line L1.

[0038] The input / output terminal 23 is electrically connected to the positive electrode of the high-voltage battery 11. The input / output terminal 24 is electrically connected to the negative electrode of the high-voltage battery 11. For the first converter 30, the AC power supplied from the external power supply PS is converted into DC power by the switching operations of the first switching element Q1 to the fourth switching element Q4 and output from the input / output terminals 23 and 24. The DC power output from the input / output terminals 23 and 24 is applied to the high-voltage battery 11. Thereby, the high-voltage battery 11 is charged. The first converter 30 boosts the voltage of the AC power and outputs it. Alternatively, the first converter 30 may step down the voltage of the AC power and output it.

[0039] The capacitor 25 is arranged between the first converter 30 and the high-voltage battery 11.

[0040] The power conversion device 20 includes two second-converter input terminals 41 and 42, a second converter 50, and two output terminals 43 and 44.

[0041] The two second-converter input terminals 41 and 42 are electrically connected to both ends of the flying capacitor 33. The second-converter input terminal 41 is electrically connected to one end of the flying capacitor 33 and the second-converter input terminal 42 is electrically connected to the other end of the flying capacitor 33.

[0042] As Figure 3 shown, the second converter 50 includes a primary-side circuit 51, a first connection line L11 and a second connection line L12, a first capacitor C1, a second capacitor C2, a secondary-side circuit 61, and a capacitor 54.

[0043] The primary-side circuit 51 includes an upper-arm switching element Q41 and a lower-arm switching element Q42. Each of the upper-arm switching element Q41 and the lower-arm switching element Q42 as a switching element includes a freewheeling diode D. The primary-side circuit 51 is a half-bridge circuit of the switching elements Q41 and Q42. The upper-arm switching element Q41 and the lower-arm switching element Q42 are connected in series with each other. The upper-arm switching element Q41 is electrically connected to the second-converter input terminal 41. The lower-arm switching element Q42 is electrically connected to the second-converter input terminal 42. The switching elements Q41 and Q42 are, for example, MOSFETs. The switching elements Q41 and Q42 may also be IGBTs or GaN-HEMTs.

[0044] The secondary-side circuit 61 includes a first branch 62, a second branch 63, a wiring 64, and a wiring 65. The first branch 62 includes a first coil L21 and a first diode D11 connected in series with each other. The second branch 63 includes a second coil L22 and a second diode D12 connected in series with each other. The secondary-side circuit 61 is electrically connected to the output terminals 43 and 44. The wiring 64 connects the first coil L21 and the second coil L22 to the output terminal 43, which is one of the two output terminals 43 and 44. The wiring 65 connects the first diode D11 and the second diode D12 to the output terminal 44, which is the other of the two output terminals 43 and 44. The wiring 64 is an example of a first wiring. The wiring 65 is an example of a second wiring.

[0045] The anode terminals of the first diode D11 and the second diode D12 are electrically connected to the negative-side output terminal among the output terminals 43 and 44. The cathode terminal of the first diode D11 is electrically connected to the first coil L21. The cathode terminal of the second diode D12 is electrically connected to the second coil L22. Thus, the cathode terminals of the first diode D11 and the second diode D12 are electrically connected to the positive-side output terminal among the output terminals 43 and 44. In one example, the anode terminals of the first diode D11 and the second diode D12 are electrically connected to the output terminal 44. The cathode terminals of the first diode D11 and the second diode D12 are electrically connected to the output terminal 43.

[0046] Each of the first connection line L11 and the second connection line L12 has a first end and a second end. The first ends of the first connection line L11 and the second connection line L12 are each electrically connected to the primary-side circuit 51. The first end of the first connection line L11 is connected to the connection point between the upper-arm switching element Q41 and the lower-arm switching element Q42. The first end of the second connection line L12 is connected to the lower-arm switching element Q42.

[0047] The second ends of the first connection line L11 and the second connection line L12 are each electrically connected to the secondary-side circuit 61. The second end of the first connection line L11 is connected to the connection point between the first coil L21 and the first diode D11. The second end of the second connection line L12 is connected to the connection point between the second coil L22 and the second diode D12. Thus, the primary-side circuit 51 and the secondary-side circuit 61 are electrically connected through the first connection line L11 and the second connection line L12.

[0048] The first capacitor C1 is provided on the first connection line L11. The second capacitor C2 is provided on the second connection line L12. For the second converter 50, the primary side circuit 51 and the secondary side circuit 61 are insulated by the first capacitor C1 and the second capacitor C2. The second converter 50 is an isolated DC / DC converter that electrically isolates the primary side circuit 51 and the secondary side circuit 61. The second converter 50 of the present embodiment is a capacitor isolation converter that isolates the primary side circuit 51 and the secondary side circuit 61 by the first capacitor C1 and the second capacitor C2.

[0049] The output terminals 43 and 44 are electrically connected to the low-voltage battery 12. The output terminal 43 is connected to the positive electrode of the low-voltage battery 12. The output terminal 44 is connected to the negative electrode of the low-voltage battery 12. Therefore, among the output terminals 43 and 44, the output terminal 43 is the positive side and the output terminal 44 is the negative side.

[0050] A capacitor 54 is provided between the secondary side circuit 61 and the low-voltage battery 12.

[0051] For the second converter 50, the voltage across both ends of the flying capacitor 33 is input to the primary side circuit 51 as an input voltage. The primary side circuit 51 converts the power input via the two input terminals 41 and 42 for the second converter into AC power by the switching operations of the switching elements Q41 and Q42. Thus, the AC power is transmitted to the secondary side circuit 61 via the first connection line L11 and the second connection line L12. The secondary side circuit 61 converts the AC power input from the first connection line L11 and the second connection line L12 into DC power and outputs it to the output terminals 43 and 44.

[0052] The power conversion device 20 includes a control unit 71. The control unit 71 includes a processor and a storage unit. The processor is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The storage unit includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit stores program codes or instructions configured to cause the processor to execute processing. The storage unit, that is, the computer-readable medium, includes all available media that can be accessed by a general-purpose or special-purpose computer. Alternatively, the control unit 71 may be constituted by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 71 as a processing circuit may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0053] <Control by the control unit>

[0054] The control unit 71 controls the voltage of the DC power supplied from the first converter 30 to the input / output terminals 23 and 24 by controlling the switching elements Q1 to Q6 and controls the voltage across the flying capacitor 33.

[0055] <Charging with power supplied from an external power source>

[0056] A case where at least one of the high-voltage battery 11 and the low-voltage battery 12 is charged with power supplied from the external power source PS will be described. When charging with power supplied from the external power source PS, the switch 34 is in the open state.

[0057] When power is supplied from the external power source PS to the high-voltage battery 11 and the low-voltage battery 12, the control unit 71 alternately switches the switching operation modes of the switching elements Q1 to Q4 between the first mode and the second mode. The first mode is a switching operation mode in which the first switching element Q1 is off, the second switching element Q2 is on, the third switching element Q3 is off, and the fourth switching element Q4 is on. The second mode is a switching operation mode in which the first switching element Q1 is on, the second switching element Q2 is off, the third switching element Q3 is on, and the fourth switching element Q4 is off.

[0058] When the first terminal T1 of the external power source PS is positive, the control unit 71 turns off the fifth switching element Q5 and turns on the sixth switching element Q6. In this case, current is allowed to flow from the sixth switching element Q6 to the second input line L4, but current flow from the second input line L4 to the fifth switching element Q5 is restricted. Current flows from the sixth switching element Q6 to the second input line L4.

[0059] When the second terminal T2 of the external power source PS is positive, the control unit 71 turns on the fifth switching element Q5 and turns off the sixth switching element Q6. In this case, current is allowed to flow from the second input line L4 to the fifth switching element Q5, but current flow from the second input line L4 to the sixth switching element Q6 is restricted. Current flows from the second input line L4 to the fifth switching element Q5.

[0060] As Figure 1 As shown by the dashed line LC1, when the first terminal T1 of the external power source PS is positive and the switching operation mode is the first mode, current flows in the order of the first terminal T1 of the external power source PS → reactor 32 → second switching element Q2 → flying capacitor 33 → fourth switching element Q4 → sixth switching element Q6 → second terminal T2 of the external power source PS. Thereby, the flying capacitor 33 is charged.

[0061] AsFigure 1 As shown by the chain double-dashed line LC2, when the first terminal T1 of the external power supply PS is positive and the switching operation mode is the second mode, a current flows in the order of the first terminal T1 of the external power supply PS → reactor 32 → third switching element Q3 → flying capacitor 33 → first switching element Q1 → high-voltage battery 11 → sixth switching element Q6 → second terminal T2 of the external power supply PS. Thereby, the flying capacitor 33 is discharged.

[0062] As Figure 2 As shown by the dashed line LC3, when the second terminal T2 of the external power supply PS is positive and the switching operation mode is the second mode, a current flows in the order of the second terminal T2 of the external power supply PS → fifth switching element Q5 → first switching element Q1 → flying capacitor 33 → third switching element Q3 → reactor 32 → first terminal T1 of the external power supply PS. Thereby, the flying capacitor 33 is charged.

[0063] As Figure 2 As shown by the chain double-dashed line LC4, when the second terminal T2 of the external power supply PS is positive and the switching operation mode is the first mode, a current flows in the order of the second terminal T2 of the external power supply PS → fifth switching element Q5 → high-voltage battery 11 → fourth switching element Q4 → flying capacitor 33 → second switching element Q2 → reactor 32 → first terminal T1 of the external power supply PS. Thereby, the flying capacitor 33 is discharged.

[0064] The control unit 71 controls the switching elements Q1 to Q6 such that the output voltage output from the input / output terminals 23, 24 follows the target value and the voltage across the flying capacitor 33 follows the target value. Thereby, the control unit 71 can charge the high-voltage battery 11 by controlling the output voltage output from the input / output terminals 23, 24. The control unit 71 can control the voltage across the flying capacitor 33.

[0065] The control unit 71 controls the voltage of the DC power output from the second converter 50 to the output terminals 43, 44 by controlling the switching elements Q41, Q42. For example, the control unit 71 alternately switches the switching operation mode of the switching elements Q41, Q42 between the third mode and the fourth mode. The third mode is a switching operation mode in which the upper-arm switching element Q41 is turned on and the lower-arm switching element Q42 is turned off. The fourth mode is a switching operation mode in which the upper-arm switching element Q41 is turned off and the lower-arm switching element Q42 is turned on.

[0066] The control unit 71 controls the switching elements Q41, Q42 such that the output voltage output from the output terminals 43, 44 follows the target value. Thereby, the control unit 71 can charge the low-voltage battery 12 by controlling the output voltage output from the output terminals 43, 44.

[0067] When the control unit 71 supplies power from the external power supply PS to the high-voltage battery 11 and does not supply power to the low-voltage battery 12, it alternately switches the switching operation modes of the switching elements Q1 to Q4 between the fifth mode and the sixth mode. The fifth mode is a switching operation mode in which the first switching element Q1 is off, the second switching element Q2 is off, the third switching element Q3 is on, and the fourth switching element Q4 is on. The sixth mode is a switching operation mode in which the first switching element Q1 is on, the second switching element Q2 is on, the third switching element Q3 is off, and the fourth switching element Q4 is off.

[0068] When the first terminal T1 of the external power supply PS is positive, the control unit 71 turns off the fifth switching element Q5 and turns on the sixth switching element Q6. In this case, current is allowed to flow from the second input / output line L2 to the sixth switching element Q6, but current flow from the first input / output line L1 to the fifth switching element Q5 is restricted. Current flows from the sixth switching element Q6 to the second input line L4.

[0069] When the second terminal T2 of the external power supply PS is positive, the control unit 71 turns on the fifth switching element Q5 and turns off the sixth switching element Q6. In this case, current is allowed to flow from the second input line L4 to the fifth switching element Q5, but current flow from the second input line L4 to the sixth switching element Q6 is restricted. Current flows from the second input line L4 to the fifth switching element Q5.

[0070] When the first terminal T1 of the external power supply PS is positive and the switching operation mode is the fifth mode, current flows in the order of the first terminal T1 of the external power supply PS → reactor 32 → third switching element Q3 → fourth switching element Q4 → sixth switching element Q6 → second terminal T2 of the external power supply PS.

[0071] When the first terminal T1 of the external power supply PS is positive and the switching operation mode is the sixth mode, current flows in the order of the first terminal T1 of the external power supply PS → reactor 32 → second switching element Q2 → first switching element Q1 → high-voltage battery 11 → sixth switching element Q6 → second terminal T2 of the external power supply PS.

[0072] When the second terminal T2 of the external power supply PS is positive and the switching operation mode is the sixth mode, current flows in the order of the second terminal T2 of the external power supply PS → fifth switching element Q5 → first switching element Q1 → second switching element Q2 → reactor 32 → first terminal T1 of the external power supply PS.

[0073] When the second terminal T2 of the external power supply PS is positive and the switching operation mode is the fifth mode, a current flows in the order of the second terminal T2 of the external power supply PS → the fifth switching element Q5 → the high-voltage battery 11 → the fourth switching element Q4 → the third switching element Q3 → the reactor 32 → the first terminal T1 of the external power supply PS.

[0074] The control unit 71 controls the switching elements Q1 to Q6 so that the output voltage output from the input / output terminals 23 and 24 follows the target value. Thus, the control unit 71 can charge the high-voltage battery 11 by controlling the output voltage output from the input / output terminals 23 and 24.

[0075] <Charging of the low-voltage battery with the power supplied from the high-voltage battery>

[0076] A case where the low-voltage battery 12 is charged by supplying power from the high-voltage battery 11 to the low-voltage battery 12 will be described. When the low-voltage battery 12 is charged by the high-voltage battery 11, the switch 34 is in a closed state.

[0077] The control unit 71 maintains the first switching element Q1 and the third switching element Q3 in the off state. The control unit 71 maintains the second switching element Q2 and the fourth switching element Q4 in the on state. In this state, by performing a chopping operation on the fifth switching element Q5 and the sixth switching element Q6, the voltage input from the high-voltage battery 11 via the input / output terminals 23 and 24 is stepped down. By alternately turning on the fifth switching element Q5 and the sixth switching element Q6, the voltage input from the high-voltage battery 11 is stepped down and output. Thereby, the voltage across the flying capacitor 33 is controlled. In the present embodiment, the switching elements Q1 to Q6 are switching elements for conversion. A buck circuit is constituted by the switching elements Q1 to Q6, and the voltage across the flying capacitor 33 is controlled by the voltage output from the buck circuit.

[0078] The control unit 71 alternately turns on the upper-arm switching element Q41 and the lower-arm switching element Q42. By the series resonance operation based on this, the output voltage of the second converter 50 is controlled. Thereby, the low-voltage battery 12 can be charged. The operation of the second converter 50 of the present embodiment will be described in detail.

[0079] Figure 4 The on and off states of the upper-arm switching element Q41 and the lower-arm switching element Q42, the current Ip flowing through the upper-arm switching element Q41, the current In flowing through the lower-arm switching element Q42, the current IL1 flowing through the first coil L21, the current IL2 flowing through the second coil L22, the voltage VCp across the first capacitor C1, the voltage VCn across the second capacitor C2, the voltage VLp across the first coil L21, and the voltage VLn across the second coil L22 are shown.

[0080] Figures 5 to 10 The load current I1 and the non-load current I2 are shown. The load current I1 is the current flowing through the low-voltage battery 12 serving as a load. The non-load current I2 is the current that does not flow through the low-voltage battery 12 serving as a load.

[0081] As Figure 4 shown, at time T11, the upper-arm switching element Q41 is turned on and the lower-arm switching element Q42 is turned off. As Figure 5 shown, at time T11, the upper-arm switching element Q41 is turned on, so that the voltage across both ends of the flying capacitor 33 serving as a DC power supply is input to the second converter 50. The load current I1 flows through the path of the upper-arm switching element Q41, the first capacitor C1, the first coil L21, the low-voltage battery 12, the second diode D12, and the second capacitor C2. The non-load current I2 flows through the path of the upper-arm switching element Q41, the first capacitor C1, the first coil L21, the second coil L22, and the second capacitor C2. The first capacitor C1 and the second capacitor C2 are charged.

[0082] At time T12, the upper-arm switching element Q41 is switched to off. As a result, power is no longer supplied from the flying capacitor 33 to the second converter 50. The load current I1 flows due to the energy stored in the first coil L21. As Figure 6 shown, the load current I1 flows through the path of the first coil L21, the low-voltage battery 12, and the first diode D11. The non-load current I2 flows due to the energy stored in the second coil L22. The non-load current I2 causes the lower-arm switching element Q42 to conduct in the reverse direction. The non-load current I2 flows through the path of the second coil L22, the second capacitor C2, the freewheeling diode D of the lower-arm switching element Q42, the first capacitor C1, and the first coil L21.

[0083] At time T13, with the lower-arm switching element Q42 conducting in the reverse direction, the lower-arm switching element Q42 is turned on. Due to the lower-arm switching element Q42 conducting in the reverse direction, the voltage across both ends of the lower-arm switching element Q42 becomes 0. Therefore, ZVS (Zero Voltage Switching) can be performed. As Figure 7 shown, the path through which the load current I1 flows is the same as at time T12. The non-load current I2 flows through the path of the second coil L22, the second capacitor C2, the lower-arm switching element Q42, the first capacitor C1, and the first coil L21.

[0084] As time elapses from time T13, the output currents from the first coil L21 and the second coil L22 become smaller. At time T14, the discharge from the first capacitor C1 and the second capacitor C2 is switched. As a result, the current polarity of the non-load current I2 changes.Figure 8 As shown, a load current I1 flows through a path including a first capacitor C1, a lower-arm switching element Q42, a second capacitor C2, a second coil L22, a low-voltage battery 12, and a first diode D11. The voltages of the first capacitor C1 and the second capacitor C2 decrease due to discharging. Energy is stored in the first coil L21 and the second coil L22.

[0085] At time T15, the lower-arm switching element Q42 is switched to the off state. As Figure 9 shown, a load current I1 flows through a path including the first capacitor C1, a freewheeling diode D of the upper-arm switching element Q41, the second capacitor C2, the second coil L22, the low-voltage battery 12, and the first diode D11. A non-load current I2 flows through a path including the second capacitor C2, the second coil L22, the first coil L21, the first capacitor C1, and the freewheeling diode D of the upper-arm switching element Q41. The load current I1 and the non-load current I2 cause the upper-arm switching element Q41 to conduct in the reverse direction.

[0086] At time T16, the upper-arm switching element Q41 is switched to the on state. Since the upper-arm switching element Q41 conducts in the reverse direction, the voltage across the upper-arm switching element Q41 is 0. Therefore, ZVS can be achieved. As Figure 10 shown, the load current I1 and the non-load current I2 change from flowing through the freewheeling diode D of the upper-arm switching element Q41 to flowing through the upper-arm switching element Q41.

[0087] [Function of this Embodiment]

[0088] The power conversion device 20 includes a switch 34. By closing this switch 34 and controlling the first switching element Q1 to the sixth switching element Q6, the voltage of the high-voltage battery 11 can be stepped down and input to the second converter 50. The second converter 50 steps down the input voltage and outputs it. Thereby, the low-voltage battery 12 is charged.

[0089] Here, the second converter 50 of the present embodiment is a capacitor isolation converter that isolates the primary side circuit 51 and the secondary side circuit 61 through the first capacitor C1 and the second capacitor C2. Since the capacitor isolation converter does not have a transformer, it is difficult to step down the input voltage. In particular, it is difficult to step down the voltage input during light load. As in the present embodiment, when a half-bridge circuit is used as the primary side circuit 51, sometimes it can only be stepped down to 1 / 2 of the input voltage. Therefore, it is sometimes necessary to reduce the voltage across the flying capacitor 33 according to the output voltage of the second converter 50. For example, if the target value of the output voltage of the second converter 50 is 15 [V], and the second converter 50 can only be reduced to 1 / 2 of the input voltage, the voltage across the flying capacitor 33, which is the input voltage of the second converter 50, is 30 [V]. The lower the voltage across the flying capacitor 33, the greater the current. The current from the high-voltage battery 11 is supplied through the second switching element Q2, the fourth switching element Q4, the fifth switching element Q5, and the sixth switching element Q6. The lower the voltage across the flying capacitor 33, the greater the current flowing through these switching elements Q2, Q4, Q5, Q6. As a result, the required rated current of the switching elements Q2, Q4, Q5, Q6 is probably larger.

[0090] In the present embodiment, the secondary side circuit 61 includes a branch 62 in which the first coil L21 and the first diode D11 are connected in series, and a branch 63 in which the second coil L22 and the second diode D12 are connected in series. In the secondary side circuit 61, output currents are generated in the coils L21, L22 of the respective branches 62, 63. The sum of the output currents of the two coils L21, L22 becomes the overall output current. Therefore, the current input to the secondary side circuit 61 can be increased. As a result, step-down using the secondary side circuit 61 can be achieved, and correspondingly, the voltage of the flying capacitor 33 can be increased.

[0091] [Effects of the Present Embodiment]

[0092] (1) The secondary side circuit 61 includes a first branch 62 in which the first coil L21 and the first diode D11 are connected in series, and a second branch 63 in which the second coil L22 and the second diode D12 are connected in series. Output currents are generated in the coils L21, L22 of the respective branches 62, 63. The sum of the output currents of the two coils L21, L22 becomes the overall output current. Therefore, the current input to the secondary side circuit 61 can be increased. The output current increases, so the output voltage of the second converter 50 becomes lower. Thereby, the output voltage output from the output terminals 43, 44 can be reduced.

[0093] (2) The second converter 50 performs power conversion using the voltage across the flying capacitor 33 as the input voltage. The voltage across the flying capacitor 33 is controlled by stepping down the voltage of the high-voltage battery 11 through the switching operations of the switching elements Q2, Q4, Q5, and Q6. The lower the voltage across the flying capacitor 33, the greater the current flowing through the switching elements Q2, Q4, Q5, and Q6, and the higher the current rating required for the switching elements Q2, Q4, Q5, and Q6. As in the embodiment, by increasing the output current of the secondary-side circuit 61, the output voltage of the secondary-side circuit 61 decreases. As a result, the step-down ratio of the second converter 50 can be increased. Even if the voltage across the flying capacitor 33 is increased, the output voltage required by the second converter 50 can be output. Therefore, it is possible to suppress the increase in the current flowing through the switching elements Q2, Q4, Q5, and Q6 due to the decrease in the voltage across the flying capacitor 33.

[0094] (3) The power conversion device 20 is mounted on the vehicle 10. The vehicle 10 includes a high-voltage battery 11 required for driving the main engine and a low-voltage battery 12 required for driving the auxiliary machine. In the case where there is no power supply from the external power source PS, etc., it may be desired to charge the low-voltage battery 12 using the high-voltage battery 11. When the voltage of the high-voltage battery 11 is higher than the voltage of the external power source PS, the current flowing through the switching elements Q2, Q4, Q5, and Q6 increases, and there is a case where the low-voltage battery 12 cannot be charged using the high-voltage battery 11. For example, when the rated current of the switching elements Q2, Q4, Q5, and Q6 only satisfies the condition of the current flowing through the charging by the external power source PS, the low-voltage battery 12 cannot be charged using the high-voltage battery 11. As in this embodiment, by reducing the current flowing through the switching elements Q2, Q4, Q5, and Q6, the low-voltage battery 12 can be charged using the high-voltage battery 11. The circuit can be shared when charging the low-voltage battery 12 using the external power source PS and when charging the low-voltage battery 12 using the high-voltage battery 11.

[0095] [Modification Example]

[0096] The embodiment can be modified as follows. The embodiment and the following modification examples can be implemented in combination with each other within a range where there is no technical contradiction.

[0097] ○ The primary-side circuit 51 of the second converter 50 only needs to be able to convert the input power into AC power. For example, the primary-side circuit 51 may also be Figure 11The structure shown. The primary-side circuit 51 includes a first upper-arm switching element Q11, a first lower-arm switching element Q12, a second upper-arm switching element Q13, and a second lower-arm switching element Q14. The primary-side circuit 51 is a full-bridge circuit of the switching elements Q11 to Q14. The first upper-arm switching element Q11 and the first lower-arm switching element Q12 are connected in series with each other. The second upper-arm switching element Q13 and the second lower-arm switching element Q14 are connected in series with each other. The upper-arm switching elements Q11, Q13 are electrically connected to the second converter input terminal 41. The lower-arm switching elements Q12, Q14 are electrically connected to the second converter input terminal 42. The switching elements Q11 to Q14 are, for example, MOSFETs. The switching elements Q11 to Q14 may also be IGBTs or GaN-HEMTs.

[0098] In the case where the primary-side circuit 51 is configured as Figure 11 described above, the switching operation modes of the switching elements Q11 to Q14 are alternately switched between the seventh mode and the eighth mode. The seventh mode is a switching operation mode in which the first upper-arm switching element Q11 is turned on, the first lower-arm switching element Q12 is turned off, the second upper-arm switching element Q13 is turned off, and the second lower-arm switching element Q14 is turned on. The eighth mode is a switching operation mode in which the first upper-arm switching element Q11 is turned off, the first lower-arm switching element Q12 is turned on, the second upper-arm switching element Q13 is turned on, and the second lower-arm switching element Q14 is turned off.

[0099] The first connection line L11 connects the connection point between the first upper-arm switching element Q11 and the first lower-arm switching element Q12 to the connection point between the first coil L21 and the first diode D11. The second connection line L12 connects the connection point between the second upper-arm switching element Q13 and the second lower-arm switching element Q14 to the connection point between the second coil L22 and the second diode D12.

[0100] The transition of the switching operation mode of the primary-side circuit 51 will be described.

[0101] As Figure 11 shown, when the switching operation mode of the primary-side circuit 51 is the seventh mode, a load current I1 flows through the path of the first upper-arm switching element Q11, the first capacitor C1, the first coil L21, the low-voltage battery 12, the second diode D12, the second capacitor C2, and the second lower-arm switching element Q14. A non-load current I2 flows through the path of the first upper-arm switching element Q11, the first capacitor C1, the first coil L21, the second coil L22, the second capacitor C2, and the second lower-arm switching element Q14. The first capacitor C1 and the second capacitor C2 are gradually charged.

[0102] As Figure 12As shown, if the first upper-arm switching element Q11 and the second lower-arm switching element Q14 are switched to the off state, a load current I1 flows due to the energy stored in the first coil L21. The load current I1 flows through the path of the first coil L21, the low-voltage battery 12, and the first diode D11. A non-load current I2 flows due to the energy stored in the second coil L22. The non-load current I2 flows through the path of the second coil L22, the second capacitor C2, the freewheeling diode D of the second upper-arm switching element Q13, the freewheeling diode D of the first lower-arm switching element Q12, the first capacitor C1, and the first coil L21. The non-load current I2 causes the first lower-arm switching element Q12 and the second upper-arm switching element Q13 to conduct in the reverse direction.

[0103] As Figure 13 shown, the control unit 71 makes the switching operation mode of the primary-side circuit 51 the eighth mode. In a state where the first lower-arm switching element Q12 and the second upper-arm switching element Q13 conduct in the reverse direction, the first lower-arm switching element Q12 and the second upper-arm switching element Q13 are turned on. By the first lower-arm switching element Q12 and the second upper-arm switching element Q13 conducting in the reverse direction, the voltage across each of the switching elements Q12 and Q13 becomes 0. Therefore, ZVS can be performed. The load current I1 flows through the path of the first coil L21, the low-voltage battery 12, and the first diode D11. The non-load current I2 flows through the path of the second coil L22, the second capacitor C2, the second upper-arm switching element Q13, the first lower-arm switching element Q12, the first capacitor C1, and the first coil L21.

[0104] As Figure 14 shown, if the output currents from the first coil L21 and the second coil L22 gradually decrease and the discharge from the first capacitor C1 and the second capacitor C2 is switched, the current polarity of the non-load current I2 changes. The load current I1 flows through the path of the first capacitor C1, the first lower-arm switching element Q12, the second upper-arm switching element Q13, the second capacitor C2, the second coil L22, the low-voltage battery 12, and the first diode D11. The voltages of the first capacitor C1 and the second capacitor C2 gradually decrease due to the discharge. Energy is gradually stored in the first coil L21 and the second coil L22.

[0105] As Figure 15As shown, the first lower-arm switching element Q12 and the second upper-arm switching element Q13 are switched to the off state. A load current I1 flows through a path including the first capacitor C1, the freewheeling diode D of the first upper-arm switching element Q11, the freewheeling diode D of the second lower-arm switching element Q14, the second capacitor C2, the second coil L22, the low-voltage battery 12, and the first diode D11. A non-load current I2 flows through a path including the second capacitor C2, the second coil L22, the first coil L21, the first capacitor C1, the freewheeling diode D of the first upper-arm switching element Q11, and the freewheeling diode D of the second lower-arm switching element Q14. The load current I1 and the non-load current I2 cause the first upper-arm switching element Q11 and the second lower-arm switching element Q14 to conduct in the reverse direction.

[0106] As Figure 16 shown, the control unit 71 sets the switching operation mode of the primary-side circuit 51 to the seventh mode. In a state where the first upper-arm switching element Q11 and the second lower-arm switching element Q14 conduct in the reverse direction, the first upper-arm switching element Q11 and the second lower-arm switching element Q14 are turned on. By the first upper-arm switching element Q11 and the second lower-arm switching element Q14 conducting in the reverse direction, the voltage across each of the switching elements Q11 and Q14 becomes 0. Therefore, ZVS can be achieved. The load current I1 and the non-load current I2 change from a path passing through the freewheeling diode D of the first upper-arm switching element Q11 and the freewheeling diode D of the second lower-arm switching element Q14 to a path passing through the first upper-arm switching element Q11 and the second lower-arm switching element Q14.

[0107] ○ The external power supply PS can also be a DC power supply. In this case, the power conversion device 20 may not include the fifth switching element Q5 and the sixth switching element Q6. When connecting the positive side of the DC power supply to the input terminal 21, it is only necessary to connect the negative side to the second input / output line L2. When connecting the negative side of the DC power supply to the input terminal 21, it is only necessary to connect the positive side to the first input / output line L1.

[0108] ○ Alternatively, the power conversion device 20 may use the high-voltage battery 11 without charging the low-voltage battery 12. Boost the voltage of the external power supply PS and output it to the flying capacitor 33.

[0109] ○ The reactor 32 is provided on the first terminal T1 side of the external power supply PS, but the reactor 32 may also be provided on the second terminal T2 side, or the reactor 32 may be provided on both sides. That is, the reactor 32 may be provided on at least one of the first input line L3 and the second input line L4.

[0110] Alternatively, the power conversion device 20 can output the power input from the high-voltage battery 11 as AC power from the input terminals 21 and 22. For example, the control unit 71 alternately switches the switching operation modes of the first switching element Q1 to the sixth switching element Q6 between the ninth mode and the tenth mode. The ninth mode is a switching operation mode in which the first switching element Q1 is turned on, the second switching element Q2 is turned on, the third switching element Q3 is turned off, the fourth switching element Q4 is turned off, the fifth switching element Q5 is turned off, and the sixth switching element Q6 is turned on. The tenth mode is a switching operation mode in which the first switching element Q1 is turned off, the second switching element Q2 is turned off, the third switching element Q3 is turned on, the fourth switching element Q4 is turned on, the fifth switching element Q5 is turned on, and the sixth switching element Q6 is turned off.

[0111] ○As Figure 17 shown, it is also possible to interchange the first coil L21 and the first diode D11, and to interchange the second coil L22 and the second diode D12. In this case, the wiring 64 is the second wiring. The wiring 65 is the first wiring.

[0112] The cathode terminals of the first diode D11 and the second diode D12 are electrically connected to the positive output terminal among the two output terminals 43 and 44. The anode terminal of the first diode D11 is electrically connected to the first coil L21. The anode terminal of the second diode D12 is electrically connected to the second coil L22. Thus, the anode terminals of the first diode D11 and the second diode D12 are electrically connected to the negative output terminal among the output terminals 43 and 44 via the coils L21 and L22.

[0113] ○Alternatively, the secondary-side circuit 61 further includes a branch. The branch is a structure obtained by connecting a coil and a diode in series. In this case, the coil of the additional branch is connected to the coils L21 and L22 of the branches 62 and 63 through the first wiring, and the diode of the additional branch is connected to the diodes D11 and D12 of the branches 62 and 63 through the second wiring.

Claims

1. A power conversion device, characterized in that: have: a primary side circuit including a switching element, and configured to convert input power into AC power and output the AC power by switching operation of the switching element; The first connecting line and the second connecting line; a first capacitor disposed on the first connecting line; a second capacitor disposed on the second connecting line; as well as The secondary circuit is configured to convert the AC power input from the primary circuit into DC power and output the DC power to two output terminals. The first connecting line and the second connecting line each include a first end electrically connected to the primary side circuit and a second end electrically connected to the secondary side circuit. The secondary side circuit comprises: a first branch having a first coil and a first diode connected in series with each other, wherein the second end of the first connecting line is connected to a connection point between the first coil and the first diode; a second branch having a second coil and a second diode connected in series with each other, wherein the second end of the second connecting line is connected to a connection point between the second coil and the second diode; a first wiring connecting the first coil and the second coil to one of the two output terminals; as well as a second wiring connecting the first diode and the second diode to the other of the two output terminals, An anode terminal of the first diode and an anode terminal of the second diode are electrically connected to a negative output terminal of the two output terminals. The cathode terminal of the first diode is electrically connected to the first coil. A cathode terminal of the second diode is electrically connected to the second coil.

2. The power conversion device according to claim 1, characterized in that: have: Flying capacitors; and The step-down circuit includes a switching element for conversion, and is configured to control the voltage across the flying capacitor by stepping down the input power and outputting the power. The voltage across the flying capacitor is input to the primary side circuit.

3. The power conversion device according to claim 2, characterized in that: The power conversion device is mounted on a vehicle, A voltage is input from a high voltage battery to the step-down circuit. The secondary side circuit is configured to output a voltage to a low voltage battery.

4. A power conversion device, characterized in that: have: a primary side circuit including a switching element, and configured to convert input power into AC power and output the AC power by switching operation of the switching element; The first connecting line and the second connecting line; a first capacitor disposed on the first connecting line; a second capacitor disposed on the second connecting line; as well as The secondary circuit is configured to convert the AC power input from the primary circuit into DC power and output the DC power to two output terminals. The first connecting line and the second connecting line each include a first end electrically connected to the primary side circuit and a second end electrically connected to the secondary side circuit. The secondary side circuit comprises: a first branch having a first coil and a first diode connected in series with each other, wherein the second end of the first connecting line is connected to a connection point between the first coil and the first diode; a second branch having a second coil and a second diode connected in series with each other, wherein the second end of the second connecting line is connected to a connection point between the second coil and the second diode; a first wiring connecting the first coil and the second coil to one of the two output terminals; as well as a second wiring connecting the first diode and the second diode to the other of the two output terminals, The cathode terminal of the first diode and the cathode terminal of the second diode are electrically connected to the positive output terminal of the two output terminals. The anode terminal of the first diode is electrically connected to the first coil, An anode terminal of the second diode is electrically connected to the second coil.

5. The power conversion device according to claim 4, characterized in that: have: Flying capacitors; and The step-down circuit includes a switching element for conversion, and is configured to control the voltage across the flying capacitor by stepping down the input power and outputting the power. The voltage across the flying capacitor is input to the primary side circuit.

6. The power conversion device according to claim 5, characterized in that: The power conversion device is mounted on a vehicle, A voltage is input from a high voltage battery to the step-down circuit. The secondary side circuit is configured to output a voltage to a low voltage battery.

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