Power conversion device

Abstract

To reduce the output voltage.SOLUTION: A power conversion device 20 includes a primary circuit 51 that converts input power into AC power and outputs it, a first connection line L11 and a second connection line L12 to which the AC power is input from the primary circuit 51, and a secondary circuit 61 that converts the AC power input from the primary circuit 51 into DC power and outputs it to two output terminals 43, 44. The secondary circuit 61 includes a first leg 62 having a first coil L21 and a first diode D11 connected in series to each other, a second leg 63 having a second coil L22 and a second diode D12 connected in series to each other, a wiring 64 that connects the first coil L21 and the second coil L22 to one of the two output terminals 43, 44, and a wiring 65 that connects the first diode D11 and the second diode D12 to the other of the two output terminals 43, 44.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] The power conversion device disclosed in Patent Document 1 includes a primary circuit, a secondary circuit, a first connection line and a second connection line connecting the primary circuit and the secondary circuit, a first capacitor provided on the first connection line, a second capacitor provided on the second connection line, a third connection line provided closer to the secondary circuit than the first capacitor and the second capacitor and connecting the first connection line and the second connection line, an exciting inductor provided on the third connection line, and a control unit. The primary circuit includes a switching element. The primary circuit converts input power into AC power by the switching element operating with a predetermined switching frequency. The secondary circuit converts the AC power input via the first connection line and the second connection line into DC power. The first capacitor and the second capacitor insulate the primary circuit and the secondary circuit. The control unit controls the switching frequency, the duty ratio, or the phase of the switching element. Thereby, the output voltage is controlled.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power conversion device that insulates a primary circuit and a secondary circuit using a capacitor, it may be required to further reduce the output voltage.

Means for Solving the Problems

[0005] The power conversion device for solving the above problems includes a switching element, a primary circuit that converts the input power into AC power by the switching operation of the switching element and outputs it, and one end of each is electrically connected to the primary circuit, and the primary circuit inputs 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 the other ends of the first connection line and the second connection line are connected, and the AC power input from the primary circuit is converted into DC power and output to two output terminals. The secondary circuit includes a first leg having a first coil and a first diode connected in series, and the other end of the first connection line is connected to the connection point between the first coil and the first diode. A second leg having a second coil and a second diode connected in series, and the other end of the second connection line is connected to the 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 first diode and the second diode are connected such that the anode terminal is on the negative side of the output terminal and the cathode terminal is on the positive side of the output terminal.

[0006] The secondary circuit includes a first leg in which a first coil and a first diode are connected in series, and a second leg in which a second coil and a second diode are connected in series. Output current is generated in any of the coils of each leg. Since the sum of the output currents of the two coils becomes the total output current, the output current of the secondary circuit can be increased. By increasing the output current, the output voltage of the secondary circuit decreases. Thereby, the output voltage output from the output terminal can be decreased.

[0007] Regarding the above power conversion device, it includes a flying capacitor and a buck circuit that includes a conversion switching element and controls the voltage across the flying capacitor by stepping down the input power and outputting it. The voltage across the flying capacitor may be input to the primary circuit.

[0008] Regarding the above power conversion device, the power conversion device is mounted on a vehicle, a voltage is input from a high-voltage battery to the step-down circuit, and the secondary-side circuit may output a voltage to a low-voltage battery.

Effect of the Invention

[0009] According to the present invention, the output voltage can be reduced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Figure 10

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DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the power conversion device will be described. As shown in FIG. 1, 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, for example, the main unit of the vehicle 10. The main unit is, for example, a driving motor that drives the vehicle 10. The low-voltage battery 12 supplies power to, for example, the auxiliary equipment of the vehicle 10. The auxiliary equipment is an electrical component other than the main unit. 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.

[0012] <Power Conversion Device> 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. Whether the first terminal T1 or the second terminal T2 becomes positive switches according to the passage of 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 power-converting the power supplied from the external power supply PS electrically connected to the input terminals 21, 22.

[0013] The first converter 30 performs power conversion on 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.

[0014] 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 configured by connecting the switching elements Q1 to Q4 in series with each other in the order of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4. The switching elements Q1 to Q4 are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switching elements Q1 to Q4 may be IGBTs (Insulated Gate Bipolar Transistors) or GaN-HEMTs.

[0015] The flying capacitor 33 electrically connects the connection point between the first switching element Q1 and the second switching element Q2 and the connection point between the third switching element Q3 and the fourth switching element Q4.

[0016] The switch 34 is provided 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 when it is in the closed state. The switching circuit 31 is electrically connected to the two input / output terminals 23, 24. Specifically, the first input / output line L1 electrically connects one of the two input / output terminals 23, 24, i.e., the input / output terminal 23, and one end of the switching circuit 31. The second input / output line L2 electrically connects the other of the two input / output terminals 23, 24, i.e., the input / output terminal 24, and the other end of the switching circuit 31. The first switching element Q1 is connected to the input / output terminal 23 via the first input / output line L1. The fourth switching element Q4 is connected to the input / output terminal 24 via the second input / output line L2.

[0017] 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 electrode line L5, and a negative electrode 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.

[0018] The first input line L3 electrically connects the first input terminal 21 and the connection point between the second switching element Q2 and the third switching element Q3. The reactor 32 is provided on the first input line L3.

[0019] The second input line L4 electrically connects the second input terminal 22 and one of the two input / output terminals 23, 24. The positive electrode line L5 electrically connects the second input line L4 and the first input / output line L1. Therefore, the second input line L4 is electrically connected to the input / output terminal 23 via the positive electrode line L5 and the first input / output line L1.

[0020] The negative electrode line L6 electrically connects the second input line L4 and the second input / output line L2. Therefore, the second input line L4 is electrically connected to the input / output terminal 24 via the negative electrode line L6 and the second input / output line L2.

[0021] 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 becomes positive or the second terminal T2 becomes positive. The fifth switching element Q5 is arranged on the positive electrode line L5. The sixth switching element Q6 is arranged on the negative electrode line L6. When the switching elements Q5 and Q6 are MOSFETs, the switching elements Q5 and Q6 are provided such that the forward direction of the parasitic diode is from the second input / output line L2 to the first input / output line L1. That is, the anode terminal of the parasitic diode is electrically connected to the second input / output line L2, and the cathode terminal of the parasitic diode is electrically connected to the first input / output line L1.

[0022] 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. In the first converter 30, the AC power supplied from the external power supply PS is power-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 and outputs the voltage of the AC power. The first converter 30 may step down and output the voltage of the AC power.

[0023] The capacitor 25 is provided between the first converter 30 and the high-voltage battery 11. The power conversion device 20 includes two input terminals 41 and 42 for the second converter, a second converter 50, and two output terminals 43 and 44.

[0024] The two input terminals 41 and 42 for the second converter are electrically connected to both ends of the flying capacitor 33. Specifically, the input terminal 41 for the second converter is electrically connected to one end of the flying capacitor 33, and the input terminal 42 for the second converter is electrically connected to the other end of the flying capacitor 33.

[0025] As shown in FIG. 3, 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.

[0026] The primary side circuit 51 includes an upper arm switching element Q41 and a lower arm switching element Q42. The upper arm switching element Q41 and the lower arm switching element Q42, which are switching elements, each include 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 input terminal 41 for the second converter. The lower arm switching element Q42 is electrically connected to the input terminal 42 for the second converter. The switching elements Q41 and Q42 are, for example, MOSFETs. The switching elements Q41 and Q42 may be IGBTs or GaN-HEMTs.

[0027] The secondary circuit 61 includes a first leg 62, a second leg 63, a wiring 64, and a wiring 65. The first leg 62 includes a first coil L21 and a first diode D11 that are connected in series with each other. The second leg 63 includes a second coil L22 and a second diode D12 that are connected in series with each other. The secondary 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 one of the two output terminals 43 and 44, which is the output terminal 43. The wiring 65 connects the first diode D11 and the second diode D12 to the other of the two output terminals 43 and 44, which is the output terminal 44. The wiring 64 is an example of a first wiring. The wiring 65 is an example of a second wiring.

[0028] The anode terminals of the first diode D11 and the second diode D12 are connected to the negative side of the output terminals 43 and 44. The cathode terminals of the first diode D11 and the second diode D12 are connected to the positive side of the output terminals 43 and 44.

[0029] One end of each of the first connection line L11 and the second connection line L12 is electrically connected to the primary circuit 51. Specifically, one 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. One end of the second connection line L12 is connected to the lower arm switching element Q42.

[0030] The other end of each of the first connection line L11 and the second connection line L12 is electrically connected to the secondary circuit 61. Specifically, the other end of the first connection line L11 is connected to the connection point between the first coil L21 and the first diode D11. The other end of the second connection line L12 is connected to the connection point between the second coil L22 and the second diode D12. Thereby, the primary circuit 51 and the secondary circuit 61 are electrically connected by the first connection line L11 and the second connection line L12.

[0031] The first capacitor C1 is provided on the first connection line L11. The second capacitor C2 is provided on the second connection line L12. In the second converter 50, the primary circuit 51 and the secondary circuit 61 are insulated by the first capacitor C1 and the second capacitor C2. The second converter 50 is an isolated DC / DC converter in which the primary circuit 51 and the secondary circuit 61 are electrically insulated. The second converter 50 of the present embodiment is a capacitor isolation converter that insulates the primary circuit 51 and the secondary circuit 61 by the first capacitor C1 and the second capacitor C2.

[0032] The output terminals 43 and 44 are electrically connected to the low-voltage battery 12. Specifically, 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.

[0033] The capacitor 54 is provided between the secondary circuit 61 and the low-voltage battery 12. In the second converter 50, the voltage across both ends of the flying capacitor 33 is input to the primary circuit 51 as the input voltage. The primary circuit 51 converts the power input through the two input terminals 41 and 42 for the second converter into AC power by the switching operation of the switching elements Q41 and Q42. Thereby, AC power is transmitted to the secondary circuit 61 through the first connection line L11 and the second connection line L12. The secondary 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.

[0034] 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 any available medium accessible by a general-purpose or dedicated computer. The control unit 71 may be configured by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 71, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0035] <Control performed by the control unit> The control unit 71 controls the voltages of the DC power output from the first converter 30 to the input / output terminals 23 and 24 and the voltage across the flying capacitor 33 by controlling the switching elements Q1 to Q6.

[0036] <Charging with power supplied from an external power source> A case where at least one of the high-voltage battery 11 and the low-voltage battery 12 is charged with the power supplied from the external power source PS will be described. When charging is performed with the power supplied from the external power source PS, the switch 34 is turned on.

[0037] When the control unit 71 supplies power from the external power supply PS to the high-voltage battery 11 and the low-voltage battery 12, it alternately switches the switching patterns of the switching elements Q1 to Q4 between a first pattern and a second pattern. The first pattern is a switching pattern 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 pattern is a switching pattern 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.

[0038] 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, while current is allowed to flow from the sixth switching element Q6 to the second input line L4, current flow from the second input line L4 to the fifth switching element Q5 is restricted. The current flows from the sixth switching element Q6 to the second input line L4.

[0039] 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, while current is allowed to flow from the second input line L4 to the fifth switching element Q5, current flow from the second input line L4 to the sixth switching element Q6 is restricted. The current flows from the second input line L4 to the fifth switching element Q5.

[0040] As shown by the broken line LC1 in FIG. 1, when the first terminal T1 of the external power supply PS is positive and in the case of the first pattern, current flows in the order of the first terminal T1 of the external power supply 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 supply PS. Thereby, the flying capacitor 33 is charged.

[0041] As shown by the two-dot chain line LC2 in Fig. 1, when the first terminal T1 of the external power supply PS is positive and in the case of the second pattern, the 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.

[0042] As shown by the broken line LC3 in Fig. 2, when the second terminal T2 of the external power supply PS is positive and in the case of the second pattern, the 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.

[0043] As shown by the two-dot chain line LC4 in Fig. 2, when the second terminal T2 of the external power supply PS is positive and in the case of the first pattern, the 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.

[0044] The control unit 71 controls the switching elements Q1 to Q6 so 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.

[0045] The control unit 71 controls the voltage of the DC power output from the second converter 50 to the output terminals 43 and 44 by controlling the switching elements Q41 and Q42. For example, the control unit 71 alternately switches the switching patterns of the switching elements Q41 and Q42 between a third pattern and a fourth pattern. The third pattern is a switching pattern in which the upper arm switching element Q41 is on and the lower arm switching element Q42 is off. The fourth pattern is a switching pattern in which the upper arm switching element Q41 is off and the lower arm switching element Q42 is on.

[0046] The control unit 71 controls the switching elements Q41 and Q42 so that the output voltage output from the output terminals 43 and 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 and 44.

[0047] 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, the control unit 71 alternately switches the switching patterns of the switching elements Q1 to Q4 between a fifth pattern and a sixth pattern. The fifth pattern is a switching pattern 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 pattern is a switching pattern 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.

[0048] 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, while current is allowed to flow from the second input / output line L2 to the sixth switching element Q6, current flow from the first input / output line L1 to the fifth switching element Q5 is restricted. The current flows from the sixth switching element Q6 to the second input line L4.

[0049] 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, while current is allowed to flow from the second input line L4 to the fifth switching element Q5, current flow from the second input line L4 to the sixth switching element Q6 is restricted. The current flows from the second input line L4 to the fifth switching element Q5.

[0050] When the first terminal T1 of the external power supply PS is positive and in the case of the fifth pattern, 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.

[0051] When the first terminal T1 of the external power supply PS is positive and in the case of the sixth pattern, 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.

[0052] When the second terminal T2 of the external power supply PS is positive and in the case of the sixth pattern, 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.

[0053] When the second terminal T2 of the external power supply PS is positive and in the case of the fifth pattern, 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 → third switching element Q3 → reactor 32 → first terminal T1 of the external power supply PS.

[0054] The control unit 71 controls the switching elements Q1 to Q6 so that the output voltage output from the input / output terminals 23, 24 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.

[0055] <Charging of the low-voltage battery with power supplied from the high-voltage battery> A case where the low-voltage battery 12 is charged by supplying power from the high-voltage battery 11 will be described. When charging the low-voltage battery 12 with the high-voltage battery 11, the switch 34 is turned to the closed state.

[0056] 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, the fifth switching element Q5 and the sixth switching element Q6 are chopper-operated to step down the voltage input from the high-voltage battery 11 via the input / output terminals 23 and 24. Specifically, 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 to control the voltage across the flying capacitor 33. In the present embodiment, the switching elements Q1 to Q6 are conversion switching elements. The switching elements Q1 to Q6 constitute a step-down circuit, and the voltage across the flying capacitor 33 is controlled by the voltage output from the step-down circuit.

[0057] 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 thereby, 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.

[0058] FIG. 4 shows the on and off 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.

[0059] Figures 5 to 10 show a load current I1 and a non-load current I2. The load current I1 is a current flowing through the low-voltage battery 12 which is a load. The non-load current I2 is a current not flowing through the low-voltage battery 12 which is a load.

[0060] As shown in FIG. 4, at time T11, the upper-arm switching element Q41 is on and the lower-arm switching element Q42 is off. As shown in FIG. 5, at time T11, since the upper-arm switching element Q41 is on, the voltage across both ends of the flying capacitor 33 which is a DC power supply is input to the second converter 50. The load current I1 flows through a path passing through 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 a path passing through 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.

[0061] At time T12, the upper-arm switching element Q41 switches 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 shown in FIG. 6, the load current I1 flows through a path passing through 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 flows through a path passing through 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. The non-load current I2 causes the lower-arm switching element Q42 to conduct in reverse.

[0062] At time T13, with the lower-arm switching element Q42 in a reverse-conduction state, the lower-arm switching element Q42 is turned on. Since the lower-arm switching element Q42 is in a reverse-conduction state, the voltage across the lower-arm switching element Q42 is 0. Therefore, ZVS (Zero Voltage Switching) becomes possible. As shown in FIG. 7, the path through which the load current I1 flows is the same as that at time T12. The non-load current I2 flows through the path passing through the second coil L22, the second capacitor C2, the lower-arm switching element Q42, the first capacitor C1, and the first coil L21.

[0063] As time elapses from time T13, the output currents from the first coil L21 and the second coil L22 decrease. At time T14, it switches to discharging from the first capacitor C1 and the second capacitor C2. As a result, the current polarity of the non-load current I2 changes. As shown in FIG. 8, the load current I1 flows through the path passing through the first capacitor C1, the lower-arm switching element Q42, 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 decrease due to discharging. Energy is stored in the first coil L21 and the second coil L22.

[0064] At time T15, the lower-arm switching element Q42 switches off. As shown in FIG. 9, the load current I1 flows through the path passing through the first capacitor C1, the 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. The non-load current I2 flows through the path passing through 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 reverse.

[0065] At time T16, the upper arm switching element Q41 switches on. Since the upper arm switching element Q41 is in reverse conduction, the voltage across the upper arm switching element Q41 is 0. Therefore, ZVS becomes possible. As shown in FIG. 10, the load current I1 and the non-load current I2 change to a path passing through the upper arm switching element Q41 from the freewheeling diode D of the upper arm switching element Q41.

[0066] [Operation of this Embodiment] 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. As a result, the low-voltage battery 12 is charged.

[0067] Here, the second converter 50 of the present embodiment is a capacitor isolation converter in which the primary circuit 51 and the secondary circuit 61 are isolated by the first capacitor C1 and the second capacitor C2. Since the capacitor isolation converter does not include a transformer, it is difficult to step down the input voltage. In particular, it is difficult to step down the input voltage during light load. When a half-bridge circuit is used as the primary circuit 51 as in the present embodiment, there are cases where the voltage can only be stepped down to 1 / 2 of the input voltage. For this reason, there may be a case where it is necessary to lower the voltage across the flying capacitor 33 according to the output voltage of the second converter 50. For example, when the target value of the output voltage of the second converter 50 is 15 [V] and the second converter 50 can only step down the voltage to 1 / 2 of the input voltage, it is necessary to set the voltage across the flying capacitor 33, which becomes the input voltage of the second converter 50, to 30 [V]. The lower the voltage across the flying capacitor 33, the larger 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 larger the current flowing through these switching elements Q2, Q4, Q5, Q6. As a result, the current rating required for the switching elements Q2, Q4, Q5, Q6 may increase.

[0068] In the present embodiment, the secondary circuit 61 includes a leg 62 in which the first coil L21 and the first diode D11 are connected in series, and a leg 63 in which the second coil L22 and the second diode D12 are connected in series. In the secondary circuit 61, an output current is generated in any of the coils L21 and L22 of the respective legs 62 and 63. Since the sum of the output currents of the two coils L21 and L22 becomes the total output current, the current input to the secondary circuit 61 can be increased. As a result, it becomes possible to step down the voltage using the secondary circuit 61, and accordingly, the voltage of the flying capacitor 33 can be increased.

[0069] [Effects of the Present Embodiment] (1) The secondary circuit 61 includes a first leg 62 in which a first coil L21 and a first diode D11 are connected in series, and a second leg 63 in which a second coil L22 and a second diode D12 are connected in series. Output current is generated in either of the coils L21 and L22 of the respective legs 62 and 63. Since the sum of the output currents of the two coils L21 and L22 becomes the overall output current, the current input to the secondary circuit 61 can be increased. By increasing the output current, the output voltage of the second converter 50 decreases. Thereby, the output voltage output from the output terminals 43 and 44 can be decreased.

[0070] (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 larger the current flowing through the switching elements Q2, Q4, Q5, and Q6, and there is a risk that the current rating required for the switching elements Q2, Q4, Q5, and Q6 increases. As in the embodiment, by increasing the output current of the secondary circuit 61, the output voltage of the secondary 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 for the second converter 50 can be output. For this reason, it is possible to suppress an increase in the current flowing through the switching elements Q2, Q4, Q5, and Q6 due to lowering the voltage across the flying capacitor 33.

[0071] (3) The power conversion device 20 is mounted on the vehicle 10. The vehicle 10 includes a high-voltage battery 11 required to drive the main machine and a low-voltage battery 12 required to drive the auxiliary machine. There may be a case where it is desired to charge the low-voltage battery 12 using the high-voltage battery 11, such as when there is no power supply from the external power source PS. 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, Q6 may become large, and there may be a case where the low-voltage battery 12 cannot be charged using the high-voltage battery 11. For example, when the current ratings of the switching elements Q2, Q4, Q5, Q6 only meet the requirements of the current flowing by charging from 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, Q6, the low-voltage battery 12 can be charged using the high-voltage battery 11. The circuit can be shared between the case of charging the low-voltage battery 12 using the external power source PS and the case of charging the low-voltage battery 12 using the high-voltage battery 11.

[0072] [Modification example] The embodiment can be implemented with the following modifications. The embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range.

[0073] ○ The primary circuit 51 of the second converter 50 only needs to be able to convert the input power into AC power. For example, the primary circuit 51 may have the configuration shown in FIG. 11. The primary 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 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 and Q13 are electrically connected to the input terminal 41 for the second converter. The lower arm switching elements Q12 and Q14 are electrically connected to the input terminal 42 for the second converter. The switching elements Q11 to Q14 are, for example, MOSFETs. The switching elements Q11 to Q14 may be IGBTs or GaN-HEMTs.

[0074] When the primary circuit 51 is configured as shown in FIG. 11, the switching patterns of the switching elements Q11 to Q14 are alternately switched between the seventh pattern and the eighth pattern. The seventh pattern is a switching pattern in which the first upper arm switching element Q11 is on, the first lower arm switching element Q12 is off, the second upper arm switching element Q13 is off, and the second lower arm switching element Q14 is on. The eighth pattern is a switching pattern in which the first upper arm switching element Q11 is off, the first lower arm switching element Q12 is on, the second upper arm switching element Q13 is on, and the second lower arm switching element Q14 is off.

[0075] 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 and 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 and the connection point between the second coil L22 and the second diode D12.

[0076] The transition of the switching pattern of the primary side circuit 51 will be described. As shown in FIG. 11, when the primary side circuit 51 is in the seventh pattern, the load current I1 flows through a path passing through 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. The non-load current I2 flows through a path passing through 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 charged.

[0077] As shown in FIG. 12, when the first upper arm switching element Q11 and the second lower arm switching element Q14 are switched off, the load current I1 flows due to the energy stored in the first coil L21. The load current I1 flows through a path passing through 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 flows through a path passing through 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 reverse-conducts the first lower arm switching element Q12 and the second upper arm switching element Q13.

[0078] As shown in FIG. 13, the control unit 71 sets the primary side circuit 51 to the eighth pattern. With the first lower arm switching element Q12 and the second upper arm switching element Q13 in a reverse conduction state, the first lower arm switching element Q12 and the second upper arm switching element Q13 are turned on. Since the first lower arm switching element Q12 and the second upper arm switching element Q13 are in a reverse conduction state, the voltage across each of the switching elements Q12 and Q13 is 0. Therefore, ZVS becomes possible. The load current I1 flows through the path passing through the first coil L21, the low-voltage battery 12, and the first diode D11. The non-load current I2 flows through the path passing through 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.

[0079] As shown in FIG. 14, when the output currents from the first coil L21 and the second coil L22 decrease and switch to the discharge from the first capacitor C1 and the second capacitor C2, the current polarity of the non-load current I2 changes. The load current I1 flows through the path passing through 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 decrease due to the discharge. Energy is stored in the first coil L21 and the second coil L22.

[0080] As shown in FIG. 15, the first lower arm switching element Q12 and the second upper arm switching element Q13 are switched off. The 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. The 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.

[0081] As shown in FIG. 16, the control unit 71 sets the primary-side circuit 51 to the seventh pattern. With the first upper arm switching element Q11 and the second lower arm switching element Q14 conducting in the reverse direction, the first upper arm switching element Q11 and the second lower arm switching element Q14 are turned on. Since the first upper arm switching element Q11 and the second lower arm switching element Q14 are conducting in the reverse direction, the voltage across each of the switching elements Q11, Q14 is 0. Therefore, ZVS becomes possible. The load current I1 and the non-load current I2 change from a path 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 through the first upper arm switching element Q11 and the second lower arm switching element Q14.

[0082] ○ The external power supply PS may 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 the positive side of the DC power supply is connected to the input terminal 21, the negative side may be connected to the second input / output line L2. When the negative side of the DC power supply is connected to the input terminal 21, the positive side may be connected to the first input / output line L1.

[0083] ○ The power conversion device 20 may not be able to charge the low-voltage battery 12 using the high-voltage battery 11. It boosts the voltage of the external power supply PS and outputs it to the flying capacitor 33. ○ The reactor 32 is provided on the first terminal T1 side of the external power supply PS, but it may be provided on the second terminal T2 side or 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.

[0084] ○ The power conversion device 20 may be able to 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 patterns of the first switching element Q1 to the sixth switching element Q6 between the ninth pattern and the tenth pattern. The ninth pattern is a switching pattern in which the first switching element Q1 is on, the second switching element Q2 is on, the third switching element Q3 is off, the fourth switching element Q4 is off, the fifth switching element Q5 is off, and the sixth switching element Q6 is on. The tenth pattern is a switching pattern in which the first switching element Q1 is off, the second switching element Q2 is off, the third switching element Q3 is on, the fourth switching element Q4 is on, the fifth switching element Q5 is on, and the sixth switching element Q6 is off.

[0085] ○ The first coil L21 and the first diode D11 may be interchanged, and the second coil L22 and the second diode D12 may be interchanged. In this case, the wiring 64 is the second wiring. The wiring 65 is the first wiring.

[0086] ○ The secondary side circuit 61 may further include legs. The leg is a series connection of a coil and a diode. In this case, the coil of the added leg and the coils L21 and L22 of the legs 62 and 63 are connected by the first wiring, and the diode of the added leg and the diodes D11 and D12 of the legs 62 and 63 are connected by the second wiring.

Explanation of symbols

[0087] C1... the first capacitor, C2... the second capacitor, D11... the first diode, D12... the second diode, L21... the first coil, L22... the second coil, Q1 to Q6... switching elements which are switching elements for conversion, 10... a vehicle, 11... a high-voltage battery, 12... a low-voltage battery, 20... a power conversion device, 33... a flying capacitor, 43, 44... output terminals, 51... a primary-side circuit, 61... a secondary-side circuit, 62... the first leg, 63... the second leg, 64, 65... wirings.

Claims

1. A primary circuit including a switching element that converts the input power into AC power by the switching operation of the switching element and outputs the converted power; A first connection line and a second connection line, each having one end electrically connected to the primary circuit and receiving AC power from the primary circuit; A first capacitor provided on the first connection line; A second capacitor provided on the second connection line; A secondary circuit, wherein the other ends of the first connection line and the second connection line are connected to each other, and the secondary circuit converts the AC power input from the primary circuit into DC power and outputs the converted power to two output terminals; The secondary circuit includes: A first leg having a first coil and a first diode connected in series with each other, and the other end of the first connection line is connected to the connection point between the first coil and the first diode; A second leg having a second coil and a second diode connected in series with each other, and the other end of the second connection line is connected to the 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; A second wiring connecting the first diode and the second diode to the other of the two output terminals; The first diode and the second diode are connected such that the anode terminal is on the negative side of the output terminal and the cathode terminal is on the positive side of the output terminal. A power conversion device.

2. A flying capacitor; A buck circuit including a conversion switching element that steps down the input power and outputs the stepped-down power to control the voltage across the flying capacitor; In the primary circuit, the voltage across the flying capacitor is input. The power conversion device according to claim 1.

3. The power conversion device is mounted on a vehicle; A voltage is input from a high-voltage battery to the step-down circuit, The power conversion device according to claim 2, wherein the secondary-side circuit outputs a voltage to a low-voltage battery.

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