Power Conversion Equipment

Abstract

To provide an electric power conversion system capable of reducing switching loss.SOLUTION: An electric power conversion system 40 includes: a transformer 80 having first to third coils 81 to 83; a first full-bridge circuit 50 having first to fourth switches Q1 to Q4 connected to the first coil 81; a second full-bridge circuit 60 having fifth to eighth switches Q5 to Q8 connected to the second coil 82; a third full-bridge circuit 70 having ninth to twelfth switches Q9 to Q12 connected to the third coil 83; and a control unit 100 for executing switching control of each of the switches Q1 to Q12 so as to supply electric power from the first full-bridge circuit 50 to the second and third full-bridge circuits 60, 70. The control unit 100, while executing the switching control, puts first to third voltages V1r to V3r per unit wound numbers of the first to third coils 81 to 83 closer to each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Conventionally, as described in, for example, Patent Document 1, a power conversion device is known that includes a transformer having a power transmission coil and a power receiving coil, a power transmission circuit having a power transmission terminal connected to the power transmission coil, and a power receiving circuit having a power receiving terminal connected to the power receiving coil. Here, the power transmission coil and the power receiving coil are magnetically coupled to each other. The power conversion device performs switching control of a power transmission switch of the power transmission circuit to convert a DC voltage input from the power transmission terminal into an AC voltage and supply it to the power transmission coil. The power conversion device also performs switching control of a power receiving switch of the power receiving circuit to convert an AC voltage output from the power receiving coil into a DC voltage and supply it to the power receiving terminal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-152687 A Summary of the Invention [Problem to be solved by the invention]

[0004] During the execution of the switching control of the power conversion device described above, switching loss may increase.

[0005] The present invention has been made in consideration of the above problems, and a main object of the present invention is to provide a power conversion device capable of reducing switching loss. [Means for solving the problem]

[0006] Means 1 includes a transformer having a transmitting coil and a receiving coil magnetically coupled to each other, a transmitting circuit having a transmitting switch and a transmitting terminal connected to the transmitting coil via the transmitting switch, a receiving circuit having a receiving switch and a receiving terminal connected to the receiving coil via the receiving switch, and a control unit that performs switching control of the transmitting switch to convert a DC voltage input from the transmitting terminal into an AC voltage and supply it to the transmitting coil, and that performs switching control of the receiving switch to convert an AC voltage output from the receiving coil into a DC voltage and supply it to the receiving terminal, and the control unit performs control to bring the voltages per unit number of turns of the transmitting coil and the receiving coil closer to each other while performing switching control of the transmitting switch and the receiving switch, respectively.

[0007] The present inventors noticed that when the voltages per unit turn of the transmitting coil and the receiving coil are different from each other, switching losses increase in the circuits of the transmitting circuit and the receiving circuit that are connected to the coil with the lower voltage per unit turn.

[0008] Therefore, in the first aspect, the voltages per unit number of turns of the power transmitting coil and the power receiving coil are made closer to each other while the switching control of the power transmitting switch and the power receiving switch is being executed, thereby reducing the switching loss of the power transmitting circuit and the power receiving circuit.

[0009] Means 2 includes a transformer having a transmitting coil and a plurality of receiving coils magnetically coupled to each other, a transmitting circuit having a transmitting switch and a transmitting terminal connected to the transmitting coil via the transmitting switch, a receiving circuit provided corresponding to each receiving coil and having a receiving switch and a receiving terminal connected to the receiving coil via the receiving switch, and a control unit that performs switching control of the transmitting switch to convert a DC voltage input from the transmitting terminal into an AC voltage and supply it to the transmitting coil, and that performs switching control of the receiving switch to convert an AC voltage output from the receiving coil into a DC voltage and supply it to the receiving terminal, and during the execution of the switching control, the control unit controls the voltage per unit number of turns of a specific coil, which is a part of the transmitting coil and each of the receiving coils, to be higher than the voltage per unit number of turns of the remaining coils.

[0010] In the second means, during execution of switching control of the power transmitting switch and the power receiving switch, the voltage per unit turn of a specific coil, which is a part of the power transmitting coil and each of the power receiving coils, is made higher than the voltage per unit turn of the remaining coils. This makes it possible to preferentially reduce switching loss in the power transmitting circuit and the power receiving circuit, which are connected to the specific coil. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing the configuration of a power conversion device according to a first embodiment. [Diagram 2] 4 is a time chart showing a control of a comparative example. [Diagram 3] FIG. 4 is a diagram showing a current path in a first period. [Figure 4] FIG. 13 is a diagram showing a current path during the dead time after the first period. [Diagram 5] FIG. 13 is a diagram showing a current path in a second period. [Figure 6] FIG. 13 is a diagram showing a current path in a third period. [Figure 7] FIG. 13 is a diagram showing a current path during the dead time after the third period. [Figure 8]FIG. 13 is a diagram showing a current path in a fourth period. [Figure 9] 4 is a time chart showing an example of control. [Figure 10] FIG. 13 is a diagram showing a current path in a fifth period. [Figure 11] FIG. 13 is a diagram showing a current path during the dead time after the fifth period. [Figure 12] FIG. 13 is a diagram showing a current path in a sixth period. [Figure 13] FIG. 13 is a diagram showing a current path in a seventh period. [Figure 14] FIG. 13 is a diagram showing a current path during the dead time after the seventh period. [Figure 15] FIG. 13 is a diagram showing a current path during the eighth period. [Figure 16] 5 is a flowchart showing the procedure of a process executed by a control unit. [Figure 17] FIG. 13 is a graph showing the effect of reducing switching loss. [Figure 18] 10 is a time chart showing an example of control according to the second embodiment. [Figure 19] FIG. 13 is a diagram showing the configuration of a power conversion device according to a third embodiment. [Figure 20] FIG. [Figure 21] FIG. 13 is a diagram showing the configuration of a power conversion device according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment A first embodiment of a power conversion device according to the present invention will be described below with reference to the drawings. The power conversion device of this embodiment is a multi-port type, and is mounted on an electric vehicle such as a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV).

[0013] As shown in Fig. 1, the power supply system includes an external power supply 10, a first storage battery 20, a second storage battery 30, and a power conversion device 40. The external power supply 10 is, for example, a 100V single-phase AC commercial power supply or a 200V three-phase AC commercial power supply. The external power supply 10 is connected to a first high potential side terminal CH1 and a first low potential side terminal CL1 of the power conversion device 40. Each of the storage batteries 20, 30 is a secondary battery that can be charged and discharged. The first storage battery 20 is, for example, a lithium ion storage battery or a nickel metal hydride storage battery, and the second storage battery 30 is, for example, a lead storage battery.

[0014] The power conversion device 40 includes an AC-DC converter 11 that converts AC power supplied from an external power source 10 into DC power. The AC-DC converter 11 is connected to the external power source 10 via a first high potential side terminal CH1 and a second high potential side terminal CH2 of the power conversion device 40. In this embodiment, the rated voltage (e.g., 400 V) output from the AC-DC converter 11 is higher than the rated voltage (e.g., 300 V) of the first storage battery 20, which is higher than the rated voltage (e.g., 14 V) of the second storage battery 30.

[0015] The power conversion device 40 includes a first full-bridge circuit 50 and a first capacitor 51. The first full-bridge circuit 50 includes first to fourth switches Q1 to Q4. In this embodiment, the first to fourth switches Q1 to Q4 are N-channel MOSFETs and include first to fourth body diodes D1 to D4. The drains of the first switch Q1 and the third switch Q3 are connected to the positive terminal of the AC-DC converter 11. The source of the first switch Q1 is connected to the drain of the second switch Q2, and the source of the third switch Q3 is connected to the drain of the fourth switch Q4. The sources of the second switch Q2 and the fourth switch Q4 are connected to the negative terminal of the AC-DC converter 11. A first end of the first capacitor 51 is connected to the positive terminal of the AC-DC converter 11, and a second end of the first capacitor 51 is connected to the negative terminal of the AC-DC converter 11. The first capacitor 51 may be provided inside the first full-bridge circuit 50.

[0016] In this embodiment, the first to fourth switches Q1 to Q4 are made of SiC (silicon carbide)-based materials, GaN (gallium nitride)-based materials, etc., and have a characteristic that the switching speed is faster than that of an N-channel MOSFET made of Si. For example, when the switch is turned off, the switching speed refers to the time required for the gate voltage to become less than the threshold voltage Vth after the gate voltage starts to drop.

[0017] The power conversion device 40 includes a second full-bridge circuit 60 and a second capacitor 61. The second full-bridge circuit 60 includes fifth to eighth switches Q5 to Q8. In this embodiment, the fifth to eighth switches Q5 to Q8 are N-channel MOSFETs made of SiC-based material, GaN-based material, or the like, and include fifth to eighth body diodes D5 to D8.

[0018] The drains of the fifth switch Q5 and the seventh switch Q7 are connected to the second high potential side terminal CH2 of the power conversion device 40. The drain of the sixth switch Q6 is connected to the source of the fifth switch Q5, and the drain of the eighth switch Q8 is connected to the source of the seventh switch Q7. The second low potential side terminal CL2 of the power conversion device 40 is connected to the sources of the sixth switch Q6 and the eighth switch Q8. A first end of the second capacitor 61 is connected to the positive terminal of the first storage battery 20 via the second high potential side terminal CH2, and a second end of the second capacitor 61 is connected to the negative terminal of the first storage battery 20 via the second low potential side terminal CL2. The second capacitor 61 may be provided inside the second full bridge circuit 60.

[0019] The power conversion device 40 includes a third full-bridge circuit 70 and a third capacitor 71. The third full-bridge circuit 70 includes ninth to twelfth switches Q9 to Q12. In this embodiment, the ninth to twelfth switches Q9 to Q12 are N-channel MOSFETs made of a SiC-based material, a GaN-based material, or the like, and include ninth to twelfth body diodes D9 to D12.

[0020] The drains of the ninth switch Q9 and the eleventh switch Q11 are connected to the third high potential side terminal CH3 of the power conversion device 40. The source of the ninth switch Q9 is connected to the drain of the tenth switch Q10, and the source of the eleventh switch Q11 is connected to the drain of the twelfth switch Q12. The sources of the tenth switch Q10 and the twelfth switch Q12 are connected to the third low potential side terminal CL3 of the power conversion device 40. A first end of the third capacitor 71 is connected to the third high potential side terminal CH3, and a second end of the third capacitor 71 is connected to the third low potential side terminal CL3. The voltage between the third high potential side terminal CH3 and the third low potential side terminal CL3 is controlled to be within a predetermined voltage range (for example, 40 to 48 V). The third capacitor 71 may be provided inside the third full bridge circuit 70.

[0021] The power conversion device 40 includes a step-down chopper circuit 72. The step-down chopper circuit 72 includes a first transformer switch SW1, a second transformer switch SW2, a reactor 73, and a fourth capacitor 74. In this embodiment, the first transformer switch SW1 and the second transformer switch SW2 are N-channel MOSFETs and include first and second rectifier diodes Di1 and Di2. The drain of the first transformer switch SW1 is connected to the third high potential side terminal CH3 of the power conversion device 40. The source of the first transformer switch SW1 is connected to the first end of the reactor 73 and the drain of the second transformer switch SW2. The second end of the reactor 73 is connected to the first end of the fourth capacitor 74 and the fourth high potential side terminal CH4 of the power conversion device 40. The source of the second transformer switch SW2 is connected to the third and fourth low potential side terminals CL3 and CL4 of the power conversion device 40 and the second end of the fourth capacitor 74. The positive terminal of the second storage battery 30 is connected to the fourth high potential side terminal CH4, and the negative terminal of the second storage battery 30 is connected to the fourth low potential side terminal CL4.

[0022] The power conversion device 40 includes a transformer 80 having a first coil 81, a second coil 82, and a third coil 83. A first end of the first coil 81 is connected to the source of the first switch Q1 and the drain of the second switch Q2, and a second end of the first coil 81 is connected to the source of the third switch Q3 and the drain of the fourth switch Q4. A first end of the second coil 82 is connected to the source of the fifth switch Q5 and the drain of the sixth switch Q6, and a second end of the second coil 82 is connected to the source of the seventh switch Q7 and the drain of the eighth switch Q8. A first end of the third coil 83 is connected to the source of the ninth switch Q9 and the drain of the tenth switch Q10, and a second end of the third coil 83 is connected to the source of the eleventh switch Q11 and the drain of the twelfth switch Q12.

[0023] In this embodiment, the number of turns N1 of the first coil 81 is 8 turns, the number of turns N2 of the second coil 82 is 7 turns, and the number of turns N3 of the third coil 83 is 1 turn. The numbers of turns N1 to N3 of the coils 81 to 83 may be changed depending on the specifications required for the power conversion device 40.

[0024] The first coil 81, the second coil 82, and the third coil 83 are magnetically coupled to each other, for example, via a core provided in the transformer 80. When the potential of the first end of the first coil 81 becomes higher relative to the second end, an induced voltage is generated in each of the second coil 82 and the third coil 83 such that the potential of the first end is higher than the second end. On the other hand, when the potential of the second end of the first coil 81 becomes higher relative to the first end, an induced voltage is generated in each of the second coil 82 and the third coil 83 such that the potential of the second end is higher than the first end.

[0025] When the potential of the first end relative to the second end of the first coil 81 becomes higher, the polarity of the voltage Vt1 of the first coil 81 is defined as positive, and the direction of the current IL1 flowing from the first end to the second end of the first coil 81 is defined as positive. When the potential of the first end relative to the second end of the second coil 82 becomes higher, the polarity of the voltage Vt2 of the second coil 82 is defined as positive, and the direction of the current IL2 flowing from the first end to the second end of the second coil 82 is defined as positive. When the potential of the first end relative to the second end of the third coil 83 becomes higher, the polarity of the voltage Vt3 of the third coil 83 is defined as positive, and the direction of the current IL3 flowing from the first end to the second end of the third coil 83 is defined as positive.

[0026] The power conversion device 40 includes first to third voltage sensors 91 to 93. The first voltage sensor 91 detects a first voltage which is a terminal voltage of the first capacitor 51, the second voltage sensor 92 detects a second voltage which is a terminal voltage of the second capacitor 61, and the third voltage sensor 93 detects a third voltage which is a terminal voltage of the third capacitor 71.

[0027] The detection values ​​V1r to V3r of the first to third voltages detected by the first to third voltage sensors 91 to 93 are input to a control unit 100 included in the power conversion device 40. The control unit 100 sets command values ​​based on the first to third voltages V1r to V3r. Here, the command values ​​include command values ​​for the first to third voltages V1r to V3r and command values ​​for the voltages Vt1 to Vt3 of the coils 81 to 83. The control unit 100 turns on and off the first to twelfth switches Q1 to Q12 and the first and second transformer switches SW1 and SW2 based on the set command values. The method of setting the command values ​​will be described later.

[0028] Hereinafter, the driving modes of the first to twelfth switches Q1 to Q12 and the first and second transformer switches SW1, SW2 will be described.

[0029] The first switch Q1 and the second switch Q2 are alternately turned on with a dead time TD therebetween, and the third switch Q3 and the fourth switch Q4 are alternately turned on with a dead time TD therebetween. When the first switch Q1 and the fourth switch Q4 are turned on and the second switch Q2 and the third switch Q3 are turned off, the polarity of the voltage Vt1 of the first coil 81 is positive. When the first switch Q1 and the fourth switch Q4 are turned off and the second switch Q2 and the third switch Q3 are turned on, the polarity of the voltage Vt1 of the first coil 81 is negative.

[0030] The fifth switch Q5 and the sixth switch Q6 are alternately turned on with a dead time TD therebetween, and the seventh switch Q7 and the eighth switch Q8 are alternately turned on with a dead time TD therebetween. When the fifth switch Q5 and the eighth switch Q8 are turned on and the sixth switch Q6 and the seventh switch Q7 are turned off, the polarity of the voltage Vt2 of the second coil 82 is positive. When the fifth switch Q5 and the eighth switch Q8 are turned off and the sixth switch Q6 and the seventh switch Q7 are turned on, the polarity of the voltage Vt2 of the second coil 82 is negative.

[0031] The ninth switch Q9 and the tenth switch Q10 are alternately turned on with a dead time TD therebetween, and the eleventh switch Q11 and the twelfth switch Q12 are alternately turned on with a dead time TD therebetween. When the ninth switch Q9 and the twelfth switch Q12 are turned on and the tenth switch Q10 and the eleventh switch Q11 are turned off, the polarity of the voltage Vt3 of the third coil 83 is positive. When the ninth switch Q9 and the twelfth switch Q12 are turned off and the tenth switch Q10 and the eleventh switch Q11 are turned on, the polarity of the voltage Vt3 of the third coil 83 is negative. In this embodiment, the switching periods of the first to twelfth switches Q1 to Q12 are the same as each other.

[0032] The power transferred between the coils 81 to 83 is controlled by the timing at which the switches Q1 to Q12 are switched on. For example, the timing at which the first switch Q1 is switched on is set as a reference timing, and the timing at which the fifth switch Q5 is switched on is delayed with respect to this reference timing, thereby controlling the power transferred between the first coil 81 and the second coil 82. Also, for example, the timing at which the first switch Q1 is switched on is set as a reference timing, and the timing at which the ninth switch Q9 is switched on is delayed with respect to this reference timing, thereby controlling the power transferred between the first coil 81 and the third coil 83.

[0033] The first transformer switch SW1 and the second transformer switch SW2 are alternately turned on. The control unit 100 controls the duty ratio, which is the on / off ratio of the first transformer switch SW1 and the second transformer switch SW2, to step down the third voltage V3r to a target voltage and supply the stepped-down voltage to the second storage battery 30.

[0034] Next, a comparative example different from this embodiment will be used to explain a case where switching loss increases in each of the full bridge circuits 50, 60, and 70. Here, a comparative example will be explained in which switching loss increases in the second full bridge circuit 60 when power is transmitted from the first coil 81 to the second and third coils 83.

[0035] Fig. 2 is a time chart showing control in a comparative example, in which (a) to (c) show the transitions of the voltages Vt1 to Vt3 of the coils 81 to 83, (d) to (f) show the transitions of the currents IL1 to IL3 flowing through the coils 81 to 83, (g) shows the transitions of the current IQ5 flowing through the fifth switch Q5, (h) shows the transitions of the voltage VQ5 between the source and drain of the fifth switch Q5, and (i) shows the operation state of the fifth switch Q5.

[0036] In the comparative example, power is transmitted from the first coil 81 to the second and third coils 82 and 83. Furthermore, the first voltage V1r is set to 400V, the second voltage V2r is set to 290V, and the third voltage V3r is set to 50V.

[0037] The first period T1 is a period immediately before the fifth switch Q5 is switched from on to off, and the second period T2 is a period immediately after the fifth switch Q5 is switched from on to off. Between the first period T1 and the second period T2, there is a dead time TD during which the fifth to eighth switches Q5 to Q8 are turned off.

[0038] 3 to 5 are diagrams showing current paths during a first period T1, a dead time TD after the first period T1, and a second period T2. In addition, in Figs. 3 to 5, the configurations shown in Fig. 1 are denoted by the same reference numerals for convenience. Also, the third full-bridge circuit 70, the third capacitor 71, the third coil 83, etc. are not shown.

[0039] 3 shows the current path in the first period T1. The current path on the first full bridge circuit 50 side is the first capacitor 51 → the second switch Q2 → the first coil 81 → the third switch Q3 → the first capacitor 51. The sign of the current IL1 flowing through the first coil 81 is positive. On the other hand, the current path on the second full bridge circuit 60 side is the second capacitor 61 → the eighth switch Q8 and the eighth body diode D8 → the second coil 82 → the fifth switch Q5 and the fifth body diode D5 → the second capacitor 61. The sign of the current IL2 flowing through the second coil 82 is negative. Charge is stored in the parasitic capacitance formed between the source and drain of the sixth and seventh switches Q6 and Q7 so that the potential on the drain side is higher than that on the source side.

[0040] 4 shows the current path of the dead time TD after the first period T1. The current path on the first full bridge circuit 50 side is the same as that in the first period T1. On the other hand, in the second full bridge circuit 60, the fifth switch Q5 and the eighth switch Q8 are switched off. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the eighth body diode D8 → the second coil 82 → the fifth body diode D5 → the second capacitor 61. In this case, the current circulates through the fifth and eighth body diodes D5 and D8 in a direction in which the sign of the current IL2 flowing through the second coil 82 is negative.

[0041] 5 shows the current path in the second period T2. The current path on the first full bridge circuit 50 side is the same as the dead time TD after the first period T1. On the other hand, in the second full bridge circuit 60, the seventh switch Q7 and the sixth switch Q6 are switched on. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the seventh switch Q7 → the second coil 82 → the sixth switch Q6 → the second capacitor 61. In this case, the switching loss caused by the sixth switch Q6 and the seventh switch Q7 being turned on increases.

[0042] More specifically, a recovery current flows through the fifth body diode D5 and the eighth body diode D8. In addition, the charges stored in the parasitic capacitances of the sixth switch Q6 and the seventh switch Q7 are discharged. As a result, a large current flows temporarily through the second full-bridge circuit 60. This increases the switching loss when the sixth switch Q6 and the seventh switch Q7 are turned on.

[0043] 2, the third period T3 is the period immediately before the fifth switch Q5 is switched from off to on, and the fourth period T4 is the period immediately after the fifth switch Q5 is switched from off to on. Between the third period T3 and the fourth period T4, there is a dead time TD during which the fifth to eighth switches Q5 to Q8 are turned off.

[0044] 6 to 8 are diagrams showing current paths during the third period T3, the dead time TD after the third period T3, and the fourth period T4. In addition, in Figs. 6 to 8, the configurations shown in Fig. 1 are denoted by the same reference numerals for convenience. Also, the third full-bridge circuit 70, the third capacitor 71, the third coil 83, etc. are not shown.

[0045] 6 shows the current path in the third period T3. The current path on the first full bridge circuit 50 side is the first capacitor 51 → the fourth switch Q4 → the first coil 81 → the first switch Q1 → the first capacitor 51. The sign of the current IL1 flowing through the first coil 81 is negative. On the other hand, the current path on the second full bridge circuit 60 side is the second capacitor 61 → the sixth switch Q6 and the sixth body diode D6 → the second coil 82 → the seventh switch Q7 and the seventh body diode D7 → the second capacitor 61. The sign of the current IL2 flowing through the second coil 82 is positive. Charge is stored in the parasitic capacitance formed between the source and drain of the fifth and eighth switches Q5 and Q8 so that the potential on the drain side is higher than that on the source side.

[0046] 7 shows the current path of the dead time TD after the third period T3. The current path on the first full bridge circuit 50 side is the same as that in the third period T3. On the other hand, in the second full bridge circuit 60, the sixth switch Q6 and the seventh switch Q7 are switched off. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the sixth body diode D6 → the second coil 82 → the seventh body diode D7 → the second capacitor 61. In this case, the current flows back through the sixth and seventh body diodes D6 and D7 in a direction in which the sign of the current IL2 flowing through the second coil 82 is positive.

[0047] 8 shows the current path in the fourth period T4. The current path on the first full bridge circuit 50 side is the same as the dead time TD after the third period T3. On the other hand, in the second full bridge circuit 60, the fifth switch Q5 and the eighth switch Q8 are switched on. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the fifth switch Q5 → the second coil 82 → the eighth switch Q8 → the second capacitor 61. In this case, the switching loss caused by the fifth switch Q5 and the eighth switch Q8 being turned on increases.

[0048] More specifically, a recovery current flows through the sixth body diode D6 and the seventh body diode D7. In addition, the charges stored in the parasitic capacitances of the fifth switch Q5 and the eighth switch Q8 are discharged. As a result, a large current flows temporarily through the second full-bridge circuit 60. This increases the switching loss when the fifth switch Q5 and the eighth switch Q8 are turned on.

[0049] Here, in the control of the comparative example, switching loss increases because the sign of the current IL2 flowing through the second coil 82 in the first period T1 is made negative, and because the sign of the current IL2 flowing through the second coil 82 in the third period T3 is made positive.

[0050] The inventor of the present application has noticed that in the control of the comparative example, when the second voltage V2r per unit turn of the second coil 82 is lower than the first and third voltages V1r and V3r per unit turn of the first and third coils 81 and 83, the switch is likely to be turned on and off in the state of the sign of the current IL2 described above. In this embodiment, the first voltage V1r per unit turn of the first coil 81 is V1r / N1, the second voltage V2r per unit turn of the second coil 82 is V2r / N2, and the third voltage per unit turn of the third coil 83 is V3r / N3. In the control of the comparative example, the first voltage V1r per unit turn of the first coil 81 is 50V, the second voltage V2r per unit turn of the second coil 82 is 41.43V, and the third voltage per unit turn of the third coil 83 is 50V.

[0051] Specifically, in the control of the comparative example, the second voltage V2r per unit winding number of the second coil 82 is lower than the first and third voltages V1r and V3r per unit winding number of the first and third coils 81 and 83, and therefore the time change amount of the current IL2 flowing through the second coil 82 becomes negative in the first control period TA. Here, the first control period TA is a period in which the switches that are turned on are Q1, Q4, Q5, Q8, Q9, and Q12, and the switches that are turned off are Q2, Q3, Q6, Q7, Q10, and Q11. In this case, the current IL2 flowing through the second coil 82 increases to the negative side, and therefore the sign of the current IL2 flowing through the second coil 82 is likely to become negative in the first period T1.

[0052] In the control of the comparative example, the second voltage V2r per unit winding number of the second coil 82 is lower than the first and third voltages V1r and V3r per unit winding number of the first and third coils 81 and 83, so that the time change amount of the current IL2 flowing through the second coil 82 becomes positive in the second control period TB. Here, the second control period TB is a period in which the switches Q2, Q3, Q6, Q7, Q10, and Q11 are turned on, and a period in which the switches Q1, Q4, Q5, Q8, Q9, and Q12 are turned off. In this case, the current IL2 flowing through the second coil 82 increases to the positive side, so that the sign of the current IL2 flowing through the second coil 82 is likely to become positive in the third period T3.

[0053] Additionally, the amount of change over time of the current IL2 flowing through the second coil 82 in each control period TA, TB will be additionally explained. Here, the relationship between the first to third coils 81 to 83 is considered as an equivalent circuit in which the first to third equivalent coils are Δ-connected. Here, the first equivalent coil represents the relationship between the first coil 81 and the second coil 82, the second equivalent coil represents the relationship between the first coil 81 and the third coil 83, and the third equivalent coil represents the relationship between the second coil 82 and the third coil 83. In this case, the current IL2 flowing through the second coil 82 is the sum of the current flowing through the first equivalent coil and the current flowing through the third equivalent coil.

[0054] In the first control period TA, if the second voltage V2r per unit turn of the second coil 82 is lower than the first voltage V1r per unit turn of the first coil 81, the time change amount of the current flowing through the first equivalent coil becomes negative. If the second voltage V2r per unit turn of the second coil 82 is lower than the third voltage V3r per unit turn of the third coil 83, the time change amount of the current flowing through the third equivalent coil becomes negative. Therefore, the time change amount of the current IL2 flowing through the second coil 82 becomes negative.

[0055] In addition, in the second control period TB, if the second voltage V2r per unit turn of the second coil 82 is lower than the first voltage V1r per unit turn of the first coil 81, the time change amount of the current flowing through the first equivalent coil is positive. If the second voltage V2r per unit turn of the second coil 82 is lower than the third voltage V3r per unit turn of the third coil 83, the time change amount of the current flowing through the third equivalent coil is positive. Therefore, the time change amount of the current IL2 flowing through the second coil 82 is positive.

[0056] Specifically, the amount of change over time of the current IL2 flowing through the second coil 82 in each of the control periods TA and TB is expressed by the following formula (c1) using the voltages Vt1 to Vt3 of the first to third coils 81 to 83.

[0057]

number

[0058] In the control of the comparative example, in the first control period TA, the voltage Vt1 of the first coil 81 is set to 400 V, the voltage Vt2 of the second coil 82 is set to 290 V, and the voltage Vt3 of the third coil 83 is set to 50 V. Therefore, in the above equation (c1), the amount of change over time of the current IL2 flowing through the second coil 82 becomes negative.

[0059] In the control of the comparative example, in the second control period TB, the voltage Vt1 of the first coil 81 is set to −400 V, the voltage Vt2 of the second coil 82 is set to −290 V, and the voltage Vt3 of the third coil 83 is set to −50 V. Therefore, in the above equation (c1), the amount of change over time of the current IL2 flowing through the second coil 82 becomes positive.

[0060] As described above, if the second voltage V2r per unit turn of the second coil 82 is lower than the first and third voltages V1r, V3r per unit turn of the first and third coils 81, 83, there is a concern that switching losses will increase in the second full bridge circuit 60.

[0061] Therefore, in this embodiment, the voltages V1r to V3r per unit number of turns of each of the coils 81 to 83 are made closer to each other. In this embodiment, the first voltage V1r is set to 330V instead of 400V, and the third voltage V3r is set to 40V instead of 50V. In this case, the first voltage V1r per unit number of turns of the first coil 81 is 41.25V, the second voltage V2r per unit number of turns of the second coil 82 is 41.43V, and the third voltage V3r per unit number of turns of the third coil 83 is 40V. As a result, the second and third voltages V2r and V3r per unit number of turns of the second and third coils 82 and 83 are reduced more than in the comparative example, and the voltages V1r to V3r per unit number of turns of each of the coils 81 to 83 are made closer to each other than in the control of the comparative example. In this case, the time change amount of the current IL2 flowing through the second coil 82 in each control period TA and TB is made approximately 0.

[0062] In addition, making the voltages V1r to V3r per unit number of turns of the coils 81 to 83 closer to each other means, for example, doing the following. The first voltage V1r per unit number of turns of the first coil 81 is V1a, the second voltage V2r per unit number of turns of the second coil 82 is V2a, and the third voltage V3r per unit number of turns of the third coil 83 is V3a. The smallest value of V1a, V2a, and V3a is Vm. In this case, when V1a / Vm, V2a / Vm, and V3a / Vm are within a predetermined range, it is considered that V1a, V2a, and V3a are close to each other. The predetermined range is, for example, 1 to 1.1, preferably 1 to 1.06, and more preferably 1 to 1.03.

[0063] 9 is a time chart showing an example of control in this embodiment, in which the time change amount of the current IL2 flowing through the second coil 82 in each control period TA, TB is set to approximately zero. In FIG. 9, (a) to (i) correspond to (a) to (i) in FIG. 2. In this embodiment as well, power is transmitted from the first coil 81 to the second and third coils 82, 83.

[0064] The fifth period T5 is a period immediately before the fifth switch Q5 is switched from on to off, and the sixth period T6 is a period immediately after the fifth switch Q5 is switched from on to off. Between the fifth period T5 and the sixth period T6, there is a dead time TD during which the fifth to eighth switches Q5 to Q8 are turned off.

[0065] 10 to 12 are diagrams showing current paths during the fifth period T5, the dead time TD after the fifth period T5, and the sixth period T6. In addition, in Figs. 10 to 12, the configurations shown in Fig. 1 are denoted by the same reference numerals for convenience. Also, the third full-bridge circuit 70, the third capacitor 71, the third coil 83, etc. are not shown.

[0066] 10 shows the current path in the fifth period T5. The current path on the first full bridge circuit 50 side is the first capacitor 51 → the third switch Q3 → the first coil 81 → the second switch Q2 → the first capacitor 51. The sign of the current IL1 flowing through the first coil 81 is negative. On the other hand, the current path on the second full bridge circuit 60 side is the second capacitor 61 → the fifth switch Q5 → the second coil 82 → the eighth switch Q8 → the second capacitor 61. The sign of the current IL2 flowing through the second coil 82 is positive. Charge is stored in the parasitic capacitance formed between the source and drain of the sixth and seventh switches Q6 and Q7 so that the potential on the drain side is higher than that on the source side.

[0067] FIG. 11 shows the current path of the dead time TD after the fifth period T5. The current path on the first full bridge circuit 50 side is the same as that in the fifth period T5. On the other hand, in the second full bridge circuit 60, the fifth switch Q5 and the eighth switch Q8 are switched off. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the sixth switch Q6 → the second coil 82 → the seventh switch Q7 → the second capacitor 61. In this case, switching loss occurs when the fifth switch Q5 and the eighth switch Q8 are turned off. However, this switching loss is smaller than the switching loss generated when the switches Q5 to Q8 are turned on in the control of the comparative example, because the current flowing through the second full bridge circuit 60 is relatively small.

[0068] In the dead time TD after the fifth period, the charges accumulated in the parasitic capacitances of the sixth switch Q6 and the seventh switch Q7 are discharged in a direction in which the sign of the current IL2 flowing through the second coil 82 becomes positive. In this embodiment, a period sufficient for the charges accumulated in the parasitic capacitances of the sixth switch Q6 and the seventh switch Q7 to be discharged is set as the dead time TD after the fifth period.

[0069] FIG. 12 shows the current path in the sixth period T6. The current path on the first full bridge circuit 50 side is the same as the dead time TD after the fifth period T5. On the other hand, in the second full bridge circuit 60, the sixth switch Q6 and the seventh switch Q7 are switched on. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the sixth switch Q6 → the second coil 82 → the seventh switch Q7 → the second capacitor 61. In this case, the sixth switch Q6 and the seventh switch Q7 are turned on in a state in which the charges stored in the parasitic capacitances of the sixth switch Q6 and the seventh switch Q7 are discharged. In addition, even if the sixth switch Q6 and the seventh switch Q7 are turned on, no recovery current flows through the fifth and eighth body diodes D5 and D8 of the opposing arm. Therefore, the sixth switch Q6 and the seventh switch Q7 are turned on in a state in which the current flowing through the second full bridge circuit 60 is reduced. As a result, it is possible to reduce the switching loss caused by turning on the sixth switch Q6 and the seventh switch Q7.

[0070] The seventh period T7 is the period immediately before the fifth switch Q5 is switched from off to on, and the eighth period T8 is the period immediately after the fifth switch Q5 is switched from off to on. Between the seventh period T7 and the eighth period T8, there is a dead time TD during which the fifth to eighth switches Q5 to Q8 are turned off.

[0071] 13 to 15 are diagrams showing current paths in the seventh period T7, the dead time TD, and the eighth period T8. In addition, in Figs. 13 to 15, the configurations shown in Fig. 1 are denoted by the same reference numerals for convenience. Also, the third full-bridge circuit 70, the third capacitor 71, the third coil 83, etc. are not shown.

[0072] 13 shows the current path in the seventh period T7. The current path on the first full bridge circuit 50 side is the first capacitor 51 → the first switch Q1 → the first coil 81 → the fourth switch Q4 → the first capacitor 51. The sign of the current IL1 flowing through the first coil 81 is positive. On the other hand, the current path on the second full bridge circuit 60 side is the second capacitor 61 → the seventh switch Q7 → the second coil 82 → the sixth switch Q6 → the second capacitor 61. The sign of the current IL2 flowing through the second coil 82 is negative. Charge is stored in the parasitic capacitance formed between the source and drain of the fifth and eighth switches Q5 and Q8 so that the potential on the drain side is higher than that on the source side.

[0073] FIG. 14 shows the current path of the dead time TD after the seventh period T7. The current path on the first full bridge circuit 50 side is the same as that in the seventh period T7. On the other hand, in the second full bridge circuit 60, the sixth switch Q6 and the seventh switch Q7 are switched off. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the eighth switch Q8 → the second coil 82 → the fifth switch Q5 → the second capacitor 61. In this case, switching loss occurs when the sixth switch Q6 and the seventh switch Q7 are turned off. This switching loss is smaller than the switching loss generated when the switches Q5 to Q8 are turned on in the control of the comparative example because the current flowing through the second full bridge circuit 60 is relatively small.

[0074] In the dead time TD after the seventh period T7, the charges accumulated in the parasitic capacitances of the fifth switch Q5 and the eighth switch Q8 are discharged in a direction in which the sign of the current IL2 flowing through the second coil 82 becomes negative. In this embodiment, a period sufficient for the charges accumulated in the parasitic capacitances of the fifth switch Q5 and the eighth switch Q8 to be discharged is set as the dead time TD after the fifth period.

[0075] FIG. 15 shows the current path in the eighth period T8. The current path on the first full bridge circuit 50 side is the same as the dead time TD after the seventh period T7. On the other hand, in the second full bridge circuit 60, the fifth switch Q5 and the eighth switch Q8 are switched on. The current path on the second full bridge circuit 60 side is the second capacitor 61 → the eighth switch Q8 → the second coil 82 → the fifth switch Q5 → the second capacitor 61. In this case, the fifth switch Q5 and the eighth switch Q8 are turned on in a state in which the charges accumulated in the parasitic capacitances of the fifth switch Q5 and the eighth switch Q8 are discharged. In addition, even if the fifth switch Q5 and the eighth switch Q8 are turned on, no recovery current flows through the sixth and seventh body diodes D6 and D7 of the opposing arms. Therefore, the fifth switch Q5 and the eighth switch Q8 are turned on in a state in which the current flowing through the second full bridge circuit 60 is reduced. As a result, it is possible to reduce the switching loss caused by turning on the fifth switch Q5 and the eighth switch Q8.

[0076] 9 to 15, it has been described that the switching loss is reduced in the second full bridge circuit 60. In this embodiment, the voltages V1r to V3r per unit turn of the coils 81 to 83 are brought closer to each other, so that the switching loss can be reduced in the first and third full bridge circuits 50, 70 for the same reason as in the second full bridge circuit 60.

[0077] Next, the control performed by the control unit 100 will be described.

[0078] The control unit 100 acquires the first to third voltages V1r to V3r detected by the first to third voltage sensors 91 to 93. The control unit 100 sets command values ​​for the first to third voltages V1r to V3r based on the acquired first to third voltages V1r to V3r.

[0079] In this embodiment, the control unit 100 sets command values ​​for the first to third voltages V1r to V3r so that the voltages V1r to V3r approach each other per unit number of turns of the coils 81 to 83. Specifically, the control unit 100 sets the first command value for the first voltage V1r to 330V, the second command value for the second voltage V2r to 290V, and the third command value for the third voltage V3r to 40V.

[0080] The control unit 100 performs switching control so that the first to third voltage detection values ​​V1r to V3r detected by the first to third voltage sensors 91 to 93 become the set first to third command values. For example, the control unit 100 controls the first voltage V1r to the first command value by controlling the output voltage of the AC-DC converter 11. Also, for example, the control unit 100 controls the third voltage V3r to the third command value by performing switching control of the ninth to twelfth switches Q9 to Q12.

[0081] FIG. 16 shows a procedure of a process that the control unit 100 repeatedly executes at a predetermined cycle.

[0082] In step S10, it is determined whether or not there is a request to drive the power conversion device 40. If a negative determination is made in step S10, the process proceeds to step S11, where the power conversion device 40 is set to a standby mode. In step S12, the first to twelfth switches Q1 to Q12 and the first and second transformer switches SW1, SW2 are turned off.

[0083] If the determination in step S10 is affirmative, the process proceeds to step S13, where the operation mode is set. In this case, a power transmission circuit that serves as a power supply source and a power receiving circuit that is fed from the power supply source are selected from the first to third full bridge circuits 50, 60, 70. Also, a loss reduction target is selected from the first to third full bridge circuits 50, 60, 70. The loss reduction target is a circuit that is a target for reducing switching loss among the first to third full bridge circuits 50, 60, 70. In this embodiment, the first full bridge circuit 50 is selected as the power transmission circuit, and the second and third full bridge circuits 60, 70 are selected as the power receiving circuits. Also, the first to third full bridge circuits 50, 60, 70 are selected as the loss reduction targets.

[0084] In this embodiment, the first high potential side terminal CH1 and the first low potential side terminal CL1 correspond to the "power transmitting terminals", and the first coil 81 corresponds to the "power transmitting coil". The second and third high potential side terminals CH2 and CH3 and the second and third low potential side terminals CL2 and CL3 correspond to the "power receiving terminals", and the second and third coils 82 and 83 correspond to the "power receiving coils". The first and third switches Q1 and Q3 correspond to the "upper arm power transmitting switch", the second and fourth switches Q2 and Q4 correspond to the "lower arm power transmitting switch", the fifth, seventh, ninth and eleventh switches Q5, Q7, Q9 and Q11 correspond to the "upper arm power receiving switch", and the sixth, eighth, tenth and twelfth switches Q6, Q8, Q10 and Q12 correspond to the "lower arm power receiving switch".

[0085] In step S14, the detection values ​​V1r to V3r of the first to third voltages detected by the first to third voltage sensors 91 to 93 are acquired. In step S15, the first to third command values ​​are set based on the acquired first to third voltages V1r to V3r. In this embodiment, the first to third command values ​​are set so that the voltages V1r to V3r per unit number of turns of the coils 81 to 83 approach each other. In step S16, switching control is performed so that the acquired first to third voltages V1r to V3r become the set first to third command values.

[0086] FIG. 17 is a diagram comparing switching losses occurring in the second full-bridge circuit 60 between the control according to this embodiment and the control according to the comparative example. FIG. 17 shows switching losses when power is transmitted from the first coil 81 side to the second and third coils 82 and 83 sides. Under condition A, the power Pout1 transmitted from the first coil 81 side to the second coil 82 side is set to 1.6 kW, and the power Pout2 transmitted from the first coil 81 side to the third coil 83 side is set to 0.6 kW. Under condition B, the power Pout1 is set to 1.6 kW, and the power Pout2 is set to 1.2 kW. Under condition C, the power Pout1 is set to 1.6 kW, and the power Pout2 is set to 1.8 kW. Under each of conditions A to C, it was confirmed that the switching losses in this embodiment can be reduced by about 90% compared to the switching losses in the comparative example.

[0087] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, the first to third command values ​​are set so that the voltages V1r to V3r per unit number of turns of the coils 81 to 83 approach each other, and a reflux period is provided within one switching cycle.

[0088] Fig. 18 is a time chart showing an example of control in this embodiment, in which a first freewheeling period TC1 and a second freewheeling period TC2 are provided within one switching period of each of the switches Q1 to Q4. In Fig. 18, (a) to (i) correspond to (a) to (i) in Fig. 9. In this embodiment as well, power is transmitted from the first coil 81 to the second and third coils 82 and 83.

[0089] The first and second free-wheeling periods TC1 and TC2 are periods during which the first and second ends of the first coil 81 are short-circuited. Specifically, in the first free-wheeling period TC1, the first and third switches Q1 and Q3 are turned on and the second and fourth switches Q2 and Q4 are turned off in the first full-bridge circuit 50. In addition, in the second free-wheeling period TC2, the second and fourth switches Q2 and Q4 are turned on and the first and third switches Q1 and Q3 are turned off in the first full-bridge circuit 50.

[0090] In the first freewheeling period TC1, the second and fourth switches Q2 and Q4 may be turned on and the first and third switches Q1 and Q3 may be turned off. In the second freewheeling period TC2, the first and third switches Q1 and Q3 may be turned on and the second and fourth switches Q2 and Q4 may be turned off.

[0091] By providing the first freewheeling period TC1 and the second freewheeling period TC2 within one switching cycle, a period occurs during which the voltage Vt1 of the first coil 81 is 0V. The greater the proportion of the first freewheeling period TC1 and the second freewheeling period TC2 within one switching cycle, the more the effective value of the voltage Vt1 of the first coil 81 is reduced. Even in this case, the same effect as that of reducing the first voltage V1r per unit number of turns of the first coil 81 can be obtained. Therefore, even if the first command value cannot be reduced due to restrictions on the setting range of the first command value of the first voltage V1r, for example, the switching loss can be reduced by providing the first and second freewheeling periods TC1 and TC2.

[0092] Therefore, the control unit 100 provides a first free-wheeling period TC1 and a second free-wheeling period TC2 in addition to reducing the first command value of the first voltage V1r. In this embodiment, instead of setting the first command value of the first voltage V1r to 330V, the control unit 100 sets the first command value of the first voltage V1r to 350V and provides the first free-wheeling period TC1 and the second free-wheeling period TC2. Even in this case, the same effect as in the first embodiment can be obtained.

[0093] <Third embodiment> Hereinafter, the third embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, the method of setting the first to third command values ​​is changed.

[0094] Due to restrictions on the setting ranges of the first to third command values, it may not be possible to bring the voltages V1r to V3r per unit number of turns of the coils 81 to 83 close to each other. In this case, switching loss increases in some of the first to third full-bridge circuits 50, 60, and 70.

[0095] Therefore, in this embodiment, a circuit in which switching loss should be reduced preferentially is selected as a loss reduction target among the first to third full bridge circuits 50, 60, and 70. In this embodiment, a full bridge circuit configured with switches having a low switching speed and a power transmission circuit in which transmitted power is likely to increase are selected as loss reduction targets, as circuits in which switching loss is likely to increase.

[0096] In this embodiment, among the first to third coils 81 to 83, the coil connected to the full bridge circuit that is the target of loss reduction is designated as a specific coil, and the voltage per unit number of turns of the specific coil is made higher than the voltage per unit number of turns of the remaining coils.

[0097] The configuration of the power conversion device 40 according to this embodiment will be described below with reference to FIG. 19. The third full-bridge circuit 70 includes thirteenth, fourteenth, fifteenth, and sixteenth switches Q13, Q14, Q15, and Q16 instead of the ninth, tenth, eleventh, and twelfth switches Q9, Q10, Q11, and Q12. The thirteenth to sixteenth switches Q13 to Q16 are IGBTs made of Si. Thirteenth to sixteenth diodes D13 to D16 are connected in reverse parallel to the switches Q13 to Q16 as freewheel diodes. The switching speed of the thirteenth to sixteenth switches Q13 to Q16 is lower than the switching speed of the first to eighth switches Q1 to Q8. In this embodiment, the third full-bridge circuit 70 corresponds to a "specific power receiving circuit."

[0098] Next, the process repeatedly executed by the control unit 100 at a predetermined cycle will be described with reference to Fig. 16. In this embodiment, in step S13, the second full bridge circuit 60 is selected as the power transmitting circuit, and the first and third full bridge circuits 50, 70 are selected as the power receiving circuits. The third full bridge circuit 70, which is configured with switches having a low switching speed, and the second full bridge circuit 60, which is the power transmitting circuit, are selected as loss reduction targets.

[0099] In this embodiment, the second high potential side terminal CH2 and the second low potential side terminal CL2 correspond to the "power transmitting terminals", the second coil 82 corresponds to the "power transmitting coil", and the fifth to eighth switches Q5 to Q8 correspond to the "power transmitting switches". The first high potential side terminal CH1 and the first low potential side terminal CL1 correspond to the "power receiving terminals", the first to fourth switches Q1 to Q4 correspond to the "power receiving switches", and the thirteenth to sixteenth switches Q13 to Q16 correspond to the "specific power receiving switches".

[0100] In this embodiment, in step S15, the second and third voltages V2r and V3r per unit number of turns of the second and third coils 82 and 83, which are the specific coils, are made higher than the first voltage V1r per unit number of turns of the first coil 81, which is the remaining coil. Specifically, the control unit 100 sets the first command value to 320V, the second command value to 300V, and the third command value to 55V. In this case, the first voltage V1r per unit number of turns of the first coil 81 is 40V, the second voltage V2r per unit number of turns of the second coil 82 is 43V, and the third voltage V3r per unit number of turns of the third coil 83 is 55V. As a result, the voltages V1r to V3r of the coils 81 to 83 per unit number of turns are higher in the order from the highest to the lowest in the third coil 83, the second coil 82, and the first coil 81. Here, the third voltage V3r per unit turn of the third coil 83 is made higher than the second voltage V2r per unit turn of the second coil 82 because reducing the switching loss of the full bridge circuit having switches with low switching speeds is given priority over reducing the switching loss of the power transmission circuit.

[0101] Fig. 20 is a time chart showing an example of control in this embodiment, which is an example of control in which the switching losses of the second and third full bridge circuits 60, 70 are preferentially reduced. In Fig. 20, (a) to (f) correspond to (a) to (f) in Fig. 9.

[0102] At time t1, the fifth and eighth switches Q5 and Q8 are turned off, and the sixth and seventh switches Q6 and Q7 are turned on. Here, the sign of the current IL2 flowing through the second coil 82 is made positive. Therefore, the switching loss of the second full-bridge circuit 60 can be reduced.

[0103] At time t2, the thirteenth and sixteenth switches Q13 and Q16 are turned off, and the fourteenth and fifteenth switches Q14 and Q15 are turned on. Here, the sign of the current IL3 flowing through the third coil 83 is made positive. Therefore, the switching loss of the third full-bridge circuit 70 can be reduced.

[0104] At time t3, the sixth and seventh switches Q6 and Q7 are turned off, and the fifth and eighth switches Q5 and Q8 are turned on. Here, the sign of the current IL2 flowing through the second coil 82 is made negative. Therefore, the switching loss of the second full-bridge circuit 60 can be reduced.

[0105] At time t4, the fourteenth and fifteenth switches Q14 and Q15 are turned off, and the thirteenth and sixteenth switches Q13 and Q16 are turned on. Here, the sign of the current IL3 flowing through the third coil 83 is made negative. Therefore, the switching loss of the third full-bridge circuit 70 can be reduced.

[0106] According to the present embodiment described above in detail, the following effects can be obtained.

[0107] Of the full bridge circuits 50, 60, and 70, the third full bridge circuit 70 is set as a target for loss reduction. Here, the slower the switching speed of the switches, the greater the switching loss tends to be. Therefore, in the third full bridge circuit 70, which has the thirteenth to sixteenth switches Q13-Q16 with low switching speeds, the switching loss can be reduced.

[0108] Of the full bridge circuits 50, 60, and 70, the second full bridge circuit 60, which is a power transmission circuit, is set as a target for loss reduction. Here, since the power transmitted in the power transmission circuit is likely to increase, switching loss is likely to increase. Therefore, in the second full bridge circuit 60, where switching loss is likely to increase, it is possible to reduce switching loss.

[0109] The voltage Vt3 of the third coil 83 per unit turn is set to be higher than the voltage Vt2 of the second coil 82 per unit turn. This makes it possible to appropriately reduce switching loss in the third full-bridge circuit 70, in which reduction of switching loss has a high priority.

[0110] <Fourth embodiment> Hereinafter, the fourth embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, as shown in Fig. 21, a power conversion device 40 includes a fourth full-bridge circuit 110 and a fifth capacitor 111. In Fig. 21, the same components as those shown in Fig. 1 are denoted by the same reference numerals for convenience.

[0111] The fourth full-bridge circuit 110 includes seventeenth to twentieth switches Q17 to Q20. In this embodiment, the seventeenth to twentieth switches Q17 to Q20 are made of Si and are N-channel MOSFETs. The drains of the seventeenth switch Q17 and the nineteenth switch Q19 are connected to the fifth high potential side terminal CH5 of the power conversion device 40. The source of the seventeenth switch Q17 is connected to the drain of the eighteenth switch Q18, and the source of the nineteenth switch Q19 is connected to the drain of the twentieth switch Q20. The sources of the eighteenth switch Q18 and the twentieth switch Q20 are connected to the fifth low potential side terminal CL5 of the power conversion device 40. The fifth high potential side terminal CH5 is connected to a first terminal of the fifth capacitor 111 and a first terminal of the electric load 32, and the fifth low potential side terminal CL5 is connected to a second terminal of the fifth capacitor 111 and a second terminal of the electric load 32. The fifth capacitor 111 may be provided inside the fourth full-bridge circuit 110.

[0112] The seventeenth to twentieth switches Q17 to Q20 may be N-channel MOSFETs made of SiC-based or GaN-based materials. The electric load 32 includes a constant voltage load that requires a constant supply voltage or that requires the supply voltage to vary within a predetermined range. Specific examples of the constant voltage load include a navigation device, an audio device, a meter device, and various ECUs.

[0113] The transformer 80 further includes a fourth coil 84. A first end of the fourth coil 84 is connected to the source of the seventeenth switch Q17 and the drain of the eighteenth switch Q18, and a second end of the fourth coil 84 is connected to the source of the nineteenth switch Q19 and the drain of the twentieth switch Q20. The fourth coil 84 is magnetically coupled to the first to third coils 81 to 83, for example, via a core. When the potential of the first end of the first coil 81 is higher than that of the second end, an induced voltage is generated in the fourth coil 84 such that the potential of the first end is higher than that of the second end.

[0114] The power conversion device 40 includes a fourth voltage sensor 94. The fourth voltage sensor 94 detects a fourth voltage V4r, which is a terminal voltage of the fifth capacitor 111. The detected fourth voltage V4r is input to the control unit 100. The control unit 100 turns on and off the first to twelfth and seventeenth to twentieth switches Q1 to Q12, Q17 to Q20, the first transformer switch SW1, and the second transformer switch SW2.

[0115] In this embodiment, the fifth high potential side terminal CH5 and the fifth low potential side terminal CL5 correspond to the "power receiving terminals", the fourth coil 84 corresponds to the "power receiving coil", the fourth full bridge circuit 110 corresponds to the "power receiving circuit", and the 17th to 20th switches Q17 to Q20 correspond to the "power receiving switches".

[0116] <Other embodiments> Each of the above embodiments may be modified as follows.

[0117] In the first embodiment, prior to the process of step S15, a process may be performed to determine whether or not the voltages V1r to V3r per unit number of turns of each coil are different from each other. Here, the first to third voltages V1r to V3r acquired in step S14 may be used to calculate the voltages V1r to V3r per unit number of turns of each coil.

[0118] For example, the above-mentioned V1a / Vm, V2a / Vm, and V3a / Vm may be used to determine whether the voltages V1r to V3r per unit number of turns of each coil are different from each other. In this case, for example, a process of selecting Vm, which is the smallest value among V1a, V2a, and V3a, and a process of dividing V1a, V2a, and V3a by Vm are performed. If V1a / Vm, V2a / Vm, and V3a / Vm are out of the above-mentioned predetermined range, it may be determined that the voltages V1r to V3r per unit number of turns of each coil are different from each other.

[0119] If it is determined that the voltages V1r-V3r per unit number of turns of each coil are different from each other, the process may proceed to step S15. On the other hand, if it is not determined that the voltages V1r-V3r per unit number of turns of each coil are different from each other, the process may proceed to step S16 while maintaining the first to third command values ​​in the previous control cycle.

[0120] In the third embodiment, prior to the process of step S15, a process may be performed to determine whether the second and third voltages V2r, V3r per unit number of turns of the second and third coils 82, 83 are equal to or less than the first voltage V1r per unit number of turns of the first coil 81. Here, the first to third voltages V1r-V3r acquired in step S14 may be used to calculate the voltages V1r-V3r per unit number of turns of each coil.

[0121] If it is determined that the second and third voltages V2r, V3r per unit turn of the second and third coils 82, 83 are equal to or lower than the first voltage V1r per unit turn of the first coil 81, the process may proceed to step S15. On the other hand, if it is determined that the second and third voltages V2r, V3r per unit turn of the second and third coils 82, 83 are higher than the first voltage V1r per unit turn of the first coil 81, the process may proceed to step S16 while maintaining the first to third command values ​​in the previous control cycle.

[0122] In the second embodiment, the first freewheeling period TC1 and the second freewheeling period TC2 are provided within one switching period of the first to fourth switches Q1 to Q4 on the power transmitting side, but this is not limited to this. A freewheeling period may be provided within one switching period of the ninth to twelfth switches Q9 to Q12 on the power receiving side.

[0123] In the third embodiment, the control unit 100 may set only the third full bridge circuit 70 as a loss reduction target, instead of setting the second and third full bridge circuits 60, 70 as loss reduction targets. In this case, the control unit 100 may set the voltage per unit turn of the third coil 83, which is a specific coil, higher than the voltage per unit turn of the first and second coils 81, 82, which are the remaining coils.

[0124] The power conversion device 40 does not need to include the AC-DC converter 11. In this case, it is sufficient that the positive terminal of the third storage battery 12 is connected to the first high potential side terminal CH1, and the negative terminal of the third storage battery 12 is connected to the first low potential side terminal CL1. The third storage battery is a secondary battery that can be charged and discharged. The third storage battery is, for example, a lithium ion storage battery or a nickel metal hydride storage battery. The rated voltage of the third storage battery (for example, 400 V) is higher than the rated voltage of the first storage battery 20 and the rated voltage of the second storage battery 30.

[0125] The power conversion device 40 may include a half-bridge circuit instead of each of the full-bridge circuits 50, 60, 70, and 110. [Explanation of symbols]

[0126] 80... transformer, 81-84... first to fourth coils, 50, 60, 70, 110... first to fourth full bridge circuits, 100... control unit, CH1-CH5... first to fifth high potential side terminals, CL1-CL5... first to fifth low potential side terminals, Q1-Q20... first to twentieth switches.

Claims

1. a transformer (80) having a power transmission coil (82) and a plurality of power receiving coils (81, 83, 84) that are magnetically coupled to each other; a power transmitting circuit (60) having power transmitting switches (Q5 to Q8) and power transmitting terminals (CH2, CL2) connected to the power transmitting coil via the power transmitting switches; a receiving circuit (50, 70, 110) provided corresponding to each of the receiving coils and having a receiving switch (Q1 to Q4, Q9 to Q20) and a receiving terminal (CH1, CH3, CH5, CL1, CL3, CL5) connected to the receiving coil via the receiving switch; a control unit (100) that executes switching control of the power transmitting switch to convert a DC voltage input from the power transmitting terminal into an AC voltage and supply the AC voltage to the power transmitting coil, and executes switching control of the power receiving switch to convert an AC voltage output from the power receiving coil into a DC voltage and supply the DC voltage to the power receiving terminal, The control unit, during execution of the switching control, controls the voltage per unit number of turns of a specific coil, which is a portion of the transmitting coil and each of the receiving coils, to be higher than the voltage per unit number of turns of the remaining coils.

2. Among the power receiving circuits, a specific power receiving circuit (70) that is a part of the power receiving circuits has low-speed switches (Q13 to Q16) whose switching speed is slower than the power receiving switches and the power transmitting switches of the remaining power receiving circuits, The power conversion device according to claim 1 , wherein the specific coil is one of the power receiving coils that is connected to the specific power receiving circuit.

3. The power conversion device according to claim 1 , wherein the specific coil is the power transmission coil.

4. the power transmitting circuit is a bridge circuit having a series connection of an upper arm power transmitting switch and a lower arm power transmitting switch as the power transmitting switch, the power receiving circuit is a bridge circuit having a series connection of an upper arm power receiving switch and a lower arm power receiving switch as the power receiving switch, The control unit, in the switching control, turning on and off the upper arm power transmitting switch and the lower arm power transmitting switch so as to provide a period in which a positive voltage is applied to the power transmitting coil and a period in which a negative voltage is applied to the power transmitting coil; The power conversion device according to any one of claims 1 to 3, wherein the upper arm receiving switch and the lower arm receiving switch are turned on and off so as to provide a period in which a positive voltage is applied to the receiving coil and a period in which a negative voltage is applied to the receiving coil.

5. The power conversion device according to claim 4 , wherein the control unit provides a period during which at least one of the power transmitting coil and the power receiving coil is short-circuited in the switching control.

6. A transformer (80) having a power transmission coil (81) and a power receiving coil (82-84) that are magnetically coupled to each other; a power transmission circuit (50) having power transmission switches (Q1 to Q4) and power transmission terminals (CH1, CL1) connected to the power transmission coil via the power transmission switches; a receiving circuit (60, 70, 110) having a receiving switch (Q5 to Q20) and receiving terminals (CH2, CH3, CH5, CL2, CL3, CL5) connected to the receiving coil via the receiving switch; a control unit (100) that executes switching control of the power transmitting switch to convert a DC voltage input from the power transmitting terminal into an AC voltage and supply the AC voltage to the power transmitting coil, and executes switching control of the power receiving switch to convert an AC voltage output from the power receiving coil into a DC voltage and supply the DC voltage to the power receiving terminal, the power transmitting circuit is a bridge circuit having a series connection of an upper arm power transmitting switch and a lower arm power transmitting switch as the power transmitting switch, the power receiving circuit is a bridge circuit having a series connection of an upper arm power receiving switch and a lower arm power receiving switch as the power receiving switch, The control unit is In the switching control of the power transmitting switch, the upper arm power transmitting switch and the lower arm power transmitting switch are turned on and off so as to provide a period in which a positive voltage is applied to the power transmitting coil and a period in which a negative voltage is applied to the power transmitting coil; In the switching control of the power receiving switch, the upper arm power receiving switch and the lower arm power receiving switch are turned on and off so as to provide a period in which a positive voltage is applied to the power receiving coil and a period in which a negative voltage is applied to the power receiving coil; In the switching control of the power transmitting switch and the power receiving switch, a period is provided in which at least one of the power transmitting coil and the power receiving coil is short-circuited; A power conversion device that performs control so that voltages per unit number of turns of the power transmitting coil and the power receiving coil approach each other while switching control of the power transmitting switch and the power receiving switch is being executed.

7. The power conversion device according to any one of claims 1 to 6, wherein the control unit controls a voltage per unit turn of each of the power transmitting coil and the power receiving coil by changing a driving mode of the switching control.

Images