WO2014199206A1

WO2014199206A1 - Power supply system, and control method therefor

Info

Publication number: WO2014199206A1
Application number: PCT/IB2014/000898
Authority: WO
Inventors: Jun Muto
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2013-06-12
Filing date: 2014-05-30
Publication date: 2014-12-18
Anticipated expiration: 2015-12-12
Also published as: JP2014241707A

Abstract

A power supply system (10) includes first and second power supply circuits (11, 12) connected with each other and capacitors (C1, C2, C3, C4). Each of the first and second power supply circuits includes: a primary circuit (20) including an electric power conversion unit (200); and a secondary circuit (30) including an electric power conversion unit (300) and being magnetically coupled to the primary circuit via a transformer (400). Each of the first and second power supply circuits converts electric power with a use of the electric power conversion units between two of first and second ports (PA, PC) of the primary circuit and third and fourth ports (PB, PD) of the secondary circuit. The capacitors are respectively provided at the first to fourth ports. Phases of switching waveforms at the electric power conversion units are different from each other between the first and second power supply circuits.

Description

POWER SUPPLY SYSTEM, AND CONTROL METHOD THEREFOR

BACKGROUND OF THE INVENTION

1.■■ Field of the Invention

[0001] The invention relates to a power supply system configured to convert electric power between any two of_. four ports.

2. Description of Related Art

[0002] There is generally known a power supply system configured to convert electric power between any two of four ports (for example, see Japanese Patent Application Publication No. 2011 - 193713 (JP 2011 - 193713 A)) .

[0003] However, according to the technique described in JP 2011-193713 A, ripple current in each of capacitors provided respectively at the four ports tends to increase. Therefore, it is difficult to reduce the size of each of those capacitors.

SUMMARY OF THE INVENTION

[0004] The invention provides a power supply system and a control method for a power supply system, which are able to easily reduce the size of each of capacitors respectively provided at ports. .

[0005] A power supply system according to the first aspect of the invention includes a first power supply circuit, a second power supply circuit, a first port, a second port, a third port, a fourth port, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, and a control circuit. The first power supply circuit includes: a first primary circuit including a first primary electric power conversion unit configured to convert electric power by switching; a first secondary circuit including a first secondary electric power conversion unit configured to convert electric power by switching; and a first transformer magnetically coupling the- first primary circuit to the first secondary circuit. The second power supply circuit is connected in parallel with the first power supply circuit, and includes: a second primary circuit including a second primary electric power conversion unit configured to convert electric power by switching; a second secondary circuit including a second secondary electric power conversion unit configured to convert electric power by switching; and a second transformer magnetically coupling the second primary circuit to the second secondary circuit. The first primary circuit and the second primary circuit are. connected to the first port. The first primary circuit and the second primary circuit are connected to the second port. The first secondary circuit and the second secondary circuit are connected to the third port. The first secondary circuit and the second secondary circuit are connected to the fourth port. The first capacitor is connected to the first port. The second capacitor is^' connected to the second port. The third capacitor is connected to the third port. The fourth capacitor is connected to the fourth port. The control circuit is connected to the first power supply circuit and the second power supply circuit and configured to vary a phase of a first switching waveform at the first primary electric power conversion unit with respect to a phase of a second switching waveform at the second primary electric power conversion unit. The first power supply circuit is configured to convert electric power with a use of at least one of the first primary electric power conversion unit and the first secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port. The second power supply circuit is configured to convert electric power with a use of at least one of the second primary electric power conversion unit and the second secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port.

[0006] A method according to the second aspect of the invention is a control method for a power supply system. The power supply system includes a first power supply circuit, a second power supply circuit, a first port, a second port, a third port, a fourth port, a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor. The first power supply circuit includes: a first primary circuit including a first primary electric power conversion unit configured to convert, electric power by switching; a first secondary circuit including a first secondary electric power conversion unit configured to convert electric power by switching; and a first transformer magnetically coupling the first primary circuit to the first secondary circuit. The second power supply circuit is connected in parallel with the first power supply circuit, and includes: a second primary circuit including a second primary electric power conversion unit configured to convert electric power by switching; a second secondary circuit including a, second secondary electric power conversion unit configured to convert electric power by switching; and a second transformer magnetically coupling the second primary circuit to the second secondary circuit. The first primary circuit and the second primary circuit are connected to the first port. The first primary circuit and the second primary circuit are connected to the second port. The first secondary circuit and the second secondary circuit are connected to the third port. The first secondary circuit and the second secondary circuit are connected to the fourth port. The first capacitor is connected to the first port. The second capacitor is connected to the second port. The third capacitor is connected to the third port. The fourth capacitor is connected to the fourth port. The first power supply circuit is configured to convert electric power with a use of at least one of the first primary electric power conversion unit and the first secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port. The second power supply circuit is configured to convert electric power with a use of at least one of the second primary electric power conversion unit and the second secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port. The control method according to the second aspect of the invention includes varying a phase of a first switching waveform at the first primary electric power conversion unit with respect to a phase of a second switching waveform at the second primary electric power conversion unit.

[0007] According to the first and second aspects of the invention, it is possible to easily reduce the size of each of the capacitors respectively provided at the ports.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a block diagram that shows an example of the configuration of an electric power conversion circuit of a power supply system according to an embodiment of the invention;

FIG. 2 is a circuit configuration diagram that shows an example of a power supply circuit configured in the electric power conversion circuit;

FIG. 3 is a block diagram that shows an example of the configuration of a control circuit;

FIG. 4 is a timing chart that shows an example of the operation of the electric power conversion circuit;

FIG. 5 shows current waveforms in simulation at the time when only one of power supply circuits is operated;

FIG. 6 is a view that shows an energization route of each current flowing in the power supply circuit in a period Tl shown in FIG 5;

FIG. 7 is a view that shows an energization route of each current flowing in the power supply circuit in a period T2 shown in FIG. 5;

FIG. 8 is a view that shows an energization route of each current flowing in the power supply circuit in a period T3 shown in FIG. 5;

FIG. 9 is a view that shows an energization route of each current flowing in the power supply circuit in a period T4 shown in FIG. 5;

FIG. 10 is a timing chart that shows an example of a state where the phase , of a switching waveform at a power conversion unit in one of the power supply circuits is different from the phase of a corresponding switching waveform at a power conversion unit in the other one of the power supply circuits;

FIG. 11 is a simulation waveform of ripple current flowing through a capacitor at the time when there is no phase difference between the power supply circuits; and

FIG. 12 is a simulation waveform of ripple current flowing through a capacitor when there is a phase difference between the power supply circuits.

DETAILED DESCRIPTION OF EMBODIMENTS

[0009] FIG. 1 is a view that shows an electric power conversion system 101 that includes an electric power conversion circuit 10 that is an embodiment of the power supply system according to the invention. The electric power conversion system 101 is, for example, an electric power conversion system configured to include the electric power conversion circuit 10 including a control circuit 50 and a sensor circuit 70.

[0010] The electric power conversion system 101 is, for example, configured to include a primary high voltage system load LA, a primary low voltage system load LC and a primary low voltage system power supply PSC. The primary high voltage system load LA is connected to a first input/output port PA. The primary low voltage system load LC and the primary low voltage system power supply PSC are connected to a second input/output port PC. The primary low voltage system power supply PSC supplies electric power to the primary low voltage system load LC that operates at the same voltage system (for example, 12 V system) as the primary low voltage system power supply PSC. The primary low voltage system power supply PSC supplies electric power, stepped up by any one of primary full-bridge circuits 200 (described later with reference to FIG. 2) of power supply circuits 11 , 12, to the primary high voltage system load LA that operates at the voltage system (for example, 48 V system higher than 12 V system) different from that of the primary low voltage system power supply PSC. A specific example of the primary low voltage system power supply PSC is a secondary battery, such as a lead-acid battery.

[0011] The electric power conversion system 101 is, for example, configured to include a secondary high voltage system load LB, a secondary high voltage system power supply PSB and a secondary low voltage system load LD. The secondary high voltage system load LB and the secondary high voltage system power supply PSB are connected to a third input/output port PB. The secondary low voltage system load LD is connected to a fourth input/output port PD. The secondary high voltage system power supply PSB supplies electric power to the secondary high voltage system load LB that operates at the same voltage system (for example, 288V system higher than 12V system or 48V system) as the secondary high voltage system power supply PSB. The secondary high voltage system power supply PSB supplies electric power, stepped down by any one of secondary full-bridge circuits 300 (described later with reference to FIG. 2) of the power supply circuits 11, 12, to the secondary low voltage system load LD that operates at the voltage system (for example, 72 V system lower than 288 V system) different from that of the secondary high voltage system power supply PSB. A specific example of the secondary high voltage system power supply PSB is a secondary battery, such as a lithium ion battery.

[0012] The electric power conversion circuit 10 is a power supply system that includes the above-described four input/output ports. The electric power conversion circuit 10 has the function of selecting any two input/output ports from among those four input/output ports and converting electric power with the use of the power supply circuits 11 , 12 between the selected two input/output ports. The power supply circuits 11, 12 are connected to the first input/output port PA in parallel with each other. The first input/output port PA is an input/output node shared between the power supply circuits 11 , 12, and allows both input and output. The above-described other three input/output ports are also configured similarly.

[0013] The electric power conversion circuit 10 is a DC-DC converter that includes the two power supply circuits 11, 12. The power supply circuits 11 , 12 are connected in parallel with each other between the first and second, input/output ports PA, PC and the third and fourth input/output ports, PB, PD. Because the plurality of power supply circuits are redundantly provided in this way, it is possible to increase output electric power that is allowed to be supplied to each of the loads LA, LB, LC, LD and to improve fail-safe performance at the time when part of the plurality of power supply circuits fails.

[0014] An electric power Wa is an input or output power of the first input/output port PA. An electric power Wc is an input or output power of the second input/output port PC. An electric power Wb is an input or output power of the third input/output port PB. An electric power Wd is an input or output power of the fourth input/output port PD. In the power supply circuit 11, an input or output electric power Wal is an electric power at a first input/output port PA1 that is connected to the first input/output port PA, an input or output electric power Wcl is an electric power at a second input/output port PCI that is connected to the second input/output port PC, an input or output electric power Wbl is an electric power at a third input/output port PBl that is connected to the third input/output port PB, and an input or output electric power Wdl is an electric power at a fourth input/output port PD1 that is connected to the fourth input/output port PD. Input or output electric powers Wa2, Wc2, Wb2, Wd2 in the power supply circuit 12 are also the same. -

[0015] The electric power conversion circuit 10 includes a capacitor CI , a capacitor C3, a capacitor C2 and a capacitor C4. The capacitor CI is provided at the first input/output port PA. The capacitor C3 is provided at the second input/output port PC. The capacitor C2 is provided at the third input/output port PB. The capacitor C4 is provided at the fourth input/output port PD. A specific example of each of the capacitors CI , C2, C3, C4 is a film capacitor, or the like.

[0016] The capacitor CI is inserted between a high-potential terminal 602 of the first input/output port PA and a low-potential terminal 604 of the first input/output port PA and second input/output port PC. The capacitor C3 is inserted between "a- high-potential terminal 606 of the second input/output port PC and the low-potential terminal 604 of the first input/output port PA and second input/output port PC. The capacitor C2 is inserted between a high-potential terminal 608 of the third input/output port PB and a low-potential terminal 610 of the third input/output port PB and fourth input/output port PD. The capacitor C4 is inserted between a high-potential terminal 612 of the fourth input/output port PD and a low-potential terminal 610 of the third input/output port PB and fourth input/output port PD.

[0017] The capacitor CI may be provided in an internal circuit on the power supply circuits 11 , 12 side with respect to the first input/output port PA, or may be provided in an external circuit on the primary high voltage system load LA side. The primary high voltage system load LA is provided on the opposite side across the first input/output port PA from the power supply circuits 11 , 12. The capacitors C2, C3, C4 may be similarly provided inside or outside the electric power conversion circuit 10.

[0018] FIG. 2 is a circuit configuration diagram of the power supply circuit 11. Next, the configuration of the power supply circuit 11 will be described also with reference to FIG. 1. The circuit configuration of the power supply circuit 12 may be the same as that of the power supply circuit 11, so the description thereof is omitted.

[0019] The power supply circuit 11 is configured to include a primary conversion circuit 20 and a secondary conversion circuit 30. The primary conversion circuit 20 and the secondary conversion circuit 30 are magnetically coupled to each other via a transformer 400 (center tap transformer).

[0020] The primary conversion circuit 20 is a primary circuit configured to include the primary full-bridge circuit 200, the first input/output port PA1 and the second input/output port PCI . The primary full-bridge circuit 200 is a primary electric power conversion unit configured to include a primary coil 202 of the transformer 400, a primary magnetic coupling reactor 204, a primary first upper arm U 1 , a primary first lower arm /Ul , a primary second upper arm VI and a primary second lower arm /VI . Here, the primary first upper arm Ul, the primary first lower arm /Ul , the primary second upper arm VI and the primary second lower arm /VI each are, for example, a switching element configured to include an N-channel MOSFET and a body diode that is a parasitic element of the MOSFET. A diode may be additionally connected in parallel with the MOSFET.

[0021] The primary full-bridge circuit 200 includes a primary positive electrode bus 298 and a primary negative electrode bus 299. The primary positive electrode bus -298 is connected to the high-potential terminal 602 of the first input/output port PA and a high-potential terminal 613 of the first input/output port PAL The primary negative electrode bus 299 is connected to the low-potential terminal 604 of the first input/output port PA and second input/output port PC and a low-potential terminal 614 of the first input/output port PA1 and second input/output port PC 1.

[0022] A primary first arm circuit 207 is connected between the primary positive electrode bus 298 and the primary negative electrode bus 299. The primary first ami circuit 207 is formed by serially connecting the primary first upper arm Ul and the primary first lower arm /Ul . The primary first arm circuit 207 is a primary first electric power conversion circuit portion (primary U-phase electric power conversion circuit portion) that is able to carry out electric power conversion operation through on/off switching operation of each of the primary , first upper arm Ul and the primary first lower arm /Ul . Furthermore, a primary second arm circuit 211 is connected between the primary positive electrode bus 298 and the primary negative electrode bus 299 in parallel with the primary first arm circuit 207. The primary second arm circuit 211 is formed by serially connecting the primary second upper arm VI and the primary second lower arm /VI . The primary second arm circuit 211 is a primary second electric power conversion circuit portion (primary V-phase electric power conversion circuit portion) that is able to carry out electric power conversion operation through on/off switching operation of each of the primary second upper arm VI and the primary second lower arm /VI .

[0023] The primary coil 202 and the primary magnetic coupling reactor 204 are provided at a bridge portion that connects a midpoint 207m of the primary first arm circuit 207 to a midpoint 21 lm of the primary second arm circuit 211. A connection relationship at the bridge portion will be described in more detail. One end of a primary first reactor 204a of the primary magnetic coupling reactor 204 is connected to the midpoint 207m of the primary first arm circuit 207. One end of the primary coil 202 is connected to the other end of the primary first reactor 204a. Furthermore, one end of a primary second reactor 204b of the primary magnetic coupling reactor 204 is connected to the other end of the primary coil 202. Moreover, the other end of the primary second reactor 204b is connected to the midpoint 211m of the primary second arm circuit 211. The primary magnetic coupling reactor 204 is configured to include the primary first reactor 204a and the primary second reactor 204b magnetically coupled to the primary first reactor 204a.

[0024] The midpoint 207m is a primary first intermediate node between the primary first upper arm Ul and the primary first lower arm /Ul . The midpoint 21 lm is a primary second intermediate node between the primary second upper arm VI and the primary second lower arm /V I . [0025] The first input/output port PA (PA1) is a port provided between the primary positive electrode bus 298 and the primary negative electrode bus 299. The first input/output port PA (PA1) is configured to include the terminal 602 (terminal 613) and the terminal 604 (terminal 614). The second input/output port PC (PCI) is a port provided between the primary negative electrode bus 299 and a center tap 202m of the primary coil 202. The second input/output port PC (PCI) is configured to include the terminal 604 (terminal 614) and the terminal 606 (terminal 616).

[0026] The center tap 202m is connected to the high-potential terminal 606 of the second input/output port PC and the high-potential terminal 616 of the second input/output port PCI . The center tap 202m is an intermediate connection point between a primary first winding 202a and a primary second winding 202b that constitute the primary coil 202.

[0027] The secondary conversion circuit 30 is a secondary circuit configured to include the secondary full-bridge circuit 300, the third input/output port PB1 and the fourth input/output port PDl . The secondary full-bridge circuit 300 is a secondary electric power conversion unit configured to include a secondary coil 302 of the transformer 400, a secondary magnetic coupling reactor 304, a secondary first upper arm U2, a secondary first lower arm /U2, a secondary second upper arm V2 and a secondary second lower arm ,/V2. Here, the secondary first upper arm U2, the secondary first lower arm /U2, the secondary second upper arm V2 and the secondary second lower arm /V2 each are, for example, a switching element configured to include an N-channel MOSFET and a body diode that is a parasitic element of the MOSFET. A diode may be additionally connected in parallel with the MOSFET.

[0028] The secondary full-bridge circuit 300 includes a secondary positive electrode bus 398 and a secondary negative electrode bus 399. The secondary positive electrode bus 398 is connected to the high-potential terminal 608 of the third input/output port PB and a high-potential terminal 618 of the third input/output port PB 1. The secondary negative electrode bus 399 is connected to the low-potential terminal 610 of the third input/output port PB and fourth input/output port PD and a low-potential terminal 620 of the third input/output port PB 1 and fourth input/output port PDl . . [0029] A secondary first arm circuit 307 is connected between the secondary positive electrode bus 398 and the secondary negative electrode bus 399. The secondary first arm circuit 307 is formed by serially connecting the secondary first upper arm U2 and the secondary first lower arm /U2. The secondary first arm circuit 307 is a secondary first electric power conversion circuit portion (secondary U-phase electric power conversion circuit portion) that is able to carry out electric power conversion operation through on/off switching operation of each of the secondary first upper arm U2 and the secondary first lower arm /U2. Furthermore, a secondary second arm circuit 311 is connected between the secondary positive electrode bus 398 and the secondary negative electrode bus 399 in parallel with the secondary first arm circuit 307. The secondary second arm circuit 311 is formed by serially connecting the secondary second upper arm V2 and the secondary second lower arm N2. The secondary second arm circuit 311 is a secondary second electric power conversion circuit portion (secondary V-phase electric power conversion circuit portion) that is able to carry out electric power conversion operation through on/off switching operation of each of the secondary second upper arm V2 and the secondary second lower arm /V2.

[0030] The secondary coil 302 and the secondary magnetic coupling reactor 304 are provided at a bridge portion that connects a midpoint 307m of the secondary first arm circuit 307 to a midpoint 311m of the secondary second arm circuit 311. A connection relationship at the bridge portion will be described in more detail. One end of a secondary first reactor 304a of the secondary magnetic coupling reactor 304 is connected to the midpoint 31 lm of the secondary second arm circuit 311. One end of the secondary coil 302 is connected to the other end of the secondary first reactor 304a. Furthermore, one end of a secondary second reactor 304b of the secondary magnetic coupling reactor 304 is connected to the other end of the secondary coil 302. Moreover, the other end of the secondary second reactor 304b is connected to the midpoint 307m of the secondary first arm circuit 307. _, The secondary magnetic coupling reactor 304 is configured to include the secondary first reactor 304a and the secondary second reactor 304b magnetically coupled to the secondary first reactor 304a. [0031] The midpoint 307m is a secondary first intermediate node between the secondary first upper arm U2 and the secondary first lower arm /U2. The midpoint 311m is a secondary second intermediate node between the secondary second upper arm V2 and the secondary second lower arm /V2.

[0032] The third input/output port PB (PB1) is a port provided between the secondary positive electrode bus 398 and the secondary negative electrode bus 399. The third input/output port PB (PB 1) is configured to include the terminal 608 (terminal 618) and the terminal 610 (terminal 620). The fourth input/output port PD (PD1) is a port provided between the secondary negative electrode bus 399 and a center tap 302m of the secondary coil 302. The fourth input/output port PD (PD1) is configured to include the terminal 610 (terminal 620) and the terminal 612 (terminal 622).

[0033] The center tap 302m is connected to the high-potential terminal 612 of the fourth input/output port PD and the. high-potential terminal 622 of the fourth input/output port PD1. The center tap 302m is an intermediate connection point between a secondary first winding 302a and a secondary second winding 302b that constitute the secondary coil 302.

[0034] In FIG. 1, the electric power conversion circuit 10 of the electric power conversion system 101 includes the sensor circuit 70. The sensor circuit 70 is a sensor unit that detects output values Do at the corresponding first to fourth input/output ports PA, PC, PB, PD at predetermined detection intervals and then outputs detected signals based on. the output values Do to the control circuit 50. Each of the output values Do, for example, includes an electric power value, an Output voltage value and an output current value of each of the electric powers Wa, Wc, Wb, Wd at each of the first to fourth input/output ports PA, PC, PB, PD. The sensor circuit 70 may be a monitoring unit , that monitors the voltages at the midpoints 207m, 211m, 307m, 311m. The sensor circuit 70 may be provided inside or outside the electric power conversion circuit 10.

[0035] The electric power conversion circuit 10 includes the control circuit 50. The control circuit 50 is a control unit that controls the outputs of the power supply circuits 11 , 12 such that the output values Do of the first to fourth input/output ports PA, PC, PB, PD respectively follow target values Dot of the first to fourth input/output ports PA, PC, PB, PD. The control circuit 50 is, for example, an electronic circuit including a microcomputer that incorporates a CPU. Each of the output target values Dot is a command value from a predetermined device, and may be an output target voltage value Vot, an output target current value lot or an output target electric power value Wot. The control circuit 50 may be provided inside or outside the electric power conversion circuit 10.

[0036] The control circuit 50, for example, feeds back the output values Do detected by the sensor circuit 70, and controls the output electric powers of the respective power supply circuits 11 , 12 such that a deviation between each output target value Dot and a detected value of a corresponding one of the fed-back output values Do becomes 0. The control circuit 50 may be a circuit that controls the output voltages of the power supply circuits 1 1, 12 or may be a circuit that controls the output currents of the power supply circuits 11 , 12.

[0037] The control circuit 50, for example, controls the output electric powers of the power supply circuits 11 , 12 through power conversion by changing the values of control parameters P. In this case, the control parameters P are two types, i.e., a phase difference φ and a duty ratio (on time δ).

[0038] The phase difference φ is a deviation (time lag) in switching timing between the same-phase electric power conversion circuit portions of the primary full-bridge circuit 200 and secondary full-bridge circuit 300. The duty ratio (on time δ) is the duty ratio (on time) of a switching waveform in each of the electric power conversion circuit portions configured in the primary full-bridge circuit 200 and the secondary full-bridge circuit 300.

[0039] These two control parameters P are controlled independently of each other. The control circuit 50 changes the outputs of the power supply circuits 11, 12 through duty ratio control and/or phase control over the primary full-bridge circuit 200 and the secondary full-bridge circuit 300 by using the phase difference φ and the duty ratio (on time δ). [0040] FIG. 3 is a block diagram of the control circuit 50.^" The control circuit 50 is a control unit that has the function of executing switching control. In switching control, the switching elements, that is, the primary first upper arm Ul , and the like, of the primary conversion circuit 20 and the switching elements, that is, the secondary first upper arm U2, and the like, of the secondary conversion circuit 30 are switched. The control circuit 50 is configured to include an electric power conversion mode determination processing unit 502, a phase difference φ determination processing unit 504, an on time δ determination processing unit 506, a primary switching processing unit 508 and a secondary switching processing unit 510. The control circuit 50 is, for example, an electronic circuit including a microcomputer that incorporates a CPU.

[0041] The electric power conversion mode determination processing unit 502 , selects and determines an operation mode from among electric power conversion modes A to L of the electric power conversion circuit TO, described below, on the basis of an external signal (not shown). Hereinafter, the electric power conversion modes A to L may be referred to as modes A to L. In the mode A, electric power input from the first input/output port PA is converted and output to the second input/output port PC. In the mode B, electric power input from the first input/output port PA is converted and output to the third input/output port PB. In the mode C, electric power input from the first input/output port PA is converted and output to the fourth input/output port PD.

[0042] In the mode D, electric power input from the second input/output port PC is converted and output to the first input/output port PA. In the mode E, electric power input from the second input/output port PC is converted and output to the third input/output port PB. In the mode F, electric power input from the second input/output port PC is converted and output to the fourth input/output port PD.

[0043] In the mode G, electric power input from the third input/output port PB is converted and output to the first input/output port PA. In the mode H, electric power input from the third input/output port PB is converted and output to the second input/output port PC. In the mode I, electric power input from the third input/output port PB is converted and output to the fourth input/output port PD. [0044] In the mode J, electric power input from the fourth input/output port PD is converted and output to the first input/output port PA. In the mode K, electric power input from the fourth input/output port PD is converted and output to the second input/output port PC. In the mode L, electric power input from the fourth input/output port PD is converted and output to the third input/output port PB.

[0045] . The phase difference φ determination processing unit 504 has the function of setting a phase difference φ in the switching period of the switching elements between the primary conversion circuit 20 and the secondary conversion circuit 30 in order to cause the electric power conversion circuit 10 to function as a DC-DC converter circuit.

[0046] The on time δ determination processing unit 506 has the function of setting an on time δ of each of the switching elements of the primary conversion circuit 20 and secondary conversion circuit 30 in order to cause each of the primary conversion circuit 20 and the secondary conversion circuit 30 to function as a step-up/step-down circuit.

[0047] The primary switching processing, unit 508 has the function of executing switching control over the corresponding switching elements on the basis of outputs of the electric power conversion mode determination processing unit 502, phase difference φ determination processing unit 504 and on time δ determination processing unit 506. The corresponding switching elements include the primary first upper arm Ul , the primary first lower arm /Ul, the primary second upper arm VI and the primary second lower arm /VI .

[0048] The secondary switching processing unit 510 has the function of executing switching control over the corresponding switching elements on the basis of the outputs of the electric power conversion mode determination processing unit 502, phase difference φ determination processing unit 504 and on time δ determination processing unit 506. The corresponding switching elements include the secondary first upper arm U2, the secondary first lower arm /U2, the secondary second upper arm V2 and the secondary second lower arm /V2.

[0049] The operation of the electric power conversion system 101 will be described with reference to FIG. 1 to FIG. 3. For example, when an external signal that requires the electric power conversion circuit 10 to operate in the mode F is input, the electric power conversion mode determination processing unit 502 of the control circuit 50 determines the electric power conversion mode of the electric power conversion circuit 10 as the mode F. At this time, the voltage input to the second input/output port PCI is stepped up by the step-up function of the primary conversion circuit 20. The stepped-up voltage is transferred to the third input/output port PB1 side by the function of the electric power conversion circuit 10 as the DC-DC converter circuit. The transferred voltage is further stepped down by the step-down function of the secondary conversion circuit 30, and is output from the fourth input/output port PD1.

[0050] Here, the details of the step-up/step-down function of the primaryconversion circuit 20 will be described in detail. Focusing on the second input/output port PCI and the first input/output port PAl , the terminal 616 of the second input/output port PC I is connected to the midpoint 207m of the primary first arm circuit 207 via the primary first winding 202a and the primary first reactor 204a serially connected to the primary first winding 202a. . Both ends of the primary first arm circuit 207 are connected to the first input/output port PAl , with the result that a step-up/step-down circuit is connected between the terminal 616 of the second input/output port PCI and the first input/output port PAl .

[0051] Furthermore, the terminal 616 of the second input/output port PCI is connected to the midpoint 211m of the primary second arm circuit 211 via the primary second winding 202b and the primary second reactor 204b serially connected to the primary second winding 202b. Both ends of the primary second arm circuit 211 are connected to the first input/output port PAl . Thus, a step-up/step-down circuit is connected in parallel between the terminal 616 of the second input/output port PCI and the first input/output port PAl . The secondary conversion circuit 30 is a circuit having a substantially similar configuration to that of the primary conversion circuit 20. Thus, two step-up/step-down circuits are connected in parallel with each other between the terminal 622 of the fourth input/output port PD 1 and the third input/output port PB1. Thus, the secondary conversion circuit 30 has a similar step-up/step-down function to that of the primary conversion circuit 20.

[0052] Next, the function of the power supply circuit 1 1 as the DC-DC converter circuit will be described in detail. Focusing on the first input/output port PAl and the third input/output port PBl, the primary full-bridge circuit 200 is connected to the first input/output port PAl . The secondary full-bridge circuit 300 is connected to the third input/output port PB 1. The primary coil 202 provided at the bridge portion of the primary full-bridge circuit 200 and the secondary coil 302 provided at the bridge portion of the secondary full-bridge circuit 300 are magnetically coupled to each other, thus functioning as the transformer 400 (the center tap transformer having a winding number ratio of 1 :N). Thus, by adjusting the phase difference of the switching period of the switching elements between the primary full-bridge circuit 200 and the secondary full-bridge circuit 300, it is possible to convert electric power input to the first input/output port PAl and transfer the electric power to the third input/output port PB 1 or convert electric power input to the third input/output port PBl and transfer the electric power to the first input/output port PAl .

[0053] FIG. 4 is a view that shows a timing chart of a switching waveform of an on/off state of each of the arms configured in the electric power conversion circuit 10 through control over the control circuit 50. In FIG. 4, Ul indicates an on/off waveform of the primary first upper arm Ul . VI indicates an on/off waveform of the primary second upper arm VI . U2 indicates an on/off waveform of the secondary first upper arm U2. V2 indicates an on/off waveform of the secondary second upper arm V2. On/off waveforms of the primary first lower arm /Ul, primary second lower arm /VI , secondary first lower arm /U2 and secondary second lower arm /V2 are respectively waveforms inverted from the on/off waveforms of the primary first upper arm Ul , primary second upper arm VI, secondary first upper arm U2 and secondary second upper arm V2 (not shown). It is desirable that a dead time be provided between both on/off waveforms of each pair of upper and lower arms such that no flow-through current flows as a result of the on states of both upper and lower arms. In FIG. 4, the high level indicates the on state, and the low level indicates the off state.

[0054] Here, by changing the on time δ of each of Ul , VI , U2, V2, it is possible to change a step-up/step-down ratio of the primary conversion circuit 20 and a step-up/step-down ratio of the secondary conversion circuit 30. For example, by equalizing the on time δ of each of Ul, VI, U2, V2 to one another, it is possible to equalize the step-up/step-down ratio of the primary conversion circuit 20 to the step-up/step-down ratio of the secondary conversion circuit 30.

[0055] The on time δ determination processing unit 506 equalizes the on time δ of each of Ul, VI , U2, V2 such that the step-up/step-down ratio of each of the primary conversion circuit 20 and the secondary conversion circuit 30 is equal to each other (each on time δ = primary on time δΐ = secondary on time δ2 = time value a).

[0056] The step-up/step-down ratio of the primary conversion circuit 20 depends on a duty ratio that is the ratio of the on time δ to a switching period T of each of the switching elements (arms) configured in the primary full-bridge circuit 200. Similarly, the step-up/step-down ratio of the secondary conversion circuit 30 depends on a duty ratio that is the ratio of the on time δ to a switching period T of each of the switching elements (arms) configured in the secondary full-bridge circuit 300. The step-up/step-down ratio of the primary conversion circuit 20 is a transformation ratio between the first input/output port PA1 and the second input/output port PC I . The step-up/step-down ratio of the secondary conversion circuit 30 is a transformation ratio between the third input/output port PB 1 and the fourth input/output port PD 1.

[0057] Thus, for example, the step-up/step-down ratio of the primary conversion circuit 20 and the step-up/step-down ratio of the secondary conversion circuit 30 are expressed as follows,

(Step-up/step-down ratio of the primary conversion circuit 20) = (Voltage of the second input/output port PC 1 )/(Voltage of the first input/output port PA 1 ) = δ 1 ΙΊ = α/Τ

(Step-up/step-down ratio of the secondary conversion circuit 30) = (Voltage of the fourth input/output port PDl)/(Voltage of the third input/output port PB1) = δ2/Τ = α/Τ

That is, the step-up/step-down ratio of each of the primary conversion circuit 20 and the secondary conversion circuit 30 is a value (= a/T) equal to each other.

[0058] The on time δ in FIG. 4 indicates the on time δΐ of the primary. first upper arm Ul and the primary second upper arm VI , and the on time 62 of the secondary first upper arm U2 and the secondary second upper arm V2. The switching period T of each of the arms configured in the primary full-bridge circuit 200 is equal to the switching period T of each of the arms configured in the secondary full-bridge circuit 300.

[0059] The phase difference between Ul and VI is set to 180 degrees (π), and the phase difference between U2 and V2 is also set to 180 degrees (π). Furthermore, by changing the phase difference φ between Ul and U2, it is possible to adjust the amount of electric power transferred between the primary conversion circuit 20 and the secondary conversion circuit 30. When the phase difference φ is larger than 0, it is possible to transfer electric power from the primary conversion circuit 20 to the secondary conversion circuit 30. When the phase difference φ is smaller than 0, it is possible to transfer electric power from the secondary conversion circuit 30 to the primary conversion circuit 20.

[0060] The phase difference φ is a deviation (time lag) in switching timing between the same-phase electric power conversion circuit portions of the primary full-bridge circuit 200 and secondary full-bridge circuit 300. For example, the phase difference φ is a deviation in switching timing between the primary first arm circuit 207 and the secondary first arm circuit 307. In addition, the phase, difference ^ is a deviation in switching timing between the primary second arm circuit 211 and the secondary, second arm circuit 311. Those deviations are controlled so as to remain equal to each other. That is, the phase difference φ between Ul and U2 and the phase difference φ between VI and V2 are controlled to the same value.

[0061] Thus, for example, when an external signal that requires the electric power conversion circuit 10 to operate in the mode F is input, the electric power conversion mode determination processing unit 502 determines to select the mode F. The on time δ determination processing unit 506 sets the on time 6 that prescribes the step-up ratio in the case where the primary conversion circuit 20 is caused to function as a step-up circuit that steps up voltage input to the second input/output port PCI and outputs the stepped-up voltage to the first input/output port PA1. The secondary conversion circuit 30 functions as a step-down circuit that steps down voltage input to the third input/output port PB 1 at the step-down ratio prescribed by the on time δ set by the on time δ determination processing unit 506 and outputs the stepped-down voltage to the fourth input/output port PD1. Furthermore, the phase difference φ determination processing unit 504 sets the phase difference φ for transferring electric power, input to the first input/output port PA1, to the third input/output port PB 1 at a desired amount of electric power transferred.

[0062J The primary switching processing unit 508 executes switching control over the switching elements, that is, the primary first upper ami Ul, the primary first lower arm /Ul , the primary second upper arm VI and the primary second lower arm /VI , such that the primary conversion circuit 20 is caused to function as the step-up circuit and the primary conversion circuit 20 is caused to function as part of the DC-DC converter circuit.

[0063] The secondary switching processing unit 510 executes switching control over the switching elements, that is, the secondary first upper arm U2, the secondary first lower arm /U2, the secondary second upper arm V2 arid the secondary second lower arm /V2, such that the secondary conversion circuit 30 is caused to function as the step-down circuit and the secondary conversion circuit 30 is caused to function as part of the DC-DC converter circuit.

[0064] As described above, it is possible to cause each of the primary conversion circuit 20 and the secondary conversion circuit 30 to function as the step-up circuit or the step-down circuit, and it is possible to cause the electric power conversion circuit 10 to also function as the bidirectional DC-DC converter circuit. Thus, it is possible to convert electric power in all of the electric power conversion modes A to L, in other words, it is possible to convert electric power between the two input/output ports selected from among the four input/output ports.

[0065] Such control is executed over both the power supply circuit 11 and the power supply circuit 12. That is, the control circuit 50 changes the duty ratio and phase difference φ of each of the power supply circuits 11 , 12 such that the output values Do of the first to fourth input/output ports PA, PC, PB, PD, detected by the sensor circuit 70, respectively follow the corresponding output target values Dot.

[0066] FIG. 5 is a simulation waveform that shows flow of current at each portion shown in FIG. 2 at the time when only one of the power supply circuit 11 and the power supply circuit 12 is operated.

[0067] Current II indicates a current flowing through the secondary coil 302 of the transformer 400. A current value is positive when the current II flows from the secondary second winding 302b side to the secondary first winding 302a side. Current 12 indicates a current flowing through the primary coil 202 of the transformer 400. A current value is positive when the current 12 flows from the primary second winding 202b side to the primary first winding 202a side. Current 13 indicates a discharge current flowing from the capacitor C I to the terminal 613 of the first input/output port PA1. A current value is positive when the current 13 flows in a direction to discharge the capacitor CI . Current 14 indicates a current flowing through a current path between the terminal 616 of the second input/output port PCI and the center tap 202m. A current value is positive when the current 14 flows from the terminal 616 side to the center tap 202m side. Current 15 indicates a ripple current flowing through the capacitor CI . A current value is positive when the current 15 flows in a direction to charge the capacitor CI .

[0068] FIG. 5 shows a state where the control circuit 50 . executes switching control over one of the power supply circuits such that electric power at the third input/output port PB1 is converted and then the converted electric power is output to the first input/output port PA1 and electric power at the first input/output port PA1 is converted and then the converted electric power is output to the second input/output port PCI .

[0069] The sum of periods Tl to T8 shown in FIG. 5 is a switching period T (360°) that is one period of the switching waveform shown in FIG. 4. Timings tl to t^'9 shown in FIG. 5 respectively correspond to timings tl to t9 shown in FIG. 4.

[0070] FIG. 6 is a view that shows an energization route of each current flowing in the power supply circuit in the period Tl shown in FIG. 5. FIG. 7 is a view that shows an energization route of each current flowing in the power supply circuit in the period T2 shown in FIG. 5. FIG. 8 is a view that shows an energization route of each current flowing in the power supply circuit in the period T3 shown in FIG. 5. FIG. 9 is a view that shows an energization route of each current flowing in the power supply circuit in the period T4 shown in FIG. 5. In FIG. 6 to FIG. 9, the arms surrounded by the dashed-line circle are arms in an on state, and the other arms are arms in an off state.

[0071] FIG. 6 shows a state where, in the period Tl shown in FIG. 5, energy is stored in an equivalent inductance L obtained by a combination of the transformer 400 and the primary magnetic coupling reactor 204 by using the current II flowing through the secondary full-bridge circuit 300.

[0072] In the period Tl, with an increase in the current II , the current 12 flowing through the primary coil 202 of the transformer 400 and the primary magnetic coupling reactor 204 increases. -On the other hand, a current component of the ripple current 15 flowing through the capacitor CI in the period Tl is a constant discharge current 13 that is supplied from the capacitor CI to the load connected to the first input/output port PAL

[0073] FIG. 7 shows a state where, in the period T2 shown in FIG. 5, energy stored in the equivalent inductance L obtained by a combination of the transformer 400 and the primary magnetic coupling reactor 204 is transferred to the first input/output port PAl .

[0074] The current value of the current 12 flowing in the period T2 is substantially constant. On the other hand, the ripple current 15 flowing through the capacitor C I in the period T2 is formed of three types of superimposed current components (currents 12, 13, 14).

[0075] The current 12 that flows in the period T2 is electric power (current) via the equivalent inductance L obtained by a combination of the transformer 400 and the primary magnetic coupling reactor 204, and is a current component for charging the capacitor CI . The current 13 that flows in the period T2 is a constant current component for discharging the capacitor CI in a direction to release electric charge from the capacitor CI to the load connected to the first input/output port PAl . The current 14 that flows in the period T2 is a current component for discharging the capacitor CI in a direction to release electric charge from the capacitor CI to the load and the capacitor C3 that are connected to the second input/output port PCI . Because of the current 14 that flows in the period T2, the voltage of the first input/output port PAl is stepped down to the voltage of the second input/output port PCI . [0076] FIG. 8 shows a state where, in the period T3 shown in FIG. 5, energy stored in the equivalent inductance L obtained by a combination of the transformer 400 and the primary magnetic coupling reactor 204 is reset by using the voltage of the first input/output port PA1. The period T3 is a preparation period for switching the energized phases of the primary and secondary electric power conversion circuit portions from the U phase to the V phase.

[0077] In the period T3, with a reduction in the current II , the current 12 flowing through the primary coil 202 of the transformer 400 and the primary magnetic coupling reactor 204 reduces. On the other hand, the ripple current 15 that flows through the capacitor C 1 in the period T3 is formed of three types of superimposed current components (currents 12, 13, 14).

[0078] The current 12 that flows in the period T3 is a current component for discharging the capacitor CI in order to reset energy stored in the equivalent inductance L obtained by a combination of the transformer 400 and the primary magnetic coupling reactor 204. The current II approaches to zero because of the action of the current 12 that flows in the period T3. The current 13 that flows in the period T3 is a constant current component for discharging the capacitor CI in a direction to release electric charge from the capacitor C I to the load connected to the first input/output port PAl . The current 14 that flows in the period T3 is a current component for discharging the capacitor CI in a direction to release electric charge from the capacitor CI to the load and the capacitor C3 that are connected to the second input/output port PCI . Because of the current 14 that flows in the period T3, the voltage of the first input/output port PAl is stepped down to the voltage of the second input/output port PCI . ·

[0079] FIG. 9 shows a state where, in the period T4 shown in FIG. 5, the voltage of the first input/output port PAl is stepped down to the voltage of the second input/output port PCI . In the period T4, no operation for transferring electric power is carried out between the first input/output port PAl and the third input/output port PB 1.

[0080] A current component of the ripple current 15 that flows through the capacitor CI in the period T4 is a constant discharge current 13 that is supplied from the capacitor C 1 to the load connected to the first input/output port PA 1. The current 14 that flows in the period T4 is a current component for discharging the capacitor CI in a direction to release electric charge from the primary coil 202 of the transformer 400 and the primary magnetic coupling reactor 204 to the load and the capacitor C3 that are connected to the second input/output port PCI . Because of the current 14 that flows in the period T4, the voltage of the first input/output port PA l is stepped down to the voltage of the second input/output port PCI .

[0081] In this way, in a state where the power supply circuit is carrying out switching operation, the discharge current 13 constantly flows from the capacitor C I to the load at the first input/output port PAl , and additionally the capacitor CI is charged and discharged with a large current in the periods T2, T3. Therefore, the root-mean-square value of the ripple current 15 tends to increase.

[0082] Control details that are executed in the periods T5, T6, T7, T8 in FIG. 5 are respectively control states similar to those in the periods Tl , T2, T3, T4, so the description thereof is omitted.

[0083] Here, as shown in FIG. 5, a positive current peak of the ripple current 15 and a negative current peak of the ripple current 15 alternately appear at intervals of 90° in one period (360°). In FIG. 5, the waveform of the positive current peak at which current flows in a direction to charge the capacitor CI is generated in the periods T2, T6, and the waveform of the negative current peak at which current flows in a direction to discharge the capacitor CI is generated in the periods T3, T7.

[0084] Therefore, the control circuit 50 has the control function of varying the phase of the switching waveform of each electric power conversion circuit portion in one of the plurality of power supply circuits with respect to the phase of the switching waveform of a corresponding one of the electric power conversion circuit portions in another of the plurality of power supply circuits in order to reduce ripple current flowing through the capacitor connected to each input/output port. Thus, for example, it is possible to bring the waveform of the positive current peak that is generated by each electric power conversion circuit portion in the first one of the plurality of power supply circuits and the waveform of the negative current peak that is generated by a corresponding one of the electric power conversion circuit portions in the second one of the plurality of power supply circuits close, to each other such that those waveforms overlap with each other. _.

[0085] As a result, mutually opposite currents flow through each capacitor, to which both the first power supply circuit and the second power supply circuit are connected, so as to cancel each other. Thus, it is possible to reduce ripple current that flows through each capacitor, so it is possible to easily reduce the size of each capacitor. By reducing ripple current, for example, noise that occurs at the input/output port to which the capacitor is connected is also reduced, so it is also possible to improve the accuracy of the output of the input/output port.

[0086] For example, the electric power conversion circuit 10 is able to convert electric power between any two of the four input/output ports PA, PB, PC, PD to which both the power supply circuits 11 , 12 are connected. Therefore, it is possible to not only reduce the ripple current that flows through the capacitor C I connected to the first input/output port PA but also reduce the ripple current that flows through any one of the capacitors C2, C3, C4 respectively connected to the input/output ports PB, PC, PD other than the first input/output port PA. By reducing the ripple currents, it is possible to easily reduce the size of each of the capacitors CI, C2, C3, C4, it is also possible to reduce noise that occurs at any one of the input/output ports PA, PB, PC, PD, so it is possible to also improve the accuracy of the outputs of the input/output ports PA, PB, PC, PD.

[0087] The control circuit 50 executes control for varying the switching timing by a phase difference ε between the same -phase electric power conversion circuit portions of the power supply circuit 11 and power supply circuit 12 such that the waveform of the positive current peak that is generated by the power supply circuit 11 and the waveform of the negative current peak that is generated by the power supply circuit 12 overlap with each other. The phase difference ε is a deviation (time lag) in switching timing between the same-phase electric power conversion circuit portions of the power supply circuit 11 and power supply circuit 12. [0088] For example, the control circuit 50 executes control for shifting the switching timing of the primary first arm circuit 207 of the power supply circuit 11 and the switching timing of the same-phase primary first arm circuit 207 of the power supply circuit 12 from each other. Similarly, the control circuit 50 shifts the switching timings of the primary second arm circuits 211 of the respective power supply circuits 11 , 12 from each other, shifts the switching timings of the secondary first arm circuits 307 of the respective power supply circuits 11 , 12 from each other, and shifts the switching timings of the secondary second arm circuits 31 1 of the respective power supply circuits 11 , 12 from each other.

[0089] FIG. 10 is a timing chart that shows the switching waveform of the on/off state of the primary first upper arm Ul of the power supply circuit 11 and the switching waveform of the on/off state of the primary first upper arm Ul of the power supply circuit 12. As shown in FIG. 10, the control circuit 50 causes both of these arms to carry out switching such that the phase difference ε occurs in both the switching waveform of the primary first upper arm U l of the power supply circuit 11 and the switching waveform of the primary first upper arm Ul of the power supply circuit 12. The control circuit 50 causes each of the other arms Ul, VI , /VI , U2, /U2, V2, /V2 to carry out switching such that the same phase difference ε as that of the arm Ul occurs in the switching waveforms of the other arms /Ul, VI , /VI, U2, /U2, V2, /V2 between the power supply circuit 11 and the power supply circuit 12.

[0090] The control circuit 50 may advance or retard the phase of the switching waveform of one of the power supply circuits with respect to the switching waveform of the other one of the power supply circuits.

[0091] The control circuit 50 controls the phase of each of the switching waveforms of the power supply circuits 11 , 12 such that the phase difference ε between the power supply circuit 11 and the power supply circuit 12 becomes a value within a predetermined range larger than zero. For example, the control circuit 50 controls the phase of each of the switching waveforms of the power supply circuits 11 , 12 such that the phase difference ε between the power supply circuit 11 and the power supply circuit 12 becomes a value larger than or equal to 70° and smaller than or equal to 110° and desirably a value larger than or equal to 80° and smaller than or equal to 100°. Because the phase difference ε is controlled to a value within such a range, it is possible to effectively reduce ripple current that flows through the capacitors connected to the input/output ports, and it is possible to easily reduce the size of each capacitor.

[0092] FIG. 11 is a simulation waveform of ripple current that flows through the capacitor CI when the phase difference ε between the power supply circuit 1 1 and the power supply circuit 12 is zero. FIG. 12 is a simulation waveform of ripple current that flows through the capacitor CI when the phase difference ε between the power supply circuit 1 1 and the power supply circuit 12 is 90°. In this way, the control circuit 50 is able to reduce the root-mean-square (RMS) value of ripple current by 70% from a to b by executing switching control over the arms such that the phase difference ε becomes 90°.

[0093] The power supply circuit and the control method for a power supply circuit are described with reference to the embodiment; however, the invention is not limited to the above-described embodiment. The scope of the invention encompasses various modifications and improvements, such as combinations and replacements of the above-described embodiment with part or all of another embodiment.

[0094] For example, in the above-described embodiment, the MOSFET that is a semiconductor element that carries out on/off operation is described as an example of each switching element. However, each switching element may be, for example, a voltage-controlled power element with an insulated gate, such as an IGBT and a MOSFET, or may be a bipolar transistor.

[0095] In addition, a power supply may be connected to the first input/output port PA or a power supply may be connected to the fourth input/output port PD. In addition, a power supply may not be connected to the second input/output port PC or a power supply may not be connected to the third input/output port PB.

[0096] The capacitor provided at each port may be a capacitor other than the film capacitor, and may be, for example, an aluminum electrolytic capacitor or a solid polymer capacitor. , [0097] The number of parallel power supply circuits may be three or more.

Claims

CLAIMS:

1. A power supply system comprising:

a first power supply circuit including: a first primary circuit including a first primary electric power conversion unit configured to convert electric power by switching; a first secondary circuit including a first secondary electric power conversion unit configured to convert electric power by switching;, and a first transformer magnetically coupling the first primary circuit to the first secondary circuit;

a second power supply circuit connected in parallel with the first power supply circuit, the second power supply circuit including: a second primary circuit including a second primary electric power conversion unit configured to convert electric power by switching; a second secondary circuit including a second secondary electric power conversion unit configured to convert electric power by switching; and a second transformer magnetically coupling the second primary circuit to the second secondary circuit;

a first port to which the first primary circuit and the second primary circuit are connected;

a second port to which the first primary circuit and the second primary circuit are connected;

a third port to which the first secondary circuit and the second secondary circuit are connected; , ·

a fourth port to which the first secondary circuit and the second secondary circuit are connected;

a first capacitor connected to the first port;

a second capacitor connected to the second port;

a third capacitor connected to the third port;

a fourth capacitor connected to the fourth port; and

a control circuit connected to the first power supply circuit and the second power supply circuit and configured to vary a phase of a first switching waveform at the first primary electric power conversion unit with respect to a phase of a second switching waveform at the second primary electric power conversion unit, wherein

the first power supply circuit is configured to convert electric power with a use of at least one of the first primary electric power conversion unit and the first secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port, and

the second power supply circuit is configured to convert electric power with a use of at least one of the second primary electric power conversion unit and the second secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port.

2. The power supply system according to claim 1, wherein

the control circuit is configured to control the phase of the first switching waveform and the phase of the second switching waveform so as to bring a peak of positive current and a peak of negative current close to each other, the positive current being caused by the first power supply circuit to flow through the first capacitor, and the negative current being caused by the second power supply circuit to flow through the first capacitor.

3. The power supply system according to claim 1 or 2, wherein

a difference between the phase of the first switching waveform and the phase of the second switching waveform is larger than or equal to 70° and smaller than or equal to 110°.

4. The power supply system according to any one of claims 1 to 3, wherein a difference between the phase of the first switching waveform and a phase of a switching waveform at the first secondary electric power conversion unit is equal to a difference between the phase of the second switching waveform and a phase of a switching waveform at the second secondary electric power conversion unit.

5. The power supply system according to any one of claims 1 to 4, wherein the first primary electric power conversion unit includes a first primary arm circuit, the second primary electric power conversion unit includes a second primary arm circuit having a phase equal to that of the first primary arm circuit, and

the control circuit is configured to vary the phase of the first switching waveform with respect to the phase of the second switching waveform by shifting a switching timing of the first primary arm circuit and a switching timing of the second primary arm circuit from each other.

6. A control method for a power supply system, the power supply system including: a first power supply circuit including: a first primary circuit including a first primary electric power conversion unit configured to convert electric power by switching; a first secondary circuit including a first secondary electric power conversion unit configured to convert electric power by switching; and a first transformer magnetically coupling the first primary circuit to the first secondary circuit; - a second power supply circuit, connected in parallel with the first power supply circuit, the second power supply circuit including: a second primary circuit including a second primary electric power conversion unit configured to convert electric power by switching; a second secondary circuit including a second secondary electric power conversion unit configured to convert electric power by switching; and a second transformer magnetically coupling the second primary circuit to the second secondary circuit;

a third port to which the first secondary circuit and the second secondary circuit are connected;

a first capacitor connected to the first port;

a second capacitor connected to the second port; a third capacitor connected to the third port; and

a fourth capacitor connected to the fourth port,

the first power supply circuit being configured to convert electric power with a use of at least one of the first primary electric power conversion unit and the first secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port, and

the second power supply circuit being configured to convert electric power with a use of at least one of the second primary electric power conversion unit and the second secondary electric power conversion unit between two of the first port, the second port, the third port and the fourth port,

the control method comprising:

varying a phase of a first switching waveform ^' at the first primary electric power conversion unit with respect to a phase of a second switching waveform at the second primary electric power conversion unit.