Power conversion circuit and program for power conversion circuit

Abstract

A power conversion circuit (30) comprises a plurality of bidirectional switches (TSW) and a control unit (33). The control unit (33) can control each bidirectional switch (TSW) according to a first switch sequence or a second switch sequence. The control unit (33) switches from the control according to the first switch sequence to the control according to the second switch sequence when the on / off state of the bidirectional switch (TSW) through which current flows in the control according to the first switch sequence matches the on / off state of the bidirectional switch (TSW) through which current flows in the control according to the second switch sequence after the switching.

Description

Power conversion circuit and program for power conversion circuit

[0001] The present disclosure relates to a power conversion circuit and a program for the power conversion circuit.

[0002] The power conversion circuit disclosed in Patent Document 1 includes three input terminals, a plurality of switch elements, and a control unit. The power conversion circuit is capable of converting three-phase AC power input to the input terminals into single-phase AC power through on / off control of the plurality of switch elements. The control unit controls the on / off of each switch element.

[0003] US Patent Application Publication No. 2018 / 0262103

[0004] Consider a case where a switch sequence is switched in a power conversion circuit. In this case, the on / off states of multiple switch elements may differ between the on / off combinations of the switch elements in the switch sequence before the switch and the on / off combinations of the switch elements in the switch sequence after the switch. When attempting to switch on / off the multiple switch elements in this manner, electrical stress is likely to be applied to a specific switch among the multiple switch elements being switched.

[0005] In order to solve the above problems, the present disclosure provides a power supply including a first input terminal, a second input terminal, and a third input terminal that are connected to a three-phase AC power supply and to which a first voltage, a second voltage, and a third voltage that are AC voltages of different phases are input in a one-to-one correspondence; a plurality of bidirectional switches that are connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal that are connected to the plurality of bidirectional switches and are capable of outputting AC power; a first switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order of switching the plurality of combinations; and a control unit capable of controlling the plurality of bidirectional switches in accordance with a second switch sequence that defines a plurality of combinations of on / off states and an order of switching between the plurality of combinations in a manner different from the first switch sequence, wherein the control unit switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching.

[0006] The present disclosure also provides a three-phase AC power supply including a first input terminal, a second input terminal, and a third input terminal connected to the three-phase AC power supply and receiving a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, in a one-to-one correspondence; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal capable of outputting AC power; a first switch sequence defining a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations; and a control unit capable of controlling the plurality of bidirectional switches in accordance with a second switch sequence that defines an order of switching between the combinations of the plurality of bidirectional switches in a manner different from the first switch sequence, and causing the control unit to switch from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching.

[0007] This can prevent electrical stress from being applied to a specific switch.

[0008] FIG. 1 is a circuit diagram of a power conversion device according to this embodiment. FIG. 2 is an explanatory diagram showing a waveform and sectors of three-phase AC power. FIG. 3 is a space vector diagram in SVPWM. FIG. 4 is a space vector diagram in SVPWM. FIG. 5 is a sequence diagram of switch on / off control in sector 1a. FIG. 6 is a sequence diagram of switch on / off control in sector 1b. FIG. 7 is a sequence diagram of switch on / off control in sector 2a. FIG. 8 is a diagram showing an example of correspondence between time and switch states in switch on / off control. FIG. 9 is a diagram explaining switch sequence switching control. FIG. 10 is a circuit diagram explaining switch sequence switching control. FIG. 11 is a circuit diagram explaining switch sequence switching control. FIG. 12 is a circuit diagram explaining switch sequence switching control. FIG. 13 is a circuit diagram explaining switch sequence switching control. FIG. 14 is a circuit diagram explaining switch sequence switching control. FIG. 15 is a circuit diagram explaining switch sequence switching control.

[0009] <One Embodiment of Power Conversion Circuit> One embodiment of a power conversion circuit will be described below. Note that the drawings merely illustrate the embodiments of the present disclosure and should not be considered to limit the present disclosure. Terms such as "first," "second," and "third" in the present disclosure are used simply to distinguish between objects and are not used to rank the objects.

[0010] (1. Configuration of the Power Conversion Device) As shown in FIG. 1 , the power conversion device 10 includes an input-side low-pass filter 20, a power conversion circuit 30, a transformer circuit 40, a rectifier circuit 50, and an output-side low-pass filter 60. The power conversion device 10 also includes three external input terminals 11 and a pair of external output terminals 12. The power conversion device 10 is a so-called three-phase insulated AC-DC converter. That is, the power conversion device 10 is capable of converting three-phase AC power input to the external input terminals 11 into DC power and outputting it from the external output terminals 12. The presence of a transformer circuit 40 on the power path from each external input terminal 11 to each external output terminal 12 electrically insulates the external input terminal 11 side from the external output terminal 12 side.

[0011] The three external input terminals 11 of the power conversion device 10 are a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C. Three phases of three-phase AC power input from a three-phase AC power supply 80 are input in a one-to-one correspondence to each external input terminal 11. The three-phase AC power supply 80 is a three-phase, three-wire commercial power system in which three AC power supplies are Y-connected.

[0012] The pair of external output terminals 12 is a first external output terminal 12A and a second external output terminal 12B. An arbitrary load 70 can be connected between the first external input terminal 11A and the second external output terminal 12B. The load 70 is, for example, an electronic device driven by DC power.

[0013] The input low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3, as well as a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0014] A first end of the first inductor L1 is connected to the first external input terminal 11A. A first end of the first capacitor C1 is connected to the second end of the first inductor L1. A first end of the second inductor L2 is connected to the second external input terminal 11B. A first end of the second capacitor C2 is connected to the second end of the second inductor L2. A second end of the second capacitor C2 is connected to the second end of the first capacitor C1.

[0015] A first end of the third inductor L3 is connected to the third external input terminal 11C. A first end of the third capacitor C3 is connected to the second end of the third inductor L3. A second end of the third capacitor C3 is connected to the second end of the first capacitor C1.

[0016] The power conversion circuit 30 includes a plurality of input terminals 31, a pair of output terminals 32, a plurality of bidirectional switches TSW, and a control unit 33. The plurality of input terminals 31 include a first input terminal 31A, a second input terminal 31B, and a third input terminal 31C. A second end of a first inductor L1 is connected to the first input terminal 31A. A second end of a second inductor L2 is connected to the second input terminal 31B. A second end of a third inductor L3 is connected to the third input terminal 31C. Thus, three-phase AC power is input to the input terminals 31 of the power conversion circuit 30 via the external input terminal 11 and the input-side low-pass filter 20. The pair of output terminals 32 include a first output terminal 32A and a second output terminal 32B. Single-phase AC power converted by the plurality of bidirectional switches TSW is output from the pair of output terminals 32.

[0017] Each bidirectional switch TSW has two switch elements. Each switch element is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). That is, each switch element has a body diode. The bidirectional switch TSW is composed of two switch elements connected in series so that the anode terminals of the body diodes are connected to each other. That is, the switch elements constituting each bidirectional switch TSW are connected to each other so that the body diodes are in opposite directions. In other words, each bidirectional switch TSW has two switch elements whose source terminals are connected to each other.

[0018] The multiple bidirectional switches TSW include a first high-side bidirectional switch HS1, a first low-side bidirectional switch LS1, a second high-side bidirectional switch HS2, a second low-side bidirectional switch LS2, a third high-side bidirectional switch HS3, and a third low-side bidirectional switch LS3.

[0019] The first high-side bidirectional switch HS1 connects the first input terminal 31A and the first output terminal 32A. Specifically, the first high-side bidirectional switch HS1 has an eleventh switch element S11 and a twenty-first switch element S21. The drain terminal of the eleventh switch element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switch element S11 is connected to the source terminal of the twenty-first switch element S21. The drain terminal of the twenty-first switch element S21 is connected to the first output terminal 32A.

[0020] The first low-side bidirectional switch LS1 connects the first input terminal 31A and the second output terminal 32B. Specifically, the first low-side bidirectional switch LS1 has a 24th switch element S24 and a 14th switch element S14. The drain terminal of the 24th switch element S24 is connected to the first input terminal 31A. The source terminal of the 24th switch element S24 is connected to the source terminal of the 14th switch element S14. The drain terminal of the 14th switch element S14 is connected to the second output terminal 32B.

[0021] The second high-side bidirectional switch HS2 connects the second input terminal 31B and the first output terminal 32A. Specifically, the second high-side bidirectional switch HS2 has a thirteenth switch element S13 and a twenty-third switch element S23. The drain terminal of the thirteenth switch element S13 is connected to the second input terminal 31B. The source terminal of the thirteenth switch element S13 is connected to the source terminal of the twenty-third switch element S23. The drain terminal of the twenty-third switch element S23 is connected to the first output terminal 32A.

[0022] The second low-side bidirectional switch LS2 connects the second input terminal 31B and the second output terminal 32B. Specifically, the second low-side bidirectional switch LS2 has a 26th switch element S26 and a 16th switch element S16. The drain terminal of the 26th switch element S26 is connected to the second input terminal 31B. The source terminal of the 26th switch element S26 is connected to the source terminal of the 16th switch element S16. The drain terminal of the 16th switch element S16 is connected to the second output terminal 32B.

[0023] The third high-side bidirectional switch HS3 connects the third input terminal 31C and the first output terminal 32A. Specifically, the third high-side bidirectional switch HS3 has a fifteenth switch element S15 and a twenty-fifth switch element S25. The drain terminal of the fifteenth switch element S15 is connected to the third input terminal 31C. The source terminal of the fifteenth switch element S15 is connected to the source terminal of the twenty-fifth switch element S25. The drain terminal of the twenty-fifth switch element S25 is connected to the first output terminal 32A.

[0024] The third low-side bidirectional switch LS3 connects the third input terminal 31C and the second output terminal 32B. Specifically, the third low-side bidirectional switch LS3 has a 22nd switch element S22 and a 12th switch element S12. The drain terminal of the 22nd switch element S22 is connected to the third input terminal 31C. The source terminal of the 22nd switch element S22 is connected to the source terminal of the 12th switch element S12. The drain terminal of the 12th switch element S12 is connected to the second output terminal 32B.

[0025] The control unit 33 has a storage device and an execution device (not shown). That is, the control unit 33 is an MCU (Microcontroller Unit). The storage device of the control unit 33 stores a program PG to be executed by the execution device.

[0026] The execution device includes, for example, a central processing unit (CPU), a micro processing unit (MPU), a field programmable gate array (FPGA), a complex programmable logic device (CPLD), an application specific integrated circuit (ASIC), etc. The execution device of the control unit 33 executes the program PG to control each bidirectional switch TSW in accordance with a switch sequence described below. Specifically, the power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit turns on and off two switch elements included in each bidirectional switch TSW. The execution device of the control unit 33 inputs switching signals to the input terminals of the gate drive circuits and outputs gate drive voltages to each switch element via the gate drive circuits, thereby controlling the on / off of each switch element. The switching signals include an eleventh switching signal SG11 to a sixteenth switching signal SG16 and a twenty-first switching signal SG21 to a twenty-sixth switching signal SG26. The eleventh switching signal SG11 to the sixteenth switching signal SG16 correspond one-to-one to the eleventh switch elements S11 to the sixteenth switch elements S16, respectively. The twenty-first switching signal SG21 to the twenty-sixth switching signal SG26 correspond one-to-one to the twenty-first switch elements S21 to the twenty-sixth switch elements S26, respectively. Note that hereinafter, the on / off control by the execution device of the control unit 33 will simply be referred to as the on / off control by the control unit 33.

[0027] Each bidirectional switch TSW can be in four on / off states depending on the on / off combination of each switch element. The following description will be given taking the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1 as examples.

[0028] The first state is a bidirectional on state. In the bidirectional on state, the eleventh switch element S11 and the twenty-first switch element S21 of the first high-side bidirectional switch HS1 are on and on, respectively. In the bidirectional on state, the first high-side bidirectional switch HS1 allows a current to flow from the first input terminal 31A to the first output terminal 32A, and also allows a current to flow from the first output terminal 32A to the first input terminal 31A.

[0029] In the first low-side bidirectional switch LS1, when the first low-side bidirectional switch LS1 is in the bidirectional on state, the fourteenth switch element S14 is on and the twenty-fourth switch element S24 is on. In the bidirectional on state, the first low-side bidirectional switch LS1 allows a current to flow from the first input terminal 31A to the second output terminal 32B, and also allows a current to flow from the second output terminal 32B to the first input terminal 31A.

[0030] The second state is a positive on state. In the positive on state, in the first high-side bidirectional switch HS1, the eleventh switch element S11 is on and the twenty-first switch element S21 is off. In the positive on state, the first high-side bidirectional switch HS1 allows current to flow from the first input terminal 31A to the first output terminal 32A through the body diode of the twenty-first switch element S21. On the other hand, the first high-side bidirectional switch HS1 does not allow current to flow from the first output terminal 32A to the first input terminal 31A.

[0031] Furthermore, when the first low-side bidirectional switch LS1 is in the on state in the positive direction, the fourteenth switch element S14 is on and the twenty-fourth switch element S24 is off. In the on state in the positive direction, the first low-side bidirectional switch LS1 allows a current to flow from the second output terminal 32B to the first input terminal 31A through the body diode of the twenty-fourth switch element S24. On the other hand, the first low-side bidirectional switch LS1 does not allow a current to flow from the first input terminal 31A to the second output terminal 32B.

[0032] The third state is a negative on state. In the negative on state, in the first high-side bidirectional switch HS1, the eleventh switch element S11 is off and the twenty-first switch element S21 is on. In the negative on state, the first high-side bidirectional switch HS1 allows current to flow from the first output terminal 32A to the first input terminal 31A through the body diode of the eleventh switch element S11. On the other hand, the first high-side bidirectional switch HS1 does not allow current to flow from the first input terminal 31A to the first output terminal 32A.

[0033] Furthermore, when the first low-side bidirectional switch LS1 is in the on state in the negative direction, the fourteenth switch element S14 is off and the twenty-fourth switch element S24 is on. In the on state in the negative direction, the first low-side bidirectional switch LS1 allows a current to flow from the first input terminal 31A to the second output terminal 32B through the body diode of the fourteenth switch element S14. On the other hand, the first low-side bidirectional switch LS1 does not allow a current to flow from the second output terminal 32B to the first input terminal 31A.

[0034] The fourth state is the off state. In the off state, the eleventh switch element S11 and the twenty-first switch element S21 of the first high-side bidirectional switch HS1 are off. In the off state, the first high-side bidirectional switch HS1 does not allow a current to flow from the first input terminal 31A to the first output terminal 32A, nor does it allow a current to flow from the first output terminal 32A to the first input terminal 31A.

[0035] In the first low-side bidirectional switch LS1, when the first low-side bidirectional switch LS1 is in the off state, the fourteenth switch element S14 is off and the twenty-fourth switch element S24 is off. In the off state, the first low-side bidirectional switch LS1 does not allow a current to flow from the first input terminal 31A to the second output terminal 32B, nor does it allow a current to flow from the second output terminal 32B to the first input terminal 31A.

[0036] The transformer circuit 40 includes a fourth inductor L4 and a transformer 41. The transformer 41 includes a primary winding 41A and a secondary winding 41B. A first end of the fourth inductor L4 is connected to a first output terminal 32A of the power conversion circuit 30. A first end of the primary winding 41A is connected to a second end of the fourth inductor L4. A second end of the primary winding 41A is connected to a second output terminal 32B of the power conversion circuit 30. The secondary winding 41B is connected to the external output terminal 12 via a rectifier circuit 50 and an output low-pass filter 60. The primary winding 41A and the secondary winding 41B are electrically insulated from each other.

[0037] The rectifier circuit 50 is a full-wave rectifier circuit composed of four diodes. Specifically, the rectifier circuit 50 includes a first diode 51, a second diode 52, a third diode 53, and a fourth diode 54. The anode terminal of the first diode 51 is connected to a first end of the secondary winding 41B of the transformer 41. The cathode terminal of the first diode 51 is connected to a cathode terminal of the third diode 53. The anode terminal of the third diode 53 is connected to a second end of the secondary winding 41B and a cathode terminal of the fourth diode 54. The anode terminal of the fourth diode 54 is connected to an anode terminal of the second diode 52. The cathode terminal of the second diode 52 is connected to a first end of the secondary winding 41B and an anode terminal of the first diode 51.

[0038] The cathode terminals of the first diode 51 and the third diode 53 are connected to the first external output terminal 12A via the output low-pass filter 60. The anode terminals of the second diode 52 and the fourth diode 54 are connected to the second external output terminal 12B. Therefore, the first diode 51 allows current to flow from the first end of the secondary winding 41B to the first external output terminal 12A. The fourth diode 54 allows current to flow from the second external output terminal 12B to the second end of the secondary winding 41B. The third diode 53 allows current to flow from the second end of the secondary winding 41B to the first external output terminal 12A. The second diode 52 allows current to flow from the second external output terminal 12B to the first end of the secondary winding 41B.

[0039] The output-side low-pass filter 60 includes a fifth inductor L5 and a fourth capacitor C4. A first end of the fifth inductor L5 is connected to the cathode terminal of the first diode 51 and the cathode terminal of the third diode 53. A second end of the fifth inductor L5 is connected to the first external output terminal 12A. A first end of the fourth capacitor C4 is connected to the second end of the fifth inductor L5. A second end of the fourth capacitor C4 is connected to the second external output terminal 12B.

[0040] (2. Definition of Sectors) As described above, three-phase AC power is input to the input terminal 31 of the power conversion circuit 30 from the three-phase AC power supply 80 via the external input terminal 11 and the input-side low-pass filter 20. As shown in FIG. 2 , the three phase voltages of the three-phase AC power are a first voltage VA, a second voltage VB, and a third voltage VC, which are AC voltages of different phases. The first input terminal 31A, the second input terminal 31B, and the third input terminal 31C are input with one-to-one correspondence to each other. Specifically, the first voltage VA is input to the first input terminal 31A. The second voltage VB is input to the second input terminal 31B. The third voltage VC is input to the third input terminal 31C. The second voltage VB has a phase difference of 120° with respect to the first voltage VA. The third voltage VC has a phase difference of 120° with respect to the second voltage VB. The "phase difference of 120°" allows for an error of about ±1°.

[0041] In the following, the timing of the phase when the first voltage VA is maximum is defined as 0°. Furthermore, the timing of the phase when the first voltage VA is minimum is defined as -180°. Therefore, one cycle of the first voltage VA, the second voltage VB, and the third voltage VC is expressed as a phase range of -180° or more and less than 180°. For convenience, the timing of the voltage phase may also be expressed as a phase of 180° or more. When the voltage phase is expressed as a phase of 180° or more, X° is synonymous with (-180° + (X - 180°)). Here, sectors 1 to 6 are defined as six periods obtained by dividing one cycle into equal parts. Specifically, when the phase of the first voltage VA is defined as "θ°," sectors 1 to 6 are defined as the following periods spaced at 60° intervals:

[0042] Sector 1: -30°≦θ°<30° Sector 2: 30°≦θ°<90° Sector 3: 90°≦θ°<150° Sector 4: 150°≦θ°<180° and -180°≦θ°<-150° Sector 5: -150°≦θ°<-90° Sector 6: -90°≦θ°<-30° Furthermore, each of sectors 1 to 6 is subdivided into two periods. In other words, one cycle of three-phase AC power is subdivided into 12 periods. In the following, n is an integer between 1 and 6, and corresponds to the sector number. In this case, sector n is subdivided into two periods, sector na and sector nb. In this embodiment, each period is defined as follows:

[0043] Sector na: (X°-30°)≦θ°<X° Sector nb: X°≦θ°<(X°+30°) Note that X° is the midpoint value of the period of sector n. The "midpoint of the period" is the intermediate value between the endpoints of each sector expressed as a half-open interval. However, in the definition of sector 4a, X=180°.

[0044] (3. Regarding Vector Sequence) In the following, the potential difference between the first output terminal 32A and the second output terminal 32B is referred to as the primary voltage Vp. That is, the primary voltage Vp is the voltage applied across the fourth inductor L4 and the primary winding 41A of the transformer 41. Furthermore, the current flowing between the first output terminal 32A and the second output terminal 32B is referred to as the primary current Ip. That is, the primary current Ip is the current flowing through the fourth inductor L4 and the primary winding 41A of the transformer 41. Note that the direction in which the primary current Ip flows from the first output terminal 32A to the second output terminal 32B is referred to as the positive direction. The direction in which the primary current Ip flows from the second output terminal 32B to the first output terminal 32A is referred to as the negative direction.

[0045] Furthermore, the phase having the first voltage VA is referred to as phase A, the phase having the second voltage VB is referred to as phase B, and the phase having the third voltage VC is referred to as phase C. Furthermore, one of the three phases is referred to as phase i, and the other phase is referred to as phase j. Hereinafter, the voltage difference obtained by subtracting the voltage of phase j from the voltage of phase i will be referred to as "line voltage Vij."

[0046] The control unit 33 controls the pulse width of each switching signal by space vector pulse width modulation (SVPWM).

[0047] As shown in Figures 3 and 4, an active vector and a zero vector Iz are defined for control using SVPWM. In this embodiment, the active vector and the zero vector Iz are current vectors of the power conversion circuit 30 in a predetermined switching state. When m is an integer between 1 and 6, the active vector is expressed as a space vector by the following mathematical expression 1. In this mathematical expression 1, "I" is the absolute value of the primary current Ip.

[0048]

[0049] The active vectors are roughly classified into positive direction active vectors and negative direction active vectors. Specifically, as shown in Fig. 3, the positive direction active vectors include the first positive direction active vector I1+ to the sixth positive direction active vector I6+. Each positive direction active vector is a current vector when the primary voltage Vp is a positive value and each bidirectional switch TSW is in the following switching state:

[0050] First positive active vector I1+: The second low-side bidirectional switch LS2 is in a bidirectional on state or a positive on state, and the first high-side bidirectional switch HS1 is in a bidirectional on state or a positive on state. At this time, the primary voltage Vp is the line voltage VAB.

[0051] Second positive active vector I2+: The first high-side bidirectional switch HS1 is in a bidirectional on state or a positive on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state or a positive on state. At this time, the primary voltage Vp is the line voltage VAC.

[0052] Third positive active vector I3+: The third low-side bidirectional switch LS3 is in a bidirectionally on state or a positively on state, and the second high-side bidirectional switch HS2 is in a bidirectionally on state or a positively on state. At this time, the primary voltage Vp is the line voltage VBC.

[0053] Fourth positive active vector I4+: The second high-side bidirectional switch HS2 is in a bidirectionally on state or a positively on state, and the first low-side bidirectional switch LS1 is in a bidirectionally on state or a positively on state. At this time, the primary voltage Vp is the line voltage VBA.

[0054] Fifth positive active vector I5+: The first low-side bidirectional switch LS1 is in a bidirectionally on state or a positively on state, and the third high-side bidirectional switch HS3 is in a bidirectionally on state or a positively on state. At this time, the primary voltage Vp is the line voltage VCA.

[0055] Sixth positive active vector I6+: The third high-side bidirectional switch HS3 is in a bidirectionally on state or a positively on state, and the second low-side bidirectional switch LS2 is in a bidirectionally on state or a positively on state. At this time, the primary voltage Vp is the line voltage VCB.

[0056] 4, the negative direction active vectors include a first negative direction active vector I1 to a sixth negative direction active vector I6. Each negative direction active vector is a current vector when the primary voltage Vp has a negative value and each bidirectional switch TSW is in the following switching state.

[0057] First negative active vector I1−: The second high-side bidirectional switch HS2 is in the on state in both directions or in the on state in the negative direction. The first low-side bidirectional switch LS1 is in the on state in both directions or in the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VAB.

[0058] Second negative active vector I2−: The first low-side bidirectional switch LS1 is in the on state in both directions or the on state in the negative direction. The third high-side bidirectional switch HS3 is in the on state in both directions or the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VAC.

[0059] Third negative active vector I3−: The third high-side bidirectional switch HS3 is in the on state in both directions or the on state in the negative direction. The second low-side bidirectional switch LS2 is in the on state in both directions or the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VBC.

[0060] Fourth negative active vector I4−: The second low-side bidirectional switch LS2 is in the on state in both directions or in the on state in the negative direction. The first high-side bidirectional switch HS1 is in the on state in both directions or in the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VBA.

[0061] Fifth negative active vector I5−: The first high-side bidirectional switch HS1 is in the on state in both directions or the on state in the negative direction. The third low-side bidirectional switch LS3 is in the on state in both directions or the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VCA.

[0062] Sixth negative active vector I6−: The third low-side bidirectional switch LS3 is in the on state in both directions or in the on state in the negative direction. The second high-side bidirectional switch HS2 is in the on state in both directions or in the on state in the negative direction. At this time, the primary voltage Vp is the line voltage −VCB.

[0063] 3 and 4, the zero vector Iz includes a seventh zero vector I7, an eighth zero vector I8, and a ninth zero vector I9. The zero vector Iz is a current vector in the following switching state. Note that in the switching state resulting in the zero vector Iz, the primary voltage Vp becomes zero. "The primary voltage Vp is zero" allows for an error of, for example, about ±10 V.

[0064] Seventh zero vector I7: The first high-side bidirectional switch HS1 is in a bidirectional on state or a positive on state, and the first low-side bidirectional switch LS1 is in a bidirectional on state or a positive on state, or the first high-side bidirectional switch HS1 is in a bidirectional on state or a negative on state, and the first low-side bidirectional switch LS1 is in a bidirectional on state or a negative on state.

[0065] Eighth zero vector I8: The second high-side bidirectional switch HS2 is in a bidirectional on state or a positive on state, and the second low-side bidirectional switch LS2 is in a bidirectional on state or a positive on state, or the second high-side bidirectional switch HS2 is in a bidirectional on state or a negative on state, and the second low-side bidirectional switch LS2 is in a bidirectional on state or a negative on state.

[0066] Ninth zero vector I9: The third high-side bidirectional switch HS3 is in a bidirectional on state or a positive on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state or a positive on state, or the third high-side bidirectional switch HS3 is in a bidirectional on state or a negative on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state or a negative on state.

[0067] The current reference vector Ir in sector n is approximated as a composite vector of the active vectors and the zero vector Iz. Specifically, when x = n and y = x + 1 (where y = 1 when x = 6), the current reference vector Ir in sector n is approximated as a composite vector of the x-th positive direction active vector Ix+, the y-th positive direction active vector Iy+, and the zero vector Iz. Alternatively, the current reference vector Ir in sector n is approximated as a composite vector of the x-th negative direction active vector Ix-, the y-th negative direction active vector Iy-, and the zero vector Iz. Note that the zero vector Iz is the seventh zero vector I7 in sectors 1 and 4. The zero vector Iz is the ninth zero vector I9 in sectors 2 and 5. The zero vector Iz is the eighth zero vector I8 in sectors 3 and 6.

[0068] In principle, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir transitions between the above-mentioned active vector or zero vector Iz in a certain order depending on the magnitude relationship between the first voltage VA, the second voltage VB, and the third voltage VC.

[0069] Specifically, in sector na, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir follows the vector sequence shown in (na) below. In sector nb, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir follows the vector sequence shown in (nb) below. (na) The order is x-th positive direction active vector Ix+, y-th positive direction active vector Iy+, zero vector Iz, x-th negative direction active vector Ix-, y-th negative direction active vector Iy-, zero vector Iz. (nb) The order is y-th positive direction active vector Iy+, x-th positive direction active vector Ix+, zero vector Iz, y-th negative direction active vector Iy-, x-th negative direction active vector Ix-, zero vector Iz.

[0070] In the sector na, the control unit 33 repeats the on / off control of each bidirectional switch TSW based on the vector sequence shown in (na) above at a constant cycle Ts. The period of the cycle Ts is very short compared to each period of the sector na.

[0071] Furthermore, in the sector nb, the control unit 33 repeats the on / off control of each bidirectional switch TSW based on the vector sequence shown in (nb) above, in the same cycle Ts as the vector sequence shown in (na) above. The period of the cycle Ts is very short compared to each period of the sector nb.

[0072] (4. Switch Sequence) The storage device of the control unit 33 stores multiple switch sequences as part of the program PG. Each switch sequence defines the switching manner of the on / off states of multiple bidirectional switches TSW based on each vector sequence. Specifically, each switch sequence defines multiple combinations of the on / off states of the bidirectional switches TSW and also defines the order of the multiple combinations.

[0073] The following describes the on / off control of the bidirectional switch TSW according to each switch sequence in sector 1a, sector 1b, and sector 2a as an example. The switch sequence in sector na is referred to as switch sequence na, and the switch sequence in sector nb is referred to as switch sequence nb.

[0074] (4-1. Regarding Switch Sequence 1a) As shown in FIG. 2, in sector 1a, of the first voltage VA to the third voltage VC, the first voltage VA is the largest. Furthermore, the third voltage VC is equal to or greater than the second voltage VB. Furthermore, in sector 1a, the absolute value of the first voltage VA is the largest. Furthermore, the absolute value of the second voltage VB is greater than the absolute value of the third voltage VC.

[0075] 3 and 4, in the sector 1a, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir follows the vector sequence shown in (1a) below. Therefore, the switch sequence 1a is defined based on the vector sequence shown in (1a) below. (1a) The order is: first positive direction active vector I1+, second positive direction active vector I2+, seventh zero vector I7, first negative direction active vector I1-, second negative direction active vector I2-, seventh zero vector I7.

[0076] The following describes the switch sequence 1a of one cycle Ts in the sector 1a. As shown in FIG. 5, this cycle Ts is the period from time t0 to time t14. Note that time t0 coincides with time t14 in the immediately preceding cycle Ts. Therefore, the state immediately before time t0 coincides with the state at time t13 in the immediately preceding cycle Ts. That is, immediately before time t0, the reference vector Ir is the seventh zero vector I7. At this time, the first high-side bidirectional switch HS1 is in the on state in both directions. The first low-side bidirectional switch LS1 is in the on state in both directions. The second high-side bidirectional switch HS2 is in the on state in the positive direction. The second low-side bidirectional switch LS2 is in the on state in the negative direction. The third high-side bidirectional switch HS3 is in the on state in the positive direction. The third low-side bidirectional switch LS3 is in the on state in the negative direction. Immediately before time t0, the primary voltage Vp is approximately zero.

[0077] At time t0 in sector 1a, that is, at time t14 in the immediately preceding cycle Ts, the control unit 33 turns on the first low-side bidirectional switch LS1 in the positive direction and turns off the third low-side bidirectional switch LS3 at time t0.

[0078] During the period from time t0 to time t3, the reference vector Ir is the first positive-direction active vector I1+. The control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the second positive-direction active vector I2+ at time t3.

[0079] Specifically, at time t1, the control unit 33 turns the second low-side bidirectional switch LS2 on in both directions. Next, at time t2, the control unit 33 turns the third low-side bidirectional switch LS3 on in the positive direction. At time t3, the control unit 33 turns the second low-side bidirectional switch LS2 on in the negative direction. Note that from time t0 to time t1, the primary voltage Vp rises from zero to the line voltage VAB. During the period from time t1 to time t3, the primary voltage Vp is substantially constant at the line voltage VAB.

[0080] During the period from time t3 to time t5, the reference vector Ir is the second positive active vector I2+. The control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the seventh zero vector I7 at time t5.

[0081] Specifically, at time t4, the control unit 33 turns on the third low-side bidirectional switch LS3 in both directions. At time t5, the control unit 33 turns on the third low-side bidirectional switch LS3 in the negative direction. From time t3 to time t4, the primary voltage Vp decreases from the line voltage VAB to the line voltage VAC. From time t4 to time t5, the primary voltage Vp remains approximately constant at the line voltage VAC.

[0082] During the period from time t5 to time t7, the reference vector Ir is the seventh zero vector I7. The control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the first negative direction active vector I1− at time t7.

[0083] Specifically, at time t6, the control unit 33 turns the first low-side bidirectional switch LS1 on in both directions. At time t7, the control unit 33 turns the first high-side bidirectional switch HS1 on in the negative direction. At time t7, the control unit 33 turns the third high-side bidirectional switch HS3 off. From time t5 to time t6, the primary voltage Vp decreases from the line voltage VAC to zero. During the period from time t6 to time t7, the primary voltage Vp is approximately zero.

[0084] During the period from time t7 to time t10, the reference vector Ir is the first negative direction active vector I1-. The control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the second negative direction active vector I2- at time t10.

[0085] Specifically, at time t8, the control unit 33 turns on the second high-side bidirectional switch HS2 in both directions. At time t9, the control unit 33 turns on the third high-side bidirectional switch HS3 in the negative direction. At time t10, the control unit 33 turns on the second high-side bidirectional switch HS2 in the positive direction.

[0086] From time t7 to time t8, the primary voltage Vp decreases from zero to the line voltage VBA. From time t8 to time t10, the primary voltage Vp remains substantially constant at the line voltage VBA. For convenience, the line voltage Vij is represented as "-Vji" in Figures 5 to 7.

[0087] 5, during the period from time t10 to time t12, the reference vector Ir is the second negative direction active vector I2-. The control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the seventh zero vector I7 at time t12.

[0088] Specifically, at time t11, the control unit 33 turns on the third high-side bidirectional switch HS3 in both directions. At time t12, the control unit 33 turns on the third high-side bidirectional switch HS3 in the forward direction. From time t10 to time t11, the primary voltage Vp increases from the line voltage VBA to the line voltage VCA. From time t11 to time t12, the primary voltage Vp remains approximately constant at the line voltage VCA.

[0089] During the period from time t12 to time t14, the reference vector Ir is the seventh zero vector I7. As described above, time t14 coincides with the on / off state of each switch element at time t0. That is, the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the first positive active vector I1+ at time t0 of the next cycle Ts.

[0090] Specifically, at time t13, the control unit 33 turns on the first high-side bidirectional switch HS1 in both directions. At time t14, the control unit 33 turns on the first low-side bidirectional switch LS1 in the positive direction. The control unit 33 also turns off the third low-side bidirectional switch LS3. When the switches are switched at time t14, one cycle Ts ends.

[0091] From time t12 to time t13, the primary voltage Vp increases from the line voltage VCA to zero, and from time t13 to time t14, the primary voltage Vp is zero.

[0092] (4-2. Regarding Switch Sequence 1b) As shown in FIG. 2, in sector 1b, of the first voltage VA to the third voltage VC, the first voltage VA is the largest. Also, the second voltage VB is equal to or greater than the third voltage VC. Also, in sector 1b, the absolute value of the first voltage VA is the largest. And the absolute value of the third voltage VC is greater than the absolute value of the second voltage VB.

[0093] 3 and 4, in sector 1b, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir follows the vector sequence shown in (1b) below. Therefore, the switch sequence 1b is defined based on the vector sequence shown in (1b) below. (1b) The order is second positive direction active vector I2+, first positive direction active vector I1+, seventh zero vector I7, second negative direction active vector I2-, first negative direction active vector I1-, seventh zero vector I7.

[0094] Therefore, the pattern of on / off control by the control unit 33 according to the switch sequence 1b is as follows, based on the magnitude relationships between the voltages, the vector sequence, etc. As shown in Figures 5 and 6, the pattern of on / off control by the control unit 33 of the first high-side bidirectional switch HS1 in sector 1b is the same as the pattern of on / off control of the first high-side bidirectional switch HS1 in sector 1a. The pattern of on / off control of the first low-side bidirectional switch LS1 in sector 1b is the same as the pattern of on / off control of the first low-side bidirectional switch LS1 in sector 1a.

[0095] The on / off control pattern of the second high-side bidirectional switch HS2 in sector 1b is the same as the on / off control pattern of the third high-side bidirectional switch HS3 in sector 1a. The on / off control pattern of the second low-side bidirectional switch LS2 in sector 1b is the same as the on / off control pattern of the third low-side bidirectional switch LS3 in sector 1a.

[0096] The on / off control pattern of the third high-side bidirectional switch HS3 in sector 1b is the same as the on / off control pattern of the second high-side bidirectional switch HS2 in sector 1a. The on / off control pattern of the third low-side bidirectional switch LS3 in sector 1b is the same as the on / off control pattern of the second low-side bidirectional switch LS2 in sector 1a.

[0097] As shown in Figure 6, in sector 1b, the value of the primary voltage Vp during the period when the reference vector Ir is the second positive direction active vector I2+ is the line voltage VAC. The value of the primary voltage Vp during the period when the reference vector Ir is the first positive direction active vector I1+ is the line voltage VAB. The value of the primary voltage Vp during the period when the reference vector Ir is the second negative direction active vector I2- is the line voltage VBA. The value of the primary voltage Vp during the period when the reference vector Ir is the first negative direction active vector I1- is the line voltage VBA.

[0098] (4-3. Regarding Switch Sequence 2a) As shown in FIG. 2, in sector 2a, of the first voltage VA to the third voltage VC, the first voltage VA is the largest. Also, the second voltage VB is equal to or greater than the third voltage VC. Also, in sector 2a, the absolute value of the third voltage VC is the largest. Also, the absolute value of the first voltage VA is greater than the absolute value of the second voltage VB.

[0099] 3 and 4, in the sector 2a, the control unit 33 controls the on / off of each bidirectional switch TSW so that the reference vector Ir follows the vector sequence shown in (2a) below. Therefore, the switch sequence 2a is defined based on the vector sequence shown in (2a) below. (2a) The order is second positive direction active vector I2+, third positive direction active vector I3+, ninth zero vector I9, second negative direction active vector I2-, third negative direction active vector I3-, ninth zero vector I9.

[0100] Therefore, the pattern of on / off control by the control unit 33 in accordance with the switch sequence 2a is as follows, based on the magnitude relationships between the voltages, the vector sequence, etc. As shown in Figures 5 and 7, the pattern of on / off control by the control unit 33 of the first high-side bidirectional switch HS1 in sector 2a is the same as the pattern of on / off control of the second low-side bidirectional switch LS2 in sector 1a. The pattern of on / off control of the first low-side bidirectional switch LS1 in sector 2a is the same as the pattern of on / off control of the second high-side bidirectional switch HS2 in sector 1a.

[0101] The on / off control pattern of the second high-side bidirectional switch HS2 in sector 2a is the same as the on / off control pattern of the third low-side bidirectional switch LS3 in sector 1a. The on / off control pattern of the second low-side bidirectional switch LS2 in sector 2a is the same as the on / off control pattern of the third high-side bidirectional switch HS3 in sector 1a.

[0102] The on / off control pattern of the third high-side bidirectional switch HS3 in sector 2a is the same as the on / off control pattern of the first low-side bidirectional switch LS1 in sector 1a. The on / off control pattern of the third low-side bidirectional switch LS3 in sector 2a is the same as the on / off control pattern of the first high-side bidirectional switch HS1 in sector 1a.

[0103] As shown in Figure 7, in sector 2a, the value of the primary voltage Vp during the period when the reference vector Ir is the second positive direction active vector I2+ is the line voltage VAC. The value of the primary voltage Vp during the period when the reference vector Ir is the third positive direction active vector I3+ is the line voltage VBC. The value of the primary voltage Vp during the period when the reference vector Ir is the second negative direction active vector I2- is the line voltage VCA. The value of the primary voltage Vp during the period when the reference vector Ir is the third negative direction active vector I3- is the line voltage VCB.

[0104] (5. Switch Sequence Switching Control) Next, switching control from an arbitrary switch sequence to a different switch sequence will be described.

[0105] Hereinafter, a switch sequence before any switching will be referred to as a first switch sequence. Furthermore, a switch sequence that specifies the switching manner of the on / off states of the multiple bidirectional switches TSW in a manner different from the first switch sequence and that is switched from the first switch sequence will be referred to as a second switch sequence. In other words, the first switch sequence specifies multiple combinations of the on / off states of the multiple bidirectional switches TSW and the order in which these combinations are switched. The second switch sequence specifies multiple combinations of the on / off states of the multiple bidirectional switches TSW and the order in which these combinations are switched in a manner different from the first switch sequence.

[0106] The control unit 33 switches from control according to the first switch sequence to control according to the second switch sequence when the on / off state of the bidirectional switch TSW through which a current flows in control according to the first switch sequence matches the on / off state of the bidirectional switch TSW through which a current flows in control according to the second switch sequence after switching.

[0107] Note that "bidirectional switches TSW through which a current flows in control according to a switch sequence" refers to bidirectional switches TSW through which a current actually flows due to an electromotive force in control according to each switch sequence. In other words, the above "bidirectional switches TSW through which a current flows" does not refer to a combination of bidirectional switches TSW through which a current can theoretically flow. In other words, the combination of bidirectional switches TSW is a combination that satisfies both of the following requirements (A) and (B).

[0108] (A) A combination of bidirectional switches TSW that serves as a current conduction path at a specific time in the first switch sequence, and also serves as a current conduction path at a specific time in the second switch sequence.

[0109] (B) A combination of bidirectional switches TSW that satisfies (A), in which the on / off state when a current flows at the specific time in the first switch sequence matches the on / off state when a current flows at the specific time in the second switch sequence.

[0110] As an example, the following describes switching control from switch sequence 1a to switch sequence 1b and switching control from switch sequence 1b to switch sequence 2a. The combination of on / off states of the bidirectional switch TSW at each time in each switch sequence is called a "switch state." As described above, each switch sequence switches the switch state at each time from time t1 to time t14. That is, each switch sequence includes 14 switch states. Here, k = (n - 1) x 28. The 14 switch states defined by switch sequence na are the (k+1)th switch state to the (k+14)th switch state. The 14 switch states defined by switch sequence nb are the (k+15)th switch state to the (k+28)th switch state.

[0111] For example, the switch sequence 6b of sector 6b defines the 155th to 168th switch states and their order. In sector 6b, the switch state from time t0 to time t1 is the 155th switch state. The switch state from time t13 to time t14 is the 168th switch state.

[0112] (5-1. Switching Control from Switch Sequence 1a to Switch Sequence 1b) After the transition from the period of sector 1a to the period of sector 1b, the control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b. That is, during the transition of the above periods, the control unit 33 executes switching control with switch sequence 1a as the "first switch sequence" and switch sequence 1b as the "second switch sequence."

[0113] As described above, during the period of sector 1a, i.e., the period during which the absolute value of the second voltage VB is greater than the absolute value of the third voltage VC, the control unit 33 controls each bidirectional switch TSW in accordance with the switch sequence 1a in principle. As shown in Fig. 8, the switch sequence 1a defines the first to fourteenth switch states and their order.

[0114] Furthermore, during the period of sector 1b, i.e., the period during which the absolute value of the second voltage VB is smaller than the absolute value of the third voltage VC, the control unit 33 controls each bidirectional switch TSW in accordance with switch sequence 1b as a general rule. As shown in Fig. 8, switch sequence 1b defines the 15th to 28th switch states and their order.

[0115] As shown in Figures 5 and 6, one or more of the switch states included in switch sequence 1b are identical to the switch states included in switch sequence 1a. Specifically, as shown in Figures 10 and 11, the seventh and fourteenth switch states of switch sequence 1a and the twenty-first and twenty-eighth switch states of switch sequence 1b all have the same combination of on / off states of the bidirectional switch TSW. That is, the above four switch states are identical in the on / off states of the bidirectional switch TSW through which current flows when controlled according to each switch sequence. Note that Figures 10 to 15 illustrate each switch element of each bidirectional switch TSW in a simplified manner. That is, for convenience, each switch element is illustrated as a single-pole, single-throw (SPST) switch.

[0116] 9 , in the control according to each switch sequence, the combination of the bidirectional switches TSW that forms a current conduction path and has the same on / off state is the combination of the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1. At this time, the primary current Ip flows through the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1.

[0117] Therefore, when the switch state becomes the seventh switch state or the fourteenth switch state in the control according to the switch sequence 1a, the control unit 33 switches to the control according to the switch sequence 1b.

[0118] More specifically, if the switch state at the time of transition from the sector 1a period to the sector 1b period is one of the first to sixth switch states, the control unit 33 continues control according to the switch sequence 1a. Then, when the switch state first becomes the seventh switch state, the control unit 33 switches to control according to the switch sequence 1b. In this embodiment, the control unit 33 controls the bidirectional switch TSW to switch to the 22nd switch state at time t7, when the switch state switches from the seventh switch state to the next switch state. In other words, instead of switching from the seventh switch state to the eighth switch state in the switch sequence 1a, the control unit 33 switches to the 22nd switch state in the switch sequence 1b.

[0119] Furthermore, if the switch state at the time of transition from the sector 1a period to the sector 1b period is one of the eighth to thirteenth switch states, the control unit 33 continues control according to the switch sequence 1a. Then, when the switch state first becomes the fourteenth switch state, the control unit 33 switches to control according to the switch sequence 1b. In this embodiment, the control unit 33 controls the bidirectional switch TSW to switch to the fifteenth switch state at time t14, when the switch state changes from the fourteenth switch state to the next switch state. In other words, instead of switching from the fourteenth switch state of the switch sequence 1a to the first switch state, the control unit 33 switches to the fifteenth switch state of the switch sequence 1b.

[0120] Furthermore, by controlling the control unit 33 as described above, the control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b when the primary voltage Vp is 5% or less of the amplitude of the first voltage VA. In this embodiment, the amplitude of the first voltage VA is 200 V. Therefore, when the primary voltage Vp is -10 V or more or +10 V or less, the control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b. Note that, as described above, in this embodiment, the primary voltage Vp is theoretically approximately zero during the period from time t6 to time t7.

[0121] If the switch state at the time of transition from the sector 1a period to the sector 1b period is the seventh switch state, the control unit 33 switches to control according to the 21st switch state. If the switch state at the same time is the 14th switch state, the control unit 33 switches to control according to the 28th switch state.

[0122] (5-2. Switching Control from Switch Sequence 1b to Switch Sequence 2a) After the transition from the period of sector 1b to the period of sector 2a, the control unit 33 switches from control according to switch sequence 1b to control according to switch sequence 2a. That is, during the transition of the above periods, the control unit 33 executes switching control by setting switch sequence 1b as the above-mentioned "first switch sequence" and by setting switch sequence 2a as the "second switch sequence."

[0123] As described above, during the period of sector 2a, i.e., the period during which the absolute value of the first voltage VA is smaller than the absolute value of the third voltage VC, the control unit 33 controls each bidirectional switch TSW in accordance with the switch sequence 2a in principle. As shown in Fig. 8, the switch sequence 2a of sector 2a defines the 29th to 42nd switch states and their order.

[0124] 6 and 7, there are combinations of bidirectional switches TSW that satisfy both of the requirements (A) and (B) in the control according to switch sequence 1b and the control according to switch sequence 2a. That is, there are combinations of bidirectional switches TSW that serve as current conduction paths in common in the above-mentioned respective controls and that also have the same on / off state.

[0125] 12, in the 16th switch state under control according to switch sequence 1b, the first high-side bidirectional switch HS1 is in an on state in both directions, and the third low-side bidirectional switch LS3 is in an on state in both directions. Therefore, in the 16th switch state, current flows through the first high-side bidirectional switch HS1 and the third low-side bidirectional switch LS3.

[0126] 13 , in the 30th switch state under control according to switch sequence 2a, the first high-side bidirectional switch HS1 is in the on state in both directions, and the third low-side bidirectional switch LS3 is in the on state in both directions. Therefore, in the 30th switch state, current flows through the first high-side bidirectional switch HS1 and the third low-side bidirectional switch LS3.

[0127] Therefore, the on / off state of the bidirectional switch TSW through which a current flows in the 16th switch state under control according to switch sequence 1b matches the on / off state of the bidirectional switch TSW through which a current flows in the 30th switch state under control according to switch sequence 2a.

[0128] 14 , in the 23rd switch state under control according to switch sequence 1b, the first low-side bidirectional switch LS1 is in an on state in both directions, and the third high-side bidirectional switch HS3 is in an on state in both directions. Therefore, in the 23rd switch state, current flows through the first low-side bidirectional switch LS1 and the third high-side bidirectional switch HS3.

[0129] 15 , in the 37th switch state under control according to switch sequence 2a, the first low-side bidirectional switch LS1 is in an on state in both directions, and the third high-side bidirectional switch HS3 is in an on state in both directions. Therefore, in the 37th switch state, current flows through the first low-side bidirectional switch LS1 and the third high-side bidirectional switch HS3.

[0130] That is, the on / off state of the bidirectional switch TSW through which a current flows in the 23rd switch state under control according to switch sequence 1b matches the on / off state of the bidirectional switch TSW through which a current flows in the 37th switch state under control according to switch sequence 2a.

[0131] Therefore, the control unit 33 switches to control according to switch sequence 2a when the switch state becomes the 16th switch state or the 23rd switch state in control according to switch sequence 1b. In this embodiment, the control unit 33 switches to control according to switch sequence 2a when the switch state is switched from the 15th switch state to the next switch state in control according to switch sequence 1b. Alternatively, the control unit 33 switches to control according to switch sequence 2a when the switch state is switched from the 23rd switch state to the next switch state in control according to switch sequence 1b.

[0132] More specifically, if the switch state at the time of transition from the sector 1b period to the sector 2a period is the 15th switch state or any of the 23rd to 28th switch states, the control unit 33 continues control according to switch sequence 1b. Then, when the switch state first becomes the 16th switch state, the control unit 33 switches to control according to switch sequence 2b. In other words, instead of switching from the 15th switch state to the 16th switch state, the control unit 33 switches from the 15th switch state to the 30th switch state of switch sequence 2a. Thus, in this embodiment, the control unit 33 controls the bidirectional switch TSW to switch to the 30th switch state at time t1, when the switch state changes from the 15th switch state to the next switch state.

[0133] Furthermore, if the switch state at the time of transition from the sector 1b period to the sector 2a period is one of the 16th to 22nd switch states, the control unit 33 continues control according to switch sequence 1b. Then, when the switch state first becomes the 23rd switch state, the control unit 33 switches to control according to switch sequence 2b. In other words, instead of switching from the 22nd switch state to the 23rd switch state, the control unit 33 switches from the 22nd switch state to the 37th switch state of switch sequence 2a. Thus, in this embodiment, the control unit 33 controls the bidirectional switch TSW to switch to the 37th switch state at time t8, when the switch state switches from the 22nd switch state to the next switch state.

[0134] Here, the maximum line voltage Vm is the potential difference with the largest absolute value among the potential difference between the first voltage VA and the second voltage VB, the potential difference between the first voltage VA and the third voltage VC, and the potential difference between the second voltage VB and the third voltage VC in control according to each switch sequence. The maximum line voltage Vm in control according to switch sequence 1b is the line voltage VAC or the line voltage VCA. The maximum line voltage Vm in control according to switch sequence 2a is the line voltage VAC or the line voltage VCA.

[0135] Specifically, immediately before switching from control according to switch sequence 1b to control according to switch sequence 2a at time t1, primary voltage Vp is approximately equal to line voltage VAC. Then, immediately after the switching, primary voltage Vp becomes line voltage VAC. Note that the direction and conduction path of primary current Ip are the same before and after the switching.

[0136] Immediately before the control is switched from the control according to switch sequence 1b to the control according to switch sequence 2a at time t8, the primary voltage Vp is approximately equal to the line voltage VCA. Immediately after the switch, the primary voltage Vp becomes the line voltage VCA. The direction and conduction path of the primary current Ip are approximately the same before and after the switch.

[0137] By controlling as described above, the control unit 33 switches from control according to the first switch sequence to control according to the second switch sequence when the primary voltage Vp is the maximum line voltage Vm. Note that "when the primary voltage Vp is the maximum line voltage Vm" refers to the time when a value reflecting the maximum line voltage Vm is output as the primary voltage Vp. Therefore, an error of ±0.5% of the amplitude of the maximum line voltage Vm is allowed, with the maximum line voltage Vm as the median.

[0138] (6. Operation of the Present Embodiment) In the above embodiment, a combination of bidirectional switches TSW that satisfies both of the above requirements (A) and (B) is specified in advance. Then, when switching from control according to the first switch sequence to control according to the second switch sequence, the control unit 33 uses the specified combination of bidirectional switches TSW to perform the switching.

[0139] If the switch sequence is switched when the on / off states of the bidirectional switches TSW do not match before and after switching, the current paths will be different before and after switching. Switching a switch element that is on and conducting current to the off state may subject the switch element to electrical stress. Note that "electrical stress" refers to the application of a larger electrical load when a switch element that is on and substantially not conducting current is switched to the off state, compared to zero-current switching or zero-voltage switching. Even if multiple switch elements are theoretically designed to switch simultaneously, there is actually a time lag between the on / off states of each switch element. Therefore, the momentary loss of a current conduction path within the circuit may result in the generation of an overvoltage, such as a surge voltage. Furthermore, the creation of a short-circuited current path within the circuit may result in the flow of a short-circuit current.

[0140] In this embodiment, the combination of bidirectional switches TSW has the same current direction and conduction path, and the same on / off state of the switches. Therefore, even if the switch sequence is changed in this combination of bidirectional switches TSW, electrical stress is unlikely to occur in the switch elements. In addition, overvoltage and short-circuit current are unlikely to occur.

[0141] (7. Effects of the Present Embodiment) (1) In the above embodiment, in the control of each switch sequence before and after switching, there is a combination of bidirectional switches TSW that form a current conduction path and have the same on / off state. The control unit 33 switches the switch sequence for this combination of bidirectional switches TSW. This makes it possible to prevent electrical stress from being applied to the switch elements that make up the bidirectional switches TSW.

[0142] (2) In the above embodiment, after the magnitude relationship of the input voltages is reversed, the switch sequence is switched when the on / off states of the bidirectional switch TSW through which current flows match for the first time under control by the switch sequence before and after the switch sequence is switched. This makes it possible to quickly switch to control according to the switch sequence that corresponds to the magnitude relationship of the input voltages while suppressing electrical stress on the switch elements.

[0143] (3) In the above embodiment, the primary voltage Vp is equal to or less than 5% of the amplitude of the first voltage VA before and after the switching of the switch sequence. Alternatively, the primary voltage Vp is equal to the maximum line voltage Vm before and after the switching of the switch sequence. In this way, the primary voltage Vp is substantially the same before and after the switching of the switch sequence, so that the value of the primary voltage Vp does not change suddenly. This makes it less likely that noise will occur in the output voltage applied to the load 70.

[0144] (4) According to the above embodiment, each bidirectional switch TSW includes two switch elements connected in series such that the anode terminals of the body diodes are connected to each other. This configuration makes it possible to configure the power conversion circuit 30 relatively simply and inexpensively.

[0145] <Modifications> The above embodiment and the following modifications can be implemented in combination with each other within the scope of technical compatibility.

[0146] (Modifications to the Configuration of the Power Conversion Device) The configuration of the power conversion device 10 is not limited to the example of the above embodiment. For example, the power conversion device 10 is not limited to a three-phase isolated AC-DC converter, and may also be applied to a non-isolated three-phase AC-DC converter. In other words, the power conversion device 10 does not have to include one or more selected from the input low-pass filter 20, the transformer circuit 40, the rectifier circuit 50, and the output low-pass filter 60.

[0147] Furthermore, the three-phase AC power supply 80 connected to the three external input terminals 11 is not limited to a three-phase three-wire type, but may be a three-phase four-wire type, or may be a delta-connected three-phase three-wire type three-phase AC power supply 80. The configuration of the power conversion device 10 may be changed as appropriate depending on the type of the three-phase AC power supply 80.

[0148] The input-side low-pass filter 20 may include a plurality of capacitors connected between the lines of each phase to which the first voltage VA, the second voltage VB, and the third voltage VC are input. The switch elements constituting each bidirectional switch TSW are not limited to those in the above embodiment. For example, the two switch elements of the bidirectional switch TSW may be P-channel MOSFETs. In this case, the drain terminals of the two switch elements of the bidirectional switch TSW are connected to each other.

[0149] The two switch elements of the bidirectional switch TSW may be transistors capable of passing a current in both the forward and reverse directions. In this case, the two switch elements are connected in series with their source terminals connected to each other. Specifically, the switch elements are gallium nitride high electron mobility transistors (GaN-High Electron Mobility Transistors, GaN-HEMTs) or the like.

[0150] The transformer circuit 40 does not need to include the fourth inductor L4. In this case, the leakage inductance of the transformer 41 can be used for resonance instead of the fourth inductor L4. The specific circuit configuration of the rectifier circuit 50 is not limited to the example of the above embodiment. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or the like.

[0151] The periods into which each sector is divided are not limited to those in the above embodiment. For example, each sector may be divided into four periods, resulting in a total of 24 periods. The above embodiment is also applicable in such a case.

[0152] (Modifications Related to Switch Sequence Switching Control) The switch sequence switching control is not limited to the examples in the above embodiment. For example, the switching control from switch sequence 1a to switch sequence 1b can be changed as shown in the following (Example 1) to (Example 4). The switching control from switch sequence 1b to switch sequence 2a can be changed as shown in the following (Example 5) to (Example 7). However, it is preferable to switch the switch sequence at a switch state having a sufficiently long period. For example, it is more preferable to switch to the second switch sequence in the (k+5)th switch state between time t4 and time t5 than to switch to the second switch sequence in the (k+4)th switch state between time t3 and time t4 of the first switch sequence.

[0153] Regarding switching control from switch sequence 1a to switch sequence 1b (Example 1) The control unit 33 may control the bidirectional switch TSW to switch to the 15th switch state at time t7 when switching from the 7th switch state to the next switch state.

[0154] (Example 2) The control unit 33 may control the bidirectional switch TSW to switch from the seventh switch state to the 21st switch state or the 28th switch state. At this time, the control unit 33 may control the bidirectional switch TSW so that time t7 of the switch sequence 1a coincides with time t6 of the switch sequence 1b, or may switch from the switch sequence 1a to the switch sequence 1b in the processing of the program PG between time t6 and time t7 of the switch sequence 1a.

[0155] (Example 3) In each switch sequence, the sixth switch state of switch sequence 1a and the twentieth switch state of switch sequence 1b all have the same combination of on / off states of the bidirectional switch TSW. Therefore, for example, at time t6 when the sixth switch state is switched to the next switch state, the switch sequence may be switched to switch sequence 1b. In other words, instead of switching to the seventh switch state of switch sequence 1a, the control unit 33 may switch to the 21st switch state or the 28th switch state of switch sequence 1b.

[0156] (Example 4) In each switch sequence, the 13th switch state of switch sequence 1a and the 27th switch state of switch sequence 1b all have the same combination of on / off states of the bidirectional switch TSW. Similarly, in this case, for example, instead of switching from the 13th switch state to the 14th switch state, the control unit 33 may switch to the 28th switch state of switch sequence 1b.

[0157] In any of (Example 1) to (Example 4), when the switch sequence 1a is the "first switch sequence" and the switch sequence 1b is the "second switch sequence," when the on / off state of the bidirectional switch TSW through which a current flows in control according to the first switch sequence matches the on / off state of the bidirectional switch TSW through which a current flows in control according to the second switch sequence after switching, control according to the first switch sequence is switched to control according to the second switch sequence.

[0158] Regarding Switching Control from Switch Sequence 1b to Switch Sequence 2a (Example 5): The control unit 33 may control the bidirectional switch TSW to switch from the 16th switch state to the 30th switch state. At this time, the control unit 33 may control the bidirectional switch TSW so that time t2 of the switch sequence 1b coincides with time t1 of the switch sequence 2a, or may switch from the switch sequence 1b to the switch sequence 2a in the processing of the program PG between time t1 and time t2 of the switch sequence 1b.

[0159] (Example 6) In each switch sequence, the 17th switch state of switch sequence 1b and the 31st switch state of switch sequence 2a all have the same combination of on / off states of the bidirectional switch TSW. Therefore, in the switch sequence switching control, the switch sequence may be switched to switch sequence 2a at time t2, when the 16th switch state is switched to the next switch state. In other words, instead of switching from the 16th switch state to the 17th switch state, the control unit 33 may switch to the 31st switch state of switch sequence 2a. Furthermore, in the processing of the program PG, the switch sequence 1b may be switched to switch sequence 2a between time t2 and time t3 of switch sequence 1b.

[0160] (Example 7) In each switch sequence, the 24th switch state of switch sequence 1b and the 38th switch state of switch sequence 2a all have the same combination of on / off states of the bidirectional switch TSW. In this case, too, the switch state may be switched to switch sequence 2a at time t9, when the switch state is switched from the 23rd switch state to the next switch state. In other words, instead of switching from the 23rd switch state to the 24th switch state, the control unit 33 may switch to the 38th switch state of switch sequence 2a. Furthermore, the program PG may switch from switch sequence 1b to switch sequence 2a between time t9 and time t10 in switch sequence 1b.

[0161] In any of (Example 5) to (Example 7), when switch sequence 1b is defined as the "first switch sequence" and switch sequence 2a is defined as the "second switch sequence," control is switched from control according to the first switch sequence to control according to the second switch sequence when the on / off state of the bidirectional switch TSW through which current flows in control according to the first switch sequence matches the on / off state of the bidirectional switch TSW through which current flows in control according to the second switch sequence after switching.

[0162] As shown in FIG. 9, the switch sequence before switching is the above-mentioned "first switch sequence" and the switch sequence after switching is the "second switch sequence." This can also be applied to switching other switch sequences as in the following example.

[0163] For example, in the control of switching from switch sequence 2a to switch sequence 2b, switch sequence 2a is designated as the "first switch sequence" and switch sequence 2b is designated as the "second switch sequence." During the period of sector 2a, i.e., the period when the first voltage VA is at its maximum and the absolute value of the first voltage VA is greater than the absolute value of the second voltage VB, the control unit 33 controls each bidirectional switch TSW according to switch sequence 2a. After the period of sector 2b has begun, i.e., after the absolute value of the second voltage VB has become greater than the absolute value of the first voltage VA, the control unit 33 may switch to switch sequence 2b when the above combination is met for the first time.

[0164] For example, in the switching control from the switch sequence 2b to the switch sequence 3a, the switch sequence 2b is defined as the "first switch sequence" and the switch sequence 3a is defined as the "second switch sequence." During the period of sector 2b, i.e., during the period when the second voltage VB is at its maximum and the absolute value of the third voltage VC is greater than that of the second voltage VB, the control unit 33 controls each bidirectional switch TSW according to the switch sequence 2b. After the period of sector 3a has begun, i.e., after the absolute value of the second voltage VB has become greater than that of the third voltage VC, the control unit 33 may switch to the switch sequence 3a when the above combination is met for the first time.

[0165] <Supplementary Notes> The following describes technical ideas that can be understood from the above-described embodiments and modified examples. [1] A first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply and receiving a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, in one-to-one correspondence; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal connected to the plurality of bidirectional switches and capable of outputting AC power; a first switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations; and a control unit capable of controlling the plurality of bidirectional switches in accordance with a second switch sequence that defines a plurality of combinations of the plurality of bidirectional switches and an order of switching the plurality of combinations in a manner different from the first switch sequence, wherein the control unit switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching.

[0166] [2] The power conversion circuit according to [1], wherein the control unit controls each of the bidirectional switches in accordance with the first switch sequence during a period in which the absolute value of the second voltage is greater than the absolute value of the third voltage, and switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence after the absolute value of the third voltage becomes greater than the absolute value of the second voltage when an on / off state of the bidirectional switch through which a current flows in the control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in the combination in the control in accordance with the second switch sequence after switching.

[0167] [3] The power conversion circuit described in [2], wherein the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the potential difference of the first output terminal with respect to the second output terminal is 5% or less of the amplitude of the first voltage.

[0168] [4] A power conversion circuit described in any one of [1] to [3], wherein one or more of the combinations included in the second switch sequence match the combinations included in the first switch sequence, and the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the combination in the control according to the first switch sequence matches the combination included in the second switch sequence.

[0169] [5] The power conversion circuit according to any one of [1] to [4], wherein the control unit controls each of the bidirectional switches in accordance with the first switch sequence during a period in which the absolute value of the first voltage is greater than the absolute value of the third voltage, and switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence after the absolute value of the third voltage becomes greater than the absolute value of the first voltage when an on / off state of the bidirectional switch through which a current flows in the control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in the combination in the control in accordance with the second switch sequence after switching.

[0170] [6] The power conversion circuit according to [5], wherein when a potential difference with the largest absolute value among the potential difference between the first voltage and the second voltage, the potential difference between the first voltage and the third voltage, and the potential difference between the second voltage and the third voltage is defined as a maximum line voltage, the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the potential difference of the first output terminal with respect to the second output terminal is the maximum line voltage.

[0171] [7] The power conversion circuit according to any one of [1] to [6], wherein the bidirectional switch has two switch elements connected in series so that the anode side terminals of the body diodes are connected to each other.

[0172] [8] A first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, to which a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, are input in a one-to-one correspondence; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal capable of outputting AC power; a first switch sequence defining a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations; a control unit capable of controlling the plurality of bidirectional switches in accordance with a second switch sequence that defines an order of switching combinations in a manner different from the first switch sequence, and causing the control unit to switch from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching.

[0173] REFERENCE SIGNS LIST 10... Power conversion device 30... Power conversion circuit 31A... First input terminal 31B... Second input terminal 31C... Third input terminal 32A... First output terminal 32B... Second output terminal 33... Control unit TSW... Bidirectional switch 80... Three-phase AC power supply

Claims

1. A power supply device comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power source, and receiving a first voltage, a second voltage, and a third voltage in one-to-one correspondence, the first voltage, the second voltage, and the third voltage being AC voltages of different phases from each other; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal connected to the plurality of bidirectional switches, and capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches in accordance with a first switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations, or a second switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations in a manner different from that of the first switch sequence, wherein the control unit switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence coincides with an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching. Power conversion circuits.

2. The power conversion circuit according to claim 1, wherein the control unit controls each of the bidirectional switches in accordance with the first switch sequence during a period in which the absolute value of the second voltage is greater than the absolute value of the third voltage, and switches from the control in accordance with the first switch sequence to the control in accordance with the second switch sequence after the absolute value of the third voltage becomes greater than the absolute value of the second voltage when an on / off state of the bidirectional switch through which a current flows in the control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in the combination in the control in accordance with the second switch sequence after switching.

3. The power conversion circuit according to claim 2, wherein the control unit switches from control according to the first switch sequence to control according to the second switch sequence when a potential difference of the first output terminal with respect to the second output terminal is 5% or less of an amplitude of the first voltage.

4. A power conversion circuit as claimed in any one of claims 1 to 3, wherein one or more of the combinations included in the second switch sequence match the combinations included in the first switch sequence, and the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the combination in the control according to the first switch sequence matches the combination included in the second switch sequence.

5. The power conversion circuit according to any one of claims 1 to 4, wherein the control unit controls each of the bidirectional switches in accordance with the first switch sequence during a period in which the absolute value of the first voltage is greater than the absolute value of the third voltage, and switches from the control in accordance with the first switch sequence to the control in accordance with the second switch sequence after the absolute value of the third voltage becomes greater than the absolute value of the first voltage when an on / off state of the bidirectional switch through which a current flows in the control in accordance with the first switch sequence matches an on / off state of the bidirectional switch through which a current flows in the combination in the control in accordance with the second switch sequence after switching.

6. The power conversion circuit according to claim 5, wherein, when a potential difference with a maximum absolute value among a potential difference between the first voltage and the second voltage, a potential difference between the first voltage and the third voltage, and a potential difference between the second voltage and the third voltage is defined as a maximum line voltage, the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the potential difference of the first output terminal with respect to the second output terminal is the maximum line voltage.

7. The power conversion circuit according to any one of claims 1 to 6, wherein the bidirectional switch has two switch elements connected in series such that the anode side terminals of the body diodes are connected to each other.

8. A power conversion circuit including: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power source and receiving a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, in one-to-one correspondence; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches in accordance with a first switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations, or a second switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching the plurality of combinations in a manner different from that of the first switch sequence, wherein the control unit switches from control in accordance with the first switch sequence to control in accordance with the second switch sequence when an on / off state of the bidirectional switch through which a current flows in control in accordance with the first switch sequence coincides with an on / off state of the bidirectional switch through which a current flows in control in accordance with the second switch sequence after switching. Program for power conversion circuits.

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