Electric power conversion circuit and program

Abstract

A control unit (33) comprises multiple bidirectional switches (TSW) and a control unit (33). The control unit is capable of controlling multiple bidirectional switches (TSW) in accordance with a first switching sequence or a second switching sequence. In specified periods, the control unit (33) controls the multiple bidirectional switches in accordance with the first switching sequence. In transient periods, the control unit (33) controls the multiple bidirectional switches in accordance with the second switching sequence. The quantity of combinations stipulated in the second switching sequence pertaining to the on / off states of the multiple bidirectional switches (TSW) is lesser than the quantity of combinations stipulated in the first switching sequence pertaining to the on / off states of the multiple bidirectional switches (TSW).

Description

Power conversion circuit and program

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

[0002] The power conversion circuit disclosed in Patent Document 1 includes three input terminals, a plurality of switch elements, and a control unit. The three input terminals are connected to a three-phase AC power supply. The control unit controls the on / off of each switch element by inputting a PWM (Pulse Width Modulation) signal to each switch element. The power conversion circuit is capable of converting a three-phase AC voltage input to the input terminals into a DC voltage through the on / off control of the plurality of switch elements.

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

[0004] In the power conversion circuit disclosed in Patent Document 1, when a PWM signal with a short pulse width is input to a specific switch element, the switch may not be switched to the ON state as intended, which may cause electrical stress to be applied to one of the switch elements.

[0005] In order to solve the above-described problems, the present disclosure provides a power supply including 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, respectively; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminal, the second input terminal, and the third input terminal and the first output terminal and the second output terminal, respectively; 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 the first switch sequence. and a control unit capable of controlling the plurality of bidirectional switches in accordance with a switch sequence, wherein a period from a phase in which any of the first voltage, the second voltage, and the third voltage is zero to a phase that is separated by a predetermined angle from the phase in which the first voltage, the second voltage, and the third voltage is zero is defined as a transition period, and a period of a phase that is temporally continuous with the transition period is defined as a specific period, the control unit controls the plurality of bidirectional switches in accordance with the first switch sequence during the specific period and controls the plurality of bidirectional switches in accordance with the second switch sequence during the transition period, and the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence.

[0006] The present disclosure also provides a power supply 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, respectively; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminal, the second input terminal, the third input terminal, and the first output terminal and the second output terminal, respectively; and 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 the first switch sequence. and a control unit capable of controlling the plurality of bidirectional switches, wherein the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence, and when a period from a phase in which any of the first voltage, the second voltage, and the third voltage is zero to a phase spaced a predetermined angle from the phase in which the first voltage, the second voltage, and the third voltage is zero is defined as a transition period, and a period of a phase temporally continuous with the transition period is defined as a specific period, the program causes the control unit to control the plurality of bidirectional switches in accordance with the first switch sequence during the specific period, and to control the plurality of bidirectional switches in accordance with the second switch sequence during the transition period.

[0007] This can prevent electrical stress from being applied to the switch element.

[0008] FIG. 1 is a circuit diagram of a power conversion device. FIG. 2 is a diagram showing a waveform of three-phase AC power, sectors, and specific periods. 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 control in sector 1a. FIG. 6 is a sequence diagram of switch control in sector 1b. FIG. 7 is a sequence diagram of switch control in sector 1b'. FIG. 8 is a sequence diagram of switch control in sector 2a. FIG. 9 is a sequence diagram of switch control in sector 2a'.

[0009] <One Embodiment of Power Conversion Circuit> An embodiment of a power conversion device 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] In addition, although multiple electronic components may be collectively referred to as a single circuit configuration, this is merely a matter of convenience to collectively describe the object. In other words, the classification and names of the circuit configuration are not limited to this. Furthermore, the term "terminal" includes a so-called node and simply means an electrical connection point.

[0011] 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.

[0012] 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 external input terminals 11 into DC power and outputting it from external output terminals 12. A transformer circuit 40 is interposed on the power path from each external input terminal 11 to each external output terminal 12, thereby electrically insulating the external input terminal 11 side from the external output terminal 12 side.

[0013] 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.

[0014] 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 output terminal 12A and the second external output terminal 12B. The load 70 is, for example, an electronic device driven by DC power.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 three 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 includes 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.

[0019] Each bidirectional switch TSW has two switch elements. Each switch element is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). 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. In other words, 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The execution device includes, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an FPGA (Field Programmable Gate Array), a CPLD (Complex Programmable Logic Device), an ASIC (Application Specific Integrated Circuit), etc. Note that, hereinafter, control by the execution device of the control unit 33 will be simply referred to as control by the control unit 33.

[0029] The execution device of the control unit 33 executes the program PG to control each bidirectional switch TSW according to a switch sequence described below. Specifically, the power conversion device 10 includes a gate drive circuit (not shown). The control unit 33 inputs a switching signal to an input terminal of the gate drive circuit. The gate drive circuit then outputs a gate drive voltage to the gate terminal of each switch element based on the switching signal. That is, the control unit 33 controls the on / off of each switch element via the gate drive circuit. 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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, it does not allow a current to flow from the second output terminal 32B to the first input terminal 31A.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] (2. Definition of Sectors) As described above, three-phase AC power is input to the three input terminals 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°.

[0044] In the following, the phase at which the first voltage VA is maximum is defined as 0°. Furthermore, the phases at which the first voltage VA is minimum are defined as -180° and 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 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:

[0045] 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 four periods. In other words, one cycle of three-phase AC power is subdivided into 24 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 four periods: sector na', sector na, sector nb, and sector nb'. In this embodiment, each period is defined as follows. The midpoint of the period of sector n is set to X°. The "midpoint of the period" is the midpoint between the endpoints of each sector expressed as a half-open interval, where X=180° in the definitions of sector 4a and sector 4a'.

[0046] ・Sector na': (X°-30°)<θ°<(X°-25°) ・Sector na: (X°-25°)<θ°<X° ・Sector nb: X°<θ°<(X°+25°) ・Sector nb': (X°+25°)<θ°<(X°+30°) For example, in the case of sector 1, the above X° is 0°. Therefore, sector 1a' is a period of -30° or more and less than -25°. Sector 1a is a period of -25° or more and less than 0°. Sector 1b is a period of 0° or more and less than 25°. Sector 1b' is a period of 25° or more and less than 30°.

[0047] (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.

[0048] In the three-phase AC power of this embodiment, the phase based on the first voltage VA is referred to as phase A, the phase based on the second voltage VB is referred to as phase B, and the phase based on the third voltage VC is referred to as phase C. When one of these three phases is referred to as phase i and another phase is referred to as phase j, the voltage difference obtained by subtracting the voltage of phase j from the voltage of phase i is referred to as the "line voltage Vij."

[0049] The control unit 33 controls the pulse width of each switching signal by space vector pulse width modulation (SVPWM).

[0050] 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.

[0051]

[0052] 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:

[0053] First positive active vector I1+: The second low-side bidirectional switch LS2 is on in both directions or in the positive on state, and the first high-side bidirectional switch HS1 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VAB.

[0054] Second positive active vector I2+: The first high-side bidirectional switch HS1 is on in both directions or in the positive on state, and the third low-side bidirectional switch LS3 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VAC.

[0055] Third positive active vector I3+: The third low-side bidirectional switch LS3 is on in both directions or in the positive on state, and the second high-side bidirectional switch HS2 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VBC.

[0056] Fourth positive active vector I4+: The second high-side bidirectional switch HS2 is on in both directions or in the positive on state, and the first low-side bidirectional switch LS1 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VBA.

[0057] Fifth positive active vector I5+: The first low-side bidirectional switch LS1 is on in both directions or in the positive on state, and the third high-side bidirectional switch HS3 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VCA.

[0058] Sixth positive active vector I6+: The third high-side bidirectional switch HS3 is on in both directions or in the positive on state, and the second low-side bidirectional switch LS2 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VCB.

[0059] 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.

[0060] First negative active vector I1−: The second high-side bidirectional switch HS2 is on in both directions or in the negative direction. The first low-side bidirectional switch LS1 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage −VAB.

[0061] Second negative active vector I2−: The first low-side bidirectional switch LS1 is on in both directions or in the negative direction. The third high-side bidirectional switch HS3 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage −VAC.

[0062] Third negative active vector I3−: The third high-side bidirectional switch HS3 is on in both directions or in the negative on state. The second low-side bidirectional switch LS2 is on in both directions or in the negative on state. At this time, the primary voltage Vp is the line voltage −VBC.

[0063] Fourth negative active vector I4−: The second low-side bidirectional switch LS2 is on in both directions or in the negative on state. The first high-side bidirectional switch HS1 is on in both directions or in the negative on state. At this time, the primary voltage Vp is the line voltage −VBA.

[0064] Fifth negative active vector I5−: The first high-side bidirectional switch HS1 is on in both directions or in the negative direction. The third low-side bidirectional switch LS3 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage −VCA.

[0065] Sixth negative active vector I6−: The third low-side bidirectional switch LS3 is on in both directions or in the negative on state. The second high-side bidirectional switch HS2 is on in both directions or in the negative on state. At this time, the primary voltage Vp is the line voltage −VCB.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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+, zero vector Iz, x-th negative direction active vector Ix-, zero vector Iz. (nb') The order is y-th positive direction active vector Iy+, zero vector Iz, y-th negative direction active vector Iy-, zero vector Iz.

[0074] 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, in a constant cycle Ts. 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 a constant cycle Ts. 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, in a constant cycle Ts. 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 a constant cycle Ts. The duration of these cycles Ts is very short compared to the duration of each sector.

[0075] (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 how the multiple bidirectional switches TSW are switched between on and off based on each vector sequence. Specifically, each switch sequence defines multiple combinations of the on and off states of the multiple bidirectional switches TSW and the order in which the multiple combinations are switched.

[0076] Hereinafter, one selected from the first voltage VA, the second voltage VB, and the third voltage VC will be referred to as the specific voltage. Furthermore, the period from the phase where any one of the first voltage VA, the second voltage VB, and the third voltage VC becomes zero to a phase separated by a specific angle from the phase where the voltage becomes zero will be referred to as the transition period. Furthermore, the period of the phase that is temporally continuous with the transition period will be referred to as the specific period. In this embodiment, the "specific angle" is greater than 0° and equal to or less than 5°. Specifically, the specific angle is 5°.

[0077] Furthermore, within the transition period, a period from the phase where the input voltage becomes zero to a phase that is a predetermined angle ahead in time is referred to as a first transition period. A period from the phase where the input voltage becomes zero to a phase that is a predetermined angle behind in time and that is consecutive in time to the first transition period is referred to as a second transition period. Furthermore, within the specific period, a period that is consecutive in time to the first transition period is referred to as a first specific period. A period that is consecutive in time to the second transition period is referred to as a second specific period.

[0078] For example, at phase 30°, the second voltage VB is zero. That is, the specific voltage at this phase is the second voltage VB. Sector 1b' is the period from phase 30° to phase 25°, which is 5° ahead of 30°. Therefore, sector 1b' is the first transition period for the second voltage VB. Sector 1b is a period of a phase that is temporally consecutive to sector 1b'. Therefore, sector 1b is the first specific period for the second voltage VB. Furthermore, sector 2a' is the period from phase 30° to phase 35°, which is 5° behind 30°. Therefore, sector 2a' is the second transition period for the second voltage VB. Sector 2a is a period of a phase that is temporally consecutive to sector 2a'. Therefore, sector 2a is the second specific period for the second voltage VB.

[0079] Similarly, for other phases where each input voltage is zero, the transition period and specific period are defined as follows: At phase 90°, the first voltage VA is zero. That is, when the first voltage VA is a specific voltage, sector 2b' is the first transition period for the first voltage VA. Sector 3a' is the second transition period for the first voltage VA. Sector 2b is the first specific period for the first voltage VA. Sector 3a is the second specific period for the first voltage VA.

[0080] At phase 150°, the third voltage VC becomes zero. That is, when the third voltage VC is a specific voltage, sector 3b' is a first transition period for the third voltage VC. Sector 4a' is a second transition period for the third voltage VC. Sector 3b is a first specific period for the third voltage VC. Sector 4a is a second specific period for the third voltage VC.

[0081] At a phase of -150°, the second voltage VB becomes zero. That is, when the second voltage VB is a specific voltage, sector 4b' is a first transition period for the second voltage VB. Sector 5a' is a second transition period for the second voltage VB. Sector 4b is a first specific period for the second voltage VB. Sector 5a is a second specific period for the second voltage VB.

[0082] At a phase of -90°, the first voltage VA becomes zero. That is, when the first voltage VA is a specific voltage, sector 5b' is a first transition period for the first voltage VA. Sector 6a' is a second transition period for the first voltage VA. Sector 5b is a first specific period for the first voltage VA. Sector 6a is a second specific period for the first voltage VA.

[0083] At phase -30°, the third voltage VC becomes zero. That is, when the third voltage VC is a specific voltage, sector 6b' is a first transition period for the third voltage VC. Sector 1a' is a second transition period for the third voltage VC. Sector 6b is a first specific period for the third voltage VC. Sector 1a is a second specific period for the third voltage VC.

[0084] The control unit 33 controls the plurality of bidirectional switches TSW according to a first switch sequence in a first specific period. The control unit 33 controls the plurality of bidirectional switches TSW according to a second switch sequence in a first transition period. The control unit 33 controls the plurality of bidirectional switches TSW according to a third switch sequence in a second transition period. The control unit 33 controls the plurality of bidirectional switches TSW according to a fourth switch sequence in a second specific period. However, the first switch sequence, second switch sequence, third switch sequence, and fourth switch sequence are defined in such a way that the on / off states of the bidirectional switches TSW are different from each other.

[0085] In this case, the number of combinations of the on / off states of the bidirectional switches TSW defined by the second switch sequence and the third switch sequence is smaller than the number of combinations of the on / off states of the bidirectional switches TSW defined by the first switch sequence. Also, the number of combinations of the on / off states of the bidirectional switches TSW defined by the second switch sequence and the third switch sequence is smaller than the number of combinations of the on / off states of the bidirectional switches TSW defined by the fourth switch sequence.

[0086] Specifically, among the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C, the input terminal 31 to which the specific voltage is input is defined as the first specific input terminal. Furthermore, among the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C, any one other than the first specific input terminal is defined as the second specific input terminal. Among the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C, any input terminal other than the first and second specific input terminals is defined as the third specific input terminal.

[0087] Furthermore, the bidirectional switch TSW connecting the first specific input terminal and the first output terminal 32A is referred to as a first specific high-side bidirectional switch, and the bidirectional switch TSW connecting the first specific input terminal and the second output terminal 32B is referred to as a first specific low-side bidirectional switch. The bidirectional switch TSW connecting the second specific input terminal and the first output terminal 32A is referred to as a second specific high-side bidirectional switch, and the bidirectional switch TSW connecting the second specific input terminal and the second output terminal 32B is referred to as a second specific low-side bidirectional switch. The bidirectional switch TSW connecting the third specific input terminal and the first output terminal 32A is referred to as a third specific high-side bidirectional switch, and the bidirectional switch TSW connecting the third specific input terminal and the second output terminal 32B is referred to as a third specific low-side bidirectional switch.

[0088] At this time, the control unit 33 controls the first specified high-side bidirectional switch and the first specified low-side bidirectional switch so that they are maintained in the off state during the transition period. Furthermore, the multiple combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, which are specified in the first switch sequence, and the order in which these combinations are switched are the same as the multiple combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, which are specified in the second switch sequence.

[0089] In the following, as a specific example, on / off control of the bidirectional switch TSW according to each switch sequence in sector 1a, sector 1b, sector 1b', sector 2a', and sector 2a will be described.

[0090] In the following, the switch sequence in sector na will be referred to as switch sequence na. The switch sequence in sector nb will be referred to as switch sequence nb. The switch sequence in sector na' will be referred to as switch sequence na'. The switch sequence in sector nb' will be referred to as switch sequence nb'. In this example, the first switch sequence is switch sequence 1b. The second switch sequence is switch sequence 1b'. The third switch sequence is switch sequence 2a'. The fourth switch sequence is switch sequence 2a.

[0091] In this example, the specific voltage is the second voltage VB. Therefore, the first specific input terminal is the second input terminal. The second specific input terminal is one of the first input terminal 31A and the third input terminal 31C. The third specific input terminal is the input terminal of the first input terminal 31A or the third input terminal 31C that is not the second specific input terminal. In this embodiment, the second specific input terminal is the first input terminal 31A. The third specific input terminal is the third input terminal 31C.

[0092] Also, in this example, the first specified high-side bidirectional switch is the second high-side bidirectional switch HS2. The first specified low-side bidirectional switch is the second low-side bidirectional switch LS2. The second specified high-side bidirectional switch is the first high-side bidirectional switch HS1. The second specified low-side bidirectional switch is the first low-side bidirectional switch LS1. The third specified high-side bidirectional switch is the third high-side bidirectional switch HS3. The third specified low-side bidirectional switch is the third low-side bidirectional switch LS3.

[0093] (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.

[0094] 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.

[0095] The following describes the switch sequence 1a of one cycle Ts in the sector 1a. As shown in FIG. 5, one cycle Ts is the period from time t0 to time t14. 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. 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.

[0096] 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.

[0097] 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. During the period from time t0 to time t3, the control unit 33 controls each switch element so that the first positive direction active vector I1+ is generated.

[0098] 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.

[0099] Next, 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. Specifically, at time t4, the control unit 33 turns the third low-side bidirectional switch LS3 on in both directions. At time t5, the control unit 33 turns the third low-side bidirectional switch LS3 on in the negative direction. Note that from time t3 to time t4, the primary voltage Vp decreases from the line voltage VAB to the line voltage VAC. During the period from time t4 to time t5, the primary voltage Vp remains approximately constant at the line voltage VAC.

[0100] Next, the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the first negative active vector I1- at time t7. 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. Note that 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.

[0101] Next, 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. Specifically, at time t8, the control unit 33 turns the second high-side bidirectional switch HS2 on in both directions. At time t9, the control unit 33 turns the third high-side bidirectional switch HS3 on in the negative direction. At time t10, the control unit 33 turns the second high-side bidirectional switch HS2 on in the positive direction.

[0102] 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.

[0103] Next, as shown in FIG. 5 , 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. Specifically, at time t11, the control unit 33 turns the third high-side bidirectional switch HS3 on in both directions. At time t12, the control unit 33 turns the third high-side bidirectional switch HS3 on in the positive direction. Note that from time t10 to time t11, the primary voltage Vp rises from the line voltage VBA to the line voltage VCA. During the period from time t11 to time t12, the primary voltage Vp remains approximately constant at the line voltage VCA.

[0104] As described above, time t14 coincides with the on / off state of each switch element at time t0. That is, during the period from time t12 to time t14, the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions to the first positive-direction active vector I1+ at time t0 of the next cycle Ts. That is, during the period from time t12 to time t14, the control unit 33 controls the each switch element so that the seventh zero vector I7 is generated.

[0105] 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.

[0106] From time t12 to time t13, the primary voltage Vp increases from the line voltage VCA to zero. In the period from time t13 to time t14, the primary voltage Vp is zero.

[0107] Furthermore, the specific time required between time t0 and time t3 and the ratio of that period to one cycle Ts vary depending on the sector, as does the period from time t3 to time t5, time t5 to time t7, time t7 to time t10, time t10 to time t12, and time t12 to time t14.

[0108] (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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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. Therefore, the number of combinations of the on / off states of the multiple bidirectional switches TSW defined by the switch sequence 1b in sector 1b is 14.

[0113] (4-3. Switch Sequence 1b') Next, the switching pattern in sector 1b' will be described. As shown in Figures 6 and 7, the on / off control performed by the controller 33 in the period of sector 1b' is the same as the on / off control in the period of sector 1b, except for the control over the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2.

[0114] Specifically, during the period of sector 1b', the control unit 33 keeps the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2 always in the OFF state. Therefore, 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. (1b') The order is second positive direction active vector I2+, seventh zero vector I7, second negative direction active vector I2-, and seventh zero vector I7.

[0115] More specifically, as shown in FIG. 7 , the control unit 33 controls each bidirectional switch TSW in sector 1b′ as follows: One cycle Ts of sector 1b′ is the period from time t0′ to time t8′. However, time t0′ coincides with time t8′ in the immediately preceding cycle Ts. 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 off state. The second low-side bidirectional switch LS2 is in the off state. 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.

[0116] 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 t2'. During the period from time t0' to time t2', the control unit 33 controls each switch element so that the second positive active vector I2+ is generated.

[0117] Specifically, at time t0' in sector 1b', in other words, at time t8' in the immediately preceding cycle Ts, the control unit 33 turns on the first low-side bidirectional switch LS1 in the positive direction. At time t1', the control unit 33 turns on the third low-side bidirectional switch LS3 in both directions. At time t2', the control unit 33 turns on the third low-side bidirectional switch LS3 in the negative direction. Note that from time t0' to time t1', the primary voltage Vp rises from zero to the line voltage VAC. From time t1' to time t3', the primary voltage Vp remains approximately constant at the line voltage VAC.

[0118] Next, 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 t4'. Specifically, at time t3', the control unit 33 turns the first low-side bidirectional switch LS1 on in both directions. At time t4', the control unit 33 turns the first high-side bidirectional switch HS1 on in the negative direction. Note that from time t2' to time t3', the primary voltage Vp decreases from the line voltage VAC to zero. During the period from time t3' to time t4', the primary voltage Vp is approximately zero.

[0119] Next, 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 t6'. Specifically, at time t5', the control unit 33 turns the third high-side bidirectional switch HS3 on in both directions. At time t6', the control unit 33 turns the third high-side bidirectional switch HS3 on in the positive direction. Note that from time t4' to time t5', the primary voltage Vp decreases from zero to the line voltage VCA. During the period from time t5' to time t6', the primary voltage Vp remains approximately constant at the line voltage VCA.

[0120] As described above, time t8' coincides with the on / off state of each switch element at time t0'. That is, in the period from time t6' to time t8', 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 t0' of the next cycle Ts. That is, in the period from time t6' to time t8', the control unit 33 controls the each switch element so that the seventh zero vector I7 is generated.

[0121] Specifically, at time t7', the control unit 33 turns on the first high-side bidirectional switch HS1 in both directions. At time t8', that is, at time t0' of the next cycle Ts, the control unit 33 turns on the first low-side bidirectional switch LS1 in the positive direction. One cycle Ts ends when the switch is switched at time t8'. Note that from time t6' to time t7', the primary voltage Vp increases from the line voltage VCA to zero. During the period from time t7' to time t8', the primary voltage Vp is zero.

[0122] Thus, the number of combinations of the on / off states of the multiple bidirectional switches TSW defined in the switch sequence 1b' of sector 1b' is 8. Therefore, the number of combinations defined in the switch sequence 1b' is less than the number of combinations defined in the switch sequence 1b.

[0123] (4-4. 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.

[0124] 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.

[0125] 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 8, 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.

[0126] 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.

[0127] 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. Therefore, the number of combinations of the on / off states of the multiple bidirectional switches TSW defined by the switch sequence 1b in sector 1b is 14.

[0128] (4-5. Switch Sequence 2a') Next, the switching pattern in the sector 2a' will be described. As shown in Figures 8 and 9, the on / off control performed by the controller 33 in the period of the sector 2a' is the same as the on / off control in the period of the sector 2a, except for the control over the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2.

[0129] Specifically, during the period of sector 2a', the control unit 33 always maintains the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2 in the off state. Therefore, during the period of 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. (2a') The order is second positive direction active vector I2+, ninth zero vector I9, second negative direction active vector I2-, and ninth zero vector I9.

[0130] Therefore, the pattern of on / off control by the control unit 33 according to the switch sequence 2a' is as follows, based on the magnitude relationships between the voltages, the vector sequence, etc. As shown in Figures 7 and 9, 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 third low-side bidirectional switch LS3 in sector 1b'. 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 third high-side bidirectional switch HS3 in sector 1b'.

[0131] The on / off control pattern of the second high-side bidirectional switch HS2 and the second low-side bidirectional switch LS2 in the sector 2a' is the same as the on / off control pattern of the second high-side bidirectional switch HS2 and the second low-side bidirectional switch LS2 in the sector 1b'. That is, the controller 33 maintains the second high-side bidirectional switch HS2 and the second low-side bidirectional switch LS2 in the off state in the sector 2a'.

[0132] 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 1b'. 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 1b'.

[0133] Thus, the number of combinations of the on / off states of the multiple bidirectional switches TSW defined in the switch sequence 2a' of the sector 2a' is 8. Therefore, the number of combinations defined in the switch sequence 2a' is less than the number of combinations defined in the switch sequence 2a.

[0134] (4-6. Regarding Other Transition Periods) As in the above example, in sectors 2b', 3a', 5b', and 6a', which are transition periods for the first voltage VA, the control unit 33 always maintains the first low-side bidirectional switch LS1 and the first high-side bidirectional switch HS1 in the OFF state. Furthermore, for the bidirectional switches TSW other than the first low-side bidirectional switch LS1 and the first high-side bidirectional switch HS1, the control unit 33 controls each switch element with the same switching pattern as the ON / OFF control in a specific period that is temporally consecutive to each transition period.

[0135] In sectors 4b' and 5a', which are transition periods for the second voltage VB, the control unit 33 always maintains the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2 in the OFF state. Furthermore, for the bidirectional switches TSW other than the second low-side bidirectional switch LS2 and the second high-side bidirectional switch HS2, the control unit 33 controls each switch element with the same switching pattern as the ON / OFF control in a specific period that is temporally consecutive to each transition period.

[0136] In sectors 3b', 4a', 6b', and 1a', which are transition periods for the third voltage VC, the control unit 33 always maintains the third low-side bidirectional switch LS3 and the third high-side bidirectional switch HS3 in the OFF state. Furthermore, for the bidirectional switches TSW other than the third low-side bidirectional switch LS3 and the third high-side bidirectional switch HS3, the control unit 33 controls each switch element with the same switching pattern as the ON / OFF control in a specific period that is temporally consecutive to each transition period.

[0137] (5. Operation of the Present Embodiment) In the above-described embodiment, the number of combinations of the on / off states of the bidirectional switches TSW defined in switch sequence 1b' is 8, which is less than the number of combinations of the on / off states of the bidirectional switches TSW defined in switch sequence 1b, which is 14. More specifically, in switch sequence 1b', on / off switching control is not performed at times t2, t3, t4, t9, t10, and t11 in switch sequence 1b.

[0138] Assume that the control unit 33 controls each switch element according to the switch sequence 1b during the first transition period of the second voltage VB. The pulse width of the PWM signal becomes shorter immediately before the second voltage VB becomes zero. Therefore, for example, the 26th switch element S26 may not switch from the OFF state to the ON state at time t4. As shown in FIG. 6 , immediately before time t4, the second low-side bidirectional switch LS2 is in the ON state in the forward direction. That is, the 26th switch element S26 is in the OFF state, and current flows through the body diode of the 26th switch element S26. Therefore, if the 26th switch element S26 does not switch to the ON state at time t4 and the 16th switch element S16 is switched to the OFF state at time t5, a so-called reverse recovery current will be generated in the 26th switch element S26. That is, if the 16th switch element S16 is switched to the OFF state while current is flowing through the body diode of the 26th switch element S26, the current flowing through the body diode will be cut off. As a result, a reverse voltage is applied to the 26th switch element S26. As a result, a reverse recovery current flows through the body diode of the 26th switch element S26. When this phenomenon occurs, a surge voltage is generated in the 26th switch element S26. As a result, a relatively large electrical stress is applied to the 26th switch element S26.

[0139] In the switch sequence 1b' of this embodiment, the number of times the switch elements are switched on and off is smaller than in the switch sequence 1b. Therefore, the period from time t1' to time t2' and the period from time t5' to time t6' in the switch sequence 1b' occupy a long period relative to one cycle Ts. This prevents the PWM signal from becoming extremely short just before the input voltage becomes zero.

[0140] (6. Effects of the Present Embodiment) (1) According to the above embodiment, the number of combinations of the on / off states of each switch element defined by the second switch sequence is smaller than the number of combinations of the on / off states of each switch element defined by the first switch sequence.

[0141] In the second switch sequence during the first transition period, the number of combinations of on / off states of the switch elements is small, so the pulse width of the PWM signal corresponding to these combinations can be made longer. This makes it less likely that a particular switch element will not switch to the on state as intended. As a result, electrical stress on the switch elements due to the reverse recovery phenomenon described above can be suppressed.

[0142] (2) According to the above embodiment, during the transition period, the control unit 33 always keeps the bidirectional switch TSW in the off state when the input voltage is approximately zero. In other words, among the combinations of on and off states of the switches defined by the second switch sequence, the bidirectional switch TSW in which the input voltage is zero is maintained in the off state. For example, in sector 1b', which is the first transition period for the second voltage VB, the control unit 33 always keeps the second high-side bidirectional switch HS2 and the second low-side bidirectional switch LS2 in the off state.

[0143] The bidirectional switch TSW when the input voltage becomes zero is switched on and off more frequently than the other bidirectional switches TSW. Therefore, the pulse width of the PWM signal is likely to become short during the transition period, and there is a high possibility that electrical stress will be applied to a specific switch element. Therefore, with the above configuration, electrical stress is unlikely to be applied to the switch elements that make up the bidirectional switch TSW when the input voltage becomes zero.

[0144] (3) According to the above embodiment, during the transition period, the combination of the on / off states of the bidirectional switches TSW other than the bidirectional switch TSW whose input voltage is zero is the same as the combination of the on / off states of the bidirectional switches TSW during a specific period that is continuous in time. This prevents the switching pattern from becoming complicated. Furthermore, electrical stress caused by switching the switching pattern is also unlikely to occur.

[0145] (4) In the above embodiment, the number of combinations of the on / off states of each switch element defined by the third switch sequence is smaller than the number of combinations of the on / off states of each switch element defined by the first switch sequence. Furthermore, the number of combinations of the on / off states of each switch element defined by the second switch sequence and the third switch sequence is smaller than the number of combinations of the on / off states of each switch element defined by the fourth switch sequence. This allows the pulse width of the PWM signal corresponding to one combination of the switch sequences to be increased not only in the first transition period but also in the second transition period. This prevents electrical stress from being applied to the switch elements.

[0146] (5) In the above embodiment, the predetermined period is greater than 0° and less than or equal to 5°. During the specific period, the control unit 33 controls each bidirectional switch TSW according to the first switch sequence or the fourth switch sequence. These switch sequences can achieve zero-current switching or zero-voltage switching, so power conversion efficiency is relatively high during the specific period. Furthermore, during the transition period, the control unit 33 controls each bidirectional switch TSW according to the second switch sequence or the third switch sequence. As described above, these switch sequences can suppress electrical stress on the switch elements due to the reverse recovery phenomenon. Therefore, by setting the predetermined period to the above period, electrical stress on each switch element can be suppressed during the transition period, and power conversion efficiency can be increased during the specific period.

[0147] <Modifications> The above embodiment can be modified as follows. The above embodiment and the following modifications can be combined and implemented as long as there is no technical contradiction. 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 can also be applied to a non-isolated three-phase AC-DC converter. In other words, the power conversion device 10 does not need to include one or more selected from the input-side low-pass filter 20, the transformer circuit 40, the rectifier circuit 50, and the output-side low-pass filter 60.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] The period into which each sector is divided is not limited to the example in the above embodiment. For example, in sector n, a sector corresponding to sector nb' may not be defined. In this case, the control unit 33 may control each bidirectional switch TSW with switch sequence nb during the period X°<θ°<(X°+30°).

[0153] The transition period and the specific period may include a phase in which the input voltage is zero. For example, the period of sector na′ may be (X°-30°)<θ°≦(X°-25°), and the period of sector na may be (X°-25°)<θ°≦X°.

[0154] The number of combinations of the on / off states of the multiple bidirectional switches TSW defined by each switch sequence is not limited to the example in the above embodiment. That is, the number of combinations defined by the switch sequence na and the switch sequence nb may be 13 or less, or 15 or more. The number of combinations defined by the switch sequence na' and the switch sequence nb' may be 7 or less, or 9 or more. However, the number of combinations of the on / off states of the multiple bidirectional switches TSW defined by the second switch sequence must be less than the number of combinations of the on / off states of the multiple bidirectional switches TSW defined by the first switch sequence.

[0155] During the transition period, the control unit 33 does not have to turn off all of the bidirectional switches TSW corresponding to the zero input voltage. For example, in sector 1b', which is the first transition period for the second voltage VB, the control unit 33 does not have to turn off all of the switch elements constituting the second high-side bidirectional switch HS2 and the second low-side bidirectional switch LS2. For example, even if the second high-side bidirectional switch HS2 is maintained in the on state in the positive direction and the second low-side bidirectional switch LS2 is maintained in the on state in the negative direction, electrical stress on the switch elements can be suppressed. Note that even in this case, the number of combinations of the on / off states of each switch element defined by the second switch sequence is smaller than the number of combinations of the on / off states of each switch element defined by the first switch sequence.

[0156] During the transition period, the combinations of the on / off states of the bidirectional switches TSW other than the bidirectional switch TSW whose input voltage is zero may be different from the combinations of the on / off states of the bidirectional switches TSW during a specific period that is continuous in time. Even in such a case, by making the number of combinations of the on / off states of each switch element during the transition period less than the number during the specific period, electrical stress on the switch elements can be suppressed.

[0157] In the above embodiment, the control unit 33 may perform control using the second switch sequence for at least one of the phases in which the input voltage is zero. For example, the control unit 33 may perform control according to the switch sequence 1b' in sector 1b', but may not perform control according to the switch sequence na' or the switch sequence nb' before or after the other phases in which the input voltage is zero.

[0158] In the above embodiment, the angle may be greater than 5°. The appropriate predetermined angle may vary depending on factors such as the operating frequency of the power conversion device 10. <Notes> The technical concepts that can be understood from the above embodiment and modified examples will be described below.

[0159] [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, respectively; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminal, the second input terminal, the third input terminal, and the first output terminal and the second output terminal, respectively; 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; or a second 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 in a manner different from that of the first switch sequence. and a control unit capable of controlling the plurality of bidirectional switches in accordance with the first switch sequence, wherein when a period from a phase in which any of the first voltage, the second voltage, and the third voltage is zero to a phase that is separated by a predetermined angle from the phase in which the first voltage, the second voltage, and the third voltage is zero is defined as a transition period, and a period of a phase that is temporally continuous with the transition period is defined as a specific period, the control unit controls the plurality of bidirectional switches in accordance with the first switch sequence during the specific period and controls the plurality of bidirectional switches in accordance with the second switch sequence during the transition period, and wherein the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence.

[0160] [2] The power conversion circuit according to [1], wherein when one selected from the first voltage, the second voltage, and the third voltage is defined as a specific voltage, and an input terminal among the first input terminal, the second input terminal, and the third input terminal to which the specific voltage is input is defined as a specific input terminal, the plurality of bidirectional switches include a specific high-side bidirectional switch connecting the specific input terminal and the first output terminal, and a specific low-side bidirectional switch connecting the specific input terminal and the second output terminal, and the control unit controls the specific high-side bidirectional switch and the specific low-side bidirectional switch to be maintained in an off state during the transition period.

[0161] [3] When one selected from the first voltage, the second voltage, and the third voltage is a specific voltage, an input terminal among the first input terminal, the second input terminal, and the third input terminal to which the specific voltage is input is a first specific input terminal, any one of the first input terminal, the second input terminal, and the third input terminal excluding the first specific input terminal is a second specific input terminal, and an input terminal among the first input terminal, the second input terminal, and the third input terminal excluding the first specific input terminal and the second specific input terminal is a third specific input terminal, the plurality of bidirectional switches include a second specific high-side bidirectional switch connecting between the second specific input terminal and the first output terminal, a second specific low-side bidirectional switch connecting between the second specific input terminal and the second output terminal, a third specific high-side bidirectional switch connecting between the third specific input terminal and the first output terminal, and a third specific high-side bidirectional switch connecting between the third specific input terminal and the first output terminal. and a third specified low-side bidirectional switch connecting between a specified input terminal and the second output terminal, wherein the first switch sequence specifies a plurality of combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, and an order of switching the plurality of combinations, and the second switch sequence specifies a plurality of combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, and an order of switching the plurality of combinations.

[0162] [4] The power conversion circuit according to any one of [1] to [3], wherein when one selected from the first voltage, the second voltage, and the third voltage is set as a specific voltage, the control unit is capable of controlling the multiple bidirectional switches in accordance with a third switch sequence that defines multiple combinations of on / off states of the multiple bidirectional switches and an order of switching the multiple combinations in a manner different from the first switch sequence and the second switch sequence, and when, within the transition period, a period from a phase at which the specific voltage becomes zero to a phase that is separated in time by the predetermined angle earlier is set as a first transition period, and a period from the phase at which the specific voltage becomes zero to a phase that is separated in time by the predetermined angle later and that is consecutive in time to the first transition period, the control unit controls the multiple bidirectional switches in accordance with the second switch sequence in the first transition period and controls the multiple bidirectional switches in accordance with the third switch sequence in the second transition period, and the number of combinations of on / off states of the multiple bidirectional switches defined by the third switch sequence is smaller than the number of combinations of on / off states of the multiple bidirectional switches defined by the first switch sequence.

[0163] [5] The power conversion circuit according to [4], wherein the control unit is capable of controlling the plurality of bidirectional switches in accordance with a fourth switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order of switching between the plurality of combinations in a manner different from the first switch sequence, the second switch sequence, and the third switch sequence, wherein within the specific period, a period that temporally precedes and follows the first transition period is defined as a first specific period, and a period that temporally precedes and follows the second transition period is defined as a second specific period, wherein the control unit controls the plurality of bidirectional switches in accordance with the first switch sequence in the first specific period, and the control unit controls the plurality of bidirectional switches in accordance with the fourth switch sequence in the second specific period, and wherein the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence and the third switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the fourth switch sequence.

[0164] [6] The power conversion circuit according to any one of [1] to [5], wherein the predetermined angle is greater than 0° and is equal to or less than 5°. [7] A power conversion circuit comprising: first input terminals, second input terminals, and third input terminals connected to a three-phase AC power supply and receiving first, second, and third voltages, which are AC voltages of different phases, respectively; first output terminals and second output terminals capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminal, the second input terminal, and the third input terminal and the first output terminal and the second output terminal, respectively; and 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 the first switch sequence. and a control unit capable of controlling the plurality of bidirectional switches, wherein the program is applied to a power conversion circuit in which the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence, and the program causes the control unit to control the plurality of bidirectional switches in accordance with the first switch sequence during the specific period, and to control the plurality of bidirectional switches in accordance with the second switch sequence during the transition period, when a period from a phase in which any of the first voltage, the second voltage, and the third voltage is zero to a phase that is separated by a predetermined angle from the phase in which the any of the first voltage, the second voltage, and the third voltage is zero is defined as a transition period, and a period of a phase that is temporally continuous with the transition period is defined as a specific period.

[0165] REFERENCE SIGNS LIST 10...power conversion device 20...input side low pass filter 30...power conversion circuit 31A...first input terminal 31B...second input terminal 31C...third input terminal 32...output terminal 33...controller PG...program VA...first voltage VB...second voltage VC...third voltage TSW...bidirectional switch 40...transformer circuit 50...rectifier circuit 60...output side low pass filter 70...load 80...three-phase AC power supply Ip...primary current Vp...primary voltage

Claims

1. A power supply comprising: first input terminals, second input terminals, and third input terminals connected to a three-phase AC power source, and into which a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, are respectively input; first output terminals and second output terminals capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminals, the second input terminals, and the third input terminals and the first output terminals and the second output terminals, respectively; 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 of 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 of switching the plurality of combinations in a manner different from the first switch sequence; wherein when a transition period is defined as a period from a phase in which any of the first voltage, the second voltage, and the third voltage is zero to a phase that is separated by a predetermined angle from the phase in question, and a period of a phase that is temporally continuous with the transition period is defined as a specific period, the control unit: a power conversion circuit in which the plurality of bidirectional switches are controlled in accordance with the first switch sequence during the specific period, and the plurality of bidirectional switches are controlled in accordance with the second switch sequence during the transition period, wherein the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence.

2. The power conversion circuit according to claim 1, wherein when one selected from the first voltage, the second voltage, and the third voltage is defined as a specific voltage, and an input terminal among the first input terminal, the second input terminal, and the third input terminal to which the specific voltage is input is defined as a specific input terminal, the plurality of bidirectional switches include a specific high-side bidirectional switch connecting the specific input terminal and the first output terminal, and a specific low-side bidirectional switch connecting the specific input terminal and the second output terminal, and the control unit controls the specific high-side bidirectional switch and the specific low-side bidirectional switch so that they are maintained in an off state during the transition period.

3. When one selected from the first voltage, the second voltage, and the third voltage is a specific voltage, and an input terminal among the first input terminal, the second input terminal, and the third input terminal to which the specific voltage is input is a first specific input terminal, any one of the first input terminal, the second input terminal, and the third input terminal excluding the first specific input terminal is a second specific input terminal, and an input terminal 31 among the first input terminal, the second input terminal, and the third input terminal excluding the first specific input terminal and the second specific input terminal is a third specific input terminal, the plurality of bidirectional switches include: a second specific high-side bidirectional switch connecting the second specific input terminal and the first output terminal, a second specific low-side bidirectional switch connecting the second specific input terminal and the second output terminal, a third specific high-side bidirectional switch connecting the third specific input terminal and the first output terminal, and a third specific low-side bidirectional switch connecting the third specific input terminal and the second output terminal, 3. The power conversion circuit according to claim 1 or 2, wherein the plurality of combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, which are specified in the first switch sequence, and the order of switching the plurality of combinations, which are specified in the second switch sequence, are the same as the plurality of combinations of the on / off state of the second specified high-side bidirectional switch, the on / off state of the second specified low-side bidirectional switch, the on / off state of the third specified high-side bidirectional switch, and the on / off state of the third specified low-side bidirectional switch, which are the same as the order of switching the plurality of combinations.

4. When one selected from the first voltage, the second voltage, and the third voltage is a specific voltage, the control unit can control the multiple bidirectional switches in accordance with a third switch sequence that defines multiple combinations of on / off states of the multiple bidirectional switches and an order of switching between the multiple combinations in a manner different from the first switch sequence and the second switch sequence, and when, within the transition period, a period from a phase at which the specific voltage becomes zero to a phase separated in time by the predetermined angle on the earlier side is defined as a first transition period, and a period from a phase at which the specific voltage becomes zero to a phase separated in time by the predetermined angle on the later side and that is consecutive in time to the first transition period is defined as a second transition period, the control unit controls the multiple bidirectional switches in accordance with the second switch sequence during the first transition period, and controls the multiple bidirectional switches in accordance with the third switch sequence during the second transition period, and the number of combinations of on / off states of the multiple bidirectional switches defined by the third switch sequence is smaller than the number of combinations of on / off states of the multiple bidirectional switches defined by the first switch sequence. The power conversion circuit according to any one of claims 1 to 3.

5. The power conversion circuit according to claim 4, wherein the control unit is capable of controlling the plurality of bidirectional switches in accordance with a fourth switch sequence that defines a plurality of combinations of on / off states of the plurality of bidirectional switches and an order for switching between the plurality of combinations in a manner different from the first switch sequence, the second switch sequence, and the third switch sequence; within the specific period, a period that temporally precedes and follows the first transition period is defined as a first specific period, and a period that temporally follows the second transition period is defined as a second specific period; during the first specific period, the plurality of bidirectional switches are controlled in accordance with the first switch sequence; and during the second specific period, the plurality of bidirectional switches are controlled in accordance with the fourth switch sequence; and the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence and the third switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the fourth switch sequence.

6. The power conversion circuit according to any one of claims 1 to 5, wherein the predetermined angle is greater than 0° and equal to or less than 5°.

7. A power conversion circuit comprising: first input terminals, second input terminals, and third input terminals connected to a three-phase AC power supply and into which a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, are respectively input; first output terminals and second output terminals capable of outputting AC power; a plurality of bidirectional switches connected between the first input terminals, the second input terminals, and the third input terminals and the first output terminals and the second output terminals, respectively; 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 of 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 of switching the plurality of combinations in a manner different from the first switch sequence; wherein the power conversion circuit is applied to a power conversion circuit in which the number of combinations of on / off states of the plurality of bidirectional switches defined by the second switch sequence is smaller than the number of combinations of on / off states of the plurality of bidirectional switches defined by the first switch sequence, a period from a phase in which any one of the first voltage, the second voltage, and the third voltage becomes zero to a phase that is separated by a predetermined angle from the phase in which the any one of the first voltage, the second voltage, and the third voltage becomes zero is defined as a transition period, and a period of a phase that is temporally continuous with the transition period is defined as a specific period, the program causing the control unit to control the plurality of bidirectional switches according to the first switch sequence during the specific period, and to control the plurality of bidirectional switches according to the second switch sequence during the transition period.

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