Power conversion circuit and program for power conversion circuit

Abstract

The power conversion circuit (30) includes multiple bidirectional switches (TSWs) and a control unit (33). The control unit (33) can control each bidirectional switch (TSW) according to either a first switch sequence or a second switch sequence. When the on / off state of a bidirectional switch (TSW) carrying current in control according to the first switch sequence is the same as the on / off state of a bidirectional switch (TSW) carrying current in control according to the second switch sequence after the switch is switched, the control unit (33) switches from control according to the first switch sequence to control according to the second switch sequence.

Description

Technical Field

[0001] This disclosure relates to power conversion circuits and programs used in power conversion circuits. Background Technology

[0002] The power conversion circuit disclosed in Patent Document 1 includes three input terminals, multiple switching elements, and a control unit. The power conversion circuit can convert three-phase AC power input to the input terminals into single-phase AC power by controlling the on / off state of the multiple switching elements. The control unit controls the on / off state of each switching element.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: U.S. Patent Application Publication No. 2018 / 0262103 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] Consider a switching sequence in a power conversion circuit. Sometimes, the on / off states of multiple switching elements differ between the initial and subsequent combinations of on / off states in the original sequence. When attempting to switch the on / off states of multiple switching elements, it is easy to apply electrical stress to any specific switch among these elements.

[0008] Technical solutions for solving the problem

[0009] To address the aforementioned problems, this disclosure provides a power conversion circuit comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, wherein a first voltage, a second voltage, and a third voltage, representing AC voltages of different phases, are input one-to-one; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal, respectively; a first output terminal and a second output terminal connected to the plurality of bidirectional switches, capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence, wherein the first switch sequence is defined as follows: The second switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch flowing with current under the control of the first switch sequence is consistent with the on / off state of the bidirectional switch flowing with current under the control of the switched second switch sequence, the control unit switches from control according to the first switch sequence to control according to the second switch sequence.

[0010] Furthermore, this disclosure discloses a program for a power conversion circuit, applied to a power conversion circuit comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, wherein a first voltage, a second voltage, and a third voltage, being AC voltages of different phases, are input one-to-one; a plurality of bidirectional switches, respectively connected to the first input terminal, the second input terminal, and the third input terminal; a first output terminal and a second output terminal capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence, wherein the first switch sequence is defined as follows: The second switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch flowing with current under the control of the first switch sequence is consistent with the on / off state of the bidirectional switch flowing with current under the control of the switched second switch sequence, the program switches the control unit from control according to the first switch sequence to control according to the second switch sequence.

[0011] Invention Effects

[0012] It can suppress the application of electrical stress to specific switches. Attached Figure Description

[0013] Figure 1 This is a circuit diagram of the power conversion device in this embodiment.

[0014] Figure 2 This is an explanatory diagram showing the waveforms and sections of three-phase alternating current.

[0015] Figure 3 It is the spatial vector diagram in SVPWM.

[0016] Figure 4 It is the spatial vector diagram in SVPWM.

[0017] Figure 5 This is a sequence diagram of the switching on and off control of the switches in section 1a.

[0018] Figure 6 This is a sequence diagram of the on / off control of the switches in section 1b.

[0019] Figure 7 This is a sequence diagram of the switching on and off control of the switches in section 2a.

[0020] Figure 8 This is a diagram showing an example of the correspondence between the timing and the state of the switch in the on / off control of the switch.

[0021] Figure 9 This is a diagram illustrating the switching control of the switch sequence.

[0022] Figure 10 It is a circuit diagram used to illustrate the switching control of a switch sequence.

[0023] Figure 11 It is a circuit diagram used to illustrate the switching control of a switch sequence.

[0024] Figure 12 It is a circuit diagram used to illustrate the switching control of a switch sequence.

[0025] Figure 13 It is a circuit diagram used to illustrate the switching control of a switch sequence.

[0026] Figure 14 It is a circuit diagram used to illustrate the switching control of a switch sequence.

[0027] Figure 15 It is a circuit diagram used to illustrate the switching control of a switch sequence. Detailed Implementation

[0028] <An Implementation Method of Power Conversion Circuit>

[0029] The following describes one embodiment of the power conversion circuit. Furthermore, the accompanying drawings are merely illustrative of embodiments of this disclosure and should not be construed as limiting this disclosure. Terms such as "first," "second," and "third" used in this disclosure are used only to distinguish objects and do not indicate any ordering of the objects.

[0030] (1. Regarding the structure of power conversion devices)

[0031] like Figure 1 As shown, 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. Furthermore, the power conversion device 10 has three external input terminals 11 and a pair of external output terminals 12. Additionally, the power conversion device 10 is a so-called three-phase isolated AC-DC converter. That is, the power conversion device 10 can convert three-phase AC power input to the external input terminals 11 into DC power and output it from the external output terminals 12. Moreover, the transformer circuit 40 is positioned along the power path from each external input terminal 11 to each external output terminal 12, thereby electrically isolating the external input terminal 11 side from the external output terminal 12 side.

[0032] The power conversion device 10 has three external input terminals 11: the first external input terminal 11A, the second external input terminal 11B, and the third external input terminal 11C. Each external input terminal 11 receives one phase of three-phase AC power from the three-phase AC power supply 80. The three-phase AC power supply 80 is a three-phase, three-wire commercial power system that connects three AC power sources in a Y-connection configuration.

[0033] A pair of external output terminals 12 are a first external output terminal 12A and a second external output terminal 12B. An arbitrary load 70 can be connected between the first external input terminal 11A and the second external output terminal 12B. The load 70 is, for example, an electronic device driven by DC power.

[0034] The input-side low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3. Additionally, the input-side low-pass filter 20 includes a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0035] The first terminal of the first inductor L1 is connected to the first external input terminal 11A. The first terminal of the first capacitor C1 is connected to the second terminal of the first inductor L1.

[0036] Terminal 1 of the second inductor L2 is connected to the second external input terminal 11B. Terminal 1 of the second capacitor C2 is connected to terminal 2 of the second inductor L2. Terminal 2 of the second capacitor C2 is connected to terminal 2 of the first capacitor C1.

[0037] Terminal 1 of the third inductor L3 is connected to the third external input terminal 11C. Terminal 1 of the third capacitor C3 is connected to terminal 2 of the third inductor L3. Terminal 2 of the third capacitor C3 is connected to terminal 2 of the first capacitor C1.

[0038] The power conversion circuit 30 includes multiple input terminals 31, a pair of output terminals 32, multiple bidirectional switches (TSW), and a control unit 33.

[0039] Multiple input terminals 31 are designated as first input terminal 31A, second input terminal 31B, and third input terminal 31C. The second terminal of the first inductor L1 is connected to the first input terminal 31A. The second terminal of the second inductor L2 is connected to the second input terminal 31B. The second terminal of the third inductor L3 is connected to the second input terminal 31C. Therefore, three-phase AC power is input to the power conversion circuit 30 via external input terminal 11 and input-side low-pass filter 20 at the input terminals 31. Furthermore, a pair of output terminals 32 are designated as first output terminal 32A and second output terminal 32B. Single-phase AC power, converted by multiple bidirectional switches (TSWs), is output from the pair of output terminals 32.

[0040] Each bidirectional TSW has two switching elements. Each switching element is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). That is, each switching element has a body diode. Furthermore, the bidirectional TSW is composed of two switching elements connected in series, with the anode terminals of the body diodes connected to each other. In other words, connecting the switching elements constituting each bidirectional TSW reverses the body diodes. In other words, each bidirectional TSW has two switching elements with their source terminals connected to each other.

[0041] The multiple bidirectional switches TSW are the first high-side bidirectional switch HS1, the first low-side bidirectional switch LS1, the second high-side bidirectional switch HS2, the second low-side bidirectional switch LS2, the third high-side bidirectional switch HS3, and the third low-side bidirectional switch LS3.

[0042] 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 switching element S11 and a twenty-first switching element S21. The drain terminal of the eleventh switching element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switching element S11 is connected to the source terminal of the twenty-first switching element S21. The drain terminal of the twenty-first switching element S21 is connected to the first output terminal 32A.

[0043] 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 switching element S24 and a 14th switching element S14. The drain terminal of the 24th switching element S24 is connected to the first input terminal 31A. The source terminal of the 24th switching element S24 is connected to the source terminal of the 14th switching element S14. The drain terminal of the 14th switching element S14 is connected to the second output terminal 32B.

[0044] 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 13th switching element S13 and a 23rd switching element S23. The drain terminal of the 13th switching element S13 is connected to the second input terminal 31B. The source terminal of the 13th switching element S13 is connected to the source terminal of the 23rd switching element S23. The drain terminal of the 23rd switching element S23 is connected to the first output terminal 32A.

[0045] 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 switching element S26 and a 16th switching element S16. The drain terminal of the 26th switching element S26 is connected to the second input terminal 31B. The source terminal of the 26th switching element S26 is connected to the source terminal of the 16th switching element S16. The drain terminal of the 16th switching element S16 is connected to the second output terminal 32B.

[0046] 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 15th switching element S15 and a 25th switching element S25. The drain terminal of the 15th switching element S15 is connected to the third input terminal 31C. The source terminal of the 15th switching element S15 is connected to the source terminal of the 25th switching element S25. The drain terminal of the 25th switching element S25 is connected to the first output terminal 32A.

[0047] 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 switching element S22 and a 12th switching element S12. The drain terminal of the 22nd switching element S22 is connected to the third input terminal 31C. The source terminal of the 22nd switching element S22 is connected to the source terminal of the 12th switching element S12. The drain terminal of the 12th switching element S12 is connected to the second output terminal 32B.

[0048] The control unit 33 has a storage device (not shown) and an execution device. That is, the control unit 33 is a MCU (Microcontroller Unit). The storage device of the control unit 33 stores the program PG executed by the execution device.

[0049] The execution device includes, for example, a CPU (Central Processing Unit), an MPU (Microprocessing Unit), a FPGA (Field Programmable Gate Array), a CPLD (Complex Programmable Logic Device), or an ASIC (Application Specific Integrated Circuit). The execution device of the control unit 33 executes a program PG to control each bidirectional switch TSW according to the switching sequence described later. Specifically, the power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit turns the two switching elements of each bidirectional switch TSW on and off. The execution device of the control unit 33 controls the on / off state of each switching element by inputting a switching signal to the input terminal of the gate drive circuit and outputting a gate drive voltage to each switching element via the gate drive circuit. The switching signals include 11th switch signals SG11 to 16th switch signals SG16 and 21st switch signals SG21 to 26th switch signals SG26. Switch signals SG11 to SG16, numbered 11 to 16, correspond one-to-one with switch elements S11 to S16, respectively. Similarly, switch signals SG21 to SG26, numbered 21 to S26, correspond one-to-one with switch elements S21 to S26, respectively. Furthermore, hereinafter, the on / off control performed by the actuator of control unit 33 will be referred to simply as on / off control performed by control unit 33.

[0050] Each bidirectional switch (TSW) can achieve four on / off states through the combination of the on / off states of its various switching elements. The following explanation uses the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1 as examples.

[0051] The first state is a bidirectional ON state. In the bidirectional ON state, in the first high-side bidirectional switch HS1, the 11th switching element S11 is turned on, and the 21st switching element S21 is turned on. In the bidirectional 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, and also allows current to flow from the first output terminal 32A to the first input terminal 31A.

[0052] Furthermore, in the first low-side bidirectional switch LS1, when in the bidirectional ON state, the 14th switching element S14 is ON, and the 24th switching element S24 is ON. In the bidirectional ON state, the first low-side bidirectional switch LS1 allows current to flow from the first input terminal 31A to the second output terminal 32B, and also allows current to flow from the second output terminal 32B to the first input terminal 31A.

[0053] The second state is the forward-on state. In the forward-on state, in the first high-side bidirectional switch HS1, the 11th switching element S11 is turned on, and the 21st switching element S21 is turned off. In the forward-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 via the body diode of the 21st switching element S21. Conversely, 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.

[0054] Furthermore, in the first low-side bidirectional switch LS1, when in the positive-on state, the 14th switching element S14 is turned on, and the 24th switching element S24 is turned off. In the positive-on state, the first low-side bidirectional switch LS1 allows current to flow from the second output terminal 32B to the first input terminal 31A via the body diode of the 24th switching element S24. On the other hand, the first low-side bidirectional switch LS1 does not allow current to flow from the first input terminal 31A to the second output terminal 32B.

[0055] The third state is the negative on state. In the negative on state, in the first high-side bidirectional switch HS1, the 11th switching element S11 is off, and the 21st switching 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 via the body diode of the 11th switching element S11. Conversely, 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.

[0056] Furthermore, in the first low-side bidirectional switch LS1, when in the negative-on state, the 14th switching element S14 is turned off, and the 24th switching element S24 is turned on. In the negative-on state, the first low-side bidirectional switch LS1 allows current to flow from the first input terminal 31A to the second output terminal 32B via the body diode of the 14th switching element S14. On the other hand, the first low-side bidirectional switch LS1 does not allow current to flow from the second output terminal 32B to the first input terminal 31A.

[0057] The fourth state is the off state. In the off state, in the first high-side bidirectional switch HS1, the 11th switching element S11 is turned off, and the 21st switching element S21 is turned off. In the off state, 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, nor does it allow current to flow from the first output terminal 32A to the first input terminal 31A.

[0058] Furthermore, in the first low-side bidirectional switch LS1, when in the off state, the 14th switching element S14 is turned off, and the 24th switching element S24 is also turned off. In the off state, the first low-side bidirectional switch LS1 does not allow current to flow from the first input terminal 31A to the second output terminal 32B, nor does it allow current to flow from the second output terminal 32B to the first input terminal 31A.

[0059] The transformer circuit 40 includes a fourth inductor L4 and a transformer 41. Furthermore, the transformer 41 includes a primary winding 41A and a secondary winding 41B. The first terminal of the fourth inductor L4 is connected to the first output terminal 32A of the power conversion circuit 30. The first terminal of the primary winding 41A is connected to the second terminal of the fourth inductor L4. The second terminal of the primary winding 41A is connected to the second output terminal 32B of the power conversion circuit 30. The secondary winding 41B is connected to an external output terminal 12 via a rectifier circuit 50 and an output-side low-pass filter 60. The primary winding 41A and the secondary winding 41B are electrically isolated.

[0060] 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 the first terminal of the secondary winding 41B of the transformer 41. The cathode terminal of the first diode 51 is connected to the cathode terminal of the third diode 53. The anode terminal of the third diode 53 is connected to the second terminal of the secondary winding 41B and the cathode terminal of the fourth diode 54. The anode terminal of the fourth diode 54 is connected to the anode terminal of the second diode 52. The cathode terminal of the second diode 52 is connected to the first terminal of the secondary winding 41B and the anode terminal of the first diode 51.

[0061] Furthermore, 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-side 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. Moreover, 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.

[0062] The output-side low-pass filter 60 includes a fifth inductor L5 and a fourth capacitor C4. Terminal 1 of the fifth inductor L5 is connected to the cathode terminals of both the first diode 51 and the third diode 53. Terminal 2 of the fifth inductor L5 is connected to the first external output terminal 12A. Terminal 1 of the fourth capacitor C4 is connected to the second terminal of the fifth inductor L5. Terminal 2 of the fourth capacitor C4 is connected to the second external output terminal 12B.

[0063] (2. Definition of a section)

[0064] As described above, three-phase AC power is input from the three-phase AC power supply 80, via the external input terminal 11 and the input-side low-pass filter 20, to the input terminal 31 of the power conversion circuit 30. Figure 2 As shown, the voltages of the three phases of this three-phase AC power are AC voltages VA, VB, and VC, which are AC voltages with different phases. Each voltage is input one-to-one to the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C. 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 120° phase difference relative to the first voltage VA. The third voltage VC has a 120° phase difference relative to the second voltage VB. Furthermore, this "120° phase difference" refers to a phase difference with an allowable error of ±1°.

[0065] Hereinafter, the timing for the first voltage VA to reach its maximum phase is set to 0°. Furthermore, the timing for the first voltage VA to reach its minimum phase is set to -180°. Therefore, one cycle of the first voltage VA, the second voltage VB, and the third voltage VC is represented by a phase range of -180° or greater but less than 180°. Additionally, for convenience, the timing of the voltage phase is sometimes represented by a phase of 180° or greater. When the voltage phase is represented by a phase of 180° or greater, X° is synonymous with (-180° + (X - 180°)). Here, segments 1 to 6 are defined as periods dividing this one cycle into 6 equal parts. Specifically, when the phase of the first voltage VA is set to "θ°", segments 1 to 6 are defined as periods of 60° intervals as follows.

[0066] Section 1: -30°≤θ°<30°

[0067] Section 2: 30°≤θ°<90°

[0068] Section 3: 90°≤θ°<150°

[0069] Section 4: 150°≤θ°<180° and -180°≤θ°<-150°

[0070] Section 5: -150°≤θ°<-90°

[0071] Section 6: -90°≤θ°<-30°

[0072] Furthermore, each of segments 1 to 6 is subdivided into two periods. In other words, one cycle of three-phase AC power is subdivided into 12 periods. Hereinafter, n is set to an integer greater than or equal to 1 and less than or equal to 6, and this n is set to the number corresponding to the segment. At this time, segment n is subdivided into two periods: segment na and segment nb. In this embodiment, each period is defined as follows.

[0073] • Section na: (X°-30°)≤θ° <X°

[0074] • Section nb: X°≤θ°<(X°+30°)

[0075] Furthermore, X° is the value of the midpoint of the period of segment n. The "midpoint of the period" is the midpoint between the endpoints of each segment represented by a half-open interval. In the definition of segment 4a, X = 180°.

[0076] (3. About vector sequences)

[0077] Hereinafter, the potential difference between the first output terminal 32A and the second output terminal 32B is defined 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 terminals of the first output terminal 32A and the second output terminal 32B is defined 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. Additionally, the direction of the primary current Ip flowing from the first output terminal 32A to the second output terminal 32B is defined as positive. The direction of the primary current Ip flowing from the second output terminal 32B to the first output terminal 32A is defined as negative.

[0078] Furthermore, the phase with the first voltage VA is designated as phase A, the phase with the second voltage VB as phase B, and the phase with the third voltage VC as phase C. Additionally, any one of these three phases is designated as phase i, and the phase different from phase i is designated as phase j. Hereinafter, the voltage difference between phase i and phase j is recorded as "line-to-line voltage Vij".

[0079] The control unit 33 controls the pulse width of each switching signal through space vector pulse width modulation (SVPWM).

[0080] like Figure 3 as well as Figure 4 As shown, in the control using SVPWM, the effective vector and the zero vector Iz are determined. In this embodiment, the effective vector and the zero vector Iz are the current vectors of the power conversion circuit 30 under a given switching state. When m is set to an integer greater than or equal to 1 and less than or equal to 6, the effective vector is represented as a space vector by the formula shown in Mathematical Equation 1 below. In Mathematical Equation 1, "I" is the absolute value of the primary current Ip.

[0081] [Mathematical Expression 1]

[0082]

[0083] Effective vectors can be broadly categorized into positive effective vectors and negative effective vectors.

[0084] Specifically, such as Figure 3 As shown, the positive effective vectors include the first positive effective vector I1+ to the sixth positive effective vector I6+. Each positive effective vector is a current vector when the primary voltage Vp is positive and each bidirectional switch TSW is in the following switching state.

[0085] • First positive effective vector I1+: Second low-side bidirectional switch LS2 is either bidirectionally on or positively on. Furthermore, first high-side bidirectional switch HS1 is either bidirectionally on or positively on. At this time, the primary voltage Vp is the line-to-line voltage VAB.

[0086] • Second positive effective vector I2+: The first high-side bidirectional switch HS1 is in a bidirectional ON state or a positive ON state. Furthermore, the third low-side bidirectional switch LS3 is in a bidirectional ON state or a positive ON state. At this time, the primary voltage Vp is the line-to-line voltage VAC.

[0087] • Third positive effective vector I3+: The third low-side bidirectional switch LS3 is in a bidirectional ON state or a positive ON state. Furthermore, the second high-side bidirectional switch HS2 is in a bidirectional ON state or a positive ON state. At this time, the primary voltage Vp is the line-to-line voltage VBC.

[0088] • Fourth positive effective vector I4+: The second high-side bidirectional switch HS2 is in a bidirectional on state or a positive on state. Furthermore, the first low-side bidirectional switch LS1 is in a bidirectional on state or a positive on state. At this time, the primary voltage Vp is the line-to-line voltage VBA.

[0089] • Fifth positive effective vector I5+: The first low-side bidirectional switch LS1 is in a bidirectional ON state or a positive ON state. Furthermore, the third high-side bidirectional switch HS3 is in a bidirectional ON state or a positive ON state. At this time, the primary voltage Vp is the line-to-line voltage VCA.

[0090] • Sixth positive effective vector I6+: The third high-side bidirectional switch HS3 is in a bidirectional ON state or a positive ON state. Furthermore, the second low-side bidirectional switch LS2 is in a bidirectional ON state or a positive ON state. At this time, the primary voltage Vp is the line-to-line voltage VCB.

[0091] like Figure 4 As shown, the negative effective vectors include the first negative effective vector I1- to the sixth negative effective vector I6-. Each negative effective vector is a current vector when the primary voltage Vp is negative and each bidirectional switch TSW is in the following switching state.

[0092] • First negative effective vector I1-: Second high-side bidirectional switch HS2 is in a bidirectional ON state or a negative ON state. Furthermore, first low-side bidirectional switch LS1 is in a bidirectional ON state or a negative ON state. At this time, the primary voltage Vp is the line-to-line voltage -VAB.

[0093] • Second negative effective vector I2-: The first low-side bidirectional switch LS1 is in a bidirectional ON state or a negative ON state. Furthermore, the third high-side bidirectional switch HS3 is in a bidirectional ON state or a negative ON state. At this time, the primary voltage Vp is the line-to-line voltage -VAC.

[0094] • Third negative effective vector I3-: The third high-side bidirectional switch HS3 is in a bidirectional ON state or a negative ON state. Furthermore, the second low-side bidirectional switch LS2 is in a bidirectional ON state or a negative ON state. At this time, the primary voltage Vp is the line-to-line voltage -VBC.

[0095] • Fourth negative effective vector I4-: The second low-side bidirectional switch LS2 is in a bidirectional ON state or a negative ON state. Furthermore, the first high-side bidirectional switch HS1 is in a bidirectional ON state or a negative ON state. At this time, the primary voltage Vp is the line-to-line voltage -VBA.

[0096] • Fifth negative effective vector I5-: The first high-side bidirectional switch HS1 is in a bidirectional ON state or a negative ON state. Furthermore, the third low-side bidirectional switch LS3 is in a bidirectional ON state or a negative ON state. At this time, the primary voltage Vp is the line-to-line voltage -VCA.

[0097] • Sixth negative effective vector I6-: The third low-side bidirectional switch LS3 is in either bidirectional or negative-side on state. Furthermore, the second high-side bidirectional switch HS2 is in either bidirectional or negative-side on state. At this time, the primary voltage Vp is the line-to-line voltage -VCB.

[0098] In addition, such as Figure 3 as well as Figure 4 As shown, the zero vector Iz includes the 7th zero vector I7, the 8th zero vector I8, and the 9th zero vector I9. The zero vector Iz is the current vector in the following switching states. Furthermore, in the switching state where the zero vector Iz is established, the primary voltage Vp becomes zero. The phrase "the primary voltage Vp is zero" means, for example, an error within ±10V is permissible.

[0099] • 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. Alternatively, 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.

[0100] • 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. Alternatively, 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.

[0101] • 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. Alternatively, 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.

[0102] The reference vector Ir of the current in segment n is approximately the composite vector of the aforementioned effective vector and the zero vector Iz. Specifically, when x=n and y=x+1 (however, when x=6, y=1), the reference vector Ir of the current in segment n is approximately the composite vector of the x-th positive effective vector Ix+, the y-th positive effective vector Iy+, and the zero vector Iz. Alternatively, the reference vector Ir of the current in segment n is approximately the composite vector of the x-th negative effective vector Ix-, the y-th negative effective vector Iy-, and the zero vector Iz. Furthermore, the zero vector Iz is the 7th zero vector I7 in segments 1 and 4. The zero vector Iz is the 9th zero vector I9 in segments 2 and 5. The zero vector Iz is the 8th zero vector I8 in segments 3 and 6.

[0103] In principle, the control unit 33 controls the opening and closing of each bidirectional switch TSW according to the magnitude relationship of the first voltage VA, the second voltage VB and the third voltage VC, so that the reference vector Ir changes in a certain order between the above effective vector or zero vector Iz.

[0104] Specifically, in section na, the control unit 33 controls the on / off state of each bidirectional switch TSW, so that the reference vector Ir follows the vector sequence shown in (na) below. In section nb, the control unit 33 controls the on / off state of each bidirectional switch TSW, so that the reference vector Ir follows the vector sequence shown in (nb) below.

[0105] (na) The order of the x-th positive effective vector Ix+, the y-th positive effective vector Iy+, the zero vector Iz, the x-th negative effective vector Ix-, the y-th negative effective vector Iy-, and the zero vector Iz.

[0106] (nb) The order of the y-th positive effective vector Iy+, the x-th positive effective vector Ix+, the zero vector Iz, the y-th negative effective vector Iy-, the x-th negative effective vector Ix-, and the zero vector Iz.

[0107] Furthermore, within segment na, control unit 33 repeatedly controls the on / off switching of each bidirectional switch TSW based on the vector sequence shown above (na) at a certain period Ts. The duration of this period Ts is very short relative to the duration of each segment na.

[0108] Furthermore, within segment nb, control unit 33 repeats the on / off control of each bidirectional switch TSW based on the vector sequence shown in (nb) with the same period Ts as the vector sequence shown in (na). The duration of this period Ts is very short relative to the duration of each segment nb.

[0109] (4. Regarding the switching sequence)

[0110] The storage device of the control unit 33 stores multiple switch sequences as part of the program PG. Each switch sequence specifies the switching method of the on / off states of multiple bidirectional switches TSW based on each vector sequence. Specifically, each switch sequence specifies a combination of multiple on / off states of each bidirectional switch TSW, and specifies the order of multiple such combinations.

[0111] The following explanation, as an example, describes the on / off control of the bidirectional switch TSW according to the switch sequences in sections 1a, 1b, and 2a. Furthermore, the switch sequence in section na is recorded as switch sequence na, and the switch sequence in section nb is recorded as switch sequence nb.

[0112] (4-1. Regarding the switching sequence 1a)

[0113] like Figure 2 As shown, in segment 1a, among the first voltage VA to the third voltage VC, the first voltage VA is the largest. Furthermore, the third voltage VC is greater than the second voltage VB. Additionally, in segment 1a, the absolute value of the first voltage VA is the largest. And the absolute value of the second voltage VB is greater than the absolute value of the third voltage VC.

[0114] like Figure 3 as well as Figure 4 As shown, in section 1a, the control unit 33 generally controls the on / off state 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.

[0115] (1a) The order of the first positive effective vector I1+, the second positive effective vector I2+, the seventh zero vector I7, the first negative effective vector I1-, the second negative effective vector I2-, and the seventh zero vector I7.

[0116] The following describes the switching sequence 1a of period Ts in segment 1a. For example... Figure 5 As shown, the period Ts of this cycle is from time t0 to time t14. Furthermore, time t0 coincides with time t14 in the immediately preceding period Ts. Therefore, the state immediately preceding time t0 is consistent with the state at time t13 in the immediately preceding period Ts. That is, immediately preceding time t0, the reference vector Ir is the 7th zero vector I7. At this time, the first high-side bidirectional switch HS1 is in a bidirectional on state. Also, the first low-side bidirectional switch LS1 is in a bidirectional on state. Furthermore, the second high-side bidirectional switch HS2 is in a positive on state. The second low-side bidirectional switch LS2 is in a negative on state. The third high-side bidirectional switch HS3 is in a positive on state. The third low-side bidirectional switch LS3 is in a negative on state. Immediately preceding time t0, the primary voltage Vp is approximately zero.

[0117] At time t0 in segment 1a, or in other words, at time t14 in the immediately preceding period Ts, the control unit 33 sets the first low-side bidirectional switch LS1 to the forward-on state. Furthermore, at time t0, the control unit 33 sets the third low-side bidirectional switch LS3 to the off state.

[0118] During the period from time t0 to time t3, the reference vector Ir is the first positive effective vector I1+. The control unit 33 controls the switching elements to turn on and off, so that at time t3, the reference vector Ir changes to the second positive effective vector I2+.

[0119] Specifically, at time t1, the control unit 33 sets the second low-side bidirectional switch LS2 to the bidirectional ON state. Then, at time t2, the control unit 33 sets the third low-side bidirectional switch LS3 to the OFF state. At time t3, the control unit 33 sets the second low-side bidirectional switch LS2 to the OFF state. Furthermore, from time t0 to time t1, the primary voltage Vp rises from zero to the line-to-line voltage VAB. During the period from time t1 to time t3, the primary voltage Vp remains approximately constant at the line-to-line voltage VAB.

[0120] During the period from time t3 to time t5, the reference vector Ir is the second positive effective vector I2+. The control unit 33 controls the switching elements to turn on and off, so that at time t5, the reference vector Ir changes to the seventh zero vector I7.

[0121] Specifically, at time t4, the control unit 33 sets the third low-side bidirectional switch LS3 to the bidirectional ON state. At time t5, the control unit 33 sets the third low-side bidirectional switch LS3 to the negative ON state. Furthermore, from time t3 to time t4, the primary voltage Vp decreases from the line-to-line voltage VAB to the line-to-line voltage VAC. During the period from time t4 to time t5, the primary voltage Vp remains approximately constant at the line-to-line voltage VAC.

[0122] During the period from time t5 to time t7, the reference vector Ir is the 7th zero vector I7. The control unit 33 performs on / off control on each switching element, so that at time t7, the reference vector Ir changes to the 1st negative effective vector I1-.

[0123] Specifically, at time t6, control unit 33 sets the first low-side bidirectional switch LS1 to the bidirectional ON state. At time t7, control unit 33 sets the first high-side bidirectional switch HS1 to the negative ON state. Also, at time t7, control unit 33 sets the third high-side bidirectional switch HS3 to the OFF state. Furthermore, from time t5 to time t6, the primary voltage Vp drops from the line-to-line voltage VAC to zero. During the period from time t6 to time t7, the primary voltage Vp is approximately zero.

[0124] During the period from time t7 to time t10, the reference vector Ir is the first negative effective vector I1-. The control unit 33 performs on / off control on each switching element, so that at time t10, the reference vector Ir changes to the second negative effective vector I2-.

[0125] Specifically, at time t8, control unit 33 sets the second high-side bidirectional switch HS2 to the bidirectional ON state. At time t9, control unit 33 sets the third high-side bidirectional switch HS3 to the negative ON state. At time t10, control unit 33 sets the second high-side bidirectional switch HS2 to the positive ON state.

[0126] From time t7 to time t8, the primary voltage Vp drops from zero to the line-to-line voltage VBA. During the period from time t8 to time t10, the primary voltage Vp remains approximately constant at the line-to-line voltage VBA. Furthermore, in... Figures 5-7 For convenience, the line-to-line voltage Vij is labeled as "-Vji".

[0127] like Figure 5 As shown, during the period from time t10 to time t12, the reference vector Ir is the second negative effective vector I2-. The control unit 33 performs on / off control on each switching element, so that at time t12, the reference vector Ir changes to the seventh zero vector I7.

[0128] Specifically, at time t11, the control unit 33 sets the third high-side bidirectional switch HS3 to the bidirectional on state. At time t12, the control unit 33 sets the third high-side bidirectional switch HS3 to the forward on state. Furthermore, from time t10 to time t11, the primary voltage Vp rises from the line-to-line voltage VBA to the line-to-line voltage VCA. During the period from time t11 to time t12, the primary voltage Vp remains approximately constant at the line-to-line voltage VCA.

[0129] During the period from time t12 to time t14, the reference vector Ir is the 7th zero vector I7. As described above, the on / off state of each switching element at time t14 is consistent with that at time t0. That is, the control unit 33 performs on / off control on each switching element, so that at time t0 of the next cycle Ts, the reference vector Ir changes to the 1st positive effective vector I1+.

[0130] Specifically, at time t13, the control unit 33 sets the first high-side bidirectional switch HS1 to the bidirectional ON state. At time t14, the control unit 33 sets the first low-side bidirectional switch LS1 to the OFF state. Furthermore, the control unit 33 sets the third low-side bidirectional switch LS3 to the OFF state. At the time of switch switching at t14, one cycle Ts ends.

[0131] Furthermore, from time t12 to time t13, the primary voltage Vp rises from the line-to-line voltage VCA to zero. During the period from time t13 to time t14, the primary voltage Vp is zero.

[0132] (4-2. Regarding switch sequence 1b)

[0133] like Figure 2 As shown, in segment 1b, among the first voltage VA to the third voltage VC, the first voltage VA is the largest. Furthermore, the second voltage VB is greater than the third voltage VC. Additionally, in segment 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.

[0134] like Figure 3 as well as Figure 4 As shown, in section 1b, the control unit 33 controls the on / off state of each bidirectional switch TSW in principle, 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.

[0135] (1b) The order of the second positive effective vector I2+, the first positive effective vector I1+, the seventh zero vector I7, the second negative effective vector I2-, the first negative effective vector I1-, and the seventh zero vector I7.

[0136] Therefore, the mode of switching on and off according to the switching sequence 1b performed by the control unit 33 becomes as follows, depending on the magnitude relationship of each voltage and the vector sequence.

[0137] like Figure 5 as well as Figure 6As shown, the switching mode of the first high-side bidirectional switch HS1 in section 1b, controlled by the control unit 33, is the same as the switching mode of the first high-side bidirectional switch HS1 in section 1a. The switching mode of the first low-side bidirectional switch LS1 in section 1b is the same as the switching mode of the first low-side bidirectional switch LS1 in section 1a.

[0138] The on / off control mode of the second high-side bidirectional switch HS2 in section 1b is the same as the on / off control mode of the third high-side bidirectional switch HS3 in section 1a. The on / off control mode of the second low-side bidirectional switch LS2 in section 1b is the same as the on / off control mode of the third low-side bidirectional switch LS3 in section 1a.

[0139] The on / off control mode of the third high-side bidirectional switch HS3 in section 1b is the same as the on / off control mode of the second high-side bidirectional switch HS2 in section 1a. The on / off control mode of the third low-side bidirectional switch LS3 in section 1b is the same as the on / off control mode of the second low-side bidirectional switch LS2 in section 1a.

[0140] In addition, such as Figure 6 As shown, in segment 1b, the value of the primary voltage Vp during the period when the reference vector Ir is the second positive effective vector I2+ is the line-to-line voltage VAC. The value of the primary voltage Vp during the period when the reference vector Ir is the first positive effective vector I1+ is the line-to-line voltage VAB. The value of the primary voltage Vp during the period when the reference vector Ir is the second negative effective vector I2- is the line-to-line voltage VBA. The value of the primary voltage Vp during the period when the reference vector Ir is the first negative effective vector I1- is the line-to-line voltage VBA.

[0141] (4-3. Regarding the switching sequence 2a)

[0142] like Figure 2 As shown, in segment 2a, among the first voltage VA to the third voltage VC, the first voltage VA is the largest. Furthermore, the second voltage VB is greater than the third voltage VC. Additionally, in segment 2a, the third voltage VC has the largest absolute value. Moreover, the absolute value of the first voltage VA is greater than the absolute value of the second voltage VB.

[0143] like Figure 3 as well as Figure 4 As shown, in section 2a, the control unit 33 controls the on / off state of each bidirectional switch TSW in principle, 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.

[0144] (2a) The order of the second positive effective vector I2+, the third positive effective vector I3+, the ninth zero vector I9, the second negative effective vector I2-, the third negative effective vector I3-, and the ninth zero vector I9.

[0145] Therefore, the mode of switching on and off according to the switching sequence 2a performed by the control unit 33 is as follows, depending on the magnitude relationship of each voltage and the vector sequence.

[0146] like Figure 5 as well as Figure 7 As shown, the mode of controlling the on / off state of the first high-side bidirectional switch HS1 in section 2a, performed by the control unit 33, is the same as the mode of controlling the on / off state of the second low-side bidirectional switch LS2 in section 1a.

[0147] The on / off control mode of the second high-side bidirectional switch HS2 in section 2a is the same as the on / off control mode of the third low-side bidirectional switch LS3 in section 1a.

[0148] The on / off control mode of the third high-side bidirectional switch HS3 in section 2a is the same as the on / off control mode of the first low-side bidirectional switch LS1 in section 1a.

[0149] In addition, such as Figure 7 As shown, in segment 2a, the value of the primary voltage Vp during the period when the reference vector Ir is the second positive effective vector I2+ is the line-to-line voltage VAC. The value of the primary voltage Vp during the period when the reference vector Ir is the third positive effective vector I3+ is the line-to-line voltage VBC. The value of the primary voltage Vp during the period when the reference vector Ir is the second negative effective vector I2- is the line-to-line voltage VCA. The value of the primary voltage Vp during the period when the reference vector Ir is the third negative effective vector I3- is the line-to-line voltage VCB.

[0150] (5. Switching control of switch sequences)

[0151] Next, the switching control from any switch sequence to different switch sequences will be explained.

[0152] Hereinafter, any switch sequence before switching is designated as the first switch sequence. Furthermore, a switch sequence that specifies the switching method for the on / off states of multiple bidirectional switches (TSWs) in a manner different from the first switch sequence, and which switches from the aforementioned first switch sequence, is designated as the second switch sequence. In other words, the first switch sequence specifies multiple combinations related to the on / off states of the multiple bidirectional switches (TSWs) and the order in which these combinations are switched. The second switch sequence specifies multiple combinations related to the on / off states of the multiple bidirectional switches (TSWs) and the order in which these combinations are switched, in a manner different from the first switch sequence.

[0153] When the on / off state of the bidirectional switch TSW carrying current in the control according to the first switch sequence is consistent with the on / off state of the bidirectional switch TSW carrying current in the control according to the second switch sequence after the switch is switched, the control unit 33 switches from control according to the first switch sequence to control according to the second switch sequence.

[0154] Furthermore, the so-called "bidirectional switch TSW that carries current in control according to the switching sequence" refers to a bidirectional switch TSW that actually carries current through electromotive force in control according to each switching sequence. That is, the aforementioned "bidirectional switch TSW that carries current" is theoretically not a combination of bidirectional switch TSWs that can conduct current. In other words, the combination of such bidirectional switch TSWs is a combination that satisfies the following conditions (A) and (B).

[0155] (A) A combination of bidirectional switches TSW that become the current conduction path at a specific moment in the first switching sequence and also become the current conduction path at a specific moment in the second switching sequence.

[0156] (B) A combination of bidirectional switches TSW that satisfies (A) and whose on / off state when current flows at the specific time in the first switch sequence is consistent with the on / off state when current flows at the specific time in the second switch sequence.

[0157] The following examples illustrate the switching control from switch sequence 1a to switch sequence 1b and the switching control from switch sequence 1b to switch sequence 2a.

[0158] Furthermore, the combination of the on / off states of the bidirectional switch TSW at each time point in each switch sequence is called a "switch state". As described above, in each switch sequence, the switch state is switched at each time point from t1 to t14. That is, each switch sequence contains 14 switch states. Here, we set k = (n-1) × 28. At this time, the 14 switch states specified by the switch sequence na are set as switch states (k+1) to (k+14). In addition, the 14 switch states specified by the switch sequence nb are set as switch states (k+15) to (k+28).

[0159] For example, the switch sequence 6b of segment 6b specifies switch states 155 through 168, and their order. In segment 6b, the switch state from time t0 to time t1 is switch state 155. The switch state from time t13 to time t14 is switch state 168.

[0160] (5-1. Switching control from switch sequence 1a to switch sequence 1b)

[0161] After the period transitions from segment 1a to segment 1b, control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b. That is, during the aforementioned period transition, control unit 33 sets switch sequence 1a as the "first switch sequence" and switch sequence 1b as the "second switch sequence" to perform switching control.

[0162] As described above, during segment 1a, i.e., when the absolute value of the second voltage VB is greater than the absolute value of the third voltage VC, the control unit 33, in principle, controls each bidirectional switch TSW according to the switching sequence 1a. Figure 8 As shown, switch sequence 1a specifies the 1st to 14th switch states and their order.

[0163] Furthermore, during the period of section 1b, i.e., when the absolute value of the second voltage VB is less than the absolute value of the third voltage VC, the control unit 33, in principle, controls each bidirectional switch TSW according to the switching sequence 1b. For example... Figure 8 As shown, switch sequence 1b specifies the 15th to 28th switch states and their order.

[0164] like Figure 5 as well as Figure 6 As shown, one or more of the switch states contained in switch sequence 1b are consistent with the switch states contained in switch sequence 1a.

[0165] Specifically, such as Figure 10 as well as Figure 11As shown, the combinations of the on / off states of the bidirectional switch TSW are all identical for the 7th and 14th switch states of switch sequence 1a and the 21st and 28th switch states of switch sequence 1b. That is, in the above four switch states, the on / off states of the bidirectional switch TSW flowing with current are identical when controlled according to each switch sequence. Furthermore, in Figures 10-15 In this diagram, the switching elements of each bidirectional switch (TSW) are simplified and illustrated. That is, for convenience, each switching element is illustrated as a single-pole single-throw (SPST) switch.

[0166] In addition, such as Figure 9 As shown, in the control according to each switch sequence, the combination of bidirectional switches TSW that become the current conduction path and have the same on / off state is the combination of the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1. At this time, the primary current Ip flows through the first high-side bidirectional switch HS1 and the first low-side bidirectional switch LS1.

[0167] Therefore, when the switch state becomes the 7th switch state or the 14th switch state in the control according to the switch sequence 1a, the control unit 33 switches to the control according to the switch sequence 1b.

[0168] More specifically, if the switch state at the time point of transition from the period of segment 1a to the period of segment 1b is any of the 1st to 6th switch states, the control unit 33 continues control according to the switch sequence 1a. Furthermore, when the switch state initially changes to the 7th switch state, the control unit 33 switches to control according to the switch sequence 1b. In this embodiment, the control unit 33 controls the bidirectional switch TSW such that at the time t7, when switching from the 7th switch state to the next switch state, it switches to the 22nd switch state. In other words, instead of switching from the 7th switch state to the 8th switch state in the switch sequence 1a, the control unit 33 switches to the 22nd switch state in the switch sequence 1b.

[0169] Furthermore, if the switch state at the point of transition from the period of segment 1a to the period of segment 1b is any of the 8th to 13th switch states, the control unit 33 continues control according to the switch sequence 1a. Moreover, when the switch state initially changes to the 14th switch state, the control unit 33 switches to control according to the switch sequence 1b. In this embodiment, the control unit 33 controls the bidirectional switch TSW such that at the moment t14, when switching from the 14th switch state to the next switch state, it switches to the 15th switch state. In other words, instead of switching from the 14th switch state of switch sequence 1a to the 1st switch state, the control unit 33 switches to the 15th switch state of switch sequence 1b.

[0170] Furthermore, by controlling the primary voltage Vp as described above, the control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b when the primary voltage Vp is less than 5% of the amplitude of the first voltage VA. In this embodiment, the amplitude of the first voltage VA is 200V. Therefore, when the primary voltage Vp is -10V or higher, or +10V or lower, the control unit 33 switches from control according to switch sequence 1a to control according to switch sequence 1b. Additionally, as described above, in this embodiment, the primary voltage Vp is theoretically approximately zero during the period from time t6 to time t7.

[0171] Furthermore, if the switch state at the time point when the transition from the period of segment 1a to the period of segment 1b is the 7th switch state, the control unit 33 switches to control according to the 21st switch state. If the switch state at the same time point is the 14th switch state, the control unit 33 switches to control according to the 28th switch state.

[0172] (5-2. Switching control from switch sequence 1b to switch sequence 2a)

[0173] After the transition from the period of segment 1b to the period of segment 2a, the control unit 33 switches from control according to switch sequence 1b to control according to switch sequence 2a. That is, during the transition of the aforementioned periods, the control unit 33 sets switch sequence 1b as the "first switch sequence" and sets switch sequence 2a as the "second switch sequence" to perform switching control.

[0174] As described above, during segment 2a, i.e., when the absolute value of the first voltage VA is less than the absolute value of the third voltage VC, the control unit 33, in principle, controls each bidirectional switch TSW according to the switching sequence 2a. Figure 8 As shown, the switch sequence 2a of section 2a specifies the 29th to 42nd switch states and their order.

[0175] like Figure 6 as well as Figure 7 As shown, in the control according to switch sequence 1b and the control according to switch sequence 2a, there exists a combination of bidirectional switch TSWs that both satisfy the conditions (A) and (B) above. That is, there exists a combination of bidirectional switch TSWs that together form the current conduction path in each of the above controls and whose on / off states are also consistent.

[0176] Specifically, such as Figure 12 As shown, in the control according to switch sequence 1b, in the 16th switching state, the first high-side bidirectional switch HS1 is in a bidirectional on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state. Therefore, in the 16th switching state, current flows through the first high-side bidirectional switch HS1 and the third low-side bidirectional switch LS3.

[0177] like Figure 13 As shown, in the control according to switch sequence 2a, in the 30th switching state, the first high-side bidirectional switch HS1 is in a bidirectional on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state. Therefore, in the 30th switching state, current flows through the first high-side bidirectional switch HS1 and the third low-side bidirectional switch LS3.

[0178] Therefore, the on / off state of the bidirectional switch TSW that carries current in the 16th switching state controlled according to switch sequence 1b is consistent with the on / off state of the bidirectional switch TSW that carries current in the 30th switching state controlled according to switch sequence 2a.

[0179] like Figure 14 As shown, in the control according to switch sequence 1b, in the 23rd switching state, the first low-side bidirectional switch LS1 is in a bidirectional on state, and the third high-side bidirectional switch HS3 is in a bidirectional on state. Therefore, in the 23rd switching state, current flows through the first low-side bidirectional switch LS1 and the third high-side bidirectional switch HS3.

[0180] like Figure 15 As shown, in the control according to switch sequence 2a, in the 37th switching state, the first low-side bidirectional switch LS1 is in a bidirectional on state, and the third high-side bidirectional switch HS3 is in a bidirectional on state. Therefore, in the 37th switching state, current flows through the first low-side bidirectional switch LS1 and the third high-side bidirectional switch HS3.

[0181] That is, the on / off state of the bidirectional switch TSW that carries current in the 23rd switching state controlled according to switch sequence 1b is consistent with the on / off state of the bidirectional switch TSW that carries current in the 37th switching state controlled according to switch sequence 2a.

[0182] Therefore, when the switch state changes to the 16th or 23rd switch state during control according to switch sequence 1b, control unit 33 switches to control according to switch sequence 2a. In this embodiment, when control unit 33 switches the switch state from the 15th switch state to the next switch state during control according to switch sequence 1b, it switches to control according to switch sequence 2a. Alternatively, when control unit 33 switches the switch state from the 23rd switch state to the next switch state during control according to switch sequence 1b, it switches to control according to switch sequence 2a.

[0183] More specifically, if the switch state at the time point of transition from the period of segment 1b to the period of segment 2a is either the 15th switch state or any of the 23rd to 28th switch states, the control unit 33 continues control according to the switch sequence 1b. Furthermore, when the switch state initially becomes the 16th switch state, the control unit 33 switches to control according to the switch sequence 2b. In other words, instead of switching from the 15th switch state to the 16th switch state, the control unit 33 switches from the 15th switch state to the 30th switch state of the switch sequence 2a. Thus, in this embodiment, the control unit 33 controls the bidirectional switch TSW such that at the time t1 when switching from the 15th switch state to the next switch state, it switches to the 30th switch state.

[0184] Furthermore, if the switch state at the point of transition from the period of segment 1b to the period of segment 2a is any of the 16th to 22nd switch states, the control unit 33 continues control according to the switch sequence 1b. Moreover, when the switch state initially changes to the 23rd switch state, the control unit 33 switches to control according to the switch sequence 2b. In other words, instead of switching from the 22nd switch state to the 23rd switch state, the control unit 33 switches from the 22nd switch state to the 37th switch state of the switch sequence 2a. Thus, in this embodiment, the control unit 33 controls the bidirectional switch TSW such that at the moment t8 when switching from the 22nd switch state to the next switch state, it switches to the 37th switch state.

[0185] Here, among the potential differences between the first voltage VA and the second voltage VB, the first voltage VA and the third voltage VC, and the second voltage VB and the third voltage VC in the control according to each switching sequence, the potential difference with the largest absolute value is set as the maximum line-to-line voltage Vm. In the control under switching sequence 1b, the maximum line-to-line voltage Vm is either the line-to-line voltage VAC or the line-to-line voltage VCA. In the control under switching sequence 2a, the maximum line-to-line voltage Vm is either the line-to-line voltage VAC or the line-to-line voltage VCA.

[0186] Specifically, immediately before the switch at time t1 from control according to switch sequence 1b to control according to switch sequence 2a, the primary voltage Vp is approximately equal to the line-to-line voltage VAC. Furthermore, immediately after the switch, the primary voltage Vp becomes the line-to-line voltage VAC. Additionally, the direction and conduction path of the primary current Ip remain consistent before and after the switch.

[0187] Furthermore, immediately before the switch at time t8 from control according to switching sequence 1b to control according to switching sequence 2a, the primary voltage Vp and the line-to-line voltage VCA are approximately equal. Moreover, immediately after the switch, the primary voltage Vp becomes the line-to-line voltage VCA. Additionally, the direction and conduction path of the primary current Ip are approximately the same before and after the switch.

[0188] By controlling as described above, the control unit 33 switches from control according to the first switching sequence to control according to the second switching sequence when the primary voltage Vp is the maximum line-to-line voltage Vm. Furthermore, "when the primary voltage Vp is the maximum line-to-line voltage Vm" means when the value of the maximum line-to-line voltage Vm is output as the primary voltage Vp. Therefore, by setting the maximum line-to-line voltage Vm as a central value, an error within ±0.5% of the amplitude of the maximum line-to-line voltage Vm is allowed.

[0189] (6. Regarding the function of this implementation method)

[0190] In the above embodiment, a combination of bidirectional switches (TSWs) that satisfies both conditions (A) and (B) above is predetermined. Furthermore, when the control unit 33 switches from control according to the first switch sequence to control according to the second switch sequence, it uses this determined combination of bidirectional switches (TSWs) to perform the switching.

[0191] If the switching sequence is switched when the on / off states of the aforementioned bidirectional switches (TSWs) are inconsistent before and after the switch, the current path becomes different before and after the switch. Furthermore, switching a switch element that is on and conducting current to the off state sometimes applies electrical stress to that switch element. "Applying electrical stress" refers to applying a larger electrical load compared to switching a switch element that is on and not conducting current to the off state—in other words, performing zero-current or zero-voltage switching. Moreover, when switching the on / off states of multiple switch elements, even if theoretically designed to switch on and off simultaneously, in reality, there is a time difference in the timing of switching on and off states for each switch element. Therefore, since there is a momentary absence of a current conduction path in the circuit, overvoltages such as surge voltages may occur. Furthermore, since a short-circuit path for current is created in the circuit, short-circuit current may flow.

[0192] In this embodiment, the current direction and conduction path are consistent for the aforementioned combination of bidirectional TSWs, and the switch on / off states are also consistent. Therefore, even when switching the switch sequence in this combination of bidirectional TSWs, it is not easy to generate electrical stress on the switching elements. Furthermore, overvoltage and short-circuit current are less likely to occur.

[0193] (7. Regarding the effects of this implementation method)

[0194] (1) In the above embodiment, in the control of each switching sequence before and after switching, there is a combination of bidirectional switches (TSWs) that serve as the conduction path for current and have the same on / off state. Moreover, the control unit 33 switches the switching sequence in the combination of bidirectional switches (TSWs). As a result, it is possible to suppress the application of electrical stress to the switching elements constituting the bidirectional switches (TSWs).

[0195] (2) In the above embodiment, after the magnitude relationship of the input voltage is changed, the switching sequence is switched when the on / off states of the bidirectional switch TSW flowing through the current in the control based on the switching sequence before and after the switch is switched are initially consistent. Thus, it is possible to quickly switch to control according to the switching sequence corresponding to the magnitude relationship of the input voltage while suppressing the application of electrical stress to the switching elements.

[0196] (3) In the above embodiment, before and after the switching sequence is switched, the primary voltage Vp is less than 5% of the amplitude of the first voltage VA. Alternatively, before and after the switching sequence is switched, the primary voltage Vp is the maximum line-to-line voltage Vm. In this way, by keeping the primary voltage Vp approximately the same before and after the switching sequence is switched, the value of the primary voltage Vp does not change drastically. As a result, noise is less likely to be generated in the output voltage applied to the load 70.

[0197] (4) According to the above embodiment, each bidirectional switch TSW has two switching elements connected in series, with the terminals of the anode side of the body diode connected to each other. According to this structure, the power conversion circuit 30 can be constructed relatively easily and inexpensively.

[0198] <Example of Change>

[0199] The above-described embodiments and the following modifications can be combined with each other to implement them within the scope of technical inconsistency.

[0200] (Examples of structural modifications related to power conversion devices)

[0201] The structure of the power conversion device 10 is not limited to the examples of the embodiments described above. For example, the power conversion device 10 is not limited to three-phase insulated AC-DC converters, but can also be applied to non-insulated three-phase AC-DC converters. That is, the power conversion device 10 may not include more than one of the input-side low-pass filter 20, transformer circuit 40, rectifier circuit 50, and output-side low-pass filter 60.

[0202] Furthermore, the three-phase AC power supply 80 connected to the three external input terminals 11 is not limited to a three-phase 3-wire type; it can also be a three-phase 4-wire type or a three-phase 3-wire type with delta connection. The structure of the power conversion device 10 can also be appropriately modified according to the type of three-phase AC power supply 80.

[0203] The input-side low-pass filter 20 may also include multiple capacitors connected between the lines of each phase of the input first voltage VA, second voltage VB and third voltage VC.

[0204] The switching elements constituting each bidirectional switch TSW are not limited to the examples of the embodiments described above. For example, the two switching elements of the bidirectional switch TSW may also be P-channel MOSFETs. In this case, the drain terminals of the two switching elements of the bidirectional switch TSW are connected to each other.

[0205] Furthermore, the two switching elements of a bidirectional switch (TSW) can also be transistors capable of both forward and reverse current flow. In this case, the two switching elements are connected in series with their source terminals connected to each other. Specifically, the switching element is a gallium nitride high electron mobility transistor (GaN-HEMT), etc.

[0206] • The transformer circuit 40 may also omit 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.

[0207] The specific circuit structure of the rectifier circuit 50 is not limited to the examples described above. For example, the rectifier circuit 50 could also be a half-wave rectifier circuit, etc.

[0208] The duration of each segment is not limited to the examples described in the above embodiments. For example, each segment can be divided into 4 segments, thereby dividing the whole into 24 periods. In such a case, the above embodiments can also be applied.

[0209] (Example of changes related to the switching control of switch sequences)

[0210] • The switch sequence switching control is not limited to the examples of the above embodiments. For example, the switching control from switch sequence 1a to switch sequence 1b can be modified as follows (Example 1) to (Example 4). The switching control from switch sequence 1b to switch sequence 2a can be modified as follows (Example 5) to (Example 7). However, the timing of switching the switch sequence is preferably switched during a switch state with a sufficiently long period. For example, rather than switching to the second switch sequence during the (k+4)th switch state between time t3 and time t4 of the first switch sequence, it is preferable to switch to the second switch sequence during the (k+5)th switch state between time t4 and time t5.

[0211] • Regarding the switching control from switch sequence 1a to switch sequence 1b

[0212] (Example 1) The control unit 33 can also control the bidirectional switch TSW so that at the moment t7 when switching from the 7th switch state to the next switch state, it switches to the 15th switch state.

[0213] (Example 2) The control unit 33 can also control the bidirectional switch TSW, causing it to switch from the 7th switch state to the 21st switch state or the 28th switch state. At this time, it can also be controlled so that the time point t7 of the switch sequence 1a becomes the time point t6 of the switch sequence 1b, or during the period from the time point t6 to the time point t7 of the switch sequence 1a, the process of the program PG can switch from the switch sequence 1a to the switch sequence 1b.

[0214] (Example 3) In each switch sequence, the combination of the on / off states of the bidirectional switch TSW is identical for the 6th switch state of switch sequence 1a and the 20th switch state of switch sequence 1b. Therefore, for example, it is also possible to switch to switch sequence 1b at the moment t6 when switching from the 6th switch state to the next switch state. In other words, the control unit 33 can also switch to the 21st or 28th switch state of switch sequence 1b instead of switching to the 7th switch state of switch sequence 1a.

[0215] (Example 4) In each switch sequence, the combination of the on / off states of the bidirectional switch TSW is identical for the 13th switch state of switch sequence 1a and the 27th switch state of switch sequence 1b. Similarly, in this case, for example, the control unit 33 can switch from the 13th switch state to the 14th switch state and instead switch to the 28th switch state of switch sequence 1b.

[0216] In any of the cases (Example 1) to (Example 4), when switch sequence 1a is set as "first switch sequence" and switch sequence 1b is set as "second switch sequence", the switch is switched from control according to the first switch sequence to control according to the second switch sequence when the on / off state of the bidirectional switch TSW that carries current under control according to the first switch sequence is the same as the on / off state of the bidirectional switch TSW that carries current under control according to the switched second switch sequence.

[0217] • Regarding the switching control from switch sequence 1b to switch sequence 2a

[0218] (Example 5) The control unit 33 can also control the bidirectional switch TSW, so that it switches from the 16th switch state to the 30th switch state. At this time, it can also control the time point t2 of switch sequence 1b to become the time point t1 of switch sequence 2a, or switch from switch sequence 1b to switch sequence 2a in the processing of program PG during the period from time point t1 to time point t2 of switch sequence 1b.

[0219] (Example 6) In each switch sequence, the combination of the on / off states of the bidirectional switch TSW is identical for the 17th switch state of switch sequence 1b and the 31st switch state of switch sequence 2a. Therefore, in the switching control of the switch sequence, it is also possible to switch to switch sequence 2a at the time t2 when switching from the 16th switch state to the next switch state. In other words, the control unit 33 can also switch to the 31st switch state of switch sequence 2a instead of switching from the 16th switch state to the 17th switch state. Furthermore, it is also possible to switch from switch sequence 1b to switch sequence 2a in the processing of program PG during the period from time t2 to time t3 of switch sequence 1b.

[0220] (Example 7) In each switch sequence, the combination of the on / off states of the bidirectional switch TSW is identical for the 24th switch state of switch sequence 1b and the 38th switch state of switch sequence 2a. Similarly, in this case, the switch can be initiated at time t9 when switching from the 23rd switch state to the next switch state. In other words, the control unit 33 can also switch to the 38th switch state of switch sequence 2a instead of switching from the 23rd switch state to the 24th switch state. Furthermore, the switch can be initiated from switch sequence 1b to switch sequence 2a during the processing of program PG between time t9 and time t10 of switch sequence 1b.

[0221] In any of the cases (Example 5) to (Example 7), when switch sequence 1b is set as "first switch sequence" and switch sequence 2a is set as "second switch sequence", the switch is switched from control according to the first switch sequence to control according to the second switch sequence when the on / off state of the bidirectional switch TSW that carries current under control according to the first switch sequence is the same as the on / off state of the bidirectional switch TSW that carries current under control according to the switched second switch sequence.

[0222] ·like Figure 9 As shown, the switch sequence before the switch is set as the "first switch sequence" mentioned above, and the switch sequence after the switch is set as the "second switch sequence". In the switching of other switch sequences, it can also be applied as in the following example.

[0223] For example, in the switching control from switch sequence 2a to switch sequence 2b, switch sequence 2a is designated as "first switch sequence" and switch sequence 2b is designated as "second switch sequence". During segment 2a, that is, during the period when the first voltage VA is at its maximum and the absolute value of the first voltage VA is greater than the absolute value of the second voltage VB, the control unit 33 controls each bidirectional switch TSW according to switch sequence 2a. After the transition to segment 2b, that is, after the absolute value of the second voltage VB becomes greater than the absolute value of the first voltage VA, when the initial combination is consistent, the switch can be made to switch sequence 2b.

[0224] Furthermore, for example, in the switching control from switch sequence 2b to switch sequence 3a, switch sequence 2b is designated as "first switch sequence" and switch sequence 3a is designated as "second switch sequence". During segment 2b, that is, during the period when the second voltage VB is at its maximum and the absolute value of the third voltage VC is greater than the absolute value of the second voltage VB, the control unit 33 controls each bidirectional switch TSW according to switch sequence 2b. After the transition to segment 3a, that is, after the absolute value of the second voltage VB becomes greater than the absolute value of the third voltage VC, when the initial combination is consistent, the switch can be made to switch sequence 3a.

[0225] <Postscript>

[0226] The technical concepts that can be grasped based on the above-described embodiments and variations are described.

[0227] [1] A power conversion circuit comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, wherein a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, are input one-to-one; a plurality of bidirectional switches respectively connected to the first input terminal, the second input terminal, and the third input terminal; a first output terminal and a second output terminal connected to the plurality of bidirectional switches, capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence, wherein the first switch sequence specifies a sequence corresponding to the plurality of bidirectional switches. The second switch sequence defines multiple combinations related to the on / off states of the multiple bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch flowing with current under the control of the first switch sequence is consistent with the on / off state of the bidirectional switch flowing with current under the control of the switched second switch sequence, the control unit switches from control according to the first switch sequence to control according to the second switch sequence.

[0228] [2] In the power conversion circuit described in [1], the control unit performs the following processing: during the period when the absolute value of the second voltage is greater than the absolute value of the third voltage, each of the bidirectional switches is controlled according to the first switching sequence; after the absolute value of the third voltage becomes greater than the absolute value of the second voltage, and when the on / off state of the bidirectional switch that carries current in the control according to the first switching sequence is consistent with the on / off state of the bidirectional switch that carries current in the combination of the control according to the switched second switching sequence, the control is switched from the control according to the first switching sequence to the control according to the second switching sequence.

[0229] [3] In the power conversion circuit described in [2], when the potential difference between the first output terminal and the second output terminal is less than 5% of the amplitude of the first voltage, the control unit switches from control according to the first switching sequence to control according to the second switching sequence.

[0230] [4] In any of the power conversion circuits described in [1] to [3], if one or more of the combinations included in the second switch sequence are the same as the combinations included in the first switch sequence, the control unit switches from control according to the first switch sequence to control according to the second switch sequence when the combination in the control according to the first switch sequence is the same as the combination included in the second switch sequence.

[0231] [5] In the power conversion circuit described in any of [1] to [4], the control unit performs the following processing: during the period when the absolute value of the first voltage is greater than the absolute value of the third voltage, each of the bidirectional switches is controlled according to the first switching sequence; after the absolute value of the third voltage becomes greater than the absolute value of the first voltage, and when the on / off state of the bidirectional switch through which current flows in the control according to the first switching sequence is consistent with the on / off state of the bidirectional switch through which current flows in the combination of the control according to the switched second switching sequence, the control is switched from the control according to the first switching sequence to the control according to the second switching sequence.

[0232] [6] In the power conversion circuit described in [5], when the maximum line-to-line voltage is set as the maximum potential difference among the potential difference between the first voltage and the second voltage, the potential difference between the first voltage and the third voltage, and the potential difference between the second voltage and the third voltage, the control unit switches from control according to the first switching sequence to control according to the second switching sequence when the potential difference between the first output terminal and the second output terminal is the maximum line-to-line voltage.

[0233] [7] In any of the power conversion circuits described in [1] to [6], the bidirectional switch has two switching elements connected in series as terminals on the anode side of a body diode.

[0234] [8] A program for a power conversion circuit, applied to a power conversion circuit comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, wherein a first voltage, a second voltage, and a third voltage, being AC voltages of different phases, are input one-to-one; a plurality of bidirectional switches connected to the first input terminal, the second input terminal, and the third input terminal respectively; a first output terminal and a second output terminal capable of outputting AC power; and a control unit capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence, wherein the first switch sequence specifies a sequence corresponding to the first phase ... The second switch sequence defines multiple combinations related to the on / off states of the multiple bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch flowing with current under the control of the first switch sequence is consistent with the on / off state of the bidirectional switch flowing with current under the control of the switched second switch sequence, the program causes the control unit to switch from control according to the first switch sequence to control according to the second switch sequence.

[0235] Explanation of reference numerals in the attached figures

[0236] 10…Power conversion device

[0237] 30…Power Conversion Circuit

[0238] 31A… Input Terminal 1

[0239] 31B…Second Input Terminal

[0240] 31C…Third Input Terminal

[0241] 32A… Output Terminal 1

[0242] 32B…Second Output Terminal

[0243] 33…Control Department

[0244] TSW…bidirectional switch

[0245] 80… Three-phase AC power supply.

Claims

1. A power conversion circuit, comprising: The first input terminal, the second input terminal, and the third input terminal are connected to a three-phase AC power supply, and the first voltage, the second voltage, and the third voltage, which are AC voltages of different phases, are input one-to-one. Multiple bidirectional switches are respectively connected to the first input terminal, the second input terminal, and the third input terminal; The first output terminal and the second output terminal are connected to the plurality of bidirectional switches and are capable of outputting AC power; and The control unit is capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence. The first switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched. The second switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch carrying current under control according to the first switch sequence is consistent with the on / off state of the bidirectional switch carrying current under control according to the second switch sequence after the switch is switched, the control unit switches from control according to the first switch sequence to control according to the second switch sequence.

2. The power conversion circuit according to claim 1, wherein, The control unit performs the following processing: During the period when the absolute value of the second voltage is greater than the absolute value of the third voltage, each of the bidirectional switches is controlled according to the first switching sequence. After the absolute value of the third voltage becomes greater than the absolute value of the second voltage, and when the on / off state of the bidirectional switch carrying current in the control according to the first switching sequence is consistent with the on / off state of the bidirectional switch carrying current in the combination of the control according to the switched second switching sequence, the control is switched from the control according to the first switching sequence to the control according to the second switching sequence.

3. The power conversion circuit according to claim 2, wherein, When the potential difference between the first output terminal and the second output terminal is less than 5% of the amplitude of the first voltage, the control unit switches from control according to the first switching sequence to control according to the second switching sequence.

4. The power conversion circuit according to any one of claims 1 to 3, wherein, One or more of the combinations included in the second switch sequence are identical to the combinations included in the first switch sequence. When the combination in the control according to the first switch sequence is consistent with the combination included in the second switch sequence, the control unit switches from control according to the first switch sequence to control according to the second switch sequence.

5. The power conversion circuit according to any one of claims 1 to 4, wherein, The control unit performs the following processing: During the period when the absolute value of the first voltage is greater than the absolute value of the third voltage, each of the bidirectional switches is controlled according to the first switching sequence. After the absolute value of the third voltage becomes greater than the absolute value of the first voltage, and when the on / off state of the bidirectional switch carrying current in the control according to the first switching sequence is consistent with the on / off state of the bidirectional switch carrying current in the combination of the control according to the switched second switching sequence, the control is switched from the control according to the first switching sequence to the control according to the second switching sequence.

6. The power conversion circuit according to claim 5, wherein, Among the potential differences between the first voltage and the second voltage, the first voltage and the third voltage, and the second voltage and the third voltage, the potential difference with the largest absolute value is set as the maximum line-to-line voltage. When the potential difference between the first output terminal and the second output terminal is the maximum line-to-line voltage, the control unit switches from control according to the first switching sequence to control according to the second switching sequence.

7. The power conversion circuit according to any one of claims 1 to 6, wherein, The bidirectional switch has two switching elements connected in series, with the terminals on the anode side of the body diode connected to each other.

8. A program for a power conversion circuit, applied to a power conversion circuit, the power conversion circuit comprising: The first input terminal, the second input terminal, and the third input terminal are connected to a three-phase AC power supply, and the first voltage, the second voltage, and the third voltage, which are AC voltages of different phases, are input one-to-one. Multiple bidirectional switches are respectively connected to the first input terminal, the second input terminal, and the third input terminal; The first and second output terminals are capable of outputting AC power; and The control unit is capable of controlling the plurality of bidirectional switches according to a first switch sequence or a second switch sequence. The first switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched. The second switch sequence defines multiple combinations related to the on / off states of the plurality of bidirectional switches and the order in which these multiple combinations are switched, in a manner different from the first switch sequence. When the on / off state of the bidirectional switch carrying current under control according to the first switch sequence is consistent with the on / off state of the bidirectional switch carrying current under control according to the switched second switch sequence, the program switches the control unit from control according to the first switch sequence to control according to the second switch sequence.

Images