Power conversion circuit and power conversion device

Abstract

A power conversion circuit (30) comprises a control unit (33). When X° is defined as the phase at which a first voltage becomes a maximum, the control unit (33) controls each two-way switch (TSW) such that there is no short-circuiting of current via an unintended route during a specific period determined in advance in the range of the period where the phase of the first voltage is X°-30° to X° and the range of the period where the phase of the first voltage is X°+180° to X°+210°, or during a specific period determined in advance in the range of the period where the phase of the first voltage is X° to X°+30° and the range of the period where the phase of the first voltage is X°+150° to X°+180°.

Description

Power conversion circuit and power conversion device

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

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

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

[0004] In the power conversion circuit described in Patent Document 1, noise may be superimposed on the voltages of each phase. When noise is superimposed on the voltages of each phase, the timing at which the voltages of each phase change magnitude may deviate from the timing at which the voltages change magnitude in an ideal state. In this case, the timing at which the control unit turns on and off the switch elements deviates from the timing at which the voltages of each phase change magnitude, which may result in current flowing through unintended paths.

[0005] In order to solve the above-described problems, one aspect of the present disclosure provides a power supply including a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply and receiving a first voltage, a second voltage, and a third voltage that are AC voltages of different phases in one-to-one correspondence; a first output terminal and a second output terminal that are capable of outputting AC power; a plurality of bidirectional switches; and a control unit that controls the bidirectional switches, wherein the plurality of bidirectional switches include a first high-side bidirectional switch connecting the first input terminal and the first output terminal; a first low-side bidirectional switch connecting the first input terminal and the second output terminal; a second high-side bidirectional switch connecting the second input terminal and the first output terminal; a second low-side bidirectional switch connecting the second input terminal and the second output terminal; a third high-side bidirectional switch connecting the third input terminal and the first output terminal; and a third low-side bidirectional switch connecting the third input terminal and the second output terminal, wherein when a phase at which the first voltage is maximized is defined as X°, the control unit the third low-side bidirectional switch and the second low-side bidirectional switch so that the on / off states of each bidirectional switch are switched without overlapping between a state in which the third low-side bidirectional switch allows a current to flow from the second output terminal to the third input terminal and a state in which the second low-side bidirectional switch allows a current to flow from the second input terminal to the second output terminal, and the second high-side bidirectional switch and the third high-side bidirectional switch so that the on / off states of each bidirectional switch are switched without overlapping between a state in which the second high-side bidirectional switch allows a current to flow from the second input terminal to the first output terminal and a state in which the third high-side bidirectional switch allows a current to flow from the first output terminal to the third input terminal.

[0006] Another aspect of the present disclosure includes a three-phase AC power supply connected to a first input terminal, a second input terminal, and a third input terminal to which a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, are input in a one-to-one correspondence; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches; and a control unit that controls the bidirectional switches, wherein the plurality of bidirectional switches include a first high-side bidirectional switch connecting the first input terminal and the first output terminal, a first low-side bidirectional switch connecting the first input terminal and the second output terminal, a second high-side bidirectional switch connecting the second input terminal and the first output terminal, a second low-side bidirectional switch connecting the second input terminal and the second output terminal, a third high-side bidirectional switch connecting the third input terminal and the first output terminal, and a third low-side bidirectional switch connecting the third input terminal and the second output terminal, and when the phase at which the first voltage is maximized is X°, the control unit The power conversion circuit controls the third low-side bidirectional switch and the second low-side bidirectional switch so that, within a predetermined specific period within a range of a period when the phase of the first voltage is equal to or greater than X° (X°+30°) and equal to or greater than (X°+150°) and equal to or greater than (X°+180°), the on / off states of each bidirectional switch are switched without overlapping between a state in which the third low-side bidirectional switch allows a current to flow from the third input terminal to the second output terminal and a state in which the second low-side bidirectional switch allows a current to flow from the second output terminal to the second input terminal, and the power conversion circuit controls the second high-side bidirectional switch and the third high-side bidirectional switch so that the on / off states of each bidirectional switch are switched without overlapping between a state in which the second high-side bidirectional switch allows a current to flow from the first output terminal to the second input terminal and a state in which the third high-side bidirectional switch allows a current to flow from the third input terminal to the first output terminal.

[0007] Another aspect of the present disclosure is a power conversion device including any of the above power conversion circuits, a transformer having a primary winding and a secondary winding, with a first end of the primary winding connected to the first output terminal and a second end of the primary winding connected to the second output terminal, and a rectifier circuit connected to the secondary winding.

[0008] This prevents current from flowing in unintended paths.

[0009] FIG. 1 is a circuit diagram of a power conversion device according to this embodiment. FIG. 2 is a diagram showing a waveform of three-phase AC power, sectors, and specific periods. FIG. 3 is a space vector diagram for SVPWM. FIG. 4 is a space vector diagram for SVPWM. FIG. 5 is a sequence diagram of switch control in sector 1a. FIG. 6 is a sequence diagram of switch control in sector 1a'. FIG. 7 is a sequence diagram of switch control in sector 1b. FIG. 8 is a sequence diagram of switch control in sector 1b'. FIG. 9 is a sequence diagram of switch control in sector 4a. FIG. 10 is a sequence diagram of switch control in sector 4a'. FIG. 11 is a sequence diagram of switch control in sector 4b. FIG. 12 is a sequence diagram of switch control in sector 4b'. FIG. 13 is a diagram showing complementary switching patterns. FIG. 14 is a diagram showing additional complementary switching patterns. FIG. 15 is a circuit diagram illustrating operation in the prior art. FIG. 16 is a circuit diagram illustrating operation in sector 1a'. FIG. 17 is a circuit diagram illustrating operation in the prior art. FIG. 18 is a circuit diagram illustrating the operation of the circuit in sector 1a'. FIG. 19 is a circuit diagram illustrating the operation in the prior art. FIG. 20 is a circuit diagram illustrating the operation in sector 1b'. FIG. 21 is a circuit diagram illustrating the operation in the prior art. FIG. 22 is a circuit diagram illustrating the operation of the circuit in sector 1b'. FIG. 23 is a circuit diagram illustrating the operation in the prior art. FIG. 24 is a circuit diagram illustrating the operation in sector 4a'. FIG. 25 is a circuit diagram illustrating the operation in the prior art. FIG. 26 is a circuit diagram illustrating the operation of the circuit in sector 4a'. FIG. 27 is a circuit diagram illustrating the operation in the prior art. FIG. 28 is a circuit diagram illustrating the operation in sector 4b'. FIG. 29 is a circuit diagram illustrating the operation in the prior art. FIG. 30 is a circuit diagram illustrating the operation of the circuit in sector 4b'.

[0010] <One Embodiment of a Power Conversion Circuit> Hereinafter, one embodiment of a power conversion circuit will be described. Note that in the drawings, components may be shown enlarged to facilitate understanding. The dimensional ratios of the components may differ from those in the actual drawings or from those in other drawings.

[0011] (1. Configuration of the Power Conversion Device) As shown in FIG. 1 , the power conversion device 10 includes an input-side low-pass filter 20, a power conversion circuit 30, a transformer circuit 40, a rectifier circuit 50, and an output-side low-pass filter 60. The power conversion device 10 also includes three external input terminals 11 and a pair of external output terminals 12. The power conversion device 10 is a so-called three-phase insulated AC-DC converter. That is, the power conversion device 10 is capable of converting three-phase AC power input to the external input terminals 11 into DC power and outputting it from the external output terminals 12. The presence of a transformer circuit 40 on the power path from each external input terminal 11 to each external output terminal 12 electrically insulates the external input terminal 11 side from the external output terminal 12 side.

[0012] The three external input terminals 11 of the power conversion device 10 are a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C. Three phases of three-phase AC power input from a three-phase AC power supply 80 are input in a one-to-one correspondence to each external input terminal 11. The three-phase AC power supply 80 is a three-phase, three-wire commercial power system in which three AC power supplies are Y-connected.

[0013] The pair of external output terminals 12 is a first external output terminal 12A and a second external output terminal 12B. An arbitrary load 70 can be connected between the first external output terminal 12A and the second external output terminal 12B. The load 70 is, for example, an electronic device driven by DC power.

[0014] The input low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3, as well as a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0015] A first end of the first inductor L1 is connected to the first external input terminal 11A. A first end of the first capacitor C1 is connected to the second end of the first inductor L1. A first end of the second inductor L2 is connected to the second external input terminal 11B. A first end of the second capacitor C2 is connected to the second end of the second inductor L2. A second end of the second capacitor C2 is connected to the second end of the first capacitor C1.

[0016] A first end of the third inductor L3 is connected to the third external input terminal 11C. A first end of the third capacitor C3 is connected to the second end of the third inductor L3. A second end of the third capacitor C3 is connected to the second end of the first capacitor C1.

[0017] The power conversion circuit 30 includes a plurality of input terminals 31, a pair of output terminals 32, a plurality of bidirectional switches TSW, and a control unit 33. The plurality of input terminals 31 include a first input terminal 31A, a second input terminal 31B, and a third input terminal 31C. A second end of a first inductor L1 is connected to the first input terminal 31A. A second end of a second inductor L2 is connected to the second input terminal 31B. A second end of a third inductor L3 is connected to the third input terminal 31C. Thus, three-phase AC power is input to the input terminals 31 of the power conversion circuit 30 via the external input terminal 11 and the input-side low-pass filter 20. The pair of output terminals 32 include a first output terminal 32A and a second output terminal 32B. Single-phase AC power can be output from the pair of output terminals 32 via the plurality of bidirectional switches TSW.

[0018] Each bidirectional switch TSW has two switch elements. Each switch element is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). That is, each switch element has a body diode. The bidirectional switch TSW is composed of two switch elements connected in series such that the anode terminals of the body diodes are connected to each other. In other words, each bidirectional switch TSW has two switch elements whose source terminals are connected to each other.

[0019] The multiple bidirectional switches TSW include a first high-side bidirectional switch HS1, a first low-side bidirectional switch LS1, a second high-side bidirectional switch HS2, a second low-side bidirectional switch LS2, a third high-side bidirectional switch HS3, and a third low-side bidirectional switch LS3.

[0020] The first high-side bidirectional switch HS1 connects the first input terminal 31A and the first output terminal 32A. Specifically, the first high-side bidirectional switch HS1 has an eleventh switch element S11 and a twenty-first switch element S21. The drain terminal of the eleventh switch element S11 is connected to the first input terminal 31A. The source terminal of the twenty-first switch element S21 is connected to the source terminal of the eleventh switch element S11. The drain terminal of the twenty-first switch element S21 is connected to the first output terminal 32A.

[0021] The first low-side bidirectional switch LS1 connects the first input terminal 31A and the second output terminal 32B. Specifically, the first low-side bidirectional switch LS1 has a 24th switch element S24 and a 14th switch element S14. The drain terminal of the 24th switch element S24 is connected to the first input terminal 31A. The source terminal of the 14th switch element S14 is connected to the source terminal of the 24th switch element S24. The drain terminal of the 14th switch element S14 is connected to the second output terminal 32B.

[0022] The second high-side bidirectional switch HS2 connects the second input terminal 31B and the first output terminal 32A. Specifically, the second high-side bidirectional switch HS2 has a thirteenth switch element S13 and a twenty-third switch element S23. The drain terminal of the thirteenth switch element S13 is connected to the second input terminal 31B. The source terminal of the twenty-third switch element S23 is connected to the source terminal of the thirteenth switch element S13. The drain terminal of the twenty-third switch element S23 is connected to the first output terminal 32A.

[0023] The second low-side bidirectional switch LS2 connects the second input terminal 31B and the second output terminal 32B. Specifically, the second low-side bidirectional switch LS2 has a 26th switch element S26 and a 16th switch element S16. The drain terminal of the 26th switch element S26 is connected to the second input terminal 31B. The source terminal of the 26th switch element S26 is connected to the source terminal of the 16th switch element S16. The drain terminal of the 16th switch element S16 is connected to the second output terminal 32B.

[0024] The third high-side bidirectional switch HS3 connects the third input terminal 31C and the first output terminal 32A. Specifically, the third high-side bidirectional switch HS3 has a fifteenth switch element S15 and a twenty-fifth switch element S25. The drain terminal of the fifteenth switch element S15 is connected to the third input terminal 31C. The source terminal of the twenty-fifth switch element S25 is connected to the source terminal of the fifteenth switch element S15. The drain terminal of the twenty-fifth switch element S25 is connected to the first output terminal 32A.

[0025] The third low-side bidirectional switch LS3 connects the third input terminal 31C and the second output terminal 32B. Specifically, the third low-side bidirectional switch LS3 has a 22nd switch element S22 and a 12th switch element S12. The drain terminal of the 22nd switch element S22 is connected to the third input terminal 31C. The source terminal of the 12th switch element S12 is connected to the source terminal of the 22nd switch element S22. The drain terminal of the 12th switch element S12 is connected to the second output terminal 32B.

[0026] The control unit 33 controls each bidirectional switch TSW. Specifically, the control unit 33 controls the on / off of each switch element by inputting switching signals to the gate terminals of two switch elements included in each bidirectional switch TSW. The switching signals include an eleventh switching signal SG11 to a sixteenth switching signal SG16 and a twenty-first switching signal SG21 to a twenty-sixth switching signal SG26. The eleventh switching signal SG11 to the sixteenth switching signal SG16 correspond one-to-one to the eleventh switching element S11 to the sixteenth switching element S16, respectively. The twenty-first switching signal SG21 to the twenty-sixth switching signal SG26 correspond one-to-one to the twenty-first switching element S21 to the twenty-sixth switching element S26, respectively.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0042] Sector 1: -30°≦θ°<30° Sector 2: 30°≦θ°<90° Sector 3: 90°≦θ°<150° Sector 4: 150°≦θ°<180° and -180°≦θ°<-150° Sector 5: -150°≦θ°<-90° Sector 6: -90°≦θ°<-30° Furthermore, each of sectors 1 to 6 is subdivided into four periods. In other words, one cycle of three-phase AC power is subdivided into 24 periods. In the following, n is an integer between 1 and 6, and corresponds to the sector number. In this case, sector n is subdivided into four periods: sector na, sector na', sector nb', and sector nb. In this embodiment, each period is defined as follows. The midpoint of the period of sector n is set to X°. The "midpoint of the period" is the midpoint between the endpoints of each sector expressed as a half-open interval, where X=180° in the definitions of sector 4a and sector 4a'.

[0043] ・Sector na: (X°-30°)≦θ°<(X°-3°) ・Sector na': (X°-3°)≦θ°<X° ・Sector nb': X°≦θ°<(X°+3°) ・Sector nb: (X°+3°)≦θ°<(X°+30°) For example, in the case of sector 1, the above X° is 0°. Therefore, sector 1a is in the period of -30° or more and less than -3°. Sector 1a' is in the period of -3° or more and less than 0°. Sector 1b' is in the period of 0° or more and less than 3°. Sector 1b is in the period of 3° or more and less than 30°.

[0044] Hereinafter, the period of sector 1a' and the period of sector 4b' will be referred to as a first specific period for the first voltage VA. The first specific period is predetermined within a range of a period in which the phase of the first voltage VA is equal to or greater than (X°-30°) and equal to or less than X°, and within a range of a period in which the phase of the first voltage VA is equal to or greater than (X°+180°) and equal to or less than (X°+210°).

[0045] The periods of sectors 1b' and 4a' are referred to as second specific periods for the first voltage VA. The second specific periods are predetermined within the range of a period during which the phase of the first voltage VA is greater than or equal to X° and less than or equal to (X°+30°) and a period during which the phase of the first voltage VA is greater than or equal to (X°+150°) and less than or equal to (X°+180°). The first and second specific periods are determined so as not to overlap with each other.

[0046] Furthermore, hereinafter, the period of sector 2a' and the period of sector 5b' are referred to as a third specific period for the third voltage VC. The third specific period is predetermined within the range of the period in which the phase of the first voltage VA is equal to or greater than (X°-30°) and equal to or less than X°, and within the range of the period in which the phase of the first voltage VA is equal to or greater than (X°+180°) and equal to or less than (X°+210°).

[0047] The period of sector 2b' and the period of sector 5a' are referred to as a fourth specific period for the third voltage VC. The fourth specific period is predetermined within the range of the period during which the phase of the first voltage VA is between X° and (X°+30°) and between X° and (X°+150°) and between X° and (X°+180°). The third specific period and the fourth specific period are determined so as not to overlap each other.

[0048] Furthermore, hereinafter, the period of sector 3a' and the period of sector 6b' are referred to as a fifth specific period for second voltage VB. The fifth specific period is predetermined within the range of the period in which the phase of first voltage VA is equal to or greater than (X°-30°) and equal to or less than X°, and within the range of the period in which the phase of first voltage VA is equal to or greater than (X°+180°) and equal to or less than (X°+210°).

[0049] The period of sector 3b' and the period of sector 6a' are referred to as a sixth specific period for second voltage VB. The sixth specific period is predetermined within the range of the period during which the phase of first voltage VA is between X° and (X°+30°) and between X° and (X°+150°) and between X° and (X°+180°). The fifth specific period and the sixth specific period are determined so as not to overlap each other.

[0050] (3. Regarding Vector Sequence) In the following, the potential difference between the first output terminal 32A and the second output terminal 32B is referred to as the primary voltage Vp. That is, the primary voltage Vp is the voltage applied across the fourth inductor L4 and the primary winding 41A of the transformer 41. Furthermore, the current flowing between the first output terminal 32A and the second output terminal 32B is referred to as the primary current Ip. That is, the primary current Ip is the current flowing through the fourth inductor L4 and the primary winding 41A of the transformer 41. Note that the direction in which the primary current Ip flows from the first output terminal 32A to the second output terminal 32B is referred to as the positive direction. The direction in which the primary current Ip flows from the second output terminal 32B to the first output terminal 32A is referred to as the negative direction.

[0051] Furthermore, the phase having the first voltage VA is referred to as the A phase, the phase having the second voltage VB is referred to as the B phase, and the phase having the third voltage VC is referred to as the C phase, with any one of these phases being referred to as the i phase. Of these three phases, the phase other than the i phase is referred to as the j phase. Hereinafter, the voltage difference obtained by subtracting the j phase voltage from the i phase voltage will be referred to as the "line voltage Vij."

[0052] The control unit 33 controls the pulse width of each switching signal by space vector pulse width modulation (SVPWM).

[0053] As shown in Figures 3 and 4, an active vector and a zero vector are defined for control using SVPWM. In this embodiment, the active vector and the zero vector are current vectors of the power conversion circuit 30 in a predetermined switching state. When m is an integer between 1 and 6, the active vector is expressed as a space vector by the following mathematical expression 1. In this mathematical expression 1, "I" is the absolute value of the primary current Ip.

[0054]

[0055] The active vectors are roughly classified into positive direction active vectors and negative direction active vectors. Specifically, as shown in Fig. 3, the positive direction active vectors include a first positive direction active vector I1+ to a sixth positive direction active vector I6+. Each positive direction active vector is a current vector when the primary voltage Vp has a positive value and each bidirectional switch TSW is in the following switching state:

[0056] First positive active vector I1+: The second low-side bidirectional switch LS2 is on in both directions or in the positive on state, and the first high-side bidirectional switch HS1 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VAB.

[0057] Second positive active vector I2+: The first high-side bidirectional switch HS1 is on in both directions or in the positive on state, and the third low-side bidirectional switch LS3 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VAC.

[0058] Third positive active vector I3+: The third low-side bidirectional switch LS3 is on in both directions or in the positive on state, and the second high-side bidirectional switch HS2 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VBC.

[0059] Fourth positive active vector I4+: The second high-side bidirectional switch HS2 is on in both directions or in the positive on state, and the first low-side bidirectional switch LS1 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VBA.

[0060] Fifth positive active vector I5+: The first low-side bidirectional switch LS1 is on in both directions or in the positive on state, and the third high-side bidirectional switch HS3 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VCA.

[0061] Sixth positive active vector I6+: The third high-side bidirectional switch HS3 is on in both directions or in the positive on state, and the second low-side bidirectional switch LS2 is on in both directions or in the positive on state. At this time, the primary voltage Vp is the line voltage VCB.

[0062] 4, the negative direction active vectors include a first negative direction active vector I1 to a sixth negative direction active vector I6. Each negative direction active vector is a current vector when the primary voltage Vp has a negative value and each bidirectional switch TSW is in the following switching state.

[0063] First negative active vector I1−: The second high-side bidirectional switch HS2 is on in both directions or in the negative direction. The first low-side bidirectional switch LS1 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage VAB.

[0064] Second negative active vector I2−: The first low-side bidirectional switch LS1 is on in both directions or in the negative direction. The third high-side bidirectional switch HS3 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage VAC.

[0065] Third negative active vector I3−: The third high-side bidirectional switch HS3 is on in both directions or in the negative direction. The second low-side bidirectional switch LS2 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage VBC.

[0066] Fourth negative active vector I4−: The second low-side bidirectional switch LS2 is on in both directions or in the negative on state. The first high-side bidirectional switch HS1 is on in both directions or in the negative on state. At this time, the primary voltage Vp is the line voltage VBA.

[0067] Fifth negative active vector I5−: The first high-side bidirectional switch HS1 is on in both directions or in the negative direction. The third low-side bidirectional switch LS3 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage VCA.

[0068] Sixth negative active vector I6−: The third low-side bidirectional switch LS3 is on in both directions or in the negative direction. The second high-side bidirectional switch HS2 is on in both directions or in the negative direction. At this time, the primary voltage Vp is the line voltage VCB.

[0069] 3 and 4, the zero vectors include a seventh zero vector I7, an eighth zero vector I8, and a ninth zero vector I9. The zero vectors are current vectors when the primary voltage Vp is zero and the following switching states are in effect:

[0070] Seventh zero vector I7: The first high-side bidirectional switch HS1 is in a bidirectional on state or a positive on state, and the first low-side bidirectional switch LS1 is in a bidirectional on state or a positive on state, or the first high-side bidirectional switch HS1 is in a bidirectional on state or a negative on state, and the first low-side bidirectional switch LS1 is in a bidirectional on state or a negative on state.

[0071] Eighth zero vector I8: The second high-side bidirectional switch HS2 is in a bidirectional on state or a positive on state, and the second low-side bidirectional switch LS2 is in a bidirectional on state or a positive on state, or the second high-side bidirectional switch HS2 is in a bidirectional on state or a negative on state, and the second low-side bidirectional switch LS2 is in a bidirectional on state or a negative on state.

[0072] Ninth zero vector I9: The third high-side bidirectional switch HS3 is in a bidirectional on state or a positive on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state or a positive on state, or the third high-side bidirectional switch HS3 is in a bidirectional on state or a negative on state, and the third low-side bidirectional switch LS3 is in a bidirectional on state or a negative on state.

[0073] The current reference vector Ir in sector n is approximated as a composite vector of the above active vectors and zero vectors. Specifically, when x = n and y = x + 1, it is approximated as follows: However, when x = 6, y = 1. The current reference vector Ir in sector n is approximated as a composite vector of the x-th positive direction active vector Ix+, the y-th positive direction active vector Iy+, and a zero vector. Alternatively, the current reference vector Ir in sector n is approximated as a composite vector of the x-th negative direction active vector Ix-, the y-th negative direction active vector Iy-, and a zero vector. Note that the zero vector is the seventh zero vector I7 in sectors 1 and 4. The zero vector is the ninth zero vector I9 in sectors 2 and 5. The zero vector is the eighth zero vector I8 in sectors 3 and 6.

[0074] In principle, the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions between the above active vectors or zero vector in a certain order depending on the magnitude relationship between the first voltage VA, the second voltage VB, and the third voltage VC. Specifically, in sectors na and na', the control unit 33 controls the on / off of each switch element so that the current vector follows the first vector sequence shown in (a) below. In sectors nb and nb', the control unit 33 controls the on / off of each switch element so that the current vector follows the second vector sequence shown in (b) below. (a) First vector sequence: In the order of x-th positive direction active vector Ix+, y-th positive direction active vector Iy+, zero vector, x-th negative direction active vector Ix-, y-th negative direction active vector Iy-, zero vector. (b) Second vector sequence: the y-th positive direction active vector Iy+, the x-th positive direction active vector Ix+, the zero vector, the y-th negative direction active vector Iy-, the x-th negative direction active vector Ix-, and the zero vector in that order.

[0075] Therefore, for example, when n=3, in sectors 3a and 3a', the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions in the following order: third positive direction active vector I3+, fourth positive direction active vector I4+, ninth zero vector I9, third negative direction active vector I3-, fourth negative direction active vector I4-, and ninth zero vector I9. Then, in sectors 3b and 3b', i.e., in the sixth specific period, the control unit 33 controls the on / off of each switch element so that the reference vector Ir transitions in the following order: fourth positive direction active vector I4+, third positive direction active vector I3+, ninth zero vector I9, fourth negative direction active vector I4-, third negative direction active vector I3-, and ninth zero vector I9.

[0076] The control unit 33 repeats the on / off control of each switch element in the first vector sequence in the sectors na and na' at a constant cycle Ts, which is very short compared to the respective cycles of the sectors na and na'.

[0077] Furthermore, the control unit 33 repeats the on / off control of each switch element in the second vector sequence in sector nb and sector nb′ with the same period Ts as that of the first vector sequence. The period Ts is much shorter than the periods of sector nb and sector nb′.

[0078] (4. Specific Example of Switching Pattern) The switching pattern according to the above vector sequence will be explained below using the periods of sector 1 and sector 4 as examples.

[0079] 2, during the period of sector 1a and the period of sector 1a', i.e., the first specific period, the first voltage VA is the largest among the voltages, and the third voltage VC is equal to or greater than the second voltage VB.

[0080] 3 and 4, in sector 1a and the first specific period, the reference vector Ir transitions according to a first vector sequence, i.e., the reference vector Ir transitions in the following order: first positive direction active vector I1+, second positive direction active vector I2+, seventh zero vector I7, first negative direction active vector I1-, second negative direction active vector I2-, and seventh zero vector I7.

[0081] First, the switching pattern in sector 1a will be described. During the sector 1a period, complementary switching control is performed when the reference vector Ir transitions. That is, as shown in FIG. 13 , the control unit 33 controls the on / off state of the 16th switch element S16 of the second low-side bidirectional switch LS2 and the on / off state of the 22nd switch element S22 of the third low-side bidirectional switch LS3 to be complementary. Furthermore, during the sector 1a period, the control unit 33 controls the on / off state of the 23rd switch element S23 of the second high-side bidirectional switch HS2 and the on / off state of the 15th switch element S15 of the third high-side bidirectional switch HS3 to be complementary. Note that complementary on / off states refer to a state in which one switch element of the two switches is in the on state and the other switch element is in the off state.

[0082] During the sector 1a period, the control unit 33 performs the following continuous on control. That is, as shown in Fig. 5, the control unit 33 controls the 21st switch element S21 of the first high-side bidirectional switch HS1 and the 14th switch element S14 of the first low-side bidirectional switch LS1 to remain in the on state during the sector 1a period. Also, the control unit 33 controls the 13th switch element S13 of the second high-side bidirectional switch HS2 and the 26th switch element S26 of the second low-side bidirectional switch LS2 to remain in the on state during the sector 1a period.

[0083] The switching pattern in sector 1a from time t0 to time t14 will be described below. Although not shown, immediately before time t0 in sector 1a, the reference vector Ir is the seventh zero vector I7. Specifically, the first high-side bidirectional switch HS1 is on in both directions. The first low-side bidirectional switch LS1 is on in both directions. The second high-side bidirectional switch HS2 is on in the positive direction. The second low-side bidirectional switch LS2 is on in the negative direction. The third high-side bidirectional switch HS3 is on in the positive direction. The third low-side bidirectional switch LS3 is on in the negative direction. The on / off states of each switch element immediately before time t0 are the same as the on / off states at time t14, which will be described later.

[0084] As shown in FIG. 5 , at time t0 in sector 1a, the control unit 33 turns the first low-side bidirectional switch LS1 on in the positive direction. Also, at time t0, the control unit 33 turns the third low-side bidirectional switch LS3 off. At time t1, the control unit 33 turns the second low-side bidirectional switch LS2 on in both directions. At time t2, the control unit 33 turns the third low-side bidirectional switch LS3 on in the positive direction. At time t3, the control unit 33 turns the second low-side bidirectional switch LS2 on in the negative direction. Therefore, during the period from time t0 to time t3, the reference vector Ir is the first positive-direction active vector I1+.

[0085] Next, at time t4, the control unit 33 turns on the third low-side bidirectional switch LS3 in both directions. At time t5, the control unit 33 turns on the third low-side bidirectional switch LS3 in the negative direction. Therefore, during the period from time t3 to time t5, the reference vector Ir is the second positive-direction active vector I2+.

[0086] At time t6, the control unit 33 turns the first low-side bidirectional switch LS1 on in both directions. At time t7, the control unit 33 turns the first high-side bidirectional switch HS1 on in the negative direction. At time t7, the control unit 33 turns the third high-side bidirectional switch HS3 off in both directions. Therefore, during the period from time t5 to time t7, the reference vector Ir coincides with the seventh zero vector I7.

[0087] At time t8, the control unit 33 turns on the second high-side bidirectional switch HS2 in both directions. At time t9, the control unit 33 turns on the third high-side bidirectional switch HS3 in the negative direction. At time t10, the control unit 33 turns on the second high-side bidirectional switch HS2 in the positive direction. Therefore, during the period from time t7 to time t10, the reference vector Ir is the first negative direction active vector I1-.

[0088] At time t11, the control unit 33 turns on the third high-side bidirectional switch HS3 in both directions. At time t12, the control unit 33 turns on the third high-side bidirectional switch HS3 in the positive direction. Therefore, during the period from time t9 to time t12, the reference vector Ir is the second negative direction active vector I2-.

[0089] At time t13, the controller 33 turns on the first high-side bidirectional switch HS1 in both directions. At time t14, a predetermined time after time t13, one cycle Ts of the switching pattern according to the first vector sequence ends. Therefore, during the period from time t12 to time t14, the reference vector Ir is the seventh zero vector I7.

[0090] Next, the switching pattern in the sector 1a' will be described. As shown in Figures 5 and 6, the on / off control performed by the controller 33 in the period of the sector 1a' is the same as the on / off control in the period of the sector 1a, except for the control over the 26th switch element S26 of the second low-side bidirectional switch LS2 and the 13th switch element S13 of the second high-side bidirectional switch HS2.

[0091] Specifically, in addition to the complementary switching control in the sector 1a, the control unit 33 performs the following complementary switching control. That is, as shown in Fig. 14, during the period of the sector 1a', the control unit 33 controls the on / off state of the 26th switch element S26 of the second low-side bidirectional switch LS2 and the on / off state of the 12th switch element S12 of the third low-side bidirectional switch LS3 so that they are complementary to each other. Furthermore, during the period of the sector 1a', the control unit 33 controls the on / off state of the 13th switch element S13 of the second high-side bidirectional switch HS2 and the on / off state of the 25th switch element S25 of the third high-side bidirectional switch HS3 so that they are complementary to each other.

[0092] Therefore, during the period of sector 1a′, i.e., the first specific period, the control unit 33 controls the third low-side bidirectional switch LS3 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third low-side bidirectional switch LS3 allows a current to flow from the second output terminal 32B to the third input terminal 31C and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second input terminal 31B to the second output terminal 32B.

[0093] Furthermore, in the first specific period, the control unit 33 controls the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the second input terminal 31B to the first output terminal 32A and a state in which the third high-side bidirectional switch HS3 allows a current to flow from the first output terminal 32A to the third input terminal 31C.

[0094] In other words, during the first specific period, the control unit 33 controls each bidirectional switch TSW of the second low-side bidirectional switch LS2 and the third low-side bidirectional switch LS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction. Also, the control unit 33 controls each bidirectional switch TSW of the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction.

[0095] More specifically, in the sector 1a', the control unit 33 controls each bidirectional switch TSW as follows. As shown in Fig. 6, from time t1' to time t6 in the sector 1a', the control unit 33 turns off the 26th switch element S26 of the second low-side bidirectional switch LS2. Note that time t1' is after time t1 and before time t2.

[0096] As a result, the second low-side bidirectional switch LS2 is in the ON state in the positive direction from time t1' to time t3. The second low-side bidirectional switch LS2 is in the OFF state from time t3 to time t6. In contrast, the third low-side bidirectional switch LS3 is in the OFF state from time t1' to time t2. The third low-side bidirectional switch LS3 is in the ON state in the positive direction from time t2 to time t4.

[0097] Furthermore, the control unit 33 turns off the thirteenth switch element S13 of the second high-side bidirectional switch HS2 from time t8' to time t13 in the sector 1a'. Note that time t8' is after time t8 and before time t9.

[0098] As a result, the second high-side bidirectional switch HS2 is in the ON state in the negative direction from time t8' to time t10. The second high-side bidirectional switch HS2 is in the OFF state from time t10 to time t13. In contrast, the third high-side bidirectional switch HS3 is in the OFF state from time t8' to time t9. The third high-side bidirectional switch HS3 is in the ON state in the negative direction from time t9 to time t11.

[0099] (4-2. Control in Sectors 1b and 1b') As shown in FIG. 2, during the period of sector 1b and the period of sector 1b', i.e., the second specific period, the first voltage VA is the largest among the voltages. Also, the second voltage VB is equal to or greater than the third voltage VC. That is, during the period of sector 1b and the period of sector 1b', the magnitude relationship between the second voltage VB and the third voltage VC is reversed compared to the period of sector 1a.

[0100] As shown in Figures 3 and 4, in sector 1b and sector 1b', the reference vector Ir transitions in the following order: second positive direction active vector I2+, first positive direction active vector I1+, seventh zero vector I7, second negative direction active vector I2-, first negative direction active vector I1-, and seventh zero vector I7.

[0101] First, the switching pattern in sector 1b will be described. In sector 1b, the following complementary switching control is performed when the reference vector Ir transitions. That is, as shown in FIG. 13 , the control unit 33 controls the on / off state of the twelfth switch element S12 of the third low-side bidirectional switch LS3 and the on / off state of the 26th switch element S26 of the second low-side bidirectional switch LS2 so that they are complementary to each other. Furthermore, during the period of sector 1b, the control unit 33 controls the on / off state of the 25th switch element S25 of the third high-side bidirectional switch HS3 and the on / off state of the thirteenth switch element S13 of the second high-side bidirectional switch HS2 so that they are complementary to each other.

[0102] 7, the control unit 33 controls the 21st switch element S21 of the first high-side bidirectional switch HS1 and the 14th switch element S14 of the first low-side bidirectional switch LS1 to remain in the on state during the sector 1b period. The control unit 33 also controls the 15th switch element S15 of the third high-side bidirectional switch HS3 and the 22nd switch element S22 of the third low-side bidirectional switch LS3 to remain in the on state during the sector 1b period.

[0103] Therefore, based on the magnitude relationship between the voltages, the vector sequence, and the complementary switching control pattern, the switching pattern in sector 1b is as follows: As shown in Figures 5 and 7, the switching pattern of the first high-side bidirectional switch HS1 in sector 1b is the same as the switching pattern of the first high-side bidirectional switch HS1 in sector 1a. The switching pattern of the first low-side bidirectional switch LS1 in sector 1b is the same as the switching pattern of the first low-side bidirectional switch LS1 in sector 1a.

[0104] The switching pattern of the second high-side bidirectional switch HS2 in sector 1b is the same as the switching pattern of the third high-side bidirectional switch HS3 in sector 1a. The switching pattern of the second low-side bidirectional switch LS2 in sector 1b is the same as the switching pattern of the third low-side bidirectional switch LS3 in sector 1a.

[0105] The switching pattern of the third high-side bidirectional switch HS3 in sector 1b is the same as the switching pattern of the second high-side bidirectional switch HS2 in sector 1a. The switching pattern of the third low-side bidirectional switch LS3 in sector 1b is the same as the switching pattern of the second low-side bidirectional switch LS2 in sector 1a.

[0106] Next, the switching pattern in sector 1b' will be described. As shown in Figures 7 and 8, the on / off control performed by the controller 33 in the period of sector 1b' is the same as the on / off control in the period of sector 1b, except for the control over the 22nd switch element S22 of the third low-side bidirectional switch LS3 and the 15th switch element S15 of the third high-side bidirectional switch HS3.

[0107] Specifically, during the period of sector 1b', in addition to the complementary switching control in sector 1b, the following complementary switching control is performed. That is, as shown in Fig. 14, during the period of sector 1b', the control unit 33 controls the on / off state of the 22nd switch element S22 of the third low-side bidirectional switch LS3 and the on / off state of the 16th switch element S16 of the second low-side bidirectional switch LS2 so that they are complementary. Furthermore, during the period of sector 1b', the control unit 33 controls the on / off state of the 15th switch element S15 of the third high-side bidirectional switch HS3 and the on / off state of the 23rd switch element S23 of the second high-side bidirectional switch HS2 so that they are complementary.

[0108] Therefore, during the period of sector 1b′, i.e., the second specific period, the control unit 33 controls the third low-side bidirectional switch LS3 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third low-side bidirectional switch LS3 allows a current to flow from the third input terminal 31C to the second output terminal 32B and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second output terminal 32B to the second input terminal 31B.

[0109] Furthermore, in the second specific period, the control unit 33 controls the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the first output terminal 32A to the second input terminal 31B and a state in which the third high-side bidirectional switch HS3 allows a current to flow from the third input terminal 31C to the first output terminal 32A.

[0110] In other words, during the second specific period, the control unit 33 controls each bidirectional switch TSW of the second low-side bidirectional switch LS2 and the third low-side bidirectional switch LS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction. Also, the control unit 33 controls each bidirectional switch TSW of the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction.

[0111] More specifically, in sector 1b', the control unit 33 controls each bidirectional switch TSW as follows. As shown in Fig. 8, from time t1' to time t6 in sector 1b', the control unit 33 turns off the 22nd switch element S22 of the third low-side bidirectional switch LS3. Note that time t1' is after time t1 and before time t2.

[0112] As a result, the third low-side bidirectional switch LS3 is in the ON state in the positive direction from time t1' to time t3. The third low-side bidirectional switch LS3 is in the OFF state from time t3 to time t6. In contrast, the second low-side bidirectional switch LS2 is in the OFF state from time t1' to time t2. The second low-side bidirectional switch LS2 is in the ON state in the positive direction from time t2 to time t4.

[0113] Furthermore, the control unit 33 turns off the fifteenth switch element S15 of the third high-side bidirectional switch HS3 from time t8' to time t13 in the sector 1b'. Note that time t8' is after time t8 and before time t9.

[0114] As a result, the third high-side bidirectional switch HS3 is in the ON state in the negative direction from time t8' to time t10. The third high-side bidirectional switch HS3 is in the OFF state from time t10 to time t13. In contrast, the second high-side bidirectional switch HS2 is in the OFF state from time t8' to time t9. The second high-side bidirectional switch HS2 is in the ON state in the negative direction from time t9 to time t11.

[0115] 2, during the period of sector 4a and the period of sector 4a', i.e., the second specific period, the first voltage VA is the smallest among the voltages. Also, the third voltage VC is equal to or lower than the second voltage VB. That is, during the period of sector 4a and the period of sector 4a', the positive and negative signs of the first voltage VA, the second voltage VB, and the third voltage VC are reversed relative to the periods of sector 1a and sector 1a'.

[0116] Also, as shown in Figures 3 and 4, during the period of sector 4a and the period of sector 4a', the reference vector Ir transitions in the following order: fourth positive direction active vector I4+, fifth positive direction active vector I5+, seventh zero vector I7, fourth negative direction active vector I4-, fifth negative direction active vector I5-, seventh zero vector I7.

[0117] First, the switching pattern in sector 4a will be described. During the period of sector 4a, the following complementary switching control is performed when the reference vector Ir transitions. That is, as shown in FIG. 13 , the control unit 33 controls the on / off state of the 26th switch element S26 of the second low-side bidirectional switch LS2 and the on / off state of the 12th switch element S12 of the third low-side bidirectional switch LS3 to be complementary. Furthermore, during the period of sector 4a, the control unit 33 controls the on / off state of the 13th switch element S13 of the second high-side bidirectional switch HS2 and the on / off state of the 25th switch element S25 of the third high-side bidirectional switch HS3 to be complementary.

[0118] During the period of sector 4a, the control unit 33 performs the following continuous on control. That is, as shown in Fig. 9, the control unit 33 controls the 11th switch element S11 of the first high-side bidirectional switch HS1 and the 24th switch element S24 of the first low-side bidirectional switch LS1 to continue to be on during the period of sector 4a. Also, the control unit 33 controls the 23rd switch element S23 of the second high-side bidirectional switch HS2 and the 16th switch element S16 of the second low-side bidirectional switch LS2 to continue to be on during the period of sector 4a.

[0119] Therefore, based on the magnitude relationship between the voltages, the vector sequence, and the complementary switching control pattern, the switching pattern in sector 4a is as follows: As shown in Figures 5 and 9, the switching pattern of the first high-side bidirectional switch HS1 in sector 4a is the same as the switching pattern of the first low-side bidirectional switch LS1 in sector 1a. The switching pattern of the first low-side bidirectional switch LS1 in sector 4a is the same as the switching pattern of the first high-side bidirectional switch HS1 in sector 1a.

[0120] The switching pattern of the second high-side bidirectional switch HS2 in the sector 4a is the same as the switching pattern of the second low-side bidirectional switch LS2 in the sector 1a. The switching pattern of the second low-side bidirectional switch LS2 in the sector 4a is the same as the switching pattern of the second high-side bidirectional switch HS2 in the sector 1a.

[0121] The switching pattern of the third high-side bidirectional switch HS3 in the sector 4a is the same as the switching pattern of the third low-side bidirectional switch LS3 in the sector 1a. The switching pattern of the third low-side bidirectional switch LS3 in the sector 4a is the same as the switching pattern of the third high-side bidirectional switch HS3 in the sector 1a.

[0122] Next, the switching pattern in the sector 4a' will be described. As shown in Figures 9 and 10, the on / off control performed by the controller 33 in the period of the sector 4a' is the same as the on / off control in the period of the sector 4a, except for the control over the 23rd switch element S23 of the second high-side bidirectional switch HS2 and the 16th switch element S16 of the second low-side bidirectional switch LS2.

[0123] Specifically, during the sector 4a' period, in addition to the complementary switching control in the sector 4a, the following complementary switching control is performed. That is, as shown in Fig. 14, during the sector 4a' period, the control unit 33 controls the on / off state of the 16th switch element S16 of the second low-side bidirectional switch LS2 and the on / off state of the 22nd switch element S22 of the third low-side bidirectional switch LS3 to be complementary. Furthermore, during the sector 4a' period, the control unit 33 controls the on / off state of the 23rd switch element S23 of the second high-side bidirectional switch HS2 and the on / off state of the 15th switch element S15 of the third high-side bidirectional switch HS3 to be complementary.

[0124] Therefore, during the period of sector 4a′, the control unit 33 controls the third low-side bidirectional switch LS3 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third low-side bidirectional switch LS3 allows a current to flow from the third input terminal 31C to the second output terminal 32B and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second output terminal 32B to the second input terminal 31B.

[0125] Furthermore, during the period of sector 4a′, the control unit 33 controls the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the first output terminal 32A to the second input terminal 31B and a state in which the third high-side bidirectional switch HS3 allows a current to flow from the third input terminal 31C to the first output terminal 32A.

[0126] In other words, during the second specific period, the control unit 33 controls each bidirectional switch TSW of the second low-side bidirectional switch LS2 and the third low-side bidirectional switch LS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction. Also, the control unit 33 controls each bidirectional switch TSW of the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction.

[0127] More specifically, in the sector 4a', the control unit 33 controls each bidirectional switch TSW as follows. As shown in Fig. 10, from time t1' to time t6 in the sector 4a', the control unit 33 turns off the 23rd switch element S23 of the second high-side bidirectional switch HS2. Note that time t1' is after time t1 and before time t2.

[0128] As a result, the second high-side bidirectional switch HS2 is in the ON state in the positive direction from time t1' to time t3. The second high-side bidirectional switch HS2 is in the OFF state from time t3 to time t6. In contrast, the third high-side bidirectional switch HS3 is in the OFF state from time t1' to time t2. The third high-side bidirectional switch HS3 is in the ON state in the positive direction from time t2 to time t4.

[0129] Furthermore, the control unit 33 turns off the sixteenth switch element S16 of the second low-side bidirectional switch LS2 from time t8' to time t13 in the sector 4a'. Note that time t8' is after time t8 and before time t9.

[0130] As a result, the second low-side bidirectional switch LS2 is in the ON state in the negative direction from time t8' to time t10. The second low-side bidirectional switch LS2 is in the OFF state from time t10 to time t13. In contrast, the third low-side bidirectional switch LS3 is in the OFF state from time t8' to time t9. The third low-side bidirectional switch LS3 is in the ON state in the negative direction from time t9 to time t11.

[0131] 2, during the period of sector 4b and the period of sector 4b', i.e., the first specific period, the first voltage VA is the smallest among the voltages. Also, the second voltage VB is equal to or lower than the third voltage VC. That is, during the period of sector 4b and the period of sector 4b', the first voltage VA, the second voltage VB, and the third voltage VC are inverted in polarity relative to the periods of sector 1b and sector 1b'.

[0132] As shown in Figures 3 and 4, during the period of sector 4b and the period of sector 4b', the reference vector Ir transitions in the following order: fifth positive direction active vector I5+, fourth positive direction active vector I4+, seventh zero vector I7, fifth negative direction active vector I5-, fourth negative direction active vector I4-, and seventh zero vector I7.

[0133] First, the switching pattern in sector 4b will be described. During the period of sector 4b, the following complementary switching control is performed when the reference vector Ir transitions. That is, as shown in FIG. 13 , the on / off state of the 22nd switch element S22 of the third low-side bidirectional switch LS3 and the on / off state of the 16th switch element S16 of the second low-side bidirectional switch LS2 are controlled to be complementary. Furthermore, during the period of sector 4b, the on / off state of the 15th switch element S15 of the third high-side bidirectional switch HS3 and the on / off state of the 23rd switch element S23 of the second high-side bidirectional switch HS2 are controlled to be complementary.

[0134] During the period of sector 4b, the control unit 33 performs the following continuous on control. That is, as shown in Fig. 11 , the control unit 33 controls the 11th switch element S11 of the first high-side bidirectional switch HS1 and the 24th switch element S24 of the first low-side bidirectional switch LS1 to continue to be on during the period of sector 4a. Also, the control unit 33 controls the 25th switch element S25 of the third high-side bidirectional switch HS3 and the 12th switch element S12 of the third low-side bidirectional switch LS3 to continue to be on during the period of sector 4a.

[0135] Therefore, based on the magnitude relationship between the voltages, the vector sequence, and the complementary switching control pattern, the switching pattern in sector 4b is as follows: As shown in Figures 7 and 11, the switching pattern of the first high-side bidirectional switch HS1 in sector 4b is the same as the switching pattern of the first low-side bidirectional switch LS1 in sector 1b. The switching pattern of the first low-side bidirectional switch LS1 in sector 4b is the same as the switching pattern of the first high-side bidirectional switch HS1 in sector 1b.

[0136] The switching pattern of the second high-side bidirectional switch HS2 in sector 4b is the same as the switching pattern of the second low-side bidirectional switch LS2 in sector 1b. The switching pattern of the second low-side bidirectional switch LS2 in sector 4b is the same as the switching pattern of the second high-side bidirectional switch HS2 in sector 1b.

[0137] The switching pattern of the third high-side bidirectional switch HS3 in sector 4b is the same as the switching pattern of the third low-side bidirectional switch LS3 in sector 1b. The switching pattern of the third low-side bidirectional switch LS3 in sector 4b is the same as the switching pattern of the third high-side bidirectional switch HS3 in sector 1b.

[0138] Next, the switching pattern in the sector 4b' will be described. As shown in Figures 11 and 12, the on / off control performed by the controller 33 in the period of the sector 4b' is the same as the on / off control in the period of the sector 4b, except for the control over the 25th switch element S25 of the third high-side bidirectional switch HS3 and the 12th switch element S12 of the third low-side bidirectional switch LS3.

[0139] Specifically, during the period of sector 4b', in addition to the complementary switching control in sector 4b, the following complementary switching control is performed. That is, as shown in Fig. 14, during the period of sector 4b', the control unit 33 controls the on / off state of the twelfth switch element S12 of the third low-side bidirectional switch LS3 and the on / off state of the 26th switch element S26 of the second low-side bidirectional switch LS2 so that they are complementary. Also, during the period of sector 4b', the control unit 33 controls the on / off state of the 25th switch element S25 of the third high-side bidirectional switch HS3 and the on / off state of the thirteenth switch element S13 of the second high-side bidirectional switch HS2 so that they are complementary.

[0140] Therefore, during the period of sector 4b′, the control unit 33 controls the third low-side bidirectional switch LS3 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third low-side bidirectional switch LS3 allows a current to flow from the second output terminal 32B to the third input terminal 31C and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second input terminal 31B to the second output terminal 32B.

[0141] Furthermore, during the period of sector 4b′, the control unit 33 controls the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the second input terminal 31B to the first output terminal 32A and a state in which the third high-side bidirectional switch HS3 allows a current to flow from the first output terminal 32A to the third input terminal 31C.

[0142] In other words, during the first specific period, the control unit 33 controls each bidirectional switch TSW of the second low-side bidirectional switch LS2 and the third low-side bidirectional switch LS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction. Also, the control unit 33 controls each bidirectional switch TSW of the second high-side bidirectional switch HS2 and the third high-side bidirectional switch HS3 so that either one of the bidirectional switches TSW is in the OFF state, both are in the ON state in the positive direction, or both are in the ON state in the negative direction.

[0143] More specifically, in the sector 4b', the control unit 33 controls each bidirectional switch TSW as follows. As shown in Fig. 12, from time t1' to time t6 in the sector 4a', the control unit 33 turns off the 25th switch element S25 of the third high-side bidirectional switch HS3. Note that time t1' is after time t1 and before time t2.

[0144] As a result, the third high-side bidirectional switch HS3 is in the ON state in the positive direction from time t1' to time t3. The third high-side bidirectional switch HS3 is in the OFF state from time t3 to time t6. In contrast, the second high-side bidirectional switch HS2 is in the OFF state from time t1' to time t2. The second high-side bidirectional switch HS2 is in the ON state in the positive direction from time t2 to time t4.

[0145] Furthermore, the control unit 33 turns off the twelfth switch element S12 of the third low-side bidirectional switch LS3 from time t8' to time t13 in the sector 4a'. Note that time t8' is after time t8 and before time t9.

[0146] As a result, the third low-side bidirectional switch LS3 is in the ON state in the negative direction from time t8' to time t10. The third low-side bidirectional switch LS3 is in the OFF state from time t10 to time t13. In contrast, the second low-side bidirectional switch LS2 is in the OFF state from time t8' to time t9. The second low-side bidirectional switch LS2 is in the ON state in the negative direction from time t9 to time t11.

[0147] (4-5. Other Switching Patterns) The switching patterns for sectors 2, 3, 5, and 6 are determined in the same manner as in the above-described examples of sector 1 and sector 4. That is, each switching pattern is determined by the magnitude relationships of the voltages shown in Fig. 2, the vector sequences shown in Figs. 3 and 4, and the combinations of switch elements for complementary switching control shown in Figs. 13 and 14.

[0148] Therefore, in sector 2a′ and sector 5b′, i.e., in the third specific period, the control unit 33 controls the first low-side bidirectional switch LS1 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the first low-side bidirectional switch LS1 allows a current to flow from the second output terminal 32B to the first input terminal 31A and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second input terminal 31B to the second output terminal 32B.

[0149] Furthermore, in the third specific period, the control unit 33 controls the second high-side bidirectional switch HS2 and the first high-side bidirectional switch HS1 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the second input terminal 31B to the first output terminal 32A and a state in which the first high-side bidirectional switch HS1 allows a current to flow from the first output terminal 32A to the first input terminal 31A.

[0150] Furthermore, in sector 2b′ and sector 5a′, i.e., in the fourth specific period, the control unit 33 controls the first low-side bidirectional switch LS1 and the second low-side bidirectional switch LS2 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the first low-side bidirectional switch LS1 allows a current to flow from the first input terminal 31A to the second output terminal 32B and a state in which the second low-side bidirectional switch LS2 allows a current to flow from the second output terminal 32B to the second input terminal 31B.

[0151] Furthermore, in the fourth specific period, the control unit 33 controls the second high-side bidirectional switch HS2 and the first high-side bidirectional switch HS1 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the second high-side bidirectional switch HS2 allows a current to flow from the first output terminal 32A to the second input terminal 31B and a state in which the first high-side bidirectional switch HS1 allows a current to flow from the first input terminal 31A to the first output terminal 32A.

[0152] Furthermore, in sector 3a′ and sector 6b′, i.e., in the fifth specific period, the control unit 33 controls the first low-side bidirectional switch LS1 and the third low-side bidirectional switch LS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the first low-side bidirectional switch LS1 allows a current to flow from the second output terminal 32B to the first input terminal 31A and a state in which the third low-side bidirectional switch LS3 allows a current to flow from the third input terminal 31C to the second output terminal 32B.

[0153] Furthermore, in the fifth specific period, the control unit 33 controls the third high-side bidirectional switch HS3 and the first high-side bidirectional switch HS1 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third high-side bidirectional switch HS3 allows a current to flow from the third input terminal 31C to the first output terminal 32A and a state in which the first high-side bidirectional switch HS1 allows a current to flow from the first output terminal 32A to the first input terminal 31A.

[0154] Furthermore, in sector 3b′ and sector 6a′, i.e., the sixth specific period, the control unit 33 controls the first low-side bidirectional switch LS1 and the third low-side bidirectional switch LS3 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the first low-side bidirectional switch LS1 allows a current to flow from the first input terminal 31A to the second output terminal 32B and a state in which the third low-side bidirectional switch LS3 allows a current to flow from the second output terminal 32B to the third input terminal 31C.

[0155] Furthermore, in the sixth specific period, the control unit 33 controls the third high-side bidirectional switch HS3 and the first high-side bidirectional switch HS1 so that the on / off state of each bidirectional switch TSW is switched without overlapping between a state in which the third high-side bidirectional switch HS3 allows a current to flow from the first output terminal 32A to the third input terminal 31C and a state in which the first high-side bidirectional switch HS1 allows a current to flow from the first input terminal 31A to the first output terminal 32A.

[0156] (5. Comparison with Prior Art) A comparison with a power conversion circuit of prior art will be described below using the periods of sector 1a', sector 1b', sector 4a', and sector 4b' as examples.

[0157] In the power conversion circuit of the prior art, the periods of sector na' and sector nb' are not defined. Specifically, when n is an integer between 1 and 6, and the phase of the first voltage VA is "θ°," the periods are defined as follows in the prior art. Note that the median value of the period of sector n is set to X°. However, in the definitions of sector 4a and sector 4a', X = 180°.

[0158] Sector na: (X°-30°)≦θ°<X° Sector nb: X°≦θ°<(X°+30°) For example, X°=0°, the boundary between sector 1a and sector 1b, is the timing when the magnitude relationship between the second voltage VB and the third voltage VC changes. However, due to noise superimposed on the voltages of each phase, the timing of the change in the magnitude relationship between the voltages may deviate from the ideal timing. That is, in the range of -30° or more and less than 0°, the second voltage VB may become equal to or greater than the third voltage VC, even though the third voltage VC is actually equal to or greater than the second voltage VB. Furthermore, in the range of 0° or more and less than 30°, the third voltage VC may become equal to or greater than the second voltage VB, even though the second voltage VB is actually equal to or greater than the third voltage VC. In such cases, as described below, current may flow through an unintended path.

[0159] 15 to 30, the switch elements of each bidirectional switch TSW are illustrated in a simplified manner. That is, each switch element is illustrated as a single-pole, single-throw (SPST) switch for convenience. Also, when the body diode of the switch element is conductive, only the diode is illustrated for convenience.

[0160] (5-1. Comparison During Sector 1a') In the period between -30° and 0°, the second voltage VB is ideally less than the third voltage VC. However, there are cases where the second voltage VB becomes greater than the third voltage VC due to noise being superimposed on each voltage.

[0161] In the power conversion circuit of the conventional technology, during the period from time t2 to time t5 in sector 1a, that is, during the period when the twelfth switch element S12 of the third low-side bidirectional switch LS3 is in the on state and the 26th switch element S26 of the second low-side bidirectional switch LS2 is in the on state, if the second voltage VB becomes larger than the third voltage VC, there is a risk of current flowing through an unintended path.

[0162] Furthermore, in the power conversion circuit of the prior art, during the period from time t10 to time t11 in sector 1a, that is, during the period when the 25th switch element S25 of the third high-side bidirectional switch HS3 is in the on state and the 13th switch element S13 of the second high-side bidirectional switch HS2 is in the on state, if the second voltage VB becomes larger than the third voltage VC, there is a risk that a current will flow through an unintended path.

[0163] Below, the control in the prior art and the control in this embodiment will be compared using the periods from time t3 to time t4 and from time t10 to time t11 in sector 1a as examples.

[0164] 15, in the case of the power conversion circuit of the conventional technology, the second low-side bidirectional switch LS2 is in the ON state in the negative direction and the third low-side bidirectional switch LS3 is in the ON state in the positive direction between time t3 and time t4. Therefore, when the second voltage VB becomes larger than the third voltage VC, a current flows through the conductive path from the second low-side bidirectional switch LS2 to the third low-side bidirectional switch LS3.

[0165] 16 , the control unit 33 of this embodiment turns off the 26th switch element S26 of the second low-side bidirectional switch LS2 at time t1′ in sector 1a′. That is, the second low-side bidirectional switch LS2 does not allow current to flow from the second input terminal 31B to the second output terminal 32B. Therefore, even if the second voltage VB becomes larger than the third voltage VC between time t3 and time t4, current is prevented from flowing through an unintended path.

[0166] 17 , in the case of the power conversion circuit of the conventional technology, the second high-side bidirectional switch HS2 is in the ON state in the positive direction and the third high-side bidirectional switch HS3 is in the ON state in the negative direction between time t10 and time t11. Therefore, when the second voltage VB becomes larger than the third voltage VC, a current flows through the conductive path from the second high-side bidirectional switch HS2 to the third high-side bidirectional switch HS3.

[0167] 18 , the control unit 33 of this embodiment turns off the thirteenth switch element S13 of the second high-side bidirectional switch HS2 at time t8′ in sector 1a′. That is, the second high-side bidirectional switch HS2 does not allow current to flow from the second input terminal 31B to the first output terminal 32A. Therefore, even if the second voltage VB becomes greater than the third voltage VC between time t10 and time t11, current is prevented from flowing through an unintended path.

[0168] (5-2. Comparison During Sector 1b') In the period between 0° and 30°, the third voltage VC is ideally equal to or lower than the second voltage VB. However, there are cases where noise is superimposed on each voltage, causing the third voltage VC to be greater than the second voltage VB.

[0169] In the power conversion circuit of the prior art, if the third voltage VC becomes larger than the second voltage VB during the period from time t2 to time t5 in sector 1b, that is, during the period when the 16th switch element S16 of the second low-side bidirectional switch LS2 is in the ON state and the 22nd switch element S22 of the third low-side bidirectional switch LS3 is in the ON state, there is a risk that a current will flow through an unintended path.

[0170] Furthermore, in the power conversion circuit of the prior art, if the third voltage VC becomes larger than the second voltage VB during the period from time t10 to time t11 in sector 1b, that is, during the period when the 23rd switch element S23 of the second high-side bidirectional switch HS2 is in the ON state and the 15th switch element S15 of the third high-side bidirectional switch HS3 is in the ON state, there is a risk that a current will flow through an unintended path.

[0171] Below, the control in the prior art and the control in this embodiment will be compared using the periods from time t3 to time t4 and from time t10 to time t11 in sector 1b as examples.

[0172] 19 , in the case of the power conversion circuit of the conventional technology, the second low-side bidirectional switch LS2 is in the ON state in the positive direction and the third low-side bidirectional switch LS3 is in the ON state in the negative direction between time t3 and time t4. Therefore, when the third voltage VC becomes larger than the second voltage VB, a current flows through the conductive path from the third low-side bidirectional switch LS3 to the second low-side bidirectional switch LS2.

[0173] 20 , the control unit 33 of this embodiment turns off the 22nd switch element S22 of the third low-side bidirectional switch LS3 at time t1' in sector 1b'. That is, the third low-side bidirectional switch LS3 does not allow current to flow from the third input terminal 31C to the second output terminal 32B. Therefore, even if the third voltage VC becomes larger than the second voltage VB between time t3 and time t4, current is prevented from flowing through an unintended path.

[0174] 21 , in the case of the power conversion circuit of the conventional technology, the second high-side bidirectional switch HS2 is in the ON state in the negative direction and the third high-side bidirectional switch HS3 is in the ON state in the positive direction between time t10 and time t11. Therefore, when the third voltage VC becomes larger than the second voltage VB, a current flows through the conductive path from the third high-side bidirectional switch HS3 to the second high-side bidirectional switch HS2.

[0175] 22 , the control unit 33 of this embodiment turns off the fifteenth switch element S15 of the third high-side bidirectional switch HS3 at time t8′ in sector 1b′. That is, the third high-side bidirectional switch HS3 does not allow current to flow from the third input terminal 31C to the first output terminal 32A. Therefore, even if the third voltage VC becomes greater than the second voltage VB between time t10 and time t11, current is prevented from flowing through an unintended path.

[0176] (5-3. Comparison in the Period of Sector 4a') In the period between 150° or more and less than 180°, the third voltage VC is less than the second voltage VB in an ideal state. However, there are cases where the third voltage VC becomes greater than the second voltage VB due to noise being superimposed on each voltage.

[0177] In the power conversion circuit of the prior art, if the third voltage VC becomes larger than the second voltage VB during the period from time t2 to time t5 in sector 4a, that is, during the period when the 15th switch element S15 of the third high-side bidirectional switch HS3 is in the on state and the 23rd switch element S23 of the second high-side bidirectional switch HS2 is in the on state, there is a risk that a current will flow through an unintended path.

[0178] Furthermore, in the power conversion circuit of the conventional technology, if the third voltage VC becomes larger than the second voltage VB during the period from time t10 to time t11 in sector 4a, that is, during the period when the 22nd switch element S22 of the third low-side bidirectional switch LS3 is in the on state and the 16th switch element S16 of the second low-side bidirectional switch LS2 is in the on state, there is a risk that a current will flow through an unintended path.

[0179] Below, the control in the prior art and the control in this embodiment will be compared using the periods from time t3 to time t4 and from time t10 to time t11 in sector 4a as examples.

[0180] 23, in the case of the power conversion circuit of the conventional technology, the second high-side bidirectional switch HS2 is in the ON state in the negative direction and the third high-side bidirectional switch HS3 is in the ON state in the positive direction between time t3 and time t4. Therefore, when the third voltage VC becomes larger than the second voltage VB, a current flows through the conductive path from the third high-side bidirectional switch HS3 to the second high-side bidirectional switch HS2.

[0181] 24 , the control unit 33 of this embodiment turns off the 23rd switch element S23 of the second high-side bidirectional switch HS2 at time t1′ in sector 4a′. That is, the second high-side bidirectional switch HS2 does not allow current to flow from the first output terminal 32A to the second input terminal 31B. Therefore, even if the third voltage VC becomes greater than the second voltage VB between time t3 and time t4, current is prevented from flowing through an unintended path.

[0182] 25, in the case of the power conversion circuit of the conventional technology, the second low-side bidirectional switch LS2 is in the on state in the positive direction and the third low-side bidirectional switch LS3 is in the on state in the negative direction between time t10 and time t11. Therefore, when the third voltage VC becomes larger than the second voltage VB, a current flows through the conductive path from the third low-side bidirectional switch LS3 to the second low-side bidirectional switch LS2.

[0183] 26 , the control unit 33 of this embodiment turns off the 16th switch element S16 of the second low-side bidirectional switch LS2 at time t8′ in sector 4b′. That is, the second low-side bidirectional switch LS2 does not allow current to flow from the second output terminal 32B to the second input terminal 31B. Therefore, even if the third voltage VC becomes larger than the second voltage VB between time t10 and time t11, current is prevented from flowing through an unintended path.

[0184] (5-4. Comparison During Sector 4b') In the period between -180° and -150°, ideally, the second voltage VB is equal to or lower than the third voltage VC. However, there are cases where the second voltage VB becomes larger than the third voltage VC due to noise being superimposed on each voltage.

[0185] In the power conversion circuit of the prior art, if the second voltage VB becomes larger than the third voltage VC during the period from time t2 to time t5 in sector 4b, that is, during the period when the thirteenth switch element S13 of the second high-side bidirectional switch HS2 is in the on state and the twenty-fifth switch element S25 of the third high-side bidirectional switch HS3 is in the on state, there is a risk that a current will flow through an unintended path.

[0186] Furthermore, in the power conversion circuit of the conventional technology, if the second voltage VB becomes larger than the third voltage VC during the period from time t10 to time t11 in sector 4b, that is, during the period when the 26th switch element S26 of the second low-side bidirectional switch LS2 is in the on state and the 12th switch element S12 of the third low-side bidirectional switch LS3 is in the on state, there is a risk that a current will flow through an unintended path.

[0187] Below, the control in the prior art and the control in this embodiment will be compared and explained using the periods from time t3 to time t4 and from time t10 to time t11 in sector 4b as examples.

[0188] 27 , in the case of the power conversion circuit of the conventional technology, the second high-side bidirectional switch HS2 is in the ON state in the positive direction and the third high-side bidirectional switch HS3 is in the ON state in the negative direction between time t3 and time t4. Therefore, when the second voltage VB becomes larger than the third voltage VC, a current flows through the conductive path from the second high-side bidirectional switch HS2 to the third high-side bidirectional switch HS3.

[0189] 28 , the control unit 33 of this embodiment turns off the 25th switch element S25 of the third high-side bidirectional switch HS3 at time t1′ in sector 4b′. That is, the third high-side bidirectional switch HS3 does not allow current to flow from the second output terminal 32B to the third input terminal 31C. Therefore, even if the second voltage VB becomes greater than the third voltage VC between time t3 and time t4, current is prevented from flowing through an unintended path.

[0190] 29 , in the case of the power conversion circuit of the conventional technology, the second low-side bidirectional switch LS2 is in the ON state in the negative direction and the third low-side bidirectional switch LS3 is in the ON state in the positive direction between time t10 and time t11. Therefore, when the second voltage VB becomes larger than the third voltage VC, a current flows through the conductive path from the second low-side bidirectional switch LS2 to the third low-side bidirectional switch LS3.

[0191] 30 , the control unit 33 of this embodiment turns off the twelfth switch element S12 of the third low-side bidirectional switch LS3 at time t8' in sector 4b'. That is, the third low-side bidirectional switch LS3 does not allow current to flow from the second output terminal 32B to the third input terminal 31C. Therefore, even if the second voltage VB becomes greater than the third voltage VC between time t10 and time t11, current is prevented from flowing through an unintended path.

[0192] (5-5. Regarding other specific periods) In the third to sixth specific periods, even if the magnitude relationship of the voltages under ideal conditions is reversed due to noise being superimposed on each voltage, current can be prevented from flowing through unintended paths, just as in the first and second specific periods.

[0193] (6. Effects of the Present Embodiment) (1) According to the above embodiment, the control unit 33 controls each bidirectional switch TSW in accordance with the magnitude relationship among the first voltage VA, the second voltage VB, and the third voltage VC. Furthermore, the control unit 33 performs complementary switching control during a specific period. Therefore, even if noise is superimposed on the voltage of each phase, it is possible to prevent current from flowing through unintended paths.

[0194] (2) According to the above embodiment, the specific period is defined within the ranges of (X°-3°) to X° and (X°+180°) to (X°+183°). Furthermore, the specific period is defined within the ranges of X° to (X°+3°) and (X°+177°) to (X°+180°). Furthermore, the specific period includes the X° and (X°+180°). The above period is a period in which the voltage magnitude relationship is likely to change due to noise superposition. Therefore, by providing a specific period within the above period, it is easy to prevent current from flowing through unintended paths. Furthermore, during the specific period, the number of on / off switching of each switch element increases. Therefore, by narrowing the specific period to the above period, switching loss can be suppressed.

[0195] (3) According to the above embodiment, each bidirectional switch TSW includes two switch elements connected in series such that the anode terminals of the body diodes are connected to each other. This configuration makes it possible to configure the power conversion circuit 30 relatively simply and inexpensively.

[0196] (4) According to the above embodiment, the power conversion device 10 is a three-phase isolated converter. The control unit 33 performs zero voltage switching. This configuration is suitable as a circuit configuration for performing complementary switching control.

[0197] <Modifications> The above embodiment and the following modifications can be implemented in combination with each other within the scope of technical compatibility.

[0198] (Modifications to the Configuration of the Power Conversion Device) The configuration of the power conversion device 10 is not limited to the example of the above embodiment. For example, the power conversion device 10 is not limited to a three-phase isolated AC-DC converter, and may also be applied to a non-isolated three-phase AC-DC converter. In other words, the power conversion device 10 does not have to include one or more selected from the input low-pass filter 20, the transformer circuit 40, the rectifier circuit 50, and the output low-pass filter 60.

[0199] Furthermore, the three-phase AC power supply 80 connected to the three external input terminals 11 is not limited to a three-phase three-wire type, but may be a three-phase four-wire type, or may be a delta-connected three-phase three-wire type three-phase AC power supply 80. The configuration of the power conversion device 10 may be changed as appropriate depending on the type of the three-phase AC power supply 80.

[0200] The input-side low-pass filter 20 may include a plurality of capacitors connected between the lines of each phase to which the first voltage VA, the second voltage VB, and the third voltage VC are input. The switch elements constituting each bidirectional switch TSW are not limited to those in the above embodiment. For example, the two switch elements of the bidirectional switch TSW may be P-channel MOSFETs. In this case, the drain terminals of the two switch elements of the bidirectional switch TSW are connected to each other.

[0201] The two switch elements of the bidirectional switch TSW may be transistors capable of passing a current in both the forward and reverse directions. In this case, the two switch elements are connected in series with their source terminals connected to each other. Specifically, the switch elements are gallium nitride high electron mobility transistors (GaN-High Electron Mobility Transistors, GaN-HEMTs) or the like.

[0202] The transformer circuit 40 does not need to include the fourth inductor L4. In this case, the leakage inductance of the transformer 41 can be used for resonance instead of the fourth inductor L4. The specific circuit configuration of the rectifier circuit 50 is not limited to the example of the above embodiment. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or the like.

[0203] (Examples of changes to the definition of sectors, etc.) The first, third, and fifth specific periods may be defined within the ranges of (X°-30°) to X° and (X°+180°) to (X°+210°), and are not limited to the periods shown in the above embodiment. The second, fourth, and sixth specific periods may be defined within the ranges of X° to (X°+30°) and (X°+150°) to (X°+180°), and are not limited to the periods shown in the above embodiment. In other words, the first, third, and fifth specific periods do not have to be defined within the ranges of (X°-3°) to X° and (X°+180°) to (X°+183°). The second, fourth, and sixth specific periods do not have to be set within the range of X° or more and (X°+3°) or less, and the range of (X°+177°) or more and (X°+180°) or less. However, the ranges of adjacent specific periods must be set so that they do not overlap.

[0204] Furthermore, it is sufficient that at least one of the first, third, and fifth specific periods is set at least once within one cycle of the three-phase AC power, and that at least one of the second, fourth, and sixth specific periods is set at least once within one cycle of the three-phase AC power.

[0205] For example, the first specific period may be in the range of -30° to 0°, and the second specific period may be greater than 0° and less than 30°. Furthermore, in a certain cycle, the period of sector 1a' and the period of sector 4a' may be set to different lengths. This also applies to the second to sixth specific periods.

[0206] In the above embodiment, which of the three input terminals 31 of the power conversion circuit 30 corresponds to the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C can be changed as appropriate.

[0207] "Within a predetermined specific period" means that the period is determined before entering each specific period. For example, even if the first specific period in a certain cycle is between -3° and 0°, the first specific period in the next cycle may be determined to be between -6° and 0° before entering the first specific period.

[0208] The control unit 33 may be configured to be able to change the length of the specific period depending on the operating conditions of the power conversion device 10. For example, the control unit 33 may make the specific period longer within a predetermined period after the control unit 33 starts operating than after the predetermined period has elapsed since the control unit 33 starts operating.

[0209] During a certain period after the control unit 33 starts driving, noise is more likely to be superimposed on the input voltage from the three-phase AC power supply 80 than after the certain period has elapsed. In other words, the certain period after the control unit 33 starts driving is a suitable situation for determining the specific period. Furthermore, by extending the specific period in this situation, it is easier to prevent current from flowing through unintended paths.

[0210] <Supplementary Notes> The technical concepts that can be derived from the above-described embodiment and modifications are described below. [1] A power supply comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, and receiving a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, in one-to-one correspondence; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches; and a control unit that controls the bidirectional switches, wherein the plurality of bidirectional switches include: a first high-side bidirectional switch connecting the first input terminal and the first output terminal; a first low-side bidirectional switch connecting the first input terminal and the second output terminal; a second high-side bidirectional switch connecting the second input terminal and the first output terminal; a second low-side bidirectional switch connecting the second input terminal and the second output terminal; a third high-side bidirectional switch connecting the third input terminal and the first output terminal; and a third low-side bidirectional switch connecting the third input terminal and the second output terminal, wherein when the phase at which the first voltage is maximum is X°, the control unit controls the third low-side bidirectional switch and the second low-side bidirectional switch so that the on / off states of the bidirectional switches are switched such that a state in which the third low-side bidirectional switch allows a current to flow from the second output terminal to the third input terminal and a state in which the second low-side bidirectional switch allows a current to flow from the second input terminal to the second output terminal do not overlap, during a specific period that is determined within a range of a period in which the phase of the first voltage is equal to or greater than (X°-30°) and equal to or less than X°, and a range of a period in which the phase of the first voltage is equal to or greater than (X°+180°) and equal to or less than (X°+210°); and controls the second high-side bidirectional switch and the third high-side bidirectional switch so that the on / off states of the bidirectional switches are switched such that a state in which the second high-side bidirectional switch allows a current to flow from the second input terminal to the first output terminal and a state in which the third high-side bidirectional switch allows a current to flow from the first output terminal to the third input terminal do not overlap.

[0211] [2] A power supply comprising: a first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, and receiving a first voltage, a second voltage, and a third voltage, which are AC voltages of different phases, in a one-to-one correspondence; a first output terminal and a second output terminal capable of outputting AC power; a plurality of bidirectional switches; and a control unit that controls the bidirectional switches, wherein the plurality of bidirectional switches include: a first high-side bidirectional switch connecting the first input terminal and the first output terminal; a first low-side bidirectional switch connecting the first input terminal and the second output terminal; a second high-side bidirectional switch connecting the second input terminal and the first output terminal; a second low-side bidirectional switch connecting the second input terminal and the second output terminal; a third high-side bidirectional switch connecting the third input terminal and the first output terminal; and a third low-side bidirectional switch connecting the third input terminal and the second output terminal, wherein when the phase at which the first voltage is maximum is X°, the control unit controls the third low-side bidirectional switch and the second low-side bidirectional switch so that the on / off states of each of the bidirectional switches are switched such that a state in which the third low-side bidirectional switch allows a current to flow from the third input terminal to the second output terminal and a state in which the second low-side bidirectional switch allows a current to flow from the second output terminal to the second input terminal do not overlap, during a predetermined specific period within a range of a period in which the phase of the first voltage is equal to or greater than X° (X° + 30°) and a range of a period in which the phase of the first voltage is equal to or greater than (X° + 150°) and greater than (X° + 180°), respectively; and controls the second high-side bidirectional switch and the third high-side bidirectional switch so that the on / off states of each of the bidirectional switches are switched such that a state in which the second high-side bidirectional switch allows a current to flow from the first output terminal to the second input terminal and a state in which the third high-side bidirectional switch allows a current to flow from the third input terminal to the first output terminal do not overlap.

[0212] [3] The power conversion circuit according to [1], wherein the specific period is determined within a range of a period in which the phase of the first voltage is greater than or equal to (X°-3°) and less than or equal to X°, and within a range of a period in which the phase of the first voltage is greater than or equal to (X°+180°) and less than or equal to (X°+183°).

[0213] [4] The power conversion circuit according to [2], wherein the specific period is determined within a range of a period in which the phase of the first voltage is greater than or equal to X° and less than or equal to (X°+3°), and within a range of a period in which the phase of the first voltage is greater than or equal to (X°+177°) and less than or equal to (X°+180°).

[0214] [5] The power conversion circuit according to any one of [1] to [4], wherein the specific period includes a time when the phase of the first voltage is X° and a time when the phase is (X°+180°).

[0215] [6] The power conversion circuit according to any one of [1] to [5], wherein the bidirectional switch has two switch elements connected in series so that anode side terminals of body diodes are connected to each other.

[0216] [7] The power conversion circuit according to any one of [1] to [5], wherein the bidirectional switch has two switch elements connected in series so that source terminals are connected to each other, and the switch elements are transistors capable of passing a current in a forward direction and a reverse direction.

[0217] [8] The power conversion circuit according to any one of [1] to [7], wherein the control unit extends the specific period within a predetermined period from when the control unit starts driving compared to after the predetermined period has elapsed from when the control unit starts driving.

[0218] [9] A power conversion device comprising: the power conversion circuit according to any one of [1] to [8]; a transformer having a primary winding and a secondary winding, wherein a first end of the primary winding is connected to the first output terminal and a second end of the primary winding is connected to the second output terminal; and a rectifier circuit connected to the secondary winding.

[0219] REFERENCE SIGNS LIST 10...Power conversion device 30...Power conversion circuit 31A...First input terminal 31B...Second input terminal 31C...Third input terminal VA...First voltage VB...Second voltage VC...Third voltage 32A...First output terminal 32B...Second output terminal 33...Control unit TSW...Bidirectional switch HS1...First high-side bidirectional switch LS1...First low-side bidirectional switch HS2...Second high-side bidirectional switch LS2...Second low-side bidirectional switch HS3...Third high-side bidirectional switch LS3...Third low-side bidirectional switch 41...Transformer 41A...Primary winding 41B...Secondary winding 50...Rectifier circuit

Claims

1. A first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, into which a first voltage, a second voltage, and a third voltage, which are AC voltages with different phases, are input in a one-to-one correspondence. A first output terminal and a second output terminal capable of outputting AC power, Multiple bidirectional switches, The system comprises a control unit that controls each of the aforementioned bidirectional switches, Multiple of the aforementioned bidirectional switches are A first high-side bidirectional switch connecting the first input terminal and the first output terminal, A first low-side bidirectional switch connecting the first input terminal and the second output terminal, A second high-side bidirectional switch connecting the second input terminal and the first output terminal, A second low-side bidirectional switch connecting the second input terminal and the second output terminal, A third high-side bidirectional switch connecting the third input terminal and the first output terminal, A third low-side bidirectional switch connecting the third input terminal and the second output terminal, Includes, When the phase at which the first voltage is maximum is denoted as X°, The control unit operates within a specific period defined within the range of the period in which the phase of the first voltage is (X° - 30°) or more and X° or less, and within the range of the period in which the phase of the first voltage is (X° + 180°) or more and (X° + 210°) or less. The third low-side bidirectional switch and the second low-side bidirectional switch are controlled so that the on / off states of each bidirectional switch do not overlap between the state in which the third low-side bidirectional switch allows current to flow from the second output terminal to the third input terminal and the state in which the second low-side bidirectional switch allows current to flow from the second input terminal to the second output terminal. Furthermore, the second high-side bidirectional switch and the third high-side bidirectional switch are controlled such that the on / off states of each bidirectional switch do not overlap between the state in which the second high-side bidirectional switch allows current to flow from the second input terminal to the first output terminal and the state in which the third high-side bidirectional switch allows current to flow from the first output terminal to the third input terminal. Power conversion circuit.

2. A first input terminal, a second input terminal, and a third input terminal connected to a three-phase AC power supply, into which a first voltage, a second voltage, and a third voltage, which are AC voltages with different phases, are input in a one-to-one correspondence. A first output terminal and a second output terminal capable of outputting AC power, Multiple bidirectional switches, The system comprises a control unit that controls each of the aforementioned bidirectional switches, Multiple of the aforementioned bidirectional switches are A first high-side bidirectional switch connecting the first input terminal and the first output terminal, A first low-side bidirectional switch connecting the first input terminal and the second output terminal, A second high-side bidirectional switch connecting the second input terminal and the first output terminal, A second low-side bidirectional switch connecting the second input terminal and the second output terminal, A third high-side bidirectional switch connecting the third input terminal and the first output terminal, A third low-side bidirectional switch connecting the third input terminal and the second output terminal, Includes, When the phase at which the first voltage is maximum is denoted as X°, The control unit operates within a predetermined specific period within the range where the phase of the first voltage is X° or more and (X° + 30°) or more and (X° + 150°) or more and (X° + 180°), The third low-side bidirectional switch and the second low-side bidirectional switch are controlled so that the on / off states of each bidirectional switch do not overlap, such that the state in which the third low-side bidirectional switch allows current to flow from the third input terminal to the second output terminal and the state in which the second low-side bidirectional switch allows current to flow from the second output terminal to the second input terminal. Furthermore, the second high-side bidirectional switch and the third high-side bidirectional switch are controlled such that the on / off states of each bidirectional switch do not overlap between the state in which the second high-side bidirectional switch allows current to flow from the first output terminal to the second input terminal and the state in which the third high-side bidirectional switch allows current to flow from the third input terminal to the first output terminal. Power conversion circuit.

3. The aforementioned specific period is defined within the range of the period in which the phase of the first voltage is between (X°-3°) and X°, and within the range of the period in which it is between (X°+180°) and (X°+183°). The power conversion circuit according to claim 1.

4. The aforementioned specific period is defined within the range of a period in which the phase of the first voltage is X° or more and (X° + 3°) or less, and within the range of a period in which the phase is (X° + 177°) or more and (X° + 180°) or less. The power conversion circuit according to claim 2.

5. The specified period includes the time when the phase of the first voltage is X° and the time when it is (X° + 180°). The power conversion circuit according to claim 1 or 2.

6. The bidirectional switch has two switch elements connected in series such that the anode terminals of the body diodes are connected to each other. The power conversion circuit according to claim 1 or 2.

7. The aforementioned bidirectional switch has two switch elements connected in series such that their source terminals are connected to each other. The aforementioned switching element is a transistor capable of conducting current in both the forward and reverse directions. The power conversion circuit according to claim 1 or 2.

8. The control unit shall, within a predetermined period of time after it starts operating, extend the specified period compared to the period after it has elapsed since it started operating. The power conversion circuit according to claim 1 or 2.

9. A power conversion circuit according to claim 1 or 2, A transformer having a primary winding and a secondary winding, wherein the first end of the primary winding is connected to the first output terminal and the second end of the primary winding is connected to the second output terminal, The rectifier circuit connected to the secondary winding, Equipped with Power converter.