Power conversion device and program for power conversion device

Abstract

A switch circuit (85) has a bidirectional switch. The switch circuit (85) is connected between a third output terminal (82A) of a second power conversion circuit (80) and a first end of a primary-side winding (41A). During execution of second control in which the second power conversion circuit (80) outputs power, a control unit (90) controls the switch circuit (85) so as to allow the flow of current from the second power conversion circuit (80) to the primary-side winding (41A). During execution of first control in which a first power conversion circuit (30) outputs power, the control unit (90) controls the switch circuit (85) so as to block the flow of current from the first power conversion circuit (30) to the second power conversion circuit (80).

Description

Power conversion device and program for power conversion device

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

[0002] The power conversion device disclosed in Patent Document 1 includes a matrix converter having six bidirectional switches, a transformer having two coils, and a control device that controls the on / off of each bidirectional switch. By switching the on / off of each bidirectional switch according to a predetermined sequence, the matrix converter converts the input three-phase AC power into DC power and outputs it to the primary coil of the transformer. Further, the power conversion device disclosed in Patent Document 1 includes a protection circuit. The protection circuit is connected between the matrix converter and the transformer. Further, the protection circuit and the matrix converter are connected in parallel to the transformer.

[0003] Japanese Patent Application Laid-Open No. 2019-68657

[0004] As in the power conversion device disclosed in Patent Document 1, some other circuit may be connected between the matrix converter and the primary coil of the transformer. And when this other circuit has a switch element, a parasitic capacitance occurs in the switch element when the switch element is in the off state. The power conversion device disclosed in Patent Document 1 has not considered such a parasitic capacitance at all.

[0005] One embodiment for solving the above problem is a power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, which can convert three-phase AC power input to the input terminals and output it from the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a switch element, a third output terminal connected between the first output terminal and the first end of the primary winding, a fourth output terminal connected between the second output terminal and the second end of the primary winding, which can output power from the third output terminal and the fourth output terminal; and a bidirectional switch. The power conversion device comprises a switch circuit connected between the third output terminal and the first end of the primary winding, or between the fourth output terminal and the second end of the primary winding, and a control unit that controls the power conversion circuit, the output circuit, and the switch circuit, wherein the control unit controls the switch circuit to block the flow of current from the power conversion circuit to the output circuit when the power conversion circuit is performing a first control in which it outputs power from the first output terminal and the second output terminal, and controls the switch circuit to allow the flow of current from the output circuit to the primary winding when the output circuit is performing a second control in which it outputs power from the third output terminal and the fourth output terminal.

[0006] One embodiment for solving the above problem is a power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, which can convert three-phase AC power input to the input terminals and output it from the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a switch element, a third output terminal connected between the first output terminal and the first end of the primary winding, a fourth output terminal connected between the second output terminal and the second end of the primary winding, which can output power from the third output terminal and the fourth output terminal; and a bidirectional switch, which has the third output terminal and the primary winding This is a program for a power converter that includes a switch circuit connected between the first terminals or between the fourth output terminal and the second terminal of the primary winding, and a control unit that controls the power conversion circuit, the output circuit, and the switch circuit, and causes the control unit to perform the following processes: controlling the switch circuit to block the flow of current from the power conversion circuit to the output circuit while the power conversion circuit is performing a first control in which the power conversion circuit outputs power from the first output terminal and the second output terminal, and controlling the switch circuit to allow the flow of current from the output circuit to the primary winding while the output circuit is performing a second control in which the output circuit outputs power from the third output terminal and the fourth output terminal.

[0007] This reduces the parasitic capacitance of the power converter when the power conversion circuit is outputting power.

[0008] Figure 1 is a circuit diagram of the power converter. Figure 2 is a circuit diagram of the first power converter circuit. Figure 3 is a circuit diagram of the second power converter circuit and the switch circuit. Figure 4 is a circuit diagram showing an example of the on / off state of the switch element of the first power converter circuit. Figure 5 is an equivalent circuit diagram of the parasitic capacitance of the power converter assuming there is no switch circuit. Figure 6 is an equivalent circuit diagram of the parasitic capacitance of the power converter.

[0009] <Embodiments of Power Converters and Programs for Power Converters> Embodiments of power converters and programs for power converters are described below. The drawings are merely illustrative of the embodiments of this disclosure and should not be considered limiting. The drawings are schematic diagrams for ease of understanding and may enlarge or omit components. Terms such as "first," "second," and "third" in this disclosure are used simply to distinguish objects and do not rank or assign any order to them.

[0010] (Configuration of the power converter) As shown in Figure 1, the power converter 10 includes an input-side low-pass filter 20, a first power conversion circuit 30, a transformer circuit 40, and a rectifier circuit 50. The power converter 10 also includes a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C, as well as a first external output terminal 12A and a second external output terminal 12B.

[0011] The power converter 10 is, as a whole, a so-called three-phase isolated AC-DC converter. That is, the power converter 10 converts the three-phase AC power input to each external input terminal into DC power, which can then be output from a pair of external output terminals. Furthermore, a transformer circuit 40 is interposed in the power path from each external input terminal to each external output terminal, thereby electrically isolating each external input terminal from each external output terminal.

[0012] For example, each external input terminal receives the three phases of three-phase AC power input from the three-phase AC power supply 100. The three-phase AC power supply 100 is a three-phase three-wire commercial power system with three AC power supplies connected in a Y-connection. The voltages of the three phases are the first voltage VA, the second voltage VB, and the third voltage VC. Each voltage is an AC voltage with a different phase from the others. The first voltage VA is input to the first external input terminal 11A. The second voltage VB is input to the second external input terminal 11B. The third voltage VC is input to the third external input terminal 11C. The second voltage VB has a phase difference of 120° from the first voltage VA. The third voltage VC has a phase difference of 120° from the second voltage VB. Note that this "120° phase difference" allows for an error of approximately ±1°.

[0013] The pair of external output terminals are a first external output terminal 12A and a second external output terminal 12B. Any load 110 can be connected between the first external output terminal 12A and the second external output terminal 12B. The load 110 is, for example, an electronic device such as a server driven by DC power.

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

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

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

[0017] The first power conversion circuit 30 includes a plurality of input terminals and a pair of output terminals. The plurality of input terminals of the first power conversion circuit 30 are the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C. The first input terminal 31A is connected to the second end of the first inductor L1. The second input terminal 31B is connected to the second end of the second inductor L2. The third input terminal 31C is connected to the second end of the third inductor L3. Therefore, three-phase AC power is input to each input terminal of the first power conversion circuit 30 via each external input terminal and the input-side low-pass filter 20. The pair of output terminals are the first output terminal 32A and the second output terminal 32B. Single-phase AC power converted by each element in the first power conversion circuit 30 is output from the pair of output terminals.

[0018] As shown in Figure 2, the first power conversion circuit 30 is equipped with a plurality of bidirectional switches TSW. Each bidirectional switch TSW has two switch elements. Each switch element is an N-channel type 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, the switch elements constituting each bidirectional switch TSW are connected to each other such that the body diodes are in opposite directions. To put it another way, each bidirectional switch TSW has two switch elements with their source terminals connected to each other.

[0019] The multiple bidirectional switches TSW are 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 twentieth switch element S21. The drain terminal of the eleventh switch element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switch element S11 is connected to the source terminal of the twentieth switch element S21. The drain terminal of the twentieth 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 includes a 24th switch element S24 and a 14th switch element S14. The drain terminal of the 24th switch element S24 is connected to the first input terminal 31A. The source terminal of the 24th switch element S24 is connected to the source terminal of the 14th switch element S14. The drain terminal of the 14th switch element S14 is connected to the second output terminal 32B.

[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 13th switch element S13 and a 23rd switch element S23. The drain terminal of the 13th switch element S13 is connected to the second input terminal 31B. The source terminal of the 13th switch element S13 is connected to the source terminal of the 23rd switch element S23. The drain terminal of the 23rd 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 15th switch element S15 and a 25th switch element S25. The drain terminal of the 15th switch element S15 is connected to the third input terminal 31C. The source terminal of the 15th switch element S15 is connected to the source terminal of the 25th switch element S25. The drain terminal of the 25th 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 22nd switch element S22 is connected to the source terminal of the 12th switch element S12. The drain terminal of the 12th switch element S12 is connected to the second output terminal 32B.

[0026] As shown in Figure 1, the transformer circuit 40 comprises a fourth inductor L4 and a transformer 41. The transformer 41 comprises a primary winding 41A and a secondary winding 41B. The first end of the fourth inductor L4 is connected to the first output terminal 32A of the first power conversion circuit 30. The first end of the primary winding 41A is connected to the second end of the fourth inductor L4. The second end of the primary winding 41A is connected to the second output terminal 32B of the first power conversion circuit 30. The secondary winding 41B is connected to a pair of external output terminals via a rectifier circuit 50. The primary winding 41A and the secondary winding 41B are electrically insulated from each other.

[0027] The rectifier circuit 50 includes four diodes, a fifth inductor L5, and a fourth capacitor C4. The four diodes are the first diode 51, the second diode 52, the third diode 53, and the fourth diode 54.

[0028] The four diodes form a full-bridge circuit. Specifically, the anode terminal of the first diode 51 is connected to the first end of the secondary winding 41B of the transformer 41. The cathode terminal of the first diode 51 is connected to the cathode terminal of the third diode 53. The anode terminal of the third diode 53 is connected to the second end of the secondary winding 41B and the cathode terminal of the fourth diode 54. The anode terminal of the fourth diode 54 is connected to the anode terminal of the second diode 52. The cathode terminal of the second diode 52 is connected to the first end of the secondary winding 41B and the anode terminal of the first diode 51.

[0029] The first terminal 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. The second terminal of the fifth inductor L5 is connected to the first terminal of the fourth capacitor C4 and the first external output terminal 12A. The second terminal of the fourth capacitor C4 is connected to the anode terminal of the second diode 52 and the anode terminal of the fourth diode 54 and the second external output terminal 12B.

[0030] 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.

[0031] As shown in Figure 1, the power converter 10 includes a three-phase rectifier circuit 60, a boost circuit 70, and a second power converter circuit 80 as an output circuit. As shown in Figure 1, the three-phase rectifier circuit 60 has first connection terminals CT1 to fifth connection terminals CT5. The first connection terminal CT1 is connected to the first external input terminal 11A. The second connection terminal CT2 is connected to the second external input terminal 11B. The third connection terminal CT3 is connected to the third external input terminal 11C. Therefore, three-phase AC power is input from the three-phase AC power supply 100 to the first connection terminals CT1 to the third connection terminals CT3 of the three-phase rectifier circuit 60. The three-phase rectifier circuit 60 converts the three-phase AC power into DC power using a plurality of rectifier diodes and inductors (not shown). The converted DC power is output from the fourth connection terminal CT4 and the fifth connection terminal CT5. Furthermore, the fourth connection terminal CT4 is a high-potential terminal, and the fifth connection terminal CT5 is a low-potential terminal.

[0032] The boost circuit 70 is equipped with a sixth connection terminal CT6 to a ninth connection terminal CT9. The sixth connection terminal CT6 is connected to the fourth connection terminal CT4 of the three-phase rectifier circuit 60. The seventh connection terminal CT7 is connected to the fifth connection terminal CT5 of the three-phase rectifier circuit 60. Therefore, DC voltages are input to the sixth connection terminal CT6 and the seventh connection terminal CT7. The boost circuit 70 boosts these DC voltages using switch elements, inductors, capacitors, etc. (not shown) and outputs them. That is, the boost circuit 70 outputs DC power with a voltage value higher than the DC power input to the sixth connection terminal CT6 and the seventh connection terminal CT7 from the eighth connection terminal CT8 and the ninth connection terminal CT9. For example, if the effective value of the voltage of the three-phase AC power is 200 Vrms, the maximum value of each voltage of the three-phase AC power in this embodiment is approximately 283 V. Therefore, the output voltage of the boost circuit 70 is greater than 283 V. Note that the maximum value of the AC voltage is the effective value of the AC voltage multiplied by √2. Also, the eighth connection terminal CT8 is the high-potential terminal, and the ninth connection terminal CT9 is the low-potential terminal.

[0033] The second power conversion circuit 80 is equipped with a plurality of input terminals and a pair of output terminals. The plurality of input terminals of the second power conversion circuit 80 are the fourth input terminal 81A and the fifth input terminal 81B. The pair of output terminals of the second power conversion circuit 80 are the third output terminal 82A and the fourth output terminal 82B. The fourth input terminal 81A is connected to the eighth connection terminal CT8 of the boost circuit 70. The fifth input terminal 81B is connected to the ninth connection terminal CT9 of the boost circuit 70.

[0034] The third output terminal 82A is connected between the first output terminal 32A of the first power conversion circuit 30 and the first end of the fourth inductor L4 via a switch circuit 85, which will be described later. Therefore, the third output terminal 82A is connected to the first end of the primary winding 41A of the transformer 41 via the fourth inductor L4. In other words, the third output terminal 82A is connected between the first output terminal 32A and the first end of the primary winding 41A. The fourth output terminal 82B is connected between the second output terminal 32B of the first power conversion circuit 30 and the second end of the primary winding 41A of the transformer 41.

[0035] As shown in Figure 3, the second power conversion circuit 80 includes a fifth capacitor C5 and first to fourth switch elements SW1 to SW4. The first end of the fifth capacitor C5 is connected to the fourth input terminal 81A. The second end of the fifth capacitor C5 is connected to the fifth input terminal 81B.

[0036] The first to fourth switching elements SW1 to SW4 are all n-channel MOSFETs. The drain terminal of the first switching element SW1 is connected to the fourth input terminal 81A and the first terminal of the fifth capacitor C5. The drain terminal of the first switching element SW1 is also connected to the drain terminal of the third switching element SW3. The source terminal of the first switching element SW1 is connected to the drain terminal of the second switching element SW2. The connection node between the source terminal of the first switching element SW1 and the drain terminal of the second switching element SW2 is the third output terminal 82A. The source terminal of the third switching element SW3 is connected to the drain terminal of the fourth switching element SW4. The connection node between the source terminal of the third switching element SW3 and the drain terminal of the fourth switching element SW4 is the fourth output terminal 82B. The source terminal of the fourth switching element SW4 is connected to the fifth input terminal 81B and the source terminal of the second switching element SW2.

[0037] As shown in Figure 1, the power converter 10 includes a switch circuit 85. The switch circuit 85 is connected between the third output terminal 82A of the second power converter circuit 80 and the first end of the primary winding 41A of the transformer circuit 40.

[0038] As shown in Figure 3, in this embodiment, the switch circuit 85 is composed of a single bidirectional switch TSW. Specifically, the switch circuit 85 includes a fifth switch element SW5 and a sixth switch element SW6. Both the fifth switch element SW5 and the sixth switch element SW6 are n-channel type MOSFETs. The drain terminal of the fifth switch element SW5 is connected to the third output terminal 82A of the second power conversion circuit 80. The source terminal of the fifth switch element SW5 is connected to the source terminal of the sixth switch element SW6. The drain terminal of the sixth switch element SW6 is connected to the first output terminal 32A of the first power conversion circuit 30 and the first end of the fourth inductor L4 of the transformer circuit 40.

[0039] As shown in Figure 1, the power converter 10 includes a power detection circuit SE and a control unit 90. The power detection circuit SE is capable of detecting the power applied to the first external input terminal 11A, the second external input terminal 11B, and the third external input terminal 11C. Specifically, the power detection circuit SE is capable of detecting the voltage and current values ​​input to each external input terminal. That is, the power detection circuit SE is capable of detecting the first voltage VA, the second voltage VB, and the third voltage VC.

[0040] The control unit 90 has a storage device and an execution device (not shown). In other words, the control unit 90 is an MCU (Microcontroller Unit). The storage device of the control unit 90 stores the program PG that is executed by the execution device.

[0041] The execution device includes, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an FPGA (Field Programmable Gate Array), or a CPLD (Complex Programmable Logic Device), or an ASIC (Application Specific Integrated Circuit). The execution device of the control unit 90 can execute the first control and second control processes described later by executing the program PG.

[0042] Specifically, the program PG contains data for executing the first and second controls. As part of this data, the program PG defines multiple different switching patterns for the multiple bidirectional switches TSW in the first power conversion circuit 30. These switching patterns define combinations of on and off states for the multiple bidirectional switches TSW. The program PG also defines the order in which the switching patterns for the bidirectional switches TSW are switched.

[0043] The power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit switches the on / off states of the two switching elements included in each bidirectional switch TSW and the first switch element SW1 to the sixth switch element SW6. The execution device of the control unit 90 inputs a switching signal to the input terminal of the gate drive circuit and outputs a gate drive voltage to each switching element via the gate drive circuit, thereby controlling each switching element.

[0044] As shown in FIG. 2, the switching signal includes the eleventh switching signal SG11 to the sixteenth switching signal SG16 and the twenty-first switching signal SG21 to the twenty-sixth switching signal SG26. The eleventh switching signal SG11 to the sixteenth switching signal SG16 respectively correspond to the eleventh switch element S11 to the sixteenth switch element S16. The twenty-first switching signal SG21 to the twenty-sixth switching signal SG26 respectively correspond to the twenty-first switch element S21 to the twenty-sixth switch element S26.

[0045] The execution device of the control unit 90 controls the on / off states of the plurality of bidirectional switches TSW in the first power conversion circuit 30 while switching the switching pattern according to a plurality of switching patterns. With these switching signals, the first power conversion circuit 30 converts the three-phase AC power input to each input terminal into AC power and outputs it. That is, when the potential difference between the first output terminal 32A and the second output terminal 32B of the first power conversion circuit 30 shown in FIG. 1 is defined as the primary voltage Vp, the primary voltage Vp is an AC voltage. Therefore, the AC voltage, i.e., the primary voltage Vp, is applied to the primary side winding 41A of the transformer 41.

[0046] As shown in FIG. 3, the switching signal includes the first switching signal SG1 to the fourth switching signal SG4. The first switching signal SG1 to the fourth switching signal SG4 respectively correspond to the first switch element SW1 to the fourth switch element SW4. With these switching signals, the second power conversion circuit 80 can convert the DC power discharged from the fifth capacitor C5 into AC power by the control described later.

[0047] As shown in FIG. 3, the switching signal includes a fifth switching signal SG5 and a sixth switching signal SG6. The fifth switching signal SG5 and the sixth switching signal SG6 respectively correspond to a fifth switching element SW5 and a sixth switching element SW6. By these switching signals, the switch circuit 85 is switched between a state that allows current to flow from the second power conversion circuit 80 to the primary winding 41A of the transformer 41 and a state that blocks current from flowing from the first power conversion circuit 30 to the second power conversion circuit 80.

[0048] (Control when voltage abnormality occurs) When power supply is started for each external input terminal of the power conversion device 10, the execution device of the control unit 90 executes each process of the first control and the second control, and each process associated therewith based on the above-described program PG. In the following, the control by the execution device of the control unit 90 will be simply described as the control by the control unit 90.

[0049] When the program PG is started, the control unit 90 first turns off the first switch element SW1 to the fourth switch element SW4. While the program PG is running, the control unit 90 acquires the voltage values ​​of the three-phase AC power input to each external input terminal detected by the power detection circuit SE. The control unit 90 then acquires the voltage values ​​of the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C of the first power conversion circuit 30 through the voltage values ​​of each external input terminal of the power conversion device 10. Furthermore, the control unit 90 determines whether the amplitude values ​​of the input voltages input to the multiple input terminals are less than or equal to a predetermined first threshold. In this embodiment, the control unit 90 determines whether the amplitude values ​​of the input voltages input to all input terminals, including the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C, are less than or equal to a predetermined first threshold. This first threshold is, for example, 1 / 20√2 of the amplitude value of the AC voltage when the three-phase AC power supply 100 is operating normally. In this embodiment, the amplitude values ​​of the first voltage VA to the third voltage VC input from the three-phase AC power supply 100 are 200√2 (approximately 283) V. Therefore, the predetermined value is 10 V. For example, if a momentary power outage occurs in which the power supplied to the power converter 10 is interrupted for several tens of milliseconds, the amplitude values ​​of each input voltage may all simultaneously become 10 V or less.

[0050] In this context, amplitude refers to the wavelength height of an AC waveform during one cycle. That is, the amplitude is a value that fluctuates during the operation of the power converter 10. For example, when the three-phase AC power supply 100 is operating normally, the amplitude values ​​of the first voltage VA to the third voltage VC are 200√2V. If a momentary power outage occurs, these voltages will decrease, and therefore the amplitude values ​​may decrease. The amplitude value is sometimes also called the peak value. Alternatively, the amplitude value may be calculated by dividing the difference between the maximum and minimum values ​​during one cycle of the AC waveform by two.

[0051] The control unit 90 executes the first control if the amplitude values ​​of the input voltages input to all input terminals are not less than or equal to a predetermined first threshold, in other words, if the amplitude values ​​of the input voltages input to one or more input terminals among the first input terminal 31A to the third input terminal 31C are greater than the predetermined first threshold. In the first control, the control unit 90 controls the first switch element SW1 to the fourth switch element SW4 so that no voltage is applied from the first output terminal 32A and the second output terminal 32B to the fifth capacitor C5. That is, the control unit 90 controls the plurality of switch elements so that the fifth capacitor C5 and each output terminal of the first power conversion circuit 30 are not electrically connected via the first switch element SW1 to the fourth switch element SW4.

[0052] Specifically, in the first control, the control unit 90 maintains the first to fourth switch elements SW1 to SW4 in the off state if the amplitude value of one or more input voltages among the first voltage VA, second voltage VB, and third voltage VC detected by the power detection circuit SE is greater than the first threshold. At this time, the control unit 90 controls the on / off state of each bidirectional switch TSW of the first power conversion circuit 30 while sequentially switching the switching patterns defined in the program PG. In other words, in this case, the first power conversion circuit 30 converts the three-phase AC voltage consisting of the first voltage VA to the third voltage VC into single-phase AC power. The converted AC voltage is then output from the first output terminal 32A and the second output terminal 32B and applied to the primary winding 41A of the transformer 41. Furthermore, this AC voltage is not applied to the fifth capacitor C5 of the second power conversion circuit 80. Thus, the first control is a control in which the first power conversion circuit 30 outputs power from the first output terminal 32A and the second output terminal 32B.

[0053] On the other hand, during the execution of the first control, the three-phase AC power input from the three-phase AC power supply 100 to the power converter 10 is converted to DC power of a predetermined voltage value via the three-phase rectifier circuit 60 and the boost circuit 70. This DC power is then used to charge the fifth capacitor C5 of the second power converter circuit 80. Due to the boost circuit 70, the power charged to the fifth capacitor C5 is greater than the maximum voltage of the three-phase AC power. That is, if the effective voltage of the three-phase AC power is 200 Vrms, the maximum voltage across the terminals of the fifth capacitor C5 is greater than 283 V.

[0054] Furthermore, during the execution of the first control, the control unit 90 controls the switch circuit 85 to block the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80. Specifically, during the execution of the first control, the control unit 90 controls both the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 to the off state.

[0055] The control unit 90 executes the second control when the amplitude values ​​of all input voltages, from the first voltage VA to the third voltage VC, detected by the power detection circuit SE, simultaneously fall below the first threshold. In the second control, the control unit 90 switches all of the multiple bidirectional switches TSW in the first power conversion circuit 30 to the off state at the timing when the primary voltage Vp falls below a predetermined second threshold. Furthermore, the control unit 90 controls the first switch element SW1 to the fourth switch element SW4 according to a predetermined pattern so that the energy stored in the fifth capacitor C5 is output to the primary side winding 41A. The second threshold is, for example, 10V. Also, "simultaneously" means that an error of a few milliseconds is permitted.

[0056] Specifically, as described above, the output voltage of the first power conversion circuit 30 is an AC voltage. That is, the primary voltage Vp periodically repeats between a positive state, a near-zero volt state, and a negative state. The control unit 90 switches all bidirectional switches TSW in the first power conversion circuit 30 to the off state when the primary voltage Vp is near-zero volts. The control unit 90 then controls each switch element in the second power conversion circuit 80 so that the DC power discharged from the fifth capacitor C5 is converted into AC power, and that this AC power is output from the third output terminal 82A and the fourth output terminal 82B. Therefore, the second control is a control that causes the second power conversion circuit 80 to output power from the third output terminal 82A and the fourth output terminal 82B.

[0057] More specifically, when the primary voltage Vp is negative, the control unit 90 switches all bidirectional switches TSW in the first power conversion circuit 30 to the off state when the amplitude values ​​of the input voltages input to all of the input terminals simultaneously fall below a first threshold, and the absolute value of the primary voltage Vp falls below a predetermined second threshold. Furthermore, the control unit 90 controls the first switch element SW1 to the fourth switch element SW4 so that the primary voltage Vp changes to the positive side when the energy stored in the fifth capacitor C5 begins to be output.

[0058] On the other hand, when the primary voltage Vp is positive, if the amplitude values ​​of the input voltages input to all of the input terminals simultaneously fall below the first threshold, the control unit 90 switches all bidirectional switches TSW in the first power conversion circuit 30 to the off state at the timing when the absolute value of the primary voltage Vp falls below a predetermined second threshold. Furthermore, the control unit 90 controls the first switch element SW1 to the fourth switch element SW4 so that the primary voltage Vp changes to the negative side when the energy stored in the fifth capacitor C5 begins to be output.

[0059] Furthermore, during the execution of the second control, the control unit 90 controls the switch circuit 85 to allow current to flow from the second power conversion circuit 80 to the primary winding 41A of the transformer 41. Specifically, during the execution of the second control, the control unit 90 controls both the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 to the ON state.

[0060] During the execution of the second control, the control unit 90 determines whether the amplitude value of the input voltage input to one or more input terminals among the first input terminal 31A to the third input terminal 31C is greater than a predetermined first threshold. Specifically, the control unit 90 determines whether the amplitude value of one or more input voltages among the first voltage VA to the third voltage VC detected by the power detection circuit SE is greater than the first threshold.

[0061] As described above, after the amplitude values ​​of all input voltages from the first voltage VA to the third voltage VC detected by the power detection circuit SE simultaneously fall below the first threshold, suppose that the amplitude value of one or more input voltages from the first voltage VA to the third voltage VC becomes greater than the first threshold. In this case, the control unit 90 executes the first control again. That is, the control unit 90 switches from the second control to the first control. When switching the control, the control unit 90 first controls the switch circuit 85 to block the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80 before switching to the first control. That is, the control unit 90 controls both the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 to the off state.

[0062] Next, the control unit 90 switches to the first control. That is, the control unit 90 controls the first to fourth switch elements SW1 to SW4 so that the first output terminal 32A and the second output terminal 32B and the fifth capacitor C5 do not conduct electricity through the respective switch elements of the second power conversion circuit 80. Specifically, the control unit 90 switches all of the first to fourth switch elements SW1 to SW4 to the OFF state. After that, the control unit 90 again controls the multiple bidirectional switches TSW of the first power conversion circuit 30 by sequentially switching the switching pattern defined in the program PG. In other words, the control unit 90 switches any of the bidirectional switches TSW to the ON state according to the predetermined switching pattern. Therefore, for example, when power supply from the three-phase AC power supply 100 is restored after a momentary power outage, the control unit 90 switches from power conversion by the second power conversion circuit 80 to power conversion by the first power conversion circuit 30.

[0063] (Regarding the operation of this embodiment) When the switch elements constituting the bidirectional switch TSW of the first power conversion circuit 30 are in the off state, parasitic capacitance is generated between the source terminal and drain terminal of the switch element. Similarly, when each switch element constituting the second power conversion circuit 80 is in the off state, parasitic capacitance is also generated between the source terminal and drain terminal of each switch element. Therefore, a potential difference may be generated between the source terminal and drain terminal of an off switch element. When a switch element is switched to the ON state while a potential difference exists between its source terminal and drain terminal, the parasitic capacitance of each switch element short-circuits, and the charge accumulated in the parasitic capacitance becomes a cause of switching loss. Therefore, in terms of reducing the switching loss of the switch elements and, consequently, increasing the efficiency of the first power conversion circuit 30, it is preferable to resonate the fourth inductor L4 and the parasitic capacitance of each switch element, and switch each switch element to the ON state when the voltage difference between the switch elements is small, ideally zero.

[0064] However, if the parasitic capacitance generated in the first power conversion circuit 30 and the second power conversion circuit 80 is large, the energy of the fourth inductor L4 required to discharge the energy stored in the parasitic capacitance needs to be increased. Since the energy of the fourth inductor L4 is determined by the load current, the load 110 needs to be increased in order to increase the energy of the fourth inductor L4. In other words, if the parasitic capacitance generated in the first power conversion circuit 30 is small, it becomes possible to discharge it completely even with a small load 110. In other words, the range in which the first power conversion circuit 30 can operate with high efficiency is expanded.

[0065] Here, we assume that the power conversion device 10 described above does not have a switch circuit 85. Also, as shown in Figure 4, while the control unit 90 is executing the first control, as part of the first control, the on / off state of each switch element of the first power conversion circuit 30 is switched using the following example switching pattern. At this time, the first voltage VA is positive, and the second voltage VB and the third voltage VC are negative.

[0066] In the above switching pattern, the 11th switch element S11 of the first power conversion circuit 30 is ON, the 21st switch element S21 is ON, the 24th switch element S24 is OFF, and the 14th switch element S14 is ON. Also, the 13th switch element S13 of the first power conversion circuit 30 is ON, the 23rd switch element S23 is OFF, the 26th switch element S26 is OFF, and the 16th switch element S16 is OFF. Furthermore, the 15th switch element S15 is ON, the 25th switch element S25 is OFF, the 22nd switch element S22 is ON, and the 12th switch element S12 is OFF. In addition, since the control unit 90 is executing the first control, all of the first switch elements SW1 to the 4th switch elements SW4 constituting the second power conversion circuit 80 are OFF.

[0067] In a power converter 10 without a switch circuit 85, when the on / off state of each switch element of the first power converter 30 is controlled according to the above switching pattern, the fourth inductor L4 is in a state as if multiple parasitic capacitances were connected to it. Specifically, as shown in Figure 5, the fourth inductor L4 is in a state as if the following three parasitic capacitance circuits generated within the first power converter 30 are connected in parallel. One of the three parasitic capacitance circuits is the parasitic capacitance PC12 caused by the twelfth switch element S12. Another of the three parasitic capacitance circuits is a circuit in which the parasitic capacitance PC26 caused by the 26th switch element S26 and the parasitic capacitance PC16 caused by the 16th switch element S16 are connected in series. The remaining of the three parasitic capacitance circuits is the parasitic capacitance PC24 caused by the 24th switch element S24.

[0068] Furthermore, the fourth inductor L4 is also connected to the second power conversion circuit 80. Therefore, in addition to the three parasitic capacitance circuits mentioned above, the parasitic capacitance PC80 generated by the first switch element SW1 to the fourth switch element SW4 that constitute the second power conversion circuit 80 is connected in parallel to the fourth inductor L4.

[0069] When the controlled state of the above switching pattern is maintained, the energy stored in the parasitic capacitance of each switch element in the off state is released, and the parasitic capacitance of each switch element that switches from the on state to the off state is charged. Therefore, the lower the value of each parasitic capacitance, the higher the probability that the potential difference between the source terminal and drain terminal of each switch element in the first power conversion circuit 30 will reach zero under the condition of a constant load 110, that is, under the condition that a constant current flows through the fourth inductor L4.

[0070] On the other hand, in the power conversion device 10 of the above embodiment, the switch circuit 85 is connected between the third output terminal 82A of the second power conversion circuit 80 and the first end of the primary winding 41A of the transformer circuit 40. In this power conversion device 10, suppose the control unit 90 controls each switch element of the first power conversion circuit 30 with the same switching pattern as hypothesized above as part of the first control. In this case, the three parasitic capacitance circuits that occur in the first power conversion circuit 30 are the same as in the example described above. On the other hand, while the first control is being executed, the control unit 90 controls both the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 to the off state. Therefore, as shown in Figure 6, the parasitic capacitance PC85 caused by each switch element in the switch circuit 85 is connected in series with the fourth inductor L4 and the parasitic capacitance PC80 generated by the first switch element SW1 to the fourth switch element SW4 that constitute the second power conversion circuit 80.

[0071] Furthermore, regardless of the switching pattern described above, the control unit 90 turns off one of the switch elements in the first power conversion circuit 30 during the first control. Therefore, parasitic capacitance is generated during the first control, corresponding to the switch element that is in the off state. Also, while the first control is being executed, the control unit 90 controls both the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 to be in the off state. Therefore, during the first control, regardless of the switching pattern used to control each switch element in the first power conversion circuit 30, parasitic capacitance PC80 is generated in the first switch element SW1 to the fourth switch element SW4 that constitute the second power conversion circuit 80. And, regardless of the switching pattern of each switch element in the first power conversion circuit 30, the parasitic capacitance PC85 caused by each switch element in the switch circuit 85 is directly connected to this parasitic capacitance PC80.

[0072] <Effects of the Embodiment> The above embodiment provides the following effects: (1) As described above, during the first control, the fifth switch element SW5 and the sixth switch element SW6 in the switch circuit 85 are controlled to the off state, so that during the first control, the parasitic capacitance PC85 generated in the switch circuit 85 is directly connected to the parasitic capacitance PC80 generated in the second power conversion circuit 80. When two capacitances are directly connected, the total capacitance value of the two capacitances is smaller than the capacitance value of each individual capacitance. In other words, in the above embodiment, during the first control, the combined capacitance value of the parasitic capacitance PC80 of the second power conversion circuit 80 and the parasitic capacitance PC85 of the switch circuit 85 is smaller than the capacitance value of the parasitic capacitance PC80 of the second power conversion circuit 80 alone. As a result, the parasitic capacitance of the first power conversion circuit 30, the second power conversion circuit 80, and the switch circuit 85 as a whole is also reduced. Therefore, it is possible to suppress the charge accumulated in the parasitic capacitance from causing switching losses. In other words, even with a small load 110, it becomes possible to completely discharge the charge accumulated in the parasitic capacitance, thus expanding the range in which the first power conversion circuit 30 can operate with high efficiency.

[0073] (2) In the above embodiment, when the control unit 90 switches from the second control to the first control, it controls the switch circuit 85 to interrupt the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80 before switching to the first control. In other words, at the time of switching to the first control, the second power conversion circuit 80 is disconnected from the first power conversion circuit 30 by the switch circuit 85. Therefore, it is possible to prevent unintended current from flowing from the first power conversion circuit 30 to the second power conversion circuit 80 immediately after switching to the first control.

[0074] (3) In the above embodiment, the second power conversion circuit 80 is capable of outputting the energy stored in the fifth capacitor C5. Therefore, the second power conversion circuit 80 is suitable as a backup power source when the power supply to the first power conversion circuit 30 is momentarily interrupted.

[0075] (4) In the above embodiment, the presence of the boost circuit 70 makes it possible to make the terminal voltage of the fifth capacitor C5 in the second power conversion circuit 80 greater than the maximum voltage of the three-phase AC power from the three-phase AC power supply 100. Therefore, during the second control, it is less likely that the voltage of the fifth capacitor C5 will be too low and power will not be output from the second power conversion circuit 80.

[0076] <Examples of Modifications> The above embodiment can be implemented with the following modifications. The above embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0077] The configuration of the power converter 10 is not limited to the examples of the above embodiment. For example, the power converter 10 is not limited to a three-phase isolated AC-DC converter, but can also be applied to a non-isolated three-phase AC-DC converter. Furthermore, the power converter 10 does not need to include one or more selected from the input-side low-pass filter 20, transformer circuit 40, and rectifier circuit 50. Moreover, the power converter 10 may include elements and circuits other than those exemplified in the above embodiment.

[0078] In the above embodiment, the three-phase AC power supply 100 connected to the three external input terminals is not limited to a three-phase three-wire system, but may also be a three-phase four-wire system or a delta-connected three-phase three-wire system. The configuration of the power converter 10 may be appropriately changed to correspond to the type of three-phase AC power supply 100.

[0079] The input-side low-pass filter 20 in the above embodiment 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.

[0080] The switching elements constituting each bidirectional switch TSW are not limited to the examples of the embodiments described above. For example, the two switching elements of the bidirectional switch TSW may be P-channel type MOSFETs. In this case, the drain terminals of the two switching elements of the bidirectional switch TSW are connected to each other.

[0081] In the above embodiment, the two switching elements of the bidirectional switch TSW may be transistors capable of conducting current in both the forward and reverse directions. In this case, the two switching elements are connected in series such that their source terminals are connected to each other. Specifically, the switching elements are gallium nitride high electron mobility transistors (GaN-HEMT), etc.

[0082] - The transformer circuit 40 in the above embodiment does not necessarily have 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.

[0083] The specific circuit configuration of the rectifier circuit 50 is not limited to the examples of the embodiments described above. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or the like. In other words, any circuit that can rectify and output the DC power flowing through the secondary winding 41B of the transformer 41 is acceptable.

[0084] The power conversion device 10 in the above embodiment does not necessarily have to include a three-phase rectifier circuit 60. For example, a power supply device other than the three-phase AC power supply 100 may be connected to the sixth connection terminal CT6 and the seventh connection terminal CT7 of the boost circuit 70. That is, the fifth capacitor C5 of the second power conversion circuit 80 may be charged by a power supply other than the three-phase AC power supply 100.

[0085] The second power conversion circuit 80 does not necessarily have to have a fifth capacitor C5. For example, the second power conversion circuit 80 may have a DC power supply instead of the fifth capacitor C5, or another power supply may be connected to the fourth input terminal 81A and the fifth input terminal 81B of the second power conversion circuit 80. In other words, the second power conversion circuit 80 can be used in any circuit configuration as long as it has a switching element and can function as an output circuit capable of outputting power from the third output terminal 82A and the fourth output terminal 82B.

[0086] - The output voltage of the boost circuit 70 in the above embodiment may be approximately 283V or less, which is the voltage input to the first input terminal 31A to the third input terminal 31C. Even in this case, the second power conversion circuit 80 can maintain power supply to the load 110 when a momentary power outage occurs.

[0087] Furthermore, the power conversion device 10 does not necessarily have to include a boost circuit 70. In this case, the maximum terminal voltage of the fifth capacitor C5 of the second power conversion circuit 80 is less than or equal to the maximum value of the input voltage of the three-phase AC power. Even in this case, since each switch element of the switch circuit 85 is controlled to be in the off state during the second control, unintended current is unlikely to flow from the output terminal of the first power conversion circuit 30 to the fifth capacitor C5 of the second power conversion circuit 80.

[0088] - The power detection circuit SE in the above embodiment may detect the voltage and current values ​​at the first input terminals 31A to the third input terminals 31C of the first power conversion circuit 30, rather than the voltage and current values ​​at the first external input terminals 11A to the third external input terminals 11C.

[0089] - The second power conversion circuit 80 in the above embodiment may include a switch element connecting the fifth capacitor C5 and the third output terminal 82A and the fourth output terminal 82B. Specifically, the second power conversion circuit 80 may include a switch element connected between the first end of the fifth capacitor C5 and the drain terminal of the first switch element SW1. By including the switch element in the second power conversion circuit 80, switching between the first control and the second control becomes easier.

[0090] In the above embodiment, when the first power conversion circuit 30 is controlled by the first control, the control unit 90 does not need to keep all the switch elements of the second power conversion circuit 80 in the off state. In particular, during the first control, each switch element of the switch circuit 85 is controlled to be in the off state, so even if any of the switch elements of the second power conversion circuit 80 is in the on state, it is possible to prevent current from flowing from the first output terminal 32A and the second output terminal 32B to the fifth capacitor C5.

[0091] In the above embodiment, the control unit 90 may switch from the first control to the second control at a time other than when the absolute value of the primary voltage Vp becomes less than or equal to the second threshold, when the amplitude value of the input voltages input to the multiple input terminals becomes less than or equal to the first threshold. As described above, in the above embodiment, the presence of the switch circuit 85 reduces the parasitic capacitance of the entire power converter 10, so even if the absolute value of the primary voltage Vp is not less than or equal to the second threshold, the potential difference between the source terminal and drain terminal of each switch element is relatively small.

[0092] In the above embodiment, the control unit 90 does not need to switch all bidirectional switches TSW to the off state when the input voltage falls below the first threshold, i.e., during the second control. The control unit 90 only needs to be able to stop the power conversion by the first power conversion circuit 30 by switching a plurality of bidirectional switches TSW to the off state, and some of the bidirectional switches TSW may remain in the on state.

[0093] - The switch circuit 85 may be connected between the fourth output terminal 82B of the second power conversion circuit 80 and the second end of the primary winding 41A of the transformer 41. Alternatively, separate switch circuits 85 may be connected between the third output terminal 82A of the second power conversion circuit 80 and the first end of the primary winding 41A of the transformer 41, and between the fourth output terminal 82B of the second power conversion circuit 80 and the second end of the primary winding 41A of the transformer 41.

[0094] The switch circuit 85 only needs to have one or more bidirectional switches. For example, it may have two or more bidirectional switches connected in series. In addition, the switch circuit 85 may have other elements in addition to the bidirectional switches.

[0095] - The on / off states of each switch element in the switch circuit 85 during the first control are not limited to the examples of the above embodiment. For example, the control unit 90 may turn on the fifth switch element SW5 and turn off the sixth switch element SW6 during the first control. In this case as well, the switch circuit 85 blocks the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80. In this case, parasitic capacitance is generated in the switch circuit 85 because the sixth switch element SW6 is off.

[0096] - The on / off states of each switch element in the switch circuit 85 during the second control are not limited to the examples of the above embodiment. For example, the control unit 90 may turn on the fifth switch element SW5 and turn off the sixth switch element SW6 during the second control. In this case, the body diode of the sixth switch element SW6 allows current to flow from the second power conversion circuit 80 to the first power conversion circuit 30. Therefore, the switch circuit 85 allows current to flow from the second power conversion circuit 80 to the primary winding 41A of the transformer 41.

[0097] The control unit 90 may, at the same time as switching from the second control to the first control, control the switch circuit 85 to block the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80.

[0098] -Incidentally, as in the power conversion device disclosed in Patent Document 1, another output circuit capable of supplying power to the primary coil of the transformer may be connected between the matrix converter and the primary coil of the transformer. In this case, it is conceivable to control the system so that power is supplied to the primary coil of the transformer from either the matrix converter or the other output circuit. When switching the circuit that supplies power to the primary coil of the transformer in this way, there is a risk that current may flow from one circuit to the other during the switching. From the standpoint of solving this problem, it is not essential for the control unit 90 to control the switch circuit 85 so as to block the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80 during the execution of the first control. That is, if the only goal is to solve the above problem, the control unit 90 only needs to control the switch circuit 85 so as to block the flow of current from the first power conversion circuit 30 to the second power conversion circuit 80 before switching from the second control to the first control. Then, during the first control, the switch circuit 85 may be configured to allow current to flow from the second power conversion circuit 80 to the primary winding 41A.

[0099] <Note> The technical concepts that can be understood from the above embodiments and modified examples are described below. [1] A power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, which can convert three-phase AC power input to the input terminals and output it from the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a switch element, a third output terminal connected between the first output terminal and the first end of the primary winding, and a fourth output terminal connected between the second output terminal and the second end of the primary winding, which can output power from the third output terminal and the fourth output terminal; and a bidirectional switch having the third output terminal and the primary winding A power conversion device comprising: a switch circuit connected between one end or between the fourth output terminal and the second end of the primary winding; the power conversion circuit, the output circuit, and a control unit that controls the switch circuit, wherein the control unit controls the switch circuit to allow current to flow from the output circuit to the primary winding while the output circuit is performing a second control in which it outputs power from the third output terminal and the fourth output terminal; and when switching from the second control to a first control in which the power conversion circuit outputs power from the first output terminal and the second output terminal, the control unit controls the switch circuit to block the flow of current from the power conversion circuit to the output circuit before switching to the first control.

[0100] 10...Power converter 11A...First external input terminal 11B...Second external input terminal 11C...Third external input terminal 12A...First external output terminal 12B...Second external output terminal 30...First power conversion circuit 32A...First output terminal 32B...Second output terminal 41...Transformer 41A...Primary winding 41B...Secondary winding 70...Boost circuit 80...Second power conversion circuit 82A...Third output terminal 82B...Fourth output terminal SW1...First switch element SW2...Second switch element SW3...Third switch element SW4...Fourth switch element 85...Switch circuit TSW...Bidirectional switch 90...Control unit 100...Three-phase AC power supply PG...Program

Claims

1. A power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, capable of converting three-phase AC power input to the input terminals and outputting it from the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, with the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; an output circuit having a switch element, a third output terminal connected between the first output terminal and the first end of the primary winding, and a fourth output terminal connected between the second output terminal and the second end of the primary winding, capable of outputting power from the third output terminal and the fourth output terminal; a switch circuit having a bidirectional switch, connected between the third output terminal and the first end of the primary winding, or between the fourth output terminal and the second end of the primary winding; and a control unit that controls the power conversion circuit, the output circuit and the switch circuit, wherein the control unit is A power conversion device in which, during the execution of a first control in which the power conversion circuit outputs power from the first output terminal and the second output terminal, the switch circuit is controlled to block the flow of current from the power conversion circuit to the output circuit, and during the execution of a second control in which the output circuit outputs power from the third output terminal and the fourth output terminal, the switch circuit is controlled to allow current to flow from the output circuit to the primary winding.

2. The power conversion device according to claim 1, wherein when the control unit switches from the second control to the first control, it controls the switch circuit to interrupt the flow of current from the power conversion circuit to the output circuit before switching to the first control.

3. The power conversion device according to claim 1 or 2, wherein, when the power conversion circuit is the first power conversion circuit, the output circuit is a second power conversion circuit having a plurality of the switch elements and a capacitor, and capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal.

4. The power conversion device according to claim 3, further comprising a boost circuit that boosts the input DC voltage and outputs it to the second power conversion circuit, wherein the output voltage of the boost circuit is greater than the maximum value of the input voltage input to the input terminal.

5. Applicable to a power conversion device comprising: a power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, capable of converting three-phase AC power input to the input terminals and outputting it from the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, with the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; an output circuit having a switch element, a third output terminal connected between the first output terminal and the first end of the primary winding, and a fourth output terminal connected between the second output terminal and the second end of the primary winding, capable of outputting power from the third output terminal and the fourth output terminal; a switch circuit having a bidirectional switch, connected between the third output terminal and the first end of the primary winding, or between the fourth output terminal and the second end of the primary winding; and a control unit that controls the power conversion circuit, the output circuit, and the switch circuit, wherein the control unit is configured to: A program for a power converter that causes the following to be executed: a process to control the switch circuit to block the flow of current from the power converter circuit to the output circuit while the power converter circuit is performing a first control in which it outputs power from the first output terminal and the second output terminal; and a process to control the switch circuit to allow the flow of current from the output circuit to the primary winding while the output circuit is performing a second control in which it outputs power from the third output terminal and the fourth output terminal.

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