Power conversion device and program for power conversion device

Abstract

A power conversion device (10) is a three-phase insulated AC-DC converter that comprises a first power conversion circuit, a transformer, and a control unit (90). The power conversion device (10) also comprises a second power conversion circuit (80). The second power conversion circuit (80) has a pair of output terminals, a plurality of switch elements, and a fifth capacitor (C5). The second power conversion circuit (80) can output power stored at the fifth capacitor (C5) to a primary winding of the transformer via the plurality of switch elements. The second power conversion circuit (80) has a specific switch element (SW7) that is connected between the fifth capacitor (C5) and the pair of output terminals.

Description

Power conversion device and program for power conversion device

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

[0002] The power conversion device disclosed in Patent Document 1 includes a plurality of nodes, a plurality of switch elements, and a control device. Three-phase AC power is input to three of the plurality of nodes. The power conversion circuit is capable of converting the three-phase AC power input to the nodes into DC power and outputting the DC power through on / off control of the plurality of switch elements by the control device.

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

[0004] When a power conversion circuit is used in a data center or other application, a protection circuit that protects the power conversion circuit in the event of an abnormality and a backup power supply that maintains power supply to the load are often connected. However, if a backup power supply is installed in addition to the protection circuit, the device may become larger and its configuration may become more complex.

[0005] In order to solve the above problems, the present disclosure provides a power conversion device comprising: a first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, and a first output terminal and a second output terminal and capable of converting three-phase AC power; 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; a second power conversion circuit having a capacitor, a plurality of switch elements, 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 and capable of converting a DC voltage discharged from the capacitor; and a control unit capable of switching on and off the plurality of bidirectional switches and on and off the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal, and the control unit is capable of switching on and off the specific switch element.

[0006] The present disclosure also provides a first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, a first output terminal and a second output terminal and capable of converting three-phase AC power; a second power conversion circuit having a primary winding and a secondary winding, 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; a capacitor; a plurality of switch elements; 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 converting DC power discharged from the capacitor. and a control unit capable of switching on and off the plurality of bidirectional switches and the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal, and the program for a power conversion device causes the control unit to switch all of the bidirectional switches to an off state when power conversion by the first power conversion circuit is to be stopped, and to control the on and off of the plurality of switch elements so that the second power conversion circuit outputs AC power when the specific switch element is in an on state.

[0007] The present disclosure also provides a first power conversion circuit capable of converting three-phase AC power input to the plurality of input terminals, a first output terminal and a second output terminal, a plurality of bidirectional switches connected between the plurality of input terminals and the first output terminal and the second output terminal, a transformer having a primary winding and a secondary winding, 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 and capable of converting AC voltage, the first power conversion circuit comprising: a capacitor; a plurality of switch elements; and a control unit capable of switching on and off the plurality of bidirectional switches and the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor, and the third output terminal and the fourth output terminal, and the control unit is capable of switching on and off the specific switch element.

[0008] The function of both the backup power supply and the function of the protection circuit can be realized while suppressing an increase in the size of the device.

[0009] Fig. 1 is a circuit diagram of a power conversion device. Fig. 2 is a circuit diagram of a first power conversion circuit. Fig. 3 is a circuit diagram of a second power conversion circuit. Fig. 4 is a circuit diagram of the second power conversion circuit in a modified example.

[0010] <One embodiment of a power conversion device and a program for the power conversion device> An embodiment of a power conversion device and a program for the power conversion device will be described below. Note that the drawings merely illustrate the embodiments of the present disclosure and should not be considered to limit the present disclosure. Furthermore, the drawings are schematic diagrams for ease of understanding, and components may be enlarged or omitted. Terms such as "first," "second," and "third" in the present disclosure are used simply to distinguish between objects and are not used to rank the objects.

[0011] 1, the power conversion device 10 includes an input-side low-pass filter 20, a first power conversion circuit 30, a second power conversion circuit 80, a transformer circuit 40, and a rectifier circuit 50. The power conversion device 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.

[0012] The power conversion device 10 is a so-called three-phase insulated AC-DC converter as a whole. That is, the power conversion device 10 converts three-phase AC power input to each external input terminal into DC power and outputs it from a pair of external output terminals. The presence of a transformer circuit 40 on the power path from each external input terminal to each external output terminal electrically insulates each external input terminal side from each external output terminal side.

[0013] Specifically, three phases of three-phase AC power input from a three-phase AC power supply 100 are input to each external input terminal in a one-to-one relationship. The three-phase AC power supply 100 is a three-phase, three-wire commercial power system in which three AC power supplies are Y-connected. The three phase voltages are a first voltage VA, a second voltage VB, and a third voltage VC. These voltages are AC voltages of different phases. The first voltage VA is input to a first external input terminal 11A. The second voltage VB is input to a second external input terminal 11B. The third voltage VC is input to a third external input terminal 11C. 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. Note that the "phase difference of 120°" allows for an error of approximately ±1°.

[0014] The pair of external output terminals is a first external output terminal 12A and a second external output terminal 12B. An arbitrary 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 driven by DC power.

[0015] The input low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3, as well as a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0016] A first end of the first inductor L1 is connected to the first external input terminal 11A. A first end of the first capacitor C1 is connected to the second end of the first inductor L1. A first end of the second inductor L2 is connected to the second external input terminal 11B. A first end of the second capacitor C2 is connected to the second end of the second inductor L2. A second end of the second capacitor C2 is connected to the second end of the first capacitor C1.

[0017] A first end of the third inductor L3 is connected to the third external input terminal 11C. A first end of the third capacitor C3 is connected to the second end of the third inductor L3. A second end of the third capacitor C3 is connected to the second end of the first capacitor C1.

[0018] The first power conversion circuit 30 includes a plurality of input terminals and a pair of output terminals. The input terminals of the first power conversion circuit 30 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 each input terminal of the first power conversion circuit 30 via each external input terminal and the input-side low-pass filter 20. The first power conversion circuit 30 includes a pair of output terminals, a first output terminal 32A, and a 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.

[0019] As shown in FIG. 2 , the first power conversion circuit 30 includes a plurality of bidirectional switches TSW. Each bidirectional switch TSW includes two switch elements. Each switch element is an N-channel metal oxide semiconductor field effect transistor (MOSFET). That is, each switch element includes a body diode. 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. That is, the switch elements that configure each bidirectional switch TSW are connected to each other such that the body diodes are oriented in opposite directions. In other words, each bidirectional switch TSW includes two switch elements whose source terminals are connected to each other.

[0020] The multiple bidirectional switches TSW include a first high-side bidirectional switch HS1, a first low-side bidirectional switch LS1, a second high-side bidirectional switch HS2, a second low-side bidirectional switch LS2, a third high-side bidirectional switch HS3, and a third low-side bidirectional switch LS3.

[0021] The first high-side bidirectional switch HS1 connects the first input terminal 31A and the first output terminal 32A. Specifically, the first high-side bidirectional switch HS1 has an eleventh switch element S11 and a twenty-first switch element S21. The drain terminal of the eleventh switch element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switch element S11 is connected to the source terminal of the twenty-first switch element S21. The drain terminal of the twenty-first switch element S21 is connected to the first output terminal 32A.

[0022] The first low-side bidirectional switch LS1 connects the first input terminal 31A and the second output terminal 32B. Specifically, the first low-side bidirectional switch LS1 has a 24th switch element S24 and a 14th switch element S14. The drain terminal of the 24th switch element S24 is connected to the first input terminal 31A. The source terminal of the 24th switch element S24 is connected to the source terminal of the 14th switch element S14. The drain terminal of the 14th switch element S14 is connected to the second output terminal 32B.

[0023] The second high-side bidirectional switch HS2 connects the second input terminal 31B and the first output terminal 32A. Specifically, the second high-side bidirectional switch HS2 has a thirteenth switch element S13 and a twenty-third switch element S23. The drain terminal of the thirteenth switch element S13 is connected to the second input terminal 31B. The source terminal of the thirteenth switch element S13 is connected to the source terminal of the twenty-third switch element S23. The drain terminal of the twenty-third switch element S23 is connected to the first output terminal 32A.

[0024] The second low-side bidirectional switch LS2 connects the second input terminal 31B and the second output terminal 32B. Specifically, the second low-side bidirectional switch LS2 has a 26th switch element S26 and a 16th switch element S16. The drain terminal of the 26th switch element S26 is connected to the second input terminal 31B. The source terminal of the 26th switch element S26 is connected to the source terminal of the 16th switch element S16. The drain terminal of the 16th switch element S16 is connected to the second output terminal 32B.

[0025] The third high-side bidirectional switch HS3 connects the third input terminal 31C and the first output terminal 32A. Specifically, the third high-side bidirectional switch HS3 has a fifteenth switch element S15 and a twenty-fifth switch element S25. The drain terminal of the fifteenth switch element S15 is connected to the third input terminal 31C. The source terminal of the fifteenth switch element S15 is connected to the source terminal of the twenty-fifth switch element S25. The drain terminal of the twenty-fifth switch element S25 is connected to the first output terminal 32A.

[0026] The third low-side bidirectional switch LS3 connects the third input terminal 31C and the second output terminal 32B. Specifically, the third low-side bidirectional switch LS3 has a 22nd switch element S22 and a 12th switch element S12. The drain terminal of the 22nd switch element S22 is connected to the third input terminal 31C. The source terminal of the 22nd switch element S22 is connected to the source terminal of the 12th switch element S12. The drain terminal of the 12th switch element S12 is connected to the second output terminal 32B.

[0027] As shown in FIG. 1 , 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 the first output terminal 32A of the first power conversion circuit 30. A first end of the primary winding 41A is connected to the second end of the fourth inductor L4. A 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.

[0028] The rectifier circuit 50 includes a fifth inductor L5, a sixth inductor L6, a first switch element SW1, and a second switch element SW2. The first switch element SW1 and the second switch element SW2 are n-channel MOSFETs. A first end of the fifth inductor L5 is connected to a first end of the secondary winding 41B of the transformer 41. A second end of the fifth inductor L5 is connected to a first end of the sixth inductor L6. A second end of the sixth inductor L6 is connected to a second end of the secondary winding 41B and the drain terminal of the second switch element SW2. A source terminal of the second switch element SW2 is connected to the source terminal of the first switch element SW1. A drain terminal of the first switch element SW1 is connected to the first end of the secondary winding 41B and the second end of the fifth inductor L5. Therefore, the rectifier circuit 50 is a so-called current doubler circuit.

[0029] The rectifier circuit 50 also includes a fourth capacitor C4. The fourth capacitor C4 is a so-called smoothing capacitor. A first end of the fourth capacitor C4 is connected to a first end of the fifth inductor L5 and a first end of the sixth inductor L6. The first end of the fourth capacitor C4 is also connected to the first external output terminal 12A. The second end of the fourth capacitor C4 is connected to the source terminal of the first switch element SW1 and the source terminal of the second switch element SW2. The second end of the fourth capacitor C4 is also connected to the second external output terminal 12B.

[0030] As shown in FIG. 1, the power conversion device 10 includes a three-phase rectifier circuit 60, a boost circuit 70, and a second power conversion circuit 80. As shown in FIG. 1, the three-phase rectifier circuit 60 includes a first connection terminal CT1 to a fifth connection terminal CT5. The first connection terminal CT1 is connected to a first external input terminal 11A. The second connection terminal CT2 is connected to a second external input terminal 11B. The third connection terminal CT3 is connected to a third external input terminal 11C. Thus, three-phase AC power is input from a three-phase AC power supply 100 to the first connection terminal CT1 to the third connection terminal 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 a fourth connection terminal CT4 and a fifth connection terminal CT5. The fourth connection terminal CT4 is a high potential terminal, and the fifth connection terminal CT5 is a low potential terminal.

[0031] The boost circuit 70 includes 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 power is input to the sixth connection terminal CT6 and the seventh connection terminal CT7. The boost circuit 70 boosts and outputs the DC power using switching elements, inductors, capacitors, and the like (not shown). That is, the boost circuit 70 outputs DC power from the eighth connection terminal CT8 and the ninth connection terminal CT9, the DC power having a voltage value higher than that of the DC power input to the sixth connection terminal CT6 and the seventh connection terminal CT7. In this embodiment, the maximum value of each voltage of the three-phase AC power is approximately 283 V. Therefore, the boost circuit 70 boosts and outputs the voltage input to the sixth connection terminal CT6 and the seventh connection terminal CT7, so the output voltage of the boost circuit 70 is greater than 283 V. Note that the maximum voltage is the effective voltage multiplied by √2. The eighth connection terminal CT8 is a high-potential terminal, and the ninth connection terminal CT9 is a low-potential terminal.

[0032] The second power conversion circuit 80 has a plurality of input terminals and a pair of output terminals. The input terminals of the second power conversion circuit 80 are a fourth input terminal 81A and a fifth input terminal 81B. The pair of output terminals of the second power conversion circuit 80 are a third output terminal 82A and a fourth output terminal 82B. The fourth input terminal 81A is connected to an eighth connection terminal CT8 of the boost circuit 70. The fifth input terminal 81B is connected to a ninth connection terminal CT9 of the boost circuit 70.

[0033] 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. 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 to 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. Therefore, the fourth output terminal 82B is connected between the second output terminal 32B and the second end of the primary winding 41A.

[0034] 3, the second power conversion circuit 80 includes a fifth capacitor C5 and a bridge circuit BC. A first end of the fifth capacitor C5 is connected to the fourth input terminal 81A. A second end of the fifth capacitor C5 is connected to the fifth input terminal 81B.

[0035] The bridge circuit BC includes a third switch element SW3, a fourth switch element SW4, a fifth switch element SW5, and a sixth switch element SW6. The third switch elements SW3 to SW6 are n-channel MOSFETs. The drain terminal of the third switch element SW3 is connected to the fourth input terminal 81A and a first end of the fifth capacitor C5 via a specific switch element SW7 (described later). The drain terminal of the third switch element SW3 is also connected to the drain terminal of the fifth switch element SW5. The source terminal of the third switch element SW3 is connected to the drain terminal of the fourth switch element SW4 and the third output terminal 82A. The source terminal of the fifth switch element SW5 is connected to the fourth output terminal 82B and the drain terminal of the sixth switch element SW6. The source terminal of the sixth switch element SW6 is connected to the fifth input terminal 81B and the source terminal of the fourth switch element SW4.

[0036] The second power conversion circuit 80 includes a specific switch element SW7. The specific switch element SW7 is an n-channel MOSFET. The specific switch element SW7 is connected between the fifth capacitor C5 and the third output terminal 82A and the fourth output terminal 82B. In this embodiment, the specific switch element SW7 is connected between the fifth capacitor C5 and the bridge circuit BC. Specifically, the source terminal of the specific switch element SW7 is connected to the fourth input terminal 81A and the first end of the fifth capacitor C5. The drain terminal of the specific switch element SW7 is connected to the drain terminal of the third switch element SW3 and the drain terminal of the fifth switch element SW5.

[0037] As shown in Fig. 1, the power conversion device 10 includes a power sensor SE, a temperature sensor TS, and a control unit 90. The power sensor SE can detect 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 sensor SE can detect the voltage and current values ​​input to each external input terminal. The temperature sensor TS is located inside the housing of the power conversion device 10. The temperature sensor TS can detect the temperature inside the housing.

[0038] The control unit 90 has a storage device and an execution device (not shown). That is, the control unit 90 is an MCU (Microcontroller Unit). The storage device of the control unit 90 stores a program PG to be executed by the execution device.

[0039] The execution device includes, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an FPGA (Field Programmable Gate Array), a CPLD (Complex Programmable Logic Device), an ASIC (Application Specific Integrated Circuit), etc. The execution device of the control unit 90 executes the program PG to switch the on and off states of each of the bidirectional switches TSW, the first switch element SW1 to the sixth switch element SW6, and the specific switch element SW7 in a predetermined switching pattern.

[0040] Specifically, the power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit switches on and off two switch elements of each bidirectional switch TSW, the first switch element SW1 to the sixth switch element SW6, and a specific switch element SW7. The execution device of the control unit 90 inputs a switching signal to an input terminal of the gate drive circuit and outputs a gate drive voltage to each switch element via the gate drive circuit, thereby controlling each switch element.

[0041] 2, the switching signals include an eleventh switching signal SG11 to a sixteenth switching signal SG16 and a twenty-first switching signal SG21 to a twenty-sixth switching signal SG26. The eleventh switching signal SG11 to the sixteenth switching signal SG16 correspond one-to-one to the eleventh switch elements S11 to the sixteenth switch elements S16, respectively. The twenty-first switching signal SG21 to the twenty-sixth switching signal SG26 correspond one-to-one to the twenty-first switch elements S21 to the twenty-sixth switch elements S26, respectively. This enables the first power conversion circuit 30 to convert three-phase AC power input to each input terminal into AC power.

[0042] 1 , the switching signals include a first switching signal SG1 and a second switching signal SG2. The first switching signal SG1 is input to the gate terminal of the first switch element SW1. The second switching signal SG2 is input to the gate terminal of the second switch element SW2. This allows the rectifier circuit 50 to convert AC power generated by the secondary winding 41B of the transformer 41 into DC power.

[0043] 3, the switching signals include a third switching signal SG3 to a seventh switching signal SG7. The third switching signal SG3 to the sixth switching signal SG6 correspond one-to-one to the third switching element SW3 to the sixth switching element SW6, respectively. The seventh switching signal SG7 corresponds to the specific switching element SW7. This allows the second power conversion circuit 80 to convert the DC voltage discharged by the fifth capacitor C5 into an AC voltage through control described below.

[0044] (Regarding control when abnormal voltage occurs) The execution device of the control unit 90 executes the above-described program PG when power supply starts to each external input terminal of the power conversion device 10. Note that, in the following description, the control by the execution device of the control unit 90 will be simply referred to as control by the control unit 90.

[0045] Immediately after starting execution of the program PG, the control unit 90 turns off the specific switch element SW7. While the program PG is being executed, the control unit 90 acquires the voltage and current values ​​of the three-phase AC power input to each external input terminal detected by the power sensor SE. While the program PG is being executed, the control unit 90 acquires the temperature detected by the temperature sensor TS.

[0046] Immediately after power supply to the power conversion device 10 starts, the control unit 90 maintains the specific switch element SW7 in the OFF state. Then, when the inter-terminal voltage of the fifth capacitor C5 becomes equal to or greater than the peak value of the AC voltage input to each external input terminal of the power conversion device 10, the control unit 90 switches the specific switch element SW7 to the ON state and maintains the ON state of the specific switch element SW7.

[0047] Specifically, when power supply to the power conversion device 10 begins, power input to the power conversion device 10 from the three-phase AC power source 100 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 charged to the fifth capacitor C5 of the second power conversion circuit 80. At this time, because the DC power passes through the boost circuit 70, the maximum value of the power charged to the fifth capacitor C5 is greater than the peak values ​​of the first voltage VA to the third voltage VC, which are AC voltages. In other words, the maximum value of the voltage across the fifth capacitor C5 is greater than 283 V. Therefore, when the voltage across the fifth capacitor C5 becomes 283 V or higher, the control unit 90 switches the specific switch element SW7 to the on state and maintains the on state.

[0048] Furthermore, while the program PG is being executed, the control unit 90 determines whether the first power conversion circuit 30 falls into any of the following cases (A) to (C) based on the voltage and current values ​​of the three-phase AC power acquired from the power sensor SE and the temperature acquired from the temperature sensor TS: (A) When the peak value of the AC voltage input to the first input terminal 31A to the third input terminal 31C is equal to or less than a predetermined value; (B) When the peak value of the AC current input to the first input terminal 31A to the third input terminal 31C is equal to or greater than a predetermined value; or (C) When it is necessary to stop the power conversion device 10 due to some abnormality.

[0049] (A) is, for example, a case where an instantaneous power outage occurs, cutting off the power supplied to the power conversion device 10 for approximately several tens of milliseconds. The predetermined value in this case is, for example, 1 / 20√2 of the peak value of the AC voltage when the three-phase AC power supply 100 is operating normally. In this embodiment, the peak values ​​of the first voltage VA to the third voltage VC input from the three-phase AC power supply 100 are 200√2 V (approximately 283 V). Therefore, the predetermined value is 10 V. Therefore, when the peak values ​​of the first voltage VA to the third voltage VC detected by the power sensor SE are 10 V or less, the control unit 90 determines that the above-mentioned (A) applies.

[0050] The peak value here refers to the wavelength height in one cycle of the AC waveform. In other words, the peak value is a value that fluctuates while the power conversion device 10 is in operation. For example, when the three-phase AC power supply 100 is operating normally, the peak values ​​of the first voltage VA to the third voltage VC are 200√2 V. If an instantaneous power outage or the like occurs, these voltages will drop, and the peak values ​​may also drop.

[0051] (B) is, for example, a case where a phase short circuit occurs in the first power conversion circuit 30. In this embodiment, the predetermined value in this case is the rated current value of the first power conversion circuit 30. Therefore, when the peak values ​​of the AC current detected by the power sensor SE simultaneously become equal to or greater than the rated current value at two or more of the first to third input terminals 31A to 31C, the control unit 90 determines that the above-mentioned (B) applies.

[0052] (C) is, for example, a case where the temperature inside the power conversion device 10 has changed significantly. In this embodiment, the control unit 90 determines that the above (C) applies when the temperature acquired from the temperature sensor TS is equal to or greater than a predetermined threshold and when the amount of change in the temperature is equal to or greater than a predetermined threshold. Note that these thresholds are determined based on the size of the power conversion device 10, the magnitude of the voltage supplied from the three-phase AC power supply 100, etc.

[0053] If the control unit 90 determines that none of the above conditions (A) to (C) applies, it keeps the third switch element SW3 to the sixth switch element SW6 in the off state. That is, in this case, no current flows from the fifth capacitor C5 of the second power conversion circuit 80 to the third output terminal 82A and the fourth output terminal 82B.

[0054] Furthermore, if the control unit 90 determines that none of the above conditions (A) to (C) applies, it controls the on / off of each bidirectional switch TSW of the first power conversion circuit 30 in accordance with a predetermined switching pattern. That is, if none of the conditions (A) to (C) applies, the first power conversion circuit 30 converts three-phase AC power into single-phase AC power. Then, the AC voltage is applied to the primary winding 41A of the transformer 41.

[0055] If the control unit 90 determines that the above case (A) applies, it stops power conversion by the first power conversion circuit 30. Specifically, the control unit 90 switches all of the bidirectional switches TSW to the OFF state. Thereafter, it controls the on / off of the third switch element SW3 to the sixth switch element SW6 according to a predetermined switching pattern. As a result, the DC voltage discharged from the fifth capacitor C5 is converted into an AC voltage. Then, the AC voltage is output from the third output terminal 82A and the fourth output terminal 82B of the second power conversion circuit 80. In other words, AC power is applied to the primary winding 41A of the transformer 41.

[0056] If the control unit 90 determines that the above case (B) or (C) applies, it stops power conversion by the first power conversion circuit 30. Specifically, the control unit 90 switches all of the bidirectional switches TSW to the OFF state. At this time, the control unit 90 also stops the second power conversion circuit 80. That is, the control unit 90 maintains all of the third switch element SW3 to the sixth switch element SW6 of the second power conversion circuit 80 in the OFF state. Furthermore, the control unit 90 maintains the specific switch element SW7 in the OFF state.

[0057] As described above, when any of the above conditions (A) to (C) is met, the control of each switch element is switched, and all of the bidirectional switches TSW are turned off. Next, when none of the above conditions (A) to (C) is met, the control unit 90 turns off the specific switch element SW7. Thereafter, the control unit 90 again controls the bidirectional switches TSW of the first power conversion circuit 30 using a predetermined switching pattern. That is, the control unit 90 switches one of the bidirectional switches TSW to the on state in accordance with the predetermined switching pattern. After this control, the fifth capacitor C5 is charged again. Then, when the inter-terminal voltage of the fifth capacitor C5 becomes equal to or greater than the peak value of the AC voltage input to each external input terminal of the power conversion device 10, the control unit 90 switches the specific switch element SW7 to the on state and maintains it in the on state.

[0058] (Operation of the Present Embodiment) In the above embodiment, the control unit 90 maintains the third switch element SW3 to the sixth switch element SW6 in the OFF state when none of the above conditions (A) to (C) applies. In this case, the high-potential terminal of the fifth capacitor C5 of the second power conversion circuit 80 and the primary winding 41A of the transformer 41 are electrically disconnected. Furthermore, when none of the above conditions (A) to (C) apply, the control unit 90 controls the ON / OFF of each bidirectional switch TSW of the first power conversion circuit 30 to enable the first power conversion circuit 30 to function. Then, at this time, when the inter-terminal voltage of the fifth capacitor C5 becomes equal to or greater than the peak values ​​of the first voltage VA to the third voltage VC, the control unit 90 switches the specific switch element SW7 to the ON state.

[0059] If the control unit 90 determines that the above case (A) applies, that is, if it determines that an instantaneous power interruption has occurred, it switches all of the bidirectional switches TSW to the OFF state, thereby stopping power conversion by the first power conversion circuit 30. Then, it controls the third switch element SW3 to the sixth switch element SW6 using a predetermined switching pattern. This allows the second power conversion circuit 80 to apply an AC voltage to the primary winding 41A using the power charged in the fifth capacitor C5 as its power source. In other words, the second power conversion circuit 80 functions as a standby power supply capable of supplying power to the load 110.

[0060] If the control unit 90 determines that the above case (B) or (C) applies, i.e., if an abnormality such as an overvoltage, overcurrent, or temperature rise is detected, it switches all bidirectional switches TSW to the OFF state, thereby stopping power conversion by the first power conversion circuit 30. It also switches all switch elements of the second power conversion circuit 80 to the OFF state. As a result, the current flowing through the primary winding 41A of the transformer 41 flows to the fifth capacitor C5 through the body diodes of the third switch element SW3 to the sixth switch element SW6 and the body diode of the specific switch element SW7. In other words, a transformer current path is secured. Therefore, even if all bidirectional switches TSW are switched to the OFF state, no surge voltage is generated. In other words, the second power conversion circuit 80 and the fifth capacitor C5 function as a protection circuit.

[0061] When the second power conversion circuit 80 operates as a standby power supply circuit, the power stored in the fifth capacitor C5 is discharged. As a result, the voltage across the fifth capacitor C5 drops and may become smaller than the maximum voltage of the three-phase AC power. If the specific switch element SW7 is not switched off at this time, the output voltage of the first power conversion circuit 30 may be applied to the fifth capacitor C5. In other words, an unintended current, such as an inrush current, may flow through the fifth capacitor C5.

[0062] In this embodiment, when none of the above conditions (A) to (C) apply, the control unit 90 switches off the specific switch element SW7 and then resumes control of the first power conversion circuit 30. In other words, when a voltage is output from each output terminal of the first power conversion circuit 30, the control unit 90 controls each switch element so that the output voltage is not applied to the fifth capacitor C5 of the second power conversion circuit 80. Therefore, with this configuration, there is no risk that the output voltage of the first power conversion circuit 30 will be applied to the fifth capacitor C5. In other words, an unintended current will not flow through the fifth capacitor C5.

[0063] (Effects of the Present Embodiment) (1) In the above embodiment, the second power conversion circuit 80 includes the specific switch element SW7. As a result, the second power conversion circuit 80 functions as both a protection circuit and a standby power supply circuit, which makes it difficult for the power conversion device 10 to become large.

[0064] (2) In the above embodiment, the specific switch element SW7 is disposed between the fifth capacitor C5 of the second power conversion circuit 80 and the bridge circuit BC. Assume that the specific switch element SW7 connects the source terminal of the third switch element SW3 to the third output terminal 82A. If the fifth switch element SW5 is turned on, the first terminal of the fifth capacitor C5 and the third output terminal 82A are electrically connected via the fifth switch element SW5, and the second terminal of the fifth capacitor C5 and the fourth output terminal 82B are electrically connected via the body diode of the sixth switch element SW6. In other words, in this case, the output voltage of the first power conversion circuit 30 may be applied to the fifth capacitor C5. Therefore, this configuration can prevent such unintended current flow.

[0065] (3) In the above embodiment, the power conversion device 10 includes the three-phase rectifier circuit 60. As a result, the fifth capacitor C5 is charged by the three-phase AC power supply 100 via the three-phase rectifier circuit 60. Therefore, it is not necessary to connect a separate power supply device for charging the fifth capacitor C5. In other words, the power conversion device 10 is unlikely to become large. Furthermore, because the first power conversion circuit 30 is not present in the conduction path from the three-phase AC power supply 100 to the second power conversion circuit 80, there is no risk of the first power conversion circuit 30 affecting the control of the bidirectional switches TSW in the first power conversion circuit 30.

[0066] (4) In the above embodiment, the output voltage of the boost circuit 70 is greater than the maximum value of the input voltage of the three-phase AC power supply 100. That is, the inter-terminal voltage of the fifth capacitor C5 is greater than the maximum value of the input voltage of the three-phase AC power supply 100. This makes it possible to prevent a short-circuit current from flowing through the fifth capacitor C5 and each switch element in the second power conversion circuit 80.

[0067] (5) When the control unit 90 determines that the above condition (A) applies, it stops power conversion by the first power conversion circuit 30. At this time, the control unit 90 switches all bidirectional switches TSW to the OFF state and controls the ON / OFF of each switch element of the bridge circuit BC so that the second power conversion circuit 80 outputs AC power when the specific switch element SW7 is in the ON state. This causes voltage to be supplied from the second power conversion circuit 80 to the primary winding 41A. In other words, even when the control unit 90 determines that an instantaneous power interruption has occurred and stops power conversion by the first power conversion circuit 30, it is possible to maintain power supply to the load 110. In other words, the second power conversion circuit 80 can function as a standby power supply circuit.

[0068] Furthermore, if the control unit 90 determines that the above (B) or (C) applies, it maintains the multiple bidirectional switches TSW of the first power conversion circuit 30 and the multiple switch elements of the second power conversion circuit 80 in the OFF state. As a result, if an abnormality such as an overvoltage, overcurrent, or temperature rise occurs, the current flowing through the primary winding 41A flows to the fifth capacitor C5 of the second power conversion circuit 80. This makes it possible to prevent an excessive current from flowing through the bidirectional switch TSW. In other words, the second power conversion circuit 80 can function as a protection circuit.

[0069] (6) When the inter-terminal voltage of the fifth capacitor C5 becomes equal to or greater than the peak value of the first voltage VA to the third voltage VC, the control unit 90 switches the specific switch element SW7 to the on state and maintains the on state. By switching the specific switch element SW7 to the on state in advance, power can be quickly supplied from the second power conversion circuit 80 to the load 110 when the above-mentioned (A) is met.

[0070] (7) In the above embodiment, when the situation falls under (B) or (C), the control unit 90 switches all of the bidirectional switches TSW to the off state while the specific switch element SW7 is in the on state. By first switching the specific switch element SW7 to the on state, the current flowing through the primary winding 41A of the transformer 41 flows to the fifth capacitor C5 through the body diodes of the third switch element SW3 to the sixth switch element SW6. By subsequently switching the bidirectional switch TSW off, it is possible to prevent an excessive electrical load, such as a surge voltage, from being applied to the bidirectional switch TSW.

[0071] (8) In the above embodiment, when none of (A) to (C) applies, the control unit 90 switches the specific switch element SW7 to the OFF state and then switches the bidirectional switch TSW to the ON state. As a result, as described above, it is possible to prevent unintended current and inrush current from flowing from the first power conversion circuit 30 to the fifth capacitor C5.

[0072] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0073] 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 insulated AC-DC converter, and may also be applied to a non-insulated three-phase AC-DC converter. Furthermore, the power conversion device 10 does not necessarily have to include one or more selected from the input-side low-pass filter 20, the transformer circuit 40, and the rectifier circuit 50. Furthermore, the power conversion device 10 may include elements and circuits other than those exemplified in the above embodiment.

[0074] The three-phase AC power supply 100 connected to the three external input terminals is not limited to a three-phase three-wire type, but may be a three-phase four-wire type or a delta-connected three-phase three-wire type three-phase AC power supply 100. Similarly, the configuration of the power conversion device 10 may be changed as appropriate in accordance with the type of three-phase AC power supply 100.

[0075] 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.

[0076] The two switch elements of the bidirectional switch TSW may be transistors capable of passing 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.

[0077] 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 in the above embodiment. That is, the rectifier circuit 50 is not limited to a current doubler circuit. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or the like. Furthermore, the rectifier circuit 50 may be a full-bridge circuit consisting of four diodes.

[0078] The power conversion device 10 does not need to include the 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.

[0079] The output voltage of the boost circuit 70 may be equal to or lower than approximately 283 V, 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 an instantaneous power interruption occurs. Furthermore, the power conversion device 10 does not need to include the boost circuit 70. In this case, the maximum inter-terminal voltage of the fifth capacitor C5 of the second power conversion circuit 80 is equal to or lower than the maximum value of the input voltage of the three-phase AC power. Even in this case, by the control unit 90 performing the control described in the above embodiment, 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.

[0080] The power conversion device 10 may not include the temperature sensor TS. In this case, the control unit 90 need not perform the determination in (C) above. The specific switch element SW7 may connect the fifth capacitor C5 to the third output terminal 82A and the fourth output terminal 82B, and the connection location is not limited to the example in the above embodiment. For example, the specific switch element SW7 may be connected between the second end of the fifth capacitor C5 and the source terminal of the fourth switch element SW4. The specific switch element SW7 may be connected between the drain terminal of the third switch element SW3 and the drain terminal of the fifth switch element SW5. The specific switch element SW7 may be connected between the source terminal of the third switch element SW3 and the third output terminal 82A. The specific switch element SW7 may be connected between the source terminal of the fifth switch element SW5 and the fourth output terminal 82B.

[0081] The second power conversion circuit 80 may be configured with elements other than those described in the above embodiment. For example, as shown in FIG. 4 , when the fifth capacitor C5 in the above embodiment is used as the main capacitor MC, the second power conversion circuit 80 may include a spare capacitor SC connected between the bridge circuit BC and the specific switch element SW7. That is, a first end of the spare capacitor SC is connected to the drain terminal of the specific switch element SW7 and the drain terminal of the third switch element SW3. A second end of the spare capacitor SC is connected to the second end of the main capacitor MC and the source terminal of the fourth switch element SW4.

[0082] Since the second power conversion circuit 80 is provided with a spare capacitor SC, even if a situation arises in which the control unit 90 cannot switch the specific switch element SW7 to the on state, if the above-mentioned (A) to (C) is met, power can be supplied from the spare capacitor SC to the primary winding 41A of the transformer 41.

[0083] In this case, the capacitance of the standby capacitor SC is preferably 1 / 10 or less of the capacitance of the main capacitor MC. Because the capacitance of the standby capacitor SC is small, the effects of discharge from the standby capacitor SC to the primary winding 41A are small when the above conditions (A) to (C) do not apply, i.e., when the first power conversion circuit 30 is operating.

[0084] The specific method by which the control unit 90 determines whether the above-mentioned (A) to (C) applies is not limited to the example of the above embodiment. For example, when determining whether the above-mentioned (B) applies, the control unit 90 does not have to make the determination based on the current value acquired from the power sensor SE.

[0085] For example, among the first high-side bidirectional switch HS1 to the third high-side bidirectional switch HS3, a specific bidirectional switch TSW is defined as a specific first high-side bidirectional switch. A high-side bidirectional switch other than the specific first high-side bidirectional switch is defined as a specific second high-side bidirectional switch. Also, among the first low-side bidirectional switch LS1 to the third low-side bidirectional switch LS3, a specific bidirectional switch TSW is defined as a specific first low-side bidirectional switch. A low-side bidirectional switch other than the specific first low-side bidirectional switch is defined as a specific second low-side bidirectional switch.

[0086] In this case, when a state in which the specific first high-side bidirectional switch allows a current to flow from its input terminal to the first output terminal 32A and a state in which the specific second high-side bidirectional switch allows a current to flow from the first output terminal 32A to its input terminal overlap, the control unit 90 may control all bidirectional switches TSW to be switched off and the specific switch element SW7 to be switched on. Furthermore, when a state in which the specific first low-side bidirectional switch allows a current to flow from its input terminal to the second output terminal 32B and a state in which the specific second low-side bidirectional switch allows a current to flow from the second output terminal 32B to its input terminal overlap, the control unit 90 may control all bidirectional switches TSW to be switched off and the specific switch element SW7 to be switched on. That is, when either of these cases occurs, it may be determined that the above-mentioned (B) applies. The control unit 90 can make this determination by monitoring the gate signal input to the gate terminal of each bidirectional switch TSW.

[0087] When the control unit 90 determines that any of the above (A) to (C) applies, it may switch all of the bidirectional switches TSW to the OFF state before switching the specific switch element SW7 to the ON state.

[0088] When the control unit 90 determines that any of the above conditions (A) to (C) applies, it is not necessary for the control unit 90 to turn off all of the bidirectional switches TSW. For example, even if some of the bidirectional switches TSW are in the on state, it is sufficient to control the bidirectional switches TSW so that an overcurrent generated in the primary winding 41A of the transformer 41 does not flow through the bidirectional switches TSW by turning off a plurality of the bidirectional switches TSW.

[0089] When determining that the above (B) or (C) applies, the control unit 90 may not stop the second power conversion circuit 80. That is, the control unit 90 may not turn off all of the switch elements of the second power conversion circuit 80. For example, the control unit 90 may turn off the third switch element SW3 to the sixth switch element SW6, while maintaining the specific switch element SW7 in the on state.

[0090] The conditions under which the control unit 90 switches the specific switch element SW7 to the ON state are not limited to those described in the above embodiment. For example, the control unit 90 may switch the specific switch element SW7 to the ON state when it determines that any of the above conditions (A) to (C) applies. That is, instead of switching the specific switch element SW7 to the ON state in advance, the control unit 90 may switch the specific switch element SW7 to the ON state when stopping power conversion by the first power conversion circuit 30.

[0091] The conditions under which the control unit 90 switches all the bidirectional switches TSW to the OFF state and switches the specific switch element SW7 to the ON state are not limited to those described in the above embodiment. That is, the control unit 90 may switch the switches under conditions other than (A) to (C). Therefore, the control unit 90 may not switch the switches when the above condition (A) applies. Furthermore, the control unit 90 may not switch the switches when the above condition (B) applies. The control unit 90 may not switch the switches when the above condition (C) applies.

[0092] The specific method for determining (C) above is not limited to the example of the embodiment. For example, the threshold for comparing the temperature may not be a constant, but may be a variable dependent on the voltage and current values ​​of the first input terminal 31A to the third input terminal 31C and the voltage and current values ​​of the first output terminal 32A and the second output terminal 32B. Furthermore, the determination of (C) does not need to be based on temperature. For example, if the power conversion device 10 is equipped with an impact sensor that detects impacts on the housing, the control unit 90 may determine that (C) applies when the detected value of the impact sensor is equal to or greater than a predetermined threshold. Furthermore, the determination of (C) above may also apply when the AC voltage input to the input terminal becomes an overvoltage, when the DC voltage output from the power conversion device 10 becomes an overvoltage, or when the DC voltage is insufficient compared to the required voltage.

[0093] Note that the classification and naming of each circuit configuration in the above embodiment are for convenience and are not limited to this. For example, in the above embodiment, the six bidirectional switches TSW are collectively referred to as the "first power conversion circuit 30," but this is not limiting. In other words, the six bidirectional switches TSW and the transformer circuit 40 and rectifier circuit 50 in the above embodiment may be collectively referred to as the "first power conversion circuit."

[0094] <Supplementary Notes> The technical ideas that can be understood from the above-described embodiments and modified examples will be described below. [1] A power conversion device comprising: a first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, and a first output terminal and a second output terminal and capable of converting three-phase AC power; a second power conversion circuit 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, a capacitor, a plurality of switch elements, 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 converting a DC voltage discharged from the capacitor; and a control unit capable of switching on and off the plurality of bidirectional switches and on and off the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal, and the control unit is capable of switching on and off the specific switch element.

[0095] [2] The power conversion device according to [1], wherein the specific switch element is disposed between the capacitor of the second power conversion circuit and the plurality of switch elements. [3] The power conversion device according to [2], wherein when the capacitor is a main capacitor, the second power conversion circuit has a spare capacitor connected between the plurality of switch elements and the specific switch element.

[0096] [4] The power conversion device according to [3], wherein the capacitance of the auxiliary capacitor is 1 / 10 or less of the capacitance of the main capacitor. [5] The power conversion device according to any one of [1] to [4], wherein the plurality of input terminals are connected to a three-phase AC power source, and further includes a three-phase rectifier circuit that connects between the three-phase AC power source and the second power conversion circuit and is capable of converting input three-phase AC power into DC power and outputting the DC power, and the capacitor is charged by the DC power output from the three-phase rectifier circuit.

[0097] [6] The power conversion device according to [5], further comprising a boost circuit connected between the three-phase rectifier circuit and the second power conversion circuit, for boosting the DC power output from the three-phase rectifier circuit, wherein the output voltage of the boost circuit is greater than the maximum value of the voltage input to the input terminal.

[0098] [7] The power conversion device according to any one of [1] to [6], wherein the control unit switches all of the bidirectional switches to an off state when stopping power conversion by the first power conversion circuit, and controls the on / off of the plurality of switch elements so that the second power conversion circuit outputs AC power when the specific switch element is in an on state.

[0099] [8] The power conversion device according to [7], wherein the control unit switches the specific switch element to an on state when the inter-terminal voltage of the capacitor becomes equal to or greater than a peak value of the AC voltage input to the plurality of input terminals.

[0100] [9] The power conversion device according to [7] or [8], wherein the control unit switches the specific switch element to an on state when stopping power conversion by the first power conversion circuit.

[10] The power conversion device according to any one of [7] to [9], wherein the control unit switches the specific switch element to an on state when stopping power conversion by the first power conversion circuit.

[11] The power conversion device according to any one of [7] to [9], wherein the control unit switches the specific switch element to an on state when stopping power conversion by the first power conversion circuit.

[0101]

[11] A power conversion device described in any one of [7] to

[10] , wherein the control unit stops power conversion by the first power conversion circuit when the peak value of the AC current input to the multiple input terminals becomes equal to or greater than a predetermined value.

[0102]

[12] The power conversion device according to any one of [7] to

[11] , wherein the control unit switches all of the bidirectional switches to an off state when the specific switch element is in an on state, when a peak value of the AC current input to the plurality of input terminals becomes equal to or greater than a predetermined value.

[0103]

[13] The plurality of bidirectional switches include a first high-side bidirectional switch connecting one of the plurality of input terminals and the first output terminal, a second high-side bidirectional switch connecting one of the plurality of input terminals other than the input terminal to which the first high-side bidirectional switch is connected and the first output terminal, a first low-side bidirectional switch connecting the input terminal to which the first high-side bidirectional switch is connected and the second output terminal, and a second low-side bidirectional switch connecting the input terminal to which the second high-side bidirectional switch is connected and the second output terminal, the power conversion device according to any one of [7] to

[12] , wherein, when a state in which the first low-side bidirectional switch allows a current to flow from the input terminal to the second output terminal overlaps with a state in which the second high-side bidirectional switch allows a current to flow from the first output terminal to the input terminal, control is performed to switch all of the bidirectional switches to an off state and to switch the specific switch element to an on state; and when a state in which the first low-side bidirectional switch allows a current to flow from the input terminal to the second output terminal overlaps with a state in which the second low-side bidirectional switch allows a current to flow from the second output terminal to the input terminal, control is performed to switch all of the bidirectional switches to an off state and to switch the specific switch element to an on state.

[0104]

[14] The power conversion device according to any one of [7] to

[13] , wherein, when all of the bidirectional switches are in an off state and the specific switch element is in an on state, the control unit switches the specific switch element to an off state and then switches any one of the bidirectional switches to an on state.

[0105]

[15] A first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, a first output terminal and a second output terminal, and capable of converting three-phase AC power; a transformer having a primary winding and a secondary winding, 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; a capacitor; a plurality of switch elements; 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, and capable of converting DC power discharged by the capacitor. and a control unit capable of switching on and off the plurality of bidirectional switches and the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal, and the program for a power conversion device causes the control unit to switch all of the bidirectional switches to an off state when power conversion by the first power conversion circuit is to be stopped, and to control the on and off of the plurality of switch elements so that the second power conversion circuit outputs AC power when the specific switch element is in an on state.

[0106]

[16] A first power conversion circuit capable of converting three-phase AC power input to the plurality of input terminals, including: a plurality of input terminals; a first output terminal and a second output terminal; a plurality of bidirectional switches connecting the plurality of input terminals and the first output terminal and the second output terminal; a transformer having a primary winding and a secondary winding, 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 and capable of converting AC voltage, the first power conversion circuit comprising: a capacitor; a plurality of switch elements; a second power conversion circuit having a third output terminal connected between a first end of the primary winding and a fourth output terminal connected between the second output terminal and a second end of the primary winding, the second power conversion circuit being capable of converting DC power discharged from the capacitor; and a control unit capable of switching on and off the plurality of bidirectional switches and the plurality of switch elements, wherein the second power conversion circuit has a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal, and the control unit is capable of switching on and off the specific switch element.

[0107] REFERENCE SIGNS LIST 10...power conversion device 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 TSW...bidirectional switch 40...transformer circuit 50...rectifier circuit 60...three-phase rectifier circuit 70...booster circuit 80...second power conversion circuit 82A...third output terminal 82B...fourth output terminal C5...fifth capacitor BC...bridge circuit 90...controller PG...program 100...three-phase AC power supply

Claims

1. A first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, a first output terminal and a second output terminal, and capable of converting three-phase AC power; 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; a capacitor; a plurality of switch elements; 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, and a second power conversion circuit capable of converting a DC voltage at which the capacitor discharges; and a control unit capable of switching on / off of the plurality of bidirectional switches and on / off of the plurality of switch elements. The second power conversion circuit has a specific switch element connected between the capacitor, the third output terminal and the fourth output terminal. The control unit is capable of switching on / off of the specific switch element. A power conversion device.

2. The power conversion device according to claim 1, wherein the specific switch element is disposed between the capacitor of the second power conversion circuit and the plurality of switch elements.

3. When the capacitor is a main capacitor, the second power conversion circuit has a standby capacitor connected between the plurality of switch elements and the specific switch element. The power conversion device according to claim 2.

4. The power conversion device according to claim 3, wherein a capacitance of the standby capacitor is 1 / 10 or less of a capacitance of the main capacitor.

5. The plurality of input terminals are connected to a three-phase AC power source, and further include a three-phase rectification circuit connected between the three-phase AC power source and the second power conversion circuit and capable of converting the input three-phase AC power into DC power and outputting it. The capacitor is charged by the DC power output by the three-phase rectification circuit. The power conversion device according to any one of claims 1 to 4.

6. Further includes a boost circuit connected between the three-phase rectification circuit and the second power conversion circuit and capable of boosting the DC power output from the three-phase rectification circuit. An output voltage of the boost circuit is greater than a maximum value of a voltage input to the input terminal. The power conversion device according to claim 5.

7. When the control unit stops the power conversion by the first power conversion circuit, it switches all the bidirectional switches to the off state, and controls the on / off of the plurality of switch elements so that the second power conversion circuit outputs AC power when the specific switch element is in the on state. The power conversion device according to any one of claims 1 to 6.

8. The control unit switches the specific switch element to the on state when the voltage between the terminals of the capacitor becomes equal to or higher than the peak value of the AC voltage input to the plurality of input terminals. The power conversion device according to claim 7.

9. The control unit switches the specific switch element to the on state when the control unit stops the power conversion by the first power conversion circuit. The power conversion device according to claim 7 or 8.

10. The control unit stops the power conversion by the first power conversion circuit when the peak value of the AC voltage input to the plurality of input terminals becomes equal to or lower than a predetermined value. The power conversion device according to any one of claims 7 to 9.

11. The control unit stops the power conversion by the first power conversion circuit when the peak value of the AC current input to the plurality of input terminals becomes equal to or higher than a predetermined value. The power conversion device according to any one of claims 7 to 10.

12. When the peak value of the AC current input to the plurality of input terminals becomes equal to or higher than a predetermined value, the control unit switches all the bidirectional switches to the off state when the specific switch element is in the on state. The power conversion device according to any one of claims 7 to 11.

13. The plurality of the bidirectional switches include a first high-side bidirectional switch that connects between one of the plurality of input terminals and the first output terminal, a second high-side bidirectional switch that connects between another one of the plurality of input terminals, which is different from the input terminal to which the first high-side bidirectional switch is connected, and the first output terminal, a first low-side bidirectional switch that connects between the input terminal to which the first high-side bidirectional switch is connected and the second output terminal among the plurality of input terminals, and a second low-side bidirectional switch that connects between the input terminal to which the second high-side bidirectional switch is connected and the second output terminal among the plurality of input terminals. When a state in which the first high-side bidirectional switch allows current to flow from the input terminal to the first output terminal and a state in which the second high-side bidirectional switch allows current to flow from the first output terminal to the input terminal overlap, the control unit performs control to switch all the bidirectional switches to an off state and switch the specific switch element to an on state. When a state in which the first low-side bidirectional switch allows current to flow from the input terminal to the second output terminal and a state in which the second low-side bidirectional switch allows current to flow from the second output terminal to the input terminal overlap, the control unit performs control to switch all the bidirectional switches to an off state and switch the specific switch element to an on state. The power conversion device according to any one of claims 7 to 12.

14. When all the bidirectional switches are in an off state and the specific switch element is in an on state, the control unit switches the specific switch element to an off state and then switches any one of the bidirectional switches to an on state. The power conversion device according to any one of claims 7 to 13.

15. A first power conversion circuit having a plurality of input terminals, a plurality of bidirectional switches, a first output terminal, and a second output terminal and capable of converting three-phase AC power; 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; a capacitor; a plurality of switch elements; 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, the second power conversion circuit capable of converting DC power discharged from the capacitor; a control unit capable of switching on / off of the plurality of bidirectional switches and on / off of the plurality of switch elements; and a program for a power conversion device, wherein the second power conversion circuit is applied to a power conversion device having a specific switch element connected between the capacitor, the third output terminal, and the fourth output terminal, and the control unit is configured to switch all the bidirectional switches to an off state when stopping power conversion by the first power conversion circuit, and control on / off of the plurality of switch elements so that the second power conversion circuit outputs AC power when the specific switch element is in an on state.

16. A first power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, a plurality of bidirectional switches connecting the plurality of input terminals to the first output terminal and the second output terminal, 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, a rectifier circuit connected to the secondary winding and capable of converting an alternating voltage, and capable of converting three-phase AC power input to the plurality of input terminals; a capacitor; a plurality of switch elements; 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; a second power conversion circuit capable of converting DC power discharged by the capacitor; a control unit capable of switching on / off of the plurality of bidirectional switches and on / off of the plurality of switch elements; the second power conversion circuit having a specific switch element connected between the capacitor and the third output terminal and the fourth output terminal; and the control unit capable of switching on / off of the specific switch element. A power conversion device.

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