Power conversion device and program for power conversion device

Abstract

A power conversion device (10) comprises a first power conversion circuit (30), a second power conversion circuit (80), a transformer (41), and a control unit (90). The first power conversion circuit (30) can convert input three-phase AC power and output the converted power from a pair of output terminals. The second power conversion circuit (80) has: a switching circuit including a plurality of switch elements; a capacitor; and a pair of output terminals. The output terminals of the first power conversion circuit (30) and the output terminals of the second power conversion circuit (80) are connected to a primary-side winding (41A) of the transformer (41). The second power conversion circuit (80) can output energy stored in the capacitor from the 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, six bidirectional switches, and a control device. Three-phase AC power is input to three of the plurality of nodes. The power conversion circuit can convert the three-phase AC power input to the nodes into DC power and output the DC power through on / off control of each bidirectional switch by the control device.

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

[0004] In a power conversion device such as that disclosed in Patent Document 1, a momentary power outage may occur, in which the power supply to each node is momentarily cut off. When such a momentary power outage occurs, there is a risk that the power conversion device will not be able to maintain the power supply to the load.

[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 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 is capable of outputting energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0006] The present disclosure also provides a power conversion circuit including: 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 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 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 is configured to convert a voltage stored in the capacitor. and a power conversion device that can output stored energy to the third output terminal and the fourth output terminal, and that causes the control unit to control the plurality of bidirectional switches so that, when an amplitude value of an input voltage input to one or more of the plurality of input terminals is greater than a predetermined threshold, the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal, and, when an amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the threshold, switch the plurality of bidirectional switches to an off state and control the plurality of switch elements so that the energy stored in the capacitor is output from the third output terminal and the fourth output terminal to the primary winding.

[0007] The present disclosure also provides a power conversion device comprising: 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 and 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, and a rectifier circuit connected to the secondary winding and capable of converting AC voltage, the first power conversion circuit being capable of converting three-phase AC power input to the plurality of input terminals; 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 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 is capable of outputting energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0008] Even if a momentary power outage occurs, the power conversion device can maintain power supply to the load.

[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 diagram showing waveforms and sectors of a three-phase AC voltage.

[0010] <First embodiment of a power conversion device and a program for the power conversion device> A first 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 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] For example, 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 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° 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 such as a server that is 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. 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. 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 four diodes: a first diode 51, a second diode 52, a third diode 53, and a fourth diode 54, a fifth inductor L5, and a fourth capacitor C4.

[0029] The four diodes form a full-bridge circuit. That is, the anode terminal of the first diode 51 is connected to a first end of the secondary winding 41B of the transformer 41. The cathode terminal of the first diode 51 is connected to a cathode terminal of the third diode 53. The anode terminal of the third diode 53 is connected to a second end of the secondary winding 41B and a cathode terminal of the fourth diode 54. The anode terminal of the fourth diode 54 is connected to an anode terminal of the second diode 52. The cathode terminal of the second diode 52 is connected to a first end of the secondary winding 41B and an anode terminal of the first diode 51.

[0030] A first end of the fifth inductor L5 is connected to the cathode terminal of the first diode 51 and the cathode terminal of the third diode 53. A second end of the fifth inductor L5 is connected to a first end of the fourth capacitor C4 and the first external output terminal 12A. A second end of the fourth capacitor C4 is connected to the anode terminal of the second diode 52, the anode terminal of the fourth diode 54, and the second external output terminal 12B.

[0031] 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.

[0032] 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.

[0033] 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, a DC voltage is input to the sixth and seventh connection terminals CT6 and CT7. The boost circuit 70 boosts and outputs the DC voltage using switching elements, inductors, capacitors, and other components (not shown). That is, the boost circuit 70 outputs DC power from the eighth and ninth connection terminals CT8 and CT9, which has a higher voltage than the DC power input to the sixth and seventh connection terminals CT6 and CT7. For example, if the effective 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. The maximum value of the AC voltage is the effective value of the AC 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.

[0034] 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.

[0035] 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.

[0036] 3, the second power conversion circuit 80 includes a fifth capacitor C5 and a switching 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.

[0037] The switching circuit BC includes a first switch element SW1, a second switch element SW2, a third switch element SW3, and a fourth switch element SW4. The first switch elements SW1 to SW4 are n-channel MOSFETs. The drain terminal of the first switch element SW1 is connected to the fourth input terminal 81A and the first end of the fifth capacitor C5. The drain terminal of the first switch element SW1 is connected to the drain terminal of the third switch element SW3. The source terminal of the first switch element SW1 is connected to the drain terminal of the second switch element SW2 and the third output terminal 82A. The source terminal of the third switch element SW3 is connected to the fourth output terminal 82B and the drain terminal of the fourth switch element SW4. The source terminal of the fourth switch element SW4 is connected to the fifth input terminal 81B and the source terminal of the second switch element SW2.

[0038] As shown in Fig. 1, the power conversion device 10 includes a power sensor SE and a control unit 90. The power sensor SE can detect the power applied to a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C. Specifically, the power sensor SE can detect the voltage and current values ​​input to each external input terminal. That is, the power sensor SE can detect a first voltage VA, a second voltage VB, and a third voltage VC.

[0039] 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.

[0040] 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 thereby perform first control and second control, which will be described later.

[0041] Specifically, the program PG includes data for executing the first control and the second control. As part of this data, the program PG defines a plurality of different switching patterns for the plurality of bidirectional switches TSW in the first power conversion circuit 30. These switching patterns define combinations of on and off states of the plurality of bidirectional switches TSW. The program PG also defines the order in which the switching patterns for the bidirectional switches TSW are switched.

[0042] The power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit switches on and off two switch elements included in each bidirectional switch TSW and the first to fourth switch elements SW1 to SW4. 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.

[0043] 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 switching element S11 to the sixteenth switching element S16, respectively. The twenty-first switching signal SG21 to the twenty-sixth switching signal SG26 correspond one-to-one to the twenty-first switching element S21 to the twenty-sixth switching element S26, respectively.

[0044] The execution device of the control unit 90 controls the on / off of the multiple bidirectional switches TSW while switching between multiple switching patterns in accordance with the multiple switching patterns. As a result, 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, as shown in FIG. 1 , when the potential difference between the first output terminal 32A and the second output terminal 32B of the first power conversion circuit 30 is defined as a primary voltage Vp, the primary voltage Vp is an AC voltage. Therefore, the primary voltage Vp, which is an AC voltage, is applied to the primary winding 41A of the transformer 41.

[0045] 3, the switching signals include a first switching signal SG1 to a fourth switching signal SG4. The first switching signal SG1 to the fourth switching signal SG4 correspond one-to-one to the first switching element SW1 to the fourth switching element SW4, respectively. This allows the second power conversion circuit 80 to convert the DC power discharged from the fifth capacitor C5 into AC power under control described below.

[0046] (Regarding control when abnormal voltage occurs) The execution device of the control unit 90 executes the first control, the second control, etc. based on the above-mentioned 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.

[0047] When execution of the program PG begins, the control unit 90 first turns off the first switch element SW1 to the fourth switch element SW4. While the control unit 90 is executing the program PG, it acquires the voltage values ​​of the three-phase AC power input to each external input terminal detected by the power sensor 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 equal to or less than a predetermined first threshold. In this embodiment, the control unit 90 determines whether the amplitude values ​​of the input voltages input to all of the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C are equal to or less than a predetermined first threshold. The 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 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, when an instantaneous power outage occurs in which the power supplied to the power conversion device 10 is cut off for several tens of milliseconds, the amplitude values ​​of the input voltages may all simultaneously become 10 V or less.

[0048] The amplitude value here refers to the wavelength height in one cycle of the AC waveform. In other words, the amplitude 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 amplitude values ​​of the first voltage VA to the third voltage VC are 200√2 V. If an instantaneous power outage occurs, these voltages will decrease, and the amplitude value may also decrease. The amplitude value may also be called a peak value. The amplitude value may also be calculated by dividing the difference between the maximum value and the minimum value in one cycle of the AC waveform by 2.

[0049] The control unit 90 executes the first control when the amplitude values ​​of the input voltages input to all input terminals are not equal to or less than a predetermined first threshold, in other words, when the amplitude values ​​of the input voltages input to one or more of 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 voltage is not applied from the first output terminal 32A and the second output terminal 32B to the fifth capacitor C5. In other words, the control unit 90 controls the plurality of switch elements so that electrical conduction between the fifth capacitor C5 and each output terminal of the first power conversion circuit 30 is not established via the first switch element SW1 to the fourth switch element SW4.

[0050] Specifically, in the first control, when the amplitude value of one or more of the input voltages among the first voltage VA, the second voltage VB, and the third voltage VC detected by the power sensor SE is greater than a first threshold, the control unit 90 maintains the first switch element SW1 to the fourth switch element SW4 in the OFF state. At this time, the control unit 90 controls the on / off of each bidirectional switch TSW of the first power conversion circuit 30 while switching the switching pattern according to the switching pattern defined in the program PG. That is, 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.

[0051] Furthermore, when the amplitude value of one or more of the input voltages, the first voltage VA to the third voltage VC, is greater than the first threshold value, the three-phase AC power input to the power conversion device 10 from the three-phase AC power supply 100 is converted into 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. Note that, because the DC power passes through the boost circuit 70, the power charged to the fifth capacitor C5 is greater than the maximum value of the voltage of the three-phase AC power. In other words, when the effective voltage of the three-phase AC power is 200 Vrms, the maximum value of the voltage between the terminals of the fifth capacitor C5 is greater than 283 V.

[0052] The control unit 90 executes the second control when the amplitude values ​​of all input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE, simultaneously become equal to or less than the first threshold. In the second control, the control unit 90 switches all of the bidirectional switches TSW to the OFF state when the primary voltage Vp becomes equal to or less than a predetermined second threshold. The control unit 90 also 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 winding 41A. In this embodiment, all of the bidirectional switches TSW are switched to the OFF state at the above timing. The second threshold is 10 V. The term "simultaneously" allows for an error of several milliseconds.

[0053] 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 alternates between a positive state, a substantially zero volt state, and a negative state. The control unit 90 switches all of the bidirectional switches TSW to the OFF state when the primary voltage Vp reaches a substantially zero volt state. The control unit 90 then controls each switch element so that the DC power discharged from the fifth capacitor C5 is converted to AC power and the AC power is output from the third output terminal 82A and the fourth output terminal 82B. That is, the control unit 90 controls each switch element so that an AC voltage is applied from each output terminal of the second power conversion circuit 80 to the primary winding 41A of the transformer 41.

[0054] More specifically, when the amplitude values ​​of the input voltages input to all the input terminals are simultaneously equal to or less than a first threshold while the primary voltage Vp is negative, the control unit 90 switches all the bidirectional switches TSW to the off state at the timing when the absolute value of the primary voltage Vp becomes equal to or less than 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 starts to be output.

[0055] Furthermore, when the amplitude values ​​of the input voltages input to all the input terminals are simultaneously equal to or less than a first threshold while the primary voltage Vp is positive, the control unit 90 switches all the bidirectional switches TSW to the off state at the timing when the absolute value of the primary voltage Vp is equal to or less than 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 starts to be output.

[0056] In this way, when the amplitudes of all of the input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE, simultaneously become equal to or less than the first threshold, the control unit 90 turns off all of the bidirectional switches TSW and controls each switch element of the switching circuit BC according to a predetermined switching pattern. In this state, the control unit 90 determines whether the amplitude value of the input voltage input to one or more of 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 of the input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE is greater than the first threshold.

[0057] As described above, suppose that the amplitude values ​​of all input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE, simultaneously fall below the first threshold, and then the amplitude value of one or more of the input voltages, the first voltage VA to the third voltage VC, exceeds the first threshold. In this case, the control unit 90 again executes the first control. That is, the control unit 90 controls the first switch element SW1 to the fourth switch element SW4 so that the first output terminal 32A, the second output terminal 32B, and the fifth capacitor C5 are not electrically connected via the switching circuit BC. Specifically, the control unit 90 switches all of the first switch element SW1 to the fourth switch element SW4 to the OFF state. Thereafter, the control unit 90 again controls the multiple bidirectional switches TSW of the first power conversion circuit 30 while switching between the switching patterns defined in the program PG. In other words, the control unit 90 switches one of the bidirectional switches TSW to the ON state in accordance with the predetermined switching pattern. Therefore, for example, when the 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.

[0058] (Operation of this embodiment) The power conversion device 10 of the above embodiment is configured as a so-called single stage. That is, the first power conversion circuit 30 converts three-phase AC power into AC power using six bidirectional switches TSW. The AC power is then converted into DC power by the transformer circuit 40 and the rectifier circuit 50. The power conversion device 10 configured as a single stage has higher power conversion efficiency than a power conversion device configured as a so-called two-stage. Furthermore, since there is no capacitor between the stages as in a two-stage configuration, the power conversion device 10 of the above embodiment with a single stage configuration has a relatively high power density.

[0059] On the other hand, a power conversion circuit with a single stage configuration, such as the first power conversion circuit 30 in the above embodiment, does not have a mechanism for storing energy, such as a capacitor. Therefore, the first power conversion circuit 30 alone may not be able to maintain the output voltage within a predetermined range when an instantaneous power interruption occurs. According to the above embodiment, the power conversion device 10 includes, in addition to the first power conversion circuit 30, a second power conversion circuit 80 having a fifth capacitor C5. Therefore, even a single-stage power conversion device 10 is likely to be able to maintain the power supply to the load 110 when an instantaneous power interruption occurs.

[0060] Furthermore, the control unit 90 executes the first control when the amplitude value of one or more of the input voltages among the first voltage VA, the second voltage VB, and the third voltage VC detected by the power sensor SE is greater than a first threshold. In this first control, the control unit 90 maintains the first switch element SW1 to the fourth switch element SW4 in the off state. Therefore, in this case, the fifth capacitor C5 of the second power conversion circuit 80 and the primary winding 41A of the transformer 41 are electrically disconnected. In this case, the control unit 90 also controls the on / off of each bidirectional switch TSW of the first power conversion circuit 30 to operate the first power conversion circuit 30.

[0061] The control unit 90 executes a second control when the amplitude values ​​of multiple input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE, simultaneously become equal to or less than a first threshold. In this second control, the control unit 90 switches multiple bidirectional switches TSW to the OFF state. The control unit 90 then controls the first switch element SW1 to the fourth switch element SW4 according to a predetermined pattern. This allows the second power conversion circuit 80 to apply an AC voltage to the primary winding 41A using the energy stored in the fifth capacitor C5 as a power source. In other words, the second power conversion circuit 80 functions as a backup power source that can supply power to the load 110 even when an instantaneous power interruption occurs.

[0062] Furthermore, the control unit 90 executes the first control again when the amplitude value of one or more of the input voltages, the first voltage VA, the second voltage VB, and the third voltage VC, becomes greater than the first threshold value after performing the above control. At this time, the control unit 90 switches each switch element of the switching circuit BC to the OFF state and then resumes control of the first power conversion circuit 30. In other words, when the power supply from the three-phase AC power supply 100 is restored, the control unit 90 controls each switch element of the switching circuit BC so that the voltage output from each output terminal of the first power conversion circuit 30 is not applied to the fifth capacitor C5 of the second power conversion circuit 80. Therefore, this control makes it unlikely that the output voltage of the first power conversion circuit 30 will be applied to the fifth capacitor C5. In other words, it is possible to prevent an unintended large current from flowing through the fifth capacitor C5.

[0063] (1-1) Regarding Effects of the First Embodiment In the first embodiment, a pair of output terminals of the second power conversion circuit 80 is connected to the primary winding 41A of the transformer 41. The control unit 90 controls the on / off of the first switch element SW1 to the fourth switch element SW4, thereby enabling the second power conversion circuit 80 to output the energy stored in the fifth capacitor C5. This increases the likelihood that the power conversion device 10 will be able to output the output voltage as designed, even in the event of an instantaneous power outage.

[0064] (1-2) In the first embodiment, when the amplitude value of the input voltage input to the multiple input terminals becomes equal to or less than the first threshold, the control unit 90 switches the multiple bidirectional switches TSW to the OFF state. Furthermore, the control unit 90 controls the multiple switch elements of the switching circuit BC so that the energy stored in the fifth capacitor C5 is output to the primary winding 41A. This allows the fifth capacitor C5 to serve as a power source and continue supplying power to the load 110, even if an instantaneous power interruption occurs. Furthermore, switching the multiple bidirectional switches TSW to the OFF state prevents unintended currents, such as inrush currents, from flowing through the fifth capacitor C5 when the power supply from the three-phase AC power supply 100 is restored.

[0065] (1-3) If control of the first power conversion circuit 30 is switched to control of the second power conversion circuit 80 when the primary voltage Vp is not substantially zero, a difference is likely to occur between the time when the primary voltage Vp is positive and the time when the primary voltage Vp is negative. This may cause a magnetic bias phenomenon in the primary winding 41A, which may lead to magnetic saturation of the transformer 41. When magnetic saturation occurs, the primary current increases sharply, which may reduce the power conversion efficiency of the transformer 41 or cause an excessive electrical load on the elements in the first power conversion circuit 30.

[0066] According to the configuration of the first embodiment, when the primary voltage Vp is substantially zero, the control unit 90 switches the bidirectional switches TSW to the OFF state and controls each switch element of the switching circuit BC so that the energy stored in the fifth capacitor C5 is output to the primary winding 41A. Therefore, according to this configuration, even if the bidirectional switch TSW and each switch element are controlled as described above, it is possible to prevent either the time during which the primary voltage Vp is positive or the time during which the primary voltage Vp is negative from becoming unevenly long. As a result, the magnetism bias phenomenon is less likely to occur, and the adverse effects associated with the magnetism bias phenomenon can also be prevented.

[0067] (1-4) In the first embodiment described above, if an instantaneous power outage occurs when the primary voltage Vp is negative, the control unit 90 controls the bidirectional switch TSW so that the primary voltage Vp becomes approximately zero, and then switches the multiple bidirectional switches TSW to the OFF state. Next, the control unit 90 controls each switch element of the switching circuit BC so that the second power conversion circuit 80 outputs a positive voltage. Furthermore, if an instantaneous power outage occurs when the primary voltage Vp is positive, the control unit 90 controls the bidirectional switch TSW so that the primary voltage Vp becomes approximately zero, and then switches the multiple bidirectional switches TSW to the OFF state. Next, the control unit 90 controls each switch element of the switching circuit BC so that the second power conversion circuit 80 outputs a negative voltage. This makes it less likely that bias magnetism will occur, and therefore the power conversion efficiency of the transformer 41 is less likely to decrease.

[0068] (1-5) In the first embodiment described above, after the power input from the three-phase AC power supply 100 is restored, the control unit 90 cuts off the electrical connection between the fifth capacitor C5 of the second power conversion circuit 80 and each output terminal of the first power conversion circuit 30, and then controls the bidirectional switch TSW of the first power conversion circuit 30. This prevents an unintended current, such as an inrush current, from flowing from the first power conversion circuit 30 to the fifth capacitor C5 of the second power conversion circuit 80.

[0069] (1-6) In the first embodiment described above, even when power conversion by the first power conversion circuit 30 is stopped to protect the output voltage from overvoltage or overcurrent, the control unit 90 controls the first to fourth switch elements SW1 to SW4, so that the current flowing through the transformer 41 flows to the second power conversion circuit 80. In other words, the second power conversion circuit 80 functions as a protection circuit for the first power conversion circuit 30.

[0070] (1-7) As described above, the second power conversion circuit 80 functions as both a protection circuit and a backup power supply circuit. Therefore, the power conversion device 10 is less likely to become large. (1-8) In so-called data centers, three-phase isolated AC-DC converters are sometimes used to supply power to equipment such as server computers. Such three-phase isolated AC-DC converters may be equipped with a backup power supply unit to continuously supply power to the servers even in the event of a momentary power outage. Such three-phase isolated AC-DC converters may also be equipped with a protection circuit to suppress electrical loads on switching elements, such as overvoltages and overcurrents. However, incorporating both a backup power supply and a protection circuit into a three-phase isolated AC-DC converter may result in an increase in device size. According to the power conversion device 10 of the first embodiment, the second power conversion circuit 80 functions as both a protection circuit and a backup power supply circuit, thereby preventing the power conversion device 10 from becoming large. Therefore, the power conversion device 10 of the above embodiment is suitable as a three-phase isolated AC-DC converter for supplying power to a server computer or the like as the load 110.

[0071] <Second embodiment of power conversion device and program for power conversion device> A second embodiment of a power conversion device and a program for the power conversion device will be described below. The circuit configuration of the power conversion device of the second embodiment is the same as that of the first embodiment. The second embodiment differs from the first embodiment mainly in that transition control is executed between the first control and the second control.

[0072] (Definition of Sectors) In the second embodiment, one cycle of the AC voltage input to each input terminal of the first power conversion circuit 30 is divided into a plurality of sectors based on the magnitude relationship between the first voltage VA, the second voltage VB, and the third voltage VC. In the second embodiment, the sectors are defined as follows.

[0073] Three-phase AC power is input to each input terminal of the first power conversion circuit 30 from a three-phase AC power supply 100 via an input-side low-pass filter 20. As shown in FIG. 4 , the three phase voltages of the three-phase AC power are a first voltage VA, a second voltage VB, and a third voltage VC, which are AC voltages of different phases. The first input terminal 31A, the second input terminal 31B, and the third input terminal 31C receive the respective voltages in a one-to-one correspondence. Specifically, the first voltage VA is input to the first input terminal 31A. The second voltage VB is input to the second input terminal 31B. The third voltage VC is input to the third input terminal 31C. The second voltage VB has a phase difference of 120° with respect to the first voltage VA. The third voltage VC has a phase difference of 120° with respect to the second voltage VB.

[0074] Here, the timing of the phase when the first voltage VA is maximum is defined as 0°. Furthermore, the timing of the phase when the first voltage VA is minimum is defined as -180°. Therefore, one cycle of the first voltage VA, the second voltage VB, and the third voltage VC is expressed as a phase range of -180° or more and less than 180°. It is also possible to express the timing of the voltage phase as a phase of 180° or more and less than 360°. When the voltage phase is expressed as a phase of 180° or more, X° is synonymous with (-180° + (X - 180°)). Here, sectors 1 to 6 are defined as six periods obtained by dividing one cycle into equal parts. Specifically, when the phase of the first voltage VA is defined as "θ°," sectors 1 to 6 are defined as the following periods spaced at 60° intervals:

[0075] ・Sector 1: -30°≦θ°<30° ・Sector 2: 30°≦θ°<90° ・Sector 3: 90°≦θ°<150° ・Sector 4: 150°≦θ°<180° and -180°≦θ°<-150° ・Sector 5: -150°≦θ°<-90° ・Sector 6: -90°≦θ°<-30° However, it does not matter which sector the boundary between each sector belongs to. For example, in the example below, if θ° = 30°, it can be treated as being included in sector 1 or sector 2.

[0076] As described above, sector 1 is a period during which the first voltage VA is positive, the absolute value of the first voltage VA is equal to or greater than the absolute value of the second voltage VB, and the absolute value of the first voltage VA is equal to or greater than the absolute value of the third voltage VC. Sector 2 is a period during which the third voltage VC is negative, the absolute value of the third voltage VC is equal to or greater than the absolute value of the first voltage VA, and the absolute value of the third voltage VC is equal to or greater than the absolute value of the second voltage VB. Sector 3 is a period during which the second voltage VB is positive, the absolute value of the second voltage VB is equal to or greater than the absolute value of the first voltage VA, and the absolute value of the second voltage VB is equal to or greater than the absolute value of the third voltage VC. Sector 4 is a period during which the first voltage VA is negative, the absolute value of the first voltage VA is equal to or greater than the absolute value of the second voltage VB, and the absolute value of the first voltage VA is equal to or greater than the absolute value of the third voltage VC. Sector 5 is a period during which the third voltage VC is positive, the absolute value of the third voltage VC is equal to or greater than the absolute value of the first voltage VA, and the absolute value of the third voltage VC is equal to or greater than the absolute value of the second voltage VB. Sector 6 is a period during which the second voltage VB is negative, the absolute value of the second voltage VB is equal to or greater than the absolute value of the first voltage VA, and the absolute value of the second voltage VB is equal to or greater than the absolute value of the third voltage VC.

[0077] Thus, the absolute value of the first voltage VA is the largest in sectors 1 and 4. The absolute value of the third voltage VC is the largest in sectors 2 and 5. And the absolute value of the second voltage VB is the largest in sectors 3 and 6.

[0078] (Regarding Control When Abnormal Voltage Occurs) The storage device of the control unit 90 stores a program PG including data for executing transition control in addition to data for executing the first control and second control in the first embodiment. When power supply to each external input terminal of the power conversion device 10 starts, the execution device of the control unit 90 executes the first control, second control, etc. based on the above-mentioned program PG. Furthermore, in the second embodiment, the control unit 90 executes transition control between the first control and the second control based on the program PG. Note that in the following description, even when a switch element that was originally in the on state is maintained in the on state, it may be expressed as being switched to the on state. This also applies to the off state of a switch element.

[0079] The control unit 90 executes the first control when the amplitude values ​​of the input voltages input to all of the input terminals are not equal to or less than a predetermined first threshold, in other words, when the amplitude values ​​of the input voltages input to one or more of the first input terminal 31A to the third input terminal 31C are greater than the predetermined first threshold. The specific control manner of the control unit 90 in the first control is the same as that in the first embodiment. That is, the control unit 90 controls each of the bidirectional switches TSW of the first power conversion circuit 30 so that AC power is output from the first output terminal 32A and the second output terminal 32B.

[0080] If, during execution of the first control, the amplitude values ​​of all input voltages, the first voltage VA to the third voltage VC, detected by the power sensor SE, simultaneously become equal to or less than the first threshold value, the control unit 90 executes transition control prior to the second control.

[0081] The transition control is composed of three processes: a first process, a second process, and a third process. When the control unit 90 executes the first process, it first determines which sector contains the phase in which the amplitude values ​​of all of the input voltages, the first voltage VA to the third voltage VC, simultaneously become equal to or less than the first threshold, i.e., the phase when the transition control is initiated. The control unit 90 then controls the on / off of the multiple bidirectional switches TSW so as to form a closed circuit extending from the first end of the primary winding 41A through one of the multiple bidirectional switches TSW of the first power conversion circuit 30 to the second end of the primary winding 41A. Note that the expression "from the first end to the second end of the primary winding 41A" refers to the path of electrical conduction, not the direction of current flow. At this time, the control unit 90 changes the on / off combination of the bidirectional switches TSW depending on which sector contains the phase when the transition control is initiated.

[0082] Specifically, it is assumed that the phase when the transition control is started is within the range of sector 1 or the range of sector 4. In this case, in the first process, the control unit 90 switches all of the switch elements of the first power conversion circuit 30, namely, the eleventh switch element S11, the twenty-first switch element S21, the twenty-fourth switch element S24, and the fourteenth switch element S14, to the on state. As a result, a closed circuit is formed that passes through the first end of the primary winding 41A, the fourth inductor L4, the twenty-first switch element S21, the eleventh switch element S11, the twenty-fourth switch element S24, and the fourteenth switch element S14, and reaches the second end of the primary winding 41A. Note that at this time, the control unit 90 maintains the on / off states of the thirteenth switch element S13, the twenty-third switch element S23, the twenty-sixth switch element S26, and the sixteenth switch element S16 when the transition control is started. Similarly, the control unit 90 maintains the on / off states of the fifteenth switch element S15, the twenty-fifth switch element S25, the twenty-second switch element S22, and the twelfth switch element S12 at the time of starting the transition control. That is, the control unit 90 maintains the on / off states of the bidirectional switch TSW connected to the second input terminal 31B and the bidirectional switch TSW connected to the third input terminal 31C.

[0083] Also, assume that the phase when the transition control is started is within the range of sector 2 or the range of sector 5. In this case, in the first process, the control unit 90 switches all of the switch elements of the first power conversion circuit 30, namely, the fifteenth switch element S15, the twenty-fifth switch element S25, the twenty-second switch element S22, and the twelfth switch element S12, to the on state. As a result, a closed circuit is formed that extends from the first end of the primary winding 41A through the fourth inductor L4, the twenty-fifth switch element S25, the fifteenth switch element S15, the twenty-second switch element S22, and the twelfth switch element S12 to the second end of the primary winding 41A. Note that at this time, the control unit 90 maintains the on / off states of the eleventh switch element S11, the twenty-first switch element S21, the twenty-fourth switch element S24, and the fourteenth switch element S14 when the transition control is started. Similarly, the control unit 90 maintains the on / off states of the 13th switch element S13, the 23rd switch element S23, the 26th switch element S26, and the 16th switch element S16 at the time of starting the transition control. That is, the on / off states of the bidirectional switch TSW connected to the first input terminal 31A and the bidirectional switch TSW connected to the second input terminal 31B are maintained as they are.

[0084] Also, assume that the phase when the transition control is started is within the range of sector 3 or the range of sector 6. In this case, in the first process, the control unit 90 switches all of the switch elements of the first power conversion circuit 30, namely the thirteenth switch element S13, the twenty-third switch element S23, the twenty-sixth switch element S26, and the sixteenth switch element S16, to the on state. As a result, a closed circuit is formed that extends from the first end of the primary winding 41A through the fourth inductor L4, the twenty-third switch element S23, the thirteenth switch element S13, the twenty-sixth switch element S26, and the sixteenth switch element S16 to the second end of the primary winding 41A. Note that at this time, the control unit 90 maintains the on / off states of the eleventh switch element S11, the twenty-first switch element S21, the twenty-fourth switch element S24, and the fourteenth switch element S14 when the transition control is started. Similarly, the control unit 90 maintains the on / off states of the fifteenth switch element S15, the twenty-fifth switch element S25, the twenty-second switch element S22, and the twelfth switch element S12 at the time of starting the transition control. That is, the on / off states of the bidirectional switch TSW connected to the first input terminal 31A and the bidirectional switch TSW connected to the third input terminal 31C are maintained as they are.

[0085] On the other hand, regardless of which sector the phase falls within when the transition control is started, the control unit 90 turns all of the first switch element SW1 to the fourth switch element SW4 of the second power conversion circuit 80 to the off state in the first process. Note that, before executing the first process of the transition control, the control unit 90 executes the first control. As described above, the control unit 90 maintains the first switch element SW1 to the fourth switch element SW4 in the off state in the first control. Therefore, in the first process, the control unit 90 maintains the on / off states of the first switch element SW1 to the fourth switch element SW4 in the off state.

[0086] After the switching of each switch element in the first process is completed, the control unit 90 then executes a second process. When executing the second process, the control unit 90 maintains the on / off state of each bidirectional switch TSW of the first power conversion circuit 30 in the state after switching in the first process. Furthermore, when executing the second process, the control unit 90 controls the on / off of the multiple switch elements so as to form a closed circuit extending from the first end of the primary winding 41A through one of the multiple switch elements of the second power conversion circuit 80 to the second end of the primary winding 41A. Specifically, the control unit 90 switches the second switch element SW2 and the fourth switch element SW4 of the second power conversion circuit 80 to the on state. Furthermore, the control unit 90 maintains the first switch element SW1 and the third switch element SW3 of the second power conversion circuit 80 in the off state. This forms a closed circuit that passes through the first end of the primary winding 41A, the fourth inductor L4, the second switch element SW2, the fourth switch element SW4, and the second end of the primary winding 41A.

[0087] After the switching of each switch element in the second process is completed, the control unit 90 then executes a third process. After executing the third process, the control unit 90 switches all of the multiple bidirectional switches TSW of the first power conversion circuit 30 to the OFF state. More specifically, the control unit 90 switches all of the switch elements included in the first power conversion circuit 30 to the OFF state. Furthermore, after executing the third process, the control unit 90 maintains the ON / OFF state of each switch element of the second power conversion circuit 80 in the state after switching in the second process.

[0088] As described above, when transition control is executed from a state in which first control is being executed, the control unit 90 executes the above three processes in the transition control in the order of first process, second process, and third process.

[0089] When the third process is completed, that is, when the transition control is completed, the control unit 90 executes the second control. The specific control mode of the control unit 90 in the second control is the same as that in the first embodiment. That is, the control unit 90 controls each switch element of the second power conversion circuit 80 so that AC power is output from the third output terminal 82A and the fourth output terminal 82B. Note that in the second control, all of the bidirectional switches TSW of the first power conversion circuit 30 are maintained in the off state. Therefore, in the second control, the state in which each of the bidirectional switches TSW of the first power conversion circuit 30 was switched in the third process of the transition control is also maintained in the second control.

[0090] When the amplitude value of one or more of the input voltages among the first voltage VA to the third voltage VC becomes larger than the first threshold value while the second control is being executed, the control unit 90 executes the transition control again. When the transition control is executed from the state where the second control is being executed, the control unit 90 executes the above-mentioned three processes in the transition control in the order of the third process, the second process, and the first process.

[0091] When transition control is executed subsequently to second control, the control unit 90 determines which sector contains the phase when the transition control is terminated and switched to first control. The control unit 90 can determine the timing to terminate the transition control from the times required for the third process, the second process, and the first process of the transition control. The control unit 90 then changes the on / off combination of the bidirectional switch TSW in the second process and the first process depending on which sector contains the phase when the transition control is terminated.

[0092] Specifically, it is assumed that the phase when the transition control is ended is within the range of sector 1 or within the range of sector 4. In this case, the control unit 90 sets the on / off combination of each bidirectional switch TSW to the same combination as when the first process of the transition control is executed subsequently from the first control and the phase when the transition control is started is within the range of sector 1 or within the range of sector 4. Also, it is assumed that the phase when the transition control is ended is within the range of sector 2 or within the range of sector 5. In this case, the control unit 90 sets the on / off combination of each bidirectional switch TSW to the same combination as when the first process of the transition control is executed subsequently from the first control and the phase when the transition control is started is within the range of sector 2 or within the range of sector 5. Furthermore, it is assumed that the phase when the transition control is ended is within the range of sector 3 or within the range of sector 6. In this case, the control unit 90 sets the on / off combination of each bidirectional switch TSW to the same combination as when the first process of the transition control is executed subsequently from the first control and the phase when the transition control is started is within the range of sector 3 or within the range of sector 6.

[0093] (Effects of the Second Embodiment) According to the power conversion device 10 of the second embodiment, in addition to the effects (1-1), (1-2), and (1-5) to (1-8) of the power conversion device 10 of the first embodiment, the following effects are achieved.

[0094] (2-1) When the control unit 90 is executing the first control, the power supply from the three-phase AC power supply 100 may be momentarily interrupted. In this case, the bidirectional switches TSW may be switched on and off even though the absolute value of the primary voltage Vp is not below the second threshold value, which may cause magnetic saturation in the transformer 41.

[0095] In the second embodiment, the control unit 90 executes transition control between the first control and the second control. In the second process of the transition control, a closed circuit is formed from the first end of the primary winding 41A to the second end of the primary winding 41A via one of the multiple bidirectional switches TSW in the first power conversion circuit 30. At the same time, a closed circuit is formed from the first end of the primary winding 41A to the second end of the primary winding 41A via one of the multiple switch elements in the second power conversion circuit 80. In this way, the formation of closed circuits on both the first power conversion circuit 30 side and the second power conversion circuit 80 side causes the primary voltage Vp to quickly approach zero. That is, in the second embodiment, when switching between the first control and the second control, a period is provided during which the primary voltage Vp is forcibly reduced to zero. Therefore, the first control and the second control can be quickly switched between regardless of the on / off states of the switch elements when switching between the first control and the second control, while reducing the risk of magnetic saturation occurring in the transformer 41.

[0096] (2-2) In the second embodiment, when switching from the first control to the second control, the control unit 90 executes a first process prior to a second process during transition control. In the first process, a closed circuit is formed from the first end of the primary winding 41A through one of the multiple bidirectional switches TSW of the first power conversion circuit 30 to the second end of the primary winding 41A. Meanwhile, each switch element of the second power conversion circuit 80 is switched to the OFF state. That is, in the first process, a closed circuit is formed only on the first power conversion circuit 30 side. As a result, in the transition control when switching from the first control to the second control, first, the closed circuit on the first power conversion circuit 30 side causes the primary voltage Vp to approach zero. Then, in the subsequent second process, a closed circuit on the second power conversion circuit 80 side is formed. Therefore, when the closed circuit on the second power conversion circuit 80 side is formed, it is highly likely that the primary voltage Vp is zero or close to zero. As a result, the moment a closed circuit on the second power conversion circuit 80 side is formed, an unintended current is prevented from flowing from the primary winding 41A of the transformer 41 to the second power conversion circuit 80.

[0097] Furthermore, when switching from the first control to the second control, in the transition control, the control unit 90 executes the third process following the second process. In this third process, a closed circuit is formed from the first end of the primary winding 41A through one of the multiple switch elements of the second power conversion circuit 80 to the second end of the primary winding 41A. Meanwhile, each bidirectional switch TSW of the first power conversion circuit 30 is switched to the OFF state. In this way, by keeping each bidirectional switch TSW of the first power conversion circuit 30 in the OFF state before the second control, it is possible to prevent current from flowing from the second power conversion circuit 80 to the first power conversion circuit 30 when the second control is started.

[0098] Although the case of switching from the first control to the second control has been described, when switching from the second control to the first control, the transition control executes the third process, the second process, and the first process in that order. In this case, the same effect as when switching from the first control to the second control is achieved.

[0099] (2-3) In the second embodiment, when the phase when the transition control is started is within the range of sector 1 or sector 4, the 11th switch element S11, the 21st switch element S21, the 24th switch element S24, and the 14th switch element S14 are switched to the ON state. Here, when the phase is within the range of sector 1 or sector 4 while the first control is being executed, the absolute value of the first voltage VA is large. This means that there is a high possibility that three or more of the four switch elements are in the ON state. Therefore, when all four switch elements are switched ON / OFF, the number of switch elements that are actually switched ON / OFF can be minimized. Note that although the case where the phase when the transition control is started is within the range of sector 1 or sector 4 has been described, the same applies when the phase when the transition control is started is within the range of another sector. Furthermore, when the transition control is executed subsequently to the second control, the number of switch elements that are switched ON / OFF when the transition control is terminated can be minimized, as described above.

[0100] <Modifications> The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0101] The configuration of the power conversion device 10 is not limited to the examples of the above-described embodiments. 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-described embodiments.

[0102] In the first embodiment, 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 the three-phase AC power supply 100.

[0103] The input-side low-pass filter 20 in each 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. The switch elements constituting each bidirectional switch TSW are not limited to those in the above-described embodiments. 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.

[0104] In each embodiment, the two switch elements of the bidirectional switch TSW may be transistors capable of passing a current in both the forward and reverse directions. In this case, the two switch elements are connected in series with their source terminals connected to each other. Specifically, the switch elements are gallium nitride high electron mobility transistors (GaN-High Electron Mobility Transistors, GaN-HEMTs) or the like.

[0105] The transformer circuit 40 in each embodiment 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.

[0106] The specific circuit configuration of the rectifier circuit 50 is not limited to the examples in the above embodiments. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or a full-bridge circuit including four diodes.

[0107] The power conversion device 10 of each embodiment 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.

[0108] The output voltage of the boost circuit 70 in each embodiment may be equal to or less 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 less 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.

[0109] - The power sensor SE in each embodiment may detect the voltage and current values ​​at the first input terminal 31A to the third input terminal 31C of the first power conversion circuit 30, rather than the voltage and current values ​​at the first external input terminal 11A to the third external input terminal 11C.

[0110] The second power conversion circuit 80 in each embodiment may include a switch element connecting the fifth capacitor C5 to 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, it becomes easy to switch between a state in which a voltage is applied from the first power conversion circuit 30 to the primary winding 41A and a state in which a voltage is applied from the second power conversion circuit 80 to the primary winding 41A.

[0111] In each embodiment, when controlling each bidirectional switch TSW of the first power conversion circuit 30 while switching the switching pattern, the control unit 90 does not need to maintain all switch elements of the second power conversion circuit 80 in the off state. For example, the second switch element SW2 and the fourth switch element SW4 may be maintained in the off state. In this way, it is sufficient that the on / off state of each switch element is such that current is prevented from flowing from the first output terminal 32A and the second output terminal 32B side to the fifth capacitor C5 side.

[0112] In each embodiment, when determining whether the amplitude values ​​of the first voltage VA to the third voltage VC detected by the power sensor SE are equal to or less than the first threshold, the control unit 90 essentially determines whether the amplitude values ​​are equal to or less than the first threshold. For example, if the first threshold is 10 V, the control unit 90 determines that the amplitude values ​​of each input voltage are equal to or less than the first threshold when the first voltage VA to the third voltage VC are equal to or greater than -10 V and equal to or less than +10 V. The same applies to the second threshold.

[0113] In the first embodiment, when the amplitude value of the input voltages input to the input terminals becomes equal to or less than the first threshold, the control unit 90 may switch the bidirectional switches TSW to the off state and control the switch elements of the switching circuit BC at a timing other than when the absolute value of the primary voltage Vp becomes equal to or less than the second threshold. Even in this case, the second power conversion circuit 80 can function as a standby power supply circuit.

[0114] In each embodiment, when the input voltage becomes equal to or lower than the first threshold, the control unit 90 does not need to switch all of the bidirectional switches TSW to the OFF state. The control unit 90 only needs to switch a plurality of the bidirectional switches TSW to the OFF state to stop power conversion by the first power conversion circuit 30, and some of the bidirectional switches TSW may be in the ON state.

[0115] In each embodiment, when the amplitude values ​​of the multiple input voltages are equal to or less than the first threshold while the primary voltage Vp is negative, the control unit 90 does not have to control the multiple switch elements so that the primary voltage Vp changes to the positive side when the energy stored in the fifth capacitor C5 starts to be output. That is, in this case, the control unit 90 may control the multiple switch elements so that the primary voltage Vp changes to the negative side when the energy stored in the fifth capacitor C5 starts to be output. This also applies to the case where the amplitude values ​​of the input voltages input to the multiple input terminals are equal to or less than the first threshold while the primary voltage Vp is positive.

[0116] In each embodiment, when the amplitude values ​​of the plurality of input voltages are equal to or less than the first threshold, the control unit 90 may switch the plurality of bidirectional switches TSW to the on state and then control the switch elements of the switching circuit BC so that the first output terminal 32A, the second output terminal 32B, and the fifth capacitor C5 are not electrically connected via the switching circuit BC if the inter-terminal voltage of the fifth capacitor C5 is higher than the maximum value of the input voltage. Even in this case, there is no risk of voltage being applied from the first output terminal 32A and the second output terminal 32B to the fifth capacitor C5.

[0117] In the second embodiment, the transition control only needs to include the second process. For example, when switching from a state in which the first control is being executed to a state in which the second control is being executed, the control unit 90 may execute only the second process in the transition control, omitting the first and third processes. Also, in the transition control, the control unit 90 may execute only the first and second processes, omitting the third process, or may execute only the second and third processes, omitting the first process. This also applies to a case in which switching from a state in which the second control is being executed to a state in which the first control is being executed.

[0118] - In the second embodiment, the control unit 90 may perform transition control only in either the case of switching from a state in which the first control is being executed to a state in which the second control is being executed, or the case of switching from a state in which the second control is being executed to a state in which the first control is being executed.

[0119] In the transition control of the second embodiment, the relationship between the range of the sector within which the phase is when the transition control is started and the path along which the closed circuit is formed is not important. For example, the closed circuit may always be formed along the same path regardless of the range of the sector within which the phase is when the transition control is started.

[0120] In the transition control of the second embodiment, when forming a closed circuit extending from the first end of the primary winding 41A through one of the plurality of bidirectional switches TSW of the first power conversion circuit 30 to the second end of the primary winding 41A, the on / off combination of the switch elements can be changed.

[0121] For example, when the phase when the transition control is started is within the range of sector 1 or the range of sector 4, the control unit 90 may control the eleventh switch element S11 and the fourteenth switch element S14 to be on and the twenty-first switch element S21 and the twenty-fourth switch element S24 to be off. Even in this case, a current flows through these switch elements due to the body diodes of the twenty-first switch element S21 and the twenty-fourth switch element S24. That is, when these switch elements are in the on / off state, a one-way closed circuit is formed that allows a current to flow from the second end of the primary winding 41A through the four switch elements toward the first end of the primary winding 41A.

[0122] Furthermore, for example, when the phase when the transition control is started is within the range of sector 1 or the range of sector 4, the control unit 90 may control the eleventh switch element S11 and the fourteenth switch element S14 to be off and the twenty-first switch element S21 and the twenty-fourth switch element S24 to be on. Even in this case, a current flows through the body diodes of the eleventh switch element S11 and the fourteenth switch element S14. That is, when these switch elements are in the on / off state, a one-way closed circuit is formed that allows a current to flow from the first end of the primary winding 41A through the four switch elements toward the second end of the primary winding 41A.

[0123] Although a detailed description is omitted, even when the phase at the time when the transition control is started is within the range of another sector, the four corresponding switch elements may be controlled in the same manner as in the two modified examples described above. That is, it is sufficient if the on / off states of the switch elements are such that a one-way closed circuit is formed using the body diodes of the switch elements.

[0124] In the transition control of the second embodiment, when a closed circuit is formed from the first end of the primary winding 41A through one of the multiple switch elements of the second power conversion circuit 80 to the second end of the primary winding 41A, the on / off combination of each switch element can be changed.

[0125] For example, the control unit 90 may switch only the second switch element SW2 to the on state and switch the other three switch elements to the off state. In this case, a current flows through the fourth switch element SW4 due to the body diode of the fourth switch element SW4. That is, when this switch element is in the on / off state, a one-way closed circuit is formed that allows a current to flow from the first end of the primary winding 41A through the second switch element SW2 and the fourth switch element SW4 to the second end of the primary winding 41A. In this way, the on / off states of the switch elements may be such that a one-way closed circuit is formed using the body diode of each switch element of the second power conversion circuit 80.

[0126] For example, the control unit 90 may switch the second switch element SW2 and the fourth switch element SW4 to the OFF state, and switch the first switch element SW1 and the third switch element SW3 to the ON state.

[0127] Furthermore, when forming a closed circuit, it is not necessary to fix the on / off combination of the switch elements to either one of the on / off combinations of the switch elements in this modified example and the on / off combinations of the switch elements exemplified in the second embodiment. In other words, the on / off combination of the switch elements may be changed every time a closed circuit is formed.

[0128] In the second embodiment, the control unit 90 may execute a specific control different from the first control and the transition control. In this example, it is assumed that one or more specific switching patterns are included among the multiple switching patterns defined by the program PG as data related to the first control. The specific switching pattern is a combination of on / off states of the multiple bidirectional switches TSW that forms a closed circuit extending from the first end of the primary winding 41A to the second end of the primary winding 41A via any of the multiple bidirectional switches TSW of the first power conversion circuit 30.

[0129] In this example, the control unit 90 controls the on / off of each bidirectional switch TSW of the first power conversion circuit 30 while switching between switching patterns during the first control. At this time, the control unit 90 switches the switching pattern at a timing linked to the magnitude of the input voltages input to the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C. When switching to the second control, the control unit 90 executes the specific control before executing the transition control.

[0130] In the specific control, the control unit 90 controls the on / off of each bidirectional switch TSW of the first power conversion circuit 30 while switching between switching patterns in the same order as in the first control. The control unit 90 also basically switches between switching patterns at the same timing as in the first control. However, when the control unit 90 controls the on / off of multiple bidirectional switches TSW according to the specific switching pattern, the control unit 90 exceptionally continues the on / off combination of the bidirectional switches TSW for a predetermined period or longer, regardless of the magnitude of the input voltage input to each input terminal. This specified period can be determined, for example, through testing or simulation, as a time sufficient for the primary voltage Vp to reach zero when the above-described closed circuit is formed on the first power conversion circuit 30 side. In the specific control, when the on / off states of the multiple bidirectional switches TSW according to the specific switching pattern continue for a predetermined period or longer, the control unit controls the on / off of each bidirectional switch TSW using a switching pattern corresponding to the magnitude of the input voltage input to each input terminal.

[0131] According to the above example, when the on / off of the multiple bidirectional switches TSW is controlled according to the specific switching pattern in the specific control, the primary voltage Vp becomes zero or close to zero. Even if the on / off of the bidirectional switches TSW is then controlled using a switching pattern other than the specific switching pattern in the specific control, the primary voltage Vp does not become very high. That is, in this example, the primary voltage Vp can be reduced in the specific control before the transition control is executed. Therefore, when the transition control is executed, the primary voltage Vp is more likely to be reduced to zero.

[0132] 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."

[0133] <Supplementary Notes> The technical ideas that can be understood from the above 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; 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 is capable of outputting energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0134] [2] The power conversion device according to [1], wherein, when an amplitude value of an input voltage input to one or more of the plurality of input terminals is greater than a predetermined threshold, the control unit executes first control to control the plurality of bidirectional switches so that the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal; and, when an amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the threshold, executes second control to switch the plurality of bidirectional switches to an off state and control the plurality of switch elements so that energy stored in the capacitor is output from the third output terminal and the fourth output terminal to the primary side winding.

[0135] [3] The power conversion device according to [2], wherein when the threshold is a first threshold and a potential difference of the first output terminal with respect to the second output terminal is a primary voltage, if an amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the first threshold, the control unit switches the plurality of bidirectional switches to an off state at a timing when an absolute value of the primary voltage becomes equal to or less than a predetermined second threshold, and controls the plurality of switch elements so that energy stored in the capacitor is output to the primary winding.

[0136] [4] The power conversion device according to [3], wherein, when an amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the first threshold while the primary voltage is negative, the control unit switches the plurality of bidirectional switches to an off state at a timing when the absolute value of the primary voltage becomes equal to or less than a predetermined second threshold, and controls the plurality of switch elements so that the primary voltage changes to a positive side when energy stored in the capacitor is output.

[0137] [5] The power conversion device according to [4], wherein when the amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the first threshold while the primary voltage is positive, the control unit switches the bidirectional switch to an off state at a timing when the absolute value of the primary voltage becomes equal to or less than a predetermined second threshold, and controls the plurality of switch elements so that the primary voltage changes to a negative side when energy stored in the capacitor is output.

[0138] [6] The power conversion device according to any one of [2] to [5], wherein, when the plurality of bidirectional switches are in an off state and the control unit is controlling the plurality of switch elements, if an amplitude value of the input voltage input to one or more of the plurality of input terminals becomes larger than a predetermined threshold, the control unit controls the plurality of switch elements so that the first output terminal, the second output terminal, and the capacitor are not electrically connected via the plurality of switch elements, and then controls the plurality of bidirectional switches to be switched on and off.

[0139] [7] The power conversion device according to any one of [1] to [6], 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 it, and wherein the capacitor is charged by the DC power output by the three-phase rectifier circuit.

[0140] [8] The power conversion device according to [7], further comprising a boost circuit connected between the three-phase rectifier circuit and the second power conversion circuit, for boosting the DC voltage output from the three-phase rectifier circuit, wherein the output voltage of the boost circuit is greater than the maximum value of the input voltage input to the input terminal.

[0141] [9] The power conversion device according to any one of [2] to [6], wherein the control unit executes transition control between the first control and the second control in at least one of a case where a switch is made from a state where the first control is being executed to a state where the second control is being executed and a case where a switch is made from a state where the second control is being executed to a state where the first control is being executed, and the control unit, in the transition control, controls the on / off of the plurality of bidirectional switches so as to form a closed circuit extending from a first end of the primary winding to a second end of the primary winding via any one of the plurality of bidirectional switches, and controls the on / off of the plurality of switch elements so as to form a closed circuit extending from the first end of the primary winding to the second end of the primary winding via any one of the plurality of switch elements.

[0142]

[10] When switching from a state in which the first control is being executed to a state in which the second control is being executed, the control unit, in the transition control, performs a first process of controlling the on / off of the plurality of bidirectional switches so that a closed circuit is formed from a first end of the primary winding to a second end of the primary winding via any of the plurality of bidirectional switches and controlling the plurality of switch elements to an off state; and a second process of controlling the on / off of the plurality of switch elements so as to form a closed circuit from a first end of the primary winding via any one of the plurality of switch elements to a second end of the primary winding; and a third process of controlling the plurality of bidirectional switches to an off state so as to form a closed circuit from the first end of the primary winding via any one of the plurality of switch elements to a second end of the primary winding, the first process being executed in the order of the second process, the second process being executed in the order of the third process, the third process being executed in the order of the third process, the second process being executed in the order of the third process, the third process being executed in the order of the third process, the third process being executed in the order of the fourth ...

[0143]

[11] When switching from a state in which the second control is being executed to a state in which the first control is being executed, the control unit, in the transition control, performs a first process of controlling the on / off of the plurality of bidirectional switches so that a closed circuit is formed from a first end of the primary winding to a second end of the primary winding via any one of the plurality of bidirectional switches and controlling the plurality of switch elements to an off state; and and controlling on / off of the plurality of switch elements so as to form a closed circuit from a first end of the primary winding to a second end of the primary winding via any one of the plurality of switch elements; and third processing of controlling the plurality of bidirectional switches to an off state and controlling on / off of the plurality of switch elements so as to form a closed circuit from the first end of the primary winding to a second end of the primary winding via any one of the plurality of switch elements, the power conversion device according to [9] or

[10] , which executes the third processing, the second processing, and the first processing in this order.

[0144]

[12] The power conversion device according to any one of [9] to

[11] , wherein, in the first control, the control unit controls the on / off of the plurality of bidirectional switches while switching the switching patterns according to a plurality of different switching patterns in which on / off combinations of the plurality of bidirectional switches are defined, the plurality of switching patterns including a specific switching pattern which is an on / off combination of the plurality of bidirectional switches that forms a closed circuit from a first end of the primary winding through any of the plurality of bidirectional switches to a second end of the primary winding, the control unit executes the specific control before executing the transition control when switching from a state in which the first control is being executed to a state in which the second control is being executed, and the control unit, in the specific control, controls the on / off of the plurality of bidirectional switches while switching the switching patterns in the same order as the first control, and continues the on / off combination of the plurality of bidirectional switches according to the specific switching pattern for a predetermined specified period or more, regardless of the magnitude of the input voltage input to the plurality of input terminals.

[0145]

[13] A power conversion circuit including 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 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 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 is configured to convert a voltage stored in the capacitor. and controlling the control unit to control the plurality of bidirectional switches so that, when an amplitude value of an input voltage input to one or more of the plurality of input terminals is greater than a predetermined threshold, the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal, and to switch the plurality of bidirectional switches to an off state when an amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the threshold, and to control the plurality of switch elements so that the energy stored in the capacitor is output from the third output terminal and the fourth output terminal to the primary side winding.

[0146]

[14] A power conversion device comprising: 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 and 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, and a rectifier circuit connected to the secondary winding and capable of converting AC voltage, the first power conversion circuit being capable of converting three-phase AC power input to the plurality of input terminals; 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 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 is capable of outputting energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0147] 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 C5...fifth capacitor BC...switching 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; A second power conversion circuit having; A control unit capable of switching on and off the plurality of bidirectional switches and on and off the plurality of switch elements; The second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal. A power conversion device.

2. When the amplitude value of the input voltage input to one or more of the plurality of input terminals is greater than a predetermined threshold value, the control unit controls the plurality of bidirectional switches so that the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal. Execute the first control; When the amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the threshold value, the plurality of bidirectional switches are switched to the off state, and the energy stored in the capacitor is output from the third output terminal and the fourth output terminal to the primary winding. The power conversion device according to claim 1, wherein a second control for controlling a plurality of the switch elements is executed.

3. When the threshold value is a first threshold value and the potential difference between the first output terminal and the second output terminal is a primary voltage, When the amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the first threshold value, the control unit switches the plurality of bidirectional switches to the off state at the timing when the absolute value of the primary voltage becomes equal to or less than a predetermined second threshold value, and The power conversion device according to claim 2, wherein a plurality of the switch elements are controlled so that the energy stored in the capacitor is output to the primary winding.

4. When the amplitude value of the input voltage input to the plurality of input terminals is equal to or less than the first threshold value in a state where the primary voltage is negative, the control unit switches the plurality of bidirectional switches to the off state at the timing when the absolute value of the primary voltage becomes equal to or less than a predetermined second threshold value, and controls the plurality of switch elements so that the primary voltage changes to the positive side when the energy stored in the capacitor is output. The power conversion device according to claim 3.

5. When the amplitude value of the input voltage input to the plurality of input terminals is equal to or less than the first threshold value in a state where the primary voltage is positive, the control unit switches the bidirectional switch to the off state at the timing when the absolute value of the primary voltage becomes equal to or less than a predetermined second threshold value, and controls the plurality of switch elements so that the primary voltage changes to the negative side when the energy stored in the capacitor is output. The power conversion device according to claim 4.

6. When the amplitude value of the input voltage input to one or more of the plurality of input terminals becomes greater than a predetermined threshold value while the plurality of bidirectional switches are in the off state and the control unit is controlling the plurality of switch elements, the control unit controls the plurality of switch elements so that the first output terminal, the second output terminal, and the capacitor are not electrically connected via the plurality of switch elements, and then performs control to switch the plurality of bidirectional switches. The power conversion device according to any one of claims 2 to 5.

7. The plurality of input terminals are connected to a three-phase AC power supply, and further include a three-phase rectifier circuit that is connected between the three-phase AC power supply and the second power conversion circuit and can convert the input three-phase AC power into DC power and output it. The capacitor is charged by the DC power output by the three-phase rectifier circuit. The power conversion device according to any one of claims 1 to 6.

8. Further includes a boost circuit that is connected between the three-phase rectifier circuit and the second power conversion circuit and boosts the DC voltage output from the three-phase rectifier circuit. The output voltage of the boost circuit is greater than the maximum value of the input voltage input to the input terminals. The power conversion device according to claim 7.

9. When the control unit switches from the state of executing the first control to the state of executing the second control, and when switching from the state of executing the second control to the state of executing the first control, in at least one of these cases, transition control is executed between the first control and the second control. The control unit, in the transition control, controls the on / off of a plurality of the bidirectional switches so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of bidirectional switches to the second end of the primary winding, and controls the on / off of a plurality of the switch elements so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of switch elements to the second end of the primary winding. The power conversion device according to any one of claims 2 to 6.

10. When the control unit switches from the state of executing the first control to the state of executing the second control, in the transition control, a first process of controlling the on / off of a plurality of the bidirectional switches so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of bidirectional switches to the second end of the primary winding and controlling the plurality of switch elements to be in an off state, a second process of controlling the on / off of a plurality of the bidirectional switches so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of bidirectional switches to the second end of the primary winding and controlling the on / off of a plurality of the switch elements so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of switch elements to the second end of the primary winding, and a third process of controlling the plurality of bidirectional switches to be in an off state and controlling the on / off of a plurality of the switch elements so that a closed circuit is formed from the first end of the primary winding through any one of the plurality of switch elements to the second end of the primary winding are executed in the order of the first process, the second process, and the third process. The power conversion device according to claim 9.

11. When the control unit switches from the state of executing the second control to the state of executing the first control, in the transition control, the first process of controlling the on / off of the plurality of bidirectional switches so that a closed circuit is formed from the first end of the primary winding to the second end of the primary winding through any one of the plurality of bidirectional switches, and controlling the plurality of switch elements to the off state; the second process of controlling the on / off of the plurality of bidirectional switches so that a closed circuit is formed from the first end of the primary winding to the second end of the primary winding through any one of the plurality of bidirectional switches, and controlling the on / off of the plurality of switch elements so that a closed circuit is formed from the first end of the primary winding to the second end of the primary winding through any one of the plurality of switch elements; the third process of controlling the plurality of bidirectional switches to the off state, and controlling the on / off of the plurality of switch elements so that a closed circuit is formed from the first end of the primary winding to the second end of the primary winding through any one of the plurality of switch elements; are executed in the order of the third process, the second process, and the first process. The power conversion device according to claim 9 or claim 10.

12. In the first control, the control unit controls the on / off states of the plurality of bidirectional switches while switching the switching pattern according to a plurality of different switching patterns in which the on / off combinations of the plurality of bidirectional switches are defined. The plurality of switching patterns include a specific switching pattern that is an on / off combination of the plurality of bidirectional switches in which a closed circuit is formed from the first end of the primary winding through any one of the plurality of bidirectional switches to the second end of the primary winding. When switching from the state of executing the first control to the state of executing the second control, the control unit executes specific control before executing the transition control. In the specific control, the control unit controls the on / off states of the plurality of bidirectional switches while switching the switching pattern in the same order as in the first control, and continues the on / off combination of the plurality of bidirectional switches according to the specific switching pattern for a predetermined period or longer regardless of the magnitude of the input voltage input to the plurality of input terminals. The power conversion device according to any one of claims 9 to 11.

13. 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 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; A control unit capable of switching on and off the plurality of bidirectional switches and on and off the plurality of switch elements; The second power conversion circuit is applied to a power conversion device capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal, In the control unit, When the amplitude value of the input voltage input to one or more of the plurality of input terminals is greater than a predetermined threshold value, the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal, and controls the plurality of bidirectional switches accordingly; When the amplitude value of the input voltage input to the plurality of input terminals becomes equal to or less than the threshold value, the plurality of bidirectional switches are switched to the off state, and the plurality of switch elements are controlled so that the energy stored in the capacitor is output from the third output terminal and the fourth output terminal to the primary winding. A program for a power conversion device.

14. A plurality of input terminals, a first output terminal and a second output terminal, a plurality of bidirectional switches connecting 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, 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 AC voltage, a first power conversion circuit 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 having the above, a control unit capable of switching on / off of the plurality of bidirectional switches and on / off of the plurality of switch elements, and the second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal. A power conversion device.

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