Power conversion device and program for power conversion device

Abstract

A power conversion device (10) includes 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) is capable of converting three-phase AC power input thereto and outputting from a pair of output terminals. The second power conversion circuit (80) has a switching circuit including a plurality of switching 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) is capable of outputting energy accumulated in the capacitor from the output terminals.

Description

Technical Field

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

[0002] The power conversion device disclosed in Patent Document 1 includes multiple nodes, six bidirectional switches, and a control device. Three-phase AC power is input to three of the multiple nodes. The power conversion circuit can convert the three-phase AC power input to the above-mentioned nodes into DC power for output by controlling the opening and closing of each bidirectional switch through the control device.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-68657 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the power conversion device disclosed in Patent Document 1, there are occasional momentary interruptions in the power supply to each node. When such a momentary interruption occurs, the power conversion device may be unable to maintain the power supply to the load.

[0008] Technical solutions for solving the problem

[0009] To address the aforementioned problems, this disclosure provides a power conversion device comprising: a first power conversion circuit having multiple input terminals, multiple bidirectional switches, a first output terminal, and a second output terminal, capable of converting three-phase AC power; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal, and the second end of the primary winding being connected to the second output terminal; a second power conversion circuit having a capacitor, multiple switching 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 the on / off states of the multiple bidirectional switches and the multiple switching elements, wherein the second power conversion circuit is capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0010] Furthermore, this disclosure discloses a program for a power conversion device, applied to a power conversion device comprising: a first power conversion circuit having multiple input terminals, multiple bidirectional switches, and a first output terminal and a second output terminal, capable of converting three-phase AC power; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal, and the second end of the primary winding being connected to the second output terminal; a second power conversion circuit having a capacitor, multiple switching 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 the on / off states of the multiple bidirectional switches and the multiple switching elements. When the components are switched on and off, the second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal. The program used by the power conversion device causes the control unit to perform the following processing: when the amplitude value of the input voltage input to one or more of the plurality of input terminals is greater than a given threshold, the plurality of bidirectional switches are controlled so that the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal; when the amplitude value of the input voltage input to the plurality of input terminals is less than the threshold, the plurality of bidirectional switches are switched to the off state, and the plurality of switching 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.

[0011] Furthermore, this disclosure discloses a power conversion device comprising: a first power conversion circuit having multiple input terminals, a first output terminal, and a second output terminal; multiple bidirectional switches connecting the multiple input terminals to the first output terminal and the second output terminal; a transformer; and a rectifier circuit. The first power conversion circuit is capable of converting three-phase AC power input to the multiple input terminals. The transformer has a primary winding and a secondary winding, with a first end of the primary winding connected to the first output terminal and a second end of the primary winding connected to the second output terminal. The rectifier circuit is connected to the secondary winding and is capable of converting AC voltage; the second power conversion circuit has a capacitor, a plurality of switching 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 the on and off of the plurality of bidirectional switches and the plurality of switching elements, the second power conversion circuit being capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0012] Invention Effects

[0013] Even in the event of a momentary interruption, the power conversion device can maintain the power supply to the load. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of a power conversion device.

[0015] Figure 2 This is the circuit diagram of the first power conversion circuit.

[0016] Figure 3 This is the circuit diagram of the second power conversion circuit.

[0017] Figure 4 It is a diagram showing the waveforms and sections of three-phase AC voltage. Detailed Implementation

[0018] <First Embodiment of Power Conversion Device and Program for Power Conversion Device>

[0019] The following describes a first embodiment of a power conversion device and a program used in that device. Furthermore, the accompanying drawings are merely illustrative of various embodiments of this disclosure and should not be construed as limiting the scope of this disclosure. Additionally, the drawings are schematic diagrams for ease of understanding, and sometimes enlarged or omitted components. Terms such as "first," "second," and "third" in this disclosure are used only to distinguish objects and are not intended to rank or order objects.

[0020] (Regarding the structure of the power conversion device)

[0021] like Figure 1 As shown, 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. Furthermore, the power conversion device 10 includes a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C, and a first external output terminal 12A and a second external output terminal 12B.

[0022] The power conversion device 10 as a whole is a so-called three-phase isolated AC-DC converter. That is, the power conversion device 10 can convert the three-phase AC power input to each external input terminal into DC power and output it from a pair of external output terminals. Moreover, the transformer circuit 40 is located in the power path from each external input terminal to each external output terminal, thereby electrically isolating the external input terminal side from the external output terminal side.

[0023] For example, each external input terminal receives one-to-one input of the three phases of three-phase AC power from the three-phase AC power supply 100. The three-phase AC power supply 100 is a three-phase, three-wire commercial power system with three AC power sources connected in a Y-connection. The voltages of the three phases are voltage VA (phase 1), voltage VB (phase 2), and voltage VC (phase 3). Each voltage is an AC voltage with a different phase. Voltage VA is input to external input terminal 11A. Voltage VB is input to external input terminal 11B. Voltage VC is input to external input terminal 11C. Voltage VB has a 120° phase difference relative to voltage VA. Voltage VC has a 120° phase difference relative to voltage VB. Furthermore, this "120° phase difference" allows for an error of ±1°.

[0024] A pair of external output terminals are 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 driven by DC power.

[0025] The input-side low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3. Additionally, the input-side low-pass filter 20 includes a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0026] The first terminal of the first inductor L1 is connected to the first external input terminal 11A. The first terminal of the first capacitor C1 is connected to the second terminal of the first inductor L1.

[0027] Terminal 1 of the second inductor L2 is connected to the second external input terminal 11B. Terminal 1 of the second capacitor C2 is connected to terminal 2 of the second inductor L2. Terminal 2 of the second capacitor C2 is connected to terminal 2 of the first capacitor C1.

[0028] Terminal 1 of the third inductor L3 is connected to the third external input terminal 11C. Terminal 1 of the third capacitor C3 is connected to terminal 2 of the third inductor L3. Terminal 2 of the third capacitor C3 is connected to terminal 2 of the first capacitor C1.

[0029] The first power conversion circuit 30 has multiple input terminals and a pair of output terminals.

[0030] The first power conversion circuit 30 has multiple input terminals: 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 terminal of the first inductor L1. The second input terminal 31B is connected to the second terminal of the second inductor L2. The third input terminal 31C is connected to the second terminal of the third inductor L3. Therefore, three-phase AC power is input to each input terminal of the first power conversion circuit 30 via each external input terminal and the input-side low-pass filter 20. Furthermore, a pair of output terminals are a first output terminal 32A and a second output terminal 32B. From these output terminals, single-phase AC power, converted by the components within the first power conversion circuit 30, is output.

[0031] like Figure 2 As shown, the first power conversion circuit 30 includes multiple bidirectional switches (TSWs). Each bidirectional switch TSW has two switching elements. Each switching element is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). That is, each switching element has a body diode. Moreover, the bidirectional switch TSW is composed of two switching elements connected in series with the anode terminals of the body diode connected to each other. In other words, the switching elements constituting each bidirectional switch TSW are connected to each other such that the body diode is reverse-biased. In other words, each bidirectional switch TSW has two switching elements with their source terminals connected to each other.

[0032] The multiple bidirectional switches TSW are the first high-side bidirectional switch HS1, the first low-side bidirectional switch LS1, the second high-side bidirectional switch HS2, the second low-side bidirectional switch LS2, the third high-side bidirectional switch HS3, and the third low-side bidirectional switch LS3.

[0033] The first high-side bidirectional switch HS1 connects the first input terminal 31A and the first output terminal 32A. Specifically, the first high-side bidirectional switch HS1 has an eleventh switching element S11 and a twenty-first switching element S21. The drain terminal of the eleventh switching element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switching element S11 is connected to the source terminal of the twenty-first switching element S21. The drain terminal of the twenty-first switching element S21 is connected to the first output terminal 32A.

[0034] The first low-side bidirectional switch LS1 connects the first input terminal 31A and the second output terminal 32B. Specifically, the first low-side bidirectional switch LS1 has a 24th switching element S24 and a 14th switching element S14. The drain terminal of the 24th switching element S24 is connected to the first input terminal 31A. The source terminal of the 24th switching element S24 is connected to the source terminal of the 14th switching element S14. The drain terminal of the 14th switching element S14 is connected to the second output terminal 32B.

[0035] The second high-side bidirectional switch HS2 connects the second input terminal 31B and the first output terminal 32A. Specifically, the second high-side bidirectional switch HS2 has a 13th switching element S13 and a 23rd switching element S23. The drain terminal of the 13th switching element S13 is connected to the second input terminal 31B. The source terminal of the 13th switching element S13 is connected to the source terminal of the 23rd switching element S23. The drain terminal of the 23rd switching element S23 is connected to the first output terminal 32A.

[0036] The second low-side bidirectional switch LS2 connects the second input terminal 31B and the second output terminal 32B. Specifically, the second low-side bidirectional switch LS2 has a 26th switching element S26 and a 16th switching element S16. The drain terminal of the 26th switching element S26 is connected to the second input terminal 31B. The source terminal of the 26th switching element S26 is connected to the source terminal of the 16th switching element S16. The drain terminal of the 16th switching element S16 is connected to the second output terminal 32B.

[0037] The third high-side bidirectional switch HS3 connects the third input terminal 31C and the first output terminal 32A. Specifically, the third high-side bidirectional switch HS3 has a 15th switching element S15 and a 25th switching element S25. The drain terminal of the 15th switching element S15 is connected to the third input terminal 31C. The source terminal of the 15th switching element S15 is connected to the source terminal of the 25th switching element S25. The drain terminal of the 25th switching element S25 is connected to the first output terminal 32A.

[0038] The third low-side bidirectional switch LS3 connects the third input terminal 31C and the second output terminal 32B. Specifically, the third low-side bidirectional switch LS3 has a 22nd switching element S22 and a 12th switching element S12. The drain terminal of the 22nd switching element S22 is connected to the third input terminal 31C. The source terminal of the 22nd switching element S22 is connected to the source terminal of the 12th switching element S12. The drain terminal of the 12th switching element S12 is connected to the second output terminal 32B.

[0039] like Figure 1As shown, the transformer circuit 40 includes a fourth inductor L4 and a transformer 41. Furthermore, the transformer 41 includes a primary winding 41A and a secondary winding 41B. The first terminal of the fourth inductor L4 is connected to the first output terminal 32A of the first power conversion circuit 30. The first terminal of the primary winding 41A is connected to the second terminal of the fourth inductor L4. The second terminal of the primary winding 41A is connected to the second output terminal 32B of the 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.

[0040] The rectifier circuit 50 includes four diodes, a fifth inductor L5, and a fourth capacitor C4. The four diodes are diode 51, diode 52, diode 53, and diode 54.

[0041] Four diodes form a full-bridge circuit. Specifically, the anode terminal of diode 51 is connected to the first terminal of the secondary winding 41B of transformer 41. The cathode terminal of diode 51 is connected to the cathode terminal of diode 53. The anode terminal of diode 53 is connected to the second terminal of the secondary winding 41B and the cathode terminal of diode 54. The anode terminal of diode 54 is connected to the anode terminal of diode 52. The cathode terminal of diode 52 is connected to the first terminal of the secondary winding 41B and the anode terminal of diode 51.

[0042] Terminal 1 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. Terminal 2 of the fifth inductor L5 is connected to terminal 1 of the fourth capacitor C4 and the first external output terminal 12A. Terminal 2 of the fourth capacitor C4 is connected to the anode terminal of the second diode 52 and the anode terminal of the fourth diode 54 and the second external output terminal 12B.

[0043] Therefore, the first diode 51 allows current to flow from the first terminal 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 terminal of the secondary winding 41B. Furthermore, the third diode 53 allows current to flow from the second terminal 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 terminal of the secondary winding 41B.

[0044] like Figure 1 As shown, the power conversion device 10 includes a three-phase rectifier circuit 60, a boost circuit 70, and a second power conversion circuit 80.

[0045] like Figure 1As shown, the three-phase rectifier circuit 60 includes first connection terminals CT1 to fifth connection terminals CT5. First connection terminal CT1 is connected to the first external input terminal 11A. Second connection terminal CT2 is connected to the second external input terminal 11B. Third connection terminal CT3 is connected to the third external input terminal 11C. Therefore, three-phase AC power is input from the three-phase AC power supply 100 through first connection terminals CT1 to third connection terminals CT3 of the three-phase rectifier circuit 60. The three-phase rectifier circuit 60 converts this three-phase AC power into DC power through a plurality of rectifier diodes (not shown) and inductors. The converted DC power is output from fourth connection terminal CT4 and fifth connection terminal CT5. Furthermore, fourth connection terminal CT4 is a high-potential terminal, and fifth connection terminal CT5 is a low-potential terminal.

[0046] The boost circuit 70 includes terminals 6 through 9 (CT9). Terminal 6 (CT6) is connected to terminal 4 (CT4) of the three-phase rectifier circuit 60. Terminal 7 (CT7) is connected to terminal 5 (CT5) of the three-phase rectifier circuit 60. Therefore, a DC voltage is input to terminals 6 (CT6) and 7 (CT7). The boost circuit 70 boosts this DC voltage and outputs it via switching elements (not shown), inductors, and capacitors. That is, the boost circuit 70 outputs DC power from terminals 8 (CT8) and 9 (CT9) with a voltage value higher than the DC power input to terminals 6 (CT6) and 7 (CT7). For example, if the effective value of the three-phase AC power is 200 Vrms, in this embodiment, the maximum value of each voltage of the three-phase AC power is approximately 283 V. Therefore, the output voltage of the boost circuit 70 is greater than 283 V. Furthermore, the maximum value of the AC voltage is the value obtained by multiplying the effective value of the AC voltage by √2. In addition, the 8th connection terminal CT8 is a high-potential terminal, and the 9th connection terminal CT9 is a low-potential terminal.

[0047] The second power conversion circuit 80 has multiple input terminals and a pair of output terminals. The multiple input terminals of the second power conversion circuit 80 are the fourth input terminal 81A and the fifth input terminal 81B. The pair of output terminals of the second power conversion circuit 80 are the third output terminal 82A and the fourth output terminal 82B. The fourth input terminal 81A is connected to the eighth connection terminal CT8 of the boost circuit 70. The fifth input terminal 81B is connected to the ninth connection terminal CT9 of the boost circuit 70.

[0048] The third output terminal 82A is connected between the first output terminal 32A of the first power conversion circuit 30 and the first terminal of the fourth inductor L4. Therefore, the third output terminal 82A is connected to the first terminal 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 terminal of the primary winding 41A. The fourth output terminal 82B is connected between the second output terminal 32B of the first power conversion circuit 30 and the second terminal 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 terminal of the primary winding 41A.

[0049] like Figure 3 As shown, the second power conversion circuit 80 includes a fifth capacitor C5 and a switching circuit BC. The first terminal of the fifth capacitor C5 is connected to the fourth input terminal 81A. The second terminal of the fifth capacitor C5 is connected to the fifth input terminal 81B.

[0050] The switching circuit BC includes a first switching element SW1, a second switching element SW2, a third switching element SW3, and a fourth switching element SW4. Switching elements SW1 to SW4 are n-channel MOSFETs. The drain terminal of the first switching element SW1 is connected to the fourth input terminal 81A and the first terminal of the fifth capacitor C5. Furthermore, the drain terminal of the first switching element SW1 is connected to the drain terminal of the third switching element SW3. The source terminal of the first switching element SW1 is connected to the drain terminal of the second switching element SW2 and the third output terminal 82A. The source terminal of the third switching element SW3 is connected to the fourth output terminal 82B and the drain terminal of the fourth switching element SW4. The source terminal of the fourth switching element SW4 is connected to the fifth input terminal 81B and the source terminal of the second switching element SW2.

[0051] like Figure 1 As shown, 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 the first external input terminal 11A, the second external input terminal 11B, and the third external input terminal 11C. Specifically, the power sensor SE can detect the voltage and current values ​​input to each external input terminal. That is, the power sensor SE can detect the first voltage VA, the second voltage VB, and the third voltage VC.

[0052] The control unit 90 has a storage device (not shown) and an execution device. That is, the control unit 90 is a MCU (Microcontroller Unit). The storage device of the control unit 90 stores the program PG executed by the execution device.

[0053] The execution device may include, for example, a CPU (Central Processing Unit), an MPU (Microprocessing Unit), a FPGA (Field Programmable Gate Array), a CPLD (Complex Programmable Logic Device), or an ASIC (Application Specific Integrated Circuit). The execution device of the control unit 90 can execute the first control and the second control described later by executing the program PG.

[0054] Specifically, the program PG contains data for performing the first control and the second control. Furthermore, as part of this data, the program PG specifies multiple different switching modes for the multiple bidirectional switches TSWs in the first power conversion circuit 30. These switching modes determine the combination of turning the multiple bidirectional switches TSWs on and off. In addition, the program PG specifies the sequence for switching the switching modes of the bidirectional switches TSWs.

[0055] The power conversion device 10 includes a gate drive circuit (not shown). The gate drive circuit switches the on / off states of the two switching elements of each bidirectional switch TSW, as well as the first switching element SW1 to the fourth switching element SW4. The execution device of the control unit 90 controls each switching element by inputting a switching signal to the input terminal of the gate drive circuit and outputting a gate drive voltage to each switching element via the gate drive circuit.

[0056] like Figure 2 As shown, the aforementioned switch signals include switch signals SG11 to SG16 (11th to 16th) and switch signals SG21 to SG26 (21st to 26th). Switch signals SG11 to SG16 correspond one-to-one with switch elements S11 to S16 (11th to 16th). Switch signals SG21 to SG26 correspond one-to-one with switch elements S21 to S26 (26th).

[0057] The actuator of the control unit 90 switches between multiple switching modes and controls the on / off states of multiple bidirectional switches (TSWs). 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... Figure 1As shown, when the potential difference between the first output terminal 32A and the second output terminal 32B of the first power conversion circuit 30 is set as the primary voltage Vp, this primary voltage Vp is an AC voltage. Therefore, this primary voltage Vp, which is an AC voltage, is applied to the primary winding 41A of the transformer 41.

[0058] like Figure 3 As shown, the aforementioned switching signals include first switching signal SG1 to fourth switching signal SG4. First switching signal SG1 to fourth switching signal SG4 correspond one-to-one with first switching element SW1 to fourth switching element SW4. Therefore, the second power conversion circuit 80, through control described later, can convert the DC power discharged from the fifth capacitor C5 into AC power.

[0059] (Regarding control in case of voltage abnormality)

[0060] When the actuator of the control unit 90 starts supplying power to each external input terminal of the power conversion device 10, it executes the first control and the second control based on the above-described program PG. Furthermore, the control performed by the actuator of the control unit 90 will be simply referred to as the control performed by the control unit 90 below.

[0061] If the execution of program PG begins, the control unit 90 first sets the first switching element SW1 to the fourth switching element SW4 to the off state. Furthermore, during the execution of program PG, the control unit 90 acquires the voltage values ​​of the three-phase AC power input to each external input terminal detected by the power sensor SE. Moreover, the control unit 90 acquires the voltage values ​​of the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C in the first power conversion circuit 30 based on the voltage values ​​of each external input terminal of the power conversion device 10. The control unit 90 then determines whether the amplitude value of the input voltage input to the multiple input terminals is below a given first threshold. In this embodiment, the control unit 90 determines whether the amplitude value of the input voltage input to all input terminals—the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C—is below a given first threshold. This first threshold is, for example, a value of 1 / 20√2 relative to the amplitude value of the AC voltage under normal operating conditions of the three-phase AC power supply 100. In this embodiment, the amplitude values ​​of the first voltage VA to the third voltage VC input from the three-phase AC power supply 100 are 200√2 (= approximately 283) V. Therefore, the given value is 10 V. For example, in the event of a momentary interruption of power supply to the power conversion device 10 for tens of milliseconds, the amplitude values ​​of each input voltage may all simultaneously become 10 V or less.

[0062] Furthermore, the amplitude value here refers to the wavelength height within one cycle of the AC waveform. That is, the amplitude value is the value that varies during the operation of the power conversion device 10. For example, when the three-phase AC power supply 100 is operating normally, the amplitude values ​​of the first voltage VA to the third voltage VC are 200√2V. Moreover, in the event of a momentary stop or similar situation, the amplitude value may decrease due to the drop in these voltages. Additionally, the amplitude value is sometimes referred to as the peak value. Furthermore, the amplitude value can also be obtained by dividing the difference between the minimum and maximum values ​​within one cycle of the AC waveform by 2.

[0063] When the amplitude of the input voltage not input to all input terminals is below a given first threshold, in other words, when the amplitude of the input voltage input to one or more of the input terminals 31A to 31C is greater than the given first threshold, the control unit 90 performs the first control. In the first control, the control unit 90 controls the first switching elements SW1 to SW4 such that no voltage is applied to the fifth capacitor C5 from the first output terminal 32A and the second output terminal 32B. That is, the control unit 90 controls these multiple switching elements such that the fifth capacitor C5 and each output terminal of the first power conversion circuit 30 are not electrically connected via the first switching elements SW1 to SW4.

[0064] Specifically, in the first control, if the amplitude of one or more of the input voltages—the first voltage VA, the second voltage VB, and the third voltage VC—detected by the power sensor SE exceeds a first threshold, the control unit 90 keeps the first switching element SW1 to the fourth switching element SW4 in the off state. Furthermore, at this time, the control unit 90 switches the switching mode according to the switching mode specified in the program PG and controls the on / off state of each bidirectional switch TSW in the first power conversion circuit 30. That is, in this case, the first power conversion circuit 30 converts the three-phase AC voltage, including the first voltage VA to the third voltage VC, into single-phase AC power. Moreover, the converted AC voltage is 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.

[0065] Furthermore, when the amplitude of one or more input voltages from the first voltage VA to the third voltage VC is greater than the first threshold, the three-phase AC power input from the three-phase AC power supply 100 to the power conversion device 10 is converted into DC power of a given 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. Additionally, the power charged to the fifth capacitor C5 via the boost circuit 70 is greater than the maximum voltage of the three-phase AC power. That is, when the effective voltage of the three-phase AC power is 200Vrms, the maximum voltage between the terminals of the fifth capacitor C5 is greater than 283V.

[0066] When the amplitude values ​​of all input voltages from the first voltage VA to the third voltage VC detected by the power sensor SE simultaneously fall below the first threshold, the control unit 90 performs the second control. In the second control, the control unit 90 switches all of the multiple bidirectional switches TSW to the off state at a timing point when the primary voltage Vp falls below the given second threshold. Furthermore, the control unit 90 controls the first switching element SW1 to the fourth switching element SW4 according to a given pattern, causing the energy stored in the fifth capacitor C5 to be output to the primary winding 41A. In this embodiment, all bidirectional switches TSW are switched to the off state at the aforementioned timing. Furthermore, the aforementioned second threshold is 10V. Also, the term "simultaneously" allows for an error of several milliseconds.

[0067] Specifically, as described above, the output voltage of the first power conversion circuit 30 is an alternating current (AC) voltage. That is, the primary voltage Vp periodically repeats a positive state, a state of approximately zero volts, and a negative state. When the primary voltage Vp reaches the state of approximately zero volts, the control unit 90 switches all bidirectional switches TSW to the off state. Furthermore, the control unit 90 controls each switching element to convert the DC power discharged from the fifth capacitor C5 into AC power, and outputs this AC power from the third output terminal 82A and the fourth output terminal 82B. In other words, the control unit 90 controls each switching element to apply an AC voltage from each output terminal of the second power conversion circuit 80 to the primary winding 41A of the transformer 41.

[0068] More specifically, when the primary voltage Vp is negative, and the amplitude values ​​of the input voltages input to all the aforementioned input terminals simultaneously fall below a first threshold, the control unit 90 switches all bidirectional switches TSW to the off state at a timing point when the absolute value of the primary voltage Vp falls below a given second threshold. Furthermore, the control unit 90 controls the first switching element SW1 to the fourth switching element SW4 so that when the energy stored in the fifth capacitor C5 begins to be output, the primary voltage Vp changes towards the positive side.

[0069] Furthermore, when the primary voltage Vp is positive, and the amplitude values ​​of the input voltages input to all the aforementioned input terminals simultaneously fall below the first threshold, the control unit 90 switches all bidirectional switches TSW to the off state at a timing point when the absolute value of the primary voltage Vp falls below a given second threshold. Moreover, the control unit 90 controls the first switching element SW1 to the fourth switching element SW4 so that when the energy stored in the fifth capacitor C5 begins to be output, the primary voltage Vp changes towards the negative side.

[0070] In this case, when the amplitudes of all input voltages from the first voltage VA to the third voltage VC detected by the power sensor SE simultaneously fall below the first threshold, the control unit 90 turns all bidirectional switches TSWs off, and each switching element of the switching circuit BC is controlled according to a given switching mode. 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 terminals 31A to 31C is greater than the given first threshold. Specifically, the control unit 90 determines whether the amplitude value of one or more of the input voltages from the first voltage VA to the third voltage VC detected by the power sensor SE is greater than the first threshold.

[0071] Suppose that, after the amplitude values ​​of all input voltages from the first voltage VA to the third voltage VC detected by the power sensor SE simultaneously fall below the first threshold, the amplitude value of one or more of the input voltages from the first voltage VA to the third voltage VC becomes greater than the first threshold. In this case, the control unit 90 executes the first control again. That is, the control unit 90 controls the first switching elements SW1 to the fourth switching elements 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 the first switching elements SW1 to the fourth switching elements SW4 to the off state. Afterward, the control unit 90 switches the switching mode specified by the program PG again and controls the multiple bidirectional switches TSW of the first power conversion circuit 30. In other words, the control unit 90 switches any bidirectional switch TSW to the on state in accordance with the given switching mode. Therefore, for example, if the power supply from the three-phase AC power source 100 is restored after a momentary stop, the control unit 90 switches from the power conversion performed by the second power conversion circuit 80 to the power conversion performed by the first power conversion circuit 30.

[0072] (Regarding the function of this implementation method)

[0073] The power conversion device 10 of the above embodiment is configured as a so-called single-stage device. That is, the first power conversion circuit 30 converts three-phase AC power into AC power through six bidirectional switches (TSWs). Then, the transformer circuit 40 and the rectifier circuit 50 convert the AC power into DC power. Compared with a so-called two-stage power conversion device, the power conversion efficiency of the single-stage power conversion device 10 is higher. In addition, since there are no capacitors between stages as in the two-stage structure, the power density of the single-stage power conversion device 10 of the above embodiment is relatively high.

[0074] On the other hand, the power conversion circuit in the single-stage structure, 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, relying solely on the first power conversion circuit 30, it may be impossible to maintain the output voltage within a given range in the event of a momentary interruption. According to the above embodiment, the power conversion device 10, in addition to the first power conversion circuit 30, also includes a second power conversion circuit 80 with a fifth capacitor C5. Therefore, even with the single-stage power conversion device 10, the possibility of maintaining power supply to the load 110 in the event of a momentary interruption is high.

[0075] Furthermore, when the amplitude of one or more of the input voltages detected by the power sensor SE—the first voltage VA, the second voltage VB, and the third voltage VC—is greater than a first threshold, the control unit 90 performs the first control. In this first control, the control unit 90 keeps the first switching element SW1 to the fourth switching 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 addition, in this case, the control unit 90 controls the on / off state of each bidirectional switch TSW of the first power conversion circuit 30 in order to enable the first power conversion circuit 30 to function.

[0076] When the amplitude values ​​of multiple input voltages, from the first voltage VA to the third voltage VC detected by the power sensor SE, simultaneously fall below a first threshold, the control unit 90 performs second control. In this second control, the control unit 90 switches multiple bidirectional switches TSW to the off state. Then, the control unit 90 controls the first switching element SW1 to the fourth switching element SW4 according to a given pattern. As a result, the second power conversion circuit 80 can use the energy charged in the fifth capacitor C5 as a power source to apply an AC voltage to the primary winding 41A. In other words, the second power conversion circuit 80 functions as a backup power source that can supply power to the load 110 even in the event of a momentary interruption.

[0077] Furthermore, if the amplitude 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 after the aforementioned control is performed, the control unit 90 executes the first control again. At this time, the control unit 90 switches each switching element of the switching circuit BC to the off state and then restarts the 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 switching 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, according to this control, the possibility of the output voltage of the first power conversion circuit 30 being applied to the fifth capacitor C5 is low. That is, unwanted large currents flowing into the fifth capacitor C5 can be prevented.

[0078] (Regarding the effects of the first embodiment)

[0079] (1-1) In the first embodiment described above, a pair of output terminals of the second power conversion circuit 80 are connected to the primary winding 41A of the transformer 41. Furthermore, by controlling the switching on and off of the first switching element SW1 to the fourth switching element SW4 by the control unit 90, the second power conversion circuit 80 can output the energy stored in the fifth capacitor C5. Therefore, even in the event of a momentary stop, the possibility of the power conversion device 10 outputting the designed output voltage is increased.

[0080] (1-2) In the first embodiment described above, when the amplitude of the input voltage input to the multiple input terminals falls below a first threshold, the control unit 90 switches the multiple bidirectional switches TSW to the off state. Furthermore, the control unit 90 controls the multiple switching elements of the switching circuit BC to output the energy stored in the fifth capacitor C5 to the primary winding 41A. Thus, even if a momentary interruption occurs, the fifth capacitor C5 can continuously supply power to the load 110 as a power source. In addition, by switching the multiple bidirectional switches TSW to the off state, it is possible to prevent undesirable currents such as surge currents from flowing into the fifth capacitor C5 when power supply from the three-phase AC power supply 100 is restored.

[0081] (1-3) Suppose that if the control of the first power conversion circuit 30 is switched to the control of the second power conversion circuit 80 when the primary voltage Vp is not approximately zero, a difference may easily occur in the time when the primary voltage Vp becomes positive and the time when the primary voltage Vp becomes negative. Moreover, as a result, a bias magnetization phenomenon occurs in the primary winding 41A, which may cause the transformer 41 to become magnetically saturated. If magnetic saturation occurs, the power conversion efficiency of the transformer 41 may decrease due to the surge in primary current, or an excessive electrical load may be placed on the components within the first power conversion circuit 30.

[0082] According to the structure of the first embodiment described above, when the primary voltage Vp is approximately zero, the control unit 90 switches the plurality of bidirectional switches TSW to the off state and controls each switching 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 structure, even when the bidirectional switches TSW and each switching element are controlled as described above, it is possible to suppress the time for the primary voltage Vp to become positive or the time for the primary voltage Vp to become negative from becoming too long. As a result, it is less likely to produce a magnetization phenomenon, and therefore the aforementioned adverse effects accompanying the magnetization phenomenon can also be prevented.

[0083] (1-4) In the first embodiment described above, if a momentary stop occurs when the primary voltage Vp is negative, the control unit 90 controls the bidirectional switches TSW to make the primary voltage Vp approximately zero, and then switches the multiple bidirectional switches TSW to the off state. Next, it controls each switching element of the switching circuit BC to make the second power conversion circuit 80 output a positive voltage. Furthermore, if a momentary stop occurs when the primary voltage Vp is positive, the control unit 90 controls the bidirectional switches TSW to make the primary voltage Vp approximately zero, and then switches the multiple bidirectional switches TSW to the off state. Next, it controls each switching element of the switching circuit BC to make the second power conversion circuit 80 output a negative voltage. This makes it less prone to magnetization, and therefore the power conversion efficiency of the transformer 41 is less likely to decrease.

[0084] (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 disconnects 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 undesirable currents, such as surge currents, from flowing from the first power conversion circuit 30 to the fifth capacitor C5 of the second power conversion circuit 80.

[0085] (1-6) In the first embodiment described above, even when the power conversion performed by the first power conversion circuit 30 is stopped for overvoltage protection and overcurrent protection of the output voltage, the current flowing to the transformer 41 flows to the second power conversion circuit 80 by controlling the first switching element SW1 to the fourth switching element SW4 through the control unit 90. In other words, the second power conversion circuit 80 functions as a protection circuit for the first power conversion circuit 30.

[0086] (1-7) As described above, the second power conversion circuit 80 serves as both a protection circuit and a backup power supply circuit. Therefore, the power conversion device 10 is not easily made large.

[0087] (1-8) In so-called data centers, three-phase insulated AC-DC converters are sometimes used in the power supply to equipment such as server computers. Furthermore, such three-phase insulated AC-DC converters sometimes include a backup power supply device to ensure continuous power supply to servers even in the event of a momentary power outage. Additionally, such three-phase insulated AC-DC converters sometimes include protection circuits to suppress overvoltage, overcurrent, and other electrical loads on switching elements. However, if both the backup power supply and protection circuits are integrated into the three-phase insulated AC-DC converter, the device may become larger. According to the power conversion device 10 of the first embodiment described above, since the second power conversion circuit 80 functions as both a protection circuit and a backup power supply circuit, the power conversion device 10 is not easily made large. Therefore, the power conversion device 10 of the above embodiment is suitable as a three-phase insulated AC-DC converter for supplying power to server computers, etc., which serve as loads 110.

[0088] <Second Embodiment of Power Conversion Device and Program for Power Conversion Device>

[0089] The following describes a second embodiment of the power conversion device and the program used in the power conversion device. Furthermore, the circuit structure of the power conversion device in the second embodiment is the same as that in the first embodiment. The main difference between the second embodiment and the first embodiment is that switching control is performed between the first control and the second control.

[0090] (Regarding the definition of a section)

[0091] In the second embodiment, based on the magnitude relationship of the first voltage VA, the second voltage VB, and the third voltage VC, one cycle of the AC voltage input to each input terminal of the first power conversion circuit 30 is divided into multiple segments. In the second embodiment, these segments are defined as follows.

[0092] At each input terminal of the first power conversion circuit 30, three-phase AC power is input from the three-phase AC power supply 100 via the input-side low-pass filter 20. For example... Figure 4 As shown, the voltages of the three phases of this three-phase AC power are AC voltages VA, VB, and VC, which are AC voltages with different phases. Each voltage is input one-to-one to the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C. Specifically, the first voltage VA is input to the first input terminal 31A. The second voltage VB is input to the second input terminal 31B. The third voltage VC is input to the third input terminal 31C. The second voltage VB has a 120° phase difference with respect to the first voltage VA. The third voltage VC has a 120° phase difference with respect to the second voltage VB.

[0093] Here, the timing for the first voltage VA to reach its maximum phase is set to 0°. Furthermore, the timing for the first voltage VA to reach its minimum phase is set to -180°. Therefore, one cycle of the first voltage VA, the second voltage VB, and the third voltage VC is represented by a phase range of -180° or more but less than 180°. Alternatively, the timing of the voltage phase can also be expressed using a phase range of 180° or more but less than 360°. When the voltage phase is expressed using a phase range of 180° or more, X° is synonymous with (-180° + (X - 180°)). Here, segments 1 to 6 are defined as periods that divide this one cycle into 6 equal parts. Specifically, when the phase of the first voltage VA is set to "θ°", segments 1 to 6 are defined as periods of 60° intervals as follows.

[0094] Section 1: -30°≤θ°<30°

[0095] Section 2: 30°≤θ°<90°

[0096] Section 3: 90°≤θ°<150°

[0097] Section 4: 150°≤θ°<180° and -180°≤θ°<-150°

[0098] Section 5: -150°≤θ°<-90°

[0099] Section 6: -90°≤θ°<-30°

[0100] However, the boundaries of each segment can belong to either segment. For example, in the following example, when θ°=30°, it can be considered as being contained in either segment 1 or segment 2.

[0101] Thus, segment 1 is the period when the first voltage VA is positive, and the absolute value of the first voltage VA is greater than or equal to the absolute value of the second voltage VB, and the absolute value of the first voltage VA is greater than or equal to the absolute value of the third voltage VC. Segment 2 is the period when the third voltage VC is negative, and the absolute value of the third voltage VC is greater than or equal to the absolute value of the first voltage VA, and the absolute value of the third voltage VC is greater than or equal to the absolute value of the second voltage VB. Segment 3 is the period when the second voltage VB is positive, and the absolute value of the second voltage VB is greater than or equal to the absolute value of the first voltage VA, and the absolute value of the second voltage VB is greater than or equal to the absolute value of the third voltage VC. Segment 4 is the period when the first voltage VA is negative, and the absolute value of the first voltage VA is greater than or equal to the absolute value of the second voltage VB, and the absolute value of the first voltage VA is greater than or equal to the absolute value of the third voltage VC. Segment 5 is the period when the third voltage VC is positive, and the absolute value of the third voltage VC is greater than or equal to the absolute value of the first voltage VA, and the absolute value of the third voltage VC is greater than or equal to the absolute value of the second voltage VB. Section 6 is the period in which the second voltage VB is negative, and the absolute value of the second voltage VB is greater than or equal to the absolute value of the first voltage VA, and the absolute value of the second voltage VB is greater than or equal to the absolute value of the third voltage VC.

[0102] Thus, in segments 1 and 4, the absolute value of the first voltage VA becomes the largest. Furthermore, in segments 2 and 5, the absolute value of the third voltage VC becomes the largest. And, in segments 3 and 6, the absolute value of the second voltage VB becomes the largest.

[0103] (Regarding control in case of voltage abnormality)

[0104] In addition to the data used to execute the first and second controls in the first embodiment, the storage device of the control unit 90 also stores a program PG containing data for executing switching control. When power supply is initiated to each external input terminal of the power conversion device 10, the execution device of the control unit 90 executes the first and second controls based on the aforementioned program PG. Furthermore, in the second embodiment, the control unit 90 executes switching control between the first and second controls based on the program PG. Also, in the following description, even when a switching element that was originally in the ON state is kept in the ON state, it is sometimes described as switching to the ON state. This also applies to the OFF state of the switching element.

[0105] When the amplitude of the input voltage not input to all input terminals is below a given first threshold value, in other words, when the amplitude of the input voltage input to one or more of the input terminals 31A to 31C is greater than the given first threshold value, the control unit 90 performs the first control. The specific control method of the control unit 90 under the first control is the same as in the first embodiment. That is, the control unit 90 controls each bidirectional switch TSW of the first power conversion circuit 30 to output AC power from the first output terminal 32A and the second output terminal 32B.

[0106] If, during the execution of the first control, the amplitude values ​​of all input voltages from the first voltage VA to the third voltage VC detected by the power sensor SE simultaneously fall below the first threshold, the control unit 90 executes a switching control before the second control.

[0107] The transition control consists of three processes: the first process, the second process, and the third process.

[0108] If the control unit 90 performs the first process, it first determines which segment contains the phase of all input voltages from the first voltage VA to the third voltage VC that simultaneously falls below the first threshold, i.e., the phase at the start of the switching control. Then, the control unit 90 controls the switching on and off of multiple bidirectional switches TSW, forming a closed circuit that extends from the first terminal of the primary winding 41A through any one of the multiple bidirectional switches TSW in the first power conversion circuit 30 to the second terminal of the primary winding 41A. Note that the description of "from the first terminal to the second terminal" describes the electrical conduction path, not the direction of current flow. At this time, the control unit 90 changes the combination of switching on and off the bidirectional switches TSW based on which segment the phase at the start of the switching control is contained within.

[0109] Specifically, assuming the phase at the start of the switching control is within the range of segment 1 or segment 4. In this case, during the first process, the control unit 90 switches all of the switching elements of the first power conversion circuit 30—the 11th switching element S11, the 21st switching element S21, the 24th switching element S24, and the 14th switching element S14—to the ON state. This forms a closed circuit that reaches the 2nd terminal of the primary winding 41A via the 1st terminal of the primary winding 41A, the 4th inductor L4, the 21st switching element S21, the 11th switching element S11, the 24th switching element S24, and the 14th switching element S14. Furthermore, at this time, the control unit 90 maintains the ON / OFF state of the 13th switching element S13, the 23rd switching element S23, the 26th switching element S26, and the 16th switching element S16 at the start of the switching control. Similarly, the control unit 90 maintains the on / off state of the 15th switching element S15, the 25th switching element S25, the 22nd switching element S22, and the 12th switching element S12 as it was at the start of the switching control. That is, the on / off state of each switching element is maintained as is for the bidirectional switch TSW connected to the second input terminal 31B and the bidirectional switch TSW connected to the third input terminal 31C.

[0110] Furthermore, assuming the phase at the start of the switching control is within the range of segment 2 or segment 5, the control unit 90, in the first process, switches all of the switching elements of the first power conversion circuit 30—the 15th switching element S15, the 25th switching element S25, the 22nd switching element S22, and the 12th switching element S12—to the ON state. This forms a closed circuit reaching the second terminal of the primary winding 41A via the first terminal of the primary winding 41A, the fourth inductor L4, the 25th switching element S25, the 15th switching element S15, the 22nd switching element S22, and the 12th switching element S12. Additionally, at this time, the control unit 90 maintains the ON / OFF state of the 11th switching element S11, the 21st switching element S21, the 24th switching element S24, and the 14th switching element S14 at the start of the switching control. Similarly, the control unit 90 maintains the on / off state of the 13th switching element S13, the 23rd switching element S23, the 26th switching element S26, and the 16th switching element S16 as it was at the start of the switching control. That is, the on / off state of each switching element is maintained as is for the bidirectional switch TSW connected to the first input terminal 31A and the bidirectional switch TSW connected to the second input terminal 31B.

[0111] Furthermore, assuming the phase at the start of the switching control is within the range of segment 3 or segment 6, in this case, during the first process, the control unit 90 switches all of the switching elements of the first power conversion circuit 30—the 13th switching element S13, the 23rd switching element S23, the 26th switching element S26, and the 16th switching element S16—to the ON state. This forms a closed circuit that reaches the 2nd terminal of the primary winding 41A via the 1st terminal of the primary winding 41A, the 4th inductor L4, the 23rd switching element S23, the 13th switching element S13, the 26th switching element S26, and the 16th switching element S16. Additionally, at this time, the control unit 90 maintains the ON / OFF state of the 11th switching element S11, the 21st switching element S21, the 24th switching element S24, and the 14th switching element S14 as it was during the start of the switching control. Similarly, the control unit 90 maintains the on / off state of the 15th switching element S15, the 25th switching element S25, the 22nd switching element S22, and the 12th switching element S12 as it was at the start of the switching control. That is, the on / off state of each switching element is maintained as is for the bidirectional switch TSW connected to the 1st input terminal 31A and the bidirectional switch TSW connected to the 3rd input terminal 31C.

[0112] On the other hand, regardless of the phase range at the start of the switching control, the control unit 90 sets all the first switching elements SW1 to SW4 of the second power conversion circuit 80 to the off state during the first process. Furthermore, in the stage prior to executing the first process of switching control, the control unit 90 is performing the first control. Moreover, as described above, the control unit 90 maintains the first switching elements SW1 to SW4 in the off state during the first control. Therefore, the control unit 90 maintains the on / off state of the first switching elements SW1 to SW4 in the off state as is during the first process.

[0113] If the switching of each switching element in the first process is completed, the control unit 90 then executes the 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 as it was after the switching in the first process. Furthermore, when executing the second process, the control unit 90 controls the on / off state of multiple switching elements, thereby forming a closed circuit from the first terminal of the primary winding 41A through any of the multiple switching elements of the second power conversion circuit 80 to the second terminal of the primary winding 41A. Specifically, the control unit 90 switches the second switching element SW2 and the fourth switching element SW4 of the second power conversion circuit 80 to the on state. Furthermore, the control unit 90 maintains the first switching element SW1 and the third switching element SW3 of the second power conversion circuit 80 in the off state as before. Thus, a closed circuit is formed that passes through the first terminal of the primary winding 41A, the fourth inductor L4, the second switching element SW2, and the fourth switching element SW4 to the second terminal of the primary winding 41A.

[0114] If the switching of each switching element in the second process is completed, the control unit 90 then executes the third process. If the control unit 90 executes the third process, it switches all the multiple bidirectional switches (TSWs) of the first power conversion circuit 30 to the off state. More specifically, it switches all the switching elements included in the first power conversion circuit 30 to the off state. Furthermore, if the control unit 90 executes the third process, it maintains the on / off state of each switching element of the second power conversion circuit 80 as it was after the switching in the second process.

[0115] As described above, when a transition control is performed from a state where the first control is being performed, the control unit 90 performs the above three processes in the transition control in the order of the first process, the second process, and the third process.

[0116] If the third process ends, i.e., the conversion control ends, then the control unit 90 executes the second control. The specific control method of the control unit 90 under the second control is the same as in the first embodiment. That is, the control unit 90 controls each switching element of the second power conversion circuit 80, causing AC power to be output from the third output terminal 82A and the fourth output terminal 82B. Furthermore, in the second control, all bidirectional switches TSW of the first power conversion circuit 30 are kept in the off state. Therefore, in the second control, each bidirectional switch TSW of the first power conversion circuit 30 is also maintained in the state after being switched in the third process of the conversion control.

[0117] If, during the execution of the second control, the amplitude of one or more of the input voltages from the first voltage VA to the third voltage VC becomes greater than the first threshold, the control unit 90 executes the transition control again. When transition control is executed from a state where the second control is being executed, the control unit 90 executes the three processes described above in the order of the third process, the second process, and the first process during the transition control.

[0118] When continuing the transition control from the second control, the control unit 90 determines which segment the phase is included when ending the transition control and switching to the first control. Furthermore, the control unit 90 can determine the timing for ending the transition control based on the required time for each of the third, second, and first processing stages of the transition control. Moreover, the control unit 90 changes the on / off combination of the bidirectional switch TSW in the second and first processing stages based on which segment the phase of ending the transition control is included in.

[0119] Specifically, assuming the phase at the end of the switching control is within the range of segment 1 or segment 4, the control unit 90 is configured with the same combination of switching on / off states as when the phase at the start of the switching control is within the range of segment 1 or segment 4, following the first process of continuing the switching control from the first control. Furthermore, assuming the phase at the end of the switching control is within the range of segment 2 or segment 5, the control unit 90 is configured with the same combination of switching on / off states as when the phase at the start of the switching control is within the range of segment 2 or segment 5, following the first process of continuing the switching control from the first control. And, assuming the phase at the end of the switching control is within the range of segment 3 or segment 6, the control unit 90 is configured with the same combination of switching on / off states as when the phase at the start of the switching control is within the range of segment 3 or segment 6, following the first process of continuing the switching control from the first control.

[0120] (Regarding the effects of the second embodiment)

[0121] In addition to the effects of (1-1), (1-2), (1-5) to (1-8) of the power conversion device 10 of the first embodiment, the power conversion device 10 of the second embodiment also has the following effects.

[0122] (2-1) When the control unit 90 is performing the first control, the power supply from the three-phase AC power supply 100 is sometimes interrupted momentarily. In this case, sometimes the switching on and off of each bidirectional switch TSW is switched even though the absolute value of the primary voltage Vp is not lower than the second threshold, which is the cause of magnetic saturation in the transformer 41.

[0123] In the second embodiment described above, the control unit 90 performs switching control between the first control and the second control. Furthermore, in this second processing of the switching control, a closed circuit is formed from the first terminal of the primary winding 41A via any one of the multiple bidirectional switches TSW of the first power conversion circuit 30 to the second terminal of the primary winding 41A. Simultaneously, a closed circuit is formed from the first terminal of the primary winding 41A via any one of the multiple switching elements of the second power conversion circuit 80 to the second terminal of the primary winding 41A. In this way, by forming closed circuits on both the first power conversion circuit 30 side and the second power conversion circuit 80 side, the primary voltage Vp rapidly approaches zero. That is, in the second embodiment, a period during which the primary voltage Vp becomes zero is forcibly set when switching between the first and second controls. Therefore, regardless of the on / off state of the switching elements when switching between the first and second controls, the switching between the first and second controls can be performed rapidly, and the risk of magnetic saturation in the transformer 41 can also be reduced.

[0124] (2-2) In the second embodiment, when switching from the first control to the second control, the control unit 90 performs the first process before the second process in the switching control. Furthermore, in this first process, a closed circuit is formed from the first terminal of the primary winding 41A to the second terminal of the primary winding 41A via any of the multiple bidirectional switches TSW of the first power conversion circuit 30. On the other hand, each switching 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. Therefore, in the switching control when switching from the first control to the second control, firstly, the primary voltage Vp approaches zero due to the closed circuit on the first power conversion circuit 30 side. Moreover, in the subsequent second process, a closed circuit is formed on the second power conversion circuit 80 side. Therefore, at the time the closed circuit on the second power conversion circuit 80 side is formed, the primary voltage Vp is highly likely to be zero or close to zero. As a result, it is possible to prevent unwanted current from flowing from the primary winding 41A of the transformer 41 to the second power conversion circuit 80 at the instant the closed circuit is formed on the second power conversion circuit 80 side.

[0125] Furthermore, when switching from the first control to the second control, in the switching control, the control unit 90 executes a third process after the second process. In this third process, a closed circuit is formed that extends from the first terminal of the primary winding 41A to the second terminal of the primary winding 41A via any of the multiple switching elements of the second power conversion circuit 80. On the other hand, each bidirectional switch TSW of the first power conversion circuit 30 is switched to the off state. In this way, by setting each bidirectional switch TSW of the first power conversion circuit 30 to the off state before the second control, current flowing from the second power conversion circuit 80 to the first power conversion circuit 30 can be prevented when the second control begins.

[0126] Furthermore, the case of switching from control 1 to control 2 has been explained. However, when switching from control 2 to control 1, the transition control executes the processing in the order of 3rd processing, 2nd processing, and 1st processing. In this case, it achieves the same effect as when switching from control 1 to control 2.

[0127] (2-3) In the second embodiment described above, when the phase at the start of the switching control is within the range of segment 1 or segment 4, the 11th switching element S11, the 21st switching element S21, the 24th switching element S24, and the 14th switching element S14 are switched to the on state. Here, during the execution of the first control, when the phase is within the range of segment 1 or segment 4, the absolute value of the first voltage VA is large. Therefore, there is a high probability that three or more of the above four switching elements will be in the on state. Therefore, when all four switching elements are set to the on state, the number of switching elements actually switched on and off can be minimized. In addition, the explanation is given when the phase at the start of the switching control is within the range of segment 1 or segment 4, but the same applies when the phase at the start of the switching control is within other segments. Furthermore, when continuing to execute the switching control from the second control, the same as above, the number of switching elements that are switched on and off when the switching control ends can be minimized.

[0128] <Example of Change>

[0129] The above embodiments can be modified as follows. The above embodiments and the following modifications can be combined with each other within the scope of technical inconsistency.

[0130] The structure of the power conversion device 10 is not limited to the examples of the embodiments described above. For example, the power conversion device 10 is not limited to a three-phase isolated AC-DC converter, but can also be applied to a non-isolated three-phase AC-DC converter. Furthermore, the power conversion device 10 may not include one or more of the input-side low-pass filter 20, transformer circuit 40, and rectifier circuit 50. Moreover, the power conversion device 10 may also include components and circuits other than those illustrated in the above embodiments.

[0131] • 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; it can also be a three-phase four-wire type, or a three-phase three-wire type with delta connection. Similarly, the structure of the power conversion device 10 can be appropriately modified according to the type of three-phase AC power supply 100.

[0132] • The input-side low-pass filter 20 in each embodiment may also include multiple capacitors connected between the lines of each phase of the input first voltage VA, second voltage VB and third voltage VC.

[0133] The switching elements constituting each bidirectional switch TSW are not limited to the examples of the embodiments described above. For example, the two switching elements of the bidirectional switch TSW may also be P-channel MOSFETs. In this case, the bidirectional switch TSW connects the drain terminals of the two switching elements to each other.

[0134] In various embodiments, the two switching elements of the bidirectional switch TSW can also be transistors capable of allowing current to flow in both the forward and reverse directions. In this case, the two switching elements are connected in series with their source terminals connected to each other. Specifically, the switching element is a gallium nitride high electron mobility transistor (GaN-HEMT), etc.

[0135] • The transformer circuit 40 in each embodiment may also omit the fourth inductor L4. In this case, the leakage inductance of the transformer 41 can be used for resonance instead of the fourth inductor L4.

[0136] The specific circuit structure of the rectifier circuit 50 is not limited to the examples of the embodiments described above. For example, the rectifier circuit 50 may also be a half-wave rectifier circuit, etc. In addition, the rectifier circuit 50 may also be a full-bridge circuit containing four diodes.

[0137] • The power conversion device 10 in each embodiment may also omit the three-phase rectifier circuit 60. For example, a power supply device different from 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 also be charged by a power source other than the three-phase AC power supply 100.

[0138] The output voltage of the boost circuit 70 in each embodiment can also be the voltage input to the first input terminals 31A to the third input terminals 31C, approximately 283V or less. In this case, the second power conversion circuit 80 can maintain power supply to the load 110 even during a momentary interruption. Furthermore, the power conversion device 10 may not 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 less than or equal to the maximum value of the input voltage of the three-phase AC power. In this case, by performing the control described in the above embodiment by the control unit 90, unwanted current is less likely 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.

[0139] • The power sensor SE in each embodiment can also 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, instead of detecting the voltage and current values ​​at the first external input terminal 11A to the third external input terminal 11C.

[0140] The second power conversion circuit 80 in each embodiment may also include a switching 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 also include a switching element connected between the first terminal of the fifth capacitor C5 and the drain terminal of the first switching element SW1. By including this switching element in the second power conversion circuit 80, switching between the state in which voltage is applied to the primary winding 41A from the first power conversion circuit 30 and the state in which voltage is applied to the primary winding 41A from the second power conversion circuit 80 becomes easier.

[0141] In each embodiment, when switching modes are changed and the bidirectional switches TSW of the first power conversion circuit 30 are controlled, the control unit 90 does not need to keep all switching elements of the second power conversion circuit 80 in the off state. For example, the second switching element SW2 and the fourth switching element SW4 can be kept in the off state. In this way, it is sufficient to prevent the switching elements from turning on and off in a way that prevents current from flowing from the first output terminal 32A and the second output terminal 32B to the fifth capacitor C5.

[0142] In each embodiment, when the control unit 90 determines whether the amplitude values ​​of the first voltage VA to the third voltage VC detected by the power sensor SE are below the first threshold, it only needs to determine whether the amplitude values ​​are substantially below the first threshold. For example, if the first threshold is 10V, and the first voltage VA to the third voltage VC are above -10V and below +10V, it is determined that the amplitude value of each input voltage is below the first threshold. The same applies to the second threshold.

[0143] In the first embodiment, the control unit 90 may switch multiple bidirectional switches TSW to the off state and control multiple switching elements of the switching circuit BC, except when the amplitude value of the input voltage input to the multiple input terminals is below a first threshold and the absolute value of the primary voltage Vp is below a second threshold. In this case, the second power conversion circuit 80 may also function as a backup power supply circuit.

[0144] In various embodiments, the control unit 90 may not switch all bidirectional switches TSW to the off state if the input voltage is below the first threshold. The control unit 90 can stop the power conversion performed by the first power conversion circuit 30 simply by switching multiple bidirectional switches TSW to the off state, and some of the bidirectional switches TSW may also be in the on state.

[0145] In each embodiment, when the amplitude values ​​of the multiple input voltages are below a first threshold when the primary voltage Vp is negative, the control unit 90 may not control the multiple switching elements to change the primary voltage Vp to the positive side when the energy stored in the fifth capacitor C5 begins to be output. That is, in this case, the control unit 90 may also control the multiple switching elements to change the primary voltage Vp to the negative side when the energy stored in the fifth capacitor C5 begins to be output. This is also true when the amplitude values ​​of the input voltages input to the multiple input terminals are below the first threshold when the primary voltage Vp is positive.

[0146] In various embodiments, when the control unit 90 is controlling the input voltage amplitude values ​​of multiple input terminals to be below a first threshold, if the amplitude value of the input voltage at one or more input terminals becomes greater than the first threshold, after switching the multiple bidirectional switches TSW to the ON state, it controls each switching element 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. In this case, as long as the voltage between the terminals of the fifth capacitor C5 is higher than the maximum value of the input voltage, there is no need to worry about applying voltage to the fifth capacitor C5 from the first output terminal 32A and the second output terminal 32B.

[0147] In the second embodiment, the transition control only needs to have at least a second process. For example, when switching from a state where the first control is being executed to a state where the second control is being executed, the control unit 90 may omit the first and third processes and only execute the second process in the transition control. Furthermore, in the transition control, the control unit 90 may omit the third process and only execute the first and second processes, or it may omit the first process and only execute the second and third processes. This also applies to the case of switching from a state where the second control is being executed to a state where the first control is being executed.

[0148] • In the second embodiment, the control unit 90 may also perform the transition control only in either the case of switching from the state of performing the first control to the state of performing the second control, or the case of switching from the state of performing the second control to the state of performing the first control.

[0149] In the transition control of the second embodiment, the relationship between the phase range at the start of transition control and the path through which a closed circuit is formed is not limited. For example, a closed circuit may always be formed through the same path regardless of the phase range at the start of transition control.

[0150] • In the switching control of the second embodiment, when a closed circuit is formed that extends 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, the combination of the on and off states of the switching elements can be changed.

[0151] For example, if the phase at the start of the switching control is within the range of segment 1 or segment 4, the control unit 90 can also control the 11th switching element S11 and the 14th switching element S14 to be turned on, and the 21st switching element S21 and the 24th switching element S24 to be turned off. In this case, current also flows through the body diodes of the 21st switching element S21 and the 24th switching element S24. That is, in the on / off state of these switching elements, a unidirectional closed circuit is formed that allows current to flow from the second terminal of the primary winding 41A through the aforementioned four switching elements to the first terminal of the primary winding 41A.

[0152] Furthermore, for example, if the phase at the start of the switching control is within the range of segment 1 or segment 4, the control unit 90 can also control the 11th switching element S11 and the 14th switching element S14 to be off, and the 21st switching element S21 and the 24th switching element S24 to be on. In this case, current also flows through the body diodes of the 11th switching element S11 and the 14th switching element S14. That is, in the on / off state of these switching elements, a unidirectional closed circuit is formed that allows current to flow from the first terminal of the primary winding 41A through the aforementioned four switching elements to the second terminal of the primary winding 41A.

[0153] Furthermore, although specific explanations are omitted, if the phase at the start of the control transition is within the range of other sections, the corresponding four switching elements can be controlled in the same way as in the two modified examples described above. That is, it is sufficient to control the on / off state of the switching elements as long as a unidirectional closed circuit utilizing the body diode of the switching element is formed.

[0154] • In the switching control of the second embodiment, when a closed circuit is formed that reaches the second terminal of the primary winding 41A from the first terminal of the primary winding 41A via any of the multiple switching elements of the second power conversion circuit 80, the combination of the on and off states of each switching element can be changed.

[0155] For example, the control unit 90 may switch only the second switching element SW2 to the ON state and switch the other three switching elements to the OFF state. In this case, current flows through the body diode of the fourth switching element SW4. That is, in the ON / OFF state of this switching element, a unidirectional closed circuit is formed that allows current to flow from the first terminal of the primary winding 41A through the second switching element SW2 and the fourth switching element SW4 to the second terminal of the primary winding 41A. In this way, the ON / OFF state of the switching elements may also be formed by utilizing the body diodes of each switching element of the second power conversion circuit 80 to create a unidirectional closed circuit.

[0156] Furthermore, for example, the control unit 90 may switch the second switching element SW2 and the fourth switching element SW4 to the off state, and switch the first switching element SW1 and the third switching element SW3 to the on state.

[0157] Furthermore, when forming a closed circuit, the combination of switching elements on and off in this modified example is not fixed, nor is it limited to either the combination of switching elements on and off illustrated in the second embodiment described above. That is, the combination of switching elements on and off can be changed each time a closed circuit is formed.

[0158] In the second embodiment, the control unit 90 may also perform specific controls different from the first control and the switching control. In this example, as a prerequisite, among the multiple switching modes defined by the program PG as data related to the first control, more than one specific switching mode is included. The specific switching mode is a combination of the on / off states of multiple bidirectional switches TSW that form a closed circuit from the first terminal of the primary winding 41A through any of the multiple bidirectional switches TSW of the first power conversion circuit 30 to the second terminal of the primary winding 41A.

[0159] In this example, the control unit 90, in the first control, switches the switching mode and controls the on / off state of each bidirectional switch (TSW) of the first power conversion circuit 30. At this time, the control unit 90 switches the switching mode at a timing that is 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. Furthermore, when switching to the second control, specific control is performed before executing the conversion control.

[0160] In this specific control, the control unit 90 switches the switching modes in the same sequence as in the first control and controls the on / off state of each bidirectional switch TSW in the first power conversion circuit 30. Furthermore, the control unit 90 switches the switching modes at essentially the same timing as in the first control. However, when controlling the on / off state of multiple bidirectional switches TSW according to the specific switching mode, the control unit 90, exceptionally, maintains the combination of on / off states of the bidirectional switches TSW for a predetermined period of time or longer, regardless of the magnitude of the input voltage to each input terminal. This predetermined period can be determined, for example, as sufficient time for the primary voltage Vp to reach zero when the aforementioned closed circuit is formed on the first power conversion circuit 30 side, through experimentation or simulation. Additionally, in this specific control, when the on / off state of multiple bidirectional switches TSW according to the specific switching mode is maintained for a predetermined period of time or longer, the control unit controls the on / off state of each bidirectional switch TSW in a switching mode corresponding to the magnitude of the input voltage to each input terminal.

[0161] Based on the above example, in the specific control, when multiple bidirectional switches (TSWs) are controlled to turn on and off according to a specific switching mode, the primary voltage Vp becomes zero or close to zero. Subsequently, in the specific control, even if the bidirectional switches (TSWs) are controlled to turn on and off using a different switching mode than the specific one, the primary voltage Vp will not become too large. That is, in this example, the primary voltage Vp can be reduced in advance in the specific control before the switching control is executed. Therefore, the probability of the primary voltage Vp being zero when the switching control is executed is increased.

[0162] Furthermore, the division of circuit structures and the naming of circuits in the above embodiments are for convenience and are not limited thereto. For example, in the above embodiments, the six bidirectional switches TSW are referred to as a whole as "first power conversion circuit 30", but this is not a limitation. That is, the six bidirectional switches TSW, the transformer circuit 40 and the rectifier circuit 50 in the above embodiments can also be collectively referred to as "first power conversion circuit".

[0163] <Postscript>

[0164] The technical concepts that can be grasped from the above-described embodiments and variations are recorded.

[0165] [1] A power conversion device comprising: 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, 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 switching 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 the on and off states of the plurality of bidirectional switches and the plurality of switching elements, wherein the second power conversion circuit is capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0166] [2] According to the power conversion device described in [1], the control unit performs a first control when the amplitude value of the input voltage input to one or more of the plurality of input terminals is greater than a given threshold. In the first control, the plurality of bidirectional switches are controlled so that the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal. When the amplitude value of the input voltage input to the plurality of input terminals is less than the threshold, the control unit performs a second control when the plurality of bidirectional switches are switched to the off state and the plurality of switching 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.

[0167] [3] According to the power conversion device described in [2], when the threshold is set to the first threshold and the potential difference between the first output terminal and the second output terminal is set to the primary voltage, the control unit switches the multiple bidirectional switches to the off state when the amplitude value of the input voltage input to the multiple input terminals is below the first threshold and the absolute value of the primary voltage is below a given second threshold, and controls the multiple switching elements to output the energy stored in the capacitor to the primary winding.

[0168] [4] According to the power conversion device described in [3], when the amplitude value of the input voltage input to the plurality of input terminals in the state where the primary voltage is negative becomes below the first threshold, the control unit switches the plurality of bidirectional switches to the off state at a timing when the absolute value of the primary voltage becomes below a given second threshold, and controls the plurality of switching elements such that the primary voltage changes to the positive side when outputting the energy stored in the capacitor.

[0169] [5] According to the power conversion device described in [4], when the amplitude value of the input voltage input to the plurality of input terminals in the state where the primary voltage is positive becomes below the first threshold, the control unit switches the bidirectional switch to the off state at a timing when the absolute value of the primary voltage becomes below a given second threshold, and controls the plurality of switching elements such that the primary voltage changes to the negative side when outputting the energy stored in the capacitor.

[0170] [6] According to any one of [2] to [5], in the case where, when the plurality of bidirectional switches are in the off state and the control unit is controlling the plurality of switching elements, the amplitude value of the input voltage input to one or more of the plurality of input terminals becomes greater than a given threshold,

[0171] After controlling the plurality of switching elements to prevent the first output terminal, the second output terminal, and the capacitor from being electrically connected via the plurality of switching elements, the control unit controls the switching of the plurality of bidirectional switches.

[0172] [7] According to any one of [1] to [6], the power conversion device is wherein the plurality of input terminals are connected to a three-phase AC power supply, the power conversion device further comprises a three-phase rectifier circuit that connects the three-phase AC power supply and the second power conversion circuit, and is capable of converting the input three-phase AC power into DC power and outputting it, wherein the capacitor is charged by the DC power output by the three-phase rectifier circuit.

[0173] [8] According to the power conversion device described in [7], the power conversion device further includes a boost circuit that connects the three-phase rectifier circuit and the second power conversion circuit, boosts the DC voltage output from the three-phase rectifier circuit, and the output voltage of the boost circuit is greater than the maximum value of the input voltage input to the input terminal.

[0174] [9] According to any one of [2] to [6], the power conversion device wherein, in at least one of the following situations, the control unit performs a switching control between the first control and the second control, wherein the control unit controls the on / off state of a plurality of the bidirectional switches to form a closed circuit from the first end of the primary winding to the second end of the primary winding via any one of the plurality of bidirectional switches, and controls the on / off state of a plurality of the switching elements to form a closed circuit from the first end of the primary winding to the second end of the primary winding via any one of the plurality of switching elements.

[0175]

[10] According to the power conversion device described in [9], when the control unit switches from a state of executing the first control to a state of executing the second control, in the conversion control, the first process, the second process, and the third process are executed in the order of the first process, the second process, and the third process. In the first process, the opening and closing of the plurality of bidirectional switches are controlled to form a closed circuit from the first end of the primary winding through any of the plurality of bidirectional switches to the second end of the primary winding, and the plurality of switching elements are controlled to be in the off state. In the second process, the control is... The switching on and off of the plurality of bidirectional switches forms a closed circuit 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 the switching on and off of the plurality of switching elements is controlled to form a closed circuit from the first end of the primary winding through any one of the plurality of switching elements to the second end of the primary winding. In the third process, the plurality of bidirectional switches are controlled to be in an off state, and the switching on and off of the plurality of switching elements is controlled to form a closed circuit from the first end of the primary winding through any one of the plurality of switching elements to the second end of the primary winding.

[0176]

[11] According to the power conversion device described in [9] or

[10] , when the control unit switches from a state of executing the second control to a state of executing the first control, in the conversion control, the first process, the second process, and the third process are executed in the order of the first process, the second process, and the third process. In the first process, the opening and closing of the plurality of bidirectional switches are controlled to form a closed circuit from the first end of the primary winding through any of the plurality of bidirectional switches to the second end of the primary winding, and the plurality of switching elements are controlled to be in the off state. In the second process... In the third process, the multiple bidirectional switches are controlled to be turned on and off, thereby forming a closed circuit from the first end of the primary winding through any one of the multiple bidirectional switches to the second end of the primary winding. The multiple switching elements are also controlled to be turned on and off, thereby forming a closed circuit from the first end of the primary winding through any one of the multiple switching elements to the second end of the primary winding.

[0177]

[12] According to any one of [9] to

[11] , the power conversion device wherein, in the first control, the control unit switches the switching mode and controls the switching of the multiple bidirectional switches according to multiple different switching modes that determine the combination of the on and off of the multiple bidirectional switches, the multiple switching modes including a specific switching mode, the specific switching mode being a combination of the on and off of the multiple bidirectional switches that form a closed circuit from the first end of the primary winding through any of the multiple bidirectional switches to the second end of the primary winding, the control unit performs the specific control before performing the conversion control when switching from the state of performing the first control to the state of performing the second control, the control unit switches the switching mode and controls the switching of the multiple bidirectional switches in the same order as the first control in the specific control, and regardless of the magnitude of the input voltage input to the multiple input terminals, the combination of the on and off of the multiple bidirectional switches according to the specific switching mode is maintained for a predetermined period of time or more.

[0178]

[13] A program for a power conversion device is applied to the power conversion device, the power conversion device comprising: a first power conversion circuit having multiple input terminals, multiple bidirectional switches, a first output terminal and a second output terminal, capable of converting three-phase AC power; a transformer having a primary winding and a secondary winding, a first end of the primary winding being connected to the first output terminal, and a second end of the primary winding being connected to the second output terminal; a second power conversion circuit having a capacitor, multiple switching 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 the on / off states of the multiple bidirectional switches and the multiple switching elements. When switched on and off, the second power conversion circuit can output the energy stored in the capacitor to the third and fourth output terminals. The program used by the power conversion device causes the control unit to perform the following processing: when the amplitude value of the input voltage input to one or more of the plurality of input terminals is greater than a given threshold, the plurality of bidirectional switches are controlled so that the first power conversion circuit converts the input voltage and outputs it from the first and second output terminals; when the amplitude value of the input voltage input to the plurality of input terminals is less than the threshold, the plurality of bidirectional switches are switched to the off state, and the plurality of switching elements are controlled so that the energy stored in the capacitor is output from the third and fourth output terminals to the primary winding.

[0179]

[14] A power conversion device includes: a first power conversion circuit having a plurality of input terminals, a first output terminal and a second output terminal, a plurality of bidirectional switches connecting the plurality of input terminals to the first output terminal and the second output terminal, a transformer and a rectifier circuit, the first power conversion circuit being capable of converting three-phase AC power input to the plurality of input terminals, the transformer having a primary winding and a secondary winding, a first end of the primary winding being connected to the first output terminal, and a second end of the primary winding being connected to the second output terminal. A rectifier circuit is connected to the secondary winding and is capable of converting AC voltage; a second power conversion circuit includes a capacitor, multiple switching 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 the on and off states of the multiple bidirectional switches and the multiple switching elements, wherein the second power conversion circuit is capable of outputting the energy stored in the capacitor to the third output terminal and the fourth output terminal.

[0180] Explanation of reference numerals in the attached figures

[0181] 10…Power conversion device

[0182] 11A…First External Input Terminal

[0183] 11B…Second External Input Terminal

[0184] 11C…3rd External Input Terminal

[0185] 12A…First External Output Terminal

[0186] 12B…Second External Output Terminal

[0187] 30…First power conversion circuit

[0188] 32A… Output Terminal 1

[0189] 32B…Second Output Terminal

[0190] TSW…bidirectional switch

[0191] 40…Transformer circuit

[0192] 50… rectifier circuit

[0193] 60…Three-phase rectifier circuit

[0194] 70…Boost Circuit

[0195] 80…Second Power Conversion Circuit

[0196] C5…Fifth capacitor

[0197] BC…Switching Circuit

[0198] 90…Control Department

[0199] PG... program

[0200] 100… Three-phase AC power supply.

Claims

1. A power conversion device, comprising: The first power conversion circuit has multiple input terminals, multiple bidirectional switches, a first output terminal, and a second output terminal, and is capable of converting three-phase AC power. A transformer has a primary winding and a secondary winding, wherein a first end of the primary winding is connected to a first output terminal, and a second end of the primary winding is connected to a second output terminal; The second power conversion circuit includes a capacitor, multiple switching 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. as well as The control unit is capable of switching the on / off states of the multiple bidirectional switches and the multiple switching elements. The second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal.

2. The power conversion device according to claim 1, wherein, When the amplitude of the input voltage input to one or more of the plurality of input terminals exceeds a given threshold, the control unit executes a first control, in which it controls the plurality of bidirectional switches to cause the first power conversion circuit to convert the input voltage and output it from the first output terminal and the second output terminal. When the amplitude of the input voltage input to the plurality of input terminals is below the threshold, the control unit performs a second control, in which the plurality of bidirectional switches are switched to the off state and the plurality of switching 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.

3. The power conversion device according to claim 2, wherein, When the threshold is set to the first threshold and the potential difference between the first output terminal and the second output terminal is set to the primary voltage, When the amplitude of the input voltage input to the plurality of input terminals is below the first threshold, and the absolute value of the primary voltage is below a given second threshold, the control unit switches the plurality of bidirectional switches to the off state and controls the plurality of switching elements to output the energy stored in the capacitor to the primary winding.

4. The power conversion device according to claim 3, wherein, When the amplitude of the input voltage input to the plurality of input terminals is below the first threshold when the primary voltage is negative, the control unit switches the plurality of bidirectional switches to the off state when the absolute value of the primary voltage is below a given second threshold, and controls the plurality of switching elements such that the primary voltage changes to the positive side when the energy stored in the capacitor is output.

5. The power conversion device according to claim 4, wherein, When the amplitude of the input voltage input to the plurality of input terminals is below the first threshold when the primary voltage is positive, the control unit switches the bidirectional switch to the off state at a time when the absolute value of the primary voltage is below a given second threshold, and controls the plurality of switching elements such that the primary voltage changes to the negative side when the energy stored in the capacitor is output.

6. The power conversion device according to any one of claims 2 to 5, wherein, When the multiple bidirectional switches are in the off state and the control unit is controlling the multiple switching elements, if the amplitude of the input voltage input to one or more of the multiple input terminals becomes greater than a given threshold, After controlling the plurality of switching elements to prevent the first output terminal, the second output terminal, and the capacitor from being electrically connected via the plurality of switching elements, the control unit controls the switching of the plurality of bidirectional switches.

7. The power conversion device according to any one of claims 1 to 6, wherein, The multiple input terminals are connected to a three-phase AC power supply. The power conversion device also includes a three-phase rectifier circuit, which connects the three-phase AC power supply and the second power conversion circuit, and is capable of converting the input three-phase AC power into DC power and outputting it. The capacitor is charged by the DC power output from the three-phase rectifier circuit.

8. The power conversion device according to claim 7, wherein, The power conversion device also includes a boost circuit that connects the three-phase rectifier circuit and the second power conversion circuit, boosting 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 terminal.

9. The power conversion device according to any one of claims 2 to 6, wherein, The control unit performs transition control between the first control and the second control in at least one of the following situations: switching from a state of executing the first control to a state of executing the second control, and switching from a state of executing the second control to a state of executing the first control. In the switching control, the control unit controls the on / off state of the plurality of bidirectional switches to form a closed circuit 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 state of the plurality of switching elements to form a closed circuit from the first end of the primary winding through any one of the plurality of switching elements to the second end of the primary winding.

10. The power conversion device according to claim 9, wherein, When the control unit switches from executing the first control state to executing the second control state, the transition control executes the first process, the second process, and the third process in the order of the first process, the second process, and the third process. In the first process, the opening and closing of the plurality of bidirectional switches are controlled to form a closed circuit from the first end of the primary winding through any of the plurality of bidirectional switches to the second end of the primary winding, and the plurality of switching elements are controlled to the off state. In the second process, the on / off states of the plurality of bidirectional switches are controlled to form a closed circuit 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 the on / off states of the plurality of switching elements are controlled to form a closed circuit from the first end of the primary winding through any one of the plurality of switching elements to the second end of the primary winding. In the third process, the plurality of bidirectional switches are controlled to be in the off state, and the multiple switching elements are controlled to be turned on and off, so as to form a closed circuit from the first end of the primary winding through any of the multiple switching elements to the second end of the primary winding.

11. The power conversion device according to claim 9 or 10, wherein, When the control unit switches from executing the second control to executing the first control, the transition control executes the first process, the second process, and the third process in the order of the first process, the second process, and the third process. In the first process, the opening and closing of the plurality of bidirectional switches are controlled to form a closed circuit from the first end of the primary winding through any of the plurality of bidirectional switches to the second end of the primary winding, and the plurality of switching elements are controlled to the off state. In the second process, the on / off states of the plurality of bidirectional switches are controlled to form a closed circuit 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 the on / off states of the plurality of switching elements are controlled to form a closed circuit from the first end of the primary winding through any one of the plurality of switching elements to the second end of the primary winding. In the third process, the plurality of bidirectional switches are controlled to be in the off state, and the multiple switching elements are controlled to be turned on and off, so as to form a closed circuit from the first end of the primary winding through any of the multiple switching elements to the second end of the primary winding.

12. The power conversion device according to any one of claims 9 to 11, wherein, In the first control, the control unit switches the switching modes and controls the on / off states of the multiple bidirectional switches according to multiple different switching modes that determine the combination of on / off states of the multiple bidirectional switches. The plurality of switching modes include a specific switching mode, which is a combination of the on / off states of the plurality of bidirectional switches forming a closed circuit from the first end of the primary winding through any of the plurality of bidirectional switches to the second end of the primary winding. When the control unit switches from a state where it is executing the first control to a state where it is executing the second control, it performs specific control before executing the transition control. In the specific control, the control unit switches the switching mode in the same order as the first control and controls the on / off state of the plurality of bidirectional switches, and regardless of the magnitude of the input voltage input to the plurality of input terminals, the combination of the on / off state of the plurality of bidirectional switches according to the specific switching mode continues for a predetermined period of time or more.

13. A program for a power conversion device, applied to the power conversion device, the power conversion device comprising: The first power conversion circuit has multiple input terminals, multiple bidirectional switches, a first output terminal, and a second output terminal, and is capable of converting three-phase AC power. A transformer has a primary winding and a secondary winding, wherein a first end of the primary winding is connected to a first output terminal, and a second end of the primary winding is connected to a second output terminal; The second power conversion circuit includes a capacitor, multiple switching 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. as well as The control unit is capable of switching the on / off states of the multiple bidirectional switches and the multiple switching elements. The second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal. The program used by the power conversion device causes the control unit to perform the following processing: If the amplitude of the input voltage input to one or more of the plurality of input terminals is greater than a given threshold, the plurality of bidirectional switches are controlled so that the first power conversion circuit converts the input voltage and outputs it from the first output terminal and the second output terminal; When the amplitude of the input voltage input to the plurality of input terminals is below the threshold, the plurality of bidirectional switches are switched to the off state, and the plurality of switching 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.

14. A power conversion device, comprising: The first power conversion circuit has multiple input terminals, a first output terminal and a second output terminal, multiple bidirectional switches, a transformer and a rectifier circuit connecting the multiple input terminals to the first output terminal and the second output terminal. The first power conversion circuit is capable of converting three-phase AC power input to the multiple input terminals. The transformer has a primary winding and a secondary winding. The first end of the primary winding is connected to the first output terminal and the second end of the primary winding is connected to the second output terminal. The rectifier circuit is connected to the secondary winding and is capable of converting AC voltage. The second power conversion circuit includes a capacitor, multiple switching 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. as well as The control unit is capable of switching the on / off states of the multiple bidirectional switches and the multiple switching elements. The second power conversion circuit can output the energy stored in the capacitor to the third output terminal and the fourth output terminal.

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