Power conversion device and program for power conversion device

Abstract

A power conversion device (10) comprises: a diode (55), an anode terminal of which is connected to a high-potential output terminal (50A) of a rectifier circuit (50); and a fifth capacitor (C5), one end of which is connected to a cathode terminal of the diode (55) and the other end of which is connected to a low-potential output terminal (50B) of the rectifier circuit (50). When starting power conversion in a power conversion circuit (30), a control unit (100) of the power conversion device (10) starts on / off switching of a plurality of bidirectional switches, said switching being in accordance with a switching sequence, when the phase of an AC voltage which is inputted to the power conversion circuit (30) is within any of the following ranges: 0±5°, (30)±5°, –(30)±5°, (60)±5°, –(60)±5°, (90)±5°, –(90)±5°, (120)±5°, –(120)±5°, (150)±5°, –(150)±5°, and (180)±5°.

Description

Power Conversion Device and Program for Power Conversion Device

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

[0002] The power conversion device disclosed in Patent Document 1 includes a matrix converter having six bidirectional switches, a transformer circuit connected to the matrix converter, and a control device that controls the on / off of each bidirectional switch. The transformer circuit has a transformer composed of a primary coil and a secondary coil. By the control device switching the on / off of each bidirectional switch according to a predetermined switching sequence, the matrix converter converts the input three-phase AC power and outputs it to the primary coil of the transformer. Also, as the magnitude of the current flowing through the primary coil changes, a current flows through the secondary coil.

[0003] Further, the power conversion device disclosed in Patent Document 1 includes a rectifier circuit, a diode, and a capacitor. The rectifier circuit rectifies and outputs the current flowing through the secondary coil. The anode terminal of the diode is connected to the high-potential-side output terminal of the rectifier circuit. The first end of the capacitor is connected to the cathode terminal of the diode. The second end of the capacitor is connected to the low-potential-side output terminal of the rectifier circuit.

[0004] Chinese Patent Application Publication No. 117937971 Specification

[0005] In a power conversion device as disclosed in Patent Document 1, when the matrix converter is not performing power conversion, the capacitor connected to the rectifier circuit may be in a state where it is not charged. In this state, when power conversion in the matrix converter is started, in an attempt to charge the capacitor connected to the rectifier circuit, a large current may flow through the elements constituting the rectifier circuit, imposing an excessive burden on the elements.

[0006] One embodiment for solving the above problem includes a power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control that can switch the on and off of the plurality of bidirectional switches. A power conversion device comprising a control unit and a control unit, wherein the AC voltage input to the first input terminal is defined as the first voltage, and the phase of the AC voltage at which the first voltage is maximum is defined as 0°. When the control unit converts three-phase AC power in the power conversion circuit, it switches the on and off of a plurality of the bidirectional switches according to a predetermined switching sequence. When the power conversion in the power conversion circuit starts, it starts switching the on and off of a plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within any of the following ranges: 0±5°, 30±5°, -30±5°, 60±5°, -60±5°, 90±5°, -90±5°, 120±5°, -120±5°, 150±5°, -150±5°, and 180±5°.

[0007] Furthermore, one embodiment for solving the above problem includes a power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; and a power conversion circuit having its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal. The power conversion device comprises a capacitor connected to a terminal output and a control unit capable of switching the on and off of a plurality of the bidirectional switches, wherein when the power conversion circuit converts power, the control unit switches the on and off of the plurality of the bidirectional switches according to a predetermined switching sequence, and when the power conversion circuit starts, the control unit starts switching the on and off of the plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within ±5° of the phase of the AC voltage at which the product of the absolute value of the applied voltage applied to the transformer and the time for which the applied voltage is applied is the minimum value.

[0008] Furthermore, one embodiment for solving the above problem is a power conversion device comprising: a power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control unit capable of switching the on and off of a plurality of bidirectional switches. This is a program for a power converter, which is applied and the AC voltage input to the first input terminal is defined as the first voltage, and the phase of the AC voltage at which the first voltage is maximum is defined as 0°. The program causes the control unit to perform the following actions when converting three-phase AC power in the power converter circuit: switching the on and off of a plurality of the bidirectional switches according to a predetermined switching sequence; and when starting power conversion in the power converter circuit, starting the on and off of a plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within any of the following ranges: 0±5°, 30±5°, -30±5°, 60±5°, -60±5°, 90±5°, -90±5°, 120±5°, -120±5°, 150±5°, -150±5°, and 180±5°.

[0009] Furthermore, one embodiment for solving the above problem includes a power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding being connected to the first output terminal and the second end of the primary winding being connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; and a capacitor whose first end is connected to the high-potential output terminal and whose second end is connected to the low-potential output terminal. This is a program for a power conversion device that includes a control unit capable of switching the on and off of a plurality of the aforementioned bidirectional switches, and which causes the control unit to perform the following: when converting power in the power conversion circuit, the process of switching the on and off of a plurality of the aforementioned bidirectional switches according to a predetermined switching sequence; and when starting power conversion in the power conversion circuit, the process of starting to switch the on and off of a plurality of the aforementioned bidirectional switches according to the switching sequence when the phase of the AC voltage is within ±5° of the phase of the AC voltage at which the product of the absolute value of the applied voltage applied to the transformer and the time for which the applied voltage is applied is the minimum value.

[0010] According to this disclosure, the burden on the elements constituting the rectifier circuit can be reduced when power conversion is initiated in a power conversion circuit.

[0011] Figure 1 is a circuit diagram of a power converter. Figure 2 is a circuit diagram of a power conversion circuit. Figure 3 shows the waveform and sector of a three-phase AC voltage. Figure 4 is a graph showing the change in the product of the absolute value of the primary voltage applied to the transformer and the application time of the primary voltage, with respect to the phase of the first voltage.

[0012] <Embodiments of Power Converters and Programs for Power Converters> Embodiments of power converters and programs for power converters are described below. The drawings are merely illustrative of the embodiments of this disclosure and should not be considered limiting. The drawings are schematic diagrams for ease of understanding and may enlarge or omit components. Terms such as "first," "second," and "third" in this disclosure are used simply to distinguish objects and do not rank or assign any order to them.

[0013] (Configuration of the power converter) As shown in Figure 1, the power converter 10 includes an input-side low-pass filter 20, a power conversion circuit 30, a transformer circuit 40, and a rectifier circuit 50. The power converter 10 also includes a first external input terminal 11A, a second external input terminal 11B, and a third external input terminal 11C, as well as a first external output terminal 12A and a second external output terminal 12B.

[0014] The power converter 10 is, as a whole, a so-called three-phase isolated AC-DC converter. That is, the power converter 10 converts the three-phase AC power input to each external input terminal into DC power, which can then be output from a pair of external output terminals. Furthermore, a transformer circuit 40 is interposed in the power path from each external input terminal to each external output terminal, thereby electrically isolating each external input terminal from each external output terminal.

[0015] For example, each external input terminal receives the three phases of three-phase AC power input from a three-phase AC power supply PS. The three-phase AC power supply PS is a three-phase, three-wire commercial power system with three AC power sources connected in a Y-connection. As shown in Figure 3, the voltages of the three phases are the first voltage VA, the second voltage VB, and the third voltage VC. Each voltage is an AC voltage with a different phase from the others. As shown in Figure 1, the first voltage VA is input to the first external input terminal 11A. The second voltage VB is input to the second external input terminal 11B. The third voltage VC is input to the third external input terminal 11C. The second voltage VB has a phase difference of 120° from the first voltage VA. The third voltage VC has a phase difference of 120° from the second voltage VB. Note that this "120° phase difference" allows for an error of approximately ±1°.

[0016] As shown in Figure 1, the pair of external output terminals are a first external output terminal 12A and a second external output terminal 12B. Any load LD can be connected between the first external output terminal 12A and the second external output terminal 12B. The load LD is, for example, an electronic device such as a server driven by DC power.

[0017] The input-side low-pass filter 20 includes a first inductor L1, a second inductor L2, and a third inductor L3. The input-side low-pass filter 20 also includes a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0018] The first terminal of the first inductor L1 is connected to the first external input terminal 11A. The first terminal of the first capacitor C1 is connected to the second terminal of the first inductor L1. The first terminal of the second inductor L2 is connected to the second external input terminal 11B. The first terminal of the second capacitor C2 is connected to the second terminal of the second inductor L2. The second terminal of the second capacitor C2 is connected to the second terminal of the first capacitor C1. The first terminal of the third inductor L3 is connected to the third external input terminal 11C. The first terminal of the third capacitor C3 is connected to the second terminal of the third inductor L3. The second terminal of the third capacitor C3 is connected to the second terminal of the first capacitor C1.

[0019] The power conversion circuit 30 includes a plurality of input terminals and a pair of output terminals. The plurality of input terminals of the power conversion circuit 30 are a first input terminal 31A, a second input terminal 31B, and a third input terminal 31C. The first input terminal 31A is connected to the second end of the first inductor L1. The second input terminal 31B is connected to the second end of the second inductor L2. The third input terminal 31C is connected to the second end of the third inductor L3. Therefore, three-phase AC power is input to each input terminal of the power conversion circuit 30 via each external input terminal and the input-side low-pass filter 20. The pair of output terminals are a first output terminal 32A and a second output terminal 32B. Single-phase AC power converted by each element in the power conversion circuit 30 is output from the pair of output terminals.

[0020] As shown in Figure 2, the power conversion circuit 30 is equipped with a plurality of bidirectional switches TSW. In Figure 2, only some of the bidirectional switches TSW are labeled with reference numerals. Each bidirectional switch TSW has two switch elements. Each switch element is an N-channel type MOSFET (Metal Oxide Semiconductor Field Effect Transistor). That is, each switch element has a body diode. A bidirectional switch TSW is composed of two switch elements connected in series such that the anode terminals of the body diodes are connected to each other. In other words, the switch elements constituting each bidirectional switch TSW are connected to each other such that the body diodes are in opposite directions. In other words, each bidirectional switch TSW has two switch elements with their source terminals connected to each other. In the following, when a bidirectional switch TSW is in the off state, it means that both switch elements constituting the bidirectional switch TSW are in the off state.

[0021] The multiple bidirectional switches TSW are a first high-side bidirectional switch HS1, a first low-side bidirectional switch LS1, a second high-side bidirectional switch HS2, a second low-side bidirectional switch LS2, a third high-side bidirectional switch HS3, and a third low-side bidirectional switch LS3.

[0022] The first high-side bidirectional switch HS1 connects the first input terminal 31A and the first output terminal 32A. Specifically, the first high-side bidirectional switch HS1 has an eleventh switch element S11 and a twentieth switch element S21. The drain terminal of the eleventh switch element S11 is connected to the first input terminal 31A. The source terminal of the eleventh switch element S11 is connected to the source terminal of the twentieth switch element S21. The drain terminal of the twentieth switch element S21 is connected to the first output terminal 32A.

[0023] The first low-side bidirectional switch LS1 connects the first input terminal 31A and the second output terminal 32B. Specifically, the first low-side bidirectional switch LS1 includes a 24th switch element S24 and a 14th switch element S14. The drain terminal of the 24th switch element S24 is connected to the first input terminal 31A. The source terminal of the 24th switch element S24 is connected to the source terminal of the 14th switch element S14. The drain terminal of the 14th switch element S14 is connected to the second output terminal 32B.

[0024] The second high-side bidirectional switch HS2 connects the second input terminal 31B and the first output terminal 32A. Specifically, the second high-side bidirectional switch HS2 has a 13th switch element S13 and a 23rd switch element S23. The drain terminal of the 13th switch element S13 is connected to the second input terminal 31B. The source terminal of the 13th switch element S13 is connected to the source terminal of the 23rd switch element S23. The drain terminal of the 23rd switch element S23 is connected to the first output terminal 32A.

[0025] The second low-side bidirectional switch LS2 connects the second input terminal 31B and the second output terminal 32B. Specifically, the second low-side bidirectional switch LS2 has a 26th switch element S26 and a 16th switch element S16. The drain terminal of the 26th switch element S26 is connected to the second input terminal 31B. The source terminal of the 26th switch element S26 is connected to the source terminal of the 16th switch element S16. The drain terminal of the 16th switch element S16 is connected to the second output terminal 32B.

[0026] The third high-side bidirectional switch HS3 connects the third input terminal 31C and the first output terminal 32A. Specifically, the third high-side bidirectional switch HS3 has a 15th switch element S15 and a 25th switch element S25. The drain terminal of the 15th switch element S15 is connected to the third input terminal 31C. The source terminal of the 15th switch element S15 is connected to the source terminal of the 25th switch element S25. The drain terminal of the 25th switch element S25 is connected to the first output terminal 32A.

[0027] The third low-side bidirectional switch LS3 connects the third input terminal 31C and the second output terminal 32B. Specifically, the third low-side bidirectional switch LS3 has a 22nd switch element S22 and a 12th switch element S12. The drain terminal of the 22nd switch element S22 is connected to the third input terminal 31C. The source terminal of the 22nd switch element S22 is connected to the source terminal of the 12th switch element S12. The drain terminal of the 12th switch element S12 is connected to the second output terminal 32B.

[0028] As shown in Figure 1, the transformer circuit 40 comprises a fourth inductor L4 and a transformer 41. The transformer 41 comprises a primary winding 41A and a secondary winding 41B. The first end of the fourth inductor L4 is connected to the first output terminal 32A of the power conversion circuit 30. The first end of the primary winding 41A is connected to the second end of the fourth inductor L4. That is, the first end of the primary winding 41A is connected to the first output terminal 32A via the fourth inductor L4. The second end of the primary winding 41A is connected to the second output terminal 32B of the 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 isolated from each other.

[0029] The rectifier circuit 50 has four semiconductor elements. These four semiconductor elements are a first switch element 51, a second switch element 52, a third switch element 53, and a fourth switch element 54. The first to fourth switch elements 51 to 54 are n-channel type MOSFETs. The rectifier circuit 50 rectifies the AC voltage applied from the secondary winding 41B and converts it into a DC voltage through the control of each switch element by the control unit 100, which will be described later.

[0030] The source terminal of the first switch element 51 is connected to the first end of the secondary winding 41B of the transformer 41. The drain terminal of the first switch element 51 is connected to the drain terminal of the third switch element 53. The source terminal of the third switch element 53 is connected to the second end of the secondary winding 41B and the drain terminal of the fourth switch element 54. The source terminal of the fourth switch element 54 is connected to the source terminal of the second switch element 52. The drain terminal of the second switch element 52 is connected to the first end of the secondary winding 41B and the source terminal of the first switch element 51.

[0031] The rectifier circuit 50 includes a high-potential output terminal 50A and a low-potential output terminal 50B. The high-potential output terminal 50A is connected to the drain terminal of the first switch element 51 and the drain terminal of the third switch element 53. The low-potential output terminal 50B is connected to the source terminal of the second switch element 52 and the source terminal of the fourth switch element 54.

[0032] The power converter 10 includes a fifth inductor L5, a fourth capacitor C4, a diode 55, and a fifth capacitor C5. The first end of the fifth inductor L5 is connected to the high-potential output terminal 50A of the rectifier circuit 50. The second end of the fifth inductor L5 is connected to the first end of the fourth capacitor C4 and the first external output terminal 12A. The second end of the fourth capacitor C4 is connected to the low-potential output terminal 50B of the rectifier circuit 50. These fifth inductor L5 and fourth capacitor C4 function as noise filters.

[0033] The anode terminal of diode 55 is connected to the high-potential output terminal 50A of the rectifier circuit 50. The first terminal of the fifth capacitor C5 is connected to the cathode terminal of diode 55. Therefore, the fifth capacitor C5 is connected to the high-potential output terminal 50A via diode 55. The second terminal of the fifth capacitor C5 is connected to the low-potential output terminal 50B of the rectifier circuit 50. Note that diode 55 and fifth capacitor C5 are sometimes referred to as clamp diode and clamp capacitor, respectively.

[0034] As shown in Figure 1, the power converter 10 includes a power detection circuit SE and a control unit 100. The power detection circuit SE is capable of detecting the power applied to the first external input terminal 11A, the second external input terminal 11B, and the third external input terminal 11C. Specifically, the power detection circuit SE is capable of detecting the voltage and current values ​​input to each external input terminal. That is, the power detection circuit SE is capable of detecting the first voltage VA, the second voltage VB, and the third voltage VC.

[0035] The control unit 100 includes a storage device and an execution device (not shown). In other words, the control unit 100 is an MCU (Microcontroller Unit). The storage device of the control unit 100 stores a program PG that is executed by the execution device. Based on this program PG, the control unit 100 can switch the on / off state of each bidirectional switch TSW of the power conversion circuit 30.

[0036] The execution device includes, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an FPGA (Field Programmable Gate Array), or a CPLD (Complex Programmable Logic Device), or an ASIC (Application Specific Integrated Circuit). The execution device of the control unit 100 can perform various processes related to power conversion by executing the program PG. In the following, the processing performed by the execution device of the control unit 100 may be simply referred to as processing performed by the control unit 100.

[0037] Specifically, program PG contains program data for performing power conversion in the power conversion circuit 30. As part of this program data, program PG defines multiple different switching patterns for multiple bidirectional switches TSW in the power conversion circuit 30. These switching patterns define combinations of on / off states for the multiple bidirectional switches TSW. Furthermore, program PG defines the order in which the switching patterns for the bidirectional switches TSW are switched. The switching patterns for the bidirectional switches TSW and their switching order are collectively referred to as the switching sequence.

[0038] The program PG contains program data for rectifying the current in the rectifier circuit 50. As part of the program data, the program PG defines the on / off combinations of each switch element in the rectifier circuit 50. One such combination is that the first switch element 51 and the fourth switch element 54 are in the ON state, and the second switch element 52 and the third switch element 53 are in the OFF state. Another such combination is that the second switch element 52 and the third switch element 53 are in the ON state, and the first switch element 51 and the fourth switch element 54 are in the OFF state.

[0039] The power converter 10 includes a gate drive circuit (not shown). The gate drive circuit switches the on / off state of the two switch elements of each bidirectional switch TSW. The gate drive circuit also switches the on / off state of each switch element of the rectifier circuit 50. The control unit 100 controls each switch element by inputting a switching signal to the input terminal of the gate drive circuit and outputting a gate drive voltage to each switch element via the gate drive circuit.

[0040] As shown in Figure 2, the switching signal includes the 11th switching signal SG11 to the 16th switching signal SG16 and the 21st switching signal SG21 to the 26th switching signal SG26. The 11th switching signal SG11 to the 16th switching signal SG16 correspond to the 11th switching element S11 to the 16th switching element S16, respectively. The 21st switching signal SG21 to the 26th switching signal SG26 correspond to the 21st switching element S21 to the 26th switching element S26, respectively.

[0041] The control unit 100 controls the on / off state of multiple bidirectional switches TSW in the power conversion circuit 30 by switching the switching patterns according to a plurality of switching patterns. That is, the control unit 100 switches the on / off state of multiple bidirectional switches TSW according to a predetermined switching sequence. Then, based on these switching signals, the power conversion circuit 30 converts the three-phase AC power input to each input terminal into AC power and outputs it. That is, when the potential difference at the first output terminal 32A with respect to the second output terminal 32B of the power conversion circuit 30 is defined as the primary voltage Vp, the primary voltage Vp is an AC voltage. Therefore, the primary voltage Vp, which is an AC voltage, is applied to the fourth inductor L4 and the primary side winding 41A of the transformer 41. In other words, the primary voltage Vp is the voltage applied to the fourth inductor L4.

[0042] As shown in Figure 1, when an AC primary voltage Vp is applied to the primary winding 41A, a single-phase AC voltage is generated in the secondary winding 41B due to electromagnetic induction. Hereafter, the current flowing through the secondary winding 41B is referred to as the secondary current iT. Of the directions in which the secondary current iT flows, the direction in which the current flows from the second end to the first end of the secondary winding 41B is defined as the positive direction. The direction of the current flowing in the opposite direction is defined as the negative direction. In Figure 1, the direction of the positive secondary current iT is indicated by an arrow.

[0043] Also, as shown in FIG. 1, the switching signal includes first to fourth switching signals SG1 to SG4. The first to fourth switching signals SG1 to SG4 respectively correspond to the first to fourth switching elements 51 to 54.

[0044] When the secondary current iT flows in the positive direction, the control unit 100 switches the first switching element 51 and the fourth switching element 54 to the on state. At the same time, the control unit 100 switches the second switching element 52 and the third switching element 53 to the off state. At this time, the secondary current iT flows from the first end of the secondary winding 41B to the first external output terminal 12A side through the first switching element 51.

[0045] Also, when the secondary current iT flows in the negative direction, the control unit 100 switches the second switching element 52 and the third switching element 53 to the on state. At the same time, the control unit 100 switches the first switching element 5i and the fourth switching element 54 to the off state. At this time, the secondary current iT flows from the second end of the secondary winding 41B to the first external output terminal 12A side through the third switching element 53. Therefore, based on the control of the control unit 100, the rectifier circuit 50 converts the AC power generated in the secondary winding 41B into DC power.

[0046] (Regarding the definition of sectors) In the present embodiment, based on the magnitude relationship among 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 power conversion circuit 30 is divided into a plurality of sectors. In the present embodiment, the sectors are defined as follows.

[0047] Three-phase AC power is input to each input terminal of the power conversion circuit 30 from a three-phase AC power supply PS via an input-side low-pass filter 20. As shown in FIG. 3, the voltages of the three phases of the three-phase AC power are a first voltage VA, a second voltage VB, and a third voltage VC, which are AC voltages with different phases from each other. The first voltage VA, the second voltage VB, and the third voltage VC are input to the first input terminal 31A, the second input terminal 31B, and the third input terminal 31C, respectively. Specifically, the first voltage VA is input to the first input terminal 31A. The second voltage VB is input to the second input terminal 31B. The third voltage VC is input to the third input terminal 31C. The second voltage VB has a phase difference of 120° with respect to the first voltage VA. The third voltage VC has a phase difference of 120° with respect to the second voltage VB.

[0048] Here, the timing of the phase at which the first voltage VA becomes maximum is set to 0°. Also, the timing of the phase at which the first voltage VA becomes minimum is set to -180°. Therefore, one cycle of the first voltage VA, the second voltage VB, and the third voltage VC is represented in the range of a phase of -180° or more and less than 180°. Note that it is also possible to represent the timing of the phase of the voltage in a phase of 180° or more and less than 360°. When the phase of the voltage is represented by a phase of 180° or more, X° is synonymous with (-180° + (X - 180°)). Here, as a period obtained by equally dividing the period of one cycle into six, sectors 1 to 6 are defined. Specifically, when the phase of the first voltage VA is "θ°", sectors 1 to 6 are defined as the following periods at intervals of 60°.

[0049] - Sector 1: -30° ≤ θ° < 30° - Sector 2: 30° ≤ θ° < 90° - Sector 3: 90° ≤ θ° < 150° - Sector 4: 150° ≤ θ° < 180° and -180° ≤ θ° < -150° - Sector 5: -150° ≤ θ° < -90° - Sector 6: -90° ≤ θ° < -30° However, regarding the boundaries of each sector, it does not matter which sector it belongs to. For example, in the following example, when θ° = 30°, it may be treated as being included in sector ˌ or it may be treated as being included in sector 2.

[0050] In the above example, the voltage input to the first input terminal 31A was treated as the first voltage VA, but it is also possible to treat the voltage input to the second input terminal 31B as the first voltage VA. Similarly, it is also possible to treat the voltage input to the second input terminal 31B as the first voltage VA. If the voltage input to the second input terminal 31B is treated as the first voltage VA, the phase of the first voltage VA will be 0°, which corresponds to 120° when the voltage input to the first input terminal 31A is treated as the first voltage VA.

[0051] (Regarding pulse width modulation control) The control unit 100 controls the time T over which the primary voltage Vp is applied to the fourth inductor L4 per unit time by controlling the on / off state of each bidirectional switch TSW based on the switching sequence described above. In other words, the control unit 100 controls the time T over which the voltage is applied to the fourth inductor L4 using pulse width modulation control.

[0052] Here, assume that the phase of the AC voltage is within the range of -30° to 0°. In this case, the absolute value of the primary voltage Vp is the value obtained by subtracting the second voltage VB from the first voltage VA. Also, assume that the phase of the AC voltage is within the range of 0° to 30°. In this case, the absolute value of the primary voltage Vp is the value obtained by subtracting the third voltage VC from the first voltage VA. As a result, when the phase of the AC voltage is in sector 1, the absolute value of the primary voltage Vp is at its maximum when the phase of the AC voltage is -30°, and decreases as the phase of the AC voltage approaches 0°. The absolute value of the primary voltage Vp is at its minimum when the phase of the AC voltage is 0°. Furthermore, the absolute value of the primary voltage Vp increases as the phase of the AC voltage approaches 30° from 0°, and the value of the primary voltage Vp is at its maximum when the phase of the AC voltage is 30°. In other words, when the phase of the AC voltage belongs to sector 1, the absolute value of the primary voltage Vp fluctuates such that it is at its minimum when the phase is 0° and at its maximum when the phase is -30° and 30°.

[0053] More specifically, the primary voltage Vp can be derived from equation (1) below when the phase of the AC voltage is within the range of -30° to 0°. Furthermore, when the phase of the AC voltage is within the range of 0° to 30°, it can be derived from equation (2) below. (1) ...√2 × Vin × cos((π / 6) + θ) (2) ...√2 × Vin × cos((π / 6) - θ) where "Vin" is the effective voltage of the first voltage VA to the third voltage VC. Therefore, for the same three-phase AC power supply PS, "Vin" can be considered a fixed value.

[0054] Furthermore, assume that the phase of the AC voltage is within the range of 150° to 180°. In this case, the absolute value of the primary voltage Vp is the second voltage VB minus the first voltage VA. Also, assume that the phase of the AC voltage is within the range of -180° to -150°. In this case, the absolute value of the primary voltage Vp is the third voltage VC minus the first voltage VA. As a result, when the phase of the AC voltage belongs to sector 4, the absolute value of the primary voltage Vp fluctuates so that it is at its minimum value when the phase is 180° and at its maximum value when the phase is 150° and -150°, similar to when it belongs to sector 1.

[0055] Similarly, the absolute value of the primary voltage Vp fluctuates when the phase of the AC voltage belongs to sectors 2, 3, 5, and 6. Specifically, the absolute value of the primary voltage Vp is at its minimum when the phase of the AC voltage is 60°, 120°, -120°, and -60°. The absolute value of the primary voltage Vp is at its maximum when it is within ±30° of the phase at which the absolute value of the primary voltage Vp is at its minimum.

[0056] The control unit 100 controls the ratio of time T per unit time for which voltage is applied to the fourth inductor L4, in accordance with fluctuations in the primary voltage Vp. Here, unit time is half the switching period of the power conversion circuit 30. The control unit 100 controls time T such that time T is at its maximum value when the absolute value of the primary voltage Vp is at its minimum value, and time T is at its minimum value when the absolute value of the primary voltage Vp is at its maximum value. Therefore, the relationship between time T and the phase of the AC voltage is the inverse of the relationship between the phase of the AC voltage and the relationship between the phase of the AC voltage and the phase of the primary voltage Vp.

[0057] More specifically, time T can be derived from equation (3) below when the phase of the AC voltage belongs to sector 1, that is, within the range of -30° to 30°. Note that time T changes similarly when the phase of the AC voltage belongs to other sectors. (3) ... 0.5 × ma × Ts {sin((π / 6) - θ) + sin((π / 6) + θ)} where "ma" is the modulation rate in the power conversion circuit 30 and "Ts" is the switching period of the power conversion circuit 30. Therefore, if the power conversion circuit 30 performs power conversion in the same manner, "ma" and "Ts" can be considered fixed values.

[0058] (Regarding the start control of the power conversion circuit) When the power conversion circuit 30 starts the conversion of three-phase AC power, the control unit 100 executes the following process based on the program PG described above. That is, the program PG causes the control unit 100 of the power conversion device 10 to execute the following process. In the following, the start of the power conversion circuit 30's conversion of three-phase AC power may be simply referred to as the power conversion circuit 30 starting to operate.

[0059] When the control unit 100 receives a start request signal SS from an external device, it executes start control based on the program PG. Examples of external devices include a higher-level control device that controls one or more power converters 10 in a unified manner, and terminals used by users, etc., for maintenance of the power converters 10.

[0060] When the start control is initiated, the control unit 100 determines the phase of the AC voltage input to each input terminal of the power conversion circuit 30 at the time of receiving the start request signal SS. At this time, the control unit 100 refers to the first voltage VA, the second voltage VB, and the third voltage VC detected by the power detection circuit SE.

[0061] Next, the control unit 100 determines whether the phase of the determined AC voltage is within one of the following ranges: 0±5°, 30±5°, -30±5°, 60±5°, -60±5°, 90±5°, -90±5°, 120±5°, -120±5°, 150±5°, -150±5°, or 180±5°. Here, "X±5°" includes X+5° and X-5°. In other words, "X±5°" means X-5° or more and X+5° or less. Also, 180+5° is synonymous with -175°.

[0062] The control unit 100 starts driving the power conversion circuit 30 if the phase of the determined AC voltage is within any of the above ranges. Specifically, the control unit 100 starts switching the on and off of the multiple bidirectional switches TSW according to the switching sequence described above. As a result, current starts to flow through the fourth inductor L4, and due to electromagnetic induction in the transformer circuit 40, current also starts to flow through the rectifier circuit 50.

[0063] On the other hand, if the determined phase of the AC voltage does not fall within any of the above ranges, the control unit 100 does not start driving the power conversion circuit 30 and remains in standby mode. That is, in this case, the control unit 100 does not switch the multiple bidirectional switches TSW on or off according to the switching sequence described above. After that, the control unit 100 remains in standby mode for a predetermined period of time. This predetermined period is set to be, for example, a time that is sufficiently short compared to the time required for the phase of the AC current to advance by 30°.

[0064] After a specified time has elapsed, the control unit 100 again determines the phase of the AC voltage input to each input terminal of the power conversion circuit 30. The control unit 100 then determines whether the determined phase of the AC voltage falls within one of the above ranges. The control unit 100 repeats this process of waiting for a specified time and determining the phase of the AC voltage until the phase of the AC voltage falls within one of the above ranges. When the phase of the AC voltage falls within one of the above ranges, the control unit 100 starts driving the power conversion circuit 30.

[0065] (Regarding the operation of the embodiment) The operation of the power converter 10 will be described below using the case where the phase of the AC voltage belongs to sector 1 as an example. However, the same applies when the phase of the AC voltage belongs to other sectors, so the explanation for the case where the phase of the AC voltage belongs to other sectors will be omitted.

[0066] When the power conversion circuit 30 has stopped converting three-phase AC power, the fifth capacitor C5 is uncharged at the time when it attempts to start converting three-phase AC power.

[0067] In this state, the primary voltage Vp derived from equation (1) or equation (2) above is applied to the fourth inductor L4 almost as is. At this time, the primary voltage Vp is applied to the fourth inductor L4 for a time T within a unit time, i.e., a period of "Ts / 2", which is half the switching period of the power conversion circuit 30. Therefore, within a unit time, the absolute value of the current flowing through the fourth inductor L4 increases from the time the primary voltage Vp is applied and reaches its maximum value when the application of the primary voltage Vp ends. Then, the absolute value of the current flowing through the fourth inductor L4 decreases after the application of the primary voltage Vp ends. The maximum current Imax, which is the maximum absolute value of the current flowing through the fourth inductor L4 within this unit time, can theoretically be derived from the following equation (4): (4) ... |Vp| × T / Lr where "Lr" is the inductance of the fourth inductor L4.

[0068] Here, when the fourth inductor L4 is considered an ideal inductor, "Lr" is a fixed value. Therefore, the maximum current Imax mentioned above is a value corresponding to the product of the absolute value of the primary voltage Vp and time T.

[0069] If we substitute an arbitrary phase value of "θ" within the range of -30° to 30° in equation (1) or equation (2), and equation (3), and calculate the product of the absolute value of the primary voltage Vp and time T, we obtain the transition shown in Figure 4. That is, the product of the absolute value of the primary voltage Vp and time T reaches a minimum when the phase of the AC voltage is -30°, 0°, and 30°, and a maximum when the phase θ of the AC voltage is -15° and 15°.

[0070] Although not shown in Figure 4, the product of the absolute value of the primary voltage Vp and time T takes local minimums at 30° intervals, with the AC voltage phase being 0° as the reference point. Therefore, the product of the absolute value of the primary voltage Vp and time T takes local minimums when the AC voltage phase is 0°, 30°, -30°, 60°, -60°, 90°, -90°, 120°, -120°, 150°, -150°, and 180°.

[0071] As shown in Figure 4, for example, when the phase of the AC voltage is -5° and 5°, the product of the absolute value of the primary voltage Vp and time T is approximately an intermediate value between the maximum and minimum values. Therefore, the range of ±5° phase in which the product of the absolute value of the primary voltage Vp and time T is at its minimum is the range in which the product of the absolute value of the primary voltage Vp and time T is approximately less than or equal to the above intermediate value.

[0072] <Effects of the Embodiment> The above embodiment provides the following effects. (1) In the above embodiment, the control unit 100 starts switching the on and off of a plurality of bidirectional switches TSW according to the switching sequence when the phase of the AC voltage is within the range of 0 ± 5°. As described above, within this range, the product of the absolute value of the primary voltage Vp and time T is generally less than or equal to the midpoint between the maximum and minimum values. Therefore, as derived from equation (4), when the phase of the AC voltage is within the range of 0 ± 5°, the absolute value of the current flowing through the fourth inductor L4 is significantly smaller than the maximum value. And if the absolute value of the current flowing through the fourth inductor L4 is small, the current flowing through the secondary winding 41B of the transformer 41, and consequently through the rectifier circuit 50, will also be small. Thus, in the above embodiment, power conversion by the power conversion circuit 30 is started at the timing when the current flowing through the rectifier circuit 50 becomes small. Therefore, even if the fifth capacitor C5 is not charged when the power conversion is started, the load on each switching element of the rectifier circuit 50 can be reduced.

[0073] (2) In the above embodiment, the power converter 10 is equipped with a diode 55 and a fifth capacitor C5. Therefore, for example, even if an unintended large voltage, a so-called surge voltage, is generated when switching the switching element of the rectifier circuit 50 on or off, the fifth capacitor C5 can be charged with that surge voltage. In other words, the surge voltage can be absorbed by the fifth capacitor C5. Therefore, it is possible to prevent a large voltage exceeding the rated voltage of the fifth capacitor C5 from being generated between the first external output terminal 12A and the second external output terminal 12B of the power converter 10.

[0074] <Examples of Modifications> The above embodiment can be implemented with the following modifications. The above embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0075] The configuration of the power converter 10 is not limited to the examples of the above embodiment. For example, the power converter 10 is not limited to a three-phase isolated AC-DC converter, but can also be applied to a non-isolated three-phase AC-DC converter. Furthermore, the power converter 10 does not need to include an input-side low-pass filter 20.

[0076] Furthermore, the power converter 10 may include elements and circuits other than those exemplified in the above embodiment. Examples of additional circuits include a backup power supply circuit, a protection circuit, and a boost circuit.

[0077] In the above embodiment, the three-phase AC power supply PS connected to the three external input terminals is not limited to a three-phase three-wire system, but may also be a three-phase four-wire system or a delta-connected three-phase three-wire system. The configuration of the power converter 10 may be appropriately changed to correspond to the type of three-phase AC power supply PS.

[0078] The input-side low-pass filter 20 in the above embodiment may include a plurality of capacitors connected between the wiring of each phase to which the first voltage VA, the second voltage VB, and the third voltage VC are input.

[0079] The switching elements constituting each bidirectional switch TSW are not limited to the examples of the embodiments described above. For example, the two switching elements of the bidirectional switch TSW may be P-channel type MOSFETs. In this case, the drain terminals of the two switching elements of the bidirectional switch TSW are connected to each other.

[0080] In the above embodiment, the two switching elements of the bidirectional switch TSW may be transistors capable of conducting current in both the forward and reverse directions. In this case, the two switching elements are connected in series such that their source terminals are connected to each other. Specifically, the switching elements are gallium nitride high electron mobility transistors (GaN-HEMT), etc.

[0081] - The transformer circuit 40 in the above embodiment does not necessarily have to include the fourth inductor L4. In this case, the leakage inductance of the transformer 41 can be used for resonance instead of the fourth inductor L4.

[0082] The specific circuit configuration of the rectifier circuit 50 is not limited to the examples of the embodiments described above. For example, the rectifier circuit 50 may be a half-wave rectifier circuit or the like. Also, the elements constituting the rectifier circuit 50 do not have to be MOSFETs. For example, the rectifier circuit 50 may include a full-bridge circuit consisting of four diodes. Furthermore, the rectifier circuit 50 may be a so-called current doubler rectifier circuit. In this way, any circuit that can rectify and output the DC power flowing through the secondary winding 41B of the transformer 41 can be used as the rectifier circuit 50.

[0083] The power converter 10 may have a circuit configuration for outputting the power charged in the fifth capacitor C5 from the first external output terminal 12A. Specifically, for example, the power converter 10 may have a switch element connecting the first terminal of the fifth capacitor C5 and the first terminal of the fifth inductor L5. In this case, the control unit 100 only needs to turn on the switch element when the terminal voltage of the fifth capacitor C5 exceeds a predetermined value.

[0084] - The power detection circuit SE in the above embodiment may detect the voltage and current values ​​at the first input terminals 31A to the third input terminals 31C of the power conversion circuit 30, rather than the voltage and current values ​​at the first external input terminals 11A to the third external input terminals 11C. Alternatively, the power detection circuit SE may detect the voltage and current values ​​at any of the first external input terminals 11A to the third external input terminals 11C. For example, if the power detection circuit SE detects only the voltage and current values ​​at the second external input terminal 11B, the voltage value at the second external input terminal 11B may be set as the "first voltage VA" and the start control of the above embodiment may be executed.

[0085] A separate control unit from the control unit 100 may control the on / off state of each switch element in the rectifier circuit 50. In other words, the control unit for the power conversion circuit 30 and the control unit for the rectifier circuit 50 may be configured as separate chips.

[0086] The control unit 100 may autonomously start driving the power conversion circuit 30 without relying on the start request signal SS. For example, the control unit 100 may start driving the power conversion circuit 30 without requiring the start request signal SS when the elapsed time since the power conversion circuit 30 stopped reaches a predetermined time, or when a predetermined time has arrived. Furthermore, the start control of the power conversion circuit 30 in the above embodiment can also be applied when starting the power conversion circuit 30 in this manner.

[0087] The control unit 100 may start switching the multiple bidirectional switches TSW on and off according to the switching sequence, but only within a narrower range of the phase range in the above embodiment. For example, the control unit 100 may start switching the multiple bidirectional switches TSW on and off when the phase of the AC voltage is within ±3° or ±1° of the phase of the AC voltage at which the product of the absolute value of the primary voltage Vp and time T is minimized. Specifically, the range of ±1° of the phase of the AC voltage at which the product of the absolute value of the primary voltage Vp and time T is minimized is 0±1°, 30±1°, -30±1°, 60±1°, -60±1°, 90±1°, -90±1°, 120±1°, -120±1°, 150±1°, -150±1°, and 180±1°. As described above, although the phase difference between the first voltage VA to the third voltage VC is 120° from each other, errors may occur in the phase of each voltage. Therefore, considering the errors, a range of ±1° from the phase of the AC voltage that is at its minimum value can be considered to be approximately the same as the phase of the AC voltage at which the product of the absolute value of the primary voltage Vp and time T is at its minimum value. According to this modified example, the control unit 100 starts switching the bidirectional switch TSW on and off when the product of the absolute value of the primary voltage Vp and time T is approximately at its minimum value, in other words, when the current flowing through the fourth inductor L4 is approximately at its minimum value. Therefore, when power conversion is started in the power conversion circuit 30, the load on the switching elements constituting the rectifier circuit 50 can be minimized.

[0088] The control unit 100 does not necessarily have to start driving the power conversion circuit 30 within the phase range of the AC voltage exemplified in the above embodiment. For example, depending on the type of switching pattern when the power conversion circuit 30 is performing power conversion, the length of time T for which the primary voltage Vp is applied to each switch element, the product of the absolute value of the primary voltage Vp and time T may not necessarily take a minimum value when the phase of the AC voltage is 0° or 30°. Even in this case, the control unit 100 only needs to start switching the bidirectional switch TSW on and off when the phase of the AC voltage is within ±5° of the phase in which the product of the absolute value of the primary voltage Vp and time T takes a minimum value, or within ±1° of that phase.

[0089] 30...Power conversion circuit 31A...First input terminal 31B...Second input terminal 31C...Third input terminal 32A...First output terminal 32B...Second output terminal TSW...Bidirectional switch 41...Transformer 41A...Primary winding 41B...Secondary winding 50...Rectifier circuit 50A...High potential output terminal 50B...Low potential output terminal 55...Diode C5...Fifth capacitor 100...Control unit

Claims

1. A power conversion circuit capable of converting three-phase AC power, having first input terminals, second input terminals, and third input terminals to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control unit capable of switching the on and off of the plurality of bidirectional switches, wherein the AC voltage input to the first input terminal is defined as the first voltage, and the phase of the AC voltage at which the first voltage is maximum is defined as 0°, the control unit, A power conversion device that, when converting three-phase AC power in the power conversion circuit, switches on and off a plurality of the bidirectional switches according to a predetermined switching sequence, and when starting power conversion in the power conversion circuit, starts switching on and off a plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within any of the following ranges: 0±5°, 30±5°, -30±5°, 60±5°, -60±5°, 90±5°, -90±5°, 120±5°, -120±5°, 150±5°, -150±5°, and 180±5°.

2. The power conversion device according to claim 1, wherein when the control unit starts power conversion in the power conversion circuit, it starts switching the on / off state of a plurality of bidirectional switches according to the switching sequence when the phase of the AC voltage is within any of the following ranges: 0±1°, 30±1°, -30±1°, 60±1°, -60±1°, 90±1°, -90±1°, 120±1°, -120±1°, 150±1°, -150±1°, and 180±1°.

3. A power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltage is applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control unit capable of switching the on and off of the plurality of bidirectional switches, wherein when the power conversion circuit converts power, the control unit switches the on and off of the plurality of bidirectional switches according to a predetermined switching sequence. A power conversion device that, when starting power conversion in the power conversion circuit, starts switching on and off a plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within ±5° of the phase of the AC voltage at which the product of the absolute value of the applied voltage applied to the transformer and the time for which the applied voltage is applied is the minimum value.

4. Applicable to a power conversion device comprising: a power conversion circuit capable of converting three-phase AC power, having a first input terminal, a second input terminal, and a third input terminal to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, with the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control unit capable of switching the on and off of the plurality of bidirectional switches, wherein the AC voltage input to the first input terminal is defined as the first voltage, and the phase of the AC voltage at which the first voltage is maximum is defined as 0°, the control unit, A program for a power conversion device that, when converting three-phase AC power in the power conversion circuit, performs the process of switching on and off a plurality of the bidirectional switches according to a predetermined switching sequence, and when starting power conversion in the power conversion circuit, performs the process of starting to switch on and off a plurality of the bidirectional switches according to the switching sequence when the phase of the AC voltage is within one of the following ranges: 0±5°, 30±5°, -30±5°, 60±5°, -60±5°, 90±5°, -90±5°, 120±5°, -120±5°, 150±5°, -150±5°, and 180±5°.

5. Applicable to a power conversion device comprising: a power conversion circuit capable of converting three-phase AC power, having first input terminals, second input terminals, and third input terminals to which AC voltages are applied with a phase difference of 120°, a plurality of bidirectional switches, a first output terminal, and a second output terminal; a transformer having a primary winding and a secondary winding, with the first end of the primary winding connected to the first output terminal and the second end of the primary winding connected to the second output terminal; a rectifier circuit having a high-potential output terminal and a low-potential output terminal, capable of rectifying the current flowing through the secondary winding and outputting it from the high-potential output terminal and the low-potential output terminal; a capacitor with its first end connected to the high-potential output terminal and its second end connected to the low-potential output terminal; and a control unit capable of switching the on and off of the plurality of bidirectional switches, wherein the control unit performs a process of switching the on and off of the plurality of bidirectional switches according to a predetermined switching sequence when converting power in the power conversion circuit. A program for a power converter that, when starting power conversion in the power conversion circuit, causes the power converter to start switching on and off a plurality of bidirectional switches according to the switching sequence when the phase of the AC voltage is within ±5° of the phase of the AC voltage at which the product of the absolute value of the applied voltage applied to the transformer and the time for which the applied voltage is applied is the minimum value.

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