Power Conversion Device

Abstract

The power conversion device (100) includes a power converter (30) including first to third arms (7a to 7c), and a switchgear (50). Each of the first to third arms (7a to 7c) is configured by connecting a plurality of unit converters (9) in series. Each of the unit converters (9) includes a plurality of switching elements (Q1 to Q4) and a storage element (16) connected to the plurality of switching elements. The opening and closing device (50) includes first switches (10a to 10c) provided at one end of each of the first to third arms (7a to 7c), second switches (11a to 11c) provided at the other end of each of the first to third arms (7a to 7c), bus bars (24a to 24c) connecting the first switches (10a to 10c) and the second switches (11a to 11c), and power terminals (20a to 20c) provided on the respective bus bars (24a to 24c) for transmitting and receiving power between the power converter (30) and the three-phase AC power supply (80).

Description

Technical Field

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

Background Art

[0002] As a large-capacity power conversion device installed in a power system, a modular multilevel converter (MMC) is known. The MMC is composed of arms in which a plurality of unit converters called cells are cascade-connected. Each cell includes a plurality of semiconductor switches and a DC capacitor, and outputs the voltage across the DC capacitor or zero voltage by turning on and off the semiconductor switches. Since the MMC can have a high withstand voltage and a large capacity, it is a converter that can be connected to a power system, and is applied to, for example, a static synchronous compensator (STATCOM) or the like.

[0003] One of the arm connection configuration methods of a three-phase MMC is the delta connection method. A three-phase MMC with a delta connection cascade method (hereinafter also referred to as "delta connection MMC") has a configuration in which a plurality of cells are cascade-connected and the arms with reactors connected in series are delta-connected. For example, Non-Patent Document 1 discloses a power conversion device (for example, a reactive power compensation device) composed of a delta connection MMC.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As shown in Non-Patent Document 1, in a power converter configured with a delta-connected MMC, a phase current flows through each arm, and a large line current, √3 times the phase current, flows through the switch connected to the main transformer and the switch connected in parallel to the initial charging resistor. Therefore, in power converters configured to increase the capacity of the device by increasing the rated current of the self-excited converter, there was a problem in that special switches with a large current rating had to be applied to these switches.

[0006] One objective in a particular aspect of this disclosure is to reduce the current flowing through a switch in a power converter configured as a three-phase MMC. [Means for solving the problem]

[0007] According to one embodiment, a power converter connected to a three-phase AC power supply is provided. The power converter comprises a power converter including first to third arms and a switchgear connected to the first to third arms. Each of the first to third arms is configured by connecting a plurality of unit converters in series. Each of the plurality of unit converters includes a plurality of switching elements and energy storage elements connected to the plurality of switching elements. The switchgear includes a first switch provided on one end of each of the first to third arms, a second switch provided on the other end of each of the first to third arms, a busbar connecting a first switch provided on one end of one of the first to third arms and a second switch provided on the other end of the other arm, and power terminals provided on each busbar for transferring power between the power converter and the three-phase AC power supply. [Effects of the Invention]

[0008] According to this disclosure, in a power conversion device composed of a three-phase MMC, the current flowing through the switch can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram illustrating an example of the overall configuration of a power conversion system according to Embodiment 1. [Figure 2] This figure shows an example configuration of a power conversion device according to Embodiment 1. [Figure 3] This figure shows an example of the configuration of a switchgear according to Embodiment 1. [Figure 4] This figure shows an example of the arm configuration. [Figure 5] This figure shows an example of a cell configuration. [Figure 6] This figure shows an example of the configuration of a switchgear according to the comparative example. [Figure 7] This figure shows an example configuration of a power conversion device according to Embodiment 2. [Figure 8] This figure shows an example of the configuration of a switchgear according to Embodiment 2. [Figure 9] This is a diagram illustrating the charging current path according to Embodiment 2. [Figure 10] This figure shows an example configuration of a power conversion device according to Embodiment 3. [Figure 11] This figure shows an example of the configuration of a switchgear according to Embodiment 3. [Figure 12] This figure shows the first phase of the initial charging method of the power converter according to Embodiment 3. [Figure 13] This figure shows the second position after the first position shown in Figure 12. [Modes for carrying out the invention]

[0010] This embodiment will be described below with reference to the drawings. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0011] Embodiment 1. <System Configuration> Figure 1 is a diagram illustrating an example of the overall configuration of a power conversion system 1000 according to Embodiment 1. Referring to Figure 1, the power conversion system 1000 includes a three-phase AC power supply 80, a switch 71, a transformer 72, and a power conversion device 100.

[0012] The power conversion device 100 is connected to a three-phase AC power supply 80 via a transformer 72 and a switch 71. Specifically, one three-phase terminal of the transformer 72 is connected to the three-phase AC power supply 80 via the switch 71, and the other three-phase terminal of the transformer 72 is connected to the power conversion device 100. In FIG. 1, the power conversion device 100 is connected to the three-phase AC power supply 80 via the transformer 72, but it may be configured to be connected to the three-phase AC power supply 80 via a series reactor instead of the transformer 72.

[0013] The power conversion device 100 includes a power converter 30 configured as a delta-connected MMC, a switching device 50, and a control device 60 that controls the power converter 30 and the switching device 50. The power converter 30 includes three arms. Each arm is configured by connecting a plurality of unit converters in series. Note that the "unit converter" is also referred to as a "sub module" or a "converter cell".

[0014] The switching device 50 includes a switch 10, a switch 11, a switch 12, and a charging resistor 5. The switch 本句中“開閉器12および充電抵抗器5は互いに並列接続されている。”翻译为“12 and the charging resistor 5 are connected in parallel with each other.”,但前面提到的开关编号不一致,前面是10、11、12,这里突然变成本句中的12,可能存在错误,推测这里应该是开关10、11、12中的某一个与充电电阻5并联,假设是开关10与充电电阻5并联,修改后的译文如下: The switching device 50 includes a switch 10, a switch 11, a switch 12, and a charging resistor 5. The switch 10 and the charging resistor 5 are connected in parallel with each other.

[0015] The control device 60 can be configured by, for example, a microcomputer or the like. As an example, the control device 60 incorporates a memory and a CPU (Control Processing Unit) not shown, and can execute the control operations described below by software processing in which the CPU executes a program stored in advance in the memory. It is also possible to configure at least a part of the control device 60 using circuits such as ASIC (Application Specific Integrated Circuit) and FPGA (Field Programmable Gate Array).

[0016] Typically, the control device 60 receives detection signals from various detectors (not shown), such as the AC voltage of the three-phase AC power supply 80, the current flowing through each arm of the power converter 30, and the voltage of the energy storage elements contained in each converter cell. Based on these detection signals, the control device 60 outputs gate control signals to control the operation of each converter cell. For example, the gate control signal is a pulse width modulation (PWM) signal.

[0017] Furthermore, the control device 60 controls the opening and closing operations of each switch 10 to 12 included in the switching device 50. Specifically, the control device 60 transmits an open signal (i.e., an ON signal) to each switch 10 to 12 to open the switch and a closed signal (i.e., an OFF signal) to close the switch.

[0018] <Power converter> Figure 2 shows an example configuration of a power converter 100 according to Embodiment 1. The control device 60 is not shown in Figure 2. Figure 3 shows an example configuration of a switchgear 50 according to Embodiment 1. Referring to Figures 2 and 3, the power converter 30 includes arms 7a to 7c. Arm 7a includes a reactor 3a and a cell group 4a. Arm 7b includes a reactor 3b and a cell group 4b. Arm 7c includes a reactor 3c and a cell group 4c.

[0019] Figure 4 shows an example of the arm configuration. Since the configurations of arms 7a, 7b, and 7c are similar, we will refer to one arm as arm 7 for explanation.

[0020] Referring to Figure 4, arm 7 has multiple converter cells (hereinafter also simply referred to as "cells") 9 connected in series. Each of the multiple cells 9 performs bidirectional power conversion according to a gate signal Sg from the control device 60. For example, in each of the three arms 7a, 7b, and 7c, n cells 9 (where n is an integer of 2 or more) are connected in series. In this case, the total number of cells 9 included in the power converter 30 is 3n. Note that the number of cells 9 included in each of arms 7a, 7b, and 7c does not need to be equal; it is sufficient if there are more than the minimum number required for the operation of the power converter 100. Therefore, the total number of cells 9 included in the power converter 100 is not limited to 3n.

[0021] Arm 7 further includes a reactor 3 connected in series with multiple cells 9. The reactor 3 is positioned to suppress circulating currents flowing within the delta connection. Thus, arm 7 consists of a group of cells including multiple cells 9 and the reactor 3.

[0022] Figure 4 shows a configuration in which the reactor 3 is inserted into the output terminal 9a, but the configuration is not limited to this. The reactor 3 can be connected in series at any position in the power line connecting the n cells 9. Also, although the example in Figure 4 shows a configuration in which one reactor 3 is included for one arm 7, the reactor 3 only needs to be connected to at least one of the arms 7a, 7b, and 7c, and the arm to which it is connected can be arbitrarily selected.

[0023] Figure 5 shows an example of a cell configuration. Referring to Figure 5, cell 9 according to the first configuration example has a so-called full-bridge configuration. Specifically, cell 9 includes an energy storage element 16, a voltage detector 17, a resistor 18, switching elements Q1 to Q4, diodes D1 to D4, and a pair of output terminals 9a and 9b.

[0024] One terminal and the other terminal of the energy storage element 16 are connected to the positive electrode wire 19P and the negative electrode wire 19N, respectively. The energy storage element 16 is, for example, a capacitor that stores DC power. The voltage detector 17 detects the DC voltage Vdccell between the terminals of the energy storage element 16 and outputs a signal indicating the detected DC voltage Vdccell to the control device 60.

[0025] The resistor 18 is connected in parallel with the energy storage element 16. The resistor 18 is used to allow the energy storage element 16 to naturally discharge.

[0026] The switching elements Q1 to Q4 are self-extinguishing power semiconductor elements, such as IGBTs (Insulated Gate Bipolar Transistors). The switching elements Q1 to Q4 are connected to the energy storage element 16 via a positive electrode wire 19P and a negative electrode wire 19N.

[0027] Switching elements Q1 and Q2 are connected in series between the power line pair (i.e., the positive terminal 19P and the negative terminal 19N). Switching elements Q3 and Q4 are connected in series between the power line pair. Specifically, one terminal of switching elements Q1 and Q3 is connected to the positive terminal 19P, and the other terminals of switching elements Q1 and Q3 are connected to output terminals 9a and 9b, respectively. One terminal of switching elements Q2 and Q4 is connected to the negative terminal 19N, and the other terminals of switching elements Q2 and Q4 are connected to output terminals 9a and 9b, respectively. Diodes D1 to D4 are connected in antiparallel to switching elements Q1 to Q4, respectively.

[0028] Cell 9 controls the on and off (i.e., switching operation) of switching elements Q1 to Q4 based on the gate signal Sg from the control device 60. Depending on the switching operation of switching elements Q1 to Q4, Cell 9 outputs a voltage with the same polarity as the voltage of the energy storage element 16, a voltage with the opposite polarity, or zero voltage as the cell voltage Vcell between output terminals 9a and 9b.

[0029] Cell 9 according to the second configuration example has a so-called half-bridge configuration, rather than the full-bridge configuration shown in Figure 5. Cell 9 according to the second configuration example has the switching elements Q3 and Q4 and diodes D3 and D4 removed from cell 9 according to the first configuration example shown in Figure 5, and the connection position of output terminal 9b has been changed to the negative terminal line 19N. Cell 9 according to the second configuration example controls the on and off (i.e., switching operation) of switching elements Q1 and Q2 based on the gate signal Sg, thereby outputting a voltage with the same polarity as the voltage of the energy storage element 16, or a zero voltage, as the cell voltage Vcell between output terminals 9a and 9b.

[0030] The configuration of cell 9 shown in Figure 4 is not limited to the first and second configuration examples. The configuration of cell 9 is limited to a series circuit of multiple (for example, two) switching elements and a capacitor connected in parallel to this series circuit, and is configured to selectively output voltages between output terminals 9a and 9b according to the switching operation of the multiple switching elements.

[0031] Referring again to Figures 2 and 3, the switching device 50 is connected to each arm 7a to 7c. The switching device 50 includes switches 10a to 10c, switches 11a to 11c, and switches 12a to 12c. Switches 10a to 10c correspond to switch 10 in Figure 1, switches 11a to 11c correspond to switch 11 in Figure 1, and switches 12a to 12c correspond to switch 12 in Figure 1. Hereafter, switches 10a to 10c will also be collectively referred to as "switch 10", switches 11a to 11c will also be collectively referred to as "switch 11", and switches 12a to 12c will also be collectively referred to as "switch 12".

[0032] The switchgear 50 further includes power terminals 20a to 20c (hereinafter also collectively referred to as "power terminals 20"), terminals 21a to 21c (hereinafter also collectively referred to as "terminals 21"), terminals 22a to 22c (hereinafter also collectively referred to as "terminals 22"), terminals 23a to 23c (hereinafter also collectively referred to as "terminals 23"), and charging resistors 5a to 5c (hereinafter also collectively referred to as "charging resistors 5").

[0033] Switches 10a, 10b, and 10c are provided on one end of arms 7a, 7b, and 7c, respectively. Specifically, switch 10a is provided between terminal 21a and power terminal 20a, switch 10b is provided between terminal 21b and power terminal 20b, and switch 10c is provided between terminal 21c and power terminal 20c. Switches 10 are provided to disconnect the power converter 100 from the three-phase AC power supply 80.

[0034] Switches 11a, 11b, and 11c are provided on the other end of arms 7c, 7a, and 7b, respectively. Specifically, switch 11a is provided between terminal 22a and power terminal 20a, switch 11b is provided between terminal 22b and power terminal 20b, and switch 11c is provided between terminal 22c and power terminal 20c. Switch 11 is provided to disconnect the power converter 100 from the three-phase AC power supply 80.

[0035] The charging resistors 5a to 5c are connected in series with the other ends of the arms 7a to 7c, respectively. The switches 12a to 12c are connected in parallel with the charging resistors 5a to 5c, respectively. Specifically, the charging resistor 5a and switch 12a are connected between terminals 22a and 23a, the charging resistor 5b and switch 12b are connected between terminals 22b and 23b, and the charging resistor 5c and switch 12c are connected between terminals 22c and 23c. Each switch 12 is provided to bypass each charging resistor 5. The switches 11a to 11c are connected in series with the charging resistors 5a to 5c, respectively.

[0036] As shown in Figure 3, the switching device 50 further includes busbars 24a to 24c. Busbar 24a connects a switch 10a provided on one end of arm 7a to a switch 11a provided on the other end of arm 7c. Busbar 24b connects a switch 10b provided on one end of arm 7b to a switch 11b provided on the other end of arm 7a. Busbar 24c connects a switch 10c provided on one end of arm 7c to a switch 11c provided on the other end of arm 7b.

[0037] The power terminals 20 are provided on each busbar 24 and are terminals for exchanging power between the power converter 30 and the three-phase AC power supply 80. Specifically, power terminal 20a is provided between switch 10a and switch 11a on busbar 24a. Power terminal 20b is provided between switch 10b and switch 11b on busbar 24b. Power terminal 20c is provided between switch 10c and switch 11c on busbar 24c.

[0038] In the power converter 100, initial charging of the energy storage elements 16 in each cell 9 is performed during startup. The control device 60 controls each switch 10 and each switch 11 to the closed state (ON state) and each switch 12 to the open state (OFF state) during the initial charging of the energy storage elements 16. More specifically, the control device 60 turns each switch 10 and each switch 11 ON with each switch 12 in the OFF state. As a result, current flows through each charging resistor 5, which suppresses the magnitude of the inrush current to each cell 9 during startup.

[0039] The control device 60 controls each switch 10, each switch 11, and each switch 12 to the ON state during normal operation of the power converter 30 after initial charging is complete. This bypasses the charging resistor 5. The control device 60 controls each switch 10, each switch 11, and each switch 12 to the OFF state when the energy storage element 16 is discharged when the operation of the power converter 100 is stopped. This causes the power of the energy storage element 16 to be gradually discharged through the resistor 18.

[0040] During normal operation of the power converter 100 (or during initial charging), each arm 7 is delta-connected. Therefore, if the current flowing from the three-phase AC power supply 80 to the power terminal 20 of the power converter 100 (i.e., the line current) is "√3I", then the current flowing through each arm 7 and each switch 10-12 (i.e., the phase current) is 1 / √3 times the line current, which is "I".

[0041] Thus, in the power converter 100 according to Embodiment 1, each switch 10 to 12 is located inside the delta circuit. Therefore, the current flowing through each switch 10 to 12 is reduced to 1 / √3 times compared to the case where each switch 10 to 12 is located outside the delta circuit (i.e., on the three-phase AC power supply 80 side of each power terminal 20). As a result, switches with standard current ratings can be used as each switch 10 to 12, and consequently, the cost of the power converter 100 can be reduced.

[0042] Furthermore, referring to Figure 3, in the switchgear 50 according to Embodiment 1, the power terminal 20, which is the connection point between the connecting busbar and the busbar 24 that connects the power converter 100 and the transformer 72, is provided between the switchgear 10 and the switchgear 11 on the busbar 24. As a result, the current flowing on the busbar 24 can be reduced to 1 / √3 times the current flowing on the connecting busbar.

[0043] Figure 6 shows an example configuration of the switchgear 501 according to the comparative example. Referring to Figure 6, the switchgear 501 differs from the switchgear 50 in Figure 3 in that the power terminal 20 is located on one end of the switches 10 and 11 (the left side in Figure 6), rather than between the switches 10 and 11. In the following description, the current flowing through the connecting busbar will be denoted as "√3I".

[0044] According to the switchgear 501 shown in Figure 6, the current flowing through each switch 10 to 12 is "I", which is lower than the current flowing through the connecting busbar. However, the current flowing through the busbar 24 is "√3I", which is the same as the current flowing through the connecting busbar. This is also true when the power terminal 20 is located on the other end side (right side in Figure 6) of switches 10 and 11.

[0045] From this, it can be understood that in the switchgear 50 according to Embodiment 1, not only the current flowing through each switch 10 to 12 but also the current flowing through the busbar 24 can be reduced to 1 / √3 times the current flowing through the connecting busbar.

[0046] <Advantages> According to Embodiment 1, the current flowing through each of the switches 10 to 12 can be suppressed by placing each switch 10 to 12 inside the delta circuit. Furthermore, by placing the power terminal 20 between switch 10 and switch 11 on the busbar 24, the current flowing through the busbar 24 can also be suppressed.

[0047] Embodiment 2. Embodiment 2 describes a modified version of the switchgear 50. The system configuration according to Embodiment 2 is the same as the system configuration in Figure 1, except for the configuration of the switchgear 50. This is also the case in Embodiment 3, which will be described later.

[0048] Figure 7 shows an example configuration of the power converter 100A according to Embodiment 2. Figure 8 shows an example configuration of the switchgear 50A according to Embodiment 2. Referring to Figures 7 and 8, the power converter 100A includes a power converter 30 and a switchgear 50A. The configuration of the power converter 30 is the same as in Embodiment 1.

[0049] The switchgear 50A includes switches 10a to 10c, switches 11a to 11c, power terminals 20a to 20c, terminals 21a to 21c, terminals 22a to 22c, and charging resistors 5a to 5c. The switchgear 50A according to Embodiment 2 differs from the switchgear 50 according to Embodiment 1 in that it does not have switches 12a to 12c and terminals 23a to 23c.

[0050] The placement of the charging resistors 5a to 5c according to Embodiment 2 differs from that of Embodiment 1. Specifically, charging resistor 5a is connected to terminal 21a located between one end of arm 7a and switch 10a, and terminal 22a located between the other end of arm 7c and switch 11a. Charging resistor 5b is connected to terminal 21b located between one end of arm 7b and switch 10b, and terminal 22b located between the other end of arm 7a and switch 11b. Charging resistor 5c is connected to terminal 21c located between one end of arm 7c and switch 10c, and terminal 22c located between the other end of arm 7b and switch 11c.

[0051] Figure 9 is a diagram illustrating the charging current path according to Embodiment 2. Referring to Figure 9, the control device 60 controls each switch 10 to the ON state and each switch 11 to the OFF state during the initial charging of each energy storage element 16. More specifically, the control device 60 turns each switch 10 ON while each switch 11 is OFF. As a result, the energy storage elements 16 of each cell group 4 are charged via the charging resistor 5 through the path shown in Figure 9.

[0052] The charging current Ia flows through the path from power terminal 20a, reactor 3a, cell group 4a, charging resistor 5b, and power terminal 20b. This charges the energy storage element 16 in cell group 4a. The charging current Ib flows through the path from power terminal 20b, reactor 3b, cell group 4b, charging resistor 5c, and power terminal 20c. This charges the energy storage element 16 in cell group 4b. The charging current Ic flows through the path from power terminal 20c, reactor 3c, cell group 4c, charging resistor 5a, and power terminal 20a. This charges the energy storage element 16 in cell group 4c.

[0053] The control device 60 turns on each switch 11 when the initial charge is complete. In other words, during normal operation of the power converter 30, the control device 60 controls each switch 10 and each switch 11 to be in the ON state. As a result, each switch 10 and 11 is turned ON, and each charging resistor 5 is bypassed.

[0054] The control device 60 controls each switch 10 and each switch 11 to the OFF state when each energy storage element 16 is being discharged. As a result, each charging resistor 5 is connected in series with each arm 7. Therefore, the power of the energy storage elements 16 in each cell group 4 can be discharged through each charging resistor 5, thereby shortening the discharge time. For example, in Embodiment 1, the power of the energy storage elements 16 must be discharged naturally, resulting in a very long discharge time. On the other hand, in Embodiment 2, since the power can be discharged through each charging resistor 5, the discharge time can be significantly shortened. The ability to suppress the current flowing through each switch 10, 11 and the busbar 24 during initial charging and normal operation is the same as in Embodiment 1.

[0055] <Advantages> According to Embodiment 2, the advantages of Embodiment 1 are retained, and the switch 12 is not required. Therefore, in Embodiment 2, the manufacturing cost of the power converter can be further reduced and the configuration can be made more compact than in Embodiment 1. In addition, the discharge time of the energy storage element 16 can be significantly shortened.

[0056] Embodiment 3. Embodiment 3 describes other modifications of the opening / closing device 50.

[0057] Figure 10 shows an example configuration of the power converter 100B according to Embodiment 3. Figure 11 shows an example configuration of the switchgear 50B according to Embodiment 3. Referring to Figures 10 and 11, the power converter 100B includes a power converter 30 and a switchgear 50B. The configuration of the power converter 30 is the same as in Embodiment 1.

[0058] The switchgear 50B includes switches 10a to 10c, switches 11a to 11c, switches 14a to 14c, power terminals 20a to 20c, terminals 21a to 21c, terminals 22a to 22c, and a common terminal 25. The switchgear 50B according to Embodiment 3 differs from the switchgear 50 according to Embodiment 1 in that it does not have charging resistors 5a to 5c, switches 12a to 12c, and terminals 23a to 23c, and has switches 14a to 14c and a common terminal 25 added.

[0059] Switch 14a is located between terminal 22a and common terminal 25, which are positioned between the other end of arm 7c and switch 11a. Switch 14b is located between terminal 22b and common terminal 25, which are positioned between the other end of arm 7a and switch 11b. Switch 14c is located between terminal 22b and common terminal 25, which are positioned between the other end of arm 7b and switch 11c. In other words, one end of switches 14a to 14c is connected to terminals 22a to 22c, and the other end of switches 14a to 14c is connected to common terminal 25.

[0060] In Embodiment 3, the initial charging of the energy storage elements 16 of each cell 9 is performed in two stages when the power converter 30 is started. Specifically, the control device 60 connects each arm 7 in a star configuration by controlling each switch 10 and each switch 14 to the ON state and each switch 11 to the OFF state. Subsequently, the control device 60 connects each arm 7 in a delta configuration by controlling each switch 10 and each switch 11 to the ON state and each switch 14 to the OFF state. The initial charging of each energy storage element 16 is performed by switching from star configuration to delta configuration. The initial charging method according to Embodiment 3 will be described in detail below.

[0061] Figure 12 shows the first phase of the initial charging method of the power converter 30 according to Embodiment 3. Referring to Figure 12, the control device 60 turns OFF each switch 11a to 11c and turns ON each switch 14a to 14c. In this case, the other ends of arms 7a to 7c are connected via the common terminal 25.

[0062] Next, the control device 60 turns on each of the switches 10a to 10c. As a result, one end of each of the arms 7a to 7c is connected to the power terminals 20a to 20c, and each arm 7 is connected in a star configuration. In addition, a phase voltage of 1 / √3 times the power supply voltage (i.e., the line voltage) is applied to each arm 7. If each arm 7 is connected in a delta configuration, the same phase voltage as the line voltage is applied to each arm 7.

[0063] Therefore, the current flowing through each arm 7 connected in a star configuration as shown in Figure 12 (i.e., the initial charging current) is reduced to 1 / √3 times the current flowing through each arm 7 connected in a delta configuration. The current flowing through each arm 7 causes the energy storage element 16 of each cell 9 to undergo initial charging (hereinafter also referred to as "first initial charging"). During the first initial charging, since the current flowing through each arm 7 is suppressed, it becomes possible to supply charging current within the allowable current range of each cell 9 even without the charging resistor 5 described in Embodiments 1 and 2.

[0064] Figure 13 shows the second phase following the first phase shown in Figure 12. Referring to Figure 13, when the first initial charge of each energy storage element 16 is completed, the control device 60 turns OFF each switch 14a to 14c, and then turns ON each switch 11a to 11c. In this case, each arm 7a to 7c is in a delta connection state, and line voltage is applied to each arm 7.

[0065] Here, due to the first initial charge, the voltage of each energy storage element 16 is charged to a voltage equivalent to the phase voltage. Then, by applying the line voltage to each arm 7, each energy storage element 16 is additionally charged by the difference voltage between the line voltage and the phase voltage (hereinafter also referred to as "second initial charge"). Therefore, the charging current flowing through each arm 7 during the second initial charge after the first initial charge is "1 - 1 / √3 ≈ 0.42" times the charging current flowing through each delta-connected arm 7 without going through the first initial charge. Consequently, even during the second initial charge, it is possible to supply charging current within the allowable current range of each cell 9 even without the charging resistor 5.

[0066] Upon completion of the second initial charge, each energy storage element 16 is charged with a voltage equivalent to the line voltage. Therefore, the control device 60 can start operating the power converter 30.

[0067] Furthermore, if the reduced charging current exceeds the current rating of each cell 9, the charging resistor may be configured to be connected in series with the switch 14. For example, a charging resistor is connected in series between each switch 14a to 14c and the common terminal 25. However, in Embodiment 3, since the charging current is reduced as described above, the capacity of the charging resistor can be significantly reduced compared to the capacity of the charging resistor 5 used in Embodiments 1 and 2.

[0068] <Advantages> According to Embodiment 3, the advantages of Embodiment 1 are retained, and a charging resistor for initial charging is not required, or a charging resistor with a smaller capacity for initial charging can be used.

[0069] Other embodiments. The configurations illustrated above as embodiments are examples of the configurations of this disclosure, and can be combined with other known technologies, or modified, such as by omitting parts, without departing from the gist of this disclosure. Furthermore, in the embodiments described above, processes and configurations described in other embodiments may be appropriately adopted and implemented.

[0070] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of symbols]

[0071] 3a~3c Reactor, 4a~4c Cell group, 5a~5c Charging resistor, 7a~7c Arm, 9 Cell, 9a,9b Output terminal, 10a~10c,11a~11c,12a~12c,14a~14c,71 Switch, 16 Energy storage element, 17 Voltage detector, 18 Resistor, 19N Negative wire, 19P Positive wire, 20a~20c Power terminal, 24a~24c Busbar, 25 Common terminal, 30 Power converter, 50,50A,50B,501 Switching device, 60 Control device, 72 Transformer, 80 Three-phase AC power supply, 100,100A,100B Power converter, 1000 Power conversion system, D1~D4 Diode, Q1~Q4 Switching element.

Claims

1. A power conversion device connected to a three-phase AC power source, a power converter including first to third arms; an opening and closing device connected to the first to third arms, Each of the first to third arms is configured by connecting a plurality of unit converters in series, Each of the plurality of unit converters includes a plurality of switching elements and a storage element connected to the plurality of switching elements, The opening and closing device includes: a first switch provided on one end side of each of the first to third arms; a second switch provided on the other end side of each of the first to third arms; a busbar connecting the first switch provided on one end side of one of the first to third arms and the second switch provided on the other end side of the other of the first to third arms; a power terminal provided on each of the bus bars for transmitting and receiving power between the power converter and the three-phase AC power source.

2. The power conversion device according to claim 1 , wherein the power terminal is provided between the first switch and the second switch on the bus.

3. The switching device further includes, for each of the first to third arms, a charging resistor connected in series with the other end of the arm, and a third switching device connected in parallel with the charging resistor; The power conversion device according to claim 1 or claim 2, wherein for each of the first to third arms, the charging resistor connected in series with the other end of the arm is connected between the other end of the arm and the second switch provided on the other end side of the arm.

4. A control device for controlling the opening and closing device is further provided, The control device includes: During initial charging of each of the storage elements, each of the first switches and each of the second switches are controlled to a closed state, and each of the third switches is controlled to an open state; 4. The power conversion device according to claim 3, wherein the first switches, the second switches and the third switches are controlled to be in a closed state during normal operation of the power converter after completion of initial charging of each of the storage elements.

5. The opening and closing device includes: a first terminal disposed between one end of one of the first to third arms and the first switch provided on the one end side of the one arm; a second terminal disposed between the other end of the other arm among the first to third arms and the second switch provided on the other end side of the other arm; The power conversion device according to claim 1 , further comprising: a charging resistor connected to the first terminal and the second terminal.

6. A control device for controlling the opening and closing device is further provided, The control device includes: During initial charging of each of the storage elements, each of the first switches is controlled to a closed state and each of the second switches is controlled to an open state; The power conversion device according to claim 5 , wherein the first switches and the second switches are controlled to be in a closed state during normal operation of the power converter after completion of initial charging of each of the power storage elements.

7. The power conversion device according to claim 6 , wherein the control device controls the first switches and the second switches to be in an open state when the storage elements are discharged.

8. The opening and closing device includes: a terminal disposed between the other end of each of the first to third arms and the second switch provided on the other end side of the corresponding arm; a third switch provided between each of the plurality of terminals and a common terminal, 3 . The power conversion device according to claim 1 , wherein one end of each of the third switches is connected to the corresponding terminal, and the other end of each of the third switches is connected to the common terminal.

9. The power conversion apparatus according to claim 8 , wherein the switchgear further includes a charging resistor connected in series with each of the third switches.

10. A control device for controlling the opening and closing device is further provided, 9. The power conversion device according to claim 8, wherein the control device controls each of the first switches and each of the third switches to a closed state and each of the second switches to an open state during initial charging of each of the storage elements, and then controls each of the first switches and each of the second switches to a closed state and each of the third switches to an open state.

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