Power Conversion Equipment

Abstract

The power converter (1) includes a power converter (2) including a plurality of converter cells (7) connected in series, and a control device (3). Each of the plurality of converter cells (7) includes a cell control unit (35), a first semiconductor circuit (25A) including a first switching element (22) and a first diode (23A), a second semiconductor circuit (25B) including a second switching element (22B) and a second diode (23A), a storage element (24) connected in parallel to a series body including the first semiconductor circuit (25A) and the second semiconductor circuit (25B) connected in series, and a thyristor (26) connected in parallel to the first semiconductor circuit (25A). When the cell control unit (35) detects an overcurrent flowing through the first semiconductor circuit (25A), it gate-blocks the first switching element (22A) and the second switching element (22B) and controls the thyristor (26) to an on state.

Description

[Technical field]

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

[0002] In recent years, modular multilevel converters (MMCs) have become known as high-voltage, large-capacity power conversion devices that are applied to high-voltage systems such as power grids. MMCs are composed of arms in which converter cells are cascaded. The converter cells include multiple semiconductor switches and capacitors, and output the voltage across the capacitor or zero voltage by turning the semiconductor switches on and off.

[0003] In an MMC that includes a half-bridge type converter cell, a method is known in which a thyristor is provided in the converter cell to prevent the reverse free-wheeling diode (FWD) from being destroyed by a short-circuit current flowing from the AC side when the DC line is short-circuited.

[0004] For example, Japanese Patent No. 5318774 (Patent Document 1) discloses a configuration in which a thyristor is connected in parallel to a reverse freewheel diode in order to protect the reverse freewheel diode from a short-circuit current when a short circuit occurs between DC voltage terminals. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5318774 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, a short circuit in a DC voltage circuit is detected by a voltage sensor or a current sensor in the DC voltage circuit and the AC terminal. Then, an evaluation unit coupled to such a sensor confirms a short circuit based on implemented logic and generates a signal to fire a thyristor. Meanwhile, the FWD, which is an element in a converter cell, needs to be protected from being destroyed by an overcurrent that occurs in the event of an accident other than a short circuit accident in the DC voltage circuit (e.g., an arm short circuit accident, a ground fault, etc.). However, Patent Document 1 does not teach or suggest any solution for achieving this protection.

[0007] An object in one aspect of the present disclosure is to provide a power conversion device capable of more appropriately protecting elements in a converter cell by detecting an overcurrent in the converter cell. [Means for solving the problem]

[0008] According to one embodiment, there is provided a power converter that performs power conversion between an AC circuit and a DC circuit. The power converter includes a power converter including a plurality of converter cells connected in series, and a control device that controls the power converter. Each of the plurality of converter cells includes a cell control unit, a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element, a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element, a storage element connected in parallel to a series body including the first and second semiconductor circuits connected in series, and a thyristor connected in parallel to the first semiconductor circuit. When the cell control unit detects an overcurrent flowing through the first semiconductor circuit, it gates-blocks the first and second switching elements and controls the thyristor to an on state.

[0009] According to another embodiment, there is provided a power converter that performs power conversion between an AC circuit and a DC circuit. The power converter includes a power converter including a plurality of converter cells connected in series, and a control device that controls the power converter. Each of the plurality of converter cells includes a cell control unit, a first switching circuit, and a second switching circuit. Each of the first switching circuit and the second switching circuit includes a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element, a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element, and a storage element connected in parallel to the series body including the first semiconductor circuit and the second semiconductor circuit connected in series. The positive electrode of the storage element is connected to the positive electrode of the second semiconductor circuit, and the negative electrode of the storage element is connected to the negative electrode of the first semiconductor circuit. Each of the converter cells further includes a third switching element provided between the positive electrode of the storage element in the first switching circuit and the negative electrode of the storage element in the second switching circuit, and a thyristor connected between the positive electrode of the first semiconductor circuit in the first switching circuit and the positive electrode of the first semiconductor circuit in the second switching circuit. When the cell control unit detects an overcurrent flowing through the third switching element, it gates the first switching element, the second switching element and the third switching element, and controls the thyristor to an on state. Effect of the Invention

[0010] According to the power conversion device according to the present disclosure, the elements in the converter cell can be more appropriately protected. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a power conversion device according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing a configuration of a converter cell according to the present embodiment; [Diagram 3] 2 is a block diagram showing an example of a hardware configuration of a control device according to the present embodiment. FIG. [Figure 4]FIG. 2 is a schematic configuration diagram showing a first modified example of a power conversion device according to the present embodiment. [Diagram 5] FIG. 13 is a diagram showing a modification of the switching circuit according to the present embodiment. [Figure 6] FIG. 11 is a schematic configuration diagram showing a second modified example of a power conversion device according to the present embodiment. [Figure 7] FIG. 13 is a diagram showing a modified example of a converter cell according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the present embodiment will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0013] <Configuration of power conversion device> Fig. 1 is a schematic configuration diagram of a power conversion device according to the present embodiment. With reference to Fig. 1, the power conversion device 1 includes a power converter 2 including a plurality of converter cells (corresponding to "cells" in Fig. 1) 7 connected in series with each other, and a control device 3 for controlling the power converter 2. A "converter cell" is also called a "submodule" or a "unit converter." The power conversion device 1 performs power conversion between a DC circuit 14 and an AC circuit 12.

[0014] The power converter 2 includes a plurality of leg circuits 4u, 4v, 4w (hereinafter, collectively referred to as "leg circuits 4" when referring to any one of them) connected in parallel between a positive DC terminal (i.e., a high potential side DC terminal) Np and a negative DC terminal (i.e., a low potential side DC terminal) Nn.

[0015] The leg circuit 4 is provided for each of the multiple phases constituting the AC. The leg circuit 4 is connected between the AC circuit 12 and the DC circuit 14, and performs power conversion between the two circuits. Fig. 1 shows a case where the AC circuit 12 is a three-phase AC system, and three leg circuits 4u, 4v, and 4w are provided corresponding to the U phase, V phase, and W phase, respectively.

[0016] The AC input terminals Nu, Nv, and Nw provided in the leg circuits 4u, 4v, and 4w, respectively, are connected to an AC circuit 12 via an interconnection transformer 13. The AC circuit 12 is, for example, an AC power system including an AC power source, etc. In order to facilitate illustration, the connection between the AC input terminals Nv, Nw and the interconnection transformer 13 is not shown in FIG.

[0017] The high potential side DC terminal Np and the low potential side DC terminal Nn, which are commonly connected to each leg circuit 4, are connected to a DC circuit 14. The DC circuit 14 is, for example, a DC power system including a DC transmission network or DC terminals of other power conversion devices. In the latter case, a BTB (Back To Back) system for connecting AC power systems having different rated frequencies, synchronization, etc. is configured by linking two power conversion devices.

[0018] Instead of using the interconnection transformer 13 in Fig. 1, the leg circuits 4u, 4v, 4w may be connected to the AC circuit 12 via an interconnection reactor. Furthermore, instead of the AC input terminals Nu, Nv, Nw, primary windings may be provided in the leg circuits 4u, 4v, 4w, respectively, and the leg circuits 4u, 4v, 4w may be connected to the interconnection transformer 13 or the interconnection reactor in an AC manner via secondary windings magnetically coupled to the primary windings. In this case, the primary windings may be reactors 8A, 8B described below. That is, the leg circuit 4 is electrically (i.e., DC or AC) connected to the AC circuit 12 via connecting parts provided in the leg circuits 4u, 4v, 4w, such as the AC input terminals Nu, Nv, Nw or the above-mentioned primary windings.

[0019] The leg circuit 4u includes an upper arm 5 from the high potential side DC terminal Np to the AC input terminal Nu, and a lower arm 6 from the low potential side DC terminal Nn to the AC input terminal Nu. The AC input terminal Nu, which is the connection point between the upper arm 5 and the lower arm 6, is connected to an interconnection transformer 13. The high potential side DC terminal Np and the low potential side DC terminal Nn are connected to a DC circuit 14. The leg circuits 4v and 4w have a similar configuration, so the leg circuit 4u will be described below as a representative example.

[0020] The upper arm 5 includes a plurality of cascaded converter cells 7 and a reactor 8A. The plurality of converter cells 7 and the reactor 8A are connected in series to each other. The lower arm 6 includes a plurality of cascaded converter cells 7 and a reactor 8B. The plurality of converter cells 7 and the reactor 8B are connected in series to each other.

[0021] The reactor 8A may be inserted at any position in the upper arm 5 of the leg circuit 4u, and the reactor 8B may be inserted at any position in the lower arm 6 of the leg circuit 4u. There may be a plurality of reactors 8A and a plurality of reactors 8B. The inductance values ​​of the reactors may be different from each other. Furthermore, only the reactor 8A in the upper arm 5 or only the reactor 8B in the lower arm 6 may be provided.

[0022] The power conversion device 1 includes an AC voltage detector 10, an AC current detector 16, DC voltage detectors 11A and 11B, and arm current detectors 9A and 9B provided in each leg circuit 4. These detectors measure electrical quantities (i.e., current, voltage) used to control the power conversion device 1. Detection signals detected by these detectors are input to the control device 3.

[0023] The control device 3 outputs an operation command for controlling the operating state of each converter cell based on these detection signals. The control device 3 receives, from each converter cell, a signal representing a detection value of the voltage of a capacitor provided in that converter cell.

[0024] The control device 3 may be configured by a dedicated circuit, or may be configured partially or entirely by a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a microprocessor, etc. The control device 3 may be configured by, for example, a digital protection relay device.

[0025] The AC voltage detector 10 detects the U-phase AC voltage Vacu, the V-phase AC voltage Vacv, and the W-phase AC voltage Vacw of the AC circuit 12. The AC current detector 16 detects the U-phase AC current Iacu, the V-phase AC current Iacv, and the W-phase AC current Iacw (hereinafter collectively referred to as "AC current Iac") of the AC circuit 12. The DC voltage detector 11A detects the DC voltage value Vdcp of the high potential side DC terminal Np connected to the DC circuit 14. The DC voltage detector 11B detects the DC voltage value Vdcn of the low potential side DC terminal Nn connected to the DC circuit 14.

[0026] The DC voltage Vdc of the DC circuit 14 is a DC voltage between the high potential side DC terminal Np and the low potential side DC terminal Nn, and is calculated from the DC voltage values ​​Vdcp and Vdcn detected by the DC voltage detectors 11A and 11B. Specifically, "Vdc=Vdcp-Vdcn."

[0027] The arm current detectors 9A and 9B provided in the U-phase leg circuit 4u detect the arm current Ipu flowing in the upper arm 5 and the arm current Inu flowing in the lower arm 6. The arm current detectors 9A and 9B provided in the V-phase leg circuit 4v detect the arm currents Ipv and Inv, respectively. The arm current detectors 9A and 9B provided in the W-phase leg circuit 4w detect the arm currents Ipw and Inw, respectively.

[0028] The DC current Idc output from the power converter 2 is detected by a DC current detector (not shown). The DC current Idc may be calculated by using each arm current Ipu to Inw.

[0029] <Converter cell configuration> 2 is a diagram showing a configuration of a converter cell according to the present embodiment. Referring to FIG. 2, the converter cell includes a half-bridge type switching circuit 20 and a control circuit 30.

[0030] The half-bridge switching circuit 20 includes a capacitor 24, semiconductor circuits 25A and 25B, a thyristor 26, and a bypass switch 27.

[0031] The semiconductor circuit 25A includes a switching element 22A and a diode 23A. The diode 23A is a freewheeling diode (hereinafter also referred to as "FWD") connected in anti-parallel (i.e., in parallel and in a reverse bias direction) to the switching element 22A. The semiconductor circuit 25B includes a switching element 22B and a diode 23B. The diode 23B is an FWD connected in anti-parallel to the switching element 22B.

[0032] The switching elements 22A and 22B are configured by self-extinguishing semiconductor switching elements such as, for example, insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field-effect transistors (MOSFETs).

[0033] Capacitor 24, which serves as a storage element, is connected in parallel to a series body including semiconductor circuit 25A and semiconductor circuit 25B connected in series, and holds a DC voltage. A connection node between switching element 22A and switching element 22B is connected to input / output terminal G1 on the high potential side. A connection node between switching element 22B and capacitor 24 is connected to input / output terminal G2 on the low potential side. In addition, the positive electrode of capacitor 24 is connected to the positive electrode of semiconductor circuit 25B, and the negative electrode of capacitor 24 is connected to the negative electrode of semiconductor circuit 25A.

[0034] The thyristor 26 is connected in parallel to the semiconductor circuit 25A. The thyristor 26 is a switching element that conducts (i.e., turns on) between the anode and the cathode when a gate current flows, and when it is on, it only allows current to flow in one direction. Once the thyristor 26 is on, it remains on until the current between the anode and the cathode becomes zero, even if the gate current becomes zero.

[0035] The bypass switch 27 is connected between the input / output terminals G1 and G2. In the example of FIG. 2, the bypass switch 27 is connected in parallel with the semiconductor circuit 25A. By turning on the bypass switch 27, the converter cell 7 is short-circuited. The bypass switch 27 is also used to short-circuit the converter cell 7 when an element of the converter cell 7 (e.g., the semiconductor circuits 25A, 25B, etc.) fails. As a result, even if any one of the multiple converter cells 7 fails, the power converter 2 can continue to operate by using the other converter cells 7.

[0036] The current detector 28 is provided between the semiconductor circuit 25A and the input / output terminal G2, and detects a current Is flowing through the semiconductor circuit 25A. The current detector 28 is configured with, for example, a shunt resistor. The detected current Is is input to the control circuit 30.

[0037] 2, the high-potential side input / output terminal G1 is connected to the connection node of the switching elements 22A and 22B, and the low-potential side input / output terminal G2 is connected to the connection node of the switching element 22A and the capacitor 24, but the configuration is not limited to this. For example, the input / output terminal G1 may be connected to the connection node of the switching element 22B and the capacitor 24, and the input / output terminal G2 may be connected to the connection node of the switching elements 22A and 22B. In this case, the thyristor 26 and the bypass switch 27 are connected in parallel to the semiconductor circuit 25B. The current detector 28 is provided between the semiconductor circuit 25B and the input / output terminal G2, and detects the current Is flowing through the semiconductor circuit 25B.

[0038] The control circuit 30 includes a voltage detection unit 31, a cell control unit 35, and a communication unit 33. Each of these functions is configured, for example, by an ASIC, an FPGA, or a combination of these.

[0039] The voltage detection unit 31 detects the voltage across the capacitor 24 (hereinafter also referred to as the “capacitor voltage”). The detected capacitor voltage is input to the cell control unit 35. The communication unit 33 transmits and receives various information to and from the control device 3.

[0040] The cell control unit 35 controls the operation of the switching circuit 20. In one aspect, the cell control unit 35 executes control according to an operation command received from the control device 3 via the communication unit 33. During normal operation (for example, when zero voltage or positive voltage is output between the input / output terminals G1 and G2), the cell control unit 35 controls one of the switching elements 22A and 22B to be in the ON state and the other to be in the OFF state. When the switching element 22A is in the OFF state and the switching element 22B is in the ON state, the voltage across the capacitor 24 is applied between the input / output terminals G1 and G2. On the other hand, when the switching element 22A is in the ON state and the switching element 22B is in the OFF state, 0V is applied between the input / output terminals G1 and G2.

[0041] By alternately turning on switching elements 22A and 22B, converter cell 7 can output zero voltage or a positive voltage that depends on the voltage of capacitor 24. Diodes 23A and 23B are provided for protection when a reverse voltage is applied to switching elements 22A and 22B, respectively.

[0042] In another aspect, the cell control unit 35 detects an overcurrent based on the current Is received from the current detector 28. Typically, the cell control unit 35 detects an overcurrent flowing through the semiconductor circuit 25A when the current Is is equal to or greater than a threshold K1. When the cell control unit 35 detects the overcurrent, it gates-blocks the switching elements 22A and 22B (for example, fixes the switching elements 22A and 22B to the off state) and controls the thyristor 26 to the on state.

[0043] For example, if a short circuit occurs in the DC circuit 14, the short circuit current flows through a path passing through the input / output terminal G2, the diode 23A, and the input / output terminal G1 in this order. In this case, the cell control unit 35 detects an overcurrent flowing through the diode 23A, gates the switching elements 22A and 22B, and controls the thyristor 26 to the on state. As a result, the short circuit current also flows through the path passing through the input / output terminal G2, the thyristor 26, and the input / output terminal G1 in this order, so that the current flowing through the diode 23A becomes smaller. This makes it possible to prevent the breakdown of the diode 23A.

[0044] The cell control unit 35 notifies the control device 3 that the overcurrent has been detected via the communication unit 33. When the control device 3 receives the notification of the detection of the overcurrent, it instructs each of all converter cells 7 included in the power converter 2 to gate-block the switching elements 22A, 22B of the converter cell 7 and control the thyristor 26 of the converter cell 7 to the on state (for example, by transmitting instruction information). The cell control unit 35 of each converter cell 7 gate-blocks the switching elements 22A, 22B and turns the thyristor 26 to the on state in accordance with the instruction. This makes it possible to more appropriately protect the elements of each converter cell 7 included in the power converter 2.

[0045] The control of the thyristor 26 to the ON state is performed, for example, as follows. The cell control unit 35 outputs a trigger signal for turning the thyristor 26 to the ON state to a trigger circuit (not shown). Upon receiving the trigger signal, the trigger circuit provides a gate pulse to the thyristor 26. This causes the thyristor 26 to turn on (i.e., to be conductive).

[0046] The cell control unit 35 receives a status signal indicating the status of the thyristor 26 from the trigger circuit, and stores the status signal in the internal memory of the control circuit 30. Specifically, the cell control unit 35 associates the trigger signal (or the gate pulse) with the status signal of the thyristor 26 and stores them in the internal memory. This allows the system operator to check the data stored in the internal memory when performing regular inspection of the converter cell 7 using an inspection terminal, thereby enabling detailed inspection.

[0047] The cell control unit 35 may transmit data associating the trigger signal (or gate pulse) with the state signal of the thyristor 26 to the control device 3. This enables the control device 3 to check the operation of the thyristor 26 of the converter cell 7.

[0048] Furthermore, even if the current Is flowing through the semiconductor circuit 25A is less than the threshold value K1, if it is equal to or greater than a relatively large threshold value K2 (where K1>K2), the cell control unit 35 may notify the control device 3 of an abnormality in the converter cell 7 via the communication unit 33. This allows the control device 3 to confirm the abnormality in the converter cell 7.

[0049] The cell control unit 35 may turn on a warning light provided in the converter cell 7 when detecting an abnormality or overcurrent in the converter cell 7. For example, a configuration may be adopted in which the warning light is monitored using a surveillance camera or the like. In this case, the surveillance camera may transmit a captured surveillance image to the control device 3.

[0050] In still another aspect, the cell control unit 35 executes processing according to an instruction received from the control device 3 via the communication unit 33. Typically, when the control device 3 detects a short-circuit fault in the DC circuit 14, it instructs each of all converter cells 7 included in the power converter 2 to gate-block the switching elements 22A, 22B of the converter cell 7 and control the thyristor 26 of the converter cell 7 to an ON state. The cell control unit 35 of each converter cell 7 gate-blocks the switching elements 22A, 22B and turns the thyristor 26 to an ON state in accordance with the instruction.

[0051] For example, when the detected DC current Idc becomes equal to or greater than a specified current threshold, the control device 3 detects a short circuit fault in the DC circuit 14. Note that the control device 3 may detect the short circuit fault using the DC voltage Vdc, the AC current Iac, the arm currents Ipu to Inw, etc.

[0052] The cell control unit 35 may have a self-diagnosis function for diagnosing a failure in the converter cell 7. For example, failures in the converter cell 7 include failures in a switching element, failures in a gate driver, damage to a capacitor, communication abnormalities, and the like. When the cell control unit 35 detects a failure in the converter cell 7, it turns on (i.e., closes) the bypass switch 27. The cell control unit 35 transmits failure information indicating the failure to the control device 3.

[0053] According to the above configuration, not only in the case of a short circuit accident in the DC circuit 14, but also in the case of an event in which an overcurrent flows in some of the converter cells 7 due to a partial short circuit or a ground fault in the arm, the cell control unit 35 of the converter cell 7 detects the overcurrent, gate blocks the switching elements 22A and 22B, and controls the thyristor 26 to the on state. This makes it possible to protect the elements of the converter cell 7 (e.g., FWD, switching element) from overcurrent caused by accidents other than the short circuit accident in the DC circuit 14. In addition, since the converter cell 7 itself detects the overcurrent, immediately gate blocks the switching elements 22A and 22B, and controls the thyristor 26 to the on state, the elements of the converter cell 7 can be protected more quickly.

[0054] Furthermore, when the control device 3 receives a notification of detection of an overcurrent occurring in one or more converter cells 7, it instructs the control device 3 to gate-block each of the switching elements 22A, 22B included in the power converter 2 and control the thyristor 26 to the on state. This makes it possible to prevent the elements of each converter cell 7 included in the power converter 2 from being destroyed.

[0055] <Control device hardware configuration> FIG. 3 is a block diagram showing an example of a hardware configuration of a control device according to the present embodiment. The control device 3 in FIG. 3 is configured based on a computer. Referring to FIG. 3, the control device 3 includes one or more input converters 70, one or more sample-and-hold (S / H) circuits 71, a multiplexer (MUX) 72, and an A / D converter 73. Furthermore, the control device 3 includes one or more central processing units (CPUs) 74, a random access memory (RAM) 75, and a read only memory (ROM) 76. Furthermore, the control device 3 includes one or more input / output interfaces 77, an auxiliary storage device 78, and a bus 79 connecting the above components to each other.

[0056] The input converter 70 includes an auxiliary transformer for each input channel. Each auxiliary transformer converts the detection signals from the detectors of various electrical quantities shown in Fig. 1 into signals of a voltage level suitable for subsequent signal processing.

[0057] A sample-and-hold circuit 71 is provided for each input converter 70. The sample-and-hold circuit 71 samples and holds a signal representing an electrical quantity received from the corresponding input converter 70 at a specified sampling frequency.

[0058] The multiplexer 72 sequentially selects the signals held in the multiple sample-and-hold circuits 71. The A / D converter 73 converts the signal selected by the multiplexer 72 into a digital value. Note that by providing multiple A / D converters 73, A / D conversion may be performed in parallel on detection signals of multiple input channels.

[0059] The CPU 74 controls the entire control device 3 and executes arithmetic processing according to a program. The RAM 75 as a volatile memory and the ROM 76 as a non-volatile memory are used as the main memory of the CPU 74. The ROM 76 stores programs and setting values ​​for signal processing, etc. The auxiliary storage device 78 is a non-volatile memory with a larger capacity than the ROM 76, and stores programs, data on detected values ​​of electricity, etc.

[0060] The input / output interface 77 is an interface circuit for communication between the CPU 74 and an external device.

[0061] At least a part of the control device 3 may be configured using circuits such as FPGA and ASIC, etc. Alternatively, at least a part of the control device 3 may be configured using analog circuits.

[0062] <Application of limiting circuits> Fig. 4 is a schematic diagram showing a first modified example of a power conversion device according to the present embodiment. With reference to Fig. 4, power conversion device 1A includes a power converter 2, a control device 3, and a limiting circuit 50. That is, power conversion device 1A has a configuration in which limiting circuit 50 is added to power conversion device 1 in Fig. 1. Here, the configuration of power conversion device 1A that differs from power conversion device 1 will be described.

[0063] The limiting circuit 50 limits the current flowing between the AC circuit 12 and the power converter 2. The limiting circuit 50 includes a charging resistor 51 and a switch 52 connected in parallel to the charging resistor 51.

[0064] The control device 3 controls the opening and closing operation of the switch 52 by transmitting a control signal to the switch 52 .

[0065] At the start-up of the power conversion device 1, the capacitors 24 are initially charged. Typically, when a breaker (not shown) for grid connection is turned on, power (current) is supplied from the AC circuit 12 to the power converter 2. At the normal start-up of the power conversion device 1 (for example, when no DC short-circuit accident has occurred), an inrush current flows to the capacitor 24, which may cause overcurrent stress on the elements of the converter cell 7 and an instantaneous voltage drop on the grid side. If a short-circuit accident has already occurred in the DC circuit 14 at the start-up stage of the power conversion device 1, a very large short-circuit current flows into the power converter 2, but the thyristor 26 cannot be turned on because the cell control unit 35 has not yet completed startup. As a result, the elements of the converter cell 7 may be destroyed.

[0066] Therefore, the control device 3 opens the switch 52 before the start of the initial charging of each capacitor 24. In this case, a charging current flows from the AC circuit 12 through the charging resistor 51 of the limiting circuit 50, and the initial charging of the capacitor 24 of each converter cell 7 is started. Therefore, the current flowing into the power converter 2 during the initial charging of the capacitor 24 can be suppressed. Furthermore, the charging resistor 51 has a resistance value that can suppress the current to a degree that can prevent the destruction of the elements (e.g., FWD) of each converter cell 7 even if a short-circuit accident occurs in the DC circuit 14. That is, the charging resistor 51 has a function of suppressing the current flowing from the AC circuit 12 to the power converter 2 when a short-circuit accident occurs in the DC circuit 14. This makes it possible to prevent the destruction of the elements of each converter cell 7 even when a DC short-circuit accident occurs during startup.

[0067] Thereafter, when the initial charging of each capacitor 24 is completed (for example, when the capacitor voltage has increased to a specified voltage), the control device 3 closes the switch 52.

[0068] With the above configuration, the capacitor 24 and the DC circuit 14 of each converter cell 7 can be appropriately charged when the power converter 2 is started up.

[0069] <Modification of switching circuit> Fig. 5 is a diagram showing a modification of the switching circuit according to the present embodiment. Referring to Fig. 5, the switching circuit 20X of the converter cell 7 is obtained by adding reactance elements 29A and 29B to the switching circuit 20 of Fig. 2. Among the configurations of the switching circuit 20X, detailed description of the configurations similar to those of the switching circuit 20 will not be repeated.

[0070] When an overcurrent is detected by the cell control unit 35 in the event of a short circuit in the DC circuit 14, the thyristor 26 is turned on. In this case, the short-circuit current flows through a first path that passes through the input / output terminal G2, the thyristor 26, and the input / output terminal G1 in this order, and a second path that passes through the input / output terminal G2, the diode 23A, and the input / output terminal G1 in this order. Since the short-circuit current contains an AC component, the current division ratios of the first and second paths are determined according to the resistance and reactance components. Specifically, the current division ratio of a path with a small reactance component is greater than the current division ratio of a path with a large reactance component.

[0071] In the switching circuit 20X, the reactance of the first path passing through the thyristor 26 is configured to be smaller than the reactance of the second path passing through the diode 23A. This makes the current division ratio of the first path larger than the current division ratio of the second path, and the current flowing through the thyristor 26 can be made larger than the current flowing through the diode 23A. This makes it possible to prevent the breakdown of the diode 23A.

[0072] 5, reactance elements (e.g., coils) 29A and 29B are provided between the semiconductor circuit 25A and the thyristor 26. Specifically, the reactance element 29A is provided on a connection node between the negative electrode of the semiconductor circuit 25A and the negative electrode of the thyristor 26. The reactance element 29B is provided on a connection node between the positive electrode of the semiconductor circuit 25A and the positive electrode of the thyristor 26. Note that, instead of the reactance elements 29A and 29B, a configuration that increases the reactance (e.g., a conductor arrangement that reduces the magnetic flux cancellation of the reciprocating current) may be used.

[0073] In order to suppress switching surges, it is preferable to make the reactance of the connection node between the diode 23A and the capacitor 24 and the reactance of the connection node between the semiconductor circuit 25B and the capacitor 24 as small as possible.

[0074] <Cooling water temperature control> Fig. 6 is a schematic configuration diagram showing a second modified example of a power conversion device according to the present embodiment. With reference to Fig. 6, power conversion device 1B includes a power converter 2, a control device 3, and a cooling device 40. That is, power conversion device 1B has a configuration in which cooling device 40 is added to power conversion device 1 in Fig. 1. Here, the configuration of power conversion device 1B that differs from power conversion device 1 will be described.

[0075] The cooling device 40 supplies cooling water for cooling the semiconductor circuits 25A, 25B (specifically, the switching elements 22A, 22B and the diodes 23A, 23B) of each converter cell 7 included in the power converter 2. For example, a part of the piping of the cooling device 40 is provided so as to be thermally coupled to the semiconductor circuits 25A, 25B within the power converter 2. The cooling water flowing through the piping cools the semiconductor circuits 25A, 25B thermally coupled to the piping.

[0076] In this way, the semiconductor circuits 25A and 25B are cooled by the cooling water, but the thyristor 26 is at room temperature (i.e., not cooled by the cooling water). Therefore, for example, when the cooling water temperature is lower than normal, such as in cold weather, the semiconductor circuits 25A and 25B are cooled more than expected. The more the semiconductor circuits 25A and 25B are cooled, the easier it is for a current to flow. Therefore, in cold weather, the diversion ratio of the first path through the thyristor 26 and the diversion ratio of the second path through the semiconductor circuit 25A change compared to normal times. Specifically, in cold weather, the diversion ratio of the first path through the thyristor 26 becomes lower and the diversion ratio of the second path through the semiconductor circuit 25A becomes higher than normal times.

[0077] Therefore, the cooling device 40 controls the cooling water temperature to be equal to or higher than a specified temperature before starting the power converter 2. For example, the cooling device 40 raises the cooling water temperature by heating with a heater, self-heating due to circulation operation, etc. When the cooling water temperature reaches or exceeds a specified temperature, the cooling device 40 notifies the control device 3 of this fact. After receiving the notification, the control device 3 executes a process to start up the power converter 2.

[0078] With the above configuration, the current division ratio of the first path and the second path can be kept constant, so that it is possible to prevent breakdown of the diode 23A due to a current greater than expected flowing through the diode 23A in the event of a short circuit or the like.

[0079] <Modification of converter cell> Fig. 7 is a diagram showing a modified example of the converter cell according to the present embodiment. Referring to Fig. 7, the converter cell 7A includes a control circuit 30A and a cell circuit 200. The cell circuit 200 includes switching circuits 21A and 21B, a thyristor 26, a bypass switch 27, and a semiconductor circuit 65.

[0080] Each of the switching circuits 21A and 21B includes a semiconductor circuit 25A, 25B and a capacitor 24. The configuration of the semiconductor circuits 25A, 25B is similar to that of Fig. 2. The positive electrode of the capacitor 24 is connected to the positive electrode of the semiconductor circuit 25B, and the negative electrode of the capacitor 24 is connected to the negative electrode of the semiconductor circuit 25A.

[0081] A connection node between switching element 22A and switching element 22B included in switching circuit 21A is connected to low potential side input / output terminal G2. A connection node between switching element 22A and switching element 22B included in switching circuit 21B is connected to high potential side input / output terminal G1.

[0082] The semiconductor circuit 65 is provided between the positive electrode of the capacitor 24 in the switching circuit 21A and the negative electrode of the capacitor 24 in the switching circuit 21B. The semiconductor circuit 65 includes a switching element 60 and a diode 61. The diode 61 is an FWD connected in anti-parallel to the switching element 60. The switching element 60 controls the conduction state of the direction of current passing through the diode 23B of the switching circuit 21A and the diode 23A of the switching circuit 21B. The switching element 60 is configured by a self-extinguishing semiconductor switching element such as an IGBT or a MOSFET, similar to the switching elements 22A and 22B.

[0083] The thyristor is connected between the positive electrode of the semiconductor circuit 25A in the switching circuit 21 A and the positive electrode of the semiconductor circuit 25A in the switching circuit 21 B. The bypass switch 27 is connected in parallel with the thyristor .

[0084] The current detector 28 detects the current Is flowing through the switching element 60. For example, the current detector 28 is provided between the negative electrode of the switching element 60 and the positive electrode of the semiconductor circuit 25B in the switching circuit 21A. The current detector 28 may be provided between the positive electrode of the switching element 60 and the negative electrode of the semiconductor circuit 25A in the switching circuit 21B.

[0085] The control circuit 30A includes a voltage detection unit 31A, a communication unit 33A, and a cell control unit 35A. The voltage detection unit 31A detects the voltage across the capacitor 24 in the switching circuits 21A and 21B (i.e., the capacitor voltage). The detected capacitor voltage is input to the cell control unit 35A. The communication unit 33A transmits and receives various information to and from the control device 3.

[0086] The cell control unit 35A controls the operation of the cell circuit 200. In one aspect, during normal operation, the cell control unit 35A controls the switching element 60 to an on state, and controls each of the switching elements 22A, 22B of the switching circuits 21A, 21B to an on state or an off state, to output zero voltage or a positive voltage between the input / output terminals G1, G2.

[0087] In another aspect, when the current Is is equal to or greater than the threshold K1, the cell control unit 35A detects an overcurrent flowing through the switching element 60. When the cell control unit 35A detects the overcurrent, it gates-blocks all of the switching elements 22A and 22B included in each of the switching circuits 21A and 21B and the switching element 60, and controls the thyristor 26 to the on state.

[0088] For example, when a short circuit occurs in the DC circuit 14, the short circuit current flows through a path passing through the input / output terminal G2, the diode 23B of the switching circuit 21A, the switching element 60, the diode 23A of the switching circuit 21B, and the input / output terminal G1 in this order. The cell control unit 35A detects an overcurrent, gates the switching elements 22A and 22B and the switching element 60 included in the switching circuits 21A and 21B, and controls the thyristor 26 to the on state.

[0089] In this case, the switching element 60 is in a gate-blocked state, so that the switching circuits 21A and 21B are electrically cut off. Therefore, the short-circuit current flows through a path passing through the input / output terminal G2, the thyristor 26, and the input / output terminal G1 in this order. In this case, the current is commutated to the thyristor 26, rather than being shunted between the thyristor 26 and the diodes of the switching circuits 21A and 21B. This makes it possible to more effectively prevent the destruction of the elements of the converter cell 7A (for example, the diode 23B of the switching circuit 21A and the diode 23A of the switching circuit 21B). Note that in a configuration example in which the semiconductor circuit 65 is not provided and the switching circuits 21A and 21B are directly connected, the current is shunted between the thyristor 26 and the diode. Even in this configuration example, the diode can be protected.

[0090] The cell control unit 35A notifies the control device 3 that the overcurrent has been detected via the communication unit 33A. When the control device 3 receives the notification of the detection of the overcurrent, it instructs all converter cells 7A included in the power converter 2 to gate-block the switching elements 22A and 22B and control the thyristors 26 to the on state.

[0091] According to the above configuration, not only in the case of a short circuit accident in the DC circuit 14, but also in the case of an event in which an overcurrent flows through some of the converter cells 7A due to a partial short circuit or a ground fault in the arm, the elements of the converter cells 7A (e.g., FWD, switching elements) can be protected from the overcurrent. In addition, the elements of the converter cells 7A can be protected more quickly. According to the configuration of the converter cells 7A, when an overcurrent occurs, the switching elements 60 are in a gate-blocked state, so that it is possible to prevent the inflow of the fault current into the switching circuits 21A and 21B.

[0092] Other embodiments. In the above-described embodiment, in FIG. 2, a configuration in which the current detector 28 is provided between the semiconductor circuit 25A and the input / output terminal G2 has been described. As another example, the current detector 28 may be further provided between the semiconductor circuit 25B and the input / output terminal G1. In this case, the cell control unit 35 can detect a current (e.g., a discharge current discharged from the capacitor 24) flowing through the semiconductor circuit 25B. For example, the cell control unit 35 detects an overcurrent flowing through the semiconductor circuit 25B when the current is equal to or greater than a threshold value Ka. When the cell control unit 35 detects the overcurrent, it may gate-block the switching elements 22A and 22B and control the thyristor 26 to the on state.

[0093] The configurations exemplified as the above-mentioned embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, without departing from the scope of the present disclosure. In addition, the above-mentioned embodiments may be implemented by appropriately adopting the processes and configurations described in other embodiments.

[0094] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0095] 1,1A,1B power conversion device, 2 power converter, 3 control device, 4u,4v,4w leg circuit, 5 upper arm, 6 lower arm, 7,7A converter cell, 8A,8B reactor, 9A,9B arm current detector, 10 AC voltage detector, 11A,11B DC voltage detector, 12 AC circuit, 13 interconnection transformer, 14 DC circuit, 16 AC current detector, 20,20X,21A,21B switching circuit, 22A,22B,60 switching element, 23A,23B diode, 24 capacitor, 25A,25B semiconductor circuit, 26 thyristor, 27 bypass switch, 28 current detector, 29A,29B reactance element, 30,30A control circuit, 31,31A voltage detection unit, 33,33A Communication unit, 35, 35A cell control unit, 40 cooling device, 50 limiting circuit, 51 charging resistor, 52 switch, 70 input converter, 71 sample-and-hold circuit, 72 multiplexer, 73 A / D converter, 74 CPU, 75 RAM, 76 ROM, 77 input / output interface, 78 auxiliary storage device, 79 bus, 200 cell circuit.

Claims

1. A power conversion device that performs power conversion between an AC circuit and a DC circuit, a power converter including a plurality of converter cells connected in series; A control device for controlling the power converter, Each of the plurality of transducer cells comprises: A cell control unit; a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element; a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element; a storage element connected in parallel to a series body including the first semiconductor circuit and the second semiconductor circuit connected in series; a thyristor connected in parallel to the first semiconductor circuit; when the cell control unit detects an overcurrent flowing through the first semiconductor circuit, the cell control unit gate-blocks the first switching element and the second switching element to control the thyristor to an on state; The cell control unit notifies the control device that the overcurrent has been detected, When the control device receives a notification of the detection of the overcurrent, it instructs each of the multiple converter cells to gate-block the first switching element and the second switching element of the converter cell and control the thyristor of the converter cell to an on state.

2. A power conversion device that performs power conversion between an AC circuit and a DC circuit, a power converter including a plurality of converter cells connected in series; A control device for controlling the power converter, Each of the plurality of transducer cells comprises: A cell control unit; a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element; a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element; a storage element connected in parallel to a series body including the first semiconductor circuit and the second semiconductor circuit connected in series; a thyristor connected in parallel to the first semiconductor circuit; when the cell control unit detects an overcurrent flowing through the first semiconductor circuit, the cell control unit gate-blocks the first switching element and the second switching element to control the thyristor to an on state; When the control device detects a short circuit fault in the DC circuit, it instructs each of the plurality of converter cells to gate-block the first switching element and the second switching element of the converter cell and to control the thyristor of the converter cell to an on state.

3. 3. The power conversion device according to claim 2, wherein a reactance of a current path passing through the thyristor is smaller than a reactance of a current path passing through the first diode in the event of a short-circuit fault in the DC circuit.

4. The power conversion device according to claim 3 , wherein each of the plurality of converter cells further includes a reactance element provided between the first semiconductor circuit and the thyristor.

5. a limiting circuit for limiting a current flowing between the AC circuit and the power converter; the limiting circuit includes a charging resistor for suppressing a current flowing from the AC circuit to the power converter when a short-circuit fault occurs in the DC circuit, and a switch connected in parallel to the charging resistor; The power conversion device according to any one of claims 1 to 4, wherein the control device opens the switch before starting initial charging of the storage elements included in each of the plurality of converter cells.

6. A power conversion device that performs power conversion between an AC circuit and a DC circuit, a power converter including a plurality of converter cells connected in series; A control device for controlling the power converter, Each of the plurality of transducer cells comprises: A cell control unit; a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element; a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element; a storage element connected in parallel to a series body including the first semiconductor circuit and the second semiconductor circuit connected in series; a thyristor connected in parallel to the first semiconductor circuit; when the cell control unit detects an overcurrent flowing through the first semiconductor circuit, the cell control unit gate-blocks the first switching element and the second switching element to control the thyristor to an on state; a cooling device that supplies cooling water for cooling the first semiconductor circuit and the second semiconductor circuit of the converter cell; The cooling device controls the temperature of the cooling water to a specified temperature or higher, When the temperature of the cooling water reaches or exceeds the specified temperature, the control device starts up the power converter.

7. The cell control unit outputting a trigger signal to a trigger circuit to turn on the thyristor; receiving a status signal from the trigger circuit indicative of a status of the thyristor; The power conversion device according to any one of claims 1 to 4, further comprising: a storage section for storing the state signal.

8. A power conversion device that performs power conversion between an AC circuit and a DC circuit, a power converter including a plurality of converter cells connected in series; A control device for controlling the power converter, Each of the plurality of transducer cells comprises: A cell control unit; a first switching circuit and a second switching circuit; Each of the first switching circuit and the second switching circuit comprises: a first semiconductor circuit including a first switching element and a first diode connected in anti-parallel to the first switching element; a second semiconductor circuit including a second switching element and a second diode connected in anti-parallel to the second switching element; a storage element connected in parallel to a series body including the first semiconductor circuit and the second semiconductor circuit connected in series; a positive electrode of the storage element is connected to a positive electrode of the second semiconductor circuit, and a negative electrode of the storage element is connected to a negative electrode of the first semiconductor circuit; Each of the plurality of transducer cells comprises: a third switching element provided between a positive electrode of the storage element in the first switching circuit and a negative electrode of the storage element in the second switching circuit; a thyristor connected between a positive electrode of the first semiconductor circuit in the first switching circuit and a positive electrode of the first semiconductor circuit in the second switching circuit, A power conversion device in which, when the cell control unit detects an overcurrent flowing through the third switching element, it gate-blocks the first switching element, the second switching element, and the third switching element, and controls the thyristor to an on state.

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