Power Conversion Equipment

Abstract

In the power conversion device (1), each sub-module (SM) includes an alarm unit (33, 79, 44, 85) that visually notifies that a bypass switch (BPS) has been operated. The power conversion device (1) includes a monitoring camera (70) that captures images of the alarm units of the multiple sub-modules collectively as a single image data, and a host control device (3) that processes the image data to determine the operating state of the bypass switch (BPS) of each sub-module.

Description

[Technical Field]

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

[0002] In recent years, modular multilevel converters (MMCs) have come into practical use as large-capacity power conversion devices applied to high-voltage systems such as electric power systems. An MMC comprises a large number of unit converters, each of which includes a storage element (typically a capacitor) and multiple semiconductor switching elements, and these unit converters are connected in cascade. Hereinafter, the unit converters are also referred to as "converter cells" or "submodules" (SMs).

[0003] MMC is a typical power conversion device for HVDC (High Voltage Direct Current) power transmission. In MMC-HVDC, redundancy is provided in the number of cascade-connected submodules. If any of the submodules fails, the submodule is short-circuited by a bypass switch, allowing operation to continue with the remaining submodules.

[0004] When the semiconductor switching elements that make up the submodule are modular elements, bypass switches are essential. Even if the semiconductor switching elements are pressure-contact elements that normally fail due to short circuits, in the case of high current specifications such as MMC-HVDC, bypass switches are essential to ensure the reliability of continuous current flow.

[0005] In order to determine whether operation can be continued after issuing a command to close the bypass switch, it is important to confirm the operation of the bypass switch, and a highly reliable confirmation method is required. For example, JP 2016-518804 A (Patent Document 1) discloses a monitoring device that detects whether the bypass switch is energized.

[0006] Specifically, in the monitoring device of this document, an optical fiber is placed at a position where it will break when a movable part of a mechanical switch constituting a bypass switch moves to turn on the mechanical switch. When the optical fiber is broken, the optical signal passing through the optical fiber is interrupted, and it is detected that the mechanical switch is in an energized state. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2016-518804 Summary of the Invention [Problem to be solved by the invention]

[0008] The results of the confirmation of the bypass switch operation are transmitted to the upper control device by the individual control unit provided in the submodule. However, to ensure reliability, it is desirable to be able to transmit the confirmation results to the upper control device directly, rather than via the individual control unit. In this case, it is possible to transmit the results to the upper control system using optical fiber wiring, but the increased number of wiring poses problems in terms of cost and space. Wireless backup communication is expensive and has the problem of noise. Patent Document 1 mentioned above does not clarify this problem.

[0009] The present disclosure has been made in consideration of the above-mentioned problems, and one of its objectives is to provide a power conversion device that can directly transmit the operation confirmation results of a bypass switch to a higher-level control device in a relatively simple manner.

[0010] However, there are other important issues to be addressed in order to ensure the reliability of the bypass switch. For example, it is important to have a backup bypass switch that can be turned on when the bypass switch fails to be turned on due to a failure in the individual control unit, and to have preventive maintenance that replaces the bypass switch in advance when the drive system that operates the bypass switch deteriorates. Means for solving these issues will be made clear in the following embodiments. [Means for solving the problem]

[0011] In one embodiment, a power conversion apparatus includes a plurality of cascade-connected sub-modules. Each of the sub-modules includes a pair of input / output terminals, a plurality of semiconductor switching elements, a storage element connected to the pair of input / output terminals via the plurality of semiconductor switching elements, a mechanical bypass switch for short-circuiting the pair of input / output terminals, an individual control unit for controlling the opening and closing of the plurality of semiconductor switching elements and the bypass switch, and an alarm unit for visually notifying that the bypass switch has been operated. The power conversion apparatus further includes a monitoring camera that collectively captures images of the alarm units of the plurality of sub-modules as a single image data, and a host control device that processes the image data to determine the operating state of each of the bypass switches of the plurality of sub-modules. [Effects of the Invention]

[0012] According to the above embodiment, each sub-module includes a notification unit that visually notifies that the bypass switch has been operated, and the power conversion device includes a monitoring camera that captures images of the notification units of the multiple sub-modules collectively as a single image data set, and a host control device that processes the image data to determine the operating state of each of the bypass switches of the multiple sub-modules. With this configuration, it is possible to provide a power conversion device that can directly transmit the results of checking the operation of the bypass switch to the host control device in a relatively simple manner. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a schematic configuration diagram of a power conversion device according to a first embodiment. [Figure 2] 2 is a circuit diagram showing an example of a converter cell that configures each leg circuit of FIG. 1. FIG. [Figure 3] FIG. 3 is a cross-sectional view showing a conceptual configuration of the bypass switch of FIG. 2. [Figure 4] FIG. 2 is a block diagram illustrating an example of a hardware configuration of a higher-level control device. [Figure 5] FIG. 2 is an external view for explaining the physical arrangement of a plurality of converter cells. [Figure 6] FIG. 6 is a cross-sectional view seen from the Y direction in FIG. 5. [Figure 7] 10 is a flowchart showing the closing operation of the bypass switch and the procedure for checking the same. [Figure 8] 10A and 10B are diagrams illustrating a modified example of a notification unit that notifies the operating state of a bypass switch. [Figure 9] FIG. 11 is a circuit diagram showing a configuration example of a submodule in a power conversion device according to a third embodiment. [Figure 10] FIG. 10 is a circuit diagram showing a configuration example of a submodule in a power conversion device according to a fourth embodiment. [Figure 11] 10 is a flowchart for explaining a protection operation for a paired sub-module. [Figure 12] FIG. 11 is a cross-sectional view showing a conceptual configuration of a bypass switch in a power conversion device according to a fifth embodiment. [Figure 13] 10 is a flowchart illustrating an example of a procedure for evaluating the health of a bypass switch. DETAILED DESCRIPTION OF THE INVENTION

[0014] Each embodiment will be described in detail below with reference to the drawings. The same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

[0015] Embodiment 1 [Overall configuration of the power conversion device] Fig. 1 is a schematic configuration diagram of a power conversion device 1 according to a first embodiment. Referring to Fig. 1, the power conversion device 1 is configured by a modular multilevel converter including a plurality of converter cells 7 (sub-modules SM) connected to each other in cascade. The power conversion device 1 performs power conversion between a DC system 14 and an AC system 12. The power conversion device 1 includes a power converter 2 and a higher-level control device 3.

[0016] The power converter 2 includes a plurality of leg circuits 4u, 4v, 4w (collectively or individually referred to as leg circuits 4) 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.

[0017] A leg circuit 4 is provided for each of the multiple phases constituting the AC. The leg circuit 4 is connected between the AC system 12 and the DC system 14, and performs power conversion between the two circuits. Fig. 1 shows a case where the AC system 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.

[0018] The AC input terminals Nu, Nv, and Nw provided in the leg circuits 4u, 4v, and 4w, respectively, are connected to an AC system 12 via a transformer 13. The AC system 12 includes an AC power source and the like. For ease of illustration, the connection between the AC input terminals Nv and Nw and the transformer 13 is not shown in FIG. 1.

[0019] A high-potential side DC terminal Np and a low-potential side DC terminal Nn, which are commonly connected to each leg circuit 4, are connected to a DC system 14. In the case of HVDC power transmission, the DC system 14 is a DC transmission network. Note that the DC system 14 can also be considered as a DC terminal of another power conversion device. In this case, by linking two power conversion devices, a BTB (Back To Back) system is configured to connect AC power systems with different rated frequencies, etc.

[0020] 1, the leg circuits 4u, 4v, and 4w may be provided with primary windings instead of the AC input terminals Nu, Nv, and Nw, and the leg circuits 4u, 4v, and 4w may be AC-connected to the transformer 13 or the interconnection reactor via secondary windings magnetically coupled to the primary windings. In this case, the primary windings may be reactors 8A and 8B described below. In summary, the leg circuit 4 is electrically (i.e., DC- or AC-connected) to the AC system 12 via connection parts provided in each of the leg circuits 4u, 4v, and 4w, such as the AC input terminals Nu, Nv, and Nw or the above-described primary windings.

[0021] The leg circuit 4u includes an upper arm circuit 5 extending from the high potential side DC terminal Np to the AC input terminal Nu, and a lower arm circuit 6 extending 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 circuit 5 and the lower arm circuit 6, is connected to a transformer 13. The high potential side DC terminal Np and the low potential side DC terminal Nn are connected to a DC system 14. The upper arm circuit 5 and the lower arm circuit 6 are collectively referred to as an arm circuit. Since the leg circuits 4v and 4w have a similar configuration, the configuration of the leg circuit 4u will be described below as a representative example.

[0022] The upper arm circuit 5 includes a plurality of cascaded submodules SM and a reactor 8A. The submodules SM and the reactor 8A are connected in series. Similarly, the lower arm circuit 6 includes a plurality of cascaded submodules SM and a reactor 8B. The submodules SM and the reactor 8B are connected in series.

[0023] In the following description, the number of submodules SM included in each of the upper arm circuit 5 and the lower arm circuit 6 is set to Ncell+Rcell, where Ncell≧2 and Rcell≧1. Ncell is the minimum number of submodules SM required for operation, and Rcell is the number of redundant cells. However, since the Ncell+Rcell submodules SM operate together, there is no distinction between redundant cells and other cells. If one of the Ncell+Rcell submodules SM fails, the failed cell is short-circuited by closing its bypass switch BPS (see Figure 2). Therefore, if Rcell submodules SM out of the Ncell+Rcell submodules SM fail, the remaining number of redundant cells becomes 0. If another submodule SM fails, the number of submodules SM included in that arm falls below Ncell, and the power converter 2 cannot be used thereafter.

[0024] The reactor 8A may be inserted at any position in the upper arm circuit 5 of the leg circuit 4u, and the reactor 8B may be inserted at any position in the lower arm circuit 6 of the leg circuit 4u. A plurality of reactors 8A and 8B may be provided. The inductance values ​​of the reactors may be different from each other. Furthermore, only the reactor 8A in the upper arm circuit 5 or only the reactor 8B in the lower arm circuit 6 may be provided. Furthermore, the transformer wiring may be devised to cancel the magnetic flux of the DC component current, and the leakage reactance of the transformer may act on the AC component current, thereby substituting for a reactor. By providing the reactors 8A and 8B, a sudden increase in fault current during a fault in the AC system 12 or the DC system 14, etc., can be suppressed.

[0025] The power conversion device 1 further includes detectors for measuring electrical quantities (current, voltage, etc.) used for control, such as an AC voltage detector 10, an AC current detector 16, DC voltage detectors 11A and 11B, arm current detectors 9A and 9B provided in each leg circuit 4, and a DC current detector 17. Signals detected by these detectors are input to the upper control device 3.

[0026] 1, for ease of illustration, the signal lines for signals input from each detector to the host controller 3 and the signal lines for signals input / output between the host controller 3 and each sub-module SM are shown together, but in reality, they are provided for each detector and each sub-module SM. Separate signal lines for transmission and reception may be provided between each sub-module SM and the host controller 3. The signal lines may be formed, for example, of optical fiber.

[0027] Next, each detector will be described in detail. The AC voltage detector 10 detects a U-phase AC voltage Vacu, a V-phase AC voltage Vacv, and a W-phase AC voltage Vacw of the AC system 12. In the following description, the AC voltages Vacu, Vacv, and Vacw of the respective phases are also collectively referred to as AC voltage Vac.

[0028] The AC current detector 16 detects a U-phase AC current Iacu, a V-phase AC current Iacv, and a W-phase AC current Iacw of the AC system 12. In the following description, the AC currents Iacu, Iacv, and Iacw of the respective phases will also be collectively referred to as AC current Iac.

[0029] The DC voltage detector 11A detects a DC voltage Vdcp at a high potential side DC terminal Np connected to the DC system 14. The DC voltage detector 11B detects a DC voltage Vdcn at a low potential side DC terminal Nn connected to the DC system 14. The difference between the high potential side DC voltage Vdcp and the low potential side DC voltage Vdcn is defined as a DC voltage Vdc.

[0030] The DC current detector 17 detects a DC current Idc flowing through the high potential side DC terminal Np or the low potential side DC terminal Nn.

[0031] The arm current detectors 9A and 9B provided in the U-phase leg circuit 4u detect the upper arm current Ipu flowing in the upper arm circuit 5 and the lower arm current Inu flowing in the lower arm circuit 6, respectively. The arm current detectors 9A and 9B provided in the V-phase leg circuit 4v detect the upper arm current Ipv and the lower arm current Inv, respectively. The arm current detectors 9A and 9B provided in the W-phase leg circuit 4w detect the upper arm current Ipw and the lower arm current Inw, respectively. In the following description, the upper arm currents Ipu, Ipv, and Ipw are also collectively referred to as upper arm current Iarmp, the lower arm currents Inu, Inv, and Inw are also collectively referred to as lower arm current Iarmn, and the upper arm current Iarmp and the lower arm current Iarmn are also collectively referred to as arm current Iarm.

[0032] [Example of converter cell configuration] Fig. 2 is a circuit diagram showing an example of a converter cell constituting each leg circuit of Fig. 1. The converter cell 7 (submodule SM) shown in Fig. 1 includes a half-bridge type conversion circuit 20, a storage element 24, a voltage detector 25, an individual control unit 27, a bypass switch BPS, and a lighting circuit 30. The conversion circuit 20 is also called a bridge circuit.

[0033] The half-bridge conversion circuit 20 includes switching elements 22A and 22B and diodes 23A and 23B connected in series. The diodes 23A and 23B are connected in anti-parallel (i.e., parallel and reverse biased) with the switching elements 22A and 22B, respectively. The diodes 23A and 23B are provided to protect the switching elements 22A and 22B when a reverse voltage is applied to them. Hereinafter, the switching elements 22A and 22B and the diodes 23A and 23B will be referred to collectively or individually as switching element 22 and diode 23, respectively.

[0034] Storage element 24 is connected in parallel with the series-connected circuit of switching elements 22A and 22B and holds a DC voltage. A DC capacitor is typically used as storage element 24. A connection node between switching elements 22A and 22B is connected to high-potential side input / output terminal 26P. A connection node between switching element 22B and storage element 24 is connected to low-potential side input / output terminal 26N.

[0035] Typically, the input / output terminals 26P are connected to the input / output terminals 26N of the adjacent submodule SM on the positive side, and the input / output terminals 26N are connected to the input / output terminals 26P of the adjacent submodule SM on the negative side.

[0036] A self-extinguishing switching element capable of controlling both on and off operations is used as each of the switching elements 22A and 22B. The switching elements 22A and 22B are, for example, an insulated gate bipolar transistor (IGBT) or a gate commutated turn-off thyristor (GCT).

[0037] The conversion circuit of the submodule SM is not limited to the above-described half-bridge type conversion circuit 20. For example, the submodule SM may be configured using a full-bridge type conversion circuit or a three-quarter-bridge type conversion circuit.

[0038] The bypass switch BPS is connected between the input / output terminals 26P and 26N. In this embodiment, a mechanical switch is used as the bypass switch BPS. The bypass switch BPS includes a main contact MC and an auxiliary contact AX that opens and closes in conjunction with the main contact MC. Closing the main contact MC shorts the high-potential side input / output terminal 26P and the low-potential side input / output terminal 26N.

[0039] The bypass switch BPS is used to short-circuit the submodule SM when any element of the converter cell 7 (submodule SM) fails. As a result, even if any one of the multiple submodules SM fails, the power conversion device 1 can continue to operate by using the other submodules SM.

[0040] Furthermore, when the bypass switch BPS is turned on, it is necessary to check the integrity of the contacts after manually opening them, and in the case of an inflator type in which the contacts are turned on by igniting explosives, the bypass switch must be replaced. Therefore, if the system cannot continue to operate even after the bypass switch is turned on, the bypass switch should not be turned on in principle. The original purpose of the bypass switch BPS is to ensure continued operation by short-circuiting the failed sub-module SM.

[0041] The decision as to whether to close the bypass switch BPS may be made by the upper control device 3 or by the individual control unit 27 of each sub-module SM. In the former case, the upper control device 3 determines whether each sub-module SM has a failure and sends a command to close the bypass switch BPS to the individual control unit 27 of the sub-module SM that has been determined to have a failure. Therefore, in the former case, there is a drawback in that a command to close the bypass switch BPS cannot be issued if there is a communication failure between the upper control device 3 and the sub-module SM.

[0042] On the other hand, in the latter case, the individual control unit 27 of each sub-module SM determines whether there is a failure, and if it determines that there is a failure, it turns on the corresponding bypass switch BPS. This latter method is adopted in this embodiment. However, in either case, there is a drawback in that if the operating mechanism of the bypass switch BPS fails, the bypass switch BPS cannot be turned on. Therefore, it is important to confirm whether the turning on of the bypass switch BPS has been completed, to have a backup means for turning on the bypass switch BPS, and to confirm the soundness of the bypass switch BPS.

[0043] It is also possible to combine the former and latter cases. Duplicating the bypass switch BPS itself is difficult due to the increased cost and space required. By providing a backup capacitor, the bypass switch BPS can be turned on even in the event of a power supply abnormality.

[0044] The lighting circuit 30 includes a DC power supply 31, a resistive element 32, and a light-emitting element 33 such as an LED (Light Emitting Diode). These components are connected in series with the auxiliary contact AX. When the auxiliary contact AX is closed, the lighting circuit 30 becomes conductive, and the light-emitting element 33 lights up. Information that the lighting circuit 30 is conducting due to the auxiliary contact AX being closed (for example, the voltage generated in the resistive element 32) is sent to the individual control unit 27.

[0045] The DC power supply 31 may be an independent battery, or may be configured to receive power from the individual control unit 27 via a backup capacitor. This allows the lighting circuit 30 to remain operational even in the event of a power supply abnormality, at least for the time required to notify that the auxiliary contact AX has been closed.

[0046] Voltage detector 25 detects the voltage across both ends of power storage element 24 (that is, capacitor voltage Vc). The detected value of voltage detector 25 is input to individual control unit 27.

[0047] The individual control unit 27 receives various commands 28, including control commands and protection commands, from the higher-level control device 3. Based on the various commands 28 received, the individual control unit 27 generates gate signals for controlling the opening and closing of the switching elements 22A and 22B that constitute the conversion circuit 20. The individual control unit 27 further transmits to the higher-level control device 3 a signal 29, which includes abnormality determination information for the submodule SM, the capacitor voltage detected by the voltage detector 25, and opening and closing information for the bypass switch BPS.

[0048] Specifically, when the individual control unit 27 receives a voltage command value as a control command, it performs phase shift PWM (Pulse Width Modulation) control based on the received voltage command value to turn one of the switching elements 22A, 22B on and the other off.

[0049] Specifically, when switching element 22A is in the ON state and switching element 22B is in the OFF state, the voltage across storage element 24 is applied between input / output terminals 26P and 26N. Conversely, when switching element 22A is in the OFF state and switching element 22B is in the ON state, 0 V is applied between input / output terminals 26P and 26N. Therefore, submodule SM can output zero voltage and a positive voltage that depends on the voltage of storage element 24 by alternately turning on switching elements 22A and 22B.

[0050] When the individual control unit 27 receives a gate block command as a protection command, it turns off all of the switching elements 22A and 22B that make up the conversion circuit 20.

[0051] The individual control unit 27 further performs a self-diagnosis to determine whether the corresponding sub-module SM has failed. A common method for the self-diagnosis is to determine whether the capacitor voltage Vc is abnormal (i.e., whether it is above an upper threshold or below a lower threshold). This is because the capacitor voltage is essential for control operations, so a voltage detector 25 is installed and available for use, and because a failure of a sub-module SM often manifests itself as an abnormality in the capacitor voltage. The individual control unit 27 may also be configured to perform self-diagnosis for power supply abnormalities, communication system abnormalities, and the like, in addition to abnormalities in the capacitor voltage Vc.

[0052] However, since the capacitor voltage drops during startup and shutdown even though there is no malfunction, the upper control device 3 sends a startup and shutdown signal to each sub-module SM to put the bypass switch BPS of each sub-module SM on hold, thereby preventing unnecessary closing of the bypass switch BPS during startup and shutdown.

[0053] Furthermore, abnormalities in the capacitor voltage can also occur in the event of a severe grid fault or a malfunction within the converter station. In this case, it is meaningless to turn on the bypass switch BPS in order to continue operating the power conversion device 1, so the upper control device 3 detects this type of fault and sends a BPS turn-on standby signal to each submodule SM. This causes each submodule SM to wait for the bypass switch BPS to be turned on. However, even in this case, if the capacitor voltage reaches the dielectric breakdown limit of the submodule SM, the individual control unit 27 will determine that the bypass switch BPS will be turned on.

[0054] The individual control unit 27 may be configured by a dedicated circuit such as an ASIC (Application Specific Integrated Circuit), or may be configured by using an FPGA (Field Programmable Gate Array), etc. Alternatively, it may be configured based on a computer including a CPU (Central Processing Unit) and memory, or may be configured by a combination of two or more of the above.

[0055] The submodule SM is provided with a power supply circuit (not shown) that generates a drive voltage for the individual control unit 27 based on the voltage of the storage element 24. Therefore, when the voltage of the storage element 24 is low, the individual control unit 27 cannot operate.

[0056] [Bypass switch configuration example] Fig. 3 is a cross-sectional view showing a conceptual configuration of the bypass switch of Fig. 2. Fig. 3 shows a conceptual diagram of a configuration example of a spring-type bypass switch BPS.

[0057] 3, the bypass switch BPS includes a VST (Vacuum Switching Valve) 40 incorporating a main contact MC, an auxiliary contact AX, a contact operating mechanism 42, a housing 46, a drive circuit 50, a main contact terminal pair 53, and an auxiliary contact terminal pair 54. The VST 40, the contact operating mechanism 42, and the auxiliary contact AX are disposed inside the housing 46. Instead of the VST 40, the main contact MC may be provided in air.

[0058] 2. Main contact MC includes movable contact 41M and fixed contact 41F, and auxiliary contact AX includes movable contact 45M and fixed contact 45F. Main contact terminal pair 53 is connected to movable contact 41M and fixed contact 41F of main contact MC, and auxiliary contact terminal pair 54 is connected to movable contact 45M and fixed contact 45F of auxiliary contact AX. Main contact terminal pair 53 is further connected to input / output terminals 26P and 26N of FIG. 2, and auxiliary contact terminal pair 54 is further connected to lighting circuit 30 of FIG. 2.

[0059] The contact operating mechanism 42 includes a spring 43, a manual lever 44, and a latch 45. When the spring 43 is energized, the movable contact 41M and the fixed contact 41F of the main contacts MC are separated from each other, and the movable contact 45M and the fixed contact 45F of the auxiliary contact AX are separated from each other. When the spring 43 is released from its energization, the movable contact 41M and the fixed contact 41F of the main contacts MC come into contact with each other, and the movable contact 45M and the fixed contact 45F of the auxiliary contact AX come into contact with each other.

[0060] The manual lever 44 rotates around a rotation axis 44S. The spring 43 is energized by manually moving the manual lever 44. The latch 45 locks the manual lever 44 in this energized state. The means for energizing the spring 43 is not limited to the manual lever 44. For example, instead of the manual lever 44, a manual handle or an electric motor may be used.

[0061] 2, the drive circuit 50 operates a relay built into the latch 45 by passing a drive current through the latch 45 of the contact operating mechanism 42. This unlocks the manual lever 44, and the spring 43 is released, causing the movable contact 41M to be pushed in by the manual lever 44. As a result, the main contact MC and the auxiliary contact AX in the VST 40 become conductive. The fact that the auxiliary contact AX has become conductive can be visually confirmed by the light emission of the light-emitting element 33, and is further detected by the individual control unit 27 via the lighting circuit 30. The continuity of the main contact MC can also be visually confirmed by the change in the position of the manual lever 44.

[0062] 3, the drive circuit 50 includes, for example, a DC power supply 51 and a switch 52. When an ON signal is received from the individual control unit 27, the switch 52 is turned on, allowing a current to flow through the relay inside the latch 45.

[0063] It should be noted that an inflator-type contact operating mechanism 42 may be used instead of the spring-type contact operating mechanism 42. In a pyrotechnic inflator, a gas generating agent is ignited by a current supplied from a drive circuit 50, and the gas generating agent burns to generate gas. The gas pressure of the generated gas pushes out the movable contact 41M of the main contact MC and the movable contact 45M of the auxiliary contact AX. As a result, the main contact MC and the auxiliary contact AX are brought into electrical contact.

[0064] In the above description, the auxiliary contact AX is a make contact that is normally open and closes when the bypass switch BPS is turned on. Alternatively, a break contact that is normally closed and opens when the bypass switch BPS is turned on may be used as the auxiliary contact AX. In this case, an inverting circuit may be provided in the lighting circuit 30 so that the light-emitting element 33 lights up when the auxiliary contact AX is open, or the turning off of the light-emitting element 33 may confirm that the bypass switch BPS is turned on. That is, the light-emitting element 33 may start or stop emitting light when the lighting circuit 30 is turned on or off when the auxiliary contact AX is closed, or may start or stop emitting light when the lighting circuit 30 is turned on or off when the auxiliary contact AX is opened.

[0065] [Example of control device hardware configuration] Fig. 4 is a block diagram showing an example of the hardware configuration of the upper control device. Fig. 4 shows an example in which the upper control device 3 is configured by a computer. Fig. 4 also shows an example in which the computer (i.e., the command generation unit 19) and each sub-module SM are connected via a relay device 18.

[0066] 4, the upper control device 3 includes a command generation unit 19 and a relay device 18. The command generation unit 19 generates various commands 28 including control commands and protection commands for controlling the operation of each submodule SM based on the detected values ​​of the AC voltage Vac, the AC current Iac, the DC voltage Vdc, the DC current Idc, the arm current Iarm, and the capacitor voltage Vc of each submodule SM. The command generation unit 19 transmits the generated various commands 28 to each submodule SM via the relay device 18.

[0067] The command generation unit 19 includes one or more input converters 60, one or more sample-and-hold (S / H) circuits 61, a multiplexer (MUX) 62, and an A / D (Analog-to-Digital) converter 63. The command generation unit 19 also includes one or more CPUs 64, a RAM (Random Access Memory) 65, and a ROM (Read Only Memory) 66. The command generation unit 19 also includes two or more input / output interfaces (I / F) 67A, 67B, ..., an auxiliary storage device 68, and a bus 69 that interconnects the above components.

[0068] The input converter 60 has an auxiliary transformer (not shown) for each input channel. Each auxiliary transformer converts the detection signal from each electrical quantity detector in FIG. 1 into a signal with a voltage level suitable for subsequent signal processing.

[0069] A sample-and-hold circuit 61 is provided for each input converter 60. The sample-and-hold circuit 61 samples and holds a signal representing an electrical quantity received from the corresponding input converter 60 at a specified sampling frequency.

[0070] The multiplexer 62 sequentially selects the signals held in the plurality of sample-and-hold circuits 61. The A / D converter 63 converts the signal selected by the multiplexer 62 into a digital value. Note that by providing a plurality of A / D converters 63, A / D conversion may be performed in parallel on detection signals of a plurality of input channels.

[0071] The CPU 64 controls the entire command generating unit 19 and executes arithmetic processing in accordance with a program. The RAM 65 as a volatile memory and the ROM 66 as a nonvolatile memory are used as the main memory of the CPU 64. The ROM 66 stores programs, setting values ​​for signal processing, and the like. The auxiliary storage device 68 is a nonvolatile memory with a larger capacity than the ROM 66, and stores programs, data on detected values ​​of electrical quantity, and the like.

[0072] Input / output interfaces 67A, 67B, ... are interface circuits for communication between CPU 64 and external devices. In the case of Fig. 1, command generation unit 19 is connected to relay device 18 via input / output interface 67A. Furthermore, command generation unit 19 is connected to surveillance camera 70 via input / output interface 67B, and acquires image data captured by surveillance camera 70.

[0073] 4, at least a part of the command generating unit 19 can be configured using circuits such as FPGA and ASIC. Also, at least a part of the functions of each functional block can be configured using analog circuits.

[0074] The relay device 18 is connected between the command generating unit 19 and each sub-module SM. The relay device 18 is connected to each sub-module SM via a star-type network. Typically, the relay device 18 is configured by a dedicated circuit, some or all of which may be configured by an FPGA.

[0075] The relay device 18 transmits various commands 28 received from the command generation unit 19 to each sub-module SM. Furthermore, the relay device 18 receives the value of the voltage of the storage element 24 (i.e., the capacitor voltage Vc) measured by the voltage detector 25 of the sub-module SM. Although the relay device 18 is not an essential component, providing the relay device 18 can reduce the communication volume and processing volume of the CPU 64, thereby enabling high-speed, low-latency communication with fewer communication lines.

[0076] [Confirming the physical layout of the converter cells and the operation of the bypass switches] Fig. 5 is an external view for explaining the physical arrangement of multiple converter cells. Fig. 6 is a cross-sectional view seen from the Y direction in Fig. 5. Figs. 5 and 6 show a configuration called a converter valve tower 72 (72A, 72B).

[0077] The converter valve tower 72 (72A, 72B) comprises a plurality of converter modules 73_1 to 73_5 stacked in the vertical direction (Z direction). Each converter module 73 comprises a plurality of sub-modules SM (eight sub-modules SM#1 to SM#8 in the case of FIG. 5) arranged in multiple horizontal directions (Y direction). Each converter module 73 is supported by support posts 76 and insulators 77. The sides of each converter module 73 are surrounded by shield plates 75. The shield plates 75 are provided to prevent partial discharge due to electric field concentration.

[0078] A display window 78 is provided on the front surface of the housing of each submodule SM for emitting light from the light-emitting element 33, which indicates the operating state of the bypass switch BPS. However, because the display window 78 is blocked by the shield plate 75, a light-guiding fiber 79 for guiding the light from the light-emitting element 33 is connected to the display window 78. The light-guiding fiber 79 is arranged so as to pass from the display window 78 through the gap between the shield plate 75 and the bottom plate 74 and reach the front of the shield plate 75. The operating state of the bypass switch BPS can be visually confirmed by whether or not the tip of the light-guiding fiber 79 is emitting light. The light-guiding fiber 79 may be made of a light-guiding material such as plastic or glass, for example.

[0079] In the power conversion device 1 of this embodiment, a monitoring camera 70 with a fisheye lens or a wide-angle lens is used to quickly identify the presence or absence of light emission at the tips of the numerous light guide fibers 79 connected to the numerous submodules SM. Specifically, as shown in FIG. 6, the converter valve towers 72A, 72B are arranged so that the sides on which the light guide fibers 79 to be identified are attached face each other. The monitoring cameras 70 (70A, 70B) are installed on a ceiling 80 or floor 81 between the converter valve towers 72A, 72B. This arrangement allows the numerous light guide fibers 79 to be photographed simultaneously.

[0080] The image data captured by the monitoring camera 70 is transmitted to, for example, the host controller 3. The host controller 3 performs image processing on the image data. Specifically, the host controller 3 corrects image distortion caused by the fisheye lens, identifies the position of the light-guiding fibers 79 attached to each submodule SM, and determines whether the bypass switch BPS is operating or not based on whether the light-guiding fibers 79 are emitting light or not. This image processing can be performed at high speed.

[0081] In addition, if the contact operating mechanism 42 of the bypass switch BPS is a pyrotechnic inflator, the light generated when the gas generating agent is ignited and burned may be collected and transmitted to the outside of the submodule SM by an optical fiber.

[0082] [Bypass switch activation and verification procedure] 7 is a flowchart showing the bypass switch closing operation and the procedure for checking it. The explanation up to this point will be summarized below with reference to FIG.

[0083] During normal operation, the upper control device 3 generates voltage command values ​​for controlling the operation of each submodule SM based on the detected values ​​of the AC voltage Vac, the AC current Iac, the DC voltage Vdc, the DC current Idc, the arm current Iarm, and the capacitor voltage Vc of each submodule SM (S102). Furthermore, the upper control device 3 transmits the generated voltage command values ​​to each submodule SM (S101). During normal operation (NO in S103), these operations are repeated.

[0084] During normal operation, the individual control unit 27 of each submodule SM controls the opening and closing of the switching elements 22A, 22B based on a voltage command value received from the upper control device 3 (S201). Furthermore, the individual control unit 27 of each submodule SM transmits a detected value of the capacitor voltage Vc to the upper control device 3 (S202). During normal operation (NO in S203), these operations are repeated.

[0085] The individual control unit 27 of the submodule SM that detected the abnormality (hereinafter referred to as the faulty submodule SM) starts closing the bypass switch BPS by sending a closing command to the bypass switch BPS (YES in S203), and further notifies the upper control device 3 of the start of closing (S204). For example, if the detected value of the capacitor voltage Vc exceeds the upper or lower limit of the threshold range and the bypass switch BPS closing standby signal or start-stop signal has not been received from the upper control device 3, it is determined that an abnormality has occurred.

[0086] When the main contact MC of the bypass switch BPS is closed in response to the closing command, the auxiliary contact AX is closed and the light-emitting element 33 emits light (S205). When the individual control unit 27 of the faulty submodule SM confirms that the auxiliary contact AX is closed from the signal from the lighting circuit 30, it notifies the upper control device 3 that the bypass switch BPS has been closed (S206).

[0087] On the other hand, when the upper control device 3 receives a notification that the bypass switch BPS has started to be turned on, or when it detects a communication abnormality with any of the bypass switches BPS (YES in S103), it proceeds to a flow (S104 to S108) to confirm whether the power converter 2 can continue operating.

[0088] Specifically, when the upper control device 3 does not receive a notification that the bypass switch BPS has been turned on from the faulty sub-module SM that notified it of the start of turning on the bypass switch BPS (NO in S104), the upper control device 3 itself confirms that the bypass switch BPS has been turned on. That is, the upper control device 3 acquires image data captured by the monitoring camera 70 (S105). Then, the upper control device 3 performs image processing on the acquired image data to determine whether the light-emitting element 33 of each sub-module SM is emitting light (S106).

[0089] If the upper control device 3 determines as a result of the above determination that the power converter 2 cannot continue to operate (NO in S107), it opens an AC circuit breaker (not shown in FIG. 1) between the power converter 2 and the AC system 12 to stop the power converter 2 (S109). For example, if the image processing of the surveillance camera video does not confirm that the bypass switch BPS of the faulty submodule SM is turned on, the upper control device 3 determines that the power converter 2 cannot continue to operate. Alternatively, if the capacitor voltage Vc received from a certain submodule SM exceeds the threshold range but the bypass switch BPS of the certain submodule SM is not confirmed to be turned on, the upper control device 3 determines that the power converter 2 cannot continue to operate.

[0090] On the other hand, if the upper control device 3 receives a notification from the faulty submodule SM that the bypass switch BPS has been turned on (YES in S104), or if it has confirmed that the bypass switch BPS of the faulty submodule SM has been turned on from the results of image processing of the surveillance camera video, even if it has not received a notification from the faulty submodule SM that the bypass switch BPS has been turned on (NO in S104), it determines that it is possible to continue operating the power converter 2 (YES in S107). In this case, the upper control device 3 changes the settings of control parameters such as the number of valid submodules (S108), and then continues operating the power converter 2 (return to S101).

[0091] In place of the above procedure, the upper control device 3 may confirm (S105, S106) whether or not a notification that the bypass switch BPS has been turned on is received based on image data from the monitoring camera 70, regardless of whether or not a notification that the bypass switch BPS has been turned on is received (YES or NO in S104). That is, the confirmation of whether or not the bypass switch BPS has been turned on may be performed in parallel by the upper control device 3 and the individual control unit 27 of the failed submodule SM.

[0092] A plurality of monitoring cameras 70 are prepared to check whether the bypass switches BPS of all the sub-modules SM constituting the power converter 2 are turned on or off. Each monitoring camera 70 is placed in a position where it can check whether the light-emitting elements 33 of as many sub-modules SM as possible are emitting light or not.

[0093] [Effects of the First Embodiment] As described above, according to the power conversion device 1 of the first embodiment, each sub-module SM is provided with a lighting circuit 30 connected to the auxiliary contact AX of the bypass switch BPS. When the auxiliary contact AX is closed, the lighting circuit 30 is brought into conduction, causing the light-emitting element 33 to emit light. The light from the light-emitting element 33 is guided to the outside of the shield plate 75 by the light-guiding fiber 79, making it easy to identify whether the light-emitting element 33 of each sub-module SM is emitting light.

[0094] Here, multiple monitoring cameras 70 are installed on the ceiling 80 and / or floor 81 of a room in which multiple sub-modules SM are housed in the form of converter valve towers 72. Each monitoring camera 70 is installed in a position where it can capture images of the light emitted by the light-emitting elements 33 of as many sub-modules SM as possible at once. This makes it possible to store information about whether the light-emitting elements 33 of the many sub-modules SM that make up the power converter 2 are emitting light in a small amount of image data.

[0095] The host controller 3 performs image processing on the image data captured by the monitoring camera 70 to determine the operating state of the bypass switch BPS of each sub-module SM constituting the power converter 2. In this way, the host controller 3 can directly and reliably grasp the operating state of the bypass switch BPS without going through the individual control unit 27 of each sub-module SM, thereby improving the operational continuity and availability of the power converter 2.

[0096] The means for checking the operating state of the bypass switch BPS is not limited to the light emission of the light-emitting element 33. For example, any visually identifiable indicator may be used, such as extinction of the light-emitting element 33, discoloration of a specific portion, a change in the reflectance of a specific portion, or a change in the shape or position of a specific portion. Therefore, more generally, each sub-module SM includes an alarm unit that visually notifies the user that the bypass switch BPS has been activated. The monitoring camera 70 then acquires information regarding the operating state of each bypass switch BPS by capturing images of the alarm units of the multiple sub-modules SM collectively as a single image data.

[0097] Furthermore, the notification unit may have multiple visually distinguishable features. For example, a visual change in a first feature may be associated with the operation of the bypass switch BPS, and a visual change in a second feature may be associated with a fault state of the corresponding submodule SM. The fault state may represent a type of fault, such as an abnormality in the capacitor voltage Vc, a power supply abnormality, or a communication abnormality. The upper control device 3 identifies the changes in the multiple features of the notification unit based on image data captured by the monitoring camera 70.

[0098] As a specific example of the above-mentioned multiple features, the first feature may be the presence or absence of light emission from the light-emitting element 33, and the second feature may be the difference in color when the light-emitting element 33 emits light. Alternatively, multiple light-emitting elements 33 may be provided at different positions to represent multiple features.

[0099] Embodiment 2 In the second embodiment, as a modification of the above-described notification unit, an example will be described in which the position of the specific part changes when the bypass switch BPS operates.

[0100] 8A and 8B are diagrams illustrating a modified example of a notification unit that notifies the operating state of a bypass switch. Fig. 8A shows an external view of a submodule SM, and Fig. 8B conceptually shows a cross-sectional view of the submodule SM as viewed from the Z direction.

[0101] 8(A), the tip of a manual lever 44 constituting the contact operating mechanism 42 of FIG. 3 protrudes from a horizontally elongated hole 48 formed in the front surface of a housing 47 of the submodule SM. When the bypass switch BPS operates, the tip of the manual lever 44 moves along the longitudinal direction of the hole 48. Therefore, it is possible to confirm whether or not the bypass switch BPS has operated based on the position of the tip of the manual lever 44.

[0102] However, the travel length of manual lever 44 is approximately the distance between movable contact 41M and fixed contact 41F of main contact MC, which is not very long and does not provide good visibility. Therefore, in order to increase the travel length and improve visibility, a lever 85 is attached to the tip of manual lever 44.

[0103] As shown in Figure 8(B), the force point 86 of the lever 85 is connected to the tip of the manual lever 44 and moves as the manual lever 44 moves. A mark such as reflective tape is attached to the point of action 88 of the lever 85 to increase visibility. The distance from the point of action 88 to the fulcrum 87 is longer than the distance from the point of action 86 to the fulcrum 87, so the length of movement can be increased. Note that, although the fulcrum 87 is provided between the point of action 86 and the point of action 88 in Figure 8(B), the point of action 86 and the point of action 88 may be provided on the same side of the fulcrum 87.

[0104] When a shield plate 75 is provided on the front surface of the submodule SM, the lever 85 is disposed so that the lever 85 protrudes forward from a gap in the shield plate 75.

[0105] The above-described structure of the submodule SM improves visibility of the operating status of the bypass switch BPS, thereby improving safety and work efficiency when workers perform maintenance work. Furthermore, it also makes it easier for the monitoring camera 70 to automatically detect the operating status of the bypass switch BPS.

[0106] The means for changing the position of the specific part when the bypass switch BPS is activated is not limited to the combination of the manual lever 44 and the lever 85. More generally, it is sufficient if the specific part that is visible from outside the submodule SM is configured to change its position in conjunction with the movable contact 41M of the main contact MC.

[0107] Embodiment 3 In the third and fourth embodiments, a backup means for turning on the bypass switch BPS when the bypass switch BPS cannot be turned on due to a failure of the individual control unit 27 of the submodule SM will be described.

[0108] Fig. 9 is a circuit diagram showing an example of the configuration of a submodule in a power conversion device according to a third embodiment. The submodule SM (converter cell 7) of Fig. 9 differs from the submodule SM of Fig. 2 in that it further includes an abnormality detection unit 90. The abnormality detection unit 90 outputs a signal for closing the bypass switch BPS (main contact MC and auxiliary contact AX) when the voltage of the storage element 24 (capacitor voltage Vc) exceeds an upper limit threshold. Since the other points in Fig. 9 are the same as those in Fig. 2, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0109] 9, the abnormality detection unit 90 includes resistance elements 91 and 92, a Zener diode 94, a relay 95, and a DC power supply 98 that configure a voltage divider circuit for dividing the voltage of the storage element 24. The relay 95 includes an electromagnetic coil 96 and a switch 97. The resistance elements 91 and 92 are connected in series between a high potential side node 24P and a low potential side node 24N of the storage element 24. The Zener diode 94 and the electromagnetic coil 96 are connected in series between a connection node (also referred to as a voltage division node 93) of the resistance elements 91 and 92 and the low potential side node 24N of the storage element 24.

[0110] According to the configuration of the abnormality detection unit 90 described above, when the voltage at the voltage division node 93 exceeds the Zener voltage (corresponding to the upper threshold) of the Zener diode 94, a current flows through the electromagnetic coil 96, causing the switch 97 to become conductive. As a result, the voltage of the DC power supply 98 is applied to the bypass switch BPS, causing the main contact MC and the auxiliary contact AX to become conductive. More specifically, when the contact operating mechanism 42 is of the spring type shown in FIG. 3, the abnormality detection unit 90 directly releases the latch 45. When the contact operating mechanism 42 is of the pyrotechnic inflator type, the abnormality detection unit 90 directly ignites and burns the gas generating agent.

[0111] In this way, by providing an abnormality detection unit 90 that operates independently of the individual control unit 27, the bypass switch BPS of the submodule SM can be turned on even if the individual control unit 27 of the failed submodule SM is abnormal. This ensures reliability in turning on the bypass switch BPS, thereby improving the continuity of operation and availability of the power converter 2.

[0112] Embodiment 4 In the fourth embodiment, a method different from that in the third embodiment is disclosed for turning on the bypass switch BPS of a failed submodule SM as a backup.

[0113] Fig. 10 is a circuit diagram showing an example of the configuration of a submodule SM in a power conversion device according to embodiment 4. The power conversion device of this embodiment differs from the power conversion device of embodiment 1 in that a pair of submodules is configured for every two adjacent submodules. Fig. 10 shows a pair of submodules 7A and 7B.

[0114] 10, the individual control unit 27 of the submodule 7A obtains the detected value of the capacitor voltage Vc from its own voltage detector 25, and obtains operation information of its own auxiliary contact AX via its own lighting circuit 30. In addition, the individual control unit 27 of the submodule 7A can output a signal to turn on its own bypass switch BPS.

[0115] Furthermore, the individual control unit 27 of the submodule 7A acquires the detected value of the capacitor voltage Vc from the counterpart voltage detector 25, and acquires operation information of the counterpart auxiliary contact AX via the counterpart lighting circuit 30. The individual control unit 27 of the submodule 7A can also output a signal to turn on the counterpart bypass switch BPS.

[0116] The same applies to the submodule 7B that is paired with the submodule 7A. Since other points in Figure 10 are the same as those in Figure 2, the same or corresponding parts will be given the same reference numerals and description will not be repeated.

[0117] Fig. 11 is a flowchart for explaining the protection operation for the paired sub-module. The individual control unit 27 of each sub-module SM executes the operation shown in the flowchart of Fig. 7 and also executes the operation shown in the flowchart of Fig. 11.

[0118] Specifically, each submodule SM acquires a detected value of the capacitor voltage Vc from the voltage detector 25 of the other submodule SM in the pair (S301). Then, each submodule SM determines whether the other submodule SM is abnormal based on the acquired capacitor voltage Vc of the other submodule (S302). For example, if the detected value of the other submodule's capacitor voltage Vc exceeds the upper or lower limit of the threshold range and a bypass switch BPS closing standby signal or a start-stop signal has not been received from the upper control device 3, the other submodule SM is determined to be abnormal (YES in S302).

[0119] When each submodule SM determines that the other submodule SM is abnormal (YES in S302), it checks whether the auxiliary contact AX of the other submodule's bypass switch BPS is closed (S303). As a result, if the other submodule's auxiliary contact AX is not closed (NO in S303), each submodule SM turns on the bypass switch BPS of the other submodule SM (S304). Furthermore, when each submodule SM confirms that the other submodule's bypass switch BPS has been turned on, it notifies the upper control device 3 of this fact (S305).

[0120] As described above, according to the power conversion device of the fourth embodiment, two adjacent submodules SM monitor the capacitor voltage Vc of the other submodule SM, and can turn on the other submodule's bypass switch BPS as a backup when an abnormality occurs in the other submodule SM. This ensures reliability in turning on the bypass switch BPS, thereby improving the continuity of operation and availability of the power converter 2.

[0121] Embodiment 5 In the fifth embodiment, each submodule SM evaluates the health of the bypass switch BPS during normal operation. Specifically, the individual control unit 27 of each submodule SM passes a weak current to the contact operating mechanism 42, which is weak enough not to turn on the bypass switch BPS, and monitors the generated voltage. This will be explained in detail below with reference to the drawings.

[0122] Fig. 12 is a cross-sectional view showing a conceptual configuration of a bypass switch in a power conversion device according to embodiment 5. Drive circuit 50A of bypass switch BPS in Fig. 12 differs from drive circuit 50 of bypass switch BPS in Fig. 3 in that it can pass a weak current to latch 45 of contact operating mechanism 42 in addition to the current that is passed when BPS is closed.

[0123] Specifically, the drive circuit 50A further includes a switch 110, a resistive element 111, and a voltage detection unit 112, in addition to the DC power supply 51 and the switch 52. The switch 110 and the resistive element 111 are connected in series with each other and in parallel with the switch 52. The voltage detection unit 112 detects a current generated in the resistive element 111. The opening and closing of the switch 52 and the switch 110 is controlled by the individual control unit 27. The detection value of the voltage detection unit 112 is transmitted to the individual control unit 27.

[0124] According to the above-described configuration of the bypass switch BPS, the individual control unit 27 controls the switches 52 and 110 to the open state during normal operation. When the individual control unit 27 detects an abnormality, such as the capacitor voltage Vc being outside the threshold range, it controls the switch 52 to the closed state. As a result, a drive current flows through the latch 45, which releases the latch 45 and turns on the bypass switch BPS.

[0125] On the other hand, when evaluating the soundness of the contact operating mechanism 42 of the bypass switch BPS during normal operation, the individual control unit 27 controls the switch 110 to the closed state. As a result, a weak current limited by the resistance element 111 flows to the latch 45, and the latch 45 is not released. At this time, the voltage of the resistance element 111 detected by the voltage detection unit 112 is sent to the individual control unit 27. The individual control unit 27 can detect the voltage generated in the contact operating mechanism 42 by subtracting the voltage of the resistance element 111 from the voltage of the DC power supply 51. If the voltage generated by the contact operating mechanism 42 increases, it can be determined that the wiring in the electromagnetic coil part of the latch 45 is about to break. Alternatively, if the voltage generated in the resistance element 111 is zero, it can be determined that the wiring in the latch 45 part is broken.

[0126] 12 is otherwise similar to that of FIG. 3, the same or corresponding parts are designated by the same reference characters and description thereof will not be repeated. Note that the configuration of drive circuit 50A in FIG. 12 is one example and is not limited to this.

[0127] Furthermore, a similar method can be used to evaluate the soundness of an inflator-type contact operating mechanism instead of the spring-type contact operating mechanism 42. For example, in a pyrotechnic inflator, a weak current that is not strong enough to ignite the gas generating agent is supplied from the drive circuit 50A.

[0128] 13 is a flowchart showing an example of a procedure for evaluating the health of the bypass switch BPS. The health evaluation is performed periodically during operation of the power conversion device (YES in S401).

[0129] First, the individual control unit 27 of each submodule SM causes the drive circuit 50A to pass a weak current to the contact operating mechanism 42, such that the bypass switch BPS is not turned on (S402). The individual control unit 27 acquires the detection value of the voltage generated in the contact operating mechanism 42 in this state.

[0130] If the detected voltage exceeds the first threshold value (YES in S403), the individual control unit 27 notifies the upper control device 3 of the deterioration of the bypass switch BPS (S404).

[0131] If the detected voltage exceeds a second threshold value that is greater than the first threshold value (YES in S405), the individual control unit 27 determines that there is an extremely high risk of failure and outputs a signal to close the bypass switch BPS (S406). Furthermore, when the individual control unit 27 confirms from the signal from the lighting circuit 30 that the auxiliary contact AX is closed, it notifies the upper control device 3 that the bypass switch BPS has been closed (S407).

[0132] As described above, according to the power conversion device of the fifth embodiment, the individual control unit 27 of each submodule SM checks the soundness of the contact operating mechanism 42 by passing a weak current through the contact operating mechanism 42 that is weak enough not to turn on the bypass switch BPS during normal operation. As a result, if it is determined that there is an extremely high risk of failure, the submodule SM turns on the bypass switch BPS before a failure occurs in the bypass switch BPS. This makes it possible to improve the reliability of the bypass switch BPS and the continuity of operation of the power converter.

[0133] Embodiment 6 In the sixth embodiment, confirmation of the soundness of the bypass switch BPS during inspection while the power converter 2 is out of operation will be described.

[0134] To check the integrity of the bypass switch BPS, an operation test is conducted for the inflator type, and a no-voltage input test is conducted for the spring type. However, due to factors such as test time, reusability, and adverse effects on equipment, the inflator type is limited to a one-time random inspection, and the no-voltage input test for the spring type is also limited to a limited number of times. This is because the mechanical shock is large even when the VST is input with no voltage.

[0135] Therefore, in the case of the spring type, the movement of the movable contact 41M of the main contact MC is limited by a buffer material during inspection. This allows the operation of the latch 45 to be repeatedly checked during periodic inspections, making it possible to replace the bypass switch BPS before an actual failure occurs. As a result, the failure rate during operation of the power converter 2 can be reduced, and the operational continuity and availability rate of the power converter 2 can be improved.

[0136] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0137] 1 power conversion device, 2 power converter, 3 upper control device, 4 leg circuit, 5 upper arm circuit, 6 lower arm circuit, 7, SM submodule (converter cell), 8 reactor, 9 arm current detector, 10 AC voltage detector, 11 DC voltage detector, 12 AC system, 13 transformer, 14 DC system, 16 AC current detector, 17 DC current detector, 18 relay device, 19 command generation unit, 20 conversion circuit, 22 switching element, 23 diode, 24 storage element, 24N low potential side node, 24P high potential side node, 25 voltage detector, 26N, 26P pair of input / output terminals, 27 individual control unit, 28 various commands, 29 signal, 30 lighting circuit, 31, 51, 98 DC power supply, 32, 91, 92, 111 resistance element, 33 light emitting element, 41F, 45F Fixed contact, 41M, 45M Movable contact, 42 Contact operating mechanism, 43 Spring, 44 Manual lever, 45 Latch, 46, 47 Housing, 48 Hole, 50, 50A Drive circuit, 52, 97, 110 Switch, 53 Main contact terminal pair, 54 Auxiliary contact terminal pair, 60 Input converter, 61 Sample-and-hold circuit, 62 Multiplexer, 63 A / D converter, 64 CPU, 65 RAM, 66 ROM, 67A, 67B Input / output interface, 68 Auxiliary storage device, 69 Bus, 70 Surveillance camera, 72 Converter valve tower, 73 Converter module, 74 Bottom plate, 75 Shield plate, 76 Support, 77 Insulator, 78 Display window, 79 Optical fiber, 85 Lever, 90 Fault detection unit, 93 Voltage divider node, 94 Zener diode, 95 Relay, 96 Electromagnet coil, 112 voltage detection unit, AX auxiliary contact, BPS bypass switch, Iac AC current, Iarm arm current, Idc DC current, MC main contact, Nn low potential side DC terminal, Np high potential side DC terminal, Nu, Nv, Nw AC input terminals, Vac AC voltage, Vc capacitor voltage, Vdc DC voltage.

Claims

1. A power conversion device comprising: a plurality of cascaded sub-modules; each of the plurality of sub-modules includes: a pair of input / output terminals; a plurality of semiconductor switching elements; a power storage element connected to the pair of input / output terminals via the plurality of semiconductor switching elements; a mechanical bypass switch for short-circuiting the pair of input / output terminals; an individual control unit for controlling opening and closing of the plurality of semiconductor switching elements and the bypass switch; a notification unit for visually notifying that the bypass switch has operated; the power conversion device further includes: a monitoring camera for collectively photographing each of the notification units of the plurality of sub-modules as one image data; a host control device for discriminating an operation state of the bypass switch of each of the plurality of sub-modules by performing image processing on the image data. A power conversion device.

2. The notification unit has a plurality of visually distinguishable features including a first feature and a second feature, a visual change of the first feature is associated with an operation of the bypass switch, a visual change of the second feature is associated with a failure state of a corresponding sub-module, the host control device discriminates changes of the plurality of features of the notification unit based on the image data by the monitoring camera. The power conversion device according to Claim 1.

3. The bypass switch includes: a main contact provided for short-circuiting the pair of input / output terminals and including a movable contact and a fixed contact; an auxiliary contact that performs a closing operation or an opening operation in conjunction with a closing operation of the main contact; the notification unit includes a light-emitting element, the light-emitting element starts or stops emitting light when a lighting circuit is conducted or cut off when the auxiliary contact is closed, or starts or stops emitting light when the lighting circuit is conducted or cut off when the auxiliary contact is opened. The power conversion device according to Claim 1 or 2.

4. The bypass switch includes a main contact including a movable contact and a fixed contact provided for short-circuiting the pair of input / output terminals, the notification unit changes its position in conjunction with the movable contact, and it can be confirmed that the bypass switch has operated by the position change of the notification unit. The power conversion device according to Claim 1 or 2.

5. The bypass switch further includes: A contact operation mechanism that operates the movable contact of the main contact by a drive current, and a drive circuit that generates the drive current according to a command of the individual control unit, wherein the drive circuit supplies a weak current to the contact operation mechanism such that the movable contact of the main contact does not operate during soundness evaluation of the bypass switch, and the individual control unit operates the bypass switch when a voltage generated in the contact operation mechanism by the weak current exceeds a threshold value. The power conversion device according to claim 3. **Claim 6** The bypass switch has a contact operation mechanism that operates the movable contact of the main contact when a spring is released, and the bypass switch is configured to limit the operation of the movable contact of the main contact by a buffer material during inspection. The power conversion device according to claim 3. **Claim 7** Each of the plurality of sub-modules further includes an abnormality detection unit that operates the bypass switch independently of the individual control unit based on a detected value of the voltage of the power storage element. The power conversion device according to claim 1 or 2. **Claim 8** The plurality of sub-modules are paired for every two adjacent sub-modules, and the individual control units of the paired sub-modules are configured to operate their own bypass switches based on the detected value of the voltage of their own power storage elements and operate the bypass switches of the other parties based on the detected values of the voltages of the power storage elements of the other parties. The power conversion device according to claim 1 or 2. **Claim 9** The bypass switch further includes a contact operation mechanism that operates the movable contact of the main contact by a drive current, and a drive circuit that generates the drive current according to a command of the individual control unit, wherein the drive circuit supplies a weak current to the contact operation mechanism such that the movable contact of the main contact does not operate during soundness evaluation of the bypass switch, and the individual control unit operates the bypass switch when a voltage generated in the contact operation mechanism by the weak current exceeds a threshold value. The power conversion device according to claim 4. **Claim 10** The bypass switch has a contact operation mechanism that operates the movable contact of the main contact when a spring is released, and the bypass switch is configured to limit the operation of the movable contact of the main contact by a buffer material during inspection. The power conversion device according to claim 4.

Images