A fault protection method and system for MMC sub-modules

Abstract

The application discloses a fault protection method and system of an MMC sub-module, wherein the fault protection method comprises the following steps: a control unit sends a turn-off instruction or a turn-on instruction to an IGCT device of a sub-module; the IGCT device executes turn-off according to the turn-off instruction of the control unit, judges a turn-off state of the IGCT device, and sends a turn-off failure signal to the control unit after turn-off failure; the control unit is locked after receiving the turn-off failure signal; the IGCT device with turn-off failure performs fault determination on the IGCT device, and sends a fault determination result to the control unit after the sub-module is locked; the control unit receives the fault determination result, and bypasses the sub-module or releases the lock of the sub-module according to the fault determination result. When the IGCT device turn-off failure is detected, the sub-module is locked in time, other IGCT devices are prevented from being turned on, and the fault spreading is effectively prevented; the application can judge whether the fault is a false alarm caused by interference through self-detection, reduce the false alarm probability of the sub-module, and prolong the maintenance period of the converter valve.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a fault protection method and system for an MMC submodule. Background Art

[0002] Direct current (DC) transmission technology has garnered widespread attention due to its advantages, including high power quality, large transmission capacity, high system stability, and ease of access to distributed energy resources. The converter is a core component of DC transmission technology, and its performance directly impacts its large-scale application. Modular multilevel converters (MMCs) have promising application prospects in DC transmission technology due to their outstanding advantages, including high power quality, good reliability, high-quality output waveforms, and low power losses. Currently, the primary power switching device in MMCs is the insulated gate bipolar transistor (IGBT), which features ease of drive, high peak current capacity, self-shutdown, and high switching frequency. Despite its significant advantages, IGBTs still suffer from significant issues compared to current-source devices, such as high on-state voltage drop, low reliability, and high manufacturing costs, leaving much room for improvement. Compared with IGBTs, integrated gate-commutated thyristors (IGCTs) have lower on-state voltage drop, higher reliability and lower manufacturing cost. They also have a compact structure, higher blocking voltage and current capacity, and are expected to significantly improve the performance of voltage-controlled devices in high-voltage, large-capacity flexible direct current transmission (MMC) converter valve applications.

[0003] However, unlike IGBTs, IGCT devices do not have a desaturation effect and their fault current shutoff capability is much smaller than that of IGBTs. Therefore, when IGCT devices are used in MMC sub-modules, after one IGCT device fails to shut down, once the other IGCT device opposite it is turned on, a 100kA-level fault surge current that cannot be shut off will be generated, damaging the sub-module and causing greater losses. Summary of the Invention

[0004] In response to the above problems, the present invention provides a fault protection method and system for an MMC submodule, which can prevent the submodule from generating surge current and damaging the submodule after any IGCT device fails to shut down.

[0005] A fault protection method for an MMC submodule comprises the following steps: a control unit sends a shutdown instruction or an opening instruction to an IGCT device of the submodule; the IGCT device shuts down according to the shutdown instruction of the control unit, determines its own shutdown state, and sends a shutdown failure signal to the control unit after a shutdown failure; the control unit locks the submodule after receiving the shutdown failure signal; after the submodule is locked, the IGCT device that failed to shut down determines its own fault and sends the fault determination result to the control unit; the control unit receives the fault determination result and, according to the fault determination result, bypasses the submodule or releases the submodule lock.

[0006] Furthermore, the IGCT device determines its own shutdown state including the following steps:

[0007] The IGCT device monitors its own anode current after shutdown, and if its own anode current does not decrease, it is determined that the shutdown has failed.

[0008] Furthermore, the IGCT device that fails to shut down determines its own fault, including the following steps:

[0009] After the first set time of the shutdown failure, the IGCT device that fails to shut down determines the cause of the shutdown failure as detection interference or IGCT device failure based on its own gate and cathode voltages;

[0010] If it is determined that the shutdown failure of the IGCT device that failed to shut down is caused by detection interference, the IGCT device that failed to shut down drives itself to perform a self-test to determine whether it is normal or faulty.

[0011] Furthermore, if it is determined that the reason for the shutdown failure of the IGCT device that failed to shut down is detection interference, the IGCT device that failed to shut down drives itself to perform a self-test to determine whether it is normal or faulty:

[0012] The IGCT device that failed to shut down drives itself to perform a turn-on trigger, and is turned on for a second set time before being turned off. If the turn-on and turn-off processes are normal, it is determined that the IGCT device that failed to shut down is normal. If an abnormal signal occurs during the turn-on or turn-off process, it is determined that the IGCT device that failed to shut down is faulty.

[0013] Furthermore, the second set time is greater than or equal to the nominal shortest turn-on time of the IGCT device.

[0014] Furthermore, the control unit receives the fault determination result and bypasses the submodule or releases the submodule blocking according to the fault determination result. Specifically:

[0015] If the control unit receives a fault confirmation signal of the IGCT device that fails to shut down, the control unit controls the bypass switch of the submodule to close and bypass the submodule; if the control unit receives a fault relief signal, the control unit controls the submodule to resume normal operation.

[0016] Furthermore, the fault protection method of the MMC submodule further includes the steps of:

[0017] The valve-level control system sends a switching instruction to the control unit, and the control unit receives the switching instruction and generates a closing instruction or an opening instruction according to the switching instruction.

[0018] Furthermore, the fault protection method of the MMC submodule further includes the steps of:

[0019] The control unit sends the fault determination result of the submodule to the valve-level control system.

[0020] Furthermore, the submodule is a half-bridge module, a full-bridge module or a clamped bridge module.

[0021] An embodiment of the present invention also provides a fault protection system for an MMC submodule, comprising a control unit and a submodule, wherein the submodule comprises a plurality of IGCT devices; the control unit is configured to send a shutdown instruction or an opening instruction to the IGCT device of the submodule; the IGCT device is configured to execute shutdown according to the shutdown instruction of the control unit, and to determine its own shutdown state, and to send a shutdown failure signal to the control unit after a shutdown failure; the control unit is further configured to lock the submodule after receiving the shutdown failure signal; the IGCT device that fails to shut down is configured to perform a fault determination on itself after the submodule is locked, and to send the fault determination result to the control unit; the control unit is further configured to receive the fault determination result, and to bypass the submodule or release the submodule lock according to the fault determination result.

[0022] Furthermore, the IGCT device that fails to shut down is specifically used to:

[0023] After the first set time of the shutdown failure, the IGCT device that fails to shut down determines the cause of the shutdown failure as detection interference or IGCT device failure based on its own gate and cathode voltages;

[0024] If it is determined that the shutdown failure of the IGCT device that failed to shut down is caused by detection interference, the IGCT device that failed to shut down drives itself to perform a self-test to determine whether it is normal or faulty.

[0025] Furthermore, if it is determined that the reason for the shutdown failure of the IGCT device that failed to shut down is detection interference, the IGCT device that failed to shut down drives itself to perform a self-test to determine whether it is normal or faulty:

[0026] The IGCT device that failed to shut down drives itself to perform a turn-on trigger, and is turned on for a second set time before being turned off. If the turn-on and turn-off processes are normal, it is determined that the IGCT device that failed to shut down is normal. If an abnormal signal occurs during the turn-on or turn-off process, it is determined that the IGCT device that failed to shut down is faulty.

[0027] Furthermore, the fault protection system of the MMC submodule further includes: a valve-level control system, which is used to send a switching instruction to the control unit and is also used to receive a fault determination result of the submodule sent by the control unit.

[0028] Furthermore, the submodule is a half-bridge module, a full-bridge module or a clamped bridge module.

[0029] Beneficial effects of the present invention:

[0030] 1. When the present invention detects that the IGCT device fails to shut down, it promptly locks the submodule to prevent another IGCT device from turning on, thereby effectively preventing the fault from spreading.

[0031] 2. The present invention can determine whether a fault is a false alarm caused by interference through self-detection, thereby reducing the probability of false alarm faults in submodules and extending the maintenance cycle of the converter valve.

[0032] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A signal transmission link diagram of a fault protection system of an MMC submodule according to an embodiment of the present invention is shown;

[0035] Figure 2 A schematic flow chart of a fault protection method for an MMC submodule according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0037] The present invention provides a fault protection method and system for MMC submodules. In MMC applications, if an IGCT fails due to shutdown, the system can promptly lock the module, preventing the corresponding IGCT from turning on, effectively preventing the fault from spreading. Furthermore, the system can self-detect whether the fault is a false alarm caused by interference, reducing the probability of false alarms and extending the converter valve maintenance cycle.

[0038] To facilitate understanding of the embodiments of the present application, the following briefly introduces the IGCT device:

[0039] The integrated gate-commutated thyristor (IGCT) is a new type of switching device used in large-capacity power electronic devices. It primarily consists of a GCT chip encapsulated within a housing and a driver integrated externally. The IGCT driver's primary function is to receive communication signals from the upper-level control system and convert them into voltage and current signals used to switch the GCT chip on and off.

[0040] A fault protection method and system for an MMC submodule according to an embodiment of the present invention is applicable to a half-bridge module, a full-bridge module, a clamped bridge module, etc., which use IGCT as a fully controlled device.

[0041] See also Figure 1 , Figure 1 A signal transmission link diagram of a fault protection system of an MMC submodule according to an embodiment of the present invention is shown.

[0042] A fault protection system for an MMC submodule includes a submodule and a control unit. The submodule includes multiple IGCT devices and a bypass switch. Gate drivers of the multiple IGCT devices are communicatively connected to the control unit via optical fibers. The control unit is also connected to the bypass switch.

[0043] The control unit is used to send a shutdown instruction or an opening instruction to the IGCT device.

[0044] The IGCT device is used to execute shutdown according to the shutdown instruction of the control unit, determine its own shutdown state, and send a shutdown failure signal to the control unit after the shutdown fails.

[0045] The control unit is further configured to lock the submodule after receiving a shutdown failure signal.

[0046] The IGCT device that fails to shut down is used to determine its own fault after the submodule is locked, and send the fault determination result to the control unit.

[0047] The control unit is further configured to receive a fault determination result and control the bypass switch to close or release the submodule lock according to the fault determination result.

[0048] For example, the control unit is a local control board, which can control one or more IGCT devices.

[0049] For example, the submodule includes electrolytic capacitors, inductors L s , resistor R s , capacitor C s , the first diode D1, the second diode D2 and the third diode D s , a first IGCT device T1, a second IGCT device T2 and a bypass switch.

[0050] Among them, the positive electrode of the electrolytic capacitor and the inductor L s The first terminal, resistor R s The first end is connected to the inductor L s The second end and the third diode D s The anode of the first IGCT device T1 and the cathode of the first diode D1 are connected. s Cathode and resistor R s The second terminal, capacitor C s The first terminal is connected to the capacitor C s The second end is connected to the negative electrode of the electrolytic capacitor, the cathode of the second IGCT device T2, the anode of the second diode D2 and the first end of the bypass switch, and the cathode of the first IGCT device T1 is connected to the anode of the first diode D1, the anode of the second IGCT device T2, the cathode of the second diode D2 and the second end of the bypass switch.

[0051] The local control board is connected to the gate driver of the first IGCT device T1 and the gate driver of the second IGCT device T2 through optical fibers.

[0052] The local control board is used to control the on and off of the bypass switch, and receive the anode current signal and the gate cathode voltage signal of the first IGCT device T1 and the second IGCT device T2. At the same time, it can lock the first IGCT device T1 and the second IGCT device T2.

[0053] It should be noted that the submodule in the embodiment of the present invention is an exemplary illustration of an IGCT device being a fully controlled device.

[0054] Furthermore, when the submodule is applied to a converter valve, the fault protection system of the MMC submodule further includes a valve-level control system, which is connected to the control unit via an optical fiber.

[0055] The valve-level control system is used to send switching instructions to the control unit.

[0056] The control unit is further used to receive switching instructions and control the IGCT device to turn off or on according to the control instructions; and is also used to send the fault determination result of the submodule to the valve-level control system.

[0057] See also Figure 2 , Figure 2 A schematic flow chart of a fault protection method for an MMC submodule according to an embodiment of the present invention is shown.

[0058] An embodiment of the present invention further provides a fault protection method for an MMC submodule, comprising the following steps:

[0059] S1. The control unit sends a shutdown command or an opening command to the IGCT device.

[0060] S2. The IGCT device performs shutdown according to the shutdown instruction of the control unit. The IGCT device determines its own shutdown state and sends a shutdown failure signal to the control unit if the shutdown fails.

[0061] Specifically, the IGCT device determines its own shutdown state including the following steps:

[0062] The IGCT device monitors its own anode current after shutdown, and if its own anode current does not decrease, it is determined that the shutdown has failed.

[0063] For example, monitoring the anode current of the IGCT device after shutdown can be achieved by setting a current coil at the anode of the IGCT device, or detecting the shutdown loop voltage drop at the gate drive of the IGCT device. The specific implementation is existing technology and will not be described in detail.

[0064] It should be noted that after the IGCT device is turned off, its anode should no longer have current. If current can still be detected at the anode of the IGCT device after the shutdown time, it means that the IGCT device is in a short-circuit state. At this time, it can be determined that the IGCT device has failed to shut down. The IGCT device can report the shutdown failure signal to the control unit via optical fiber.

[0065] S3. After receiving the shutdown failure signal, the control unit locks the submodule.

[0066] Specifically, the locking submodule is a control unit that no longer sends an opening instruction to any IGCT device in the submodule.

[0067] The control unit receives the IGCT device shutdown failure signal and no longer triggers the corresponding IGCT device to turn on, thereby avoiding the capacitor being short-circuited through an IGCT device that failed to turn off (in a short-circuit state) and a newly turned-on IGCT device, causing a fault surge current.

[0068] S4. After the submodule is locked, the IGCT device that fails to shut down determines its own fault and sends the fault determination result to the control unit.

[0069] Specifically, the IGCT device that fails to shut down determines its own fault including the following steps:

[0070] S41 : After a first set time has passed since the IGCT device failed to shut down, the IGCT device determines that the cause of the shutdown failure is detection interference or IGCT device failure based on its own gate and cathode voltages.

[0071] The first setting time can be set adaptively. The first setting time is reserved to provide time for the gate cathode voltage to drop, thereby avoiding a short-time test that results in inaccurate test values.

[0072] For example, the first set time is 10ms. After the first set time of the shutdown failure, the IGCT device that fails to shut down detects its own gate and cathode voltages. If the absolute value of the voltage is higher than the fault threshold, it is determined that the shutdown failure is a detection interference. If the absolute value of the voltage is lower than the fault threshold, it is determined that it is a self-fault.

[0073] It's important to note that because current detection is susceptible to interference, further investigation is needed to determine the cause of the IGCT device's shutdown failure to avoid false fault alarms. If the shutdown failure is due to a malfunctioning IGCT shutdown function, then an internal short circuit has occurred in the IGCT chip. The IGCT's shutdown capacitors will discharge through the shorted chip, causing the gate and cathode voltages to decrease in absolute value. Over time, this signal will fall below the fault threshold. This more stable signal is therefore suitable for fault determination. If it falls below the fault threshold, the chip can be determined to be damaged.

[0074] S42: If it is determined that the shutdown failure of the IGCT device that has failed to shut down is caused by detection interference, the IGCT device that has failed to shut down drives itself to perform a self-check to determine whether it is normal or faulty.

[0075] For example, the IGCT device that failed to shut down drives itself to perform a turn-on trigger, and is turned off after the turn-on continues for a second set time. If the turn-on and turn-off processes are normal, it is determined that the IGCT device that failed to shut down is normal. If an abnormal signal occurs during the turn-on or turn-off process, it is determined that the IGCT device that failed to shut down is faulty.

[0076] Specifically, the second set time is greater than or equal to the nominal shortest turn-on time of the IGCT device. For example, the second set time is 100 μs.

[0077] It should be noted that when the absolute value of the gate cathode voltage exceeds the aforementioned fault threshold, there may be errors or interference in detecting the IGCT's off state. Alternatively, the IGCT may be damaged and in a high-impedance state. In this case, further verification is required to rule out the possibility that the IGCT is damaged but in a high-impedance state, causing the off-capacitor bank to discharge slowly.

[0078] After determining that the shutdown failure is caused by detection interference, the IGCT device that failed to shut down cycles itself on and off again for a duration equal to or greater than the IGCT's nominal minimum on-time to minimize the impact on converter valve operation. If both on- and off-times are normal, the IGCT shutdown failure signal is determined to be a false alarm. During this process, since the submodule is locked, the remaining IGCT devices in the submodule are also off, preventing the high fault current of a capacitor short circuit.

[0079] S5. The control unit receives the fault determination result and bypasses the submodule or unlocks the submodule according to the fault determination result.

[0080] Specifically, the IGCT device that fails to shut down sends an IGCT device fault confirmation signal or a fault relief signal to the control unit via the optical fiber.

[0081] If the control unit receives a fault confirmation signal indicating that the IGCT device has failed to shut down, the control unit controls the bypass switch to close, bypassing the submodule. If the control unit receives a fault clearance signal, the control unit controls the submodule to resume normal operation.

[0082] Furthermore, a fault protection method for an MMC submodule further includes the following steps before step S1:

[0083] S0. The valve-level control system sends a switching instruction to the control unit. The control unit receives the switching instruction and generates a closing instruction or an opening instruction according to the switching instruction.

[0084] Furthermore, a fault protection method for an MMC submodule further includes the following steps after step S5:

[0085] S6. The control unit sends the fault determination result of the submodule to the valve-level control system.

[0086] It should be noted that the dead zone of the sub-module in the embodiment of the present application should not be lower than the IGCT device shutdown delay, the IGCT device fault determination delay and the control unit fault judgment delay to ensure that the module can be locked in time after the shutdown fails. The dead zone of the sub-module refers to the delay from the shutdown of one IGCT device to the opening of another IGCT device under normal working conditions.

[0087] To facilitate understanding of the embodiments of the present application, the fault protection method disclosed in the present application is described in more detail by taking the failure of the first IGCT device T1 of the submodule to turn off as an example.

[0088] The valve-level control system sends a switching instruction to the control unit. The control unit receives the switching instruction and controls the first IGCT device T1 in the submodule to turn off according to the control instruction. The anode current of the first IGCT device T1 does not decrease. The first IGCT device T1 sends a shutdown failure signal to the control unit through the optical fiber. After receiving the shutdown failure signal of the first IGCT device T1, the control unit immediately locks the submodule, that is, it no longer triggers the second IGCT device T2 to turn on after the dead zone.

[0089] Taking into account the internal delay of the first IGCT device T1, the first IGCT device T1 detects its own gate and cathode voltages after the first set time after the shutdown failure. If the voltage is abnormal, it is determined that it is faulty and the fault determination result is sent to the control unit. The control unit controls the bypass switch to close to bypass the sub-module and sends the fault determination result to the valve-level control system.

[0090] After a first set time after the first IGCT device T1 fails to shut down, it detects its own gate and cathode voltages. If the voltages are normal, the first IGCT device T1 triggers itself for a short time and performs fault detection throughout the triggering process. If the triggering process is determined to be normal, the first IGCT device T1 is determined to be fault-free, the fault is considered a false alarm, and the control unit releases the submodule lockout state. If the triggering process of the first IGCT device T1 is determined to be abnormal, the first IGCT device T1 is determined to be faulty and the fault determination result is sent to the control unit. The control unit controls the bypass switch to close to bypass the submodule and sends the fault determination result to the valve-level control system.

[0091] The fault protection method for the MMC submodule of the embodiment of the present invention is implemented based on the control of the IGCT device and is applicable to all submodules with the IGCT device as the fully controlled device, for example, a half-bridge module, full-bridge module or clamped bridge module with the IGCT device as the fully controlled device.

[0092] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fault protection method for an MMC submodule, characterized in that: The following steps are involved: The control unit sends a shutdown command or an opening command to the IGCT device of the submodule; The IGCT device shuts down according to the shutdown instruction of the control unit, determines its own shutdown state, and sends a shutdown failure signal to the control unit if the shutdown fails. The IGCT device determines its own shutdown state includes the following steps: the IGCT device monitors its own anode current after shutdown, and determines that the shutdown has failed if the own anode current does not decrease; After receiving the shutdown failure signal, the control unit locks the submodule; After the submodule is locked, the IGCT device that failed to shut down determines its own fault and sends the fault determination result to the control unit; wherein, the IGCT device that failed to shut down determines its own fault including the following steps: after a first set time after the shutdown failure, the IGCT device that failed to shut down determines whether the cause of the shutdown failure is detection interference or IGCT device failure based on its own gate and cathode voltages; if it is determined that the shutdown failure cause of the IGCT device that failed to shut down is detection interference, the IGCT device that failed to shut down drives itself to perform a self-check to determine whether it is normal or faulty, specifically: the IGCT device that failed to shut down drives itself to perform a turn-on trigger, and the turn-on continues for a second set time before shutting down; if the turn-on and turn-off processes are normal, the IGCT device that failed to shut down is determined to be normal; if an abnormal signal occurs during the turn-on or turn-off process, the IGCT device that failed to shut down is determined to be faulty; The control unit receives the fault determination result and bypasses the submodule or unlocks the submodule according to the fault determination result.

2. The fault protection method according to claim 1, characterized in that: The second set time is greater than or equal to the nominal minimum turn-on time of the IGCT device.

3. The fault protection method according to claim 1, characterized in that: The control unit receives the fault determination result and bypasses the submodule or releases the submodule lock according to the fault determination result. Specifically: If the control unit receives a fault confirmation signal of the IGCT device that fails to shut down, the control unit controls the bypass switch of the submodule to close and bypass the submodule; if the control unit receives a fault relief signal, the control unit controls the submodule to resume normal operation.

4. The fault protection method according to any one of claims 1 to 3, characterized in that: The fault protection method of the MMC submodule further includes the following steps: The valve-level control system sends a switching instruction to the control unit, and the control unit receives the switching instruction and generates a closing instruction or an opening instruction according to the switching instruction.

5. The fault protection method according to claim 4, characterized in that: The fault protection method of the MMC submodule further includes the following steps: The control unit sends the fault determination result of the submodule to the valve-level control system.

6. The fault protection method according to any one of claims 1 to 3, characterized in that: The submodules are half-bridge modules, full-bridge modules or clamped bridge modules.

7. A fault protection system for an MMC submodule, characterized in that: It includes a control unit and a submodule, wherein the submodule includes a plurality of IGCT devices; A control unit, used to send a shutdown instruction or an opening instruction to the IGCT device of the submodule; The IGCT device is configured to shut down according to a shutdown instruction from the control unit, determine its own shutdown state, and send a shutdown failure signal to the control unit if the shutdown fails. The IGCT device determines its own shutdown state by monitoring its own anode current after shutdown, and determining that the shutdown has failed if the own anode current does not decrease. The control unit is further configured to lock the submodule after receiving a shutdown failure signal; The IGCT device that fails to shut down is used to determine its own fault after the submodule is locked, and send the fault determination result to the control unit; wherein, the IGCT device that fails to shut down determines its own fault including the following steps: after a first set time after the shutdown failure, the IGCT device that fails to shut down determines whether the cause of the shutdown failure is detection interference or IGCT device failure based on its own gate and cathode voltages; if it is determined that the shutdown failure cause of the IGCT device that fails to shut down is detection interference, the IGCT device that fails to shut down drives itself to perform a self-check to determine whether it is normal or faulty, specifically: the IGCT device that fails to shut down drives itself to perform a turn-on trigger, and the turn-on continues for a second set time before shutting down; if the turn-on and turn-off processes are normal, the IGCT device that fails to shut down is determined to be normal; if an abnormal signal occurs during the turn-on or turn-off process, the IGCT device that fails to shut down is determined to be faulty; The control unit is further configured to receive a fault determination result and bypass the submodule or unlock the submodule according to the fault determination result.

8. The fault protection system according to claim 7, characterized in that: The fault protection system further includes: a valve-level control system, which is used to send switching instructions to the control unit and is also used to receive the fault determination result of the submodule sent by the control unit.

9. The fault protection system according to claim 7, characterized in that: The submodules are half-bridge modules, full-bridge modules or clamped bridge modules.

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