MMC sub-module breakdown test loop and method based on turning thyristors

Abstract

The invention discloses an MMC sub-module breakdown test loop and method based on a turning thyristor. The loop comprises an adjustable direct-current power supply, a first pre-charging loop, a second pre-charging loop and a sample sub-loop which are controlled by a control unit. A first pre-charging loop and a second pre-charging loop which are connected in parallel are arranged between the sample sub-loop and the adjustable direct-current power supply; the first pre-charging loop consists of a first current-limiting resistor and a first switch which are sequentially connected in series, and is used for charging a first voltage-stabilizing capacitor in the sample sub-loop; the second pre-charging loop is composed of a second current-limiting resistor, a second voltage-stabilizing capacitor, a second switch and an electric reactor; the second pre-charging loop is used for responding to a corresponding control instruction and generating instantaneous current to enable a diode corresponding to an upper switch tube of the test sample sub-loop to reversely fail to form direct connection of the upper switch tube and a lower switch tube; according to the loop structure, the reliability and effectiveness of verifying the breakover voltage and the explosion-proof capability of the thyristor can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage direct current power transmission, and in particular to a MMC submodule breakdown test circuit and method based on a transition thyristor. Background Art

[0002] As the core component of flexible DC transmission technology, flexible DC converter valves mostly adopt modular multi-level topology (MMC). With the increase of transmission power of flexible DC converter valves, crimped IGBTs have become the core switching devices of MMC submodules. During the operation of MMC, the capacitor voltage fluctuations caused by the continuous charging and discharging of submodule capacitors may cause power device breakdown. Therefore, in the design stage of MMC submodule structure, it is necessary to test and verify whether the protection measures taken after the short-circuit breakdown of the power device are safe and effective.

[0003] Traditional thyristor breakdown tests cannot guarantee the formation of a straight-through path, making it difficult to form an effective breakdown, resulting in failure to meet test requirements.

[0004] It can be seen that how to effectively improve the effectiveness of the MMC submodule test has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0005] The present invention provides a MMC submodule breakdown test circuit and method based on a transition thyristor, so as to solve the problem of how to ensure that the reverse recovery failure of the upper tube diode is caused when the thyristor fails, and improve the reliability of verifying the transition breakdown voltage of the submodule thyristor and verifying the explosion-proof capability of the tested MMC submodule.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides an MMC submodule breakdown test circuit based on a turn-on thyristor, comprising: It includes an adjustable DC power supply, a first pre-charging circuit, a second pre-charging circuit and a test sample sub-circuit which are respectively controlled by a control unit; The first pre-charging circuit and the second pre-charging circuit connected in parallel are provided between the sample sub-circuit and the adjustable DC power supply; The first pre-charging circuit is composed of a first current limiting resistor and a first switch connected in series, and the first pre-charging circuit is used to charge the first voltage stabilizing capacitor in the test sub-circuit; The second pre-charging circuit is composed of a second current limiting resistor, a second voltage stabilizing capacitor, a second switch and a reactor; one end of the second current limiting resistor is connected to the output end of the adjustable DC power supply, the other end of the second current limiting resistor is connected to one end of the second switch, the other end of the second switch is connected to one end of the reactor, the other end of the reactor is connected to the input end of the test sub-circuit, and the second voltage stabilizing capacitor is arranged between the second current limiting resistor and the second switch; and the second pre-charging circuit is used to respond to the corresponding control instruction, generate an instantaneous current to make the diode corresponding to the upper switch tube of the test sub-circuit reversely fail to form a direct connection between the upper and lower switch tubes; The control unit is used to at least control the state of the first switch and / or the second switch so that the upper and lower switch tubes of the test sample sub-loop are directly connected.

[0007] Furthermore, the port voltage output end of the test sample sub-loop is connected to the control unit, so that the control unit sends the generated control instruction to the second pre-charging loop.

[0008] Furthermore, the MMC submodule breakdown test circuit based on the turn-on thyristor further includes a cooling water circuit connected to the test subcircuit for dissipating heat from the test subcircuit.

[0009] Furthermore, in response to the opening signal sent by the control unit, the cooling water circuit opens the bypass switch of the test product sub-circuit and shields the closing function.

[0010] Furthermore, the topology of the test sub-loop includes a half-bridge topology and a full-bridge topology.

[0011] Furthermore, the adjustable DC power supply is composed of a power supply, a switching relay, a voltage regulator and a rectifier bridge. The output end of the power supply is connected to one end of the switching relay, the other end of the switching relay is connected to one end of the voltage regulator, and the other end of the voltage regulator is connected to the rectifier bridge to provide a controllable DC voltage.

[0012] Furthermore, the second switch or the first switch is a model with a millimeter-level opening speed.

[0013] Another embodiment of the present invention provides a MMC submodule breakdown test method based on a turn-on thyristor, which is applied to the above-mentioned MMC submodule breakdown test circuit based on a turn-on thyristor, comprising: Turn on the adjustable DC power supply and start the cooling water loop, and turn on the bypass switch of the test sample sub-loop; Closing the first switch, charging the voltage of the first voltage-stabilizing capacitor in the sample sub-circuit to the first preset voltage range via the first pre-charging circuit, and charging the voltage of the second voltage-stabilizing capacitor in the second pre-charging circuit to the second preset voltage range; The control unit monitors the thyristor port voltage of the test sub-loop, and when the monitoring result meets the first preset condition, the second switch is triggered to close.

[0014] Further, when the monitoring result satisfies the first preset condition, triggering the second switch to close includes: When it is monitored that the voltage waveform generated by the thyristor port voltage has a periodic drop, the second switch is triggered to close.

[0015] Another embodiment of the present invention provides a thyristor, which is designed to be obtained by testing the MMC sub-module breakdown test circuit based on the above-mentioned turn-thyristor, or the thyristor is obtained by the MMC sub-module breakdown test method based on the above-mentioned turn-thyristor.

[0016] Compared with the prior art, the embodiments of the present invention have the following advantages: The embodiment of the present invention designs a test circuit consisting of an adjustable DC power supply, a first pre-charging circuit, a second pre-charging circuit, a control unit and a test product sub-circuit, and the circuit structure is simple and consumes less resources; and through a double-stage trigger mechanism based on the first pre-charging circuit and the second pre-charging circuit, the sub-module forms a straight-through explosion, thereby improving the accuracy and reliability of verifying the thyristor turning voltage and explosion-proof capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the topological structure of the MMC submodule breakdown test circuit in one embodiment of the present invention; Figure 2 It is a schematic diagram of the MMC submodule direct explosion process in one embodiment of the present invention; Figure 3 is a flowchart of a breakdown test of an MMC submodule in one embodiment of the present invention; Figure 4 It is a typical waveform diagram of the voltage drop across the monitoring thyristor in one embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0020] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0021] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0022] The operation process of MMC is that the submodules output different voltages, so that the bridge arm outputs a step-shaped bridge arm voltage and approaches its reference value, and finally achieves the purpose of controlling AC and DC current. When the power module becomes uncontrollable due to a failure of the energy source or the control board, the capacitor in operation will be continuously charged. When the capacitor voltage exceeds its tolerance range, the MMC submodule power device may first short-circuit and break down. At this time, if the explosion-proof design of the MMC is insufficient, it may cause a greater accident.

[0023] Based on this, in order to be able to perform reliable explosion-proof capability tests on MMC submodules, an embodiment of the present invention provides an MMC submodule breakdown test circuit based on a turn thyristor. For details, see Figure 1 , Figure 1 The figure shows a schematic diagram of the topological structure of the MMC submodule breakdown test circuit in one embodiment of the present invention. It can be seen that the structure of the circuit mainly includes: a charging circuit, i.e., an adjustable DC power supply A, a first pre-charging circuit B1 and a second pre-charging circuit B2 connected in parallel, and a tested product submodule, i.e., a test product sub-circuit C, all of which are controlled by a control unit D.

[0024] The first pre-charging loop B1 and the second pre-charging loop B2 are connected in parallel with each other between the sample sub-loop C and the adjustable DC power supply A.

[0025] Specifically, the adjustable DC power supply A consists of a power supply DC, a switching relay KM, a voltage regulator TY and a rectifier bridge UR. The output end of the power supply DC is connected to one end of the switching relay KM, the other end of the switching relay KM is connected to one end of the voltage regulator TY, and the other end of the voltage regulator TY is connected to the rectifier bridge UR, so as to provide a controllable DC voltage for the entire test circuit.

[0026] During the test, the control unit D will control the start and stop of the power supply DC through the switch relay KM, and control the voltage regulator TY to adjust the charging voltage, charge the test sub-mode capacitor voltage to a preset value, and simultaneously charge the second voltage stabilizing capacitor C2 corresponding to the second pre-charging circuit B2 to a preset voltage value.

[0027] from Figure 1It can be seen that the structure of the test sub-loop C configured in the present invention includes a voltage-equalizing resistor R3, a first voltage-stabilizing capacitor C1, an upper switch tube T1, and a lower switch tube T2. Among them, the upper switch tube T1 and the lower switch tube T2 are connected in series, and the upper switch tube T1 corresponds to a reverse-connected diode D1, and the lower switch tube T2 corresponds to a reverse-connected diode D2. One end of the upper switch tube T1 is connected to one end of the resistor R3, and the other end of the resistor R3 is connected to an end of the lower switch tube T2 away from the upper switch tube T1. The first voltage-stabilizing capacitor C1 is connected in parallel at both ends of the voltage-equalizing resistor R3. A turning thyristor Thy and a bypass switch Tk are also connected in parallel at both ends of the lower switch tube T2.

[0028] It can be understood that the topology structure of the test sub-loop configured in this embodiment includes a half-bridge topology and a full-bridge topology, so as to match different test requirements by adjusting the control logic.

[0029] The first pre-charging loop B1 is composed of a first current limiting resistor R1 and a first switch K1 connected in series. Specifically, as an example, the first pre-charging loop B1 of this embodiment is used to charge the first voltage stabilizing capacitor C1 in the test sub-loop C and charge it to the lower limit range of the thyristor breakover voltage, so that the thyristor breaks over, thereby generating an instantaneous charging current.

[0030] The second pre-charging loop B2 is composed of a second current limiting resistor R2, a second voltage stabilizing capacitor C2, a second switch K2 and a reactor L1. Specifically, the connection between the components in the second pre-charging loop B2 is as follows: one end of the second current limiting resistor R2 is connected to the output end of the adjustable DC power supply A, the other end of the second current limiting resistor R2 is connected to one end of the second switch K2, the other end of the second switch K2 is connected to one end of the reactor L1, the other end of the reactor L1 is connected to the input end of the test sub-loop C, and a second voltage stabilizing capacitor C2 connected in parallel to the positive and negative ends of the rectifier bridge UR is provided between the second current limiting resistor and the second switch. During the test of the test loop of this embodiment, the second pre-charging loop B2 will be used to respond to the control instruction issued by the control unit C, generate an instantaneous current to make the diode D1 corresponding to the upper switch tube T1 of the test sub-loop C reversely fail to form a direct connection between the upper and lower switch tubes, thereby producing a reliable explosion.

[0031] The control unit D is used to at least control the state of the first switch K1 and / or the second switch K2, so that the upper and lower switch tubes of the test sub-circuit C form a direct explosion as described above. Exemplarily, the control unit D is connected to the port voltage output end of the test sub-circuit C, monitors the fluctuation of the thyristor port voltage, and generates a control instruction at an appropriate time and sends it to the second pre-charging circuit B1, closing the second switch K2 to generate an instantaneous charging current on the upper switch tube T1 diode D1.

[0032] It is worth noting that in order to ensure the accuracy of the test loop test, the second switch K1 or the first switch K2 will use a model with a millimeter-level opening speed.

[0033] It is understandable that if the thyristor is overheated due to insufficient heat dissipation, it may cause an unplanned short circuit or device burnout, interfering with the test process. Therefore, in order to further ensure the safety and controllability of the test and maintain the stable operation of the power device, this embodiment is also provided with a cooling water loop E connected to the test sub-loop C, which is used to dissipate heat from the test sub-loop C. The cooling water loop E can avoid unexpected failures by stabilizing the temperature and ensure that the explosion is triggered by a preset direct path.

[0034] Since the function of the bypass switch is to close when a submodule fault is detected, it will bypass it to protect the system. However, in the explosion test, if the bypass switch is closed, the fault path will be bypassed, preventing the direct explosion from occurring, resulting in test failure. Based on this, in an embodiment of the present invention, in response to the opening signal sent by the control unit D, the cooling water loop E will open the bypass switch TK of the test subloop C and shield the closing function, which can ensure that the MMC submodule cannot be bypassed in the event of a fault, forcing the energy to be released through the thyristor and diode path. It is worth noting that in some other embodiments of the present invention, the startup of the cooling water loop E can be completed by external operation, but the control unit D still needs to verify whether its parameters (such as flow rate, conductivity) meet the standards.

[0035] The following is combined with Figure 2 The above contents of the present invention are further described in detail with specific implementation modes.

[0036] Example 1 The test circuit provided in this embodiment includes a switch relay KM, a voltage regulator TY, a rectifier bridge UR, a control unit D, current limiting resistors R1 and R2, an inductor L1, a second voltage stabilizing capacitor C2, fast switches K1 and K2, a test sample sub-circuit C and a corresponding cooling water circuit E.

[0037] The power supply DC, the switch relay KM, the voltage regulator TY and the rectifier bridge UR are connected to form an adjustable DC power supply, the output end of which is connected to the first pre-charging loop B1 and the second pre-charging loop B2 and connected in series with current limiting resistors R1 and R2 respectively. In this embodiment, the current limiting resistor is set to make the charging current small enough to simulate the charging condition of the flexible DC converter valve in the actual project as realistically as possible.

[0038] Specifically, in the first pre-charging loop B1, the current limiting resistor R1 is connected in series with the fast switch K1 and then connected to the positive port of the test sub-loop C. After the control unit controls the switch K1 to be closed, the capacitor C1 of the test sub-loop C is charged to the first preset voltage UN1, i.e., the lower limit of the thyristor transition voltage, through the diode D1 anti-parallel to the upper switch tube T1 of the test sub-loop.

[0039] In the second pre-charging loop B2, the current limiting resistor R2 is connected in series with the fast switch K2 and the reactor L1 and is also connected to the positive port of the test sub-loop C, while the voltage-stabilizing capacitor C2 in loop B2 is connected to the positive and negative ends of the rectifier bridge UR through the current limiting resistor R2. Preferably, the capacitance of C2 will be set to the uF level to quickly reach the second preset voltage UN2 required for the test. Then, after closing the switch K2, C2 generates an instantaneous charging current through the reactor L1, which flows through the diode D1 anti-parallel to the upper switch tube T1, causing D1 to fail and break down during the reverse recovery process. Before K2 is closed, the thyristor Thy is already in the transition process. Therefore, at this time, with the damage of D1, the voltage of the capacitor C1 is all applied to the thyristor Thy, causing a through explosion in the MCC sub-module. For the specific through explosion process, please refer to Figure 2 As shown by the red arrow in the figure, it is understandable that when the thyristor Thy is broken down, the voltage of capacitor C1 will be directly applied to Thy, forming a low impedance path, and the transient current will flow to the diode of the lower switch tube T2 through the path D1→Thy→T2, eventually causing the upper and lower tubes to explode directly.

[0040] After a direct explosion occurs in the test loop, the integrity of the explosion-proof design needs to be further verified. As an example, on the one hand, after the test, it is necessary to verify whether the cooling water circuit is punctured or blocked by flying debris when the submodule explodes. If the water circuit is intact, it proves that the explosion-proof design is effective. On the other hand, if there is no leakage of coolant after the explosion and the water resistance value changes by <10%, it indicates that the water circuit is not damaged.

[0041] In summary, the test circuit designed by the present invention includes an adjustable DC power supply, a dual pre-charging circuit, a control unit and a test sub-module. The sub-module capacitor is charged to the thyristor transition voltage range through the first pre-charging circuit, and the second pre-charging circuit is used to inject transient current when the thyristor breaks down, so that the upper tube diode reverse recovery fails, forming a direct path for the upper and lower switch tubes, triggering a reliable explosion; a cooling system is also provided to ensure the safety of the test. The entire circuit structure is very simple, and can accurately verify the thyristor transition voltage and explosion-proof capability.

[0042] Another embodiment of the present invention provides a MMC submodule breakdown test method based on a turn-on thyristor and applied to the above test circuit. For details, see Figure 3 , Figure 3The figure shows a flowchart of a breakdown test of an MMC submodule in one embodiment of the present invention. The test method mainly includes the following steps: S1, turn on the adjustable DC power supply and start the cooling water circuit, and turn on the bypass switch of the test sub-circuit. Figure 1 The test circuit topology shown is used to connect the test circuit. After the connection configuration is completed, the test is started. First, the power supply and cooling water circuit need to be started, and the water flow rate and conductivity of the cooling water circuit must meet the working condition requirements. As an example, the flow rate can be maintained at ≥5L / min and the conductivity can be maintained at <0.5μS / cm.

[0043] S2. Close the first switch to charge the voltage of the first voltage-stabilizing capacitor in the sample sub-circuit to the first preset voltage range via the first pre-charging circuit, and charge the voltage of the second voltage-stabilizing capacitor in the second pre-charging circuit to the second preset voltage range.

[0044] In the embodiment of the present invention, a dual trigger mechanism is actually set up. Specifically, the first trigger mechanism is equivalent to the input of the first pre-charging circuit, that is, the first switch corresponding to the first pre-charging circuit is closed by the control unit, and the capacitor corresponding to the MMC sub-module, that is, the test sub-circuit is charged to the lower limit of the thyristor transition voltage, and at the same time, the voltage of the corresponding second stabilizing capacitor in the second pre-charging circuit is charged to the second preset voltage range.

[0045] S3. The control unit monitors the thyristor port voltage of the test sub-circuit, and when the monitoring result meets the first preset condition, triggers the second switch to close.

[0046] This step is the second trigger mechanism. Specifically, the control unit samples the thyristor port voltage of the test sub-circuit. When the voltage waveform generated by the thyristor port voltage is detected to drop periodically, the thyristor transition voltage value is reached, triggering the second switch to close. When it is detected that the upper switch tube and the lower switch tube of the test sub-module produce through discharge and explosion, and the contact resistance at the thyristor port of the test sub-module meets the second preset condition, the test is completed to achieve the purpose of dual verification of the thyristor transition breakdown voltage and explosion-proof capability of the MMC sub-module. Preferably, the contact resistance should be less than 1mΩ.

[0047] For an example of a periodic drop in voltage waveform, please refer to Figure 4 shown.

[0048] Another embodiment of the present invention provides a thyristor, characterized in that the thyristor is designed to be obtained by testing the MMC submodule breakdown test circuit based on the above-mentioned turn thyristor, or the thyristor is obtained by the MMC submodule breakdown test method based on the above-mentioned turn thyristor. It can be understood that after analyzing the test results, in the process of designing the MMC submodule, it will be internally ensured that the thyristor has good explosion-proof ability.

[0049] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A MMC submodule breakdown test circuit based on a turn-on thyristor, characterized in that: It includes an adjustable DC power supply, a first pre-charging circuit, a second pre-charging circuit and a test sample sub-circuit which are respectively controlled by a control unit; The first pre-charging circuit and the second pre-charging circuit connected in parallel are provided between the sample sub-circuit and the adjustable DC power supply; The first pre-charging circuit is composed of a first current limiting resistor and a first switch connected in series, and the first pre-charging circuit is used to charge the first voltage stabilizing capacitor in the test sub-circuit; The second pre-charging circuit is composed of a second current limiting resistor, a second voltage stabilizing capacitor, a second switch and a reactor; one end of the second current limiting resistor is connected to the output end of the adjustable DC power supply, the other end of the second current limiting resistor is connected to one end of the second switch, the other end of the second switch is connected to one end of the reactor, the other end of the reactor is connected to the input end of the test sub-circuit, and the second voltage stabilizing capacitor is arranged between the second current limiting resistor and the second switch; and the second pre-charging circuit is used to respond to the corresponding control instruction, generate an instantaneous current to make the diode corresponding to the upper switch tube of the test sub-circuit reversely fail to form a direct connection between the upper and lower switch tubes; The control unit is used to at least control the state of the first switch and / or the second switch so that the upper and lower switch tubes of the test sample sub-loop are directly connected.

2. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 1, characterized in that: The port voltage output end of the sample sub-circuit is connected to the control unit, so that the control unit sends the generated control instruction to the second pre-charging circuit.

3. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 1, characterized in that: The MMC submodule breakdown test circuit based on the turn-on thyristor further includes a cooling water circuit connected to the test subcircuit for dissipating heat for the test subcircuit.

4. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 3, characterized in that: In response to the opening signal sent by the control unit, the cooling water circuit opens the bypass switch of the test product sub-circuit and shields the closing function.

5. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 1, characterized in that: The topological structure of the test sub-loop includes a half-bridge topology and a full-bridge topology.

6. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 1, characterized in that: The adjustable DC power supply consists of a power supply, a switching relay, a voltage regulator and a rectifier bridge. The output end of the power supply is connected to one end of the switching relay, the other end of the switching relay is connected to one end of the voltage regulator, and the other end of the voltage regulator is connected to the rectifier bridge to provide a controllable DC voltage.

7. The MMC submodule breakdown test circuit based on the transition thyristor according to claim 1, characterized in that: The second switch or the first switch is a model with a millimeter-level opening speed.

8. A breakdown test method for MMC submodule based on transition thyristor, characterized in that: The MMC submodule breakdown test circuit based on the turn thyristor as described in any one of claims 1 to 7 above comprises: Turn on the adjustable DC power supply and start the cooling water loop, and turn on the bypass switch of the test sample sub-loop; Closing the first switch, charging the voltage of the first voltage-stabilizing capacitor in the sample sub-circuit to a first preset voltage range via the first pre-charging circuit, and charging the voltage of the second voltage-stabilizing capacitor in the second pre-charging circuit to a second preset voltage range; The control unit monitors the thyristor port voltage of the test sub-loop, and when the monitoring result meets the first preset condition, the second switch is triggered to close.

9. The MMC submodule breakdown test method based on the transition thyristor according to claim 8, characterized in that: When the monitoring result meets the first preset condition, triggering the second switch to close includes: When it is monitored that the voltage waveform generated by the thyristor port voltage has a periodic drop, the second switch is triggered to close.

10. A thyristor, characterized in that: The thyristor is designed to be obtained by testing the MMC sub-module breakdown test circuit based on the turn thyristor as described in any one of claims 1 to 7, or the thyristor is obtained by the MMC sub-module breakdown test method based on the turn thyristor as described in claims 8 to 9.

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