A method, system, device, and medium for turning off a thyristor in combination with a fully controlled device

Abstract

A method, system, device and medium for turning off a thyristor in combination with a full-controlled device, the method comprising: when the current flows in both directions, first determining the inductance current direction to determine the thyristor to be turned off; performing a turning-off operation based on the current direction and then performing a verification operation; when the current flows in one direction, performing a turning-off operation based on the direction of the thyristor and then performing a verification operation; the turning-off operation is to control the full-controlled device to apply a reverse bias voltage across the thyristor to be turned off to force the thyristor to be turned off; the verification operation is to control the full-controlled device to apply a forward bias voltage across the thyristor to verify the off state of the thyristor. The system, device and medium are used to implement the method; the application accelerates the turning off of the thyristor by applying a voltage opposite to the current direction to the thyristor by the full-controlled device, verifies the off state of the thyristor by applying a same direction voltage, forms a closed loop turning off mechanism, and enables the thyristor to be quickly and reliably turned off under direct / alternating current working conditions.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control technology, and particularly relates to a method, system, device and medium for turning off a thyristor used in combination with a fully controllable device. Background Technology

[0002] In the field of power electronic conversion, there are often scenarios where thyristors, which have low conduction losses and low cost, are combined with fully controllable devices that have high switching speeds and good controllability. These scenarios include inverter power frequency bypass switching systems, modular reconfigurable converters, dynamic voltage restorers, uninterruptible power supplies (UPS), energy storage converters in grid-connected and off-grid systems, and other scenarios where inverters are combined with solid-state relays. However, as a semi-controlled device, once a thyristor is turned on, it cannot be directly turned off through its gate; an external circuit must be used to force its current to zero. Thyristor turn-off failure will lead to system mode switching failure, protection failure, and even short-circuit faults, seriously threatening the safety of equipment and systems.

[0003] There are three types of turn-off methods for thyristors used as solid-state relays. The first type involves using a thyristor in series with a fully controlled device. The fully controlled device blocks the waveform, causing the thyristor current to drop below the holding current, thus turning off the thyristor naturally. However, this method is susceptible to interference from parallel devices, leading to turn-off failure and system malfunction (J. Di et al., "A Reconfigurable Modular Topology for PV Converter to Improve OvercurrentCapacity and Flexibility," IEEE Open J. Power Electron, vol. 7, pp. 1117-1132, 2026.). The second type utilizes the characteristic of AC current naturally crossing zero every half cycle to turn off the thyristor. However, this method requires a stable power grid and is slow, requiring up to 10ms. The third type involves applying a reverse voltage across the thyristor to be turned off using an auxiliary circuit (usually composed of capacitors, inductors, and auxiliary switching devices), forcing its current to cross zero. However, this method relies on a bulky auxiliary circuit, increasing the overall circuit complexity and cost. Furthermore, none of the above methods can obtain information about the thyristor's turn-off state. In the event of power grid disturbances, load changes, or auxiliary circuit failures, misjudgment of the thyristor's turn-off state may lead to system failure. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a thyristor turn-off method, system, device, and medium for use in conjunction with a fully controllable device. By controlling the fully controllable device to apply a voltage opposite to the inductor current direction to the thyristor, the thyristor turn-off is accelerated. Then, a voltage in the same direction is applied to confirm the thyristor's turn-off state, forming a closed-loop thyristor turn-off mechanism. This method fundamentally eliminates the risk of thyristor turn-off failure due to disturbances and enables the thyristor to turn off rapidly under both DC and AC operating conditions.

[0005] To achieve the objectives of this invention, the technical solution adopted is as follows: A method for turning off a thyristor used in combination with a fully controllable device, comprising: Obtain the current flow pattern in the current circuit; When the current flows bidirectionally, the direction of the inductor current is first determined to identify the thyristor to be turned off; the turn-off operation is performed based on the current direction, and a verification operation is performed after the turn-off. When the current flows in one direction, a turn-off operation is performed based on the thyristor direction, and a verification operation is performed after the turn-off. The shutdown operation is as follows: the fully controlled device applies a reverse bias voltage to both ends of the thyristor to be shut down, thereby forcibly shutting down the thyristor; The verification operation is as follows: the fully controlled device applies a forward bias voltage to both ends of the thyristor to verify the thyristor's turn-off state; if the inductor current is lower than the set safety threshold, the thyristor is successfully turned off; if the inductor current is higher than the set safety threshold, the thyristor fails to turn off and the turn-off operation is returned.

[0006] The logic for determining the direction of the inductor current to identify the thyristor to be turned off is as follows: if the sign of the sampled or integrated value of the inductor current is positive, then the direction of the inductor current is determined to be outflow from the switching unit, denoted as... The forward thyristor is identified as the thyristor to be turned off; if the sampled or integrated value of the inductor current is negative, the direction of the inductor current is determined to be flowing into the switching unit, denoted as... The reverse thyristor is identified as the thyristor to be turned off; the switching unit includes a fully controllable device and a thyristor.

[0007] The specific process for forcibly turning off the thyristor is as follows: If The fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm; if The fully controlled device outputs a voltage at the midpoint of the bridge arm that is higher than the voltage at node 1.

[0008] The turn-off method also includes: before forcibly turning off the thyristor, controlling the fully controlled device to apply a reverse bias voltage across the thyristor to be turned off to verify whether the determined thyristor to be turned off is correct; if the inductor current is lower than the safety threshold, it indicates that the thyristor to be turned off is correctly determined; if the inductor current exceeds the safety threshold, it indicates that the thyristor to be turned off is misjudged, and the direction of the inductor current is reversed.

[0009] The specific process of applying a forward bias voltage across the thyristor using the fully controlled device is as follows: If The fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm; if The fully controlled device outputs a voltage at the midpoint of the bridge arm that is higher than the voltage at node 1.

[0010] The set safety threshold Higher than the peak inductor current The set abnormal value of inductor current Exceeding the set safety threshold .

[0011] When applying the reverse bias and forward bias, it is necessary to ensure that the ground potential of node 1 is between the negative terminal ground potential of the busbar and the positive terminal ground potential of the busbar.

[0012] The present invention also provides a thyristor turn-off system for use in combination with a fully controllable device, comprising: Judgment Module: Obtains the current flow pattern in the current circuit; when the current is bidirectional, first determines the direction of the inductor current to identify the thyristor to be turned off; performs a turn-off operation based on the current direction, and performs a verification operation after turn-off; when the current is unidirectional, performs a turn-off operation based on the thyristor direction, and performs a verification operation after turn-off. Shutdown module: Used to control the fully controlled device to apply reverse bias voltage across the thyristor to be turned off, thereby forcibly turning off the thyristor; Verification module: Used to control the fully controlled device to apply a forward bias voltage across the thyristor to verify the thyristor's turn-off state; if the inductor current is lower than the set safety threshold, the thyristor is successfully turned off; if the inductor current is higher than the set safety threshold, the thyristor fails to turn off and returns to the turn-off module.

[0013] The present invention also provides an electronic device, comprising: Memory: A computer program that stores the above-described thyristor turn-off method, and is a computer-readable device; Processor: Used to implement the above-described thyristor turn-off method when executing the computer program.

[0014] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described thyristor turn-off method.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes a closed-loop thyristor turn-off method consisting of "inductor current direction detection - reverse bias forced thyristor turn-off - forward bias verification of thyristor turn-off state". This method does not rely on device characteristics, grid natural zero crossing, load characteristics, or dedicated auxiliary commutation circuits. It can achieve active and rapid thyristor turn-off simply by controlling a fully controllable device connected in series with the thyristor. The reliability of the thyristor turn-off result is ensured by verifying the thyristor turn-off state.

[0016] 2. This invention uses a fully controllable device to provide reverse voltage, enabling the thyristor to be normally turned off in both DC and AC circuits, thus expanding the application range of the thyristor.

[0017] 3. The present invention sets up a current direction verification step in the initial stage of forced thyristor turn-off by applying reverse bias voltage, which has the ability to self-correct after misjudgment, effectively deal with detection errors, and ensure the reliability of the turn-off process.

[0018] 4. This invention is implemented solely through software algorithms, without the need for additional hardware or circuit topology modifications. It can be achieved simply by controlling the switching state of fully controllable devices, resulting in low implementation costs and ease of promotion and application.

[0019] In summary, the method proposed in this invention does not rely on device characteristics, power grid, load, or auxiliary circuits. Instead, it actively turns off the thyristor by applying a reverse bias voltage to a fully controllable device and verifies the thyristor's turn-off state by applying a forward bias voltage, forming an active, closed-loop, and reliable turn-off mechanism. This method fundamentally eliminates the risk of thyristor turn-off failure caused by PWM (Pulse Width Modulation) switching interference or power grid voltage disturbances, thereby ensuring the safe and reliable operation of the system. Simultaneously, this method enables the thyristor to be used in both DC and AC circuits and significantly shortens the thyristor turn-off time. Attached Figure Description

[0020] Figure 1 This is a circuit topology diagram of a switching unit consisting of fully controlled devices and thyristor groups.

[0021] Figure 2 The flowchart illustrates the turn-off method for a thyristor used in combination with a fully controllable device, as provided by this invention.

[0022] Figure 3 The waveform of the inductor current when a voltage excitation is applied to a fully controllable device.

[0023] Figure 4The circuit topology diagram of a modular reconfigurable photovoltaic energy storage power generation system using a combination of thyristors and fully controlled devices.

[0024] Figure 5 The waveform diagram shows a system fault caused by a short circuit between the photovoltaic side and the grid side capacitors due to the failure of the flexible switch to turn off.

[0025] Figure 6 The waveform diagram shows a system fault caused by a short circuit between the photovoltaic side and the grid side capacitors due to the failure of the flexible switch to turn off. Detailed Implementation

[0026] The turn-off method proposed in this invention is applicable to scenarios where fully controllable devices are used in combination with thyristors. A switching switch composed of thyristors is used to change the circuit's connection state. When current flows in one direction, a thyristor corresponding to that current direction is used; when current flows in both directions, a bidirectional thyristor or an anti-parallel thyristor is used. Figure 1 As shown, the switching unit, which includes fully controllable devices and thyristors, uses anti-parallel thyristors, i.e. It is a forward thyristor. It is a reverse thyristor; As a fully controllable device, The second type of fully controllable device. To be compatible with fully controllable devices Anti-parallel diode one, To be compatible with fully controllable device two Two diodes connected in antiparallel; The absorption resistor is connected in parallel with the thyristor. This is an absorption capacitor connected in parallel with the thyristor; For bus capacitors; This is the bridge arm filter inductor. The switching unit is connected in series between the DC bus and node 1, where node 1 can be a renewable energy power generation unit, a power grid, an energy storage unit, or a load, etc.

[0027] like Figure 2 As shown, a thyristor turn-off method for use in combination with fully controllable devices is proposed. For scenarios where fully controllable devices are used in combination with thyristors, an active, closed-loop, fast and reliable turn-off method is presented. This method does not rely on the power grid or auxiliary circuits. Instead, it actively applies a reverse bias voltage to force the thyristor to turn off and verifies the turn-off state by applying a forward bias voltage, thus achieving fast and reliable thyristor turn-off. Simultaneously, this method embeds a direction verification and self-correction mechanism during the turn-off process to ensure the reliability of the turn-off operation. Specifically, it includes: The current flow pattern in the current circuit is obtained; when the current is bidirectional, the direction of the inductor current is first determined to identify the thyristor to be turned off; a turn-off operation is performed based on the current direction, and a verification operation is performed after turn-off; when the current is unidirectional, a turn-off operation is performed based on the known direction of the inductor current in the system, and a verification operation is performed after turn-off; wherein... The shutdown operation is as follows: the fully controlled device applies a reverse bias voltage to both ends of the thyristor to be turned off, thereby forcibly turning off the thyristor; The verification operation is as follows: the fully controlled device applies a forward bias voltage to both ends of the thyristor to verify the thyristor's turn-off state; if the inductor current is lower than the set safety threshold, the thyristor is successfully turned off; if the inductor current is higher than the set safety threshold, the thyristor fails to turn off and the turn-off operation is returned.

[0028] Furthermore, when current flows bidirectionally, the specific logic for determining the inductor current direction to identify the thyristor to be turned off is as follows: After the system receives the turn-off command, it first blocks all gate drive signals of the fully controlled device and the trigger signal of the thyristor; at this time, the current flowing through the thyristor will freewheel through the anti-parallel diode of the fully controlled device and gradually decay to zero. Since forcing the thyristor to turn off requires applying a bias voltage opposite to its original current direction, it is necessary to determine the current direction before turn-off. This invention detects the inductor current during this period by sampling it: either by directly sampling the inductor current or by integrating the current value during the decay to zero, and determining the initial direction of the current based on the sign of the sampled or integrated value. If positive, the inductor current is determined to flow out of the switching unit, denoted as . At this point, the forward thyristor needs to be turned off. If the value is negative, the inductor current is determined to flow into the switching unit, denoted as . At this point, the reverse thyristor needs to be turned off. This invention uses an integral method to determine the direction of inductor current, which can effectively avoid misjudgments caused by noise and ripple interference.

[0029] Based on the determined current direction By controlling the fully controlled device in the switching unit to turn on, an electric current is applied across the thyristor to be turned off in the same direction as the current. The opposite bias voltage, denoted as reverse bias, forces the thyristor to turn off. Specifically: if At this time, the fully controlled device outputs a voltage higher than the voltage at node 1 at the midpoint of the bridge arm, so as to control the thyristor. Applying a reverse voltage across the terminals turns off the reverse thyristor. ;like At this time, the fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm, so as to control the thyristor. Applying a reverse voltage across the terminals turns off the forward thyristor. .

[0030] To prevent the direction of the current Misjudgment leading to system failure can be addressed by incorporating a verification step at the initial stage of reverse bias application. This involves controlling the fully controlled device to continuously apply a bias voltage across the thyristor to be turned off. The reverse bias voltage is used to determine if the identified thyristor to be turned off is correct and to ensure that the applied voltage does not cause uncontrolled current rise. If during the verification time... Internal inductor current detected Exceeding the preset security threshold This indicates a misjudgment of the thyristor to be turned off, and the current direction needs to be immediately reversed. Invert; then follow the correct current direction The turn-off operation is then re-executed, meaning a reverse bias voltage is applied to the current thyristor for a period of time to ensure that the current thyristor is completely turned off under the influence of the reverse voltage. The duration of the reverse bias voltage application during the turn-off operation is related to the parameters of the actual thyristor device used. It should be noted that if... After inversion, the inductor current Exceeding the preset safety threshold again If the error is not detected, it indicates a short circuit fault in the switching unit, and the unit must be deactivated. This self-correction mechanism effectively addresses circuit disturbances and sampling errors, ensuring the reliability of the turn-off process.

[0031] After the turn-off operation is completed, the fully controlled device in the control switching unit is turned on, and an electric current is applied across the thyristor in the direction of the current. The same bias voltage, denoted as the forward bias voltage, is used to verify whether the thyristor to be turned off has truly been turned off. Specifically: when current flows bidirectionally, if At this point, the fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm to verify the reverse thyristor. Should it be turned off? If so... At this point, the fully controlled device outputs a voltage higher than that at node 1 at the midpoint of the bridge arm to verify the forward thyristor. Is it turned off? If the thyristor has been successfully turned off, the inductor current will be [not specified] since the circuit is open. It should be below the safety threshold. If during the verification time Internal inductor current Exceeding the safety threshold again This indicates that the thyristor turn-off has failed and the turn-off procedure must be re-executed immediately; if the inductor current... During verification time Below the safety threshold If the thyristor is reliably turned off, the turn-off process ends.

[0032] Verifying the correctness of the thyristor to be turned off before applying reverse bias has a similar verification logic to verifying whether the thyristor is turned off. Both involve applying a voltage excitation to the circuit containing the thyristor by controlling a fully controlled device, and verifying the switching state of the thyristor by judging whether the inductor current is within the safe threshold.

[0033] Thyristor turn-off state verification method: Apply continuous pressure to fully controlled devices When excited by a positive voltage, the response of the inductor current is as follows: Figure 3 As shown, if the thyristor is turned off, the inductor current... It will first rise to the peak inductor current. The current then drops to zero; if the thyristor is not turned off, the inductor current... It will continue to rise and may trigger an overcurrent failure.

[0034] Under the worst-case scenario, the voltage at node 1 equals the bus capacitance. When the voltage is zero or equal to zero, the peak value of the sampled inductor current is... Therefore, the preset safety threshold It should be higher than the peak inductor current. If the thyristor is not turned off, the inductor current will rise to an abnormal value. For accurate detection, an abnormal inductor current value should be set. Above the safety threshold Therefore, the verification time can be calculated. ,in, This is the voltage across the inductor.

[0035] It should be noted that although the implementation scheme described in this invention is for calculating verification time... However, actual control systems often use a fixed control cycle, which can also be... This can be converted into a duty cycle of one control cycle or a number of control cycles to achieve the same effect.

[0036] When applying voltage, this invention requires ensuring that the ground potential of node 1 is between the negative terminal ground potential (0V) and the positive terminal ground potential (VDC) of the busbar. Otherwise, it is necessary to wait for the ground potential of node 1 to recover to 0-VDC.

[0037] When current flows in one direction only, since there is only one thyristor in the switching unit, it is not necessary to determine the thyristor to be turned off based on the direction of the inductor current. The turn-off and verification operations can be performed directly based on the thyristor's direction. It should be noted that since the thyristor's connection direction is fixed, the system can directly obtain the inductor current direction based on the thyristor's connection direction. Then, based on the current direction, it controls the fully controlled device to apply a reverse bias voltage across the thyristor to be turned off, forcibly turning off the thyristor. Subsequently, it controls the fully controlled device to apply a forward bias voltage across the thyristor to verify the thyristor's turn-off state. Furthermore, when current flows in one direction only, the single thyristor in the switching unit, regardless of whether it is a forward-biased thyristor... Or reverse thyristor The specific logic for its shutdown and verification is the same as when the current flows bidirectionally. It is controlled by comparing the output voltage of the fully controlled device at the midpoint of the bridge arm with the voltage of node 1. It will not be described in detail here.

[0038] The following are specific implementation examples of the fast and reliable thyristor turn-off method proposed in this invention: Typical scenarios for the combined use of thyristors and fully controllable devices include: Figure 4 The modular reconfigurable photovoltaic energy storage power generation system shown herein, wherein, C PV For photovoltaic module filter capacitors, C SC For supercapacitors, V DC This is the DC bus voltage; L f-Flex , L f-G , L G and C f These are the flexible module-side inductor, LCL grid-side filter inductor, grid equivalent inductance, and filter capacitor; absorption resistor. R snb and absorption capacitor C snbAn RC parallel absorption circuit constitutes the flexible switch. The system includes one fixed module, three flexible modules (#1, #2, #3), and one energy storage module. The energy storage module is fixedly connected to a supercapacitor, the fixed module is fixedly connected to the power grid, and the flexible modules employ a three-phase bridge converter. The high-voltage side of the flexible module is connected to the DC bus, and the low-voltage side is connected to either the photovoltaic side or the grid side via corresponding flexible switches. The flexible switches are configured according to the current direction: thyristors are used as unidirectional flexible switches when the current flows in one direction, and anti-parallel thyristors are used as bidirectional flexible switches when the current flows in both directions. When the flexible module is connected to the photovoltaic side, it operates in DC / DC mode; when it is connected to the grid side, it operates in DC / AC mode. During low-voltage ride-through or grid frequency disturbances, this topology can achieve scheduling of the flexible module between the photovoltaic side and the grid side by changing the on / off state of the flexible switches, thereby dynamically changing the grid-side current carrying capacity according to the grid-side current demand. To achieve the above functions, the method described in this invention is required to enable the thyristors to turn off quickly and reliably.

[0039] The method proposed in this invention is unrelated to the photovoltaic and grid-side control methods of the example system, and will not be elaborated upon here. The flexible module needs to execute the method described in this invention during the switching process from the photovoltaic side to the grid side; this process will be used as an example. Specific implementation flow: All gate drive signals and thyristor trigger signals of the fully controlled device are blocked. As the inductor current freewheels through the anti-parallel diode of the fully controlled device and decreases to zero, the inductor current value is sampled and integrated. Finally, the initial direction of the current is determined based on the sign of the integrated value. .

[0040] according to The direction is determined by the thyristor turn-off state judgment method, which controls the fully controlled device to apply a continuous pressure to both ends of the thyristor to be turned off. The reverse bias voltage is used to determine whether the thyristor to be turned off is conducting; if the thyristor is conducting, it indicates... If the judgment is incorrect, it needs to be corrected. Invert. Then follow the correct... The reverse pressure is continued to be applied for a period of time to turn off the thyristor.

[0041] according to The direction is determined by applying a forward voltage to the fully controlled device for a period of time according to the thyristor turn-off state judgment method, and judging whether the thyristor is conducting. If the thyristor is conducting, it means that the thyristor has not been turned off, and the reverse voltage needs to be applied again to turn off the thyristor; if the thyristor is not conducting, the turn-off is successful.

[0042] Figure 5 The fault waveforms caused by thyristor turn-off failure when the method of this invention is not used are given. Figure 5 middle, For the bridge arm inductor current, This refers to the grid-side thyristor current. This represents the thyristor current on the photovoltaic side. After the turn-off command is issued, the bridge arm inductor current... When the voltage drops to zero, the control system enters a blocking waiting phase, and the thyristors commutate naturally. However, due to voltage and current ripple interference in the circuit, the photovoltaic-side thyristors are not truly turned off. When the grid-side thyristors turn on, because the photovoltaic-side thyristors are still in the conducting state, the photovoltaic-side capacitor and the grid-side capacitor are directly short-circuited, generating a high-amplitude fault current and causing a system failure.

[0043] Figure 6 Experimental waveforms of thyristor turn-off using the method proposed in this invention are presented. Figure 6 middle, and These are the drive signals for the upper and lower switching transistors (fully controlled devices) of the C-phase bridge arm, respectively. For the C-phase inductor current, This refers to the voltage across the flexible switch on the photovoltaic side. The initial condition for the flexible module is that the flexible switch on the photovoltaic side is open, and the flexible module operates in DC / DC mode. After the switching command is issued, the thyristor closed-loop turn-off logic proposed in this invention, which involves "inductor current direction judgment - reverse bias forced thyristor turn-off - forward bias verification of thyristor turn-off state," is executed. After the turn-off process is completed, the grid-side flexible switch is turned on, and the module successfully switches to DC / AC mode for grid-connected operation. From Figure 6 It can be seen that the entire process of switching from DC / DC photovoltaic mode to DC / AC mode is completed within 1ms. The shutdown process is fast and smooth, and no overcurrent or short circuit faults occur.

[0044] The above experimental results show that the thyristor turn-off method proposed in this invention, used in combination with fully controllable devices, can achieve fast and reliable thyristor turn-off, ensuring the safe and stable operation of the power conversion system.

Claims

1. A method for turning off a thyristor used in combination with a fully controllable device, characterized in that, include: Obtain the current flow pattern in the current circuit; When the current flows bidirectionally, first determine the direction of the inductor current to identify the thyristor to be turned off. The shutdown operation is performed based on the current direction, and a verification operation is performed after shutdown. When the current flows in one direction, a turn-off operation is performed based on the thyristor direction, and a verification operation is performed after the turn-off. The shutdown operation is as follows: the fully controlled device applies a reverse bias voltage to both ends of the thyristor to be shut down, thereby forcibly shutting down the thyristor; The verification operation is as follows: the fully controlled device applies a forward bias voltage to both ends of the thyristor to verify the thyristor's turn-off state; if the inductor current is lower than the set safety threshold, the thyristor is successfully turned off; if the inductor current is higher than the set safety threshold, the thyristor fails to turn off and the turn-off operation is returned.

2. The thyristor turn-off method according to claim 1, characterized in that: The logic for determining the direction of the inductor current to identify the thyristor to be turned off is as follows: if the sign of the sampled or integrated value of the inductor current is positive, then the direction of the inductor current is determined to be outflow from the switching unit, denoted as... The forward thyristor is identified as the thyristor to be turned off; if the sampled or integrated value of the inductor current is negative, the direction of the inductor current is determined to be flowing into the switching unit, denoted as... The reverse thyristor is identified as the thyristor to be turned off; the switching unit includes a fully controllable device and a thyristor.

3. The thyristor turn-off method according to claim 2, characterized in that: The specific process for forcibly turning off the thyristor is as follows: If The fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm; if The fully controlled device outputs a voltage at the midpoint of the bridge arm that is higher than the voltage at node 1.

4. The thyristor turn-off method according to claim 1, characterized in that: The turn-off method also includes: before forcibly turning off the thyristor, controlling the fully controlled device to apply a reverse bias voltage across the thyristor to be turned off to verify whether the determined thyristor to be turned off is correct; if the inductor current is lower than the safety threshold, it indicates that the thyristor to be turned off is correctly determined; if the inductor current exceeds the safety threshold, it indicates that the thyristor to be turned off is misjudged, and the direction of the inductor current is reversed.

5. The thyristor turn-off method according to claim 2, characterized in that: The specific process of applying a forward bias voltage across the thyristor using the fully controlled device is as follows: If The fully controlled device outputs a voltage lower than the voltage at node 1 at the midpoint of the bridge arm; if The fully controlled device outputs a voltage at the midpoint of the bridge arm that is higher than the voltage at node 1.

6. The thyristor turn-off method according to claim 1, characterized in that: The set safety threshold Higher than the peak inductor current ; The set abnormal value of inductor current Exceeding the set safety threshold .

7. The thyristor turn-off method according to claim 1, characterized in that: When applying the reverse bias and forward bias, it is necessary to ensure that the ground potential of node 1 is between the negative terminal ground potential of the busbar and the positive terminal ground potential of the busbar.

8. A thyristor turn-off system used in combination with a fully controllable device, characterized in that, include: Judgment module: Obtains the current flow pattern in the current circuit; When the current flows bidirectionally, first determine the direction of the inductor current to identify the thyristor to be turned off. The shutdown operation is performed based on the current direction, and a verification operation is performed after shutdown. When the current flows in one direction, a turn-off operation is performed based on the thyristor direction, and a verification operation is performed after the turn-off. Shutdown module: Used to control the fully controlled device to apply reverse bias voltage across the thyristor to be turned off, thereby forcibly turning off the thyristor; Verification module: Used to control the fully controlled device to apply a forward bias voltage across the thyristor to verify the thyristor's turn-off state; if the inductor current is lower than the set safety threshold, the thyristor is successfully turned off; if the inductor current is higher than the set safety threshold, the thyristor fails to turn off and returns to the turn-off module.

9. An electronic device, characterized in that, include: Memory: A computer program storing the turn-off method of the thyristor according to any one of claims 1-7, which is a computer-readable device; Processor: Used to implement the thyristor turn-off method according to any one of claims 1-7 when executing the computer program.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the thyristor turn-off method as described in any one of claims 1-7.

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