Device for suppressing active overvoltage, composite bypass switch, control method and system

Abstract

The application provides a device for suppressing active overvoltage, a composite bypass switch, a control method and a system, the device for suppressing active overvoltage comprising three single-phase bodies in parallel, each of the bodies comprising an iron core composed of four iron core columns, two excitation windings reversely wound on the two middle iron core columns respectively, and a net side winding wound on the outside of the two excitation windings. The device for suppressing active overvoltage is connected in parallel with the composite bypass switch, the composite bypass switch comprising a bidirectional thyristor, a mechanical switch and a reactor, and a series branch composed of the reactor and the mechanical switch is connected in parallel with the bidirectional thyristor and each single-phase body in the device for suppressing active overvoltage. The application eliminates the self-excitation of the generator, and the active overvoltage suppression device can be automatically adjusted to a suitable reactive power compensation capacity to eliminate the conditions and phenomena of self-excitation, thereby creating conditions for directly connecting large units to the power grid.

Description

Technical Field

[0001] The present invention relates to the field of ultra-high / ultra-high voltage power grids, and in particular to a device for suppressing active overvoltage, a composite bypass switch, a control method and a system. Background Art

[0002] Ultra-high / ultra-high voltage power grids are the backbone of my country's power system. Reactive voltage and electromagnetic transient problems are key factors affecting their safe and stable operation. These problems are mainly manifested in the following aspects: 1) large reactive power, prominent overvoltage and sub-current problems in long-line charging, high risk of reclosing failure, and endangerment to the safety of the power grid and equipment; 2) large-scale centralized access of clean energy and intensified power flow changes have made high / low voltage limit problems more prominent, seriously restricting the transmission capacity of the power grid; 3) overvoltage caused by system faults may induce large-scale grid disconnection accidents of nearby new energy units.

[0003] In ultra-high / ultra-high voltage (UHV) power grids, connecting conventional equipment such as shunt reactors can cause overvoltage under light loads and undervoltage under heavy loads. Controllable devices such as magnetic overvoltage suppression devices can address these steady-state voltage issues. However, due to limitations in their operating mechanisms and control modes, they have a slow response to fast transient overvoltages, such as switching overvoltage and power frequency overvoltage, resulting in poor suppression effectiveness.

[0004] Therefore, it is necessary to develop a fast active overvoltage suppression device for ultra-high / ultra-high voltage power grids to achieve dynamic reactive power compensation and suppress fast active overvoltage. Summary of the Invention

[0005] In response to the above problems, the present invention provides a device for suppressing active overvoltage, a composite bypass switch, a control method and a system.

[0006] A device for suppressing active overvoltage includes three single-phase bodies connected in parallel, wherein the bodies include: an iron core, a grid-side winding, and two excitation windings; the iron core includes at least two iron core legs, namely a second iron core leg and a third iron core leg; the two excitation windings are respectively wound in opposite directions on the second iron core leg and the third iron core leg, and the grid-side winding is wound outside the two excitation windings.

[0007] The excitation windings in the three single-phase bodies are connected in an open triangle anti-parallel manner; wherein, the opposite-name end of the first excitation winding in the first single-phase body is connected to the same-name end of the first excitation winding in the third single-phase body, and the opposite-name end of the first excitation winding in the third single-phase body is connected to the same-name end of the first excitation winding in the second single-phase body; the same-name end of the second excitation winding in the first single-phase body is connected to the opposite-name end of the second excitation winding in the third single-phase body, and the same-name end of the second excitation winding in the third single-phase body is connected to the opposite-name end of the second excitation winding in the second single-phase body; the same-name end of the first excitation winding in the first single-phase body is connected to the opposite-name end of the second excitation winding in the first single-phase body, and the opposite-name end of the first excitation winding in the second single-phase body is connected to the same-name end of the second excitation winding in the second single-phase body.

[0008] The iron core further includes a first iron core leg and a fourth iron core leg, and the first iron core leg and the fourth iron core leg are located outside the grid-side winding.

[0009] The device for suppressing active overvoltage also includes: a voltage transformer and a rectifier; the single-phase body is connected in parallel with the rectifier and then in series with the voltage transformer.

[0010] A composite bypass switch includes the above device and further comprises: a bidirectional thyristor, a mechanical switch and a reactor; the series branch composed of the reactor and the mechanical switch is respectively connected in parallel with the bidirectional thyristor and the device for suppressing active overvoltage.

[0011] A control method for implementing reactive power control using the composite bypass switch includes: when a transient overvoltage occurs, a controller issues a turn-on command to the composite bypass switch, causing a bidirectional thyristor in the composite bypass switch to conduct, and then closing a mechanical switch connected in parallel to both ends of the bidirectional thyristor. By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive power compensation capacity of the composite bypass switch's active overvoltage suppression device; when the transient overvoltage disappears, the controller issues a turn-off command to the composite bypass switch, and the composite bypass switch is disconnected.

[0012] After the bidirectional thyristor in the composite bypass switch is turned on, the mechanical switch connected in parallel at both ends of the bidirectional thyristor is closed, including: after the controller issues a turn-on command, the bidirectional thyristor is immediately turned on, and the excitation winding in the active overvoltage suppression device is bypassed; after the controller issues a close command, the mechanical switch is closed after the closing time, and the bidirectional thyristor is turned off.

[0013] By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third iron core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage. The method includes: a controller uses a fast reactive power method to obtain instantaneous reactive power, and then calculates the difference between the instantaneous reactive power and a set reference voltage to obtain a per-unit value of the delayed trigger angle; inputting the per-unit value into a pulse trigger generation circuit to control the delayed trigger angle of the bidirectional thyristor in the composite bypass switch; inputting the delayed trigger angle into a rectifier in the device for suppressing active overvoltage, and changing the excitation current in the active overvoltage suppression device through the output voltage of the rectifier, thereby changing the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third iron core legs, so that the magnetic flux in the second and third iron core legs is alternately saturated in the positive half-cycle and negative half-cycle of the sine wave, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage.

[0014] Calculate the instantaneous reactive power as follows:

[0015]

[0016] Among them, e a 、e b and e c are the instantaneous sampling values ​​of the three-phase voltages, i a 、i b and i c They are the instantaneous sampling values ​​of the three-phase currents respectively.

[0017] The value range of the delayed trigger angle is between 0° and 180°, and the adjustment range of the reactive compensation capacity is between 5% and 100%.

[0018] A control system comprises: the aforementioned composite bypass switch and a control module; the control module is configured to: when a transient overvoltage occurs, a controller issues a turn-on command to the composite bypass switch, causing a bidirectional thyristor in the composite bypass switch to conduct and a mechanical switch connected in parallel across the bidirectional thyristor to close; by controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage; and when the transient overvoltage disappears, the controller issues a turn-off command to the composite bypass switch, causing the composite bypass switch to open.

[0019] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects:

[0020] 1. The present invention uses a fast active overvoltage suppression device to directly connect to the EHV / UHV power grid, which can flexibly adjust the system voltage, suppress overvoltage and improve the reclosing success rate. It has the advantages of high compensation efficiency, low operating loss, small footprint and is not limited by the main transformer capacity.

[0021] 2. The device of the present invention outputs continuously variable reactive power, regulating the generalized natural power of the EHV / UHV transmission line to 30% to 100% of the line natural power. This effectively resolves the contradiction between excessively high voltage in small-scale operation and excessively low voltage in large-scale operation. In emergency situations, it can provide strong compensation to suppress power frequency overvoltage and switching overvoltage. In combination with a small neutral point reactance, it can also suppress backflow current and reduce the recovery voltage.

[0022] 3. The present invention adopts a three-winding four-core column structure. The two excitation windings are respectively wound on the two middle cores, and a grid-side winding is wound on the two excitation windings at the same time. This structure eliminates the influence of parasitic loops and improves the dynamic response speed of the system under steady state. Under the same excitation capacity ratio, the response speed is increased by 26%, realizing fast and accurate capacity output.

[0023] 4. The present invention adopts a composite switch to replace the original mechanical switch, which maximizes the rapid capacity adjustment speed of the fast active overvoltage suppression device under transient conditions, reduces the response time from about 100ms to less than 10ms, can greatly suppress the transient overvoltage of the system, and does not have the problem of switching arc, effectively extending the service life of the equipment.

[0024] 5. The present invention uses instantaneous sampling values ​​of voltage and current to calculate reactive power, which does not generate delay and shortens the time required for the reactive power calculation link; the closed-loop reactive power control strategy adopted can effectively ensure the steady-state voltage regulation accuracy of the fast active overvoltage suppression device.

[0025] 6. The present invention eliminates the self-excitation of the generator. The active overvoltage suppression device can automatically adjust to the appropriate reactive compensation capacity to eliminate the conditions and phenomena that produce self-excitation, creating conditions for large units to be directly connected to the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the main wiring diagram of the present invention;

[0027] Figure 2 This is a schematic diagram of the single-phase winding and magnetic circuit of the fast active overvoltage suppression device of the present invention;

[0028] Figure 3 This is a schematic diagram of the connection of the open triangle anti-parallel connection of the present invention;

[0029] Figure 4 a) It is a conventional mechanical switch bypass;

[0030] Figure 4 b) is a fast composite switch bypass of the present invention;

[0031] Figure 5 It is the reactive power closed-loop control strategy of the present invention;

[0032] Figure 6 It is a schematic diagram of the operating principle of the fast active overvoltage suppression device of the present invention. DETAILED DESCRIPTION

[0033] The embodiments of the present invention will be further described from the following aspects with reference to the accompanying drawings:

[0034] 1. Composition of the fast active overvoltage suppression device system

[0035] like Figure 1 The connection relationship of the active overvoltage suppression device shown is that for active overvoltage suppression devices used in ultra / ultra-high voltage applications, a single-phase structure is usually adopted due to its large body capacity.

[0036] like Figure 2 As shown in the figure, each phase of the ultra-high / ultra-high voltage active overvoltage suppression device consists of an iron core and a winding. The iron core is split into four core columns. The primary winding (i.e., the grid-side winding, also called the working winding) is wound on the two middle core columns, and a secondary winding (i.e., the excitation winding, also called the control winding) is wound on each core column.

[0037] Among them, L A 、L B 、L C They are respectively the grid-side winding of the ultra-high / ultra-high voltage active overvoltage suppression device, L a1 、L a2 、L b1 、L b2 、L c1 、L c2 They are respectively the excitation windings of the ultra-high / ultra-high voltage active overvoltage suppression devices. a1 、L b1 、L c1 With L a2 、L b2 、L c2 After connecting end to end, use Figure 3 The open triangle is connected in anti-parallel. The open end is connected to the output of the rectifier, which is powered by an external excitation power supply. a1 、B b1 、B c1 With B a2 、B b2 、B c2 They respectively constitute three-phase compound switches and are connected in parallel at both ends of the corresponding excitation windings.

[0038] The present invention short-circuits the secondary winding by closing the composite bypass switch. This short-circuit causes a large short-circuit current to flow through the secondary winding, rapidly increasing the current in the primary winding, thereby achieving maximum inductive output. If the line current is heavy and a three-phase trip at the end causes load shedding, the fast active overvoltage suppression device bypasses the secondary control winding via the composite bypass switch, rapidly adjusting its reactive capacity to its maximum value and effectively limiting power-frequency overvoltages.

[0039] 2. Winding connection method and single-phase magnetic circuit structure

[0040] Wiring method and magnetic circuit structure of single-phase winding of fast active overvoltage suppression device.

[0041] Winding 1 Figure 1 Middle working winding L A , winding 2 is Figure 1 Intermediate excitation winding L a1 , winding 3 is Figure 1 Intermediate excitation winding L a2 .

[0042] The working winding 1 of the fast active overvoltage suppression device is wound on the iron core II and the iron core III at the same time. Under the action of the AC working voltage, the two iron cores II and III will generate AC magnetic induction intensities B1 and B2 in the same direction, with the same magnitude and direction. Among them, B1 forms a closed magnetic circuit through the I and II columns, and B2 forms a closed magnetic circuit through the III and IV columns.

[0043] The control (excitation) winding 2 and control (excitation) winding 3 of the fast active overvoltage suppression device are wound on cores II and III, respectively, in opposite directions. Under the action of the DC control current, a DC magnetic flux density B0 is generated in cores II and III, closing the gap between cores II and III. Consequently, the DC magnetic flux magnetizes and demagnetizes cores II and III, respectively, causing them to saturate alternately during the positive and negative halves of the sine wave. Changing the DC excitation level changes the magnetic saturation of the cores, which in turn changes the equivalent magnetic permeability, thereby smoothly varying the reactance and capacitance.

[0044] 3. Fast bypass switch

[0045] like Figure 4 The conventional bypass switch shown in a uses a mechanical switch, which is limited by the mechanism's action time, which generally reaches 100ms. The transient response speed is slow, and the system will be subjected to a high overvoltage shock for a short time.

[0046] The present invention adopts Figure 4The fast composite bypass switch structure shown in Figure b reduces its equivalent closing time to less than 10ms. Upon receiving a command from the controller, the thyristor quickly conducts, bypassing the excitation winding. This rapidly increases the capacity of the active overvoltage suppression device, enabling rapid suppression of transient overvoltages. However, if the overvoltage persists for a long time, the thyristor valve will continue to flow currents exceeding kA, generating significant heat. Without a heat sink, the thyristor valve will inevitably burn out due to excessive junction temperature. A mechanical switch is connected in parallel with the thyristor valve. After the thyristor valve conducts, the mechanical switch quickly bypasses it. After the mechanical switch closes, the thyristor valve ceases conduction, preventing prolonged winding current from flowing through the thyristor valve. This eliminates the need for a thyristor valve cooling device, eliminating cooling components while maintaining speed.

[0047] When the transient overvoltage disappears and the bypass switch needs to be opened, there is no special requirement for the response time. The thyristor valve can be triggered first and then the mechanical switch. Finally, the controller issues a thyristor valve cut-off command. This does not require the mechanical switch to extinguish the arc, extending the service life of the mechanical switch. The transient process response time is generally 100ms.

[0048] If an operational overvoltage or power frequency overvoltage occurs at the installation point or on the line, the fast compound switch will be quickly bypassed, the DC excitation circuit will be cut off, and the reactive output of the active overvoltage suppression device will be quickly increased to the maximum value, and may even exceed the rated capacity of the device for a short time, thereby achieving the purpose of actively and quickly limiting overvoltage.

[0049] 4. Rapid detection algorithm and control strategy of reactive power

[0050] In order to shorten the reactive power calculation time and improve the compensation accuracy of the device that quickly suppresses active overvoltage, the controller adopts Figure 5 The reactive power closed-loop control strategy shown in the figure, the specific algorithm and strategy are as follows:

[0051] 1) Fast reactive power calculation method shortens calculation time

[0052] The instantaneous sampling values ​​of the voltage and current of each phase of the three-phase circuit are e a 、e b 、e c and i a 、i b 、i c , directly calculate the three-phase active power p and three-phase reactive power q according to the following formula

[0053] p=e a i a +e b i b +e c i c

[0054]

[0055] 2) Closed-loop reactive power control strategy improves compensation accuracy

[0056] The calculated instantaneous reactive power q is related to a set reference voltage Q set The comparison is then performed, and the difference is calculated to obtain a trigger angle per unit value, which is then sent to the pulse trigger generation circuit to control the trigger angle of the excitation circuit of the fast active overvoltage suppression device.

[0057] 5. Operating principle of fast active overvoltage suppression device

[0058] like Figure 6 The operating principle of the fast active overvoltage suppression device shown in the figure is that the measurement system (TV and TA) generates voltage and current signals that are input to the controller. The controller then calculates and outputs the delayed trigger angle α for the thyristors in the excitation circuit. By adjusting the rectifier output voltage, the DC excitation current is rapidly changed, thereby changing the iron core saturation. This enables the fast active overvoltage suppression device to quickly, continuously and smoothly regulate the inductive reactive power, thereby suppressing voltage fluctuations at the installation point. As the voltage rises, the fast active overvoltage suppression device can achieve continuous and precise adjustment from 5% to 100% capacity.

[0059] Based on the same inventive concept, the present invention also provides a reactive power control method and control system, which are described below.

[0060] A reactive power control method is provided, which implements reactive power control using the composite bypass switch. The method comprises: when a transient overvoltage occurs, a controller issues a turn-on command to the composite bypass switch. After a bidirectional thyristor in the composite bypass switch is turned on, a mechanical switch connected in parallel to both ends of the bidirectional thyristor is closed. By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the active overvoltage suppression device of the composite bypass switch. When the transient overvoltage disappears, the controller issues a turn-off command to the composite bypass switch, and the composite bypass switch is disconnected.

[0061] After the bidirectional thyristor in the composite bypass switch is turned on, the mechanical switch connected in parallel at both ends of the bidirectional thyristor is closed, including: after the controller issues a turn-on command, the bidirectional thyristor is immediately turned on, and the excitation winding in the active overvoltage suppression device is bypassed; after the controller issues a close command, the mechanical switch is closed after the closing time, and the bidirectional thyristor is turned off.

[0062] By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third iron core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage. The method includes: a controller uses a fast reactive power method to obtain instantaneous reactive power, and then calculates the difference between the instantaneous reactive power and a set reference voltage to obtain a per-unit value of the delayed trigger angle; inputting the per-unit value into a pulse trigger generation circuit to control the delayed trigger angle of the bidirectional thyristor in the composite bypass switch; inputting the delayed trigger angle into a rectifier in the device for suppressing active overvoltage, and changing the excitation current in the active overvoltage suppression device through the output voltage of the rectifier, thereby changing the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third iron core legs, so that the magnetic flux in the second and third iron core legs is alternately saturated in the positive half-cycle and negative half-cycle of the sine wave, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage.

[0063] Calculate the instantaneous reactive power as follows:

[0064]

[0065] Among them, e a 、e b and e c are the instantaneous sampling values ​​of the three-phase voltages, i a 、i b and i c They are the instantaneous sampling values ​​of the three-phase currents respectively.

[0066] The value range of the delayed trigger angle is between 0° and 180°, and the adjustment range of the reactive compensation capacity is between 5% and 100%.

[0067] A reactive power control system comprises: the aforementioned composite bypass switch and a control module; the control module is configured to: when a transient overvoltage occurs, a controller issues a turn-on command to the composite bypass switch, causing a bidirectional thyristor in the composite bypass switch to conduct and a mechanical switch connected in parallel to both ends of the bidirectional thyristor to close; by controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage; and when the transient overvoltage disappears, the controller issues a turn-off command to the composite bypass switch, causing the composite bypass switch to open.

[0068] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0069] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0070] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0071] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Ordinary technicians in the relevant field can still modify or replace the specific implementation methods of the present invention with equivalents by referring to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A control method for a device for suppressing active overvoltage, characterized in that: The control method realizes reactive power control by using a composite bypass switch, comprising: When a transient overvoltage occurs, the controller issues a turn-on command to the composite bypass switch. After the bidirectional thyristor in the composite bypass switch is turned on, the mechanical switch connected in parallel at both ends of the bidirectional thyristor is closed. By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the active overvoltage suppression device of the composite bypass switch; When the transient overvoltage disappears, the controller sends a cut-off command to the composite bypass switch, and the composite bypass switch is disconnected; The composite bypass switch includes: a device for suppressing active overvoltage; and also includes: a bidirectional thyristor, a mechanical switch and a reactor; The series branch formed by the reactor and the mechanical switch is respectively connected in parallel with the bidirectional thyristor and the device for suppressing active overvoltage; The device for suppressing active overvoltage includes three single-phase bodies connected in parallel, and the bodies include: an iron core, a grid-side winding and two excitation windings; The iron core includes at least two iron core legs, namely a second iron core leg and a third iron core leg; The two excitation windings are respectively wound on the second iron core column and the third iron core column in opposite directions, and the grid-side winding is wound outside the two excitation windings.

2. The control method according to claim 1, wherein: The excitation windings in the three single-phase bodies are connected in open delta anti-parallel mode; The opposite-name end of the first excitation winding in the first single-phase body is connected to the same-name end of the first excitation winding in the third single-phase body, and the opposite-name end of the first excitation winding in the third single-phase body is connected to the same-name end of the first excitation winding in the second single-phase body; The same-name end of the second excitation winding in the first single-phase body is connected to the opposite-name end of the second excitation winding in the third single-phase body, and the same-name end of the second excitation winding in the third single-phase body is connected to the opposite-name end of the second excitation winding in the second single-phase body; The same-name end of the first excitation winding in the first single-phase body is connected to the opposite-name end of the second excitation winding in the first single-phase body, and the opposite-name end of the first excitation winding in the second single-phase body is connected to the same-name end of the second excitation winding in the second single-phase body.

3. The control method according to claim 1, wherein: The iron core further includes a first iron core leg and a fourth iron core leg, and the first iron core leg and the fourth iron core leg are located outside the grid-side winding.

4. The control method according to claim 1, wherein: Also includes: voltage transformers and rectifiers; The single-phase body is connected in parallel with the rectifier and then in series with the voltage transformer.

5. The control method according to claim 1, wherein: After the bidirectional thyristor in the composite bypass switch is turned on, the mechanical switch connected in parallel at both ends of the bidirectional thyristor is closed, including: After the controller issues a turn-on command, the bidirectional thyristor is immediately turned on, and the excitation winding in the active overvoltage suppression device is bypassed; The mechanical switch is closed after the controller issues a closing command and the closing time, and the bidirectional thyristor is turned off.

6. The control method according to claim 5, wherein: By controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage, including: The controller uses a fast reactive power method to obtain instantaneous reactive power, and then calculates the difference between the instantaneous reactive power and the set reference voltage to obtain the per-unit value of the delayed trigger angle. Inputting the per-unit value into a pulse trigger generating circuit to control the delayed trigger angle of the bidirectional thyristor in the composite bypass switch; The delayed trigger angle is input into the rectifier in the device for suppressing active overvoltage, and the excitation current in the active overvoltage suppression device is changed by the output voltage of the rectifier, thereby changing the DC excitation size in the excitation windings wound in opposite directions on the second iron core leg and the third iron core leg, so that the magnetic flux in the second iron core leg and the third iron core leg is alternately saturated in the positive half cycle and the negative half cycle of the sine wave, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage.

7. The control method according to claim 6, wherein: The instantaneous reactive power is calculated as follows: ； Among them, e a 、e b and e c are the instantaneous sampling values ​​of the three-phase voltages, i a 、i b and i c They are the instantaneous sampling values ​​of the three-phase currents respectively.

8. The control method according to claim 6, wherein: The value range of the delay trigger angle is The adjustment range of the reactive compensation capacity is between between.

9. A control system for a device for suppressing active overvoltage, using the control method according to claim 1, characterized in that: Also includes: Control module; The control module is configured to: when a transient overvoltage occurs, the controller issues a turn-on command to the composite bypass switch, causing the bidirectional thyristor in the composite bypass switch to conduct and the mechanical switch connected in parallel at both ends of the bidirectional thyristor to close; by controlling the delayed trigger angle of the bidirectional thyristor, the DC excitation magnitude in the excitation windings wound in opposite directions on the second and third core legs is changed, thereby adjusting the reactive compensation capacity of the device for suppressing active overvoltage; and when the transient overvoltage disappears, the controller issues a turn-off command to the composite bypass switch, causing the composite bypass switch to open.

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