Assembly type controllable MOV for full-controlled LCC converter valve and control method thereof, full-controlled LCC converter valve

Abstract

The application belongs to a component type controllable MOV, and aims at the technical problems that the operating voltage of the existing MOV protection device lacks active controllability, and the dynamic voltage distribution in the high-voltage series protection is difficult to coordinate, and provides a component type controllable MOV for full-controlled LCC converter valve, a control method thereof and a full-controlled LCC converter valve, wherein the light-controlled thyristor silicon stack and the lightning arrester resistor group are connected in series to realize active triggering of the controllable MOV; the anti-parallel light-controlled thyristor is used to form a bidirectional current path, the dynamic voltage between the thyristor stages is balanced through the first resistance-capacitance branch, and the voltage distribution between the light-controlled thyristor silicon stack and the lightning arrester resistor group is coordinated through the second resistance-capacitance branch, so as to reduce the risk of local overvoltage and improve the voltage resistance reliability of the device.

Description

Technical Field

[0001] This application pertains to a modular controllable MOV, specifically relating to a modular controllable MOV for a fully controllable LCC converter valve and its control method, as well as the fully controllable LCC converter valve. Background Technology

[0002] Conventional DC transmission converter valves mostly use thyristor devices. Thyristors can only control turn-on, and commutation failure is prone to occur on the inverter side when there are AC system faults, waveform distortion, or pulse loss. By replacing thyristors with IGCTs, forced commutation can be achieved through active turn-off. When the IGCT actively turns off the conduction current, it generates overvoltage. The larger the turn-off current, the more significant the device overvoltage, loss, and junction temperature rise. Therefore, MOVs are needed to absorb energy and limit the voltage amplitude.

[0003] Existing IGCT-type LCC converter valves typically use a small MOV connected in parallel for every two IGCT stages for segmented protection, with a valve surge arrester installed throughout the converter valve. The MOV relies on the volt-ampere characteristics of zinc oxide varistors to switch from a high-resistance state to a low-resistance state during overvoltage. This approach involves a large number of small MOVs, limited by installation size, resulting in limited energy absorption capacity. They are prone to overheating under high current or continuous shutdown, and the valve surge arrester must be retained, leading to complex configuration. Furthermore, the operation of the MOVs primarily depends on their inherent volt-ampere characteristics, lacking active controllability of the operating voltage and making it difficult to address the dynamic voltage distribution in high-voltage series protection. Summary of the Invention

[0004] This application addresses the technical problems of existing MOV protection devices lacking active controllability of operating voltage and difficulty in coordinating dynamic voltage distribution in high-voltage series protection by providing a component-type controllable MOV for a fully controllable LCC converter valve, its control method, and the fully controllable LCC converter valve.

[0005] To achieve the above objectives, this application adopts the following technical solution: In the first aspect, this application proposes a modular controllable MOV for a fully controllable LCC converter valve, including a photoelectric thyristor silicon stack and a surge arrester resistor array connected in series. The optically controlled thyristor silicon stack includes multiple thyristor stages connected in series. Each thyristor stage includes a first optically controlled thyristor, a second optically controlled thyristor connected in antiparallel to the first optically controlled thyristor, and a first RC branch connected in parallel to the first optically controlled thyristor and the second optically controlled thyristor. The surge arrester resistor array includes multiple zinc oxide surge arrester resistors connected in series, and a second RC branch is connected in parallel at both ends of the surge arrester resistor array.

[0006] Furthermore, the first RC branch includes a first damping capacitor and a first damping resistor connected in series; The second RC branch includes a second damping capacitor and a second damping resistor connected in series.

[0007] Furthermore, the capacitance values ​​of the first damping capacitors in each of the thyristor stages are the same, and the resistance values ​​of the first damping resistors in each of the thyristor stages are the same.

[0008] Furthermore, the voltage that the optically controlled thyristor silicon stack withstands... and the voltage borne by the surge arrester resistor array satisfy:

[0009]

[0010] in, This indicates the voltage across the modular controllable MOV. This indicates the capacitance value of the second damping capacitor. This indicates the capacitance value of the first damping capacitor. This indicates the number of thyristor stages in a photoelectric thyristor silicon stack.

[0011] Furthermore, the optically controlled thyristor silicon stack is connected in series with the surge arrester resistor assembly.

[0012] Furthermore, the series-pressed optically controlled thyristor silicon stack and the surge arrester resistor assembly are integrated into an insulating sheath.

[0013] Secondly, this application proposes a fully controllable LCC converter valve, including an IGCT silicon stack and a valve reactor connected in series with the IGCT silicon stack; it also includes a modular controllable MOV. The modular controllable MOV includes a series-connected optically controlled thyristor silicon stack and a surge arrester resistor array. The two ends of the modular controllable MOV are respectively connected to the two ends of the IGCT silicon stack, so that the valve reactor is located outside the parallel range formed by the modular controllable MOV and the IGCT silicon stack.

[0014] Furthermore, it also includes a valve control device; the IGCT silicon stack includes multiple IGCT stages with voltage detection function; The valve control device is connected to the IGCT stage and the optically controlled thyristor silicon stack respectively, and is used to send a trigger signal to the optically controlled thyristor silicon stack according to the voltage signal output by the IGCT stage.

[0015] Thirdly, this application proposes a control method for a modular controllable MOV used in a fully controllable LCC converter valve, wherein the fully controllable LCC converter valve employs the aforementioned fully controllable LCC converter valve; the control method includes: Obtain the voltage signals detected at each IGCT stage in the IGCT silicon stack; The voltage signal is used to determine whether the voltage experienced by the IGCT silicon stack has entered the preset protection range. When the voltage across the IGCT silicon stack enters the preset protection range, a trigger signal is sent to the optically controlled thyristor silicon stack to turn it on and cause the surge arrester resistor array to limit the voltage across the IGCT silicon stack.

[0016] Furthermore, the lower limit between the preset protection zones is determined based on the maximum peak operating voltage of the IGCT silicon stack after considering commutation overshoot, the dynamic voltage distribution non-uniformity coefficient, and the corresponding safety factor; the upper limit between the preset protection zones is determined based on the protective trigger voltage of each IGCT stage in the IGCT silicon stack, the number of IGCT stages, the non-uniformity coefficient of the protective trigger voltage of each IGCT stage, and the corresponding safety factor.

[0017] Compared with the prior art, this application has the following beneficial effects: This application proposes a modular controllable MOV for a fully controllable LCC converter valve. By connecting a photocontrolled thyristor silicon stack in series with a surge arrester resistor array, the active triggering of the photocontrolled thyristor controls the surge arrester resistor array to apply voltage limiting, thus achieving controllable operating voltage of the modular controllable MOV. By connecting multiple thyristor stages in series, the photocontrolled thyristor silicon stack acquires corresponding voltage withstand capability, and the first and second photocontrolled thyristors connected in anti-parallel in each thyristor stage form forward and reverse current paths. By connecting a first RC branch in parallel across each thyristor stage, the dynamic voltage between multiple thyristor stages can be balanced, reducing voltage deviation between thyristor stages; by connecting a second RC branch in parallel across the surge arrester resistor array, the dynamic voltage distribution between the photocontrolled thyristor silicon stack and the surge arrester resistor array can be coordinated, thereby reducing the risk of local devices being subjected to excessive voltage and improving the voltage withstand reliability of the modular controllable MOV. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the existing IGCT-based LCC converter valve MOV device topology; Figure 2 This is a schematic diagram illustrating the basic principle of the modular controllable MOV of this application. Figure 3This is a schematic diagram of the circuit topology of the component-type controllable MOV of this application; Figure 4 The current-voltage characteristic curve of the resistor element of the zinc oxide surge arrester is shown. Figure 5 This is a schematic diagram of the connection topology of the component-type controllable MOV in the fully controllable LCC converter valve of this application; Figure 6 This is a schematic diagram of the protection and control method for the component-type controllable MOV of this application.

[0020] Among them, 1-first optically controlled thyristor, 2-second optically controlled thyristor, 3-zinc oxide arrester resistor sheet; 4-valve arrester; 5-small MOV; 6-IGCT level; 7-valve reactor; 8-optically controlled thyristor silicon stack; 9-arrester resistor sheet group; 10-module-type controllable MOV; 11-IGCT silicon stack. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] This application provides a modular controllable MOV for a fully controllable LCC converter valve. The modular controllable MOV includes a photoelectric thyristor silicon stack 8 and a surge arrester resistor array 9, with the photoelectric thyristor silicon stack 8 and the surge arrester resistor array 9 connected in series. The photoelectric thyristor silicon stack 8 is used to change the conduction state of the modular controllable MOV according to an external trigger signal. The surge arrester resistor array 9 is used to absorb overvoltage energy and limit the voltage amplitude across the protected equipment when the modular controllable MOV is turned on and the voltage across its terminals reaches the corresponding operating level.

[0024] The photoelectric thyristor silicon stack 8 comprises multiple thyristor stages connected in series. By setting multiple thyristor stages, each thyristor stage can share the voltage applied to the photoelectric thyristor silicon stack 8 when the modular controllable MOV is in a non-conducting state, thereby meeting the high-voltage application requirements of the fully controlled LCC converter valve. The number of thyristor stages can be determined based on the operating voltage of the fully controlled LCC converter valve, the withstand voltage capability of the selected photoelectric thyristors, and the reserved safety margin.

[0025] Each thyristor stage includes a first light-controlled thyristor 1 and a second light-controlled thyristor 2, which are connected in anti-parallel. The first light-controlled thyristor 1 forms a controlled conduction path in the first current direction of the thyristor stage, and the second light-controlled thyristor 2 forms a controlled conduction path in the second current direction, opposite to the first current direction. Therefore, regardless of whether the transient voltage experienced by the modular controllable MOV is a positive or negative transient voltage, the corresponding energy release path can be formed by triggering the light-controlled thyristor in the corresponding direction.

[0026] Each thyristor stage is also provided with a first RC branch, which is connected in parallel across the first optically controlled thyristor 1 and the second optically controlled thyristor 2 in that thyristor stage. During the dynamic voltage load of the optically controlled thyristor silicon stack 8, each first RC branch cooperates with the corresponding thyristor stage to adjust the dynamic voltage distribution between multiple series-connected thyristor stages, reducing the inter-stage voltage deviation caused by differences in device parameters and transient processes, and preventing local thyristor stages from experiencing excessively high dynamic voltages.

[0027] The surge arrester resistor array 9 comprises multiple zinc oxide surge arrester resistor elements 3 connected in series. These multiple zinc oxide surge arrester resistor elements 3 collectively bear the voltage applied to the surge arrester resistor array 9, and vary between a high-resistance state and a low-resistance state according to the nonlinear volt-ampere characteristics of the zinc oxide material. When the voltage applied does not reach the corresponding operating level, the surge arrester resistor array 9 is in a high-resistance state, with only a small leakage current; after the voltage applied reaches the corresponding operating level, the surge arrester resistor array 9 enters a low-resistance state, allowing the overvoltage current to flow and absorbing the corresponding energy, thereby limiting the voltage across the modular controllable MOV and the protected equipment connected in parallel with it.

[0028] A second RC branch is connected in parallel across the two ends of the surge arrester resistor array 9. This second RC branch, together with the first RC branch corresponding to each thyristor stage, participates in the dynamic voltage distribution between the photocontrolled thyristor silicon stack 8 and the surge arrester resistor array 9. This ensures that when the modular controllable MOV is in a blocking state or subjected to transient voltage, the photocontrolled thyristor silicon stack 8 and the surge arrester resistor array 9 can share the voltage across the modular controllable MOV according to a set relationship. By coordinating the first and second RC branches, both the withstand voltage safety of the photocontrolled thyristor silicon stack 8 and the operating stress of the surge arrester resistor array 9 can be considered.

[0029] Under normal operating conditions, the photoelectric thyristor silicon stack 8 remains in a blocking state, and the surge arrester resistor array 9 is in a high-resistance state, preventing the modular controllable MOV from forming a large current path. When an overvoltage requiring suppression occurs in the protected equipment, the external control device sends a trigger signal to the photoelectric thyristor silicon stack 8, causing either the first photoelectric thyristor 1 or the second photoelectric thyristor 2 corresponding to the current voltage direction to conduct. The surge arrester resistor array 9 then connects to the overvoltage energy release path. The surge arrester resistor array 9 utilizes its nonlinear volt-ampere characteristics to absorb overvoltage energy and limit the voltage across the protected equipment to a corresponding range.

[0030] Therefore, the operation of the modular controllable MOV no longer depends entirely on the fixed volt-ampere characteristics of the zinc oxide arrester resistor element 3 itself, but can be actively controlled by the triggering time of the optically controlled thyristor silicon stack 8. At the same time, the first RC branch and the second RC branch can coordinate the dynamic voltage distribution between multiple thyristor stages and between the optically controlled thyristor silicon stack 8 and the arrester resistor element group 9, thereby addressing the problems of lack of active controllability of the operating voltage of existing MOV protection devices and the difficulty in coordinating dynamic voltage distribution in high-voltage series protection, and realizing active triggering protection and reasonable voltage division.

[0031] like Figure 1 The diagram shows a schematic of an existing IGCT-based LCC valve MOV device topology. Existing IGCT-based LCC converter valves typically employ segmented small MOVs 5 for protection, for example, one small MOV 5 connected in parallel for every two IGCT stages 6, with separate valve surge arresters 4 configured at both ends of the overall converter valve. Each small MOV 5 provides overvoltage limiting for its corresponding local IGCT stage 6, while the valve surge arresters 4 provide overall overvoltage protection for the converter valve.

[0032] The above connection method requires configuring multiple small MOVs 5 according to the number of IGCTs 6, resulting in a large number of devices and complex installation and connection relationships. Due to the limited installation space and size of the small MOVs 5, their energy absorption capacity is limited. When the IGCT silicon stack 11 shuts off a large current, the energy transferred to the small MOVs 5 may cause their temperature to rise continuously. In actual operation, it is usually necessary to monitor the number of times each small MOV 5 operates or the cumulative energy absorbed; when the corresponding energy reaches the allowable threshold, it may also be necessary to deactivate the IGCT's active shutdown function to avoid overheating and damage to the small MOVs 5. At the same time, the original valve surge arrester 4 still needs to be retained and used in conjunction with multiple small MOVs 5, increasing the redundancy of the protection device configuration.

[0033] This application adopts a modular controllable MOV centralized protection IGCT silicon stack 11, and uses the optically controlled thyristor silicon stack 8 to control the timing of the surge arrester resistor group 9 connecting to the overvoltage release path, so that the surge arrester protection action can be actively triggered according to the actual voltage of the IGCT silicon stack 11, and coordinate the dynamic voltage distribution between the optically controlled thyristor silicon stack 8 and the surge arrester resistor group 9 through the RC branch.

[0034] like Figure 2 The diagram shown illustrates the principle of the IGCT anti-parallel thyristor device of this application. The modular controllable MOV includes a photoelectric thyristor silicon stack 8 formed by multiple thyristor stages connected in series, and a surge arrester resistor array 9 connected in series with the photoelectric thyristor silicon stack 8. Each thyristor stage has two anti-parallel photoelectric thyristors, which respectively form a forward current path and a reverse current path. A first RC branch for dynamic voltage equalization is provided at both ends of the thyristor stage. The surge arrester resistor array 9 is formed by multiple zinc oxide surge arrester resistors 3 connected in series, and a second RC branch is provided at both ends of the surge arrester resistor array 9.

[0035] like Figure 3 The diagram shown is a schematic of the circuit topology of the component-type controllable MOV in this application. In one specific structure, the first optically controlled thyristor 1 is a forward optically controlled thyristor, the second optically controlled thyristor 2 is an anti-parallel optically controlled thyristor, and the zinc oxide surge arrester resistor 3 constitutes the surge arrester resistor group 9. The first RC branch includes a first damping capacitor C1 and a first damping resistor R1 connected in series, and the capacitance value of the first damping capacitor C1 is denoted as R1. The resistance value of the first damping resistor R1 is denoted as The second RC branch includes a second damping capacitor Cr and a second damping resistor Rr connected in series. The capacitance value of the second damping capacitor Cr is denoted as... The resistance value of the second damping resistor Rr is denoted as .

[0036] The first optically controlled thyristor 1 and the second optically controlled thyristor 2 are connected in anti-parallel to form a bidirectional controlled thyristor unit. A first RC branch, formed by the first damping capacitor C1 and the first damping resistor R1 connected in series, is connected across the two ends of this thyristor unit. The first optically controlled thyristor 1, the second optically controlled thyristor 2, the first damping capacitor C1, and the first damping resistor R1 together constitute a thyristor stage. Multiple thyristor stages with the same structure are connected in series to form an optically controlled thyristor silicon stack 8 capable of withstanding the operating voltage of a fully controlled LCC converter valve.

[0037] In this embodiment, the capacitance value of the first damping capacitor C1 in each thyristor stage is the same, which is... The resistance value of the first damping resistor R1 is the same in each thyristor stage. By using the same damping capacitor and damping resistor parameters, each thyristor stage can have similar voltage division characteristics under the same dynamic conditions, reducing the dynamic voltage deviation between multiple series-connected thyristor stages.

[0038] When the modular controllable MOV is subjected to AC voltage or transient voltage changes, each first RC branch balances the dynamic voltage across the corresponding thyristor stage, allowing multiple thyristor stages to share the voltage across the photo-controlled thyristor silicon stack 8. The first damping resistor R1 and the first damping capacitor C1 are connected in series to provide damping while achieving dynamic voltage equalization. The parameters of each first RC branch are consistent, which helps to prevent any thyristor stage from reaching its withstand voltage limit prematurely due to uneven dynamic voltage distribution.

[0039] Multiple zinc oxide arrester resistors 3 in the arrester resistor group 9 are connected in series. The number of zinc oxide arrester resistors 3 can be determined based on the continuous operating voltage, operating voltage, energy absorption requirements that the arrester resistor group 9 needs to withstand, and the electrical parameters of each individual zinc oxide arrester resistor 3. The second damping capacitor Cr and the second damping resistor Rr are connected in series to form the second RC branch, which is connected in parallel across the entire arrester resistor group 9.

[0040] The second RC branch participates in the dynamic voltage regulation of the surge arrester resistor array 9 on one hand, and forms a voltage divider relationship with multiple first RC branches in the optically controlled thyristor silicon stack 8 on the other hand. By selecting , , and This allows for the configuration of dynamic voltage distribution between the optically controlled thyristor silicon stack 8 and the surge arrester resistor array 9. In a preferred embodiment of this application, it mainly utilizes... , and the number of thyristor stages Determine the voltage distribution relationship between the two, and the damping resistor is used to form an RC branch with the corresponding damping capacitor.

[0041] Let the voltage across the modular controllable MOV be... The voltage that the photo-controlled thyristor silicon stack 8 withstands is The voltage that the surge arrester resistor group 9 withstands is Then all three conditions are met:

[0042] When the optically controlled thyristor silicon stack 8 includes n thyristor stages, the first damping capacitance of each thyristor stage is... The second damping capacitor across the resistor array 9 of the surge arrester is At that time, the dynamic voltage division relationship between the optically controlled thyristor silicon stack 8 and the surge arrester resistor array 9 satisfies:

[0043] The above two relationships can be further converted to obtain:

[0044]

[0045] Therefore, when , and Once determined, the dynamic voltage across the modular controllable MOV can be distributed to the photocontrolled thyristor silicon stack 8 and the surge arrester resistor array 9 according to a predetermined ratio. This can be achieved by increasing... Compared to The ratio of the voltage ratio can be adjusted to increase the proportion of voltage borne by the optically controlled thyristor silicon stack 8; conversely, decreasing this ratio can decrease the proportion of voltage borne by the optically controlled thyristor silicon stack 8. When selecting parameters, both the allowable withstand voltage of the optically controlled thyristor silicon stack 8 and the continuous operating stress of the surge arrester resistor array 9 should be considered to ensure sufficient blocking margin for the optically controlled thyristor silicon stack 8 and to prevent the surge arrester resistor array 9 from experiencing excessive voltage stress during normal operation.

[0046] In this embodiment, the optically controlled thyristor silicon stack 8 and the surge arrester resistor array 9 are connected in series to form a modular controllable MOV. The optically controlled thyristor silicon stack 8 and the surge arrester resistor array 9 are integrated as a series-connected unit in an insulating sleeve. The insulating sleeve provides external insulation protection for the series-connected structure and makes the optically controlled thyristor silicon stack 8, the surge arrester resistor array 9, and the corresponding RC branches form a component that is easy to install and connect in the converter valve.

[0047] like Figure 4As shown, the zinc oxide surge arrester resistor element 3 exhibits nonlinear volt-ampere characteristics. During normal operation of the fully controlled LCC converter valve, when the voltage across the surge arrester resistor element group 9 does not reach its operating level, the surge arrester resistor element group 9 is in a high-resistance state, and the current flowing through it is typically in the milliampere range or less. The volt-ampere characteristic curve is approximately 10... -3 The A-level indicates the low-current range. As the voltage continues to rise and enters the operating region, the equivalent resistance of the surge arrester's resistor array 9 rapidly decreases, enabling it to carry large currents in the kiloampere range. The volt-ampere characteristic curve then changes at approximately 10... 3 The A-level indicates a high current range, while the voltage across it changes only relatively little, thus limiting the voltage across the IGCT silicon stack 11 connected in parallel to it within a safe range. Once the overvoltage disappears, the zinc oxide arrester resistor 3 returns to its high-resistance state.

[0048] This application also provides a fully controlled LCC converter valve employing the aforementioned modular controllable MOV. The fully controlled LCC converter valve includes an IGCT silicon stack 11, a valve reactor 7, a modular controllable MOV, and a valve control device. The IGCT silicon stack 11 includes multiple IGCT stages 6 connected in series, each IGCT stage 6 having a voltage detection function; the valve reactor 7 is connected in series with the IGCT silicon stack 11 to meet the corresponding commutation and current change requirements of the converter valve.

[0049] like Figure 5 As shown, the two ends of the modular controllable MOV 10 are connected to the two ends of the IGCT silicon stack 11, respectively, so that the modular controllable MOV 10 and the IGCT silicon stack 11 form a parallel connection. Although the valve reactor 7 is connected in series with the IGCT silicon stack 11, it is located outside the parallel range formed by the modular controllable MOV 10 and the IGCT silicon stack 11, and the modular controllable MOV 10 is not connected across the valve reactor 7.

[0050] When the IGCT silicon stack 11 performs active shutdown, a positive overvoltage is generated across the IGCT silicon stack 11, and a voltage opposite to this positive overvoltage is generated across the valve reactor 7. If the modular controllable MOV 10 is connected in parallel across the series connection formed by the IGCT silicon stack 11 and the valve reactor 7, the modular controllable MOV 10 detects and withstands the terminal voltage resulting from the superposition of the voltage of the IGCT silicon stack 11 and the voltage of the valve reactor 7. The reverse voltage on the valve reactor 7 will weaken the response of the modular controllable MOV 10 to the actual overvoltage of the IGCT silicon stack 11, preventing the modular controllable MOV 10 from providing timely protection according to the actual voltage state of the IGCT silicon stack 11.

[0051] Therefore, the modular controllable MOV 10 is connected in parallel only across the IGCT silicon stack 11. When the IGCT silicon stack 11 is actively turned off and an overvoltage is generated, the modular controllable MOV 10 directly bears the voltage across the IGCT silicon stack 11, and after being triggered, forms an energy transfer path in parallel with the IGCT silicon stack 11, so that the energy generated during the IGCT turn-off process is transferred to the surge arrester resistor group 9 for absorption, and is not affected by the reverse voltage of the valve reactor 7.

[0052] The valve control device can be a converter valve control device (VBE). The valve control device is connected to each IGCT stage 6 and the photo-controlled thyristor silicon stack 8. Each IGCT stage 6 sends the detected voltage signal to the valve control device. The valve control device determines the current voltage of the IGCT silicon stack 11 based on the voltage signals of multiple IGCT stages 6, and sends a trigger signal to the photo-controlled thyristor silicon stack 8 after the voltage of the IGCT silicon stack 11 enters the preset protection range.

[0053] In a preferred embodiment of this application, the optically controlled thyristor silicon stack 8 is connected to the valve control device via an optical fiber. The valve control device generates an optical trigger signal and transmits it to the corresponding optically controlled thyristor via the optical fiber. By using optically controlled thyristors, the trigger signal can be generated centrally by the valve control device, eliminating the need to set up corresponding electrical trigger circuits locally at each thyristor stage of the modular controllable MOV.

[0054] Since IGCT stage 6 has its own voltage detection function, the valve control device can directly receive the voltage signals output by each IGCT stage 6, eliminating the need for a separate voltage detection unit in the photoelectric thyristor stack 8 of the modular controllable MOV. This reduces the number of high-potential side detection and triggering components, simplifying the local circuit configuration of the modular controllable MOV.

[0055] In some embodiments of this application, the valve control device can also count the voltage signals reported by each IGCT stage 6, and determine the authenticity of the overvoltage of the IGCT silicon stack 11 based on the number of signals that meet the corresponding voltage conditions. When the voltage feedback of multiple IGCT stages 6 meets the corresponding counting conditions, the valve control device confirms that the IGCT silicon stack 11 has entered an overall overvoltage state, and then sends a trigger signal to the photocontrolled thyristor silicon stack 8. This counting determination method can be used to reduce the possibility of false operation caused by a single abnormal detection signal. The specific counting conditions can be set according to the number of IGCT stages 6 and the protection strategy of the converter valve.

[0056] The protection action setting value of the modular controllable MOV is set between the maximum peak operating voltage of the IGCT silicon stack 11 after considering commutation overshoot and the protective trigger voltage of the entire valve. Let the maximum peak operating voltage of the IGCT silicon stack 11 after considering commutation overshoot be... The number of IGCT stages 6 contained in IGCT silicon stack 11 is The protective trigger voltage for each IGCT level 6 is: The dynamic voltage distribution non-uniformity coefficient is The safety factor corresponding to the dynamic voltage distribution is The non-uniformity coefficient of the 6-protection trigger voltage of each IGCT level is: The safety factor corresponding to the protective trigger voltage is The preset protection range of the modular controllable MOV then satisfies:

[0057] Lower limit between protected areas This is higher than the maximum peak operating voltage after considering commutation overshoot, dynamic voltage unevenness, and safety margin. Therefore, unnecessary triggering of the modular controllable MOV can be avoided during normal operation of the converter valve and during permissible commutation overshoot.

[0058] Upper limit between protected areas This is lower than the overall valve protection triggering level after considering the dispersion and safety margin of the IGCT stage 6 protection triggering voltage. Therefore, the modular controllable MOV can operate before the overall voltage of the IGCT silicon stack 11 reaches the overall valve protection triggering level, preventing multiple IGCT stages 6 from entering the protection triggering state simultaneously.

[0059] For localized overvoltages caused by abnormal control or triggering of a single IGCT stage 6, protection can be provided by the integrated positive overvoltage protection triggering function of that IGCT stage 6. For abnormal overvoltages occurring throughout the IGCT silicon stack 11, a component-type controllable MOV is actively connected to limit the overall voltage amplitude. Through the above protection levels, both single-stage device abnormality protection and overall IGCT silicon stack 11 overvoltage protection can be achieved.

[0060] When the modular controllable MOV is in the blocking state, the voltage borne by the photo-controlled thyristor silicon stack 8 Voltage across IGCT silicon stack 11 The following conditions must be met:

[0061] Therefore, after converting the preset protection range at both ends of the modular controllable MOV to the optically controlled thyristor silicon stack 8, the trigger voltage range corresponding to the optically controlled thyristor silicon stack 8 satisfies:

[0062] The valve control device can calculate or convert the overall voltage of the IGCT silicon stack 11 based on the voltage signals detected by each IGCT stage 6. and further according to , and the number of thyristor stages nThe voltage corresponding to the optically controlled thyristor silicon stack 8 was calculated. When converted to When the above-mentioned trigger voltage range is entered, the valve control device actively sends a trigger pulse to the optically controlled thyristor silicon stack 8.

[0063] like Figure 6 As shown, the control process of the modular controllable MOV includes voltage signal acquisition, overvoltage authenticity judgment, protection zone judgment, and optical trigger signal transmission.

[0064] During the operation of the fully controlled LCC converter valve, each IGCT stage 6 continuously or according to a set cycle detects the voltage across its terminals and feeds back the detected voltage signal to the valve control device. The voltage signals of each IGCT stage 6 collectively reflect the current overall voltage distribution and total voltage level of the IGCT silicon stack 11.

[0065] After receiving the voltage signals output by each IGCT stage 6, the valve control device determines the voltage that the IGCT silicon stack 11 is subjected to based on each voltage signal. In the embodiment using counting determination, the valve control device also counts the feedback signals of IGCT stage 6 that reach the corresponding voltage conditions to determine whether the current overvoltage belongs to the overall overvoltage of the IGCT silicon stack 11 that needs to be handled by the component-type controllable MOV 10.

[0066] The valve control device compares the determined voltage of the IGCT silicon stack 11 with the preset protection range. When the voltage of the IGCT silicon stack 11 does not enter the preset protection range, the valve control device does not send a protection trigger signal to the optically controlled thyristor silicon stack 8, the optically controlled thyristor silicon stack 8 remains blocked, and the surge arrester resistor group 9 remains in a high-resistance state.

[0067] When the voltage across the IGCT silicon stack 11 exceeds the lower limit of the preset protection zone and enters the preset protection interval, the valve control device sends a trigger signal to the optically controlled thyristor silicon stack 8 via optical fiber. Based on the current voltage direction across the component-type controllable MOV 10, either the first optically controlled thyristor 1 or the second optically controlled thyristor 2 forms a conduction path, and multiple thyristor stages conduct together, connecting the surge arrester resistor array 9 to the overvoltage energy release path of the IGCT silicon stack 11.

[0068] After the optically controlled thyristor silicon stack 8 is turned on, the overvoltage across the IGCT silicon stack 11 is applied to the surge arrester resistor array 9. When the surge arrester resistor array 9 enters its nonlinear low-resistance region, the current flowing through it increases rapidly. The energy generated by the active turn-off of the IGCT silicon stack 11 is transferred to the surge arrester resistor array 9 and absorbed by it. The voltage across the surge arrester resistor array 9 is limited to a corresponding range, thereby limiting the voltage across the IGCT silicon stack 11 connected in parallel, preventing the overall voltage of the IGCT silicon stack 11 from reaching the overall valve protection trigger level or the device damage level.

[0069] After the overvoltage process ends, the arrester resistor array 9 returns to a high-resistance state as the voltage it has been subjected to decreases, causing the current flowing through the modular controllable MOV 10 to drop to a lower level. The modular controllable MOV 10 thus concludes the overvoltage energy release process and can continue to be used for subsequent protection.

[0070] Through the above structure and control process, the connection time of the surge arrester resistor array 9 is actively determined by the valve control device based on the actual voltage of the IGCT silicon stack 11, changing the traditional MOV's passive operation based solely on its fixed volt-ampere characteristics. The first and second RC branches coordinate the dynamic voltage within the optically controlled thyristor silicon stack 8 and between the optically controlled thyristor silicon stack 8 and the surge arrester resistor array 9, ensuring that both the optically controlled thyristor and the zinc oxide surge arrester resistor array 3 maintain reasonable working stress.

[0071] Optionally, the modular controllable MOV can directly replace the multiple segmented small MOVs 5 and valve arresters 4 in the original converter valve to provide centralized protection for the IGCT silicon stack 11. The modular structure allows for the configuration of a larger number and volume of zinc oxide arrester resistors 3, improving the overall energy absorption capacity. This frees the active shutdown strategy of the IGCT silicon stack 11 from the strict constraints of the limited energy withstand capability of the original small MOVs 5, and reduces the number of protection devices and the complexity of connections.

[0072] In an application example of a fully controlled LCC converter valve, the converter valve operates in inverter mode. When the AC system experiences distortion, pulse loss, or other abnormal conditions that may cause commutation failure, the valve control device controls the IGCT silicon stack 11 to perform active shutdown, thereby utilizing the active shutdown capability of the IGCT device to implement forced commutation and suppress commutation failure.

[0073] After the IGCT silicon stack 11 actively turns off the conduction current, a forward overvoltage is formed across its terminals, and a reverse voltage is formed across the valve reactor 7. The modular controllable MOV is connected in parallel across the IGCT silicon stack 11 and is not connected across the valve reactor 7, thus it can directly reflect the actual overvoltage generated by the active turn-off of the IGCT silicon stack 11.

[0074] Each IGCT stage 6 detects its own voltage and sends the voltage signal to the valve control device. The valve control device determines the overall voltage of the IGCT silicon stack 11 based on the voltage signals from multiple IGCT stages 6, and can confirm that the overvoltage is not caused by a single abnormal detection signal by counting feedback signals that meet the corresponding conditions. When the overall voltage of the IGCT silicon stack 11 enters the range specified by the valve control device... , , , m , , and When the set protection range is reached, the valve control device sends a trigger pulse to the optically controlled thyristor silicon stack 8 via optical fiber.

[0075] Multiple optically controlled thyristors corresponding to the current voltage direction are triggered and turned on, and the surge arrester resistor array 9 is connected to both ends of the IGCT silicon stack 11. The zinc oxide surge arrester resistor 3 enters the low-resistance region, transferring the energy generated by the active turn-off of the IGCT to the modular controllable MOV, and limiting the voltage amplitude across the IGCT silicon stack 11. The local abnormal overvoltage of a single IGCT stage 6 can still be handled by the protective triggering function of the IGCT stage 6 itself, while the overall abnormal overvoltage of the IGCT silicon stack 11 is handled by the modular controllable MOV.

[0076] In this application example, the modular controllable MOV does not require a separate thyristor-level voltage detection unit, nor does it require local electrical triggering circuits at each thyristor level. The existing voltage detection signal at IGCT level 6 is received uniformly by the valve control device, which completes optical thyristor triggering via optical fiber, thereby reducing the number of high-potential-side detection and triggering components while achieving active overvoltage protection.

[0077] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modular controllable MOV for a fully controllable LCC converter valve, characterized in that, It includes a series-connected optically controlled thyristor silicon stack (8) and a surge arrester resistor array (9). The optically controlled thyristor silicon stack (8) includes multiple thyristor stages connected in series. Each thyristor stage includes a first optically controlled thyristor (1), a second optically controlled thyristor (2) connected in antiparallel to the first optically controlled thyristor (1), and a first RC branch connected in parallel to the first optically controlled thyristor (1) and the second optically controlled thyristor (2). The surge arrester resistor group (9) includes multiple zinc oxide surge arrester resistors (3) connected in series, and a second RC branch is connected in parallel at both ends of the surge arrester resistor group (9).

2. The modular controllable MOV for a fully controllable LCC converter valve according to claim 1, characterized in that, The first RC branch includes a first damping capacitor and a first damping resistor connected in series; The second RC branch includes a second damping capacitor and a second damping resistor connected in series.

3. The modular controllable MOV for a fully controllable LCC converter valve according to claim 2, characterized in that, The capacitance values ​​of the first damping capacitors in each of the thyristor stages are the same, and the resistance values ​​of the first damping resistors in each of the thyristor stages are the same.

4. The modular controllable MOV for a fully controllable LCC converter valve according to claim 2, characterized in that, The voltage that the optically controlled thyristor silicon stack (8) withstands The voltage borne by the surge arrester resistor array (9) satisfy: in, This represents the voltage across the component-type controllable MOV (10). This indicates the capacitance value of the second damping capacitor. This indicates the capacitance value of the first damping capacitor. This indicates the number of thyristor stages in the optically controlled thyristor silicon stack (8).

5. The modular controllable MOV for a fully controllable LCC converter valve according to claim 1, characterized in that, The optically controlled thyristor silicon stack (8) is connected in series with the surge arrester resistor assembly (9) by crimping.

6. The modular controllable MOV for a fully controllable LCC converter valve according to claim 5, characterized in that, The series-pressed optical thyristor silicon stack (8) and the surge arrester resistor assembly (9) are integrated into the insulating sheath.

7. A fully controllable LCC converter valve, comprising an IGCT silicon stack (11) and a valve reactor (7) connected in series with the IGCT silicon stack (11); characterized in that, It also includes modular controllable MOV (10); The modular controllable MOV (10) includes a series-connected optically controlled thyristor silicon stack (8) and a surge arrester resistor sheet group (9). The two ends of the modular controllable MOV (10) are respectively connected to the two ends of the IGCT silicon stack (11), so that the valve reactor (7) is located outside the parallel range formed by the modular controllable MOV (10) and the IGCT silicon stack (11).

8. The fully controllable LCC converter valve according to claim 7, characterized in that: It also includes a valve control device; the IGCT silicon stack (11) includes multiple IGCT stages (6) with voltage detection function. The valve control device is connected to the IGCT stage (6) and the optical thyristor silicon stack (8) respectively, and is used to send a trigger signal to the optical thyristor silicon stack (8) according to the voltage signal output by the IGCT stage (6).

9. A control method for a modular controllable MOV for a fully controllable LCC converter valve as described in any one of claims 1 to 6, characterized in that, The fully controllable LCC converter valve is the fully controllable LCC converter valve as described in claim 7 or 8; the control method includes: Obtain the voltage signals detected by each IGCT stage (6) in the IGCT silicon stack (11); Based on the voltage signal, determine whether the voltage borne by the IGCT silicon stack (11) has entered the preset protection range; When the voltage across the IGCT silicon stack (11) enters the preset protection range, a trigger signal is sent to the optically controlled thyristor silicon stack (8) to turn on the optically controlled thyristor silicon stack (8) and to limit the voltage across the IGCT silicon stack (11) by the surge arrester resistor group (9).

10. The control method for a modular controllable MOV for a fully controllable LCC converter valve according to claim 9, characterized in that, The lower limit between the preset protection zones is determined based on the maximum peak operating voltage of the IGCT silicon stack (11) after considering commutation overshoot, the dynamic voltage distribution non-uniformity coefficient, and the corresponding safety factor; the upper limit between the preset protection zones is determined based on the protective trigger voltage of each IGCT stage (6) in the IGCT silicon stack (11), the number of IGCT stages (6), the non-uniformity coefficient of the protective trigger voltage of each IGCT stage (6), and the corresponding safety factor.

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