A controllable phase-commutated converter auxiliary fully controlled sub-valve arrester topology and operation method

Abstract

Disclosed are a topology and an operating method for a controllable phase-commutation converter auxiliary fully controlled sub-valve arrester. In the controllable phase-commutation converter auxiliary fully controlled sub-valve arrester topology, a main branch low-voltage IGBT valve is connected in series with a main branch thyristor valve; an auxiliary branch is connected in parallel with the main branch; a high-voltage low-current IGBT valve includes n identical arresters, each arrester is connected via n mechanical switches K1 to K n Connected to the common bus, during the operation of the controlled commutation converter auxiliary full-controlled sub-valve arrester topology, K1~K n Among the n mechanical switches, only one is closed and only one lightning arrester is in working state; the high-voltage and low-current thyristor valve is connected in series with the high-voltage and low-current IGBT valve.

Description

Technical Field

[0001] The present invention relates to the technical field of controllable phase-commutation converter auxiliary fully-controlled sub-valve arrester topology, and in particular to a controllable phase-commutation converter auxiliary fully-controlled sub-valve arrester topology and an operation method. Background Art

[0002] Traditional line commutated converter high voltage direct current (LCC-HVDC) transmission systems are widely used worldwide due to their advantages, including long-distance, high-capacity power transmission and controllable active power. However, because the thyristors used in their converters rely on the AC system for commutation voltage, commutation failures are prone to occur in situations such as AC system failures, leading to a surge in DC current and a rapid loss of DC transmission power. Currently, valve arresters commonly use ZnO resistors, but this does not significantly improve the thermal tolerance of ZnO resistors. The only way to increase the thermal tolerance of the arrester is to increase the number of parallel resistor columns. However, simply increasing the number of parallel columns increases the unevenness of the arrester's current distribution. When the arrester operates, the current in some resistor columns is too high while that in others is too low, which does not effectively improve the arrester's thermal tolerance. Therefore, a feasible method to increase the thermal tolerance of the arrester is needed.

[0003] The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0004] In view of the shortcomings or defects of the prior art, a controllable phase-commutated converter auxiliary fully controlled sub-valve arrester topology and operation method is provided, wherein the main branch is a thyristor valve (V 11 sub-valve) and low-voltage IGBT valve (V 12 The auxiliary branch is composed of a high-voltage and low-current IGBT valve (V 13 sub valve) and high voltage low current thyristor valve (V 14 The controllable commutation converter assisted fully controlled sub-valve arrester topology can achieve controllable bridge arm current in both steady state and during AC fault conditions, completely resolving commutation failure issues. When the AC grid voltage drops and the controllable commutation converter assisted fully controlled sub-valve arrester topology is required to provide reactive power support, the controllable commutation converter assisted fully controlled sub-valve arrester topology may operate at a zero extinction angle or even a negative extinction angle for a long time. At this time, the controllable commutation converter assisted fully controlled sub-valve arrester topology will operate in the active shutdown state for a long time, and the arrester energy accumulation is far higher than in normal operation. This invention will significantly increase the reactive power support operation time of the controllable commutation converter assisted fully controlled sub-valve arrester topology.

[0005] The purpose of the present invention is achieved through the following technical solutions.

[0006] A controllable commutation converter auxiliary fully controlled sub-valve arrester topology includes:

[0007] It includes a bridge arm, and the bridge arm includes,

[0008] The main branch includes,

[0009] Main branch thyristor valve,

[0010] A main branch low-voltage IGBT valve, which is connected in series with a main branch thyristor valve;

[0011] An auxiliary branch, connected in parallel to the main branch, the auxiliary branch includes:

[0012] High-voltage and low-current IGBT valve, the high-voltage and low-current IGBT valve includes n identical lightning arresters, each of which is connected to the same circuit by n mechanical switches K1~K n Connected to the common bus, during the operation of the controlled commutation converter auxiliary full-controlled sub-valve arrester topology, K1~K n Among the n mechanical switches, only one is closed and only one arrester is in working condition;

[0013] A high-voltage, low-current thyristor valve is connected in series with a high-voltage, low-current IGBT valve.

[0014] In the controllable phase-commutated converter auxiliary fully controlled sub-valve arrester topology, the main branch low-voltage IGBT valve includes an IGBT and a lightning arrester connected in parallel.

[0015] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology, the high-voltage and low-current IGBT valve further includes n IGBTs of the arrester connected in parallel and series capacitors and resistors of the parallel IGBTs.

[0016] In the controllable commutation converter assisted fully controlled sub-valve arrester topology, the high-voltage and low-current thyristor valve includes a thyristor and an arrester connected in parallel.

[0017] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology, the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is a 6-pulse converter.

[0018] The operation method of the controllable commutated converter assisted fully controlled sub-valve arrester topology includes:

[0019] Step 1: The controllable commutated converter assisted fully controlled sub-valve arrester topology is connected to the DC transmission power system, and n arresters of high-voltage and low-current IGBT valves are connected to the common bus through mechanical switches;

[0020] Step 2: Determine the energy consumed by the arrester of the high-voltage and low-current IGBT valve in each working cycle based on the phase change time from the shut-off valve to the open valve under the active shut-off condition;

[0021] Step 3: Determine the minimum number of lightning arresters based on the maximum active shutdown duration in the project and the energy consumed by each lightning arrester per working cycle;

[0022] Step 4: When the number of arrester actions exceeds the upper limit, the arrester is shut down and the next arrester is put into operation. The arrester operation is completed during the conduction period of the main branch thyristor valve or the high-voltage and low-current IGBT valve. At this time, the mechanical switch is not subjected to voltage.

[0023] Step 5: When the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is not actively shut down for a long time, the arrester in parallel with the high-voltage and low-current IGBT valve is switched at regular intervals.

[0024] In the operating method, in step 2, the main branch thyristor valve actively commutates to the high-voltage, low-current IGBT valve. At time t0, the main branch thyristor valve commutates to the high-voltage, low-current IGBT valve. At the same time, the main branch thyristor valve switches to the main and auxiliary branches. The time from time t0 to time t1 is the natural commutation time; at time t1, the main branch thyristor valve assists the high-voltage, low-current IGBT valve to turn off, and active commutation begins. At time t2, the active commutation is completed, and the active shutdown time is:

[0025] ,

[0026] During active shutdown, V 13 Energy consumed by the sub-valve arrester for:

[0027] ,

[0028] in, I d is the effective value of the DC current of the bridge arm; E is the effective value of the line voltage on the converter transformer valve side; L μ is the leakage inductance of the commutation transformer; α is the triggering angle of the main branch thyristor valve; The time from the adjacent bridge arm is triggered to the high-voltage and low-current IGBT valve in the bridge arm is turned off, that is, the natural commutation time of the bridge arm; f is the grid frequency; I 13 is flowing through V 13 Valve current, V 13 The establishment voltage of the sub-valve lightning arrester.

[0029] In the operation method, step 3, according to the maximum active shutdown duration in the project is T max, the energy tolerance of a single lightning arrester is M ar , the minimum number of lightning arresters is:

[0030] ,

[0031] Among them, the duration of a single system failure is .

[0032] The number of redundant lightning arresters is n re , the actual number of lightning arresters is:

[0033] .

[0034] In the operating method, the lightning arrester includes a ZnO resistor.

[0035] In the described operating method, when the DC transmission power system requires the controllable commutation converter to assist the fully controlled sub-valve arrester topology to provide reactive support, the controllable commutation converter to assist the fully controlled sub-valve arrester topology operates at a 0 arc extinction angle or even a negative arc extinction angle, and the controllable commutation converter to assist the fully controlled sub-valve arrester topology will operate in an active shutdown state for a long time.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention combines the controllable phase-commutated converter auxiliary fully controlled sub-valve arrester topology auxiliary branch fully controlled sub-valve (V 13 The arrester is divided into n identical arresters, each of which is connected to the common busbar through a mechanical switch, which greatly improves the V 13 The energy tolerance capability of the sub-valve arrester and the continuous working time of the active shutdown condition of the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology help to further improve the support capability of the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology for the power grid; especially when the AC power grid voltage drops and the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology is required to provide reactive support, the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology may work for a long time at 0 arc extinction angle or even negative arc extinction angle. At this time, the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology will work in the active shutdown state for a long time, and the energy accumulation of the arrester is much higher than the normal operating state. The present invention will greatly improve the reactive support operation time of the controllable phase-commutating converter assisted fully-controlled sub-valve arrester topology.

[0038] The above description is only an overview of the technical solution of the present invention. In order to make the technical means of the present invention clearer and easier to understand, so that those skilled in the art can implement it according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are illustrated below. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are intended only to illustrate preferred embodiments and are not to be construed as limiting the present invention. It should be understood that the drawings described below are merely examples of the present invention, and that those skilled in the art will be able to derive other drawings from these drawings without inventive effort. Throughout the drawings, identical reference numerals are used to denote identical components.

[0040] In the attached figure:

[0041] Figure 1 This is a schematic diagram of the topological structure of the auxiliary fully controlled sub-valves of the controllable commutation converter according to an embodiment of the present invention, wherein all sub-valves are shown as V1 in the figure;

[0042] Figure 2 This is a schematic diagram of the active shutdown voltage and current waveforms of the present invention;

[0043] Figure 3 This is a schematic diagram of the topology of a fully controlled sub-valve arrester of a controllable commutated converter according to an embodiment of the present invention, which is composed of n parallel-connected arresters;

[0044] Figure 4 This is a schematic diagram of the active shutdown commutation process of the present invention.

[0045] The present invention will be further explained below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0046] Specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0047] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the present invention shall be as defined in the attached claims.

[0048] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings. However, the accompanying drawings do not limit the embodiments of the present invention.

[0049] For better understanding, Figures 1 to 4 As shown, a controllable commutation converter auxiliary fully controlled sub-valve arrester topology includes:

[0050] It includes a bridge arm, and the bridge arm includes,

[0051] The main branch includes,

[0052] Main branch thyristor valve,

[0053] A main branch low-voltage IGBT valve, which is connected in series with a main branch thyristor valve;

[0054] An auxiliary branch, connected in parallel to the main branch, the auxiliary branch includes:

[0055] High-voltage and low-current IGBT valve, the high-voltage and low-current IGBT valve includes n identical lightning arresters, each of which is connected to the same circuit by n mechanical switches K1~K n Connected to the common bus, during the operation of the controlled commutation converter auxiliary full-controlled sub-valve arrester topology, K1~K n Among the n mechanical switches, only one is closed and only one arrester is in working condition;

[0056] A high-voltage, low-current thyristor valve is connected in series with a high-voltage, low-current IGBT valve.

[0057] In a preferred embodiment of the controllable commutation converter assisted fully controlled sub-valve arrester topology, the main branch low-voltage IGBT valve includes an IGBT and an arrester connected in parallel.

[0058] In a preferred embodiment of the controllable commutation converter auxiliary fully controlled sub-valve arrester topology, the high-voltage and low-current IGBT valve further includes n IGBTs of the arrester connected in parallel and series capacitors and resistors of the parallel IGBTs.

[0059] In a preferred embodiment of the controllable commutation converter assisted fully controlled sub-valve arrester topology, the high-voltage and low-current thyristor valve includes a thyristor and an arrester connected in parallel.

[0060] In a preferred embodiment of the controllable commutation converter assisted fully controlled sub-valve arrester topology, the controllable commutation converter assisted fully controlled sub-valve arrester topology is a 6-pulse converter.

[0061] The operation method of the controllable commutated converter assisted fully controlled sub-valve arrester topology includes:

[0062] Step 1: The controllable commutated converter assisted fully controlled sub-valve arrester topology is connected to the DC transmission power system, and n arresters of high-voltage and low-current IGBT valves are connected to the common bus through mechanical switches;

[0063] Step 2: Determine the energy consumed by the arrester of the high-voltage and low-current IGBT valve in each working cycle based on the phase change time from the shut-off valve to the open valve under the active shut-off condition;

[0064] Step 3: Determine the minimum number of lightning arresters based on the maximum active shutdown duration in the project and the energy consumed by each lightning arrester per working cycle;

[0065] Step 4: When the number of arrester actions exceeds the upper limit, the arrester is shut down and the next arrester is put into operation. The arrester operation is completed during the conduction period of the main branch thyristor valve or the high-voltage and low-current IGBT valve. At this time, the mechanical switch is not subjected to voltage.

[0066] Step 5: When the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is not actively shut down for a long time, the arrester in parallel with the high-voltage and low-current IGBT valve is switched at regular intervals.

[0067] In a preferred embodiment of the operation method, in step 2, the main branch thyristor valve actively commutates to the high-voltage, low-current IGBT valve. At time t0, the main branch thyristor valve commutates to the high-voltage, low-current IGBT valve. At the same time, the main branch thyristor valve switches to the main and auxiliary branches. The time from time t0 to time t1 is the natural commutation time; at time t1, the main branch thyristor valve assists the high-voltage, low-current IGBT valve to turn off, and active commutation begins. At time t2, the active commutation is completed, and the active shutdown time is:

[0068] ,

[0069] During active shutdown, V 13 Energy consumed by the sub-valve arrester for:

[0070] ,

[0071] in, I d is the effective value of the DC current of the bridge arm; E is the effective value of the line voltage on the converter transformer valve side; L μ is the leakage inductance of the commutation transformer; α is the triggering angle of the main branch thyristor valve; The time from the adjacent bridge arm is triggered to the high-voltage and low-current IGBT valve in the bridge arm is turned off, that is, the natural commutation time of the bridge arm; f is the grid frequency; I 13 is flowing through V 13 Valve current; V 13 The establishment voltage of the sub-valve lightning arrester.

[0072] In a preferred embodiment of the operation method, step 3, according to the maximum active shutdown duration in the project is T max , the energy tolerance of a single lightning arrester is M ar , the minimum number of lightning arresters is:

[0073] ,

[0074] in, is the duration of a single system failure.

[0075] The number of redundant lightning arresters is n re , the actual number of lightning arresters is:

[0076] .

[0077] In a preferred embodiment of the operating method, the arrester comprises a ZnO resistor.

[0078] In a preferred embodiment of the operating method, when the DC transmission power system needs the controllable commutation converter to assist the fully controlled sub-valve arrester topology to provide reactive support, the controllable commutation converter to assist the fully controlled sub-valve arrester topology operates at 0 arc extinction angle or even negative arc extinction angle conditions, and the controllable commutation converter to assist the fully controlled sub-valve arrester topology will operate in an active shutdown state for a long time.

[0079] In one embodiment, in a certain DC transmission project, the controllable commutation converter auxiliary fully controlled sub-valve arrester topology can be as follows: Figure 1 In a 6-pulse controlled commutation converter auxiliary fully controlled sub-valve arrester topology, each bridge arm is composed of a main branch and an auxiliary branch in parallel. The main branch is the original conventional thyristor valve (V 11 sub-valve) and low-voltage IGBT valve (V 12The auxiliary branch is composed of a high-voltage and low-current IGBT valve (V 13 sub valve) and high voltage low current thyristor valve (V 14 The main branch and the auxiliary branch are connected in parallel to form a converter bridge arm. For a 6-pulse converter, the bridge arm is represented by valves V1 to V6.

[0080] Auxiliary branch high voltage and low current V 13 Sub-valve arrester A 13 Divided into n identical lightning arresters A1~A n Each lightning arrester is connected to the mechanical switch K1~K n Connected to the common bus and connected in parallel at V 13 Both ends of the sub valve.

[0081] Determine the V of each working cycle according to the commutation time from the off bridge arm to the on bridge arm under the active shutdown condition. 13 Sub-valve arrester A 13 The specific process of energy consumption is as follows:

[0082] Taking the active commutation from V1 valve to V3 valve as an example, the active commutation process is as follows: Figure 4 As shown, at time t0, the V1 valve switches to the V3 valve. During the phase-commutation overlap period, the main and auxiliary branches in the V1 valve bridge arm are switched on. The time from t0 to t1 is the natural phase-commutation time. At t1, the auxiliary branch of the V1 valve V 13 The sub-valve is closed and active commutation begins. Active commutation is completed at time t2. In the interval t1~t2, V 13 In the shutdown process, t0 is the time when the main branch current switches to the auxiliary branch, that is, the time when the main branch current transfers to the auxiliary branch. △t1 is the natural commutation current transfer stage between the two bridge arms. At t1, V 13 At the time when the valve is actively disconnected, the current in this bridge arm will transfer to the next bridge arm faster, V 13 The valve receives the trigger signal but does not conduct (voltage is low) at the initial moment, conducts (voltage is low) at t0, and is closed (voltage is high) at t1. t2 is the time point when commutation is completed.

[0083] Taking time t0 as the starting point, the V3 valve current between time t0 and time t1 is:

[0084] (1)

[0085] (2)

[0086] in:

[0087] E : Effective value of line voltage on converter transformer valve side;

[0088] L μ : Commutation transformer leakage inductance.

[0089] : is the current flowing through the V3 valve.

[0090] I 1 : is the current flowing through the V1 valve.

[0091] V3 valve current at time t1:

[0092] (3)

[0093] Taking time t1 as the starting point, V 13 Sub-valve arrester establishes voltage U ar , between time t1 and time t2:

[0094] (4)

[0095] Integrate to get V 13 The current on is:

[0096] (5)

[0097] make t =0, we can get:

[0098] (6)

[0099] Substituting formula (6) into formula (5), we can get:

[0100] (7)

[0101] At t2, the V3 valve current is equal to I d ,have:

[0102] (8)

[0103] Since after time t1, U ar Much larger than the power frequency commutation voltage, Δ can be ignored t The power frequency commutation voltage in the 2 time period, formula (8) can be rewritten as:

[0104] (9)

[0105] The active shutdown time can be solved as:

[0106] (10)

[0107] During active shutdown, V 13The energy consumed by the sub-valve arrester is:

[0108] (11)

[0109] Substituting (7) and (10) into (11) we can calculate V 13 The sub-valve arrester is in one power frequency cycle T f Energy consumed internally.

[0110] The minimum number of arresters is determined based on the maximum active shutdown duration that may occur in the project and the energy consumed by each arrester in each working cycle. On this basis, the arrester margin is designed. Assume that the maximum active shutdown duration that may occur in the project is T max , the energy tolerance of a single lightning arrester is M ar , the minimum number of arresters required is:

[0111] (12)

[0112] Assume the number of redundant arresters is n re , the actual number of lightning arresters is:

[0113] (13)

[0114] During the operation of the controllable commutation converter auxiliary full-controlled sub-valve arrester topology, K1~K n Among the n mechanical switches, only one is closed and only one arrester is in working condition.

[0115] Count the number of times the arrester operates. When the number of times the arrester operates exceeds the upper limit, the arrester will exit operation and the next arrester will be put into operation. The arrester operation is as follows: Figure 4 The t shown rotate Completed within the time period, at this time V 11 or V 13 The sub-valve is on and the mechanical switch does not bear voltage. 11 For the flow through V1 valve V 11 The current of the thyristor valve, that is, the main branch current of the V1 valve, I 13 is flowing through V 13 The current of the IGBT sub-valve, that is, the auxiliary branch current of the V1 valve, I3 is the current flowing through the V3 valve, U1 is the voltage across the V1 valve, U3 is the voltage across the V3 valve, and Uar is the V during the active shutdown period of the V1 valve. 13 Voltage across the sub-valve arrester.

[0116] The AC system voltage connected to the controllable commutation converter assisted fully controlled sub-valve arrester topology is stable for a long time. When the controllable commutation converter assisted fully controlled sub-valve arrester topology does not need to be actively shut down for a long time, the parallel arrester is switched at regular intervals to perform self-checks on the arrester status and control circuit.

[0117] Example

[0118] Taking a DC project as an example, the rated DC voltage of the project is U dc = ±800kV, rated DC power is 8000MW, the receiving end converter adopts the controllable commutation converter auxiliary full-controlled sub-valve arrester topology; the effective value of the line voltage on the valve side of the converter transformer is E = 163kV, the leakage inductance of the converter transformer is L μ =13.5mH,

[0119] Active commutation V 13 Sub-valve arrester establishes voltage U ar =220kV, Δ t 1 takes a fixed value of 1.5ms, the inverter trigger angle α =160°, and from (10) we can get Δ t 2=0.4ms; From formula (11), we can get V 13 The sub-valve arrester is in one power frequency cycle T f Energy consumed internally E ar =0.4MJ; the maximum active shutdown duration that may occur in the project is T max =3s, the energy tolerance of a single lightning arrester is M ar =24MJ, the minimum number of arresters required n can be obtained from formula (12) min =5, number of redundant lightning arresters n re =1, the actual number of lightning arresters n=6;

[0120] During the operation of the controllable commutation converter auxiliary full-controlled sub-valve arrester topology, only one of the six mechanical switches K1~K6 is closed, and only one arrester is in working state; the number of times the arrester operates is counted, and when the number of times the arrester operates exceeds the upper limit, the arrester is shut down and the next arrester is put into operation. The arrester operation is carried out as follows: Figure 4 The t shown rotate Completed within the time period, t rotate The time period is V 13 The allowable switching time of the valve arrester. During this time period, V 13 There is no overvoltage on the 13 To shut down, and there will be overvoltage, at this time V 11 or V 13The sub-valve is turned on and the mechanical switch is not subjected to voltage. When the controllable commutation converter assists the fully controlled sub-valve arrester topology and does not need to be actively shut down for a long time, the parallel arrester is switched at regular intervals to perform self-test on the arrester status and control circuit.

[0121] In the design of the main branch and auxiliary branch, the main branch: consists of a main branch thyristor valve and a main branch low-voltage IGBT valve connected in series, providing the main current channel and capable of effective on and off under normal operating conditions. The auxiliary branch: connected in parallel to the main branch, contains a high-voltage, low-current IGBT valve and a high-voltage, low-current thyristor valve, used to provide additional control capabilities in specific situations (such as during active commutation) to ensure system stability and safety. N identical lightning arresters are integrated into the high-voltage, low-current IGBT valve. Each lightning arrester is connected to the common bus through a mechanical switch to ensure that only one lightning arrester is in operation during one working cycle, which helps to extend the service life of the lightning arrester and improve system reliability. The minimum number of lightning arresters required is determined by calculation, based on the maximum active shutdown duration and the energy tolerance capability of each lightning arrester, to ensure the safe operation of the system under extreme conditions.

[0122] The energy consumed by the V13 sub-valve arrester during the active shutdown process is calculated through a detailed mathematical model, which is crucial for evaluating the arrester workload and selecting the appropriate number of arresters.

[0123] When the number of times a lightning arrester has operated exceeds the upper limit, it automatically switches to the next lightning arrester. This process is completed while the main branch or auxiliary branch is on, ensuring operational safety. Regularly switching lightning arresters not only enables self-testing functions, but also ensures that all lightning arresters are in good working condition, improving the overall reliability of the system. ZnO resistors have excellent nonlinear volt-ampere characteristics and can respond quickly under high voltages, effectively absorbing overvoltages and protecting power equipment from damage. The system design takes into account the reactive power support requirements under conditions of zero or even negative arc extinction angles, enabling the controllable phase-commutated converter assisted fully controlled sub-valve lightning arrester topology to operate stably in a long-term active shutdown state, enhancing the system's flexibility and adaptability.

[0124] By analyzing specific project parameters (such as rated DC voltage, power, commutation parameters, etc.), the practical feasibility and effectiveness of the topology were verified, providing a reference for similar projects.

[0125] This invention proposes a novel topology in which the main branch consists of a main branch thyristor valve and a main branch low-voltage IGBT valve in series, responsible for conducting and shutting off the system's primary current path. The auxiliary branch, consisting of a high-voltage, low-current IGBT valve (with n internal lightning arresters) connected in series with a high-voltage, low-current thyristor valve, is connected in parallel with the main branch to enhance the system's responsiveness and stability under unusual operating conditions. By combining high-voltage, low-current IGBTs with thyristors, the system achieves higher control accuracy and operational stability during critical control operations such as active commutation, significantly improving overall operational safety and reliability.

[0126] The n lightning arresters configured inside the high-voltage, low-current IGBT valve are physically connected to the common bus through mechanical switches. In any working cycle, only one lightning arrester is allowed to be in operation, and the others remain on standby to reduce load accumulation. This rotation mechanism significantly extends the service life of a single lightning arrester and avoids performance degradation or structural damage caused by continuous high-energy impacts. At the same time, to ensure the continuous operation capability of the system, the lightning arresters are configured with redundancy. When a lightning arrester fails, other backup units can be put into use immediately, thereby enhancing the system's fault resistance. The system has an automatic counting function for the number of lightning arrester actions. When any lightning arrester reaches the preset action upper limit, it automatically switches to the next lightning arrester. The switching process is strictly controlled to be completed during the conduction period of the main branch or auxiliary branch to avoid arcing when the mechanical switch is subjected to voltage, thereby ensuring the safety of the operation process.

[0127] Furthermore, this rotational operation mechanism, combined with regular self-tests, helps promptly identify potential faults and maintain optimal operating conditions for all arresters, effectively reducing maintenance frequency and costs while ensuring system safety. The number of arresters is calculated based on the maximum active shutdown duration and the energy tolerance of a single arrester. In actual engineering applications, the number is appropriately increased in accordance with redundant design principles to ensure adequate system protection even under extreme operating conditions, achieving an optimal balance between system safety and resource allocation efficiency.

[0128] The arrester's core utilizes zinc oxide (ZnO) varistor sheets with excellent nonlinear volt-ampere characteristics. These varistor sheets exhibit exceptional high-voltage, rapid response capabilities, and are capable of efficiently absorbing and limiting overvoltages, effectively protecting power system equipment. This material's superior electrical properties significantly enhance overall system stability and reduce the risk of damage caused by overvoltage.

[0129] At the system design level, this topology fully considers the grid's need for reactive power support under low or even negative arc extinction angle conditions, ensuring stable operation even during extended active shutdown periods. This enhances the system's adaptability and flexibility in complex grid environments. This topology is particularly well-suited for applications requiring frequent reactive power compensation and demanding grid stability requirements. It effectively expands the system's application boundaries and engineering applicability, enhancing its technological sophistication and market competitiveness.

[0130] The basic principles of the present application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in this application are merely illustrative and not restrictive, and it should not be assumed that these advantages, strengths, and effects are required of each embodiment of this application. In addition, the specific details disclosed above are merely illustrative and facilitating understanding, and are not restrictive. The above details do not limit this application to necessarily being implemented using the above specific details.

[0131] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A method for operating a controllable phase-commutated converter assisted fully controlled sub-valve arrester topology, characterized in that: The controllable commutation converter auxiliary fully controlled sub-valve arrester topology includes a bridge arm, the bridge arm includes, The main branch includes, Main branch thyristor valve, A main branch low-voltage IGBT valve, which is connected in series with a main branch thyristor valve; An auxiliary branch, connected in parallel to the main branch, the auxiliary branch includes: High-voltage and low-current IGBT valve, the high-voltage and low-current IGBT valve includes n identical lightning arresters, each of which is connected to the same circuit by n mechanical switches K1~K n Connected to the common bus, during the operation of the controlled commutation converter auxiliary full-controlled sub-valve arrester topology, K1~K n Among the n mechanical switches, only one is closed and only one arrester is in working condition; High-voltage, low-current thyristor valve, which is connected in series with a high-voltage, low-current IGBT valve; The operation method includes: Step 1: The controllable commutated converter assisted fully controlled sub-valve arrester topology is connected to the DC transmission power system, and n arresters of high-voltage and low-current IGBT valves are connected to the common bus through mechanical switches; Step 2: Determine the energy consumed by the arrester of the high-voltage and low-current IGBT valve in each working cycle based on the phase change time from the shut-off valve to the open valve under the active shut-off condition; Step 3: Determine the minimum number of lightning arresters based on the maximum active shutdown duration in the project and the energy consumed by each lightning arrester per working cycle; Step 4: When the number of arrester actions exceeds the upper limit, the arrester is shut down and the next arrester is put into operation. The arrester operation is completed during the conduction period of the main branch thyristor valve or the high-voltage and low-current IGBT valve. At this time, the mechanical switch is not subjected to voltage. Step 5: When the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is not actively shut down for a long time, the arrester in parallel with the high-voltage and low-current IGBT valve is switched at regular intervals.

2. The operating method according to claim 1, characterized in that: The main branch low-voltage IGBT valve includes an IGBT and a lightning arrester connected in parallel.

3. The operating method according to claim 1, characterized in that: The high-voltage, low-current IGBT valve further includes n IGBTs of lightning arresters connected in parallel and a series capacitor and a resistor of the parallel IGBTs.

4. The operating method according to claim 1, wherein: The high-voltage and low-current thyristor valve includes a thyristor and a lightning arrester connected in parallel.

5. The operating method according to claim 1, characterized in that: The topology of the controllable commutated converter auxiliary fully controlled sub-valve arrester is a 6-pulse converter.

6. The operating method according to claim 1, characterized in that: In step 2, the main branch thyristor valve actively commutates to the high-voltage, low-current IGBT valve. At t0, the main branch thyristor valve commutates to the high-voltage, low-current IGBT valve. At the same time, the main branch thyristor valve switches to the main and auxiliary branches. The time from t0 to t1 is the natural commutation time. At t1, the main branch thyristor valve assists the high-voltage, low-current IGBT valve to turn off, and active commutation begins. At t2, the active commutation is completed. The active shutdown time is: ， During active shutdown, V 13 Energy consumed by the sub-valve arrester for: ， Among them, I d is the effective value of the DC current of the bridge arm; E is the effective value of the line voltage on the converter valve side; L μ is the leakage inductance of the commutation transformer; α is the triggering angle of the main branch thyristor valve; The time from the adjacent bridge arm being triggered to the high-voltage, low-current IGBT valve being turned off in the current bridge arm is the natural commutation time of the bridge arm; f is the grid frequency; I 13 is flowing through V 13 Valve current; V 13 The establishment voltage of the sub-valve lightning arrester.

7. The operating method according to claim 6, characterized in that: Step 3: According to the maximum active shutdown duration T in the project max , the energy tolerance of a single lightning arrester is M ar , the minimum number of lightning arresters is: ， The number of redundant lightning arresters is n re , the actual number of lightning arresters is: ， in, The duration of a single system failure is .

8. The operating method according to claim 1, characterized in that: The lightning arrester includes a ZnO resistor.

9. The operating method according to claim 1, characterized in that: When the DC transmission power system requires a controllable commutated converter assisted by a fully controlled sub-valve arrester topology to provide reactive power support, the controllable commutated converter assisted by a fully controlled sub-valve arrester topology operates at a zero arc extinction angle or even a negative arc extinction angle, and the controllable commutated converter assisted by a fully controlled sub-valve arrester topology will operate in an active shutdown state for a long time.

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