Controllable commutation converter auxiliary full-control sub-valve lightning arrester topology and operation method

Abstract

According to the controllable commutation converter auxiliary full-control sub-valve lightning arrester topology and the operation method, in the controllable commutation converter auxiliary full-control sub-valve lightning arrester topology, a main branch low-voltage IGBT valve is connected with a main branch thyristor valve in series; the auxiliary branch is connected with the main branch in parallel, the high-voltage small-current IGBT valve comprises n identical lightning arresters, each lightning arrester is connected with a common bus through n mechanical switches K1-Kn, and during the topological operation period of the auxiliary full-control sub-valve lightning arrester of the controllable commutation converter, only one of the n mechanical switches K1-Kn is closed, and only one lightning arrester is in a working state; and the high-voltage small-current thyristor valve is connected in series with the high-voltage small-current IGBT valve.

Description

Technical Field

[0001] The present invention relates to the technical field of thyristor commutated converter auxiliary fully controlled sub-valve arrester topologies, and particularly to a thyristor commutated converter auxiliary fully controlled sub-valve arrester topology and an operation method thereof. Background Art

[0002] Traditional line commutated converter high voltage direct current (LCC-HVDC) transmission systems have advantages such as long-distance and large-capacity power transmission and controllable active power, and are widely used worldwide. However, since the thyristors used in its converters rely on the AC system to provide commutation voltage, commutation failures are likely to occur in the event of AC system faults, etc., resulting in a sharp increase in DC current and a rapid and large loss of DC transmission power. Currently, ZnO varistors are commonly used in valve arresters, and it is impossible to significantly improve the thermal tolerance of ZnO varistors. Only by increasing the number of parallel columns of arrester varistors can the thermal tolerance of the arrester be increased. However, blindly increasing the number of parallel columns of the arrester will increase the non-uniformity of the current distribution of the arrester. When the arrester operates, the current in some varistor columns is too large, and the current in some varistor columns is too small, and the thermal tolerance of the arrester cannot be effectively increased; a feasible method for increasing the thermal tolerance of the arrester needs to be found.

[0003] The information disclosed in the background art section is only used to enhance the understanding of the background of the present invention, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] Aiming at the deficiencies or defects existing in the prior art, a thyristor commutated converter auxiliary fully controlled sub-valve arrester topology and an operation method thereof are provided. The main branch is composed of a thyristor valve (V 11 sub-valve) and a low-voltage IGBT valve (V 12 sub-valve) connected in series, and the auxiliary branch is composed of a high-voltage small-current IGBT valve (V 13 sub-valve) and a high-voltage small-current thyristor valve (V 14 sub-valve) connected in series. Whether in the steady state or during AC faults, the thyristor commutated converter auxiliary fully controlled sub-valve arrester topology can achieve controllable arm current and solve the commutation failure problem 100%. When the AC grid voltage drops and the thyristor commutated converter auxiliary fully controlled sub-valve arrester topology is required to provide reactive power support, the thyristor commutated converter auxiliary fully controlled sub-valve arrester topology may work in the 0 extinction angle or even negative extinction angle condition for a long time. At this time, the thyristor commutated converter auxiliary fully controlled sub-valve arrester topology will work in the active turn-off state for a long time, and the energy accumulation of the arrester is much higher than that in the normal operation state. The present invention will greatly increase the reactive power support operation time of the thyristor commutated converter auxiliary fully controlled sub-valve arrester topology.

[0005] The object of the present invention is achieved by the following technical solutions.

[0006] A controllable commutation converter auxiliary fully controlled sub-valve arrester topology includes It includes an arm, and the arm includes A main branch, which includes A main branch thyristor valve A main branch low-voltage IGBT valve, which is connected in series with the main branch thyristor valve; An auxiliary branch, which is connected in parallel with the main branch. The auxiliary branch includes A high-voltage small-current IGBT valve. The high-voltage small-current IGBT valve includes n arresters that are exactly the same. Each arrester is connected to the common bus through n mechanical switches K1~K n During the operation of the controllable commutation converter auxiliary fully controlled sub-valve arrester topology, only one of the n mechanical switches in K1~K n is closed, and only one arrester is in the working state; A high-voltage small-current thyristor valve, which is connected in series with the high-voltage small-current IGBT valve.

[0007] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology described above, the main branch low-voltage IGBT valve includes an IGBT and an arrester connected in parallel.

[0008] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology described above, the high-voltage small-current IGBT valve further includes an IGBT connected in parallel with n arresters, and a series capacitor and resistor connected in parallel with the IGBT.

[0009] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology described above, the high-voltage small-current thyristor valve includes a thyristor and an arrester connected in parallel.

[0010] In the controllable commutation converter auxiliary fully controlled sub-valve arrester topology described above, the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is a 6-pulse converter.

[0011] The operation method of the controllable commutation converter auxiliary fully controlled sub-valve arrester topology includes Step 1, the controllable commutation converter auxiliary fully controlled sub-valve arrester topology is connected to the DC power transmission system, and the n arresters of the high-voltage small-current IGBT valve are connected to the common bus through mechanical switches; Step 2, according to the commutation time from the turn-off valve to the turn-on valve under the active turn-off condition, determine the energy consumed by the arrester of the high-voltage small-current IGBT valve in each working cycle; Step 3, determine the minimum number of arresters according to the maximum active turn-off duration in the project and the energy consumed by each arrester in each working cycle; Step 4: When the operation times of the arrester exceed the upper limit value, the arrester exits the operation, and the next arrester is put into operation. The switching operations of the arrester are all completed during the conduction period of the main branch thyristor valve or the high-voltage small-current IGBT valve. At this time, the mechanical switch does not bear voltage. Step 5: When the auxiliary fully-controlled sub-valve arrester topology of the controllable commutation converter does not actively turn off for a long time, the arresters in parallel with the high-voltage small-current IGBT valve are switched every once in a while.

[0012] In the operation method described above, in Step 2, the main branch thyristor valve actively commutates to the high-voltage small-current IGBT valve. At time t0, the main branch thyristor valve commutates to the high-voltage small-current IGBT valve, and at the same time, the main and auxiliary branches of the main branch thyristor valve are switched. The natural commutation time is from time t0 to time t1. At time t1, the main branch thyristor valve assists the high-voltage small-current IGBT valve to turn off and starts active commutation. Active commutation is completed at time t2, and the active turn-off time is: , During the active turn-off process, the energy consumed by the V 13 sub-valve arrester is: , where 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 valve side of the converter transformer; L μ is the leakage inductance of the converter transformer; α is the trigger angle of the main branch thyristor valve; is the time from the trigger of the adjacent bridge arm to the turn-off of the high-voltage small-current IGBT valve in this bridge arm, that is, the natural commutation time of the bridge arm; f is the power grid frequency; I 13 is the current flowing through the V 13 valve, and 13 is the established voltage of the V

[0013] In the operation method described above, in Step 3, according to the maximum active turn-off duration T max in the project, and the energy tolerance of a single arrester is M ar , the minimum number of arresters is: , where is the duration of a single system fault.

[0014] The number of redundant arresters is n re , and the actual number of arresters is: .

[0015] In the described operation method, the lightning arrester includes ZnO resistor chips.

[0016] In the described operation method, when the HVDC power system needs the thyristor-controlled converter (TCC) assisted fully controlled sub-valve lightning arrester topology to provide reactive power support, the TCC assisted fully controlled sub-valve lightning arrester topology operates at a zero extinction angle or even a negative extinction angle condition, and the TCC assisted fully controlled sub-valve lightning arrester topology will operate in the active commutation-off state for a long time.

[0017] Compared with the prior art, the beneficial effects brought by the present invention are as follows: The present invention divides the TCC assisted fully controlled sub-valve lightning arrester topology assisted branch fully controlled sub-valve (V 13 sub-valve) lightning arrester into n completely identical lightning arresters, and each lightning arrester is connected to the common bus through a mechanical switch, greatly improving the energy tolerance of the V 13 sub-valve lightning arrester and the continuous working time of the TCC assisted fully controlled sub-valve lightning arrester topology in the active commutation-off condition, which helps to further improve the support ability of the TCC assisted fully controlled sub-valve lightning arrester topology for the power grid; especially when the AC grid voltage drops and the TCC assisted fully controlled sub-valve lightning arrester topology needs to provide reactive power support, the TCC assisted fully controlled sub-valve lightning arrester topology may operate at a zero extinction angle or even a negative extinction angle condition for a long time. At this time, the TCC assisted fully controlled sub-valve lightning arrester topology will operate in the active commutation-off state for a long time, and the energy accumulation of the lightning arrester is much higher than that in the normal operation state. The present invention will greatly improve the reactive power support operation time of the TCC assisted fully controlled sub-valve lightning arrester topology.

[0018] 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 to enable those skilled in the art to implement it according to the content of the specification, and to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following takes the specific embodiments of the present invention as examples for illustration. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of showing the preferred embodiments and are not considered as limiting the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. And throughout the drawings, the same reference numerals are used to represent the same components.

[0020] In the drawings: Figure 1Schematic diagram of the topology of the auxiliary fully controlled sub-valve of a controllable commutation converter according to an embodiment of the present invention, where all sub-valves are as shown by V1 in the figure; Figure 2 Schematic diagram of the active turn-off voltage and current waveforms according to the present invention; Figure 3 Schematic diagram of the topology of the arrester for the fully controlled sub-valve of a controllable commutation converter according to an embodiment of the present invention, all composed of n parallel arresters; Figure 4 Schematic diagram of the active turn-off commutation process according to the present invention.

[0021] The present invention will be further explained below in conjunction with the drawings and embodiments. Detailed implementation manners

[0022] The specific embodiments of the present invention will be described in more detail below with reference to the drawings. Although specific embodiments of the present invention are shown in the 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. On the contrary, 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.

[0023] It should be noted that in the description of the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different terms to refer to the same component. The specification and claims do not use the difference in terms as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. As mentioned throughout the specification and claims, "comprising" or "including" is an open-ended term and should be interpreted as "including but not limited to". The subsequent description of the specification is the preferred implementation manner for implementing the present invention, but the description is for the purpose of the general principle of the specification and is not used to limit the scope of the present invention. The protection scope of the present invention shall be determined by the scope defined by the appended claims.

[0024] For the convenience of understanding the embodiments of the present invention, the following will further explain with several specific embodiments as examples in conjunction with the drawings, and each drawing does not constitute a limitation on the embodiments of the present invention.

[0025] For better understanding, as Figures 1 to 4 shown, a topology of the arrester for the auxiliary fully controlled sub-valve of a controllable commutation converter includes, It includes a bridge arm, and the bridge arm includes, The main branch, which includes, The main branch thyristor valve, The main branch low-voltage IGBT valve, which is connected in series with the main branch thyristor valve; The auxiliary branch, which is connected in parallel with the main branch, and 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 lightning arrester is connected to the common bus through n mechanical switches K1~K n During the operation of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, only one of the n mechanical switches in K1~K n is closed, and only one lightning arrester is in the working state; High-voltage and low-current thyristor valve, which is connected in series with the high-voltage and low-current IGBT valve.

[0026] In the preferred embodiment of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, the main branch low-voltage IGBT valve includes an IGBT and a lightning arrester connected in parallel.

[0027] In the preferred embodiment of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, the high-voltage and low-current IGBT valve further includes an IGBT in parallel with n lightning arresters, and a series capacitor and resistor in parallel with the IGBT.

[0028] In the preferred embodiment of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, the high-voltage and low-current thyristor valve includes a thyristor and a lightning arrester connected in parallel.

[0029] In the preferred embodiment of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter is a 6-pulse converter.

[0030] The operation method of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter includes, Step 1, the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter is connected to the DC power transmission system. The n lightning arresters of the high-voltage and low-current IGBT valve are connected to the common bus through mechanical switches; Step 2, according to the commutation time from the turn-off valve to the turn-on valve under the active turn-off condition, determine the energy consumed by the lightning arrester of the high-voltage and low-current IGBT valve in each working cycle; Step 3, determine the minimum number of lightning arresters according to the maximum active turn-off duration in the project and the energy consumed by each lightning arrester in each working cycle; Step 4, when the action times of the lightning arrester exceed the upper limit value, withdraw from operation and put into the next lightning arrester. The switching operations of the lightning arrester are all completed during the conduction of the main branch thyristor valve or the high-voltage and low-current IGBT valve. At this time, the mechanical switch does not bear voltage; Step 5, when the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter does not actively turn off for a long time, switch the parallel lightning arresters of the high-voltage and low-current IGBT valve every once in a while.

[0031] In the preferred embodiment of the operation method, in step 2, the main-branch thyristor valve actively commutates to the high-voltage and low-current IGBT valve. At time t0, the main-branch thyristor valve commutates to the high-voltage and low-current IGBT valve, and at the same time, the main and auxiliary branches of the main-branch thyristor valve are switched. The time from t0 to t1 is the natural commutation time; at time t1, the main-branch thyristor valve assists the high-voltage and low-current IGBT valve to turn off and starts active commutation. At time t2, the active commutation is completed, and the active turn-off time is: , During the active turn-off process, the energy consumed by the V 13 sub-valve arrester is : , where 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 valve side of the converter transformer; L μ is the leakage inductance of the converter transformer; α is the trigger angle of the main-branch thyristor valve; is the time from the trigger of the adjacent bridge arm to the turn-off of the high-voltage and low-current IGBT valve in this bridge arm, that is, the natural commutation time of the bridge arm; f is the power grid frequency; I 13 is the current flowing through the V 13 valve; is the breakdown voltage of the V 13 sub-valve arrester.

[0032] In the preferred embodiment of the operation method, in step 3, according to the maximum active turn-off duration in the project being T max , the energy tolerance of a single arrester is M ar , the minimum number of arresters is: , where is the duration of a single system fault.

[0033] The number of redundant arresters is n re , and the actual number of arresters is: .

[0034] In the preferred embodiment of the operation method, the arrester includes ZnO resistor chips.

[0035] In the preferred embodiment of the operation method, when the HVDC power system needs the controllable commutation converter to assist the fully controlled sub-valve arrester topology to provide reactive power support, the controllable commutation converter-assisted fully controlled sub-valve arrester topology operates at a 0 extinction angle or even a negative extinction angle condition, and the controllable commutation converter-assisted fully controlled sub-valve arrester topology will work in the active turn-off state for a long time.

[0036] In one embodiment, in a certain HVDC transmission project, the topology of the thyristor controlled phase converter (TCPC) auxiliary fully controlled sub-valve arrester can be as follows Figure 1 shown. In the topology of a 6-pulse TCPC auxiliary fully controlled sub-valve arrester, each bridge arm is composed of a main branch and an auxiliary branch in parallel. The main branch is composed of the original conventional thyristor valve (V 11 sub-valve) and a low-voltage IGBT valve (V 12 sub-valve) connected in series; the auxiliary branch is composed of a high-voltage small-current IGBT valve (V 13 sub-valve) and a high-voltage small-current thyristor valve (V 14 sub-valve) connected in series; the main branch and the auxiliary branch are connected in parallel to form a converter bridge arm. For a 6-pulse converter, this bridge arm is referred to as valves V1 to V6.

[0037] The high-voltage small-current V 13 sub-valve arrester A 13 of the auxiliary branch is divided into n identical arresters A1 to A n , and each arrester is connected to the common bus through mechanical switches K1 to K n and is connected in parallel across the V 13 sub-valve.

[0038] Determine the energy consumed by each working cycle of the V 13 sub-valve arrester A 13 according to the commutation time from the turned-off bridge arm to the turned-on bridge arm under the active commutation condition. The specific process is as follows: Taking the active commutation from valve V1 to valve V3 as an example, during the active commutation process, the process is as Figure 4 shown. At time t0, valve V1 commutates to valve V3. During the commutation overlap arc, the main and auxiliary branches in the V1 valve bridge arm switch to conduction. From time t0 to time t1 is the natural commutation time; at time t1, the V 13 sub-valve of the V1 valve auxiliary branch turns off and starts active commutation, and active commutation is completed at time t2. In the interval from t1 to t2, V 13 is in the turn-off process. t0 is the switching of the main and auxiliary branches, that is, the time point when the main branch current transfers to the auxiliary branch. △t1 is the natural commutation current transfer stage between the two bridge arms. Starting from t1 is the time point when the V 13 valve actively disconnects, and the current of this bridge arm will transfer to the next bridge arm faster. The V 13 valve receives a trigger signal at the initial moment but does not conduct (low voltage), conducts at time t0 (low voltage), turns off at time t1 (high voltage), and t2 is the time point when commutation is completed.

[0039] Taking time t0 as the starting point of timing, the current of valve V3 between time t0 and time t1: (1) (2) Wherein: E : The effective value of the line voltage on the valve side of the converter transformer; L μ : The leakage inductance of the converter transformer.

[0040] : The current flowing through valve V3.

[0041] I 1 : The current flowing through valve V1.

[0042] The current of valve V3 at time t1: (3) Taking time t1 as the starting point of timing, the voltage of the arrester of valve V 13 builds up U ar , between time t1 and time t2: (4) By integrating, the current on V 13 is: (5) Let t = 0, we can get: (6) Substituting equation (6) into equation (5), we can get: (7) The current of valve V3 at time t2 is equal to I d , and we have: (8) Since after time t1, U ar is much greater than the power frequency commutation voltage, the power frequency commutation voltage during the Δ t 2 time period can be ignored, and equation (8) can be rewritten as: (9) The active turn-off time can be solved: (10) During the active turn-off process, the energy consumed by the arrester of valve V 13 is: (11) Substituting equations (7) and (10) into equation (11), we can calculate the arrester of valve V 13 in a power frequency cycle T fThe energy consumed internally.

[0043] Determine the minimum number of arresters based on the maximum active turn-off duration that may occur in the project and the energy consumed by each arrester per working cycle. On this basis, design the arrester margin. Let the maximum active turn-off duration that may occur in the project be T max , and the energy tolerance of a single arrester be M ar , then the minimum number of arresters required is: (12) Let the number of redundant arresters be n re , and the actual number of arresters is: (13) During the operation of the arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, only one of the n mechanical switches K1~K n is closed, and only one arrester is in the working state.

[0044] Count the number of operations of the arrester. When the number of operations of the arrester exceeds the upper limit of operations, it exits the operation and the next arrester is put into operation. The switching operations of the arrester are all completed within the time period t Figure 4 as shown. At this time, V rotate or V 11 sub-valve conducts, and the mechanical switch does not bear voltage. Among them, I 13 11 is the current flowing through the V 11 thyristor sub-valve of the V1 valve, that is, the main branch current of the V1 valve. I 13 13 is the current flowing through the IGBT sub-valve of the V 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. Uar is the voltage across the V 13 sub-valve arrester during the active turn-off period of the V1 valve.

[0045] When the AC system voltage connected to the arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter is long-term stable and the arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter does not require active turn-off for a long time, switch the parallel arresters every once in a while to self-check the status of the arresters and the control circuit.

[0046] Example Taking a certain DC project as an example, the rated DC voltage U dc = ±800 kV, the rated DC power is 8000 MW, and the receiving-end converter adopts the arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter; the effective value of the line voltage on the valve side of the converter transformer E = 163 kV, and the leakage inductance of the converter transformer L μ= 13.5 mH, When actively commuting, V 13 The voltage of the sub - valve arrester is established U ar = 220 kV, Δ t 1 takes a fixed value of 1.5 ms, and the trigger angle of the converter α = 160°. From equation (10), Δ can be solved t 2 = 0.4 ms; From equation (11), V can be obtained 13 The sub - valve arrester consumes energy within one power frequency cycle T f within E ar = 0.4 MJ; The maximum possible active turn - off duration in engineering is T max = 3 s, and the energy withstand capacity of a single arrester is M ar = 24 MJ. From equation (12), the minimum number of arresters required, n min = 5, the number of redundant arresters n re = 1, and the actual number of arresters n = 6; During the operation of the auxiliary fully - controlled sub - valve arrester topology of the controllable commutation converter, only one of the six mechanical switches K1 - K6 is closed, and only one arrester is in the working state; The number of operations of the arrester is counted. When the number of operations of the arrester exceeds the upper limit of operations, it exits the operation, and the next arrester is put into operation. The switching operations of the arresters are all completed within the Figure 4 t as shown rotate time period, and the t rotate time period is the allowable switching time of the V 13 valve arrester. During this time period, there is no over - voltage on V 13 ; In the remaining time periods, V 13 needs to be turned off, and over - voltage will occur. At this time, V 11 or V 13 sub - valves conduct, and the mechanical switch does not bear voltage; When the auxiliary fully - controlled sub - valve arrester topology of the controllable commutation converter does not require active turn - off for a long time, the parallel arresters are switched every once in a while to self - check the status of the arresters and the control circuit.

[0047] In the design of the main branch and the auxiliary branch, the main branch: consists of a series connection of the main branch thyristor valve and the main branch low-voltage IGBT valve, provides the main current path, and can be effectively turned on and off under normal operating conditions. The auxiliary branch: is connected in parallel to the main branch, includes a high-voltage small-current IGBT valve and a high-voltage small-current thyristor valve, and is used to provide additional control capabilities in specific situations (such as during active commutation) to ensure the stability and safety of the system. n identical lightning arresters are integrated in the high-voltage small-current IGBT valve, and each lightning arrester is connected to the common bus through a mechanical switch to ensure that only one lightning arrester is in the working state within one operating cycle, which helps to extend the service life of the lightning arrester and improve the reliability of the system. The minimum number of required lightning arresters is determined by calculation based on the maximum active turn-off duration and the energy tolerance of each lightning arrester to ensure the safe operation of the system under extreme conditions.

[0048] The energy consumed by the V13 sub-valve lightning arrester during the active turn-off process is calculated through a detailed mathematical model, which is crucial for evaluating the working load of the lightning arrester and selecting the appropriate number of lightning arresters.

[0049] When the number of operations of a certain lightning arrester exceeds the upper limit, it automatically switches to the next lightning arrester, and this process is completed during the conduction period of the main branch or the auxiliary branch to ensure the safety of the operation. Regularly switching the lightning arresters can not only achieve the self-check function but also ensure that all lightning arresters are in good working condition, improving the overall reliability of the system. The ZnO varistor has excellent non-linear volt-ampere characteristics, can quickly respond under high voltage, effectively absorb overvoltage, and protect power equipment from damage. The system design takes into account the reactive power support requirements under the condition of 0 extinction angle or even negative extinction angle, enabling the topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester to operate stably in the long-term active turn-off state, enhancing the flexibility and adaptability of the system.

[0050] Through the analysis of specific engineering parameters (such as rated DC voltage, power, converter transformer parameters, etc.), the practical feasibility and effectiveness of this topology are verified, providing a reference basis for similar projects.

[0051] The present invention proposes a new topology, in which the main branch is composed of a series connection of the main branch thyristor valve and the main branch low-voltage IGBT valve, undertaking the on and off tasks of the main current path of the system; while the auxiliary branch is composed of a series connection of a high-voltage small-current IGBT valve (with n lightning arresters integrated inside) and a high-voltage small-current thyristor valve, and is connected in parallel with the main branch to enhance the response ability and stability of the system under special working conditions. By jointly using the high-voltage small-current IGBT and thyristor, the system has higher control accuracy and operation stability when performing key control operations such as active commutation, thus significantly improving the safety and reliability of the overall operation.

[0052] The n surge arresters configured inside the high-voltage and low-current IGBT valve are all connected to the common bus through mechanical switches in terms of physical structure. During any working cycle, only one surge arrester is allowed to be in the operating state, and the rest remain on standby to reduce load accumulation. This rotation mechanism significantly extends the service life of a single surge arrester and avoids performance degradation or structural damage caused by continuous high-energy impacts. At the same time, to ensure the continuous operation ability of the system, the surge arresters are configured redundantly. When a certain surge arrester fails, other standby units can be immediately put into use, thereby enhancing the system's fault resistance ability. The system has an automatic counting function for the number of operations of the surge arrester. When any surge arrester reaches the preset operation upper limit, it automatically switches to the next surge arrester. The switching process is strictly controlled to be completed during the conduction period of the main branch or the auxiliary branch to avoid the generation of electric arcs when the mechanical switch bears voltage, thus ensuring the safety of the operation process.

[0053] In addition, this rotation operation mechanism combined with regular self-checks helps to timely identify potential faults and maintain the best operating state of all surge arresters, thereby effectively reducing the maintenance frequency and cost while ensuring the safe operation of the system. The configuration of the number of surge arresters is calculated based on the maximum active turn-off duration and the energy tolerance ability of a single surge arrester, and the number is appropriately increased in actual engineering applications in combination with the redundancy design principle to ensure that the system still has sufficient protection ability under extreme operating conditions, achieving the optimal balance between system safety and resource allocation efficiency.

[0054] The core of the surge arrester adopts zinc oxide (ZnO) varistor chips with excellent non-linear volt-ampere characteristics, which have excellent high-voltage fast response ability and can efficiently absorb and limit overvoltage, thus effectively protecting the power system equipment. The electrical performance of this material is superior, significantly improving the overall operation stability of the system and reducing the damage risk caused by overvoltage.

[0055] At the system design level, this topology also fully considers the demand for reactive power support of the power grid under low or even negative extinction angle conditions, ensuring that the system can still operate stably during a long-time active turn-off state, thereby enhancing its adaptability and flexibility in a complex power grid environment. This structure is particularly suitable for application scenarios that require frequent reactive power compensation and have strict requirements for power grid stability, effectively expanding the application boundary and engineering applicability of the system, and enhancing its technical advancement and market competitiveness.

[0056] The basic principles of the present application have been described in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present application are only examples and not limitations, and it cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present application. Additionally, the specific details disclosed above are only for illustrative and easy-to-understand purposes and not limitations, and these details do not limit the present application to necessarily implementing with the above specific details.

[0057] The above description has been given for purposes of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although multiple 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 topology of an auxiliary fully-controlled sub-valve arrester for a controllable phase-shifting converter, characterized in that, It includes bridge arms, and the bridge arms include a main branch, which includes a main branch thyristor valve a main branch low-voltage IGBT valve, which is connected in series with the main branch thyristor valve; an auxiliary branch, which is connected in parallel with the main branch. The auxiliary branch includes High-voltage and low-current IGBT valve. The high-voltage and low-current IGBT valve includes n completely identical lightning arresters. Each lightning arrester is connected to the common bus through n mechanical switches K1~K n During the operation of the lightning arrester topology of the auxiliary fully controlled sub-valve of the controllable commutation converter, only one of the n mechanical switches in K1~K n is closed, and only one lightning arrester is in the working state; a high-voltage small-current thyristor valve, which is connected in series with a high-voltage small-current IGBT valve.

2. The controllable commutation converter auxiliary fully-controlled sub-valve arrester topology 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 auxiliary fully-controlled sub-valve arrester topology of the controllable phase-shifting converter according to claim 1, characterized in that The high-voltage small-current IGBT valve further includes an IGBT with n lightning arresters connected in parallel, and a series capacitor and resistor connected in parallel with the IGBT.

4. The controllable commutation converter auxiliary fully-controlled sub-valve arrester topology according to claim 1, characterized in that, The high-voltage small-current thyristor valve includes a thyristor and a lightning arrester connected in parallel.

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

6. The operation method of the controllable commutation converter auxiliary fully controlled sub-valve arrester topology according to any one of claims 1-5, characterized in that, It includes Step 1: The topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester is connected to the DC power transmission system. The n lightning arresters of the high-voltage small-current IGBT valve are connected to the common bus through mechanical switches; Step 2: According to the commutation time from the turn-off valve to the turn-on valve under the active turn-off condition, determine the energy consumed by the lightning arrester of the high-voltage small-current IGBT valve in each working cycle; Step 3: Determine the minimum number of lightning arresters according to the maximum active turn-off duration in the project and the energy consumed by each lightning arrester in each working cycle; Step 4: When the action times of the lightning arrester exceed the upper limit value, it exits the operation and the next lightning arrester is put into operation. The switching operation of the lightning arrester is completed during the conduction period of the main branch thyristor valve or the high-voltage small-current IGBT valve. At this time, the mechanical switch does not bear voltage; Step 5: When the topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester does not actively turn off for a long time, switch the lightning arresters connected in parallel to the high-voltage small-current IGBT valve at regular intervals.

7. The operating method according to claim 6, characterized in that, In Step 2, the main branch thyristor valve actively commutes to the high-voltage small-current IGBT valve. At time t0, the main branch thyristor valve commutes to the high-voltage small-current IGBT valve. At the same time, the main and auxiliary branches of the main branch thyristor valve are switched. The natural commutation time is from time t0 to time t1; at time t1, the main branch thyristor valve assists the high-voltage small-current IGBT valve to turn off and starts active commutation. At time t2, the active commutation is completed. The active turn-off time is: ， V during the active shutdown process 13 Energy consumed by the sub-valve arrester is as follows: ， 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 valve side of the converter transformer; L μ is the leakage inductance of the converter transformer; α is the trigger angle of the thyristor valve in the main branch; is the time period from the triggering of the adjacent bridge arm to the turn-off of the high-voltage small-current IGBT valve in this bridge arm, that is, the natural commutation time of the bridge arm; f is the grid frequency; I 13 is the current flowing through V 13 valve; is the breakdown voltage of the V 13 sub-valve arrester.

8. The operating method according to claim 7, wherein Step 3: Based on 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 , and the actual number of lightning arresters is: 。 9. The operating method according to claim 6, wherein The lightning arrester includes ZnO resistor chips.

10. The operating method according to claim 6, characterized in that, When the DC power transmission system needs the topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester to provide reactive power support, the topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester operates under the condition of 0 extinction angle or even negative extinction angle, and the topology of the controllable commutation converter auxiliary fully controlled sub-valve lightning arrester will work in the active turn-off state for a long time.

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