Converter valve section voltage-sharing capacitance parameter determination method

Abstract

The invention relates to a converter valve section voltage-sharing capacitance parameter determination method, and belongs to the technical field of valve section voltage-sharing capacitance parameter determination. The method comprises the following steps: S1, building a converter valve broadband equivalent model by using set valve tower structure parameters, acquired stray parameters of a converter valve and preliminarily set valve section voltage-sharing capacitance parameters; s2, respectively calculating the maximum non-uniform coefficients between the valve sections of the equivalent model under the impact of operation, thunder and lightning and steep wave voltage, judging whether the maximum non-uniform coefficients between the valve sections under each impact are in the corresponding range meeting the control requirements, if not, increasing the voltage-sharing capacitance parameter of the valve section of the equivalent model by M% and then repeating the S2, and if so, executing the S3; s3, reducing the voltage-sharing capacitance parameter by N%, calculating again, judging whether the maximum nonuniform coefficient between the valve sections under each impact is within the corresponding range meeting the control requirement, and if not, adopting the voltage-sharing capacitance parameter before the reduction; if so, repeating S3; m is greater than or equal to a set multiple of N, and the set multiple is greater than or equal to 2.

Description

Technical Field

[0001] The invention relates to a method for determining parameters of a pressure-equalizing capacitor for a valve section of a converter valve, and belongs to the technical field of determining parameters of a pressure-equalizing capacitor for a valve section. Background Art

[0002] The converter valve is the core equipment in DC transmission technology. The converter valve tower is usually composed of 2 or 4 single valves, each of which contains dozens to hundreds of thyristor stages. There are many key components in the valve tower and the structure is compact, showing a very complex stray capacitance distribution. Under the impact of the surge voltage of operation, lightning and steep waves, the converter valve will be affected by the stray capacitance, causing uneven voltage distribution on the converter valve. This is mainly because the converter valve system is capacitive under the impact of the surge voltage, and different spatial positions may cause uneven voltage distribution. Therefore, equalizing capacitors are usually connected in parallel at both ends of the converter valve section to improve the voltage distribution between valve sections under various surge voltages.

[0003] The Chinese invention patent with application publication number CN102723879A discloses a design method for a voltage-equalizing capacitor of a converter valve assembly. The method first sets the initial value of the voltage-equalizing capacitor, then establishes a converter valve impact circuit model, analyzes the voltage peak value that the converter valve withstands, and then determines whether the voltage-equalizing coefficient meets the requirements. If not, the voltage-equalizing capacitor of the assembly is increased, and the above steps are repeated until the voltage-equalizing coefficient meets the requirements. The method corrects the voltage-equalizing capacitor of the converter valve assembly by judging the voltage-equalizing coefficient. However, according to the method of increasing the capacitance, if the amplitude of each adjustment is too large, although it can be quickly adjusted, The capacitance value that meets the requirements can be obtained, but the capacitance value of the voltage-equalizing capacitor is likely to exceed the minimum capacitance value that satisfies the requirements of the voltage-equalizing coefficient to a large extent, thereby increasing the cost of the converter valve assembly; if the amplitude of each adjustment is too small, although the capacitance value that meets the requirements can be made closer to the minimum capacitance value that satisfies the requirements of the voltage-equalizing coefficient, the number of adjustments required will increase significantly, thereby reducing the efficiency of determining the voltage-equalizing capacitor. Therefore, the design method of the voltage-equalizing capacitor is affected by the amplitude of each adjustment, making it difficult to take into account both the cost of the converter valve assembly and the efficiency of obtaining the capacitance value of the voltage-equalizing capacitor. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining the parameters of the equalizing capacitor of the valve section of a converter valve, so as to solve the problem that the current method for determining the equalizing capacitor is affected by the amplitude of each adjustment, making it difficult to take into account both the cost of the converter valve component and the efficiency of obtaining the capacitance of the equalizing capacitor.

[0005] In order to solve the above technical problems, the present invention provides a method for determining parameters of a converter valve section grading capacitor, the method comprising:

[0006] S1: A broadband equivalent model of the converter valve is constructed using the set valve tower structural parameters, the obtained stray parameters of the converter valve, and the preliminarily set valve section equalizing capacitor parameters;

[0007] S2: Calculate the maximum uneven coefficients between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage respectively, and judge whether the maximum uneven coefficients between valve sections under each impact are all within the corresponding range that meets the control requirements. If not, increase the valve section equalizing capacitor parameter of the equivalent model by M% and repeat S2. If yes, proceed to S3.

[0008] S3: After reducing the valve section pressure-equalizing capacitor parameter by N%, recalculate and determine whether the maximum unevenness coefficient between valve sections under each impact is within the corresponding range that meets the control requirements. If not, use the valve section pressure-equalizing capacitor parameter before this reduction; if yes, repeat S3; M is greater than or equal to the set multiple of N, and the set multiple is greater than or equal to 2.

[0009] Furthermore, the methods of respectively calculating the maximum non-uniformity coefficient between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage include: respectively using the operating voltage, lightning voltage and steep wave voltage as the voltage of the shock wave generator of the equivalent model, applying shock waves corresponding to the operating voltage, lightning voltage and steep wave voltage to the equivalent model, respectively obtaining and determining the maximum non-uniformity coefficient between valve sections under the corresponding impact based on the maximum value of the voltages of each valve section of the equivalent model under the shock waves corresponding to the applied operating voltage, lightning voltage and steep wave voltage and the average value of the voltages of each valve section.

[0010] Furthermore, the method for preliminarily setting the valve section pressure equalizing capacitor parameters includes: determining the upper limit threshold of the valve section pressure equalizing capacitor parameters according to the set valve tower structure parameters and the obtained stray parameters of the converter valve, and selecting a value less than or equal to the upper limit threshold as the preliminary setting of the valve section pressure equalizing capacitor parameters.

[0011] Furthermore, the maximum non-uniform coefficient between valve sections under the corresponding impact is determined according to the maximum value of the voltage of each valve section under the impact wave corresponding to the applied operating voltage, lightning voltage and steep wave voltage and the average value of the voltage of each valve section:

[0012]

[0013] Wherein, K is the maximum uneven coefficient between the valve sections, including the maximum uneven coefficient between the valve sections under the shock wave corresponding to the operating voltage, lightning voltage and steep wave voltage; V max is the maximum value of the voltage of each valve section, is the average voltage of each valve section, P is the number of valve sections per valve layer, Q is the number of single valve layers, V iis the voltage of the i-th valve section, i∈{1, 2, 3...P×Q}.

[0014] Further, the method of judging whether the maximum non-uniform coefficient between valve sections under each impact is within the corresponding range that meets the control requirement includes:

[0015] Determine whether the maximum uneven coefficient between valve sections under the operating voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage impact; determine whether the maximum uneven coefficient between valve sections under the lightning voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage impact; determine whether the maximum uneven coefficient between valve sections under the steep wave voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact; the upper limit thresholds of the range that meets the control requirements corresponding to the operating voltage, lightning voltage and steep wave voltage impact are all greater than 1, and the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage, and the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact.

[0016] Furthermore, the value range of M is: [10, 50].

[0017] Furthermore, the value range of N is: [5, 25].

[0018] Furthermore, the stray parameters include: stray capacitance between the thyristor and the ground, stray capacitance between the thyristors of the upper and lower valve layers, and stray capacitance between the valve section and the ground; the method of obtaining the stray parameters includes:

[0019] A converter valve simulation model is built according to the set valve tower structural parameters, and the value of the stray parameter of the converter valve simulation model is extracted to obtain the stray parameter.

[0020] Furthermore, the valve tower structural parameters include: the number of single valve layers, the number of valve sections per valve layer, and the number of thyristors per valve section.

[0021] Furthermore, the method of determining the upper limit threshold of the valve section equalizing capacitor parameter according to the set valve tower structural parameters and the obtained stray parameters of the converter valve includes:

[0022]

[0023] In the formula, C max is the upper threshold of the valve section equalizing capacitor parameter value, P is the number of valve sections per valve layer, Q is the number of single valve layers, C bg Stray capacitance between valve section and ground.

[0024] Beneficial effect: The present invention provides a new method for determining the valve section equalizing capacitor parameters of a converter valve. The method, based on a wide-band equivalent model close to the actual operating conditions constructed by using the set valve tower structural parameters, the obtained stray parameters of the converter valve and the preliminarily set valve section equalizing capacitor parameters, makes more flexible settings for adjusting the valve section equalizing capacitor parameters. That is, if the preliminarily set valve section equalizing capacitor parameters can already meet the control requirements corresponding to the maximum unevenness coefficient, then adjust downward at a relatively small ratio; if the control requirements are not met, first increase (i.e., increase) the valve section equalizing capacitor parameters by a large ratio, and then adjust downward (i.e., reduce) them one by one at a relatively small ratio after the control requirements are met; after each downward adjustment, if it is found that the downward adjustment is too much and the control requirements are not met , then the voltage-equalizing capacitor parameter value before this downward adjustment (i.e., reduction) is taken. This way of back-and-forth adjustment and corresponding analysis and selection is relatively less affected by the amplitude of each adjustment, and can effectively avoid the problem that the voltage-equalizing capacitor determination method in the prior art is affected by the amplitude of each adjustment, resulting in difficulty in taking into account both the cost of the converter valve assembly and the efficiency of obtaining the capacitance of the voltage-equalizing capacitor; therefore, the present invention can make the ultimately determined valve section voltage-equalizing capacitor closer to the minimum voltage-equalizing capacitor parameter that can meet the control requirements, while also taking into account the efficiency requirements, thereby improving the reliability of the converter valve equipment while ensuring the efficiency of determining the valve section voltage-equalizing capacitor parameters, while saving the production and testing costs of the voltage-equalizing capacitor, and providing support for the safe and stable operation of the power grid system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a flow chart of a method for determining parameters of a converter valve section voltage-equalizing capacitor in an embodiment of the method for determining parameters of a converter valve section voltage-equalizing capacitor of the present invention;

[0026] Figure 2 is an exemplary diagram of the converter valve tower structure in the embodiment of the method for determining the parameters of the converter valve valve section grading capacitor of the converter valve of the present invention;

[0027] Figure 3 It is an example diagram of a single-valve broadband equivalent model of a converter valve in an embodiment of the method for determining parameters of a grading capacitor of a converter valve section of the present invention. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0029] Embodiment of a method for determining parameters of a voltage-equalizing capacitor in a converter valve section

[0030] This embodiment provides a technical solution for a method for determining parameters of a grading capacitor of a converter valve section, the method comprising:

[0031] S1: A broadband equivalent model of the converter valve is constructed using the set valve tower structural parameters, the obtained stray parameters of the converter valve, and the preliminarily set valve section equalizing capacitor parameters;

[0032] S2: Calculate the maximum uneven coefficients between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage respectively, and judge whether the maximum uneven coefficients between valve sections under each impact are all within the corresponding range that meets the control requirements. If not, increase the valve section equalizing capacitor parameter of the equivalent model by M% and repeat S2. If yes, proceed to S3.

[0033] S3: After reducing the valve section equalizing capacitor parameter by N%, recalculate and determine whether the maximum unevenness coefficient between valve sections under each impact is within the corresponding range that meets the control requirements. If not, use the valve section equalizing capacitor parameter before this reduction; if yes, repeat S3; M is greater than or equal to the set multiple of N, and the set multiple is greater than or equal to 2.

[0034] The method is equivalent to a broadband equivalent model close to the actual working conditions built by using the set valve tower structural parameters, the obtained stray parameters of the converter valve and the preliminarily set valve section equalizing capacitor parameters, and a more flexible setting is made for the adjustment of the valve section equalizing capacitor parameters. If the preliminarily set valve section equalizing capacitor parameters can already meet the control requirements corresponding to the maximum unevenness coefficient, then they are adjusted downward at a relatively small ratio; if the control requirements are not met, the valve section equalizing capacitor parameters are first adjusted up (i.e. increased) by a large ratio, and then adjusted downward (i.e. reduced) by a relatively small ratio after they are met; after each downward adjustment, if it is found that the downward adjustment is too much and the control requirements are not met, the current downward adjustment (i.e. reduction) is taken as the maximum control requirement. The equalizing capacitor parameter value before is determined. This method of adjusting back and forth and performing corresponding analysis and selection is relatively less affected by the amplitude of each adjustment, which can effectively avoid the problem that the method for determining the equalizing capacitor in the prior art is affected by the amplitude of each adjustment, resulting in difficulty in taking into account both the cost of the converter valve component and the efficiency of obtaining the capacitance of the equalizing capacitor; therefore, this method can make the final determined valve section equalizing capacitor closer to the minimum equalizing capacitor parameter that can meet the control requirements, while also taking into account the efficiency requirements. Therefore, on the basis of ensuring the efficiency of determining the valve section equalizing capacitor parameters, the reliability of the converter valve equipment is improved, while saving the production and testing costs of the equalizing capacitor, providing support for the safe and stable operation of the power grid system.

[0035] The flow chart of the method for determining the parameters of the converter valve section equalizing capacitor is as follows: Figure 1 As shown, the following takes the process of determining the parameters of the converter valve section equalizing capacitor under a certain working condition as an example to specifically explain the method for determining the parameters of the converter valve section equalizing capacitor:

[0036] S1: A broadband equivalent model of the converter valve is constructed using the set valve tower structural parameters, the obtained stray parameters of the converter valve, and the preliminarily set valve section equalizing capacitor parameters;

[0037] The valve section of the converter valve is composed of several thyristor stages and saturated reactors connected in series and then connected in parallel with a voltage-equalizing capacitor; the valve section voltage-equalizing capacitor is connected in parallel with each valve section in the converter valve, and has the function of evenly distributing the voltage between the valve sections of the converter valve. The example diagram of the converter valve tower structure in this embodiment is as follows: Figure 2 As shown, the valve tower structure is a quadruple valve, and the valve tower structural parameters include: the number of single valve layers Q, the number of valve sections per valve layer P, and the number of thyristors per valve section n. The specific method of determining the form of the converter valve tower structure includes: calculating the number of single valve thyristors according to the parameters of the actual engineering design, thereby correspondingly determining the form of the converter valve tower structure (i.e., the structural parameters of each valve tower);

[0038] The stray parameters include: stray capacitance C between thyristor and ground g , the stray capacitance C between the thyristors of the upper and lower valve layers cc And the stray capacitance C between the valve section and the ground bg The method of obtaining stray parameters includes: building a converter valve simulation model according to the set valve tower structural parameters, specifically using a general electromagnetic field numerical analysis method, building a converter valve simulation model according to the set valve tower structural parameters, and extracting the value of the stray parameter of the converter valve simulation model to obtain the stray parameter. Since the method of obtaining stray parameters using the general electromagnetic field numerical analysis method belongs to the prior art, it will not be repeated here.

[0039] The method of preliminarily setting the valve section equalizing capacitor parameter C includes: determining the upper limit threshold value C of the valve section equalizing capacitor parameter according to the set valve tower structure parameters and the obtained stray parameters of the converter valve. max , select a value less than or equal to the upper limit threshold as the preliminary setting of the valve section equalizing capacitor parameter C.

[0040] The method of determining the upper limit threshold of the valve section equalizing capacitor parameter according to the set valve tower structural parameters and the obtained stray parameters of the converter valve is specifically as follows:

[0041]

[0042] In the formula, C max is the upper threshold of the valve section equalizing capacitor parameter value, P is the number of valve sections per valve layer, Q is the number of single valve layers, C bg is the stray capacitance between the valve section and the ground. The preliminary setting principle of the valve section capacitance parameter C can be expressed as:

[0043]

[0044] The DC voltage balancing resistor R is also used when building the broadband equivalent model of the converter valve. DC , Damping resistance R B and damping capacitor C B Parameters such as, these parameters are necessary parameters for building a broadband equivalent model of a converter valve in the prior art, and will not be described in detail here;

[0045] In summary, the example diagram of the converter valve single valve broadband equivalent model is as follows: Figure 3 As shown, each valve includes Q valve layers, each valve layer includes P valve sections, wherein the shock wave generator is used to apply shock waves corresponding to the operating voltage, lightning voltage and steep wave voltage to each valve section of the single valve broadband equivalent model of the converter valve.

[0046] S2: Calculate the maximum uneven coefficient between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage respectively, and judge whether the maximum uneven coefficient between valve sections under each impact is within the corresponding range that meets the control requirements. If not, increase the valve section equalizing capacitor parameter of the equivalent model by M% and repeat S2. If yes, proceed to S3; the value range of M is [10, 50]. In this embodiment, M is 20;

[0047] Among them, the equivalent model is calculated respectively at the operating voltage V SIWL , lightning voltage V LIWL and steep wave voltage V FWWL The maximum uneven coefficient K between valve sections under the impact of S , K L and K F The method includes: respectively taking the operating voltage, the lightning voltage and the steep wave voltage as the voltages of the shock wave generator of the equivalent model, applying shock waves corresponding to the operating voltage, the lightning voltage and the steep wave voltage to the equivalent model, respectively obtaining and determining the maximum non-uniformity coefficient between the valve sections under the corresponding shock according to the maximum value of the voltages of each valve section of the equivalent model under the shock waves corresponding to the applied operating voltage, the lightning voltage and the steep wave voltage and the average value of the voltages of each valve section.

[0048] The maximum non-uniform coefficient between valve sections under the corresponding impact is determined according to the maximum value of the voltage of each valve section under the impact wave corresponding to the applied operating voltage, lightning voltage and steep wave voltage and the average value of the voltage of each valve section:

[0049]

[0050] Where K is the maximum uneven coefficient between valve sections (including the equivalent model at the operating voltage V SIWL , lightning voltage V LIWL and steep wave voltage V FWWL The maximum uneven coefficient K between valve sections under the impact of S, K L and K F ), V max is the maximum value of the voltage of each valve section, is the average voltage of each valve section, P is the number of valve sections per valve layer, Q is the number of single valve layers, V i is the voltage of the i-th valve section, i∈{1, 2, 3...P×Q}.

[0051] Methods for judging whether the maximum non-uniform coefficients between valve sections under each impact are all within the corresponding range that meets the control requirements include:

[0052] Determine the operating voltage V SIWL Maximum uneven coefficient K between valve sections under impact S Is it less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage impact; determine whether the lightning voltage V LIWL Maximum uneven coefficient K between valve sections under impact L Is it less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage impulse; determine whether the steep wave voltage V FWWL The maximum uneven coefficient K between valve sections under impact F Whether it is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact; the upper limit thresholds of the range that meets the control requirements corresponding to the operating voltage, the lightning voltage and the steep wave voltage impact are all greater than 1, and the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage, and the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact. In this embodiment, the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage impact is 1.07, the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage impact is 1.1, and the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact is 1.2.

[0053] The method for judging whether the maximum uneven coefficient between valve sections under each impact is within the corresponding range that meets the control requirements is to judge whether K S ≤1.07, K L ≤1.1 and K F ≤1.2;

[0054] S3: after reducing the valve section equalizing capacitor parameter by N%, recalculate and judge whether the maximum non-uniform coefficient between valve sections under each impact is within the corresponding range that meets the control requirements. If not, the valve section equalizing capacitor parameter before this reduction is used; if it is, repeat S3; M is greater than or equal to the set multiple of N, and the set multiple is greater than or equal to 2, that is, compared with the larger adjustment range of increasing the valve section equalizing capacitor parameter of the equivalent model mentioned above, the adjustment range of reducing the valve section equalizing capacitor parameter here is relatively small, so as to ensure that the maximum difference between the final determined valve section equalizing capacitor and the minimum equalizing capacitor parameter that can meet the control requirements (that is, the equalizing capacitor parameter that can meet the control requirements and has the lowest cost, the smaller the difference between the actual equalizing capacitor parameter and the equalizing capacitor parameter that can meet the control requirements and has the lowest cost, the lower the cost) is not greater than N%. The value range of N is [5, 25]. In this embodiment, N is 5; M is equal to four times N.

[0055] Through the above implementation, the parameters of the valve section equalizing capacitor can be effectively determined, the reliability of the converter valve equipment can be improved, and at the same time, support can be provided for the safe and stable operation of the power grid system on the basis of saving the production, manufacturing and testing costs of the equalizing capacitor.

Claims

1. A method for determining parameters of a converter valve section voltage-sharing capacitor, characterized in that: include: S1: A broadband equivalent model of the converter valve is constructed using the set valve tower structural parameters, the obtained stray parameters of the converter valve, and the preliminarily set valve section equalizing capacitor parameters; S2: Calculate the maximum uneven coefficients between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage respectively, and judge whether the maximum uneven coefficients between valve sections under each impact are all within the corresponding range that meets the control requirements. If not, increase the valve section equalizing capacitor parameter of the equivalent model by M% and repeat S2. If yes, proceed to S3. S3: After reducing the valve section pressure-equalizing capacitor parameter by N%, recalculate and determine whether the maximum unevenness coefficient between valve sections under each impact is within the corresponding range that meets the control requirements. If not, use the valve section pressure-equalizing capacitor parameter before this reduction; if yes, repeat S3; M is greater than or equal to the set multiple of N, and the set multiple is greater than or equal to 2.

2. The method for determining the parameters of the converter valve section grading capacitor according to claim 1, characterized in that: The method of respectively calculating the maximum non-uniform coefficient between valve sections of the equivalent model under the impact of operating voltage, lightning voltage and steep wave voltage includes: respectively taking the operating voltage, lightning voltage and steep wave voltage as the voltage of the shock wave generator of the equivalent model, applying shock waves corresponding to the operating voltage, lightning voltage and steep wave voltage to the equivalent model, respectively obtaining and determining the maximum non-uniform coefficient between valve sections under the corresponding impact according to the maximum value of the voltage of each valve section of the equivalent model under the shock waves corresponding to the applied operating voltage, lightning voltage and steep wave voltage and the average value of the voltage of each valve section.

3. The method for determining the parameters of the converter valve section grading capacitor according to claim 1 or 2, characterized in that: The method for preliminarily setting the valve section equalizing capacitor parameters includes: determining the upper limit threshold of the valve section equalizing capacitor parameters according to the set valve tower structure parameters and the obtained stray parameters of the converter valve, and selecting a value less than or equal to the upper limit threshold as the preliminary setting of the valve section equalizing capacitor parameters.

4. The method for determining the parameters of the converter valve section grading capacitor according to claim 2, characterized in that: The maximum non-uniform coefficient between valve sections under the corresponding impact is determined according to the maximum value of the voltage of each valve section under the impact wave corresponding to the applied operating voltage, lightning voltage and steep wave voltage and the average value of the voltage of each valve section: Wherein, K is the maximum uneven coefficient between the valve sections, including the maximum uneven coefficient between the valve sections under the shock wave corresponding to the operating voltage, lightning voltage and steep wave voltage; V max is the maximum value of the voltage of each valve section, is the average voltage of each valve section, P is the number of valve sections per valve layer, Q is the number of single valve layers, V i is the voltage of the i-th valve section, i∈{1, 2, 3...P×Q}.

5. The method for determining the parameters of the converter valve section grading capacitor according to claim 3, characterized in that: Methods for judging whether the maximum non-uniform coefficients between valve sections under each impact are all within the corresponding range that meets the control requirements include: Determine whether the maximum uneven coefficient between valve sections under the operating voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage impact; determine whether the maximum uneven coefficient between valve sections under the lightning voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage impact; determine whether the maximum uneven coefficient between valve sections under the steep wave voltage impact is less than or equal to the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact; the upper limit thresholds of the range that meets the control requirements corresponding to the operating voltage, lightning voltage and steep wave voltage impact are all greater than 1, and the upper limit threshold of the range that meets the control requirements corresponding to the operating voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage, and the upper limit threshold of the range that meets the control requirements corresponding to the lightning voltage is greater than the upper limit threshold of the range that meets the control requirements corresponding to the steep wave voltage impact.

6. The method for determining the parameters of the converter valve section grading capacitor according to claim 1, characterized in that: The value range of M is: [10, 50].

7. The method for determining the parameters of the converter valve section grading capacitor according to claim 1, characterized in that: The value range of N is: [5, 25].

8. The method for determining the parameters of the converter valve section grading capacitor according to claim 3, characterized in that: The stray parameters include: stray capacitance between the thyristor and the ground, stray capacitance between the thyristors of the upper and lower valve layers, and stray capacitance between the valve section and the ground; the method for obtaining the stray parameters includes: A converter valve simulation model is built according to the set valve tower structural parameters, and the value of the stray parameter of the converter valve simulation model is extracted to obtain the stray parameter.

9. The method for determining the parameters of the converter valve section grading capacitor according to claim 8, characterized in that: The valve tower structural parameters include: the number of single valve layers, the number of valve sections per valve layer, and the number of thyristors per valve section.

10. The method for determining the parameters of the converter valve section grading capacitor according to claim 9, characterized in that: Methods for determining the upper threshold of the valve section equalizing capacitor parameter according to the set valve tower structural parameters and the obtained stray parameters of the converter valve include: In the formula, C max is the upper threshold of the valve section equalizing capacitor parameter value, P is the number of valve sections per valve layer, Q is the number of single valve layers, C bg Stray capacitance between valve section and ground.

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