High-voltage direct-current transmission receiving end tap switch control method, system, equipment and medium

Abstract

The invention relates to the technical field of power transmission systems, in particular to a high-voltage direct-current power transmission receiving end tap switch control method, system and device and a medium. An initial tap switch gear is selected from the tap switch gear interval, and the lowest steady-state alternating current system voltage is determined based on the initial tap switch gear; calculating a minimum valve side ideal no-load direct-current voltage according to the minimum steady-state alternating-current system voltage; according to the minimum valve side ideal no-load direct-current voltage and the minimum direct-current resistance, the minimum steady-state direct-current voltage value of the sending end is calculated; calculating the maximum steady-state direct-current voltage value of the sending end based on the maximum alternating-current system voltage and the maximum direct-current resistance; and carrying out iterative adjustment on the tap switch gear based on the lowest steady-state direct-current voltage value of the sending end and the highest steady-state direct-current voltage value of the sending end to obtain an optimal target gear of the tap switch. According to the invention, the optimal control of the tap switch gear is realized, the action times of the tap switch are effectively reduced, and the stability and reliability of a power transmission system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission systems, and in particular to a method, system, equipment and medium for controlling a tap switch at a receiving end of a high-voltage direct current transmission. Background Art

[0002] In the field of high-voltage direct current transmission projects, the converter station is the core equipment for power transmission, and its safety and reliability have a vital impact on the overall operating performance of the converter station. The converter transformer tap changer is a key component to ensure equipment safety and maintain economical operation. It mainly adjusts the output voltage of the converter transformer. When the AC system voltage and DC power change, it cooperates with the adjustment of the trigger angle and DC voltage to achieve stable power transmission and ensure that the reactive power consumption and the operating angle of the converter valve are not too large. In the actual application of high-voltage direct current transmission, especially in the scenario where a fixed turn-off angle control strategy is adopted at the receiving end, the role of the tap changer is particularly prominent. On the rectifier side, the tap changer maintains the trigger angle within the set range through tap adjustment; on the inverter side, the tap changer directly participates in the control of the DC voltage or works in conjunction with the rectifier side to ensure that the turn-off angle remains within the set range.

[0003] However, most of the HVDC transmission projects that have been put into operation currently adopt a fixed shut-off angle control strategy. This mechanism will lead to a significant increase in the number of tap changer operations when facing large-scale fluctuations in AC system voltage or frequent adjustments in DC power. Frequent operations not only aggravate the mechanical wear of the tap changer, but also lead to an increase in the acetylene content inside the converter transformer, which is one of the key factors affecting the life of the transformer and even threatens the safe and stable operation of the power grid. Especially in the current context of an increasing number of HVDC transmission projects and increasing requirements for equipment reliability, how to effectively reduce the number of tap changer operations has become an urgent problem to be solved in HVDC transmission projects.

[0004] Although the existing fixed cut-off angle control strategy has achieved accurate control of DC voltage to a certain extent, these measures are often difficult to effectively cope with the frequent fluctuations of AC system voltage and DC power in the complex and changeable power grid environment. Especially under the fixed cut-off angle control strategy at the receiving end, the number of tap changer actions is still relatively large, which is difficult to fundamentally solve the problem. Therefore, there is an urgent need for a method that can effectively reduce the number of tap changer actions while maintaining stable system operation, which is of great significance for improving the overall operating efficiency of the converter station, extending the service life of the equipment, and ensuring the safety of the power grid. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method, system, device and medium for controlling a high-voltage direct current transmission receiving-end tap changer.

[0006] In a first aspect, the present invention provides a method for controlling a tap changer at a receiving end of a high-voltage direct current transmission, the method comprising the following steps: Determine the tap changer position range according to the voltage fluctuation range of the AC system and the DC power operation range of the high-voltage DC transmission project; Selecting an initial tap switch gear from the tap switch gear range, and determining a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; According to the minimum steady-state AC system voltage, the minimum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; Under different DC transmission operation modes, the lowest steady-state DC voltage value at the sending end is calculated based on the lowest ideal no-load DC voltage at the valve side and the minimum DC resistance; Under different DC transmission operation modes, the highest steady-state DC voltage value at the sending end is calculated based on the highest AC system voltage and the maximum DC resistance; The tap changer gear position is iteratively adjusted based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain an optimal target gear position of the tap changer that meets a preset voltage range.

[0007] In a further embodiment, the step of calculating the minimum valve-side ideal no-load DC voltage based on the minimum steady-state AC system voltage using the rated transformation ratio of the converter transformer and the on-load tap changer step size comprises: Determine the rated transformation ratio of the converter transformer according to the ratio of the actual AC voltage effective value on the AC system grid side to the actual AC voltage effective value on the AC system valve side; Based on the on-load tap changer step length and the initial tap changer gear position, a tap changer adjustment proportional coefficient is calculated; The converter transformer valve side voltage conversion coefficient is calculated according to the tap changer adjustment proportional coefficient and the converter transformer rated transformation ratio; A three-phase rectification conversion coefficient is introduced, and the lowest valve-side ideal no-load DC voltage is calculated by the lowest steady-state AC system voltage and the converter transformer valve-side voltage conversion coefficient.

[0008] In a further embodiment, the step of calculating the minimum steady-state DC voltage value at the sending end according to the minimum valve-side ideal no-load DC voltage and the minimum DC resistance under different DC transmission operation modes comprises: The per-unit value of the commutation impedance voltage drop is calculated based on the difference between the per-unit value of the inductor voltage drop and the per-unit value of the resistor voltage drop. The commutation impedance coefficient is calculated based on the per unit value of the commutation impedance voltage drop, the rated ideal no-load DC voltage and the rated DC current; Determine the minimum DC resistance of the lowest steady-state AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the minimum DC resistance of the lowest steady-state AC system, and determining a first actual DC current value under a target DC power transmission operation mode according to the comparison result; The effective commutation voltage base value is calculated based on the product of the lowest ideal no-load DC voltage on the valve side and the cosine value of the turn-off angle, and the superposition of the forward conduction voltage drop of the converter valve; Calculate the difference between the minimum DC resistance and the commutation impedance coefficient to obtain a dynamic resistance compensation term, and multiply the first actual DC current value and the dynamic resistance compensation term to obtain a current compensation voltage drop; The minimum steady-state DC voltage value at the sending end is calculated based on the effective commutation voltage base value and the current compensation voltage drop.

[0009] In a further embodiment, the step of determining the first actual DC current value under the target DC power transmission operation mode according to the comparison result comprises: When the minimum DC resistance is not less than the commutation impedance coefficient, setting the first actual DC current value to a low per-unit multiple of the rated DC current; When the minimum DC resistance is less than the commutation impedance coefficient, the first actual DC current value is set to a high per-unit multiple of the rated DC current.

[0010] In a further embodiment, the step of calculating the highest steady-state DC voltage value at the sending end based on the highest AC system voltage and the maximum DC resistance under different DC transmission operation modes comprises: Determining a corresponding maximum AC system voltage based on the initial tap changer position; According to the maximum AC system voltage, the maximum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; Determine the maximum DC resistance of the highest AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the maximum DC resistance of the highest AC system, and determining a second actual DC current value under the target DC power transmission operation mode according to the comparison result; The highest steady-state DC voltage value at the sending end is calculated according to the highest ideal no-load DC voltage on the valve side, the cosine value of the shut-off angle and the second actual DC current value.

[0011] In a further embodiment, the step of determining the second actual DC current value under the target DC power transmission operation mode according to the comparison result comprises: When the maximum DC resistance is not less than the commutation impedance coefficient, setting the second actual DC current value to a high per-unit multiple of the rated DC current; When the maximum DC resistance is less than the commutation impedance coefficient, the second actual DC current value is set to a low per-unit multiple of the rated DC current.

[0012] In a further embodiment, the step of iteratively adjusting the tap changer gear position based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain the tap changer optimal target gear position that meets the preset voltage range includes: Comparing the lowest steady-state DC voltage value at the sending end with a preset minimum DC voltage threshold, if the lowest steady-state DC voltage value at the sending end is less than the minimum DC voltage threshold, adjusting the current tap changer gear to a higher gear with the on-load tap changer step size; If the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold, then comparing the highest steady-state DC voltage value at the sending end with a preset maximum DC voltage threshold; If the highest steady-state DC voltage value at the sending end is greater than the maximum DC voltage threshold, the current tap changer gear is iteratively adjusted to a low gear with the on-load tap changer step size until a tap changer gear that satisfies the conditions that the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold and the highest steady-state DC voltage value at the sending end is not greater than the maximum DC voltage threshold is found, and the optimal target gear of the tap changer is output.

[0013] In a second aspect, the present invention provides a high-voltage direct current transmission receiving-end tap changer control system, the system comprising: The switch position determination module is used to determine the tap switch position interval according to the voltage fluctuation range of the AC system and the DC power operation range of the high-voltage DC transmission project; an initial voltage determination module, configured to select an initial tap switch gear from the tap switch gear interval, and determine a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; A no-load voltage analysis module, used to calculate the lowest ideal no-load DC voltage on the valve side according to the lowest steady-state AC system voltage using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; The minimum voltage analysis module is used to calculate the minimum steady-state DC voltage value at the sending end according to the minimum ideal no-load DC voltage and minimum DC resistance on the valve side under different DC transmission operation modes; The maximum voltage analysis module is used to calculate the maximum steady-state DC voltage value at the sending end based on the maximum AC system voltage and the maximum DC resistance under different DC transmission operation modes; The optimal gear position determination module is used to iteratively adjust the tap switch gear position based on the lowest steady-state DC voltage value at the sending end and the highest steady-state DC voltage value at the sending end to obtain the optimal target gear position of the tap switch that meets the preset maximum DC voltage threshold.

[0014] In a third aspect, the present invention further provides a computer device, comprising a processor and a memory, wherein the processor is connected to the memory, the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory so that the computer device performs the steps of implementing the above method.

[0015] In a fourth aspect, the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program implements the steps of the above method when executed by a processor.

[0016] The present invention provides a method, system, device and medium for controlling a tap changer at a receiving end of a high-voltage direct current transmission. The method determines a tap changer gear interval according to an AC system voltage fluctuation range and a DC power operation range of a high-voltage direct current transmission project; selects an initial tap changer gear from the tap changer gear interval, and determines a corresponding minimum steady-state AC system voltage based on the initial tap changer gear; obtains a minimum valve-side ideal no-load DC voltage according to the minimum steady-state AC system voltage by using a rated transformation ratio of a converter transformer and a step size of an on-load tap changer; obtains a minimum steady-state DC voltage value at a sending end according to the minimum valve-side ideal no-load DC voltage and a minimum DC resistance under different DC transmission operation modes; obtains a maximum steady-state DC voltage value at a sending end according to a maximum AC system voltage and a maximum DC resistance under different DC transmission operation modes; and iteratively adjusts the tap changer gear based on the minimum steady-state DC voltage value at the sending end and the maximum steady DC voltage value at the sending end to obtain an optimal target gear of the tap changer that meets a preset voltage range. Compared with the existing technology, this method achieves optimized control of the tap changer gear position by iteratively adjusting the tap changer gear position at the high-voltage direct current transmission receiving end, effectively reduces the number of tap changer actions, ensures stable operation of the DC system under voltage fluctuations and power changes, and improves the stability and reliability of the transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of a method for controlling a high-voltage direct current transmission receiving-end tap changer provided by an embodiment of the present invention; Figure 2 It is a block diagram of a high-voltage direct current transmission receiving-end tap changer control system provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the structure of a computer device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0019] refer to Figure 1 The embodiment of the present invention provides a method for controlling a high-voltage direct current transmission receiving-end tap changer, such as Figure 1 As shown, the method comprises the following steps: S1. Determine the tap changer position range based on the AC system voltage fluctuation range and DC power operation range of the high voltage DC transmission project.

[0020] According to the actual situation of the high-voltage direct current transmission project, this embodiment determines the upper and lower limits of the DC voltage tap switch by comprehensively considering the daily fluctuation of the AC system voltage and the actual operation requirements of the DC power, and obtains the tap switch gear range, so as to ensure that the set upper and lower limits of the tap switch can not only meet the stability requirements of the system operation, but also minimize unnecessary tap switch actions, and ensure that the tap switch remains in a non-action state within the upper and lower limits of the DC voltage dead zone. At the same time, when the current reaches a preset fixed value, the exit mechanism of the tap switch is directly triggered, thereby reducing the number of actions of the converter transformer tap switch, thereby extending its service life, and effectively improving the operation efficiency and reliability of the converter station.

[0021] S2. Selecting an initial tap changer gear from the tap changer gear range, and determining a corresponding minimum steady-state AC system voltage based on the initial tap changer gear.

[0022] Specifically, after determining the tap switch gear range, the present embodiment needs to select an initial tap switch gear according to the actual operation and demand of the power system. For example, the present embodiment may select the lowest tap switch gear from the tap switch gear range, or may select the middle value of the tap switch gear range or determine the tap switch gear that is more commonly used under normal operation according to historical data as the initial gear. For example, the present embodiment analyzes the operation data of the past year and finds that the system operates at the tap switch gear position of 2.0 most of the time, so 2.0 is selected as the initial tap switch gear, and then the corresponding minimum steady-state AC system voltage is calculated according to the rated voltage and load conditions of the power system, while ensuring that the selected initial tap switch gear and the corresponding minimum steady-state AC system voltage can meet the actual operation requirements of the power system, thereby ensuring the safe and stable operation of the system.

[0023] S3. According to the minimum steady-state AC system voltage, the minimum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer.

[0024] In some embodiments, the step of calculating the minimum valve-side ideal no-load DC voltage based on the minimum steady-state AC system voltage using the rated transformation ratio of the converter transformer and the on-load tap changer step size comprises: Determine the rated transformation ratio of the converter transformer according to the ratio of the actual AC voltage effective value on the AC system grid side to the actual AC voltage effective value on the AC system valve side; Based on the on-load tap changer step length and the initial tap changer gear position, a tap changer adjustment proportional coefficient is calculated; The converter transformer valve side voltage conversion coefficient is calculated according to the tap changer adjustment proportional coefficient and the converter transformer rated transformation ratio; A three-phase rectification conversion coefficient is introduced, and the lowest valve-side ideal no-load DC voltage is calculated by the lowest steady-state AC system voltage and the converter transformer valve-side voltage conversion coefficient.

[0025] Specifically, in this embodiment, the actual AC voltage effective value on the grid side of the AC system can be measured by a voltage transformer in the power system. The actual AC voltage RMS value on the valve side of the AC system , divide the measured grid-side voltage RMS by the valve-side voltage RMS to get the rated transformation ratio of the converter transformer, and then determine the on-load tap changer step length The on-load tap changer step length is a fixed parameter when designing the converter transformer, which is usually provided by the manufacturer. It indicates the change in transformer ratio when the tap changer is adjusted by one gear. The adjustment proportional coefficient of the tap changer is calculated according to the on-load tap changer step length and the initial tap changer gear. The tap changer adjustment proportional coefficient reflects the voltage adjustment capability of the tap changer at different gears. The calculated tap changer adjustment proportional coefficient is multiplied by the rated transformation ratio of the converter transformer to obtain the conversion coefficient of the valve-side voltage of the converter transformer. The valve-side voltage conversion coefficient of the converter transformer is used to convert the grid-side voltage to the valve-side voltage for subsequent calculation and analysis. Finally, this embodiment introduces a three-phase rectification conversion coefficient. According to the minimum steady-state AC system voltage, the valve-side voltage conversion coefficient of the converter transformer and the three-phase rectification conversion coefficient, the minimum ideal no-load DC voltage on the valve side is calculated. This voltage value is the voltage value of the DC system under the ideal operating state under specific conditions, which is of great significance to the stable operation of the power system. In this embodiment, the mathematical expression of the minimum ideal no-load DC voltage on the valve side is: In the formula, It is the lowest ideal no-load DC voltage on the valve side; is the minimum steady-state AC system voltage; TC is the initial tap changer position; is the on-load tapchanger step length; is the rated transformation ratio of the converter transformer, ; is the three-phase rectification conversion coefficient; where, Adjust the proportionality factor for the tap changer; is the conversion factor of the valve side voltage of the converter transformer.

[0026] S4. Under different DC transmission operation modes, the minimum steady-state DC voltage value at the sending end is calculated based on the minimum valve-side ideal no-load DC voltage and the minimum DC resistance.

[0027] In some implementations, the step of calculating the minimum steady-state DC voltage value at the sending end according to the minimum valve-side ideal no-load DC voltage and the minimum DC resistance under different DC transmission operation modes includes: The per-unit value of the commutation impedance voltage drop is calculated based on the difference between the per-unit value of the inductor voltage drop and the per-unit value of the resistor voltage drop. The commutation impedance coefficient is calculated based on the per unit value of the commutation impedance voltage drop, the rated ideal no-load DC voltage and the rated DC current; Determine the minimum DC resistance of the lowest steady-state AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the minimum DC resistance of the lowest steady-state AC system, and determining a first actual DC current value under a target DC power transmission operation mode according to the comparison result; The effective commutation voltage base value is calculated based on the product of the lowest ideal no-load DC voltage on the valve side and the cosine value of the turn-off angle, and the superposition of the forward conduction voltage drop of the converter valve; Calculate the difference between the minimum DC resistance and the commutation impedance coefficient to obtain a dynamic resistance compensation term, and multiply the first actual DC current value and the dynamic resistance compensation term to obtain a current compensation voltage drop; The minimum steady-state DC voltage value at the sending end is calculated based on the effective commutation voltage base value and the current compensation voltage drop.

[0028] Specifically, this embodiment can select different operating modes such as bipolar full voltage, monopolar full voltage and monopolar metal full voltage as the DC transmission operating mode according to the specific wiring mode. Among them, the monopolar metal operating mode belongs to a more stringent working condition in the verification of the DC voltage level. This embodiment comprehensively considers different DC transmission operating modes, divides the inductance voltage drop and the resistance voltage drop by the reference voltage respectively, obtains the per-unit value of the inductance voltage drop and the per-unit value of the resistance voltage drop, and subtracts the per-unit value of the inductance voltage drop from the per-unit value of the resistance voltage drop to obtain the per-unit value of the commutation impedance voltage drop. Combined with the known rated ideal no-load DC voltage and rated DC current, this embodiment uses the per-unit value of the commutation impedance voltage drop, the rated ideal no-load DC voltage and the rated DC current to calculate the commutation impedance coefficient. The commutation impedance coefficient reflects the comprehensive influence of the commutation impedance on the DC voltage. The mathematical expression of the commutation impedance coefficient is: In the formula, is the commutation impedance coefficient; n is the number of pulsations (12); is the standard value of the inductor voltage drop on the inverter side of the receiving end; is the unit value of the resistance voltage drop on the inverter side of the receiving end; is the rated ideal no-load DC voltage on the inverter side of the receiving end; is the rated DC current.

[0029] In different operation modes, the selection of DC resistance is also different. This embodiment selects the minimum DC resistance of the corresponding steady-state AC system according to the target DC transmission operation mode (such as unipolar operation or bipolar operation) and the characteristics of the steady-state AC system. Specifically, 2Rd is selected as the DC resistance in the unipolar metal operation mode; Rd+Re is selected in the unipolar pole operation mode, where Re is the grounding resistance of the grounding electrode; and Rd is directly selected in the bipolar pole operation mode; the larger the resistance value, the more stringent the working conditions faced when calculating the maximum operating voltage. In actual engineering projects, due to different topological structures, the resistance parameters in the DC current path will also be different. In this embodiment, the commutation impedance coefficient With minimum DC resistance The first actual DC current value is adjusted according to the comparison result, and the minimum DC resistance is Not less than the commutation impedance coefficient When the first actual DC current value is set to a lower per-unit multiple of the rated DC current; at the minimum DC resistance Less than the commutation impedance coefficient When the first actual DC current value is set to a multiple of the high per unit value of the rated DC current, for example, if ,but ,otherwise .

[0030] In other implementations, under complex working conditions, the present embodiment can obtain the actual DC current value corresponding to each power by solving a quadratic equation. In this process, the minimum DC resistance selects the DC resistance under the dual-polarity operation mode. The specific solution process of the actual DC current value is: In the formula, is the lowest steady-state DC voltage value at the sending end; n is the number of pulsations of 12; It is the lowest ideal no-load DC voltage on the valve side; is the cut-off angle; is the standard value of the inductor voltage drop on the inverter side of the receiving end; is the unit value of the resistance voltage drop on the inverter side of the receiving end; is the actual operating current; is the rated DC current; is the rated ideal no-load DC voltage on the inverter side of the receiving end; The forward conduction pressure drop of the converter valve; is the actual DC voltage on the rectifier side of the sending end; is the minimum DC resistance, which represents the DC line resistance under the current operation mode; is the DC power on the rectifier side of the sending end; the subscript R represents the rectifier side of the sending end; the subscript I represents the inverter side of the receiving end; the subscript min represents the minimum value; and the subscript max represents the maximum value.

[0031] In this embodiment, the first actual DC current value under different powers can be obtained by combining the above three formulas, which is specifically expressed as: Then, based on the lowest ideal no-load DC voltage on the valve side and the cosine value of the turn-off angle, this embodiment superimposes the forward conduction voltage drop of the converter valve to obtain the effective commutation voltage base value, calculates the difference between the minimum DC resistance and the commutation impedance coefficient, obtains the dynamic resistance compensation term, and multiplies the first actual DC current value and the dynamic resistance compensation term to obtain the current compensation voltage drop, subtracts the effective commutation voltage base value from the current compensation voltage drop, and obtains the lowest steady-state DC voltage value at the sending end. This embodiment needs to ensure that the lowest steady-state DC voltage value at the sending end is not less than the lowest ideal no-load DC voltage on the valve side to ensure system stability. The calculation formula for the lowest steady-state DC voltage value at the sending end is: in, is the commutation impedance coefficient.

[0032] This embodiment calculates the minimum DC voltage at the sending end under the condition of minimum DC resistance of the lowest steady-state AC system by comprehensively considering multiple operating modes (including bipolar full voltage, monopolar full voltage and monopolar metal full voltage, etc.).

[0033] S5. Under different DC transmission operation modes, the highest steady-state DC voltage value at the sending end is calculated based on the highest AC system voltage and the maximum DC resistance.

[0034] In some implementations, the step of calculating the maximum steady-state DC voltage value at the sending end based on the maximum AC system voltage and the maximum DC resistance under different DC transmission operation modes includes: Determining a corresponding maximum AC system voltage based on the initial tap changer position; According to the maximum AC system voltage, the maximum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; Determine the maximum DC resistance of the highest AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the maximum DC resistance of the highest AC system, and determining a second actual DC current value under the target DC power transmission operation mode according to the comparison result; The highest steady-state DC voltage value at the sending end is calculated according to the highest ideal no-load DC voltage on the valve side, the cosine value of the shut-off angle and the second actual DC current value.

[0035] Specifically, in this embodiment, according to the highest AC system voltage, the highest valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer. The calculation formula of the highest valve-side ideal no-load DC voltage is: In the formula, It is the ideal no-load DC voltage on the highest valve side; is the highest AC system voltage; TC is the initial tap changer position; is the on-load tapchanger step length; is the rated transformation ratio of the converter transformer, ; is the three-phase rectification conversion coefficient.

[0036] Then, this embodiment determines the maximum DC resistance of the highest AC system under the target DC transmission operation mode according to the target DC transmission operation mode (such as unipolar operation or bipolar operation) and the characteristics of the steady-state AC system. For the sake of convenience, this embodiment sets the maximum DC resistance to , the commutation impedance coefficient With maximum DC resistance The comparison is performed, and a second actual DC current value is obtained according to the comparison result. Not less than the commutation impedance coefficient When the second actual DC current value is set to a high per-unit multiple of the rated DC current; Less than the commutation impedance coefficient When the second actual DC current value is set to the lower per unit value multiple of the rated DC current, for example, if ,but ,otherwise .

[0037] In other implementations, under complex working conditions, the present embodiment can obtain the actual DC current value corresponding to each power by solving a quadratic equation. The specific solution process of the actual DC current value is: In the formula, is the highest steady-state DC voltage value at the sending end; n is the number of pulsations of 12; It is the ideal no-load DC voltage on the highest valve side; is the cut-off angle; is the standard value of the inductor voltage drop on the inverter side of the receiving end; is the unit value of the resistance voltage drop on the inverter side of the receiving end; is the second actual DC current value; is the rated DC current; is the rated ideal no-load DC voltage on the inverter side of the receiving end; The forward conduction pressure drop of the converter valve; is the actual DC voltage on the rectifier side of the sending end; is the minimum DC resistance, which represents the DC line resistance under the current operation mode; is the DC power on the rectifier side of the sending end; the subscript R represents the rectifier side of the sending end; the subscript I represents the inverter side of the receiving end; the subscript min represents the minimum value; and the subscript max represents the maximum value.

[0038] In this embodiment, the above three formulas are combined to obtain the second actual DC current value under different powers, which is specifically expressed as: Then, based on the lowest ideal no-load DC voltage on the valve side and the cosine value of the turn-off angle, this embodiment superimposes the forward conduction voltage drop of the converter valve to obtain the effective commutation voltage base value, calculates the difference between the minimum DC resistance and the commutation impedance coefficient, obtains the dynamic resistance compensation term, and multiplies the first actual DC current value and the dynamic resistance compensation term to obtain the current compensation voltage drop, subtracts the effective commutation voltage base value from the current compensation voltage drop, and obtains the lowest steady-state DC voltage value at the sending end. This embodiment needs to ensure that the lowest steady-state DC voltage value at the sending end is not less than the lowest ideal no-load DC voltage on the valve side to ensure system stability. The calculation formula for the lowest steady-state DC voltage value at the sending end is: This embodiment calculates the highest steady-state DC voltage value at the sending end under the conditions of the highest AC system voltage and the maximum DC resistance by comprehensively considering multiple operating modes (including bipolar full voltage, monopolar full voltage and monopolar metal full voltage, etc.).

[0039] S6. Iteratively adjust the tap changer gear position based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain an optimal target gear position of the tap changer that meets a preset voltage range.

[0040] In some embodiments, the step of iteratively adjusting the tap switch gear position based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain the tap switch optimal target gear position that meets the preset voltage range includes: Comparing the lowest steady-state DC voltage value at the sending end with a preset minimum DC voltage threshold, if the lowest steady-state DC voltage value at the sending end is less than the minimum DC voltage threshold, adjusting the current tap changer gear to a higher gear with the on-load tap changer step size; If the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold, then comparing the highest steady-state DC voltage value at the sending end with a preset maximum DC voltage threshold; If the highest steady-state DC voltage value at the sending end is greater than the maximum DC voltage threshold, the current tap changer gear is iteratively adjusted to a low gear with the on-load tap changer step size until a tap changer gear that satisfies the conditions that the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold and the highest steady-state DC voltage value at the sending end is not greater than the maximum DC voltage threshold is found, and the optimal target gear of the tap changer is output.

[0041] Specifically, in this embodiment, the lowest steady-state DC voltage value at the sending end is compared with a preset minimum DC voltage threshold. If the lowest steady-state DC voltage value at the sending end is less than the minimum DC voltage threshold, it indicates that the DC voltage at the current gear is too low and the voltage level needs to be increased. At this time, the current tap changer gear TC is adjusted to a higher gear with the on-load tap changer step size, that is, If the lowest steady-state DC voltage value at the sending end is greater than or equal to the minimum DC voltage threshold, the next step is entered to compare the highest steady-state DC voltage value at the sending end. It should be noted that when adjusting the gear position of the tap changer, the present embodiment may consider the lowest gear in the gear range that does not consider the step-down operation mode. However, according to actual conditions, the present embodiment may also flexibly select the second lowest gear or the second lowest gear as the gear position of the tap changer.

[0042] In this embodiment, the maximum steady-state DC voltage value of the sending end is compared with the preset maximum DC voltage threshold. If the maximum steady-state DC voltage value of the sending end is greater than the maximum DC voltage threshold, it indicates that the DC voltage is too high at the current gear and the voltage level needs to be reduced. At this time, the current tap changer gear TC is adjusted to a low gear with the on-load tap changer step size, that is, , if the highest steady-state DC voltage value at the sending end is less than or equal to the maximum DC voltage threshold, the current gear position meets the preset voltage range and no further adjustment is required. After each gear position adjustment, the lowest and highest steady-state DC voltage values ​​at the sending end need to be recalculated, and the above-mentioned comparison and adjustment logic is repeated until the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold, and the highest steady-state DC voltage value at the sending end is not greater than the maximum DC voltage threshold. The optimal target gear position of the tap changer that meets the preset voltage range is output. During the adjustment process, this embodiment needs to ensure that the adjustment range of the tap changer gear position does not exceed the maximum gear position limit of the engineering design (such as plus or minus 31 gears). If the adjusted gear position exceeds If the DC voltage reaches the rated value, the closest allowable gear is taken as the final result. The optimal target gear of the tap changer should ensure that the DC voltage operates stably within the preset range. It should be noted that for existing projects, when the DC current reaches the rated value, this embodiment should limit its further increase; while for new projects, a certain current margin can be reserved during design so that the current can be further increased when needed. In order to achieve DC operation within the full power range, this embodiment can flexibly adjust the dead zone range value of the DC voltage to adapt to different operating requirements. Through the above steps, this embodiment realizes iterative adjustment and optimization of the tap changer gear, ensuring the voltage stability and reliability of the DC power transmission system under different operating modes.

[0043] For the sake of convenience, this embodiment takes the Shanghai Temple-Shandong DC project as an example to illustrate the specific implementation process of iterative adjustment of the tap changer position: This embodiment assumes that the DC voltage of the Shanghai Temple-Shandong DC project is ±800kV, the maximum DC voltage does not exceed 816kV, the maximum DC voltage controlled by the tap changer is limited to 808kV, the AC system voltage fluctuation range is 500kV to 550kV, the DC resistance varies between 2.896Ω and 3.777Ω, and the rated DC resistance is 3.512Ω. In addition, the DC power of the project is as high as 8000MW, and the DC rated current is 6.25kA. Regarding the design range of the tap changer gear, the converter gear of the Shanghai Temple converter station is +24 / -6, while the high-end converter gear of the Shandong station is +2 5 / -5, the low-end converter gear is +21 / -9. Here, this embodiment takes Shandong high-end converter as an example. Without considering the step-down operation mode, the initial gear of Linyi high-end converter is set to +5 gear, and its rated converter ratio nnom is 3.138. Next, this embodiment calculates the two gears of TC=5 and TC=10 respectively. When TC=5, this embodiment selects 5 gears to calculate the minimum DC voltage without considering the step-down operation mode. Taking into account the maximum DC resistance and the minimum AC system voltage (500kV), it is assumed that the DC resistance under the dual-polar operation mode is is 2.896Ω. In this embodiment, the minimum DC voltage on the rectifier side is calculated to be 202.54kV. When the DC current is 1.0pu, the corresponding minimum DC voltage It is 724.79kV.

[0044] Similarly, without considering the step-down operation mode, this embodiment selects 5 gears to calculate the highest DC voltage, taking into account the DC resistance under the unipolar metal operation mode. =2*2.896Ω. This embodiment calculates the maximum DC voltage when the DC current is 0.1pu. It is 844.67 kV, which exceeds the limit of 808 kV. Therefore, the dead band range of DC voltage is determined to be [724.79, 844.67] kV.

[0045] When TC=10, this embodiment also selects 10 gears to calculate the minimum DC voltage without considering the step-down operation mode, taking into account the maximum DC resistance, the minimum AC system voltage (500kV) and the DC resistance under the dual-polar operation mode. , this embodiment calculates the minimum DC voltage corresponding to the minimum DC voltage on the rectifier side is 663.50 kV. Similarly, without considering the step-down operation mode, this embodiment selects 10 gears to calculate the maximum DC voltage. Considering the DC resistance Rd under the unipolar metal operation mode, this embodiment calculates the maximum DC voltage when the DC current is 0.1 pu. It is 802.13 kV, which meets the upper limit of 808 kV. If the current gear still cannot meet the requirement, this embodiment can further adopt +11 gear and repeat the above iterative calculation process until a suitable gear is found that meets the DC voltage upper limit of less than 808 kV.

[0046] This embodiment is based on a DC engineering project that is actually in operation. A closed-loop simulation joint debugging test of a DC control and protection device is performed using a high-voltage engineering RTDS (real-time digital simulation) test platform. In this test, this embodiment uses a DC control and protection system that is consistent with the DC field equipment model and has the same program core functions but with simplified redundant configuration and interfaces to verify the test effect of the project. One of the core purposes of the test is to verify the number of tap changer operations. To this end, this embodiment compares the theoretical calculation results with the joint debugging test results. The specific data is shown in Table 1: Table 1 By comparison, it can be found that after adopting this strategy in this embodiment, the tap switch of Zhongzhou Station did not operate at any power level, which fully proves the effectiveness of this strategy in significantly reducing the number of tap switch operations. Through the above steps, this embodiment effectively reduces the number of tap switch operations through iterative adjustment and optimization of the tap switch gear, greatly reduces the risk of tap switch failure, thereby ensuring the stable operation of the converter station and the voltage stability and reliability of the DC power transmission system under different operating modes. At the same time, the control method proposed in this embodiment can accurately set the lower limit of the DC voltage dead zone according to the fluctuation of the AC system voltage, the variation range of the DC power, and the goal of reducing the number of tap switch operations. This design significantly reduces the operation frequency of the receiving end tap switch, further improves the stability and efficiency of the system, and when the DC current reaches the rated value, the control method of this embodiment can automatically trigger the exit mechanism. This function not only ensures the stable operation of the system under rated conditions, but also effectively avoids the potential risks that may be caused by unnecessary tap switch operations, thereby achieving effective control of the number of tap switch operations and improving the operation reliability and overall performance of the converter station.

[0047] An embodiment of the present invention provides a method for controlling a tap changer at a receiving end of a high-voltage direct current transmission. The method comprises determining a tap changer gear interval according to an AC system voltage fluctuation range and a DC power operation range of a high-voltage direct current transmission project; selecting an initial tap changer gear from the tap changer gear interval, and determining a corresponding minimum steady-state AC system voltage based on the initial tap changer gear; calculating a minimum valve-side ideal no-load DC voltage according to the minimum steady-state AC system voltage using a rated transformation ratio of a converter transformer and a step size of an on-load tap changer; calculating a minimum steady-state DC voltage value at a sending end according to the minimum valve-side ideal no-load DC voltage and a minimum DC resistance under different DC transmission operation modes; calculating a maximum steady-state DC voltage value at a sending end according to a maximum AC system voltage and a maximum DC resistance under different DC transmission operation modes; and iteratively adjusting the tap changer gear based on the minimum steady-state DC voltage value at the sending end and the maximum steady-state DC voltage value at the sending end to obtain an optimal target gear of the tap changer that meets a preset voltage range. Compared with the existing technology, this method achieves optimized control of the tap changer gear position by iteratively adjusting the tap changer gear position at the high-voltage direct current transmission receiving end, effectively reduces the number of tap changer actions, ensures stable operation of the DC system under voltage fluctuations and power changes, and improves the stability and reliability of the transmission system.

[0048] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0049] In one embodiment, Figure 2 As shown, an embodiment of the present invention provides a high-voltage direct current transmission receiving-end tap switch control system, the system comprising: The switch gear determination module 101 is used to determine the tap switch gear range according to the AC system voltage fluctuation range and DC power operation range of the high-voltage DC power transmission project; An initial voltage determination module 102, configured to select an initial tap switch gear from the tap switch gear interval, and determine a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; The no-load voltage analysis module 103 is used to calculate the lowest ideal no-load DC voltage on the valve side according to the lowest steady-state AC system voltage by using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; The minimum voltage analysis module 104 is used to calculate the minimum steady-state DC voltage value of the sending end according to the minimum ideal no-load DC voltage on the valve side and the minimum DC resistance under different DC transmission operation modes; The maximum voltage analysis module 105 is used to calculate the maximum steady-state DC voltage value at the sending end based on the maximum AC system voltage and the maximum DC resistance under different DC transmission operation modes; The optimal gear position determination module 106 is used to iteratively adjust the tap switch gear position based on the sending end minimum steady-state DC voltage value and the sending end maximum steady-state DC voltage value to obtain the tap switch optimal target gear position that meets a preset maximum DC voltage threshold.

[0050] For the specific definition of a high-voltage direct current transmission receiving-end tap changer control system, please refer to the above-mentioned definition of a high-voltage direct current transmission receiving-end tap changer control method, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0051] The embodiment of the present invention provides a high-voltage direct current transmission receiving-end tap switch control system, wherein a switch gear determination module of the system determines a tap switch gear interval according to an AC system voltage fluctuation range and a DC power operation range of a high-voltage direct current transmission project; a voltage initial determination module selects an initial tap switch gear from the tap switch gear interval, and determines a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; a no-load voltage analysis module calculates a minimum valve-side ideal no-load DC voltage according to the minimum steady-state AC system voltage using a converter transformer rated transformation ratio and an on-load tap switch step size; a minimum voltage analysis module calculates a minimum steady-state DC voltage value of a sending end according to a minimum valve-side ideal no-load DC voltage and a minimum DC resistance under different DC transmission operation modes; a maximum voltage analysis module calculates a maximum steady-state DC voltage value of a sending end according to a maximum AC system voltage and a maximum DC resistance under different DC transmission operation modes; an optimal gear determination module iteratively adjusts the tap switch gear based on the minimum steady-state DC voltage value of the sending end and the maximum steady-state DC voltage value of the sending end to obtain an optimal target gear of the tap switch that meets a preset voltage range. Compared with the existing technology, this system achieves optimized control of the tap changer gear position by iteratively adjusting the tap changer gear position at the high-voltage DC transmission receiving end, effectively reducing the number of tap changer operations, ensuring the stable operation of the DC system under voltage fluctuations and power changes, and improving the stability and reliability of the transmission system.

[0052] Figure 3 A computer device provided by an embodiment of the present invention includes a memory, a processor and a transceiver, which are connected via a bus; the memory is used to store a set of computer program instructions and data, and can transmit the stored data to the processor, and the processor can execute the program instructions stored in the memory to perform the steps of the above method.

[0053] The memory may include a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories; the processor may be a central processing unit, a microprocessor, an application-specific integrated circuit, a programmable logic device, or a combination thereof. By way of example but not limitation, the programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic, or any combination thereof.

[0054] Additionally, the memory may be a physically separate unit or may be integrated with the processor.

[0055] It can be understood by those skilled in the art that Figure 3 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have the same component arrangement.

[0056] In one embodiment, the present invention provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are implemented.

[0057] The embodiments of the present invention provide a method, system, device and medium for controlling a high-voltage direct current transmission receiving-end tap switch. The method for controlling a high-voltage direct current transmission receiving-end tap switch achieves optimized control of the tap switch gear position by iteratively adjusting the tap switch gear position of the high-voltage direct current transmission receiving-end, thereby effectively reducing the number of tap switch actions, ensuring stable operation of the DC system under voltage fluctuations and power changes, and improving the stability and reliability of the transmission system.

[0058] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) mode. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., an SSD), etc.

[0059] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing related hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods.

[0060] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A method for controlling a high voltage direct current transmission receiving end tap changer, characterized in that: The following steps are involved: Determine the tap changer position range according to the voltage fluctuation range of the AC system and the DC power operation range of the high-voltage DC transmission project; Selecting an initial tap switch gear from the tap switch gear range, and determining a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; According to the minimum steady-state AC system voltage, the minimum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; Under different DC transmission operation modes, the lowest steady-state DC voltage value at the sending end is calculated based on the lowest ideal no-load DC voltage at the valve side and the minimum DC resistance; Under different DC transmission operation modes, the highest steady-state DC voltage value at the sending end is calculated based on the highest AC system voltage and the maximum DC resistance; The tap changer gear position is iteratively adjusted based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain an optimal target gear position of the tap changer that meets a preset voltage range.

2. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 1, characterized in that: The step of calculating the lowest valve-side ideal no-load DC voltage based on the lowest steady-state AC system voltage by using the rated transformation ratio of the converter transformer and the step length of the on-load tap changer comprises: Determine the rated transformation ratio of the converter transformer according to the ratio of the actual AC voltage effective value on the AC system grid side to the actual AC voltage effective value on the AC system valve side; Based on the on-load tap changer step length and the initial tap changer gear position, a tap changer adjustment proportional coefficient is calculated; The converter transformer valve side voltage conversion coefficient is calculated according to the tap changer adjustment proportional coefficient and the converter transformer rated transformation ratio; A three-phase rectification conversion coefficient is introduced, and the lowest valve-side ideal no-load DC voltage is calculated by the lowest steady-state AC system voltage and the converter transformer valve-side voltage conversion coefficient.

3. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 1, characterized in that: The step of calculating the minimum steady-state DC voltage value at the sending end according to the minimum ideal no-load DC voltage at the valve side and the minimum DC resistance under different DC transmission operation modes comprises: The per-unit value of the commutation impedance voltage drop is calculated based on the difference between the per-unit value of the inductor voltage drop and the per-unit value of the resistor voltage drop. The commutation impedance coefficient is calculated based on the per unit value of the commutation impedance voltage drop, the rated ideal no-load DC voltage and the rated DC current; Determine the minimum DC resistance of the lowest steady-state AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the minimum DC resistance of the lowest steady-state AC system, and determining a first actual DC current value under a target DC power transmission operation mode according to the comparison result; The effective commutation voltage base value is calculated based on the product of the lowest ideal no-load DC voltage on the valve side and the cosine value of the turn-off angle, and the superposition of the forward conduction voltage drop of the converter valve; Calculate the difference between the minimum DC resistance and the commutation impedance coefficient to obtain a dynamic resistance compensation term, and multiply the first actual DC current value and the dynamic resistance compensation term to obtain a current compensation voltage drop; The minimum steady-state DC voltage value at the sending end is calculated based on the effective commutation voltage base value and the current compensation voltage drop.

4. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 3, characterized in that: The step of determining the first actual DC current value under the target DC power transmission operation mode according to the comparison result comprises: When the minimum DC resistance is not less than the commutation impedance coefficient, setting the first actual DC current value to a low per-unit multiple of the rated DC current; When the minimum DC resistance is less than the commutation impedance coefficient, the first actual DC current value is set to a high per-unit multiple of the rated DC current.

5. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 3, characterized in that: The step of calculating the maximum steady-state DC voltage value at the sending end based on the maximum AC system voltage and the maximum DC resistance under different DC transmission operation modes comprises: Determining a corresponding maximum AC system voltage based on the initial tap changer gear position; According to the maximum AC system voltage, the maximum valve-side ideal no-load DC voltage is calculated using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; Determine the maximum DC resistance of the highest AC system under the target DC transmission operation mode; Comparing the commutation impedance coefficient with the maximum DC resistance of the highest AC system, and determining a second actual DC current value under the target DC power transmission operation mode according to the comparison result; The highest steady-state DC voltage value at the sending end is calculated according to the highest ideal no-load DC voltage on the valve side, the cosine value of the shut-off angle and the second actual DC current value.

6. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 5, characterized in that: The step of determining the second actual DC current value under the target DC power transmission operation mode according to the comparison result comprises: When the maximum DC resistance is not less than the commutation impedance coefficient, setting the second actual DC current value to a high per-unit multiple of the rated DC current; When the maximum DC resistance is less than the commutation impedance coefficient, the second actual DC current value is set to a low per-unit multiple of the rated DC current.

7. A method for controlling a high-voltage direct current transmission receiving-end tap changer according to claim 1, characterized in that: The step of iteratively adjusting the tap switch gear position based on the sending-end minimum steady-state DC voltage value and the sending-end maximum steady-state DC voltage value to obtain the tap switch optimal target gear position that meets the preset voltage range includes: Comparing the lowest steady-state DC voltage value at the sending end with a preset minimum DC voltage threshold, if the lowest steady-state DC voltage value at the sending end is less than the minimum DC voltage threshold, adjusting the current tap changer gear to a higher gear with the on-load tap changer step size; If the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold, then comparing the highest steady-state DC voltage value at the sending end with a preset maximum DC voltage threshold; If the highest steady-state DC voltage value at the sending end is greater than the maximum DC voltage threshold, the current tap changer gear is iteratively adjusted to a low gear with the on-load tap changer step size until a tap changer gear that satisfies the conditions that the lowest steady-state DC voltage value at the sending end is greater than the minimum DC voltage threshold and the highest steady-state DC voltage value at the sending end is not greater than the maximum DC voltage threshold is found, and the optimal target gear of the tap changer is output.

8. A high-voltage direct current transmission receiving-end tap changer control system, characterized in that: The system comprises: The switch position determination module is used to determine the tap switch position interval according to the voltage fluctuation range of the AC system and the DC power operation range of the high-voltage DC transmission project; an initial voltage determination module, configured to select an initial tap switch gear from the tap switch gear interval, and determine a corresponding minimum steady-state AC system voltage based on the initial tap switch gear; A no-load voltage analysis module, used to calculate the lowest ideal no-load DC voltage on the valve side according to the lowest steady-state AC system voltage using the rated transformation ratio of the converter transformer and the step size of the on-load tap changer; The minimum voltage analysis module is used to calculate the minimum steady-state DC voltage value at the sending end according to the minimum ideal no-load DC voltage and minimum DC resistance on the valve side under different DC transmission operation modes; The maximum voltage analysis module is used to calculate the maximum steady-state DC voltage value at the sending end based on the maximum AC system voltage and the maximum DC resistance under different DC transmission operation modes; The optimal gear position determination module is used to iteratively adjust the tap switch gear position based on the lowest steady-state DC voltage value at the sending end and the highest steady-state DC voltage value at the sending end to obtain the optimal target gear position of the tap switch that meets the preset maximum DC voltage threshold.

9. A computer device, characterized in that: The computer device comprises a processor and a memory, wherein the processor is connected to the memory, the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the computer device executes the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed, the method according to any one of claims 1 to 7 is implemented.

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