A reactive power coordination control method and device for a VSC / LCC DC parallel hybrid system considering AC filter set life balance

Abstract

A reactive power coordination control method and device for a VSC / LCC DC parallel hybrid system considering the lifetime balancing of AC filter banks. This method monitors the lifetime loss parameters of each AC filter bank; when the reactive power of the LCC exceeds its limit, the VSC prioritizes reactive power adjustment; if the VSC reaches its limit and continues to exceed it after a timeout, switching is triggered; based on the lifetime loss parameters, the filter with the lowest loss in the off-state is selected for switching, and the filter with the highest loss in the on-state is selected for switching; the logic exits after lifetime balancing. This invention, based on VSC-prioritized reactive power adjustment to significantly reduce the total number of LCC AC filter switching operations, replaces the mechanical "first-on, first-off" sequential switching with a priority decision mechanism based on real-time lifetime loss parameters, using the minimum / maximum lifetime loss as the switching criterion. This ensures that each switching moves towards lifetime balancing, effectively solving the overwork problem of specific filter banks under conditions of small power fluctuations and long-term stable operation, and reducing the total lifecycle maintenance cost.

Description

Technical Field

[0001] This invention relates to the field of reactive power control technology for high-voltage direct current transmission systems, specifically a reactive power coordination control method and device for a VSC / LCC DC parallel hybrid system that takes into account the lifespan balancing of AC filter banks. Background Technology

[0002] High-voltage direct current (HVDC) transmission technology has been widely applied in my country, with its two main technical routes—conventional direct current (LCC DC) and flexible direct current (VSC DC)—both having been extensively implemented in engineering projects. As the number of DC transmission points becomes increasingly dense, a "hybrid multi-infeed" pattern has emerged, where multiple VSC DC and LCC DC lines terminate on the same AC grid and are very close in electrical distance. Notably, after the ±420kV Chongqing-Hubei back-to-back interconnection project was put into operation, a typical VSC / LCC DC parallel hybrid system structure was formed in Longquan, Hubei Province, where the VSC DC converter station and the LCC DC converter station form a strong electrical coupling through an AC bus.

[0003] In this strongly coupled DC-DC parallel hybrid system, LCC DC converter stations are typically equipped with multiple AC filter banks of the same rated capacity (hereinafter collectively referred to as "AC filter banks") to compensate for the large amount of reactive power consumed by the LCC DC converter itself during operation and to filter out characteristic harmonics. The switching of the AC filter banks is determined by the reactive power control function of the LCC DC itself based on the electrical quantity of "reactive power exchanged between the LCC DC converter station and the AC system" to maintain local reactive power balance. A "first-in, first-out" sequential switching logic is often used to achieve a rough balance in the number of switching operations for each filter bank.

[0004] Because the VSC DC and LCC DC converter stations are electrically close, the VSC can independently and quickly perform reactive power regulation. Changes in its reactive power output significantly affect the reactive power distribution at the parallel connection points, thus impacting the reactive power exchanged between the LCC DC and AC systems. This is the physical basis for the VSC DC to provide reactive power coordination for the LCC DC in this system.

[0005] Existing technologies propose a two-stage coordinated control approach: VSC DC priority followed by LCC DC filter switching. This effectively reduces the total number of switching operations, but it neglects the balanced distribution of remaining switching tasks among groups. Furthermore, the commonly used "first-in, first-out" sequential switching method in engineering suffers from severe imbalance blind spots under the following common operating conditions:

[0006] LCC DC power fluctuates within a small range: the change in reactive power demand is only enough to trigger repeated switching of a single filter group, causing the switching logic to stall, resulting in the frequent use of a specific group.

[0007] When the LCC DC system remains at a stable power level for an extended period, the "first-in, first-out" switching mechanism of the DC system is completely halted. If fluctuations necessitate switching, the existing sequence will be followed directly, potentially exacerbating the existing imbalance.

[0008] Furthermore, the "first-in, first-out" system is a mechanical, time-based static rotation that cannot detect or correct uneven actual lifespan losses caused by maintenance withdrawals, differences in electrical stress, etc.

[0009] In summary, to address the aforementioned issues, this invention proposes "lifetime balancing of all AC filter banks in the LCC DC system" as the control objective. The core innovation lies in this: when the LCC DC system needs to switch on or off a group of AC filters, for multiple filter banks of the same model that meet the conditions, the mechanical "first-on, first-off" sequence is no longer followed. Instead, priority decisions are made based on the real-time "lifetime loss parameters" of each group, fundamentally ensuring that each switching operation moves towards lifetime balancing. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a reactive power coordination control method and device for a VSC / LCC DC parallel hybrid system that takes into account the life balance of AC filter banks. In a VSC / LCC DC parallel hybrid strongly coupled system, how to overcome the inherent limitations of the "first to switch" mechanical rotation logic under actual operating conditions while significantly reducing the total number of switching of LCC DC AC filters, and achieve fine balance of life loss of each group of LCC DC AC filters.

[0011] A reactive power coordination control method for a VSC / LCC DC parallel hybrid system considering AC filter bank lifetime balancing, wherein the VSC / LCC DC parallel hybrid system includes a VSC DC converter station and an LCC DC converter station, the AC sides of the VSC DC converter station and the LCC DC converter station are connected in parallel with close electrical distance through an AC power grid, and the AC bus side of the LCC DC converter station is equipped with multiple AC filter banks of the same rated capacity, the method comprising:

[0012] The lifespan parameter monitoring step involves online monitoring and calculation of the lifespan loss parameters of each group of AC filter banks. The lifespan loss parameters are determined based on at least one of the cumulative number of switching operations and the cumulative energized operating time of each group of AC filter banks.

[0013] The VSC priority reactive power regulation step is as follows: when the reactive power exchanged between the LCC DC converter station and the AC system exceeds the preset reactive power coordination control dead zone, the VSC DC converter station will prioritize regulating the reactive power output to smooth out the reactive power fluctuations of the LCC DC converter station.

[0014] In the switching trigger determination step, when the reactive power output of the VSC DC converter station reaches the preset adjustable capacity upper or lower limit and the duration exceeds the preset delay threshold, and the switching reactive power still exceeds the reactive power control dead zone of the LCC AC filter, it is determined that a set of AC filter groups needs to be put into or cut off.

[0015] The target filter bank selection step involves determining the target AC filter bank from the current AC filter banks of the same model that simultaneously meet the switching criteria, based on the lifetime loss parameters of each AC filter bank: when it needs to be put into operation, the group with the smallest lifetime loss parameter is selected from the current disconnected group of the same model as the target input group; when it needs to be disconnected, the group with the largest lifetime loss parameter is selected from the current input group of the same model as the target disconnected group.

[0016] The switching execution step involves sending the switching command of the target AC filter bank to the LCC DC reactive power control system to execute the switching operation.

[0017] In the equalization exit step, when the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, the control logic of the target filter bank selection step and the switching execution step is exited, and the default sequential switching logic is restored.

[0018] Furthermore, in the lifetime parameter monitoring step, the lifetime loss parameter L i Calculate using the following formula:

[0019] ;

[0020] In the formula, N i T represents the cumulative switching count of the i-th AC filter bank. i Let w1 be the cumulative energized operating time of the i-th AC filter bank, w2 be the preset weighting coefficients that satisfy w1+w2=1, and n be the total number of AC filter banks.

[0021] Furthermore, the parallel connection method between the VSC DC converter station and the LCC DC converter station is any one of the following:

[0022] The sending or receiving end of the VSC DC converter station is connected to the same AC bus as the rectifier station or inverter station of the LCC DC converter station.

[0023] Alternatively, the VSC DC converter station and the LCC DC converter station may be electrically connected via a short-distance AC tie line, the length of which allows the electrical distance between the two converter stations to influence each other through reactive power regulation.

[0024] Furthermore, the VSC priority reactive power regulation step and the switching trigger determination step constitute the first level control and the second level control, and the target filter bank selection step and the switching execution step constitute the third level control; wherein, in the first level control, the reactive power regulation response time of the VSC DC converter station is less than the switching response time of the LCC DC AC filter bank; the preset delay threshold value of the second level control is in the range of 400ms to 600ms, which is greater than the action cycle of the LCC DC AC filter bank switching operation.

[0025] Furthermore, the VSC DC converter station achieves decoupled control of active and reactive power through dual closed-loop current vector control, including an outer loop power controller and an inner loop current controller; the outer loop power controller adopts a constant reactive power control mode or a constant AC voltage control mode.

[0026] Furthermore, the control signal transmission delay for the electrical distance between the VSC DC converter station and the LCC DC converter station is less than a preset value; the AC filter bank configured on the AC bus side of the LCC DC converter station adopts a default sequential switching logic of "first to switch, last to switch".

[0027] Furthermore, it also includes a safety interlocking step: when a transient fault is detected in the VSC DC or LCC DC, the control logic of the target filter bank selection step and the switching execution step is interlocked, and the LCC DC default sequence rotation logic is switched.

[0028] A reactive power coordination control device for a VSC / LCC DC parallel hybrid system considering AC filter bank lifetime balancing, the system including a VSC DC converter station and an LCC DC converter station, the AC sides of which are connected in parallel via an AC power grid and are electrically close to each other, the LCC DC converter station being equipped with multiple sets of AC filter banks with the same rated capacity on its AC bus side, the device comprising:

[0029] The lifetime parameter monitoring module is used to monitor and calculate the lifetime loss parameters of each group of AC filter banks online. The lifetime loss parameters are determined based on at least one of the cumulative number of switching operations and the cumulative energized operating time.

[0030] The VSC priority reactive power regulation module is used to prioritize controlling the VSC DC converter station to adjust the reactive power output when the reactive power exchanged between the LCC DC converter station and the AC system exceeds the preset reactive power coordination control dead zone, so as to smooth the reactive power fluctuation of the LCC DC converter station.

[0031] The switching trigger determination module is used to determine whether to switch on or off a group of AC filters when the reactive power output of the VSC DC converter station reaches the upper or lower limit of the preset adjustable capacity and the duration exceeds the preset delay threshold, and the switching reactive power still exceeds the reactive power control dead zone of the LCC AC filter.

[0032] The target filter bank selection module is used to determine the target AC filter bank from the AC filter banks of the same model that simultaneously meet the switching criteria based on the lifetime loss parameters of each AC filter bank: when it needs to be put into operation, the group with the smallest lifetime loss parameter is selected from the group of the same model that is currently in the off state as the target input group; when it needs to be cut off, the group with the largest lifetime loss parameter is selected from the group of the same model that is currently in the input state as the target cut-off group.

[0033] The switching execution module is used to send the switching command of the target AC filter bank to the LCC DC reactive power control system to execute the switching operation;

[0034] The equalization exit module is used to exit the control logic of the target filter bank selection module and the switching execution module when the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, and restore the default sequential switching logic.

[0035] Furthermore, the lifespan parameter monitoring module calculates the lifespan loss parameter L. i The formula is:

[0036]

[0037] In the formula, N i T represents the cumulative switching count of the i-th AC filter bank. i Let w1 be the cumulative energized operating time of the i-th AC filter bank, w2 be the preset weighting coefficients that satisfy w1+w2=1, and n be the total number of AC filter banks.

[0038] Furthermore, it also includes a safety interlocking module, which is used to interlock the control logic of the target filter bank selection module and the switching execution module when a transient fault is detected in the VSC DC or LCC DC, and switch to the LCC DC default sequence rotation logic.

[0039] This invention, while significantly reducing the total number of switching operations, intelligently supplements the "first-in, first-out" logic through a "balanced optimization layer." It collaboratively optimizes from two dimensions—"reduction in frequency" and "balanced operation"—significantly reducing the full lifecycle maintenance cost of the AC filter bank in an LCC DC converter station. This method requires only a software upgrade, does not add any primary equipment, has extremely low implementation costs, and features a robust automatic shutdown mechanism, making it user-friendly for operation and maintenance. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the VSC / LCC DC parallel hybrid system structure according to an embodiment of the present invention.

[0041] Figure 2 This is a flowchart of a reactive power coordination control method for a VSC / LCC DC parallel hybrid system that takes into account the lifetime balancing of AC filter banks, according to an embodiment of the present invention.

[0042] Figure 3 This is a schematic diagram illustrating the specific implementation process of the third-level "LCC DC-AC filter switching sequence equalization optimization" of the present invention.

[0043] Figure 4 This is a comparison diagram of the switching allocation and lifetime balancing effects between the embodiments of the present invention and existing methods. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This embodiment uses a VSC / LCC DC parallel hybrid system as an example. Figure 1 As shown, the system includes VSC DC and LCC DC. The receiving end of the VSC DC converter station and the rectifier station of the LCC DC converter station are connected to the same common AC bus through a short-distance AC tie line, forming a parallel relationship with a very close electrical distance.

[0046] VSC DC is a back-to-back converter station with a rated DC voltage of ±420kV and a single-unit rated transmission capacity of 1250MW. LCC DC is a bipolar polarity connection station with a rated DC voltage of ±500kV, a bipolar rated capacity of 3000MW, and a rated DC current of 3000A.

[0047] The LCC DC converter station is equipped with multiple AC filter banks of the same rated capacity on the AC bus side, each with a rated reactive power capacity of 170 Mvar. These AC filter banks are dedicated reactive power compensation and harmonic filtering devices for the LCC DC converter station. The switching is controlled by the LCC DC converter station's own reactive power control function based on the exchange reactive power. By default, the switching selection adopts a "first-in, first-out" sequential switching logic.

[0048] The control system of the VSC DC converter station adopts a dual-loop current vector control strategy, including an outer-loop power controller and an inner-loop current controller. The reactive power control channel of the outer-loop power controller can be selected in either constant reactive power control mode or constant AC voltage control mode. The inner-loop current controller achieves independent regulation of active and reactive currents through dq decoupling control.

[0049] like Figure 2 As shown, this embodiment of the invention provides a reactive power coordination control method for a VSC / LCC DC parallel hybrid system that takes into account the lifetime balancing of AC filter banks, including the following steps:

[0050] Step S1: Collect and store the cumulative switching count and cumulative energized operation time of each AC filter bank online, and calculate the current life loss parameters of each AC filter bank according to the preset life assessment model.

[0051] Lifetime loss parameter L i Calculated using the following normalized weighted formula:

[0052]

[0053] In the formula, N i T represents the cumulative switching count of the i-th AC filter bank. i Let w1 be the cumulative energized operating time of the i-th AC filter bank, and w2 be preset weighting coefficients that satisfy w1 + w2 = 1. i The value range is [0,1]. The larger the value, the higher the lifespan loss of the AC filter bank and the shorter the remaining lifespan.

[0054] Step S2: When the reactive power exchanged between the LCC DC rectifier station and the AC system exceeds the preset reactive power coordination control dead zone, the receiving end of the VSC DC converter station will preferentially adjust the reactive power output. The VSC DC converter station absorbs the reactive power fluctuations of the LCC DC converter station by changing the reactive power distribution at the common AC bus, thus avoiding unnecessary switching operations of the AC filter bank.

[0055] The reactive power step response time of the VSC DC converter station is on the order of tens of milliseconds, which is much faster than the second-level switching response time of the AC filter bank. Therefore, it can effectively absorb the short-term reactive power fluctuations of the LCC DC converter station.

[0056] Step S3: When the reactive power output of the receiving end of the VSC DC converter station reaches the preset adjustable capacity upper or lower limit, and the duration of this extreme state exceeds the preset delay threshold, and the reactive power exchanged between the LCC DC rectifier station and the AC system still exceeds the reactive power control dead zone of the LCC DC AC filter, it is determined that the LCC DC rectifier station needs to put on or cut off a set of AC filter groups.

[0057] The preset delay threshold ranges from 400ms to 600ms; in this embodiment, it is set to 500ms. This delay threshold is greater than the operation cycle of the AC filter bank switching operation, which can avoid false triggering caused by short-term transient fluctuations.

[0058] Step S4: Based on the lifetime loss parameter L of each AC filter bank i The target AC filter bank is determined from the current AC filter banks of the same model that simultaneously meet the switching criteria.

[0059] When a set of AC filter banks needs to be put into operation, select the lifetime loss parameter L from the AC filter banks of the same model that are currently in the off state. i The smallest group is designated as the target input group. Physically, this means prioritizing the group using the fewest filters for reactive power support.

[0060] When it is necessary to disconnect a group of AC filter banks, select the life loss parameter L from the AC filter banks of the same model that are currently in operation. i The largest group is designated as the target cut-off group. The physical meaning of this is to allow the "most frequently used filter" to rest first.

[0061] Step S5: The coordinating controller sends the switching command of the target AC filter bank to the LCC DC reactive power control system, which then executes the switching operation.

[0062] If the target AC filter bank is unavailable due to equipment failure or protection lockout, the remaining candidate groups are sorted according to their lifetime loss parameters, and the next best group is selected in turn to perform the switching operation, ensuring that the switching operation can be completed smoothly.

[0063] Steps S2 and S3 constitute the first-level and second-level control, while steps S4 and S5 constitute the third-level control (i.e., the LCC DC / AC filter switching sequence equalization optimization process; please refer to the detailed implementation flow). Figure 3 In the first-level control, the reactive power regulation response time of the VSC DC converter station is less than the switching response time of the LCC DC-AC filter bank; the preset delay threshold value of the second-level control ranges from 400ms to 600ms, which is greater than the operation cycle of the LCC DC-AC filter bank switching operation.

[0064] Step S6: When the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, exit the control logic of steps S4 to S5 and restore the default "first to switch, last to switch" sequential switching logic of the LCC DC reactive power control system.

[0065] In this embodiment, the preset equalization threshold is set to 0.05. When each group Li When the maximum difference between them is less than 0.05, it indicates that the lifespan of each group of AC filter banks has become consistent, the equalization control objective has been achieved, and the system automatically simplifies the control logic.

[0066] This embodiment also includes safety interlocking control: when a transient fault such as AC grounding fault or DC commutation failure is detected in the VSC DC converter station or LCC DC converter station, the control logic of steps S4 to S5 is immediately interlocked and switched to the LCC DC default sequence switching logic to ensure that the safe and stable operation of the system is prioritized under transient conditions.

[0067] When the DC transmission power of the LCC fluctuates repeatedly within a small range, the "first-to-start" sequential switching logic of the LCC DC reactive power control is actually stagnant because the change in reactive power demand is only enough to trigger the switching of one set of filters each time. This results in the same set of AC filters being switched repeatedly, bearing a much greater cumulative number of switching times than other sets.

[0068] In this embodiment, through priority decision-making based on real-time lifetime loss parameters in step S4, whenever the LCC DC reactive power control determines that an AC filter needs to be switched, it actively selects the filter group most conducive to lifetime equalization from multiple groups of filters of the same type that simultaneously meet the switching criteria, thus ensuring that each switching decision moves towards lifetime equalization. When the lifetime parameters of each group become consistent, step S6 automatically exits the equalization control and restores the simplified default sequence rotation logic.

[0069] Through the above method, this embodiment effectively achieves a balanced distribution of lifespan losses among the AC filter banks while maintaining the same total number of switching operations as the existing VSC DC coordinated control scheme. It synergistically reduces the full lifecycle maintenance cost of the AC filter banks in the LCC DC converter station from two dimensions: "reducing the number of switching operations" and "balancing the switching distribution." For specific results, see [link to relevant documentation]. Figure 4 .

[0070] This invention also provides a reactive power coordination control device for a VSC / LCC DC parallel hybrid system that considers the lifespan balancing of AC filter banks. The system includes a VSC DC converter station and an LCC DC converter station, whose AC sides are connected in parallel via an AC power grid and are electrically close to each other. The LCC DC converter station is equipped with multiple AC filter banks of the same rated capacity on its AC bus side. The device includes:

[0071] The lifetime parameter monitoring module is used to monitor and calculate the lifetime loss parameters of each group of AC filter banks online. The lifetime loss parameters are determined based on at least one of the cumulative number of switching operations and the cumulative energized operating time.

[0072] The VSC priority reactive power regulation module is used to prioritize controlling the VSC DC converter station to adjust the reactive power output when the reactive power exchanged between the LCC DC converter station and the AC system exceeds the preset reactive power coordination control dead zone, so as to smooth the reactive power fluctuation of the LCC DC converter station.

[0073] The switching trigger determination module is used to determine whether to switch on or off a group of AC filters when the reactive power output of the VSC DC converter station reaches the upper or lower limit of the preset adjustable capacity and the duration exceeds the preset delay threshold, and the switching reactive power still exceeds the reactive power control dead zone of the LCC AC filter.

[0074] The target filter bank selection module is used to determine the target AC filter bank from the AC filter banks of the same model that simultaneously meet the switching criteria based on the lifetime loss parameters of each AC filter bank: when it needs to be put into operation, the group with the smallest lifetime loss parameter is selected from the group of the same model that is currently in the off state as the target input group; when it needs to be cut off, the group with the largest lifetime loss parameter is selected from the group of the same model that is currently in the input state as the target cut-off group.

[0075] The switching execution module is used to send the switching command of the target AC filter bank to the LCC DC reactive power control system to execute the switching operation;

[0076] The equalization exit module is used to exit the control logic of the target filter bank selection module and the switching execution module when the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, and restore the default sequential switching logic.

[0077] This invention constructs a three-tiered reactive power coordination control architecture consisting of a VSC DC-priority reactive power regulation layer, an LCC DC-AC filter switching triggering layer, and an AC filter switching sequence balancing optimization layer. The VSC DC-priority reactive power regulation layer utilizes its rapid reactive power response capability to smooth reactive power fluctuations in the LCC DC converter station, significantly reducing the total number of LCC DC-AC filter switching operations. The LCC DC-AC filter switching sequence balancing optimization layer, after determining that AC filters need to be switched by the LCC DC reactive power control, prioritizes switching multiple groups of AC filters of the same model that simultaneously meet the switching criteria. Based on real-time lifetime loss parameters such as the cumulative number of switching operations and the cumulative energized operating time of each group of AC filters, it prioritizes switching on the filter with the lowest lifetime loss or switching on the filter with the highest lifetime loss. This priority decision based on real-time lifetime parameters replaces the mechanical "first to switch, last to switch" sequential rotation. This invention, while significantly reducing the total number of LCC DC-AC filter switching operations, further achieves a balance in the lifetime loss of each group of LCC DC-AC filter groups, effectively reducing the total lifecycle maintenance cost of the converter station.

[0078] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A reactive power coordination control method for a VSC / LCC DC parallel hybrid system considering AC filter bank lifetime balancing, wherein the VSC / LCC DC parallel hybrid system includes a VSC DC converter station and an LCC DC converter station, the AC sides of the VSC DC converter station and the LCC DC converter station are connected in parallel with close electrical distance through an AC power grid, and the LCC DC converter station is equipped with multiple sets of AC filter banks with the same rated capacity on its AC bus side, characterized in that, The method includes: The lifespan parameter monitoring step involves online monitoring and calculation of the lifespan loss parameters of each group of AC filter banks. The lifespan loss parameters are determined based on at least one of the cumulative number of switching operations and the cumulative energized operating time of each group of AC filter banks. The VSC priority reactive power regulation step is as follows: when the reactive power exchanged between the LCC DC converter station and the AC system exceeds the preset reactive power coordination control dead zone, the VSC DC converter station will prioritize regulating the reactive power output to smooth out the reactive power fluctuations of the LCC DC converter station. In the switching trigger determination step, when the reactive power output of the VSC DC converter station reaches the preset adjustable capacity upper or lower limit and the duration exceeds the preset delay threshold, and the switching reactive power still exceeds the reactive power control dead zone of the LCC AC filter, it is determined that a set of AC filter groups needs to be put into or cut off. The target filter bank selection step involves determining the target AC filter bank from the current AC filter banks of the same model that simultaneously meet the switching criteria, based on the lifetime loss parameters of each AC filter bank: when it needs to be put into operation, the group with the smallest lifetime loss parameter is selected from the current disconnected group of the same model as the target input group; when it needs to be disconnected, the group with the largest lifetime loss parameter is selected from the current input group of the same model as the target disconnected group. The switching execution step involves sending the switching command of the target AC filter bank to the LCC DC reactive power control system to execute the switching operation. In the equalization exit step, when the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, the control logic of the target filter bank selection step and the switching execution step is exited, and the default sequential switching logic is restored.

2. The method according to claim 1, characterized in that, In the lifetime parameter monitoring step, the lifetime loss parameter L i Calculate using the following formula: ； In the formula, N i T represents the cumulative switching count of the i-th AC filter bank. i Let w1 be the cumulative energized operating time of the i-th AC filter bank, w2 be the preset weighting coefficients, satisfying w1+w2=1, and n be the total number of AC filter banks.

3. The method according to claim 1, characterized in that, The parallel connection method between the VSC DC converter station and the LCC DC converter station is any one of the following: The sending or receiving end of the VSC DC converter station is connected to the same AC bus as the rectifier station or inverter station of the LCC DC converter station. Alternatively, the VSC DC converter station and the LCC DC converter station may be electrically connected via a short-distance AC tie line, the length of which allows the electrical distance between the two converter stations to influence each other through reactive power regulation.

4. The method according to claim 1, characterized in that, The VSC priority reactive power regulation step and the switching trigger determination step constitute the first level control and the second level control, and the target filter bank selection step and the switching execution step constitute the third level control; wherein, in the first level control, the reactive power regulation response time of the VSC DC converter station is less than the switching response time of the LCC DC AC filter bank; the preset delay threshold value of the second level control is in the range of 400ms to 600ms, which is greater than the action cycle of the LCC DC AC filter bank switching operation.

5. The method according to claim 1, characterized in that, The VSC DC converter station achieves decoupled control of active and reactive power through dual closed-loop current vector control, including an outer loop power controller and an inner loop current controller; the outer loop power controller adopts a constant reactive power control mode or a constant AC voltage control mode.

6. The method according to claim 1, characterized in that, The control signal transmission delay for the electrical distance between the VSC DC converter station and the LCC DC converter station is less than a preset value; the AC filter bank configured on the AC bus side of the LCC DC converter station adopts a default sequential switching logic of "first to switch, last to switch".

7. The method according to claim 1, characterized in that, It also includes a safety interlocking step: when a transient fault is detected in the VSC DC or LCC DC, the control logic of the target filter bank selection step and the switching execution step is interlocked, and the LCC DC default sequence rotation logic is switched.

8. A reactive power coordination control device for a VSC / LCC DC parallel hybrid system considering the lifespan balancing of AC filter banks, the system comprising a VSC DC converter station and an LCC DC converter station, the AC sides of which are connected in parallel via an AC power grid and are electrically close to each other, wherein the LCC DC converter station is equipped with multiple sets of AC filter banks with the same rated capacity on its AC bus side, characterized in that, The device includes: The lifetime parameter monitoring module is used to monitor and calculate the lifetime loss parameters of each group of AC filter banks online. The lifetime loss parameters are determined based on at least one of the cumulative number of switching operations and the cumulative energized operating time. The VSC priority reactive power regulation module is used to prioritize controlling the VSC DC converter station to adjust the reactive power output when the reactive power exchanged between the LCC DC converter station and the AC system exceeds the preset reactive power coordination control dead zone, so as to smooth the reactive power fluctuation of the LCC DC converter station. The switching trigger determination module is used to determine whether to switch on or off a group of AC filters when the reactive power output of the VSC DC converter station reaches the upper or lower limit of the preset adjustable capacity and the duration exceeds the preset delay threshold, and the switching reactive power still exceeds the reactive power control dead zone of the LCC AC filter. The target filter bank selection module is used to determine the target AC filter bank from the AC filter banks of the same model that simultaneously meet the switching criteria based on the lifetime loss parameters of each AC filter bank: when it needs to be put into operation, the group with the smallest lifetime loss parameter is selected from the group of the same model that is currently in the off state as the target input group; when it needs to be cut off, the group with the largest lifetime loss parameter is selected from the group of the same model that is currently in the input state as the target cut-off group. The switching execution module is used to send the switching command of the target AC filter bank to the LCC DC reactive power control system to execute the switching operation; The equalization exit module is used to exit the control logic of the target filter bank selection module and the switching execution module when the maximum difference between the lifetime loss parameters of all AC filter banks is less than the preset equalization threshold, and restore the default sequential switching logic.

9. The apparatus according to claim 8, characterized in that, The lifespan parameter monitoring module calculates the lifespan loss parameter L. i The formula is: ； In the formula, N i T represents the cumulative switching count of the i-th AC filter bank. i Let w1 be the cumulative energized operating time of the i-th AC filter bank, w2 be the preset weighting coefficients, satisfying w1+w2=1, and n be the total number of AC filter banks.

10. The apparatus according to claim 8, characterized in that, It also includes a safety interlocking module, which is used to interlock the control logic of the target filter bank selection module and the switching execution module when a transient fault is detected in the VSC DC or LCC DC, and switch to the default sequence switching logic of LCC DC.

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