Method and device for controlling super capacitor valve in static synchronous phase modifier system

Abstract

The invention relates to the field of static synchronous phase modifiers, and discloses a control method and device for a super-capacitor valve in a static synchronous phase modifier system, and the device comprises an MMC converter valve AC side equipped with a circuit breaker, a pre-charging resistor and a bypass switch, and the super-capacitor valve equipped with a current limiting reactor, a current limiting resistor, a bypass switch and an anode and cathode circuit breaker. A current-limiting resistor and a bypass switch are additionally arranged at a direct current bus between a modular multilevel converter and a super-capacitor valve, so that the impact current at the closing moment of a direct current circuit breaker can be obviously reduced, and in combination with a controllable charging strategy of the super-capacitor valve, the capacitor voltage of each sub-module can be charged to a rated value and is kept consistent; according to controllable charging and frequency-active power control of the super-capacitor valve of the static synchronous phase modifier, active power output of the super-capacitor valve can be automatically adjusted according to the frequency of the grid-side voltage after the system is started, frequency stabilization of a power grid is facilitated, primary frequency modulation and inertia supporting are achieved, and stable starting of the static synchronous phase modifier and the power grid supporting capacity are achieved.

Description

Technical Field

[0001] This invention relates to the field of stationary synchronous condensers, specifically to a control method and apparatus for a supercapacitor valve in a stationary synchronous condenser system. Background Technology

[0002] With the deepening of the construction of new power systems, the large-scale integration of new energy sources such as wind power and photovoltaics into the power grid has led to a significant decrease in the equivalent inertia and damping characteristics of the power system. Most new energy power generation equipment is connected to the grid through power electronic converters, which do not have the inertial response and reactive power support capabilities of synchronous generators. This results in increased frequency changes and decreased voltage stability of the power grid when facing power fluctuations. Against this background, static synchronous condensers, as a reactive power compensation and inertia support device based on power electronics technology, have received widespread attention.

[0003] The topology of a static synchronous condenser typically consists of a modular multilevel converter (MMC), a DC link, and a supercapacitor valve group connected in parallel to the DC bus. This valve group is formed by a large number of supercapacitor cells connected in series and parallel to store and release necessary transient energy. This topology achieves efficient reactive power compensation and active power support, enabling it not only to support grid voltage but also to simulate synchronous machine inertia and participate in system frequency regulation, thereby effectively improving the stability and renewable energy integration capabilities under weak grid conditions.

[0004] Existing technologies do not adequately consider the startup process of supercapacitor valve groups. If a controllable charging strategy is not adopted and the valve group is started directly, it is easy to cause capacitor voltage imbalance or even divergence, threatening system safety. At the same time, existing control strategies mainly focus on reactive power support and fail to enable supercapacitor valve groups to effectively respond to grid frequency changes, thus limiting their active frequency support capability. Therefore, there is an urgent need for a technology that can achieve controllable charging and voltage balancing of supercapacitor valve groups and integrate active power support control strategies to improve the startup reliability of static synchronous condensers and their comprehensive support capability for the power grid. Summary of the Invention

[0005] The purpose of this invention is to provide a control method and device for a supercapacitor valve in a static synchronous condenser system, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A control method for a supercapacitor valve in a static synchronous condenser system, comprising the following steps: When the three-phase circuit breaker on the AC side of the MMC converter valve is closed, the power grid performs uncontrolled charging of the MMC through the pre-charging resistor. After the MMC converter valve finishes uncontrolled charging, close the pre-charge resistor bypass switch, unlock the MMC, and control the DC side voltage of the MMC at the preset value through constant DC voltage measurement control. The supercapacitor valve closes the positive and negative circuit breakers, and the MMC charges the supercapacitor valve uncontrolled through the DC reactor and the starting current-limiting resistor. After the uncontrolled charging of the supercapacitor valve is completed, close the start-up current-limiting resistor bypass switch and calculate the SOC of the supercapacitor in each sub-module of the supercapacitor valve. The supercapacitor valve controls the execution of a controllable charging program based on SOC sorting and balancing. The cyclic controllable charging process ensures that the capacitor voltage of each submodule reaches a preset value, and stops when the voltage-capacitance imbalance of the submodule is less than a set threshold. Supercapacitor valve execution frequency-active power control.

[0007] As a further aspect of the present invention: the number of sub-modules of the supercapacitor valve has redundancy, and the number of sub-modules is even to ensure symmetrical voltage of the upper and lower bridge arms. The formula for determining the number of sub-modules is as follows: in N sc This refers to the number of sub-modules required for the supercapacitor valve. U dcn This refers to the rated voltage of the supercapacitor valve. δ For redundancy, U c The rated voltage of a single submodule capacitor. f ( x ) is the floor function.

[0008] As a further embodiment of the present invention: in the step of unlocking the MMC and controlling the DC-side voltage of the MMC to a preset value through constant DC voltage measurement, the DC-side voltage of the MMC is controlled by PI, and its time-domain expression is: in i dref (t) represents the reference value of the d-axis current in the inner current loop. U dcref (t) represents the reference value of the DC-side voltage of the MMC. U dc (t) represents the actual value of the DC-side voltage. U dref (t) represents the reference value of the d-axis voltage of the inner current loop. i d (t) represents the actual value of the d-axis current. U d (t) represents the actual value of the d-axis voltage on the grid side. ωThe grid-side voltage angular frequency, L For MMC bridge arm inductors, i q (t) represents the actual value of the q-axis current.

[0009] As a further embodiment of the present invention: the starting current-limiting resistor is used to limit the starting current of the overcapacity valve, and its value is calculated using the following formula: in R min The minimum value of the current-limiting resistor is set to start, and L is the value of the DC reactor.

[0010] As a further aspect of the present invention: the formula for calculating the value of the starting current resistor is an implicit equation, which is solved... R min The specific steps include: set up R min The initial value is: ; Numerical iteration is performed, and the formula is: ; when When, output R min = R k+1 , ε This is the preset error.

[0011] As a further aspect of the present invention: the formula for calculating the SOC of the supercapacitor in each sub-module of the supercapacitor valve is characterized as follows: in V 0 represents the initial voltage of the supercapacitor. C This is the value of the supercapacitor. I sc Supercapacitor discharge current, V max The charging cutoff voltage for supercapacitors. V min This is the discharge cutoff voltage of the supercapacitor.

[0012] As a further aspect of the present invention: the step of executing a controllable charging control program based on SOC sorting and equalization through supercapacitor valve control, and cyclically controlling the charging to make the capacitor voltage of each sub-module reach a preset value specifically includes: The supercapacitor submodules of the upper and lower bridge arms are sorted by SOC from high to low. Calculate the number of sub-modules that need to be cut in the upper and lower bridge arms respectively. N pnex The calculation expression is: in N This represents the total number of supercapacitor valve cascade submodules. V cn The rated voltage for a single submodule, f ( x ) is the floor function; Calculate the total capacitor voltage of the upper and lower bridge arms. U psum , U nsum The calculation expression is: ; The judgment is based on the total capacitor voltage of the upper and lower bridge arms: like U psum > U nsum + α Then, the lower bridge arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the upper bridge arm does not cut off the submodule. like U psum < U nsum + α Then, the upper arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the lower bridge arm does not cut off the submodule. like The upper and lower bridge arms were cut off from high to low according to the State of Charge (SOC). N pnex There are several sub-modules, where α is the decision threshold.

[0013] As a further aspect of the present invention: the calculation of the voltage-capacitance imbalance of the submodule is expressed as follows: in This represents the average capacitor voltage of the supercapacitor valve submodule.

[0014] As a further embodiment of the present invention: in the frequency-active power control performed by the supercapacitor valve, the frequency-active power control includes a frequency outer loop and a current inner loop; The outer frequency loop uses a PI controller, and its time-domain expression is as follows: in: in i sc_ref (t () is the reference value for the inner loop current. k p The proportional gain of the PI controller. k i Δ is the integral coefficient of the PI controller. f For frequency error; f ref This is a frequency reference value. f mean This is a frequency measurement value. f d This is the dead zone frequency of primary frequency modulation. f n This is the frequency rating; The inner current loop uses a PI controller, and its time-domain expression is as follows: in N ref0 The initial number of input submodules for the supercapacitor valve should be set as follows: in, N ref This refers to the number of sub-modules required for the supercapacitor valve. k p The proportional gain of the PI controller. k i The integral coefficient of the PI controller. i sc ( t The value is the DC current measurement of the supercapacitor valve. f (u) is the floor function.

[0015] This invention aims to provide a control device for a supercapacitor valve in a stationary synchronous condenser system. The control device, when scheduled by executing one or more programs through one or more processors, implements the control method described in any one of the control methods for the supercapacitor valve in a stationary synchronous condenser system. In the control device: The power grid and the MMC converter valve are connected via a three-phase transformer, a three-phase circuit breaker, a pre-charging resistor, and a pre-charging resistor bypass switch. The DC side of the MMC is connected to the supercapacitor valve via positive and negative circuit breakers, DC reactors, and starting current-limiting resistors. The supercapacitor valve is composed of multiple cascaded sub-modules, each of which consists of a supercapacitor array and a half-bridge circuit. The supercapacitor valve is divided into an upper bridge arm and a lower bridge arm. Each bridge arm has an equal number of sub-modules, and the neutral point between the upper and lower bridge arms is grounded through a large resistor to provide a DC-side reference point to ground for the system.

[0016] Compared with existing technologies, the present invention proposes a control method and device for a supercapacitor valve in a static synchronous condenser system. Its advantages are as follows: by adding a current-limiting resistor and a bypass switch at the DC bus between the modular multilevel converter and the supercapacitor valve, the inrush current at the moment of DC circuit breaker closure can be significantly reduced. Combined with the controllable charging strategy of the supercapacitor valve, the capacitor voltage of each submodule can be charged to its rated value and kept consistent. Simultaneously, by adopting a frequency-active power control strategy, the active power output of the supercapacitor valve can be automatically adjusted according to the frequency of the grid-side voltage after system startup, which helps stabilize the grid frequency and achieve primary frequency regulation and inertia support. Attached Figure Description

[0017] Figure 1 This is a diagram of a control system for a supercapacitor valve in a static synchronous condenser system.

[0018] Figure 2 This is a control flowchart of a control method for a supercapacitor valve in a static synchronous condenser system.

[0019] Figure 3 This is a block diagram of the DC voltage control of a modular multilevel converter valve in a control method for a supercapacitor valve in a static synchronous condenser system.

[0020] Figure 4 This is a block diagram of the frequency-active power control of a supercapacitor valve in a control method for a supercapacitor valve in a static synchronous condenser system.

[0021] Figure 5 This is a waveform diagram of the active power response of a system when the frequency response suddenly drops in a control method for a supercapacitor valve in a static synchronous condenser system.

[0022] Figure 6 This is a waveform diagram of the active power response of a system when the frequency response suddenly increases in a control method for a supercapacitor valve in a static synchronous condenser system. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] The specific implementation of the present invention is described in detail below with reference to specific embodiments, including: the AC side of the MMC converter valve is equipped with a circuit breaker, a pre-charging resistor, and a bypass switch; the supercapacitor valve is equipped with a current-limiting reactor, a current-limiting resistor, a bypass switch, and positive and negative circuit breakers; the MMC valve closes the AC side circuit breaker to enter an uncontrolled charging state; after uncontrolled charging is completed, the bypass switch is closed, and the MMC is unlocked to control the DC side voltage to reach a preset value; the supercapacitor valve closes the positive and negative circuit breakers to enter an uncontrolled charging state; after uncontrolled charging is completed, the bypass switch is closed, and the current-limiting resistor is removed; the supercapacitor valve is unlocked, and controlled charging and submodule capacitor voltage balancing control are performed to make the voltages of all submodule capacitors reach the preset value and tend to be consistent; the supercapacitor valve performs frequency-active power control; compared with the prior art, the present invention achieves smooth startup and grid support capability of the static synchronous condenser through the controlled charging and frequency-active power control of the supercapacitor valve of the static synchronous condenser.

[0025] An embodiment of the present invention provides a control method for a supercapacitor valve in a static synchronous condenser system, comprising the following steps: When the three-phase circuit breaker on the AC side of the MMC converter valve is closed, the power grid performs uncontrolled charging of the MMC through the pre-charging resistor.

[0026] In this embodiment, to prevent excessive current from damaging electrical equipment during uncontrolled charging of the MMC, a pre-charging circuit needs to be added between the grid side and the MMC; for example... Figure 1 As shown, the three-phase circuit breaker S on the AC side of the closed MMC converter valve... ac1 The power grid passes through the pre-charging resistor R pre Uncontrolled charging of MMC.

[0027] After the uncontrolled charging of the MMC converter valve is completed, close the pre-charge resistor bypass switch, unlock the MMC, and control the DC side voltage of the MMC to a preset value through constant DC voltage measurement control.

[0028] In this embodiment, as Figure 1 As shown, the DC side voltage U after the MMC converter valve uncontrolled charging is completed. dc Once stable, the pre-charge resistor bypass switch is closed, the MMC is unlocked, and the constant DC side voltage control is initiated, setting the MMC DC side voltage U... dc Control it within the preset value.

[0029] like Figure 3 As shown, the DC-side voltage is controlled by a PI controller, which is achieved by controlling the d-axis component of the grid-side current. Its time-domain expression is as follows: in i dref (t) represents the reference value of the d-axis current in the inner current loop. U dcref(t) represents the reference value of the DC-side voltage of the MMC. U dc (t) represents the actual value of the DC-side voltage. U dref (t) represents the reference value of the d-axis voltage of the inner current loop. i d (t) represents the actual value of the d-axis current. U d (t) represents the actual value of the d-axis voltage on the grid side. ω The grid-side voltage angular frequency, L For MMC bridge arm inductors, i q (t) represents the actual value of the q-axis current.

[0030] The supercapacitor valve closes the positive and negative circuit breakers, and the MMC performs uncontrolled charging of the supercapacitor valve through the DC reactor and the starting current-limiting resistor.

[0031] In this embodiment, as Figure 1 As shown, the DC side voltage U dc After tracking the reference value, the supercapacitor valve closes the positive and negative circuit breakers S. dc1 and S dc2 At this time, the supercapacitor valve submodule is not energized, and the MMC is powered by the DC reactor L. dc1 L dc2 and the starting current limiting resistor R dc1 R dc2 Uncontrolled charging of the supercapacitor valve.

[0032] After the uncontrolled charging of the supercapacitor valve is completed, close the start-up current-limiting resistor bypass switch and calculate the SOC of the supercapacitor in each sub-module of the supercapacitor valve.

[0033] In this embodiment, as Figure 1 and Figure 2 As shown, after the uncontrolled charging of the supercapacitor valve is completed, the voltage of each submodule is stable, and the bypass switch S of the start-up current-limiting resistor is closed. dc3 S dc4 And calculate the SOC of the supercapacitor in each submodule of the supercapacitor valve; the calculation formula is as follows: in V 0 represents the initial voltage of the supercapacitor. C This is the value of the supercapacitor. I sc Supercapacitor discharge current, V max The charging cutoff voltage for supercapacitors. V min This is the discharge cutoff voltage of the supercapacitor.

[0034] The supercapacitor valve controls the execution of a controllable charging program based on SOC sorting and balancing. The cyclic controllable charging process ensures that the capacitor voltage of each submodule reaches a preset value, and stops when the voltage-capacitance imbalance of the submodule is less than a set threshold.

[0035] In this embodiment, this step includes two parts: First, the supercapacitor valve controller executes a controllable charging control program based on SOC sorting and balancing to control the capacitor voltage of each submodule to reach a preset value. Second, if the voltage imbalance of the submodule capacitors of the supercapacitor valve is calculated, if the imbalance is less than a set threshold, the controllable charging ends; if it is greater than the set threshold, the process returns to the previous step. Figure 2 As shown, the controllable charging procedure of the supercapacitor valve includes the following steps: The supercapacitor submodules SC_SM1~SC_SM of the upper and lower bridge arms are respectively... N / 2 SC_SM N / 2+1 ~SC_SM N Sort the SOC from highest to lowest; Calculate the number of sub-modules that need to be cut in the upper and lower bridge arms respectively. N pnex The calculation expression is: in N This represents the total number of supercapacitor valve cascade submodules. V cn The rated voltage for a single submodule, f ( x ) is the floor function; Calculate the total capacitor voltage of the upper and lower bridge arms. U psum , U nsum The calculation expression is: ; Based on the total capacitance voltage of the upper and lower bridge arms U psum , U nsum Make a judgment: like U psum > U nsum + α Then, the lower bridge arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the upper bridge arm does not cut off the submodule. like U psum < U nsum + αThen, the upper arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the lower bridge arm does not cut off the submodule. like The upper and lower bridge arms were cut off from high to low according to the State of Charge (SOC). N pnex There are several sub-modules, where α is the decision threshold.

[0036] The calculation of the voltage-capacitance imbalance of the submodule is expressed as follows: in This represents the average capacitor voltage of the supercapacitor valve submodule.

[0037] Supercapacitor valve execution frequency-active power control.

[0038] In this embodiment, the frequency-active power control performed by the supercapacitor valve includes a frequency outer loop and a current inner loop. like Figure 4 As shown, the outer frequency loop uses a PI controller, and its time-domain expression is as follows: in: in i sc_ref ( t () is the reference value for the inner loop current. k p The proportional gain of the PI controller. k i Δ is the integral coefficient of the PI controller. f For frequency error; f ref This is a frequency reference value. f mean This is a frequency measurement value. f d This is the dead zone frequency of primary frequency modulation. f n This is the frequency rating; The inner current loop uses a PI controller, and its time-domain expression is as follows: in N ref0 The initial number of input submodules for the supercapacitor valve should be set as follows: in, N ref This refers to the number of sub-modules required for the supercapacitor valve.k p The proportional gain of the PI controller. k i The integral coefficient of the PI controller. i sc ( t The value is the DC current measurement of the supercapacitor valve. f (u) is the floor function; it is worth noting that the number of each of the upper and lower bridge arms of the supercapacitor valve should be [number missing]. N ref Half of it.

[0039] like Figure 5 As shown, when the grid connection point voltage frequency suddenly drops, the static synchronous condenser rapidly increases its output active power to support the grid frequency; as Figure 6 As shown, when the voltage frequency at the grid connection point suddenly increases, the active power output of the static synchronous condenser decreases rapidly to restore the grid frequency.

[0040] like Figure 1 As shown, the present invention also provides a control device for a supercapacitor valve in a stationary synchronous condenser system. When the control device is scheduled by executing one or more programs through one or more processors, it implements the control method described in any one of the control methods for the supercapacitor valve in a stationary synchronous condenser system. In the control device: The power grid and the MMC converter valve are connected via a three-phase transformer, a three-phase circuit breaker, a pre-charging resistor, and a pre-charging resistor bypass switch. The DC side of the MMC is connected to the supercapacitor valve via positive and negative circuit breakers, DC reactors, and starting current-limiting resistors. The supercapacitor valve is composed of multiple cascaded sub-modules, each of which consists of a supercapacitor array and a half-bridge circuit. The supercapacitor valve is divided into an upper bridge arm and a lower bridge arm. Each bridge arm has an equal number of sub-modules, and the neutral point between the upper and lower bridge arms is grounded through a large resistor to provide a DC-side reference point to ground for the system.

[0041] In this embodiment, the static synchronous condenser includes a modular multilevel converter valve and a supercapacitor valve. The AC side of the modular multilevel converter valve is connected to the AC power grid through a soft-start circuit, and the DC side is connected to the supercapacitor valve through positive and negative circuit breakers, a DC reactor, and a starting current-limiting resistor. The supercapacitor valve is composed of multiple cascaded sub-modules, divided into an upper bridge arm and a lower bridge arm. Each bridge arm has an equal number of sub-modules, and the neutral point between the upper and lower bridge arms is grounded through a large resistor to provide a DC-side reference point for the system.

[0042] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0043] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the disclosure in the specification and embodiments. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0044] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A control method for a supercapacitor valve in a static synchronous condenser system, characterized in that, Includes the following steps: When the three-phase circuit breaker on the AC side of the MMC converter valve is closed, the power grid performs uncontrolled charging of the MMC through the pre-charging resistor. After the MMC converter valve finishes uncontrolled charging, close the pre-charge resistor bypass switch, unlock the MMC, and control the DC side voltage of the MMC at the preset value through constant DC voltage measurement control. The supercapacitor valve closes the positive and negative circuit breakers, and the MMC charges the supercapacitor valve uncontrolled through the DC reactor and the starting current-limiting resistor. After the uncontrolled charging of the supercapacitor valve is completed, close the start-up current-limiting resistor bypass switch and calculate the SOC of the supercapacitor in each sub-module of the supercapacitor valve. The supercapacitor valve controls the execution of a controllable charging program based on SOC sorting and balancing. The cyclic controllable charging process ensures that the capacitor voltage of each submodule reaches a preset value, and stops when the voltage-capacitance imbalance of the submodule is less than a set threshold. Supercapacitor valve execution frequency-active power control.

2. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, The number of sub-modules in the supercapacitor valve has redundancy, and the number of sub-modules is even to ensure symmetrical voltage between the upper and lower bridge arms. The formula for determining the number of sub-modules is as follows: in N sc This refers to the number of sub-modules required for the supercapacitor valve. U dcn This refers to the rated voltage of the supercapacitor valve. δ For redundancy, U c The rated voltage of a single submodule capacitor. f ( x ) is the floor function.

3. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, In the step of unlocking the MMC and controlling the DC-side voltage of the MMC to a preset value through constant DC voltage measurement, the DC-side voltage of the MMC is controlled by PI, and its time-domain expression is as follows: in i dref (t) represents the reference value of the d-axis current in the inner current loop. U dcref (t) represents the reference value of the DC-side voltage of the MMC. U dc (t) represents the actual value of the DC-side voltage. U dref (t) represents the reference value of the d-axis voltage of the inner current loop. i d (t) represents the actual value of the d-axis current. U d (t) represents the actual value of the d-axis voltage on the grid side. ω The grid-side voltage angular frequency, L For MMC bridge arm inductors, i q (t) represents the actual value of the q-axis current.

4. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, The starting current-limiting resistor is used to limit the starting current of the overcapacity valve, and its value is calculated using the following formula: in R min The minimum value of the current-limiting resistor is set to start, and L is the value of the DC reactor.

5. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 4, characterized in that, The formula for calculating the value of the starting current resistor is an implicit equation, which needs to be solved. R min The specific steps include: set up R min The initial value is: ; Numerical iteration is performed, and the formula is: ; when When, output R min = R k+1 , ε This is the preset error.

6. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, The formula for calculating the SOC of the supercapacitor in each submodule of the supercapacitor valve is expressed as follows: in V 0 represents the initial voltage of the supercapacitor. C This is the value of the supercapacitor. I sc Supercapacitor discharge current, V max The charging cutoff voltage for supercapacitors. V min This is the discharge cutoff voltage of the supercapacitor.

7. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, The steps of executing a controllable charging control program based on SOC sorting and equalization through supercapacitor valve control, and cyclically controlling the charging to make the capacitor voltage of each submodule reach a preset value, specifically include: The supercapacitor submodules of the upper and lower bridge arms are sorted by SOC from high to low. Calculate the number of sub-modules that need to be cut in the upper and lower bridge arms respectively. N pnex The calculation expression is: in N This represents the total number of supercapacitor valve cascade submodules. V cn The rated voltage for a single submodule, f ( x ) is the floor function; Calculate the total capacitor voltage of the upper and lower bridge arms. U psum , U nsum The calculation expression is: ； The judgment is based on the total capacitor voltage of the upper and lower bridge arms: like U psum > U nsum + α Then, the lower arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the upper bridge arm does not cut off the submodule. like U psum < U nsum + α Then, the upper arm is cut off 2 sections according to the SOC from high to low. N pnex Each submodule, the lower bridge arm does not cut off the submodule. like The upper and lower bridge arms were cut off from high to low according to the State of Charge (SOC). N pnex There are several sub-modules, where α is the decision threshold.

8. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, The calculation of the voltage-capacitance imbalance of the submodule is expressed as follows: in This represents the average capacitor voltage of the supercapacitor valve submodule.

9. The control method for a supercapacitor valve in a static synchronous condenser system according to claim 1, characterized in that, In the frequency-active power control performed by the supercapacitor valve, the frequency-active power control includes a frequency outer loop and a current inner loop; The outer frequency loop uses a PI controller, and its time-domain expression is as follows: in: in i sc_ref ( t () is the reference value for the inner loop current. k p The proportional gain of the PI controller. k i Δ is the integral coefficient of the PI controller. f For frequency error; f ref This is a frequency reference value. f mean This is a frequency measurement value. f d This is the dead zone frequency of primary frequency modulation. f n This is the frequency rating; The inner current loop uses a PI controller, and its time-domain expression is as follows: in N ref0 The initial number of input submodules for the supercapacitor valve should be set as follows: in, N ref This refers to the number of sub-modules required for the supercapacitor valve. k p The proportional gain of the PI controller. k i The integral coefficient of the PI controller. i sc ( t The value is the DC current measurement of the supercapacitor valve. f (u) is the floor function.

10. A control device for a supercapacitor valve in a static synchronous condenser system, characterized in that, When the control device schedules the execution of one or more programs through one or more processors, it implements the control method as described in any one of claims 1 to 9, wherein the control device: The power grid and the MMC converter valve are connected via a three-phase transformer, a three-phase circuit breaker, a pre-charging resistor, and a pre-charging resistor bypass switch. The DC side of the MMC is connected to the supercapacitor valve via positive and negative circuit breakers, DC reactors, and starting current-limiting resistors. The supercapacitor valve is composed of multiple cascaded sub-modules, each of which consists of a supercapacitor array and a half-bridge circuit. The supercapacitor valve is divided into an upper bridge arm and a lower bridge arm. Each bridge arm has an equal number of sub-modules, and the neutral point between the upper and lower bridge arms is grounded through a large resistor to provide a DC-side reference point to ground for the system.

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