Control method and system for static synchronous condenser of DC transmission converter station

Abstract

A control method and system for a static synchronous condenser in a DC transmission converter station uses the minimum reactive power exchange between the converter station and the power grid as a reactive power optimization indicator, adopts voltage reactive power control, takes AC bus voltage stability as a control target, and adjusts the parameters of voltage reactive power control; determines the support power of the energy storage unit according to the rated power of the converter station, and determines the support time according to the power change rate of the converter station and the support power of the energy storage unit; when an AC voltage drop is detected, the static synchronous condenser injects capacitive reactive power and active power into the AC system based on the voltage reactive power control parameters, the support power of the energy storage unit, and the support time; based on the injected active power, low-voltage current limiting control is adopted to update the DC current instruction of the converter; when an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode; utilizes the harmonic compensation function of the converter to filter out harmonics of set characteristic orders, prevent commutation failure, and improve adaptability to weak AC power grids.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel power systems, and in particular relates to a control method and system for a static synchronous condenser configured in a direct current transmission converter station. Background Art

[0002] Ultra-high voltage direct current (UHVDC) transmission offers the advantages of long-distance, high-capacity power transmission. However, its converter stations, particularly those at the receiving end, can experience voltage collapse during grid faults due to insufficient reactive power support. Traditional reactive power compensation equipment, such as capacitors and reactors, has a slow response speed and cannot meet dynamic requirements. Furthermore, according to recent DC project failure statistics, commutation failures in DC systems caused by switching on and off AC filters account for approximately 5%, making it the second-leading cause of failure after AC line failures. The discrete mechanical characteristics of filter switches make this risk difficult to fully eliminate.

[0003] To mitigate voltage issues and DC commutation failures caused by AC and DC faults, existing technologies utilize the large-capacity, bidirectional reactive power regulation and dynamic reactive power output capabilities of phase-shifting (SCs) to enhance the support capabilities of UHVDC grids and promote their development, safety, and stability. SCs, due to their rapid dynamic reactive power regulation capabilities, are a key solution. For example, the deployment of large SCs in converter stations, such as the Changji-Guquan ±1100kV DC transmission project, reduced voltage fluctuations at the receiving end by over 60% and the probability of commutation failure by approximately 40%-50%. Furthermore, in flexible DC converter station applications, to address insufficient power receiving capacity at the receiving end and voltage fluctuations caused by excessive DC line power, SCs, as rotating equipment with inherent generator characteristics, can provide a certain degree of inertia support during grid frequency fluctuations, effectively improving the grid's short-circuit ratio.

[0004] However, large-scale phase-converters still have their shortcomings, primarily in the following areas: Unlike traditional power stations, converter stations lack rotating generating equipment and instead utilize power electronic converters and their controllers as their primary systems. Due to their rotating mechanical structure, large-scale phase-converters require frequent maintenance, which involves extensive mechanical overhaul and is costly. Annual maintenance days are approximately 15 to 30 days, lower than the annual availability of power electronic equipment. Phase-converter losses are 1.5% to 2.5% under rated operating conditions, and between 3% and 4% under light load, exceeding those of power electronic equipment. Furthermore, synchronous machines are less economical in terms of land occupation, initial investment, and lifecycle maintenance. Summary of the Invention

[0005] To address the deficiencies in the prior art, the present invention provides a control method and system for a static synchronous condenser configured in a DC transmission converter station, which fully utilizes the functions of the static synchronous condenser to improve the operational reliability of the converter station, prevent commutation failures, and improve the adaptability of weak AC power grids.

[0006] The present invention adopts the following technical solutions.

[0007] The present invention proposes a control method for a static synchronous condenser of a DC transmission converter station, comprising:

[0008] Obtain the reactive power exchange between the converter station and the power grid, and use the minimum reactive power exchange as the reactive power optimization index for the static synchronous condenser. Based on the reactive power optimization index, adopt voltage reactive power control, take AC bus voltage stability as the control target, and set the voltage reactive power control parameters.

[0009] Determine the support power of the energy storage unit according to the rated power of the converter station, and determine the support time according to the power change rate of the converter station and the support power of the energy storage unit;

[0010] When an AC voltage drop is detected, the static synchronous condenser injects capacitive reactive power into the AC system based on the set voltage reactive power control parameters. Simultaneously, based on the support power and support time of the energy storage unit, the static synchronous condenser injects active power into the AC system. Based on the injected active power, low-voltage current limiting control is used to update the DC current command of the converter. When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode.

[0011] The harmonic compensation function of the converter in the static synchronous condenser is used to filter out harmonics of set characteristic orders.

[0012] Under steady-state operation, the reactive exchange between the converter station and the power grid is entirely provided by the static synchronous condenser. In an ideal state, the reactive exchange between the converter station and the power grid is 0.

[0013] The voltage reactive power control adopted includes: droop control and constant voltage control.

[0014] If the rate of change of the AC bus voltage within a unit sampling period is not greater than 2% and not less than -2%, the AC bus voltage is determined to be stable.

[0015] The supporting power of the energy storage unit shall not exceed 60% of the rated power of the converter station, and the supporting time shall not exceed 1s.

[0016] When the AC voltage drop of 0.9 pu is detected, the static synchronous condenser injects capacitive reactive power within 0.1 second.

[0017] Characteristic subharmonics include 11th and 13th harmonics.

[0018] The present invention also proposes a control system for a static synchronous condenser of a DC transmission converter station, comprising:

[0019] Control parameter setting module, support parameter setting module, commutation failure prevention module, harmonic compensation module;

[0020] The control parameter setting module is used to obtain the reactive power exchange between the converter station and the power grid, with the minimum reactive power exchange amount as the reactive power optimization index of the static synchronous condenser. Based on the reactive power optimization index, voltage reactive power control is adopted, with AC bus voltage stability as the control target, to set the voltage reactive power control parameters.

[0021] A support parameter setting module is used to determine the support power of the energy storage unit according to the rated power of the converter station, and to determine the support time according to the power change rate of the converter station and the support power of the energy storage unit;

[0022] The commutation failure prevention module is used to inject capacitive reactive power into the AC system based on the set voltage reactive power control parameters when an AC voltage drop is detected. Simultaneously, the static synchronous condenser injects active power into the AC system based on the support power and support time of the energy storage unit. Based on the injected active power, the low-voltage current limiting control is used to update the DC current command of the converter. When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode.

[0023] The harmonic compensation module is used to utilize the harmonic compensation function of the converter in the static synchronous phase condenser to filter out harmonics of set characteristic orders.

[0024] The present invention also provides a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions; and the processor is used to operate according to the instructions to execute steps of the method.

[0025] The present invention also relates to a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method when the program is executed by a processor.

[0026] The present invention offers significant advantages over existing technologies, including replacing the traditional reactive power compensation device, passive filter, and phase condenser combination in a power station with a static synchronous condenser. This offers multiple advantages, including cost advantages, a small footprint, high reliability, and simplified operation and maintenance.

[0027] Static synchronous condensers, employing an MMC and DC-side direct-mounted supercapacitor topology, offer flexible inertia configuration and inertia support capabilities far exceeding those of large condensers. Through parameter adaptation, they can significantly outperform synchronous condensers in reactive power compensation capacity, response speed, and inertia support, making them particularly suitable for UHVDC converter stations.

[0028] For the first time, a step-down SSC is integrated on the AC side of a converter station, balancing voltage adaptation with power density optimization, reducing equipment size and cost. A commutation failure prevention algorithm based on DC current slope prediction, combined with rapid charge and discharge of the energy storage medium, reduces the probability of commutation failure by over 50%. The system is compatible with both conventional DC (LCC) and flexible DC (VSC) converter stations, supporting stable operation in weak grid conditions (SCR ≥ 1.5). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of a control method for a static synchronous condenser of a DC transmission converter station proposed by the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Static synchronous condensers are connected to the 500kV or 220kV busbar within the station via a connecting transformer, simplifying their implementation. They utilize power electronic converters to further integrate and coordinate control of the supercapacitor energy storage system with the grid control algorithm, enabling dynamic reactive power compensation, active power support, harmonic suppression, and fault ride-through capabilities. This significantly improves the stability of the DC transmission system and reduces the probability of commutation failure. Furthermore, the number of reactive power compensation devices and filter branches required in traditional DC stations is significantly reduced.

[0032] The static synchronous condenser (SSC) is a novel static VAR compensation device based on power electronics technology. It utilizes a grid-forming control strategy to autonomously establish its internal potential. By adjusting the amplitude and phase of its output voltage, it controls the voltage of the connected AC system and achieves active / reactive power interaction. During AC system fault transients, the SSC can simulate the rotor characteristics of the synchronous condenser to release energy stored in the accumulator valve, providing active inertia support for the AC system.

[0033] In the main circuit topology of a DC transmission converter station equipped with a static synchronous condenser, both the sending and receiving ends include, but are not limited to: a high-voltage DC transmission converter, a converter transformer, and a control system. The HVDC transmission converter is an LCC converter, whose AC-side port is connected to the three-phase output of the converter transformer. The static synchronous condenser is connected to the converter transformer's AC busbar via a connecting transformer. The DC transmission converter is a line-commutated converter (LCC) or a voltage-source converter (VSC), or a combination of the two. Typically, a DC transmission converter includes a sending end and a receiving end, each equipped with a corresponding number of static synchronous condensers based on inertia support requirements. Static synchronous condensers must have coordinated control capabilities for multiple units connected to the same line.

[0034] In this embodiment, a static synchronous condenser (SSC) is connected to the AC bus of a converter station via a step-down transformer. The SSC employs a grid-building strategy and control algorithm to autonomously generate internal electromotive force and maintain grid voltage and frequency stability. The SSC employs a three-phase full-bridge converter topology based on fully controlled semiconductor switching devices. The DC bus is connected to an energy storage carrier on the DC side. Its functions include providing dynamic reactive power and harmonic current compensation required by the converter through the fully controlled three-phase full-bridge converter, and transient active inertia support through the DC-side energy storage carrier. Fully controlled semiconductor switching devices include, but are not limited to, IGBTs and IGCTs; energy storage carriers on the DC bus include, but are not limited to, supercapacitors and energy storage batteries. This SSC replaces existing reactive power compensation, AC filtering, and SSC equipment within the converter station.

[0035] The present invention provides a system architecture for configuring a step-down energy storage static synchronous condenser (SSC) on the AC side of a converter station, comprising: a step-down transformer, a multi-level converter, an energy storage unit, and a coordination controller; the AC side of the multi-level converter is connected to the AC side of the converter station via the step-down transformer, and the DC side of the multi-level converter is connected to the energy storage unit;

[0036] The step-down transformer is used to reduce the AC bus voltage of the converter station to the operating voltage level of the static synchronous condenser, significantly reducing project implementation difficulty, equipment costs, and losses. In this embodiment, the step-down transformer for a 66kV, 300Mvar static synchronous condenser is a 525kV / 66kV, 300MVA connecting transformer. The step-down transformer has a three-fold current overload capacity, and the entire unit has a three-fold reactive overcurrent capability for 10 seconds and a three-fold active current overcurrent capability for 0.5 seconds. The static synchronous condenser's power devices are 4500V / 5000A IGBTs.

[0037] The multi-level converter adopts the MMC topology. The DC side of the multi-level converter is connected to the energy storage unit to achieve four-quadrant operation and independent regulation of active and reactive power, thereby improving the utilization rate of the energy storage unit.

[0038] The coordination controller is integrated into the main control system of the converter station and is used to collect parameters such as AC bus voltage, frequency, and power in real time, and dynamically adjust the output of the multi-level converter.

[0039] Configuration quantity: Based on the total active and reactive power requirements of the system, design the power of a single static synchronous phase condenser according to the optimal cost and minimum footprint, and calculate the number of devices required and the access location.

[0040] By adding a static synchronous phase condenser device to the AC power grid of the converter station to replace the passive filter and reactive power compensation device configured on the AC grid side of the traditional converter station, the commutation failure of the LCC DC system caused by the switching of the AC filter can be reduced, and the risks brought by the discrete mechanical characteristics of the filter switch can be eliminated.

[0041] The present invention proposes a control method for a static synchronous condenser of a DC transmission converter station. Figure 1 Shown, including:

[0042] Step 1: Obtain the reactive power exchange between the converter station and the power grid, and use the minimum reactive power exchange as the reactive power optimization index of the static synchronous condenser. Based on the reactive power optimization index, voltage reactive power control is adopted, with AC bus voltage stability as the control target, and the parameters of voltage reactive power control are set.

[0043] Specifically, in steady-state operation, the reactive power exchange between the converter station and the power grid is entirely provided by the static synchronous condenser. In an ideal state, the reactive power exchange between the converter station and the power grid is zero.

[0044] The voltage and reactive power control adopted includes but is not limited to: droop control, constant voltage control;

[0045] If the rate of change of the AC bus voltage within a unit sampling period is not greater than 2% and not less than -2%, the AC bus voltage is determined to be stable.

[0046] Step 2: Determine the support power of the energy storage unit according to the rated power of the converter station, and determine the support time according to the power change rate of the converter station and the support power of the energy storage unit;

[0047] To smooth power fluctuations, the energy storage unit in the static synchronous condenser is used to absorb or release active power to suppress power fluctuations at the converter station, such as DC power oscillations caused by wind power / photovoltaic fluctuations.

[0048] Energy storage units include: lithium battery energy storage, supercapacitor, and hybrid energy storage; energy storage units are used to provide short-term high-power support. The support power of the energy storage unit is no more than 60% of the rated power of the converter station, and the support time is no more than 1s.

[0049] Step 3: When an AC voltage drop is detected, the static synchronous condenser injects capacitive reactive power into the AC system based on the set voltage and reactive power control parameters. Simultaneously, based on the support power and support time of the energy storage unit, the static synchronous condenser injects active power into the AC system. Based on the injected active power, low-voltage current limiting control is used to update the DC current command of the converter.

[0050] When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode;

[0051] In the control method proposed by the present invention, when the AC voltage drops to 0.9pu, the AC voltage is increased to above the critical value by instantaneously injecting capacitive reactive power within 0.1 second. At the same time, by releasing the stored active power and coordinating with the low-voltage current limiting control, the DC current command value is reduced, thereby effectively preventing commutation failure. When an AC voltage short-circuit fault is detected, the static synchronous phase condenser switches to voltage source mode to provide virtual inertia and short-circuit current support to avoid converter station locking.

[0052] The control method proposed in the present invention can automatically respond to reactive power and inertia support when voltage or frequency fluctuations occur in the AC power grid due to an out-of-area fault, thereby reducing system deterioration and shortening fault recovery time.

[0053] Step 4: Using the harmonic compensation function of the converter in the static synchronous condenser, filter out harmonics of the set characteristic order;

[0054] The present invention uses the harmonic compensation function of the converter to actively filter out the characteristic subharmonics generated by the converter, which are 11 / 13 subharmonics in the embodiment, and reduce the total harmonic distortion rate on the AC side to below 3%.

[0055] The control method proposed in the present invention monitors the AC bus voltage, frequency and power parameters in real time, dynamically switches between steady-state voltage regulation, transient fault ride-through and harmonic control modes, and coordinates over-capacity charging and discharging and reactive power compensation functions.

[0056] Integrating a step-down SSC on the AC side of the converter station balances voltage adaptation and power density optimization, reducing equipment size and cost. Through coordinated control of the energy storage unit and the phase regulator, it achieves a "three-in-one" function: reactive power compensation, active power support, and harmonic control. This improves dynamic response efficiency and achieves a response time of less than 10ms. Compatible with both conventional DC (LCC) and flexible DC (VSC) converter stations, it supports stable operation in weak grid conditions (SCR ≥ 1.5).

[0057] A commutation failure prevention control strategy is also proposed, combined with rapid charging and discharging of energy storage media, to reduce the probability of commutation failure by more than 50%.

[0058] The capacity and key parameters of the static synchronous condenser are determined based on the actual project to meet the DC transmission converter's support performance for the AC power grid. The configuration parameter design method for the static synchronous condenser is as follows:

[0059] The main parameters of the static synchronous condenser, the number and location of the station configuration are confirmed by system simulation;

[0060] 1) The access voltage level of the static synchronous condenser is consistent with the low-voltage side voltage of the connected transformer.

[0061] 2) The steady-state reactive power of a static synchronous condenser is the reactive power required to support the commutation of the converter at the rated transmission power, which is generally 65% ​​of the rated active transmission power;

[0062] 3) Transient reactive power demand is the reactive power demand required to meet the AC grid in grid-building mode when a fault occurs in the receiving grid. The overload capacity of the static synchronous condenser itself must be considered. If the transient reactive power demand exceeds the device's inherent overload capacity, consider connecting multiple devices in parallel.

[0063] 3) After calculating the grid-building capability of the DC transmission converter, the active power of the static synchronous condenser P es is the total active power required under the grid characteristics minus the converter transmission power.

[0064] 4) Based on the supported power and support time of the energy storage unit, the capacitance and internal resistance of the overcapacity module, calculate the overcapacity cluster configuration DC voltage and overcapacity cluster starting output voltage of the overcapacity branch, and consider configuring an overcapacity redundant cluster to improve reliability.

[0065] The total DC bus current, the maximum DC current of a single branch overcapacity is 2500A, and multiple branches can be connected in parallel.

[0066] The equivalent circuit of the entire supercapacitive branch is a series circuit of an ideal capacitor and an ideal resistor. The capacitance of the capacitor is the equivalent capacitance value of the supercapacitors in series in all the supercapacitive branches under all the input states, and the resistance value of the resistor is the internal resistance value of the supercapacitors under all the input states.

[0067] The overcapacitor installation capacity needs to meet the following conditions: when the overcapacitor release energy > active energy requirement + overcapacitor internal resistance loss energy, it is the optimal overcapacitor configuration.

[0068] 5) The harmonic current compensation capability is based on the harmonic output content of the converter at maximum power, with a certain design margin retained.

[0069] 6) Calculate the output voltage requirement of the bridge arm valve based on the transformer impedance parameters, AC access voltage, DC side voltage, harmonic compensation current, bridge arm inductance, etc., and calculate the number of power units in each bridge arm based on the rated operating voltage of the power unit.

[0070] The present invention also proposes a control system for a static synchronous condenser of a DC transmission converter station, comprising:

[0071] Control parameter setting module, support parameter setting module, commutation failure prevention module, harmonic compensation module;

[0072] The control parameter setting module is used to obtain the reactive power exchange between the converter station and the power grid, with the minimum reactive power exchange amount as the reactive power optimization index of the static synchronous condenser. Based on the reactive power optimization index, voltage reactive power control is adopted, with AC bus voltage stability as the control target, to set the voltage reactive power control parameters.

[0073] A support parameter setting module is used to determine the support power of the energy storage unit according to the rated power of the converter station, and to determine the support time according to the power change rate of the converter station and the support power of the energy storage unit;

[0074] The commutation failure prevention module is used to inject capacitive reactive power into the AC system based on the set voltage reactive power control parameters when an AC voltage drop is detected. Simultaneously, the static synchronous condenser injects active power into the AC system based on the support power and support time of the energy storage unit. Based on the injected active power, the low-voltage current limiting control is used to update the DC current command of the converter. When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode.

[0075] The harmonic compensation module is used to utilize the harmonic compensation function of the converter in the static synchronous phase condenser to filter out harmonics of set characteristic orders.

[0076] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0077] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0078] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0079] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., utilizing an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions. The electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A control method for a static synchronous condenser of a DC transmission converter station, characterized in that: include: Obtain the reactive power exchange between the converter station and the power grid, and use the minimum reactive power exchange as the reactive power optimization index of the static synchronous condenser; Based on the reactive power optimization index, voltage reactive power control is adopted, with AC bus voltage stability as the control target, and the parameters of voltage reactive power control are adjusted; Determine the support power of the energy storage unit according to the rated power of the converter station, and determine the support time according to the power change rate of the converter station and the support power of the energy storage unit; When an AC voltage drop is detected, the static synchronous condenser injects capacitive reactive power into the AC system based on the set voltage reactive power control parameters. Simultaneously, based on the support power and support time of the energy storage unit, the static synchronous condenser injects active power into the AC system. Based on the injected active power, low-voltage current limiting control is used to update the DC current command of the converter. When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode. The harmonic compensation function of the converter in the static synchronous condenser is used to filter out harmonics of set characteristic orders.

2. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: Under steady-state operation, the reactive exchange between the converter station and the power grid is entirely provided by the static synchronous condenser. In an ideal state, the reactive exchange between the converter station and the power grid is 0.

3. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: The voltage reactive power control adopted includes: droop control and constant voltage control.

4. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: If the rate of change of the AC bus voltage within a unit sampling period is not greater than 2% and not less than -2%, the AC bus voltage is determined to be stable.

5. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: The supporting power of the energy storage unit shall not exceed 60% of the rated power of the converter station, and the supporting time shall not exceed 1s.

6. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: When the AC voltage drops to 0.9 pu, the static synchronous condenser injects capacitive reactive power within 0.1 seconds.

7. The control method of a static synchronous condenser of a DC transmission converter station according to claim 1, characterized in that: Characteristic subharmonics include 11th and 13th harmonics.

8. A control system for a static synchronous condenser in a DC transmission converter station, characterized in that: include: Control parameter setting module, support parameter setting module, commutation failure prevention module, harmonic compensation module; The control parameter setting module is used to obtain the reactive power exchange between the converter station and the power grid, with the minimum reactive power exchange amount being the reactive power optimization index of the static synchronous condenser. Based on the reactive power optimization index, voltage reactive power control is adopted, with AC bus voltage stability as the control target, and the parameters of voltage reactive power control are adjusted; A support parameter setting module is used to determine the support power of the energy storage unit according to the rated power of the converter station, and to determine the support time according to the power change rate of the converter station and the support power of the energy storage unit; The commutation failure prevention module is used to inject capacitive reactive power into the AC system based on the set voltage reactive power control parameters when an AC voltage drop is detected. Simultaneously, the static synchronous condenser injects active power into the AC system based on the support power and support time of the energy storage unit. Based on the injected active power, the low-voltage current limiting control is used to update the DC current command of the converter. When an AC voltage short-circuit fault is detected, the static synchronous condenser switches to voltage source mode. The harmonic compensation module is used to utilize the harmonic compensation function of the converter in the static synchronous phase condenser to filter out harmonics of set characteristic orders.

9. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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