Method and system for controlling static synchronous phase modifier of direct current transmission converter station

Abstract

According to the control method and system for the static synchronous phase modifier of the direct-current transmission converter station, the minimum reactive exchange capacity of the converter station and a power grid serves as a reactive optimization index, voltage reactive control is adopted, and voltage reactive control parameters are set with alternating-current bus voltage stabilization serving as a control target; determining the support power of the energy storage unit according to the rated power of the converter station, and determining the support time according to the power change rate of the converter station and the support power of the energy storage unit; when it is detected that the alternating current voltage drops, the static synchronous phase modifier injects capacitive reactive power and active power into the alternating current system based on the voltage reactive power control parameters and the supporting power and supporting time of the energy storage unit; based on the injected active power, low-voltage current limiting control is adopted, and a direct current instruction of the converter is updated; when an alternating-current voltage short-circuit fault is detected, the static synchronous phase modifier is switched to a voltage source mode; the harmonic compensation function of the converter is utilized to filter out harmonic waves with set characteristic times, thereby preventing commutation failure and improving adaptability of a weak AC power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of new power systems, and particularly relates to a control method and system for a static synchronous compensator configured in a DC transmission converter station. Background Art

[0002] UHV DC transmission (UHVDC) has the advantages of long-distance and large-capacity power transmission. However, its converter stations, especially the receiving-end converter stations, may cause voltage collapse due to insufficient reactive power support during grid faults. Traditional reactive power compensation devices, such as capacitors and reactors, have slow response speeds and cannot meet dynamic requirements. Moreover, according to the fault data statistics of DC projects in recent years, commutation failures caused by the switching of AC filters in the DC system account for about 5%, becoming the second largest cause after AC line faults. The discrete mechanical characteristics of filter switches make it difficult to completely eliminate the risk.

[0003] In the prior art, in order to alleviate voltage problems caused by AC and DC faults and DC commutation failures, etc., the large-capacity bidirectional reactive power regulation ability and dynamic reactive power output characteristics of the synchronous compensator are utilized to improve the support ability of the UHV DC grid and promote the development and safety and stability level of the UHV grid. The synchronous compensator has become a key solution due to its fast dynamic reactive power regulation ability. After configuring a large synchronous compensator at the converter station, taking the Changji-Guquan ±1100 kV DC transmission project as an example, the voltage fluctuation amplitude at the receiving end is reduced by more than 60%, and the commutation failure probability drops by about 40% - 50%. In addition, in the application of VSC-HVDC converter stations, in order to solve the problem of insufficient power receiving capacity of weak receiving-end grids and voltage fluctuations in the receiving-end grid caused by excessive DC line power, at the same time, the synchronous compensator is a rotating device and itself has the characteristics of a generator, and can provide a certain amount of inertia support ability when the grid frequency fluctuates, which is equivalent to increasing the short-circuit ratio of the grid.

[0004] However, large synchronous compensators still have their deficiencies, mainly in the following aspects: Different from traditional power plants, there is a lack of rotating power generation equipment in the converter station, and power electronic converters and their controllers are used as the main system. Large synchronous compensators use a rotating mechanical structure, with a high maintenance frequency and involving large-scale mechanical maintenance, resulting in high costs; the annual maintenance days are about 15 - 30 days, which is lower than the annual availability of power electronic equipment. The losses of the synchronous compensator are 1.5% - 2.5% under rated conditions and between 3% - 4% under light load, which are higher than those of power electronic equipment; at the same time, in terms of floor area, primary investment, operation and maintenance in the whole life cycle, etc., the economy of synchronous machines is relatively low. Summary of the Invention

[0005] To solve the deficiencies in the prior art, the present invention provides a control method and system for a static synchronous compensator configured in a DC transmission converter station, which makes full use of the functions of the static synchronous compensator to improve the operation reliability of the converter station, prevent commutation failures and improve the adaptability to weak AC grids.

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

[0007] The present invention provides a control method for a static synchronous compensator in a DC transmission converter station, including:

[0008] Obtain the reactive power exchange amount between the converter station and the power grid, and take the minimum reactive power exchange amount as the reactive power optimization index of the static synchronous compensator; based on the reactive power optimization index, adopt voltage-reactive power control, with the stable AC bus voltage as the control target, and set the parameters of the voltage-reactive power control;

[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 detecting an AC voltage dip, based on the set parameters of the voltage-reactive power control, the static synchronous compensator injects capacitive reactive power into the AC system, and at the same time, based on the support power and support time of the energy storage unit, the static synchronous compensator injects active power into the AC system; based on the injected active power, adopt low-voltage current limiting control to update the DC current command of the converter; when detecting an AC voltage short-circuit fault, the static synchronous compensator switches to the voltage source mode;

[0011] Utilize the harmonic compensation function of the converter in the static synchronous compensator to filter out harmonics of the set characteristic orders.

[0012] Under steady-state operation, all the reactive power exchange amount between the converter station and the power grid is provided by the static synchronous compensator, and the reactive power exchange amount between the converter station and the power grid is 0 under ideal conditions.

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

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

[0015] The support power of the energy storage unit is not greater than 60% of the rated power of the converter station, and the support time is not greater than 1 s.

[0016] When detecting that the AC voltage drops to 0.9 p.u., the static synchronous compensator injects capacitive reactive power within 0.1 second.

[0017] The characteristic harmonics include 11 / 13th harmonics.

[0018] The present invention also provides a control system for a static synchronous compensator in a DC transmission converter station, including:

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

[0020] The control parameter tuning module is used to obtain the reactive power exchange between the converter station and the power grid, and take the minimum reactive power exchange as the reactive power optimization index of the static synchronous compensator; based on the reactive power optimization index, voltage-reactive power control is adopted, with the stability of the AC bus voltage as the control target, and the parameters of the voltage-reactive power control are tuned.

[0021] The support parameter tuning module is used to 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;

[0022] The commutation failure prevention module is used to inject capacitive reactive power into the AC system by the static synchronous compensator based on the tuned parameters of the voltage-reactive power control when detecting an AC voltage dip, and at the same time inject active power into the AC system by the static synchronous compensator based on the support power and support time of the energy storage unit; based on the injected active power, low-voltage current limiting control is adopted to update the DC current command of the converter; when detecting an AC voltage short-circuit fault, the static synchronous compensator switches to the voltage source mode;

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

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

[0025] The present invention is also a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the method are implemented.

[0026] The beneficial effects of the present invention are at least as follows compared with the prior art: using a static synchronous compensator to replace the combination of a traditional reactive power compensation device + passive filter + synchronous compensator in the converter station. It has many beneficial benefits such as cost advantages, small floor area, high reliability, and simple operation and maintenance.

[0027] The static synchronous compensator adopting the MMC + DC-side directly-connected supercapacitor topology has the ability to flexibly configure the inertia capacity, and its inertia support ability is much greater than that of a large synchronous compensator. Through parameter adaptation, it can be completely superior to the synchronous compensator in terms of reactive power compensation capacity, response speed, inertia support ability, etc., and is more suitable for UHV DC transmission converter stations.

[0028] For the first time, a buck-type SSC is integrated on the AC side of the converter station, taking into account voltage adaptation and power density optimization, reducing the equipment volume and cost. A commutation failure prevention algorithm based on DC current slope prediction is proposed. Combining the fast charge and discharge of the energy storage medium, the probability of commutation failure is reduced by more than 50%. It is compatible with conventional DC (LCC) and flexible DC (VSC) converter stations and supports stable operation under weak grid conditions (SCR≥1.5). Brief Description of the Drawings

[0029] Figure 1 It is a flowchart of a control method for a static synchronous compensator of a DC transmission converter station proposed by the present invention. Detailed Embodiments

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0031] The static synchronous compensator is connected to the 500 kV or 220 kV bus in the station through a connecting transformer, which can reduce the engineering implementation difficulty of the static synchronous compensator. The static synchronous compensator uses a power electronic converter to increase the deep integration and coordinated control of the super-capacity energy storage system and the grid-forming control algorithm, realizing functions such as dynamic reactive power compensation, active power support, harmonic suppression and fault ride-through, significantly improving the stability of the DC transmission system and reducing the probability of commutation failure. On the other hand, the reactive power compensation device and the filter branch configured in the traditional DC station are greatly reduced.

[0032] The static synchronous compensator is a new type of static var compensator based on power electronic technology. The static synchronous compensator adopts a grid-forming control strategy, independently establishes an internal potential, and realizes the control of the voltage of the connected AC system and the active / reactive power interaction by adjusting the amplitude and phase of its output voltage. During the transient process of an AC system fault, the static synchronous compensator can also release the energy stored in the energy storage valve by simulating the rotor characteristics of a synchronous compensator to provide active inertia support for the AC system.

[0033] In the main circuit topology of a HVDC converter station equipped with a static synchronous compensator (STATCOM), both the sending end and the receiving end include, but are not limited to: a high-voltage DC converter, a converter transformer, and a control system. The high-voltage DC converter is an LCC converter, and the AC side port of the LCC converter is connected to the three phases of the converter transformer; the static synchronous compensator is connected to the AC bus of the converter transformer through a connection transformer; the DC converter is a line-commutated converter (LCC) or a voltage-source converter (VSC), or a combined converter device of the above two types of converters. Usually, the DC converter includes a sending end and a receiving end, and corresponding numbers of static synchronous compensators are configured at the sending and receiving ends according to the inertia support requirements. The static synchronous compensator needs to have the coordinated control function of multiple machines accessing the same line.

[0034] In the embodiment, a static synchronous compensator is connected through a step-down transformer on the AC bus side of the converter station. The static synchronous compensator adopts a grid-forming strategy and its control algorithm, and can independently establish an internal electromotive force and maintain the stability of the grid voltage and frequency. The static synchronous compensator adopts a three-phase full-bridge converter topology constructed based on fully controlled semiconductor switch devices, and a DC bus is led out from the DC side of the converter to connect to an energy storage carrier. 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 providing transient active inertia support through the energy storage carrier on the DC side, etc. The fully controlled semiconductor switch devices include, but are not limited to, IGBTs, IGCTs, etc.; the energy storage carriers on the DC bus side include, but are not limited to, supercapacitors, energy storage batteries, etc. It is used to replace the original reactive power compensation device, AC filtering device, and synchronous condenser device in the converter station.

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

[0036] Among them, 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 compensator, which can greatly reduce the engineering implementation difficulty, equipment cost, and loss. In the embodiment, for a 66 kV, 300 Mvar static synchronous compensator, the step-down transformer is selected as a 525 kV / 66 kV, 300 MVA connection transformer. The step-down transformer has an overload capacity of 3 times the current, and the whole machine has the ability of 3 times the reactive current overload for 10 s and 3 times the active current overload for 0.5 s. The power device of the static synchronous compensator is selected as 4500 V / 5000 A IGBT.

[0037] The multilevel converter adopts an MMC topology. The DC side of the multilevel converter is led out to connect to the energy storage unit, realizing four-quadrant operation and independent regulation of active power / reactive power, and improving the utilization rate of the energy storage unit.

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

[0039] Configuration quantity: According to the total active and reactive power demands of the system, design the power of a single static synchronous compensator according to the optimal cost and least floor area, and calculate the number of devices to be configured and the connection positions.

[0040] By adding a static synchronous compensator device to the AC power grid of the converter station, replacing the passive filter and reactive power compensation device configured on the AC network side of the traditional converter station, reduce the commutation failure caused by the switching of the AC filter in the LCC DC system, and eliminate the risk brought by the discreteness of the mechanical characteristics of the filter switch.

[0041] The present invention proposes a control method for a static synchronous compensator of a DC transmission converter station, as Figure 1 shown, including:

[0042] Step 1: Obtain the reactive power exchange amount between the converter station and the power grid, and take the minimum reactive power exchange amount as the reactive power optimization index of the static synchronous compensator; based on the reactive power optimization index, adopt voltage-reactive power control, with the stability of the AC bus voltage as the control target, and set the parameters of the voltage-reactive power control.

[0043] Specifically, under steady-state operation, all the reactive power exchange amount between the converter station and the power grid is provided by the static synchronous compensator. Ideally, the reactive power exchange amount between the converter station and the power grid is 0.

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

[0045] If the change rate of the AC bus voltage within a unit sampling period is not greater than 2% and not less than -2%, it is determined that the AC bus voltage is 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 achieve power fluctuation suppression, use the energy storage unit in the static synchronous compensator to absorb or release active power to suppress the power fluctuation of the converter station, such as the DC power oscillation caused by the fluctuation of wind power / solar power.

[0048] The energy storage unit includes: lithium battery energy storage, super capacitor, hybrid energy storage; the energy storage unit is used to provide short-term high-power support, and the support power of the energy storage unit is not greater than 60% of the rated power of the converter station, and the support time is not greater than 1 s.

[0049] Step 3: When an AC voltage drop is detected, based on the set voltage reactive power control parameters, the static synchronous condenser injects capacitive reactive power into the AC system. At the same time, 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 adopted to update the DC current instruction 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 in the present invention, when it is detected that the AC voltage drops to 0.9pu, the AC voltage is increased to above the critical value by injecting capacitive reactive power instantaneously in response 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 is switched to the voltage source mode to provide virtual inertia and short-circuit current support to avoid the converter station from being locked.

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

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

[0054] The present invention actively filters out characteristic subharmonics generated by the converter through the harmonic compensation function of the converter, which are 11 / 13 subharmonics in the embodiment, and reduces 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 the steady-state voltage regulation, transient fault ride-through and harmonic control modes, and coordinates the over-capacity charging and discharging and reactive power compensation functions.

[0056] Integrate step-down SSC on the AC side of the converter station, taking into account voltage adaptation and power density optimization, reducing equipment size and cost. Through the coordinated control of energy storage units and phase regulators, the "three-in-one" function of reactive power compensation, active power support, and harmonic control is realized, and the dynamic response efficiency is improved, with a response time of <10ms. Compatible with conventional DC (LCC) and flexible DC (VSC) converter stations, supporting stable operation under weak grid conditions (SCR≥1.5).

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

[0058] Determine the capacity and key parameters of the static synchronous compensator according to the actual engineering project to meet the grid-forming support performance of the DC transmission converter for the AC power grid. The design method of the configuration parameters of the static synchronous compensator is as follows:

[0059] The main parameters of the static synchronous compensator device, the number and location configured in the substation are confirmed by system simulation;

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

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

[0062] 3) The transient reactive power demand is to meet the reactive power demand of the AC power grid in the grid-forming mode when a fault occurs in the receiving-end power grid. The overload capacity of the static synchronous compensator itself needs to be considered. If the transient reactive power demand exceeds the overload capacity of the device itself, the parallel connection of multiple devices needs to be considered.

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

[0064] 4) According to the support power and support time of the energy storage unit, the capacitance value and internal resistance of the supercapacitor module, calculate the starting output voltage of the supercapacitor cluster configured for the supercapacitor branch, and consider configuring a supercapacitor redundant cluster to improve reliability.

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

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

[0067] The installed capacity of the supercapacitor needs to meet: when the energy that can be released by the supercapacitor > the active power demand energy + the energy loss of the supercapacitor internal resistance, it is the optimal supercapacitor configuration.

[0068] 5) The harmonic current compensation ability is compensated according to the harmonic output content of the converter at the maximum power, and a certain design margin is reserved.

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

[0070] The present invention also provides a control system for a static synchronous compensator in a HVDC converter station, including:

[0071] a control parameter setting module, a support parameter setting module, a commutation failure prevention module, and a harmonic compensation module;

[0072] The control parameter setting module is configured to obtain the reactive power exchange amount between the converter station and the power grid, and use the minimum reactive power exchange amount as the reactive power optimization index for the static synchronous compensator; based on the reactive power optimization index, voltage-reactive power control is adopted, with the stable AC bus voltage as the control target, and the parameters of the voltage-reactive power control are set.

[0073] The support parameter setting module is configured to 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.

[0074] The commutation failure prevention module is configured to, when detecting an AC voltage dip, based on the set parameters of the voltage-reactive power control, inject capacitive reactive power from the static synchronous compensator into the AC system, and at the same time, based on the support power and support time of the energy storage unit, inject active power from the static synchronous compensator into the AC system; based on the injected active power, low-voltage current limiting control is adopted to update the DC current command of the converter; when detecting an AC voltage short-circuit fault, the static synchronous compensator switches to the voltage source mode.

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

[0076] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer-readable storage medium having thereon 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 retain and store instructions for use by an instruction execution device. A computer-readable storage medium may 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 of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium 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 disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punched card or raised structures in grooves storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage medium used herein is not construed as being an instantaneous 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., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0078] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to respective computing / processing devices, or can be 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 may include a copper transmission cable, an optical fiber transmission, a wireless transmission, a router, a firewall, a switch, a gateway computer, and / or an edge server. A 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 for storage in a 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-related 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++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand-alone software package, partially on the user's computer and 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 through 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., via the Internet using an Internet service provider). In some embodiments, by using the state information of the computer-readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer-readable program instructions to implement 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 and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A control method for a static synchronous compensator in a DC transmission converter station, characterized in that, Including: Obtain the reactive power exchange between the converter station and the power grid, and take the minimum reactive power exchange as the reactive power optimization index of the static synchronous compensator; Based on the reactive power optimization index, adopt voltage and reactive power control, with the stability of the AC bus voltage as the control target, and set the parameters of the voltage and reactive power control; 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 dip is detected, based on the set parameters of the voltage and reactive power control, the static synchronous compensator injects capacitive reactive power into the AC system, and at the same time, based on the support power and support time of the energy storage unit, the static synchronous compensator injects active power into the AC system; Based on the injected active power, adopt low-voltage current limiting control to update the DC current command of the converter; When an AC voltage short-circuit fault is detected, the static synchronous compensator switches to the voltage source mode; Utilize the harmonic compensation function of the converter in the static synchronous compensator to filter out harmonics of the set characteristic orders.

2. The control method of the static synchronous compensator of the DC transmission converter station according to claim 1, characterized in that, Under steady-state operation, all the reactive power exchange between the converter station and the power grid is provided by the static synchronous compensator. Ideally, the reactive power exchange between the converter station and the power grid is 0.

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

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

5. The control method of the static synchronous compensator of the DC transmission converter station according to claim 1, characterized in that, The support power of the energy storage unit is not greater than 60% of the rated power of the converter station, and the support time is not greater than 1 s.

6. The control method of the static synchronous compensator of the DC transmission converter station according to claim 1, characterized in that, When it is detected that the AC voltage drops to 0.9 p.u., the static synchronous compensator injects capacitive reactive power within 0.1 second.

7. The control method of the static synchronous compensator of the DC transmission converter station according to claim 1, characterized in that, The characteristic harmonics include 11 / 13 harmonics.

8. A control system for a static synchronous compensator in a HVDC converter station, characterized in that, Including: 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, and take the minimum reactive power exchange as the reactive power optimization index of the static synchronous compensator; Based on the reactive power optimization index, adopt voltage and reactive power control, with the stability of the AC bus voltage as the control target, and set the parameters of the voltage and reactive power control; The 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 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 by the static synchronous compensator based on the set parameters of voltage and reactive power control when detecting an AC voltage dip, and at the same time inject active power into the AC system by the static synchronous compensator based on the support power and support time of the energy storage unit; based on the injected active power, adopt low-voltage current limiting control to update the DC current command of the converter; when detecting an AC voltage short-circuit fault, the static synchronous compensator switches to the voltage source mode; The harmonic compensation module is used to filter out harmonics of set characteristic orders by using the harmonic compensation function of the converter in the static synchronous compensator.

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

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

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