Offshore wind power low-frequency power transmission system test method and system

Abstract

The invention discloses an offshore wind power low-frequency power transmission system test method and system, belongs to the technical field of offshore wind power low-frequency power transmission, and realizes simulation of different operation conditions such as starting, steady-state operation and short-circuit fault of an offshore wind power low-frequency power transmission system. The method mainly comprises the following steps: 1) determining a primary system structure and parameters of an offshore wind power low-frequency power transmission system; 2) construction and programming of a control and protection secondary system of the offshore wind power low-frequency power transmission system; 3) building and debugging a complete primary system and a complete secondary system of the simulation model of the offshore wind power low-frequency power transmission control system; 4) establishing control logics such as system start control, short circuit fault, converter valve locking, circuit breaker tripping and reclosing; 5) testing the starting process of the operation system, performing steady-state operation, simulating the short-circuit fault of each region, and verifying the protection action characteristics; and 6) constructing a model data analysis module, outputting simulation data of the system under various operation conditions, and analyzing electrical characteristics of each operation condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-frequency power transmission, and more specifically, relates to a modeling and testing method of an offshore wind power low-frequency power transmission system simulation model based on M3C. Background Art

[0002] With the rapid development of renewable energy power generation, scenarios such as large-scale renewable energy clusters gathering and long-distance transmission have also emerged in large numbers. At present, there are three main ways to transmit renewable energy, represented by offshore wind power: industrial frequency AC transmission, flexible DC transmission, and flexible low-frequency transmission. Industrial frequency AC transmission is the most mature technology and is the main transmission method for offshore wind farms at home and abroad. However, the capacitance of submarine cables to the ground is relatively large, and the charging reactive power is large, which limits the transmission of active power and is suitable for scenarios with an offshore distance of less than 50 kilometers. There is no problem of cable charging reactive power in the offshore wind power transmission system through the flexible DC transmission system. It is the main way to transmit offshore wind power at home and abroad, but it requires the construction of offshore converter stations, which requires high investment and heavy operation and maintenance workload.

[0003] LFTS (Low-Frequency Transmission System) technology, also known as FFTS (Fractional Frequency Transmission System) technology, uses AC-AC frequency conversion devices to reduce 50Hz industrial frequency power to non-industrial frequency for transmission, or directly generates low-frequency power from renewable energy for transmission. Compared with traditional industrial frequency high-voltage AC transmission, offshore wind power LFTS reduces the line reactance by reducing the transmission frequency, and has more advantages than high-voltage AC transmission in increasing the line transmission capacity. Compared with flexible high-voltage DC transmission for offshore wind power transmission, LFTS does not require the construction of expensive and complex offshore converter stations, and is a competitive COSCO offshore wind power transmission solution. High-power offshore wind turbines mainly use direct-drive wind turbines. The converter can flexibly change the output frequency without changing the motor body. The control strategy, filter, and energy source of LFTS need to be low-frequency modified, but there is no technical difficulty and the cost is low.

[0004] In addition, the M3C (Modular Multilevel Matrix Converter) based on the full-bridge structure can be used in LFTS to directly realize AC-AC frequency conversion, and has the advantages of modular design, power decoupling on both sides of the industrial frequency and low frequency, controllable power factor, fast dynamic response and flexible power flow control.

[0005] At present, my country's first flexible low-frequency transmission demonstration project, the Taizhou 35kV flexible low-frequency transmission demonstration project, has been put into operation in Taizhou City, Zhejiang Province. In addition, the State Grid Jiangsu Electric Power Research Institute has cooperated with domestic wind power equipment manufacturing and operation companies, and plans to jointly build an offshore wind power low-frequency transmission test and verification platform in Dafeng, Yancheng with Jiangsu Goldwind Technology. However, the above engineering practices focus more on the technical verification of offshore wind farms through flexible low-frequency transmission. The scale of low-frequency wind power is relatively small, and the low-frequency voltage level is mainly 35kV and below. There is still a certain gap with the low-frequency high-voltage transmission scenario of future medium and long-distance million-kilowatt offshore wind power bases.

[0006] In order to simulate the million-kilowatt offshore wind power low-frequency AC transmission project based on M3C and provide a basis for studying the control strategy, fault characteristics and protection principles of the low-frequency AC transmission system, it is necessary to establish a detailed, accurate and close to the project offshore wind power low-frequency transmission system test model and provide its test method. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, based on the above-mentioned low-frequency transmission engineering background technology, the present invention provides an offshore wind power low-frequency transmission system test method and system based on M3C. By establishing an offshore wind power low-frequency transmission system simulation model, it is possible to simulate different operating conditions such as the startup process, steady-state operation, short-circuit fault and protection action of the offshore wind power low-frequency transmission project.

[0008] The present invention adopts the following technical solution.

[0009] A first aspect of the present invention provides a method for testing an offshore wind power low-frequency transmission system, comprising the following steps:

[0010] Obtaining the structure and parameters of a primary system of an offshore wind power low-frequency transmission system to be tested, wherein the offshore wind power low-frequency transmission system includes an M3C converter valve;

[0011] Build a secondary control and protection system model for offshore wind power low-frequency transmission systems;

[0012] Build the primary system model of the offshore wind power low-frequency transmission system and debug the primary and secondary systems of the complete offshore wind power low-frequency transmission system simulation model;

[0013] Build the start-up control, short-circuit fault, converter valve lockout, circuit breaker tripping and reclosing control logic of the offshore wind power low-frequency transmission system; add fault modules at different locations in the primary system model of the offshore wind power low-frequency transmission system, set short-circuit faults of different types and different transition resistances, and simulate short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system;

[0014] Construct a model data analysis model to output simulation data under various operating conditions of the offshore wind power low-frequency transmission system.

[0015] Preferably, the primary system structure of the offshore wind power low-frequency transmission to be tested that needs to be obtained includes: an offshore low-frequency wind power system with an operating frequency that is a set frequency lower than the industrial frequency, which passes through an offshore collection line, an offshore low-frequency step-up transformer and a low-frequency transmission line, and then passes through a low-frequency step-down transformer and an M3C converter valve to obtain industrial frequency 50Hz AC power, and finally passes through an industrial frequency step-up transformer and an industrial frequency transmission line in parallel with the industrial frequency main grid.

[0016] Preferably, the parameters of the offshore wind power low-frequency transmission primary system to be tested that need to be obtained are the parameters of the electrical equipment in the electrical main connection diagram provided according to the actual project site, including: offshore wind power, low-frequency collection lines, low-frequency step-up transformers, low-frequency transmission lines, low-frequency step-down transformers, M3C converter valves, industrial frequency step-up transformers, industrial frequency transmission lines and primary electrical equipment parameters of the industrial frequency power grid system.

[0017] Preferably, building a secondary control model for an offshore wind power low-frequency transmission system includes: building an offshore wind power control system and an M3C converter valve control system;

[0018] The offshore wind power control system includes: machine-side control and grid-side control. The machine-side control includes speed control, and the grid-side control includes decoupling control of active and reactive power and fault ride-through.

[0019] The M3C converter valve control system adopts a hierarchical control structure, including: system-level control, converter station-level control and converter valve-level control system.

[0020] Preferably, the system-level control converts the set values ​​of active and reactive physical quantities into reference values ​​for the lower-level control;

[0021] The converter station level control includes: voltage and current dual closed-loop vector control on the power frequency side and the low frequency side, circulating current suppression control, and capacitor voltage balancing control between submodules in the M3C bridge arm;

[0022] The converter valve level control system includes: IGBT submodule modulation and capacitor voltage balancing control of the M3C converter valve.

[0023] Preferably, the converter station-level control includes: controlling the power frequency negative sequence current injection in the dq rotating coordinate system with the goal of balancing the voltage of the bridge arm capacitors between phases of the M3C converter valve; and controlling the power frequency circulating current of the bridge arm with the goal of balancing the voltage of the parallel bridge arm capacitors within the phase of the M3C converter valve.

[0024] Preferably, the secondary protection system for the offshore wind power low-frequency transmission system includes: low-frequency wind power collection line protection, low-frequency busbar protection, low-frequency transformer protection, low-frequency transmission line protection, M3C body protection, power frequency transformer protection and power frequency transmission line protection.

[0025] Preferably, according to the control strategy and protection zoning configuration requirements of the offshore wind power low-frequency transmission system, the parameters of the offshore wind power control system and the M3C converter valve control system are determined, and the control and protection functions are realized by using library modules and custom modules, which are added to the control systems of the offshore wind power and the M3C converter valves respectively to realize the control and protection strategy of the offshore wind power low-frequency transmission system, thereby completing the construction of the low-frequency transmission control and protection secondary system.

[0026] Preferably, in step 3, a primary system model is established according to the determined primary system structure of the offshore wind power low-frequency transmission system and the parameters of each electrical equipment, and then connected with the offshore wind power low-frequency transmission control and protection secondary system model to establish a complete offshore wind power low-frequency transmission system simulation model.

[0027] Preferably, the start-up control process of the offshore wind power low-frequency transmission system is:

[0028] S1: Close the power frequency side circuit breaker, and each submodule of the M3C converter valve charges the DC capacitor through uncontrolled rectification;

[0029] S2: After the M3C converter valve uncontrolled charging DC capacitor voltage becomes stable, each submodule of the M3C converter valve enters the autonomous voltage-balanced charging state, continues to increase the capacitor voltage of each module, and maintains voltage balance;

[0030] S3: After the controllable charging of the M3C converter valve is completed and all submodules of the M3C converter valve are raised to the rated value, the converter station-level control system of the M3C converter valve unlocks the M3C converter valve and sends a PWM control signal to the converter valve IGBT device to control the DC side voltage of the module to the rated value;

[0031] S4: The M3C converter valve establishes a low-frequency AC voltage through the voltage outer loop VF control;

[0032] S5: Close the wind turbine low-frequency circuit breaker and start the wind turbine to connect to the grid for power generation.

[0033] Preferably, short-circuit fault modules are added inside and outside the low-frequency bus protection zone, outside the protection zone, the beginning, midpoint and end of the low-frequency collector line, low-frequency transmission line and power frequency transmission line, and outside, inside and between turns of the power frequency transformer and low-frequency transformer in the simulation model of the offshore wind power low-frequency transmission system, respectively, to simulate short-circuit faults of different positions, types or transition resistances of the low-frequency bus, power frequency or low-frequency line, power frequency or low-frequency transformer, as well as to simulate the lockout of the converter valve, protection action, circuit breaker tripping and reclosing during short-circuit faults.

[0034] Preferably, outputting simulation data under various operating conditions of the offshore wind power low-frequency transmission system includes: analyzing various short-circuit fault characteristics, performing electrical transient characteristics analysis, and verifying the control strategy, protection principle and algorithm of the offshore wind power low-frequency transmission system.

[0035] A second aspect of the present invention provides an offshore wind power low-frequency transmission system test system, which runs the offshore wind power low-frequency transmission system test method, including:

[0036] A data entry module, used to enter the structure and parameters of the primary system of the offshore wind power low-frequency transmission system to be tested into the offshore wind power low-frequency transmission system test system;

[0037] Secondary system modeling module, used to build the secondary control and protection system model of offshore wind power low-frequency transmission system;

[0038] System coordination module, used to build the primary system model of the offshore wind power low-frequency transmission system and debug the primary and secondary systems of the complete offshore wind power low-frequency transmission system simulation model;

[0039] The simulation logic module is used to build the start-up control, short-circuit fault, converter valve lock, circuit breaker tripping and reclosing control logic of the offshore wind power low-frequency transmission system; fault modules are added at different locations in the primary system model of the offshore wind power low-frequency transmission system, short-circuit faults of different types and different transition resistances are set, and short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system are simulated;

[0040] The data analysis module outputs simulation data of offshore wind power low-frequency transmission system under various operating conditions.

[0041] The third aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded into the processor, implements the offshore wind power low-frequency transmission system testing method.

[0042] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for testing an offshore wind power low-frequency transmission system is implemented.

[0043] Compared with the prior art, the beneficial effects of the present invention include at least: the offshore wind power low-frequency transmission system test method and system provided by the present invention can simulate the startup process and steady-state operation of an actual project, can simulate short-circuit faults of different types in different locations such as the system's power frequency or low-frequency transmission lines, power frequency or low-frequency transformer areas, and can also simulate the converter valve locking, protection action, circuit breaker tripping and reclosing during short-circuit faults. Through the waveform display and data export module, the simulation data under various operating conditions of the system are output, and the voltage, current, sequence component and differential current of each measuring point are analyzed. The characteristics under various operating conditions can be analyzed, which provides a basis for studying the control strategy, fault characteristics and protection principles of the offshore wind power low-frequency transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the structure of the offshore wind power low-frequency transmission system;

[0045] Figure 2 Schematic diagram of the test method steps for offshore wind power low-frequency transmission system. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0047] like Figure 2 As shown, embodiment 1 of the present invention provides a method for testing an offshore wind power low-frequency transmission system, comprising the following steps:

[0048] Step 1: Obtain the structure and parameters of the primary system of the offshore wind power low-frequency transmission system to be tested, wherein the offshore wind power low-frequency transmission system includes an M3C converter valve.

[0049] The primary system structure of the offshore wind power low-frequency transmission to be tested includes: an offshore low-frequency wind power system with an operating frequency of 20Hz or 50 / 3Hz, which passes through an offshore collector line, an offshore low-frequency step-up transformer and a low-frequency transmission line, and then passes through a low-frequency step-down transformer and an M3C converter valve to obtain an industrial frequency 50Hz AC power, and finally passes through an industrial frequency step-up transformer and an industrial frequency transmission line in parallel with the industrial frequency main grid. Among them, the M3C converter valve includes three phases and nine bridge arms. From the industrial frequency side and the low-frequency side, each phase of the M3C converter valve contains three bridge arms, and each bridge arm includes multiple full-bridge IGBT submodules and bridge arm inductors connected in series.

[0050] The parameters of the offshore wind power low-frequency transmission primary system that need to be obtained include: the parameters of the electrical equipment in the electrical main connection diagram provided according to the actual project site, mainly including: the primary equipment parameters of the offshore low-frequency wind power system, low-frequency collection line, low-frequency step-up transformer, low-frequency transmission line, low-frequency step-down transformer, M3C converter valve, power frequency step-up transformer, power frequency transmission line and power frequency power grid system.

[0051] In an exemplary but non-limiting embodiment of the present invention, Figure 1 As shown in the figure, it is a structural schematic diagram of the offshore wind power low-frequency transmission system. In the figure, the various parts of the offshore wind power low-frequency transmission system are divided into protection zones, namely: low-frequency wind power collection line protection, low-frequency busbar protection, low-frequency transformer protection, low-frequency transmission line protection, M3C body protection, power frequency transformer protection and power frequency transmission line protection.

[0052] Continue to see Figure 1 , the circuit structure diagram is the main circuit topology of the M3C-based offshore wind power low-frequency transmission system, in which the rated operating frequency of offshore wind power is low-frequency 20Hz, the single-machine power is 2MW, and the AC rated voltage is 690V. It is boosted to 35kV through a box-type Δ / Y step-up transformer, and then multiple low-frequency wind power is connected in parallel to the collector line; each collector line is gathered to form a low-frequency 35kV busbar, and then it is boosted from 35kV to 220kV through a low-frequency Y / Δ step-up transformer. It is stepped down to 60kV through a low-frequency transmission line and a low-frequency Y / Δ converter transformer, and then converted into industrial frequency 50Hz AC after passing through an M3C converter valve, and the voltage level remains unchanged; then it is boosted from 60kV to 220kV through an industrial frequency Δ / Y transformer. Finally, it is connected in parallel with the 220kV industrial frequency power grid through an industrial frequency transmission line.

[0053] Step 2: Construct a secondary control and protection system model for the offshore wind power low-frequency transmission system, that is, complete the construction and program writing of the secondary control and protection system for the offshore wind power low-frequency transmission system.

[0054] The offshore wind power low-frequency transmission secondary control system mainly includes: offshore wind power control system and M3C converter valve control system.

[0055] In a preferred but non-restrictive embodiment of the present invention, the offshore wind power control system is divided into machine-side control and grid-side control. The machine-side control mainly realizes speed control, and the grid-side control mainly realizes decoupling of active and reactive power, fault ride-through, etc.

[0056] In a preferred but non-limiting embodiment of the present invention, the M3C converter valve control system adopts a hierarchical control structure, including: system-level control, converter station-level control and converter valve-level control system. The system-level control converts the set values ​​of active and reactive physical quantities into reference values ​​for lower-level control, the converter station-level control is mainly the voltage and current double closed-loop vector control on the power frequency side and the low-frequency side, the circulating current suppression control and the capacitor voltage balancing control between the submodules in the M3C bridge arm, and the converter valve-level control system is mainly the IGBT submodule modulation and capacitor voltage balancing control of the M3C converter valve.

[0057] The construction and program writing process of the offshore wind power low-frequency transmission control and protection secondary system is as follows: According to the control strategy and protection zone configuration requirements of the offshore wind power low-frequency transmission system, the parameters of the offshore wind power control system and the M3C converter valve control system are determined, and the control and protection functions are realized by using library modules and custom modules formed by writing programs. They are added to the control and protection systems of offshore wind power and M3C converter valves respectively to realize the control and protection strategy of the offshore wind power low-frequency transmission system, thereby completing the construction of the low-frequency transmission control and protection secondary system.

[0058] It is worth noting that the basic module library in the current simulation tools contains many built-in modules, which can meet many basic requirements and functions and facilitate the establishment of basic simulation models. However, in actual use, there are still some functions that cannot be realized, especially the control strategy of M3C, whose internal calculation logic is relatively complex and the existing modules are difficult to meet the simulation requirements.

[0059] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, in order to realize the control strategy and protection configuration functional requirements of the above-mentioned offshore wind power low-frequency transmission system, the present invention determines the control strategy parameters and protection configuration parameters of the system, and forms custom modules by utilizing library modules and writing programs, which are added to the control system and protection system of the offshore wind power and M3C converter valve respectively, to realize the control and protection strategy of the offshore wind power low-frequency transmission system, thereby completing the construction of the low-frequency transmission control and protection secondary system.

[0060] The experimental control objectives are: under the symmetrical and asymmetrical system operation states, there is no industrial frequency current on the low-frequency side of the M3C converter valve, there is no low-frequency current on the industrial frequency side, and only non-industrial frequency power fluctuations are coupled inside the M3C converter valve.

[0061] In a further preferred but non-limiting embodiment, the converter station-level control includes: controlling the power frequency negative sequence current injection in the dq rotating coordinate system with the goal of balancing the voltage of the bridge arm capacitors between phases of the M3C converter valve; and controlling the power frequency circulating current of the bridge arm with the goal of balancing the voltage of the parallel bridge arm capacitors within the phase of the M3C converter valve.

[0062] More specifically, in the dq rotating coordinate system, the power frequency side controls the absorption of total active current injected into the M3C converter valve, that is, the total active power exchange between the M3C converter valve and the power frequency AC system, and controls the sum of the voltages of the 9 bridge arm capacitors; and then in the dq rotating coordinate system, the power frequency side controls the power frequency negative sequence current injected into the M3C converter valve to control the inter-phase balance of the sum of the voltages of the power module capacitors in the three bridge arms contained in each of the three phases; further, the power frequency circulating current is controlled to be zero in the three bridge arms of the three phases, and then the intra-phase balance of the sum of the power module capacitor voltages. Based on the control of the power frequency side, the voltages of the 9 bridge arm capacitors of the M3C converter valve are stabilized, the input current on the low frequency side and the low frequency circulating current on the bridge arm are avoided, and the power on the power frequency side and the low frequency side are decoupled and controlled.

[0063] The capacitor voltage balance of the power modules in the parallel bridge arms within the M3C converter valve phase is achieved through the nearest level approximation control. During the steady-state test, the converter valve loss is set to 0, the active power on the power frequency side and the low frequency side is balanced, and the reactive power is decoupled from each other.

[0064] The secondary protection system of offshore wind power low-frequency transmission mainly includes: low-frequency wind power collection line protection, low-frequency busbar protection, low-frequency transformer protection, low-frequency transmission line protection, M3C body protection, power frequency transformer protection and power frequency transmission line protection, etc. Among them, busbar protection is mainly differential protection, line protection mainly includes distance protection, differential protection, zero-sequence overcurrent protection, transformer protection mainly includes differential protection, low voltage protection, zero-sequence overcurrent protection, and M3C body protection mainly includes overvoltage protection and overcurrent protection.

[0065] Step 3: Build and commission the primary and secondary systems of the complete offshore wind power low-frequency transmission system.

[0066] According to the circuit structure of the offshore wind power low-frequency transmission system and the parameters of each electrical equipment determined in step 1, the primary system model of the main circuit is established, and then connected with the offshore wind power low-frequency transmission control and protection secondary system model completed in step 2 to establish a complete offshore wind power low-frequency transmission system.

[0067] Step 4: Build control logic for system startup control, fault interlocking, short-circuit fault, short-circuit fault tripping and reclosing, and test the system startup process, steady-state operation and short-circuit fault process.

[0068] It is worth noting that both the industrial frequency side and the low-frequency side of the M3C converter valve are AC. During the system startup process, directly closing the line switch for interconnection cannot be performed when the M3C converter valve is unlocked. Therefore, the amplitude, frequency and phase of the low-frequency side voltage must be controlled to meet the line switch closing conditions, which makes the control complexity of the system startup increase sharply.

[0069] To this end, in a preferred non-limiting embodiment of the present invention, the offshore wind power low-frequency transmission system startup control process used in the experiment is:

[0070] S1: Close the power frequency side circuit breaker, and each submodule of the M3C converter valve charges the DC capacitor through uncontrolled rectification. More specifically, the initialization system is started, and when the power supply of each submodule of the M3C converter valve is normal, close the power frequency side circuit breaker, and the M3C converter valve charges the DC capacitor through uncontrolled rectification until the voltage of each submodule of the M3C converter valve tends to be stable, and the uncontrolled charging of the M3C converter valve is completed.

[0071] S2: When the DC capacitor voltage of the M3C converter valve is stabilized after the uncontrolled charging is completed, each submodule of the M3C converter valve enters the autonomous voltage-equalizing charging state, continues to increase the capacitor voltage of each module, and maintains voltage balance; more specifically, at this time, the converter valve-level control system of the M3C converter valve starts active voltage-equalizing control, and at the same time reduces the number of submodules connected in series in the charging circuit, so that the voltage of all submodules of the M3C converter valve rises steadily and evenly, until all submodules of the M3C converter valve rise to the rated value, completing the controllable charging of the M3C converter valve.

[0072] S3: When the controllable charging of the M3C converter valve is completed and all submodules of the M3C converter valve are increased to the rated value, the converter station-level control system of the M3C converter valve unlocks the M3C converter valve, sends a PWM control signal to the converter valve switch device, and controls the DC side voltage of the module to the rated value.

[0073] S4: The M3C converter valve establishes a low-frequency AC voltage through the voltage outer loop VF control.

[0074] S5: Close the 35kV low-frequency circuit breaker of the wind turbine and start the wind turbine to connect to the grid for power generation.

[0075] In view of the possible faults that may occur in actual projects, short-circuit fault modules are added inside and outside the protection zone of the low-frequency busbar, low-frequency collector line, low-frequency transmission line, outside the protection zone, the beginning, midpoint and end of the power frequency transmission line, and outside, inside and between turns of the power frequency transformer and low-frequency transformer in the test model of the offshore wind power low-frequency transmission system to simulate short-circuit faults of different positions, types or transition resistances of the low-frequency busbar, power frequency or low-frequency transmission line, power frequency or low-frequency transformer, as well as the closure of the converter valve, protection action, circuit breaker tripping and reclosing during simulated short-circuit faults.

[0076] When one phase of the low-frequency transmission line is out of operation for some reason, the remaining healthy phase can still form a power transmission circuit, and the low-frequency transmission system switches to a two-phase operation mode.

[0077] In order to provide a theoretical basis for the protection principle and configuration of low-frequency transmission projects, on the basis of the previously constructed test model, control logics such as system startup control, fault interlocking, short-circuit fault, short-circuit fault tripping and reclosing are constructed, fault modules are added at different positions in the primary system model of the offshore wind power low-frequency transmission system, short-circuit faults of different types and different transition resistances are set, short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system are simulated, and the system startup process, steady-state operation and short-circuit fault process are tested. For example, but not limited to: when a phase line in the low-frequency transmission line is out of operation for some reason, the remaining healthy phases can still form a power transmission loop, and the low-frequency transmission system is switched to a two-phase operation mode, and the two-phase operation mode is tested with the test model. For another example, in the test model, the energy storage module is added to the M3C converter valve submodule to test the use of energy storage to support the M3C converter valve fault crossing. For another example, in the test model, the energy consumption device and the M3C converter station are coordinated and controlled.

[0078] Step 5: Construct a model data analysis model to observe and analyze electrical quantities such as voltage and current at each important measurement point.

[0079] In the offshore wind power low-frequency transmission system test model, in order to facilitate the observation and analysis of electrical quantities such as voltage and current at each important measurement point, voltage and current measurement modules, sequence component analysis modules, differential current calculation modules and power calculation modules are added to the offshore wind power low-frequency transmission system test model. The oscilloscope can be used for display, and the data can be exported through the data export module to analyze the three-phase voltage and current, sequence component and differential current of each measurement point. Various short-circuit fault characteristics can be analyzed, so as to facilitate the analysis of electrical transient characteristics and realize the control strategy, protection principle and algorithm of the offshore wind power low-frequency transmission system.

[0080] Embodiment 2 of the present invention provides an offshore wind power low-frequency transmission system test system, which runs an offshore wind power low-frequency transmission system test method as described in Embodiment 1, including:

[0081] A data entry module, used to enter the structure and parameters of the primary system of the offshore wind power low-frequency transmission system to be tested into the offshore wind power low-frequency transmission system test system;

[0082] Secondary system modeling module, used to build the secondary control and protection system model of offshore wind power low-frequency transmission system;

[0083] System coordination module, used to build the primary system model of the offshore wind power low-frequency transmission system and debug the primary and secondary systems of the complete offshore wind power low-frequency transmission system simulation model;

[0084] The simulation logic module is used to build the start-up control, short-circuit fault, converter valve lock, circuit breaker tripping and reclosing control logic of the offshore wind power low-frequency transmission system; fault modules are added at different locations in the primary system model of the offshore wind power low-frequency transmission system, short-circuit faults of different types and different transition resistances are set, and short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system are simulated;

[0085] The data analysis module outputs simulation data of offshore wind power low-frequency transmission system under various operating conditions.

[0086] Embodiment 3 of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is loaded into the processor, a method for testing an offshore wind power low-frequency transmission system according to Embodiment 1 is implemented.

[0087] Embodiment 4 of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for testing an offshore wind power low-frequency transmission system according to Embodiment 1 is implemented.

[0088] Compared with the prior art, the beneficial effects of the present invention include at least: the offshore wind power low-frequency transmission system test method and system provided by the present invention can simulate the startup process and steady-state operation of an actual project, can simulate short-circuit faults of different types in different locations such as the system's power frequency or low-frequency transmission lines, power frequency or low-frequency transformer areas, and can also simulate the converter valve locking, protection action, circuit breaker tripping and reclosing during short-circuit faults. Through the waveform display and data export module, the simulation data under various operating conditions of the system are output, and the voltage, current, sequence component and differential current of each measuring point are analyzed. The characteristics under various operating conditions can be analyzed, which provides a basis for studying the control strategy, fault characteristics and protection principles of the offshore wind power low-frequency transmission system.

[0089] 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 carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0090] 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 relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A test method for an offshore wind power low-frequency transmission system, characterized in that: The following steps are involved: Obtaining the structure and parameters of a primary system of an offshore wind power low-frequency transmission system to be tested, wherein the offshore wind power low-frequency transmission system includes an M3C converter valve; Build a secondary control and protection system model for offshore wind power low-frequency transmission systems; Build the primary system model of the offshore wind power low-frequency transmission system and debug the primary and secondary systems of the complete offshore wind power low-frequency transmission system simulation model; Build the start-up control, short-circuit fault, converter valve lockout, circuit breaker tripping and reclosing control logic of the offshore wind power low-frequency transmission system; add fault modules at different locations in the primary system model of the offshore wind power low-frequency transmission system, set short-circuit faults of different types and different transition resistances, and simulate short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system; Construct a model data analysis model to output simulation data under various operating conditions of the offshore wind power low-frequency transmission system.

2. A method for testing an offshore wind power low-frequency transmission system according to claim 1, characterized in that: The primary system structure of the offshore wind power low-frequency transmission to be tested that needs to be obtained includes: an offshore low-frequency wind power system with an operating frequency lower than the set frequency of the industrial frequency, which passes through an offshore collector line, an offshore low-frequency step-up transformer and a low-frequency transmission line, and then passes through a low-frequency step-down transformer and an M3C converter valve to obtain industrial frequency 50Hz AC power, and finally passes through an industrial frequency step-up transformer and an industrial frequency transmission line in parallel with the industrial frequency main grid.

3. A method for testing an offshore wind power low-frequency transmission system according to claim 1 or 2, characterized in that: The parameters of the offshore wind power low-frequency transmission primary system to be tested that need to be obtained are the parameters of the electrical equipment in the electrical main connection diagram provided according to the actual project site, including: offshore wind power, low-frequency collection lines, low-frequency step-up transformers, low-frequency transmission lines, low-frequency step-down transformers, M3C converter valves, power frequency step-up transformers, power frequency transmission lines and primary electrical equipment parameters of the power frequency grid system.

4. A method for testing an offshore wind power low-frequency transmission system according to claim 1, characterized in that: The secondary control model of the offshore wind power low-frequency transmission system includes: building an offshore wind power control system and an M3C converter valve control system; The offshore wind power control system includes: machine-side control and grid-side control. The machine-side control includes speed control, and the grid-side control includes decoupling control of active and reactive power and fault ride-through. The M3C converter valve control system adopts a hierarchical control structure, including: system-level control, converter station-level control and converter valve-level control system.

5. A method for testing an offshore wind power low-frequency transmission system according to claim 4, characterized in that: System-level control converts the set values ​​of active and reactive physical quantities into reference values ​​for lower-level control; The converter station level control includes: voltage and current dual closed-loop vector control on the power frequency side and the low frequency side, circulating current suppression control, and capacitor voltage balancing control between submodules in the M3C bridge arm; The converter valve level control system includes: IGBT submodule modulation and capacitor voltage balancing control of the M3C converter valve.

6. A method for testing an offshore wind power low-frequency transmission system according to claim 5, characterized in that: The converter station-level control includes: controlling the power frequency negative sequence current injection in the dq rotating coordinate system with the goal of balancing the voltage of the bridge arm capacitors between the phases of the M3C converter valve; and controlling the power frequency circulating current of the bridge arm with the goal of balancing the voltage of the parallel bridge arm capacitors within the phase of the M3C converter valve.

7. The offshore wind power low-frequency transmission system test method according to claim 1, characterized in that: The secondary protection system for the offshore wind power low-frequency transmission system includes: wind power collection line protection, low-frequency busbar protection, low-frequency transformer protection, low-frequency transmission line protection, M3C body protection, power frequency transformer protection and power frequency transmission line protection.

8. A method for testing an offshore wind power low-frequency transmission system according to any one of claims 1, 4 or 7, characterized in that: According to the control strategy and protection zoning configuration requirements of the offshore wind power low-frequency transmission system, the parameters of the offshore wind power control system and the M3C converter valve control system are determined. The control and protection functions are realized by using library modules and custom modules, which are added to the control systems of offshore wind power and M3C converter valves respectively to realize the control and protection strategy of the offshore wind power low-frequency transmission system, thereby completing the construction of the low-frequency transmission control and protection secondary system.

9. The offshore wind power low-frequency transmission system test method according to claim 1, characterized in that: In step 3, according to the determined primary system structure of the offshore wind power low-frequency transmission system and the parameters of each electrical equipment, a primary system model is established, and then connected with the offshore wind power low-frequency transmission control and protection secondary system model to establish a complete offshore wind power low-frequency transmission system simulation model.

10. A method for testing an offshore wind power low-frequency transmission system according to any one of claims 1, 4 or 7, characterized in that: The startup control process of the offshore wind power low-frequency transmission system is as follows: S1: Close the power frequency side circuit breaker, and each submodule of the M3C converter valve charges the DC capacitor through uncontrolled rectification; S2: After the M3C converter valve uncontrolled charging DC capacitor voltage becomes stable, each submodule of the M3C converter valve enters the autonomous voltage-balanced charging state, continues to increase the capacitor voltage of each module, and maintains voltage balance; S3: After the controllable charging of the M3C converter valve is completed and all submodules of the M3C converter valve are raised to the rated value, the converter station-level control system of the M3C converter valve unlocks the M3C converter valve and sends a PWM control signal to the converter valve IGBT device to control the DC side voltage of the module to the rated value; S4: The M3C converter valve establishes a low-frequency AC voltage through the voltage outer loop VF control; S5: Close the wind turbine low-frequency circuit breaker and start the wind turbine to connect to the grid for power generation.

11. A method for testing an offshore wind power low-frequency transmission system according to any one of claims 1, 4 or 7, characterized in that: Short-circuit fault modules are added inside and outside the low-frequency bus protection zone, outside the protection zone, the beginning, midpoint and end of the low-frequency collector line, low-frequency transmission line and power frequency transmission line, and outside, inside and between turns of the power frequency transformer and low-frequency transformer in the simulation model of the offshore wind power low-frequency transmission system to simulate short-circuit faults of different positions, types or transition resistances of the low-frequency bus, power frequency or low-frequency line, power frequency or low-frequency transformer, as well as the converter valve locking, protection action, circuit breaker tripping and reclosing during short-circuit faults.

12. A method for testing an offshore wind power low-frequency transmission system according to any one of claims 1, 4 or 7, characterized in that: Output simulation data of offshore wind power low-frequency transmission system under various operating conditions, including: analysis of various short-circuit fault characteristics, electrical transient characteristics analysis, and verification of offshore wind power low-frequency transmission system control strategy, protection principle and algorithm.

13. An offshore wind power low-frequency transmission system test system, running an offshore wind power low-frequency transmission system test method according to any one of claims 1 to 12, characterized in that: include: A data entry module, used to enter the structure and parameters of the primary system of the offshore wind power low-frequency transmission system to be tested into the offshore wind power low-frequency transmission system test system; Secondary system modeling module, used to build the secondary control and protection system model of offshore wind power low-frequency transmission system; System coordination module, used to build the primary system model of the offshore wind power low-frequency transmission system and debug the primary and secondary systems of the complete offshore wind power low-frequency transmission system simulation model; The simulation logic module is used to build the start-up control, short-circuit fault, converter valve lock, circuit breaker tripping and reclosing control logic of the offshore wind power low-frequency transmission system; fault modules are added at different locations in the primary system model of the offshore wind power low-frequency transmission system, short-circuit faults of different types and different transition resistances are set, and short-circuit faults and protection actions in various areas of the offshore wind power low-frequency transmission system are simulated; The data analysis module outputs simulation data of offshore wind power low-frequency transmission system under various operating conditions.

14. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the computer program is loaded into a processor, an offshore wind power low-frequency transmission system testing method according to any one of claims 1 to 12 is implemented.

15. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, an offshore wind power low-frequency transmission system testing method according to any one of claims 1 to 12 is implemented.

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