Wind power plant black start system and black start method

Abstract

The invention discloses a wind power plant black start system and a black start method, the wind power plant black start system comprises a wind power plant and an energy storage system, the wind power plant comprises m net-forming type fans and n net-following type fans mgt; n is greater than or equal to 0, and the configuration of the net-forming type fan is not less than 5% of the capacity of the wind power plant; all fans of the wind power plant form a cluster and then are connected with an external alternating-current power grid through a booster station; and the energy storage system is configured inside and / or outside the wind power plant. According to the technical scheme, the requirement of rapid black start of a large wind power plant for energy storage system configuration can be reduced, and voltage construction support is provided for large power grid start.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation, and specifically relates to a black start system and black start method for wind farms. Background Technology

[0002] As the penetration rate of new energy sources continues to increase, their impact on the stable operation of the power grid is also growing, especially in the event of a complete grid blackout, when the auxiliary system of wind turbines cannot start without external power supply. If external energy storage is configured, traditional wind turbine converter grid-connected control requires large-capacity energy storage to maintain the grid voltage at the wind farm. Furthermore, wind farms with grid-connected control cannot provide voltage support for blackout startup of the external power grid, which requires improvement. Summary of the Invention

[0003] The purpose of this invention is to provide a black start system and method for wind farms, which can reduce the requirements for energy storage system configuration for rapid black start of large wind farms and provide voltage construction support for the start-up of large power grids.

[0004] To achieve the above objectives, the solution of the present invention is:

[0005] A black start method for wind farms, comprising,

[0006] Activate the energy storage system to establish the AC power grid of the wind farm; wherein the energy storage system is configured inside and / or outside the wind farm;

[0007] A black start is performed on N1 grid-connected wind turbines to establish an off-grid AC voltage and connect them to the wind farm's AC power grid; wherein the power required for the auxiliary system startup process of the N1 grid-connected wind turbines is not higher than the available output of the energy storage system;

[0008] Start N2,…,N in sequence (black start) m For grid-connected wind turbines, establish off-grid AC voltage and connect them to the wind farm's AC power grid until the predetermined number of grid-connected wind turbines that have undergone black-start operation is reached, m = 2, 3, ...; where N... m The power required for the auxiliary system startup process of the grid-type wind turbine is no higher than the available output of the energy storage system at this time and the power of N1,…,N already black-started. m-1 The sum of the usable output of the platform-type wind turbine.

[0009] Once a predetermined number of grid-connected wind turbines that have already been black-started have been reached, all remaining grid-connected wind turbines in the wind farm will be started; wherein, the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

[0010] Once the predetermined number of grid-connected wind turbines that have already been black-started have been reached, all grid-connected wind turbines in the wind farm will be started. Grid-connected wind turbines are located within the wind farm. The predetermined number is equal to the total number of grid-connected wind turbines in the wind farm.

[0011] Once the predetermined number of grid-connected wind turbines that have already been black-started has been reached, all remaining grid-connected wind turbines and all grid-following wind turbines in the wind farm will be started; wherein, the grid-following wind turbines are configured in the wind farm; the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

[0012] Among them, black-start grid-type wind turbines include...

[0013] The auxiliary system of the grid-type wind turbine, which is waiting for black start, draws energy from the AC grid of the wind farm to drive the grid-type wind turbine to accelerate to a predetermined speed and generate off-grid AC voltage.

[0014] A virtual impedance is applied to synchronize the phase and frequency of the off-grid AC voltage with the phase and frequency of the AC grid voltage of the wind farm.

[0015] The off-grid AC voltage is connected to the AC grid of the wind farm. After the voltage and current stabilize, the virtual impedance is removed, and the black start of the grid-connected wind turbine is completed.

[0016] The virtual impedance input includes detecting the AC current value of the grid-connected wind turbine connected to the wind farm's AC grid, multiplying the current value by a pre-set impedance, and then superimposing it onto the voltage reference wave.

[0017] A black start system for wind farms, comprising,

[0018] An energy storage system startup device is configured to start the energy storage system and establish an AC power grid for the wind farm; wherein the energy storage system is located inside and / or outside the wind farm; and,

[0019] A black start device for grid-connected wind turbines is configured to sequentially black start the grid-connected wind turbines in a wind farm; wherein the grid-connected wind turbines are black started in the following order:

[0020] A black start is performed on N1 grid-connected wind turbines to establish an off-grid AC voltage and connect them to the wind farm's AC power grid; wherein the power required for the auxiliary system startup process of the N1 grid-connected wind turbines is not higher than the available output of the energy storage system;

[0021] Start N2,…,N in sequence (black start) m For grid-connected wind turbines, establish off-grid AC voltage and connect them to the wind farm's AC power grid until the predetermined number of grid-connected wind turbines that have undergone black-start operation is reached, m = 2, 3, ...; where N... m The power required for the auxiliary system startup process of the grid-type wind turbine is no higher than the available output of the energy storage system at this time and the power of N1,…,N already black-started.m-1 The sum of the usable output of the platform-type wind turbine.

[0022] The wind farm black start system also includes,

[0023] The first wind turbine starting device is configured to start all remaining grid-type wind turbines in the wind farm after a predetermined number of grid-type wind turbines that have already been black-started have been started; wherein the predetermined number is less than the total number of grid-type wind turbines in the wind farm.

[0024] The wind farm black start system also includes,

[0025] The second wind turbine starting device, after a predetermined number of grid-connected wind turbines that have already been black-started are configured, starts all grid-connected wind turbines in the wind farm; wherein, the grid-connected wind turbines are configured in the wind farm; the predetermined number is equal to the total number of grid-connected wind turbines in the wind farm.

[0026] The wind farm black start system also includes,

[0027] The third wind turbine starting device, after the number of grid-connected wind turbines that have been black-started reaches a predetermined number, starts all remaining grid-connected wind turbines and all grid-following wind turbines in the wind farm; wherein, the grid-following wind turbines are configured in the wind farm; the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

[0028] The aforementioned black start device for grid-type wind turbines is configured for black start grid-type wind turbines, including,

[0029] The auxiliary system control module is configured to control the auxiliary system of the grid-connected wind turbine awaiting black start to draw energy from the AC grid of the wind farm, drive the grid-connected wind turbine to accelerate to a predetermined speed, and generate off-grid AC voltage; and

[0030] The synchronization module is configured to synchronize the phase and frequency of the off-grid AC voltage with the phase and frequency of the AC grid voltage of the wind farm by applying a virtual impedance, and to remove the virtual impedance after the voltage and current stabilize.

[0031] The aforementioned synchronization module employs virtual impedance, including detecting the AC current value of the grid-connected wind turbine connected to the wind farm's AC grid, multiplying the current value by a pre-set impedance, and then superimposing it onto the voltage reference wave.

[0032] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor; the processor executes the computer program to implement the steps of the wind farm black start method as described above.

[0033] A computer-readable storage medium storing a computer program; when executed by a processor, the computer program implements the steps of the wind farm black-start method as described above.

[0034] The wind farm black start system provided by this invention, using the above scheme, includes a wind farm and an energy storage system. The wind farm contains several grid-connected wind turbines. The energy storage system first establishes the AC voltage of the wind farm, supplying power to the auxiliary systems of the first batch of grid-connected wind turbines to achieve black start. Then, the off-grid AC voltage of the started grid-connected wind turbines is connected to the wind farm voltage to continue supplying power to the auxiliary systems of the next batch of grid-connected wind turbines, achieving black start for that batch of grid-connected wind turbines, until the entire wind farm completes its black start. This invention, by using an energy storage system to first start the first batch of wind turbines to participate in grid connection, and then continuously starting larger batches of wind turbines to connect to the grid, achieves rapid black start of a large wind farm driven by a small-capacity energy storage system. This reduces the requirements for energy storage system configuration for rapid black start of large wind farms and can provide voltage construction support for the startup of large power grids. Attached Figure Description

[0035] Figure 1 This is an architectural diagram of the wind farm black start system of the present invention;

[0036] Figure 2 This is a schematic diagram of the grid-connected converter principle in this invention. Detailed Implementation

[0037] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] The wind farm black start system implemented in this invention includes a wind farm and an energy storage system. The wind farm comprises at least a number of grid-connected wind turbines and may also include a number of follow-up grid-connected wind turbines, with the grid-connected wind turbines accounting for no less than 5% of the wind farm's capacity. After all the wind turbines in the wind farm form a cluster, they are connected to the external AC power grid via a step-up substation. (See reference...) Figure 1 As shown; the energy storage system can be configured inside the wind farm, using a centralized or decentralized energy storage configuration, or it can be configured outside the wind farm, or even both inside and outside the wind farm. Figure 1 The diagram shows the structure of a wind farm with energy storage systems both inside and outside.

[0039] This invention also provides a black start method for wind farms, including:

[0040] The energy storage system is activated to charge the wind farm circuits and establish the wind farm's AC power grid; wherein the output of the energy storage system is P. enstrg0 ;

[0041] Black-start N1 grid-connected wind turbines establish off-grid voltage and connect to the wind farm's AC power grid, with the following:

[0042]

[0043] Among them, P narg The power requirements during the startup process of the auxiliary system for a single grid-type wind turbine awaiting black start;

[0044] Start N2,…,N in sequence (black start) m For grid-connected wind turbines, an off-grid AC voltage is established and connected to the wind farm's AC power grid until a predetermined number of grid-connected wind turbines that have undergone black-start are reached, m = 2, 3, ...; Specifically, in this embodiment, the sum of the available output P of the N1 grid-connected wind turbines that have undergone black-start at this time is evaluated. stw1 And at this time, the available output P of the energy storage system enstrg1 Among them, the available output P of the energy storage system is evaluated. enstrg1 This includes, if the energy storage system shuts down or ceases operation and no further operation is required, then P... enstrg1 =0, if the energy storage system needs to absorb energy, then P enstrg1 <0;

[0045] Continue to start the N2 grid-connected wind turbines, establish off-grid AC voltage and connect them to the wind farm's AC power grid. Then:

[0046]

[0047] Among them, P narg The power requirements during the startup process of the auxiliary system for a single grid-type wind turbine awaiting black start;

[0048] Determine whether the predetermined number of grid-connected wind turbines that have already undergone black-start has been reached. If so, the wind farm can be considered to have completed black-start; if not, assess the sum of the available output P of the N1+N2 grid-connected wind turbines that have already undergone black-start. stw2 And at this time, the available output P of the energy storage system enstrg2 And continue to black-start N3 grid-type wind turbines, and make

[0049]

[0050] The system then checks again whether the number of grid-connected wind turbines that have been black-started has reached the predetermined number. If not, it black-starts the grid-connected wind turbines again, and repeats this process until the predetermined number of grid-connected wind turbines have all been black-started, at which point the grid-connected wind turbines are connected to the wind farm's AC power grid.

[0051] Among them, the black start of grid-type wind turbines includes,

[0052] The auxiliary system of the grid-type wind turbine, which is waiting for black start, draws energy from the AC grid of the wind farm to drive the grid-type wind turbine to accelerate to a predetermined speed and generate off-grid AC voltage.

[0053] A virtual impedance is applied to synchronize the phase and frequency of the off-grid AC voltage with the phase and frequency of the AC grid voltage of the wind farm; wherein, applying the virtual impedance includes detecting the AC current value of the grid-connected wind turbine connected to the AC grid of the wind farm, multiplying the current value by a pre-set impedance and then superimposing it onto the voltage reference wave;

[0054] The off-grid AC voltage is connected to the AC grid of the wind farm. After the voltage and current stabilize, the virtual impedance is removed, and the black start of the grid-connected wind turbine is completed.

[0055] In a preferred embodiment of the present invention, if all the wind turbines in the wind farm are grid-type wind turbines, then when the predetermined number is less than the total number of all grid-type wind turbines in the wind farm, the remaining grid-type wind turbines in the wind farm will be started after the predetermined number of grid-type wind turbines have all been started.

[0056] In another preferred embodiment of the present invention, if the wind farm includes both grid-connected and grid-fed wind turbines in addition to grid-connected turbines, then when the predetermined number equals the total number of grid-connected turbines in the wind farm, after the predetermined number of grid-connected turbines have all been started, all grid-fed turbines in the wind farm will be started.

[0057] In another preferred embodiment of the present invention, if the wind farm includes grid-connected wind turbines in addition to grid-connected wind turbines, then when the predetermined number is less than the total number of grid-connected wind turbines in the wind farm, after the predetermined number of grid-connected wind turbines have all been started, the remaining grid-connected wind turbines and all grid-connected wind turbines in the wind farm will be started.

[0058] An embodiment of the present invention provides a wind farm black start system, such as Figure 1 As shown, in a completely dark grid environment, the electrical energy required for wind turbine startup to perform operations such as yaw and pitch control must come from an external power source. Therefore, black start requires a corresponding energy storage system, which can be internal to the wind farm or an external energy storage station. Internal energy storage systems within the wind farm can include centralized or distributed energy storage configurations.

[0059] In this embodiment, it is assumed that the wind farm has a scale of 1000MW, the capacity of a single wind turbine is 4MW, and the wind farm has a total of 250 wind turbines, including 200 grid-type wind turbines and 50 follow-the-grid type wind turbines.

[0060] The present invention provides a black start method for wind farms, the specific steps of which are as follows:

[0061] Step 1: The energy storage system first establishes an AC grid connection with the wind farm and assesses the available output power of the energy storage at this time as P. enstrg0 In this embodiment, the energy storage system can output 10MW.

[0062] Step 2: Black start of N1 grid-connected wind turbine, establishing off-grid AC voltage and connecting to the wind farm's AC grid, and having

[0063]

[0064] Among them, P narg The power requirements of the auxiliary system during the startup process of a single standby blackout fan;

[0065] In this embodiment, P narg The demand is 1MW, so this batch can start 10 grid-type wind turbines;

[0066] Step 3: Evaluate the sum of available output P of the first batch of black-start grid-type wind turbines. stw1 And at this time, the available output power of the energy storage system is P. enstrg1 ;

[0067] In this embodiment, P enstrg1 Still 10MW, single wind turbine P narg The demand is 1MW, and each grid-connected wind turbine can output 1MW, therefore P stw1 =10 * 1MW = 10MW;

[0068] Step 4: Start up two black-start grid-connected wind turbines (N2 units), establish off-grid AC voltage and connect them to the wind farm's AC power grid, and ensure...

[0069]

[0070] Among them, P narg The power requirements of the auxiliary system during the startup process of a single standby blackout fan;

[0071] In this embodiment, 20 grid-type wind turbines can be started in this batch;

[0072] Step 5: Repeat steps 3 and 4 until all grid-connected wind turbines or the predetermined number of grid-connected wind turbines have been started and connected to the wind farm's AC power grid;

[0073] Step 6: Start the remaining wind turbines in the wind farm that are yet to be started;

[0074] In this embodiment, the startup details of each batch of wind turbines are shown in the table below. The entire wind farm was started up in just 6 batches:

[0075] Table 1

[0076] batch Number of wind turbines in the current batch Total number of fans already started 1 10 units network 10 units 2 10 + 10 = 20 units to form a network 30 units 3 10 + 30 = 40 units to form a network 70 units 4 10 + 70 = 80 units to form a network 150 units 5 50 units network 200 units 6 50 units and network 250 units

[0077] In this embodiment, if the energy storage system is only used for the startup of the first batch of wind turbines, that is, from the second batch onwards P enstrg2 =0, then the details of each batch of wind turbine startup are shown in the table below. Only 7 batches were needed to complete the startup of the entire wind farm:

[0078] Table 2

[0079] batch Number of wind turbines in the current batch Total number of fans already started 1 10 units network 10 units 2 0 + 10 = 10 units to form a network 20 units 3 0 + 20 = 20 units to form a network 40 units 4 0 + 40 = 40 units to form a network 80 units 5 0 + 80 = 80 units to form a network 160 units 6 40 units network 200 units 7 50 units and network 250 units

[0080] In this embodiment, P can be allowed enstrg1 <0 indicates that the energy storage system also draws power from the wind farm.

[0081] The embodiments of the present invention can be adopted Figure 2 The wind turbine converter system shown enables black start of grid-connected wind turbines. It includes a turbine-side converter connected to the wind turbine and a grid-side converter connected to the AC grid of the wind farm. The turbine-side converter is responsible for establishing the DC voltage of the converter system. After establishing the DC voltage on the turbine side, the grid-side converter has the ability to establish off-grid voltage and provide grid support.

[0082] The generator-side converter control consists of inner and outer loop control. The outer loop control is a DC voltage control. The difference between the measured DC voltage value and the DC voltage command value of the converter is controlled by a PI controller to output the stator current command of the fan. The inner loop control adopts rotor position-oriented vector control. The stator current control command output by the outer loop control and the stator current are controlled by a PI controller, and the stator current dq decoupling term is superimposed to output a reference wave.

[0083] The grid-side converter control consists of inner and outer loop control. The outer loop control generates AC voltage command values ​​and phase angles based on power droop control or virtual synchronization control. The inner loop control is a voltage and current dual closed-loop control using directional vector control. This inner loop control can be a direct control without sequence decomposition, or it can be a voltage and current dual closed-loop control based on positive and negative sequence currents respectively.

[0084] During the black start process of a wind farm, the start-up method for a single grid-connected wind turbine is as follows:

[0085] Step a: Keep the grid-side AC switch of the generator-side converter open;

[0086] Step b: The wind turbine auxiliary system draws energy from the wind farm's AC grid and starts the wind turbine pitch control to drive the wind turbine to accelerate to the predetermined speed;

[0087] Step c: Unlock the machine-side converter and establish the converter DC voltage;

[0088] Step d: Start the grid-side converter to establish the grid-side AC grid voltage (off-grid AC voltage);

[0089] Step e: Pre-synchronize the grid phase and apply virtual impedance;

[0090] The phase pre-synchronization method in this embodiment is as follows:

[0091] The AC voltage on both sides of the grid-side converter switch is detected, and the frequency and phase of the grid-side voltage of the switch are measured; the frequency and phase of the AC voltage of the grid-side converter are synchronized with the frequency and phase of the grid-side voltage of the switch.

[0092] The method for introducing virtual impedance in this embodiment is as follows:

[0093] The AC current value of the motor passing through the AC grid of the wind farm connected to the grid-side converter is detected, and this current value is multiplied by a pre-set impedance and then superimposed onto the voltage reference wave.

[0094] Step f: Close the switch and, after the voltage and current stabilize, exit the virtual impedance, and the wind turbine participates in the construction of the wind farm grid.

[0095] This invention also provides another computer device, including a processor and a memory configured to store a computer program capable of running on the processor; wherein, when the processor is configured to run the computer program, it executes the method steps of the wind farm black start method in the foregoing embodiments.

[0096] In practical applications, the aforementioned processor includes a Field-Programmable Gate Array (FPGA), and the processor can be a Central Processing Unit (CPU) or a Digital Signal Processor (DSP). It is understood that for different devices, the electronic devices used to implement the functions of the aforementioned processor can also be other types, and this embodiment of the invention does not impose specific limitations.

[0097] The aforementioned memory can be volatile memory, such as random-access memory (RAM); or non-volatile memory, such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid-state drive (SSD); or a combination of the above types of memory, and provides instructions and data to the processor.

[0098] In an exemplary embodiment, the present invention also provides a computer-readable storage medium for storing a computer program.

[0099] Optionally, the computer-readable storage medium can be applied to any of the methods in the embodiments of the present invention, and the computer program causes the computer to execute the corresponding processes implemented by the processor in the various methods of the embodiments of the present invention. For the sake of brevity, these will not be described in detail here.

[0100] In the several embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0101] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0102] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0103] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0104] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0105] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0106] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A black start method for wind farms, characterized in that: include, Activate the energy storage system to establish the AC power grid of the wind farm; wherein the energy storage system is configured inside and / or outside the wind farm; A black start is performed on N1 grid-connected wind turbines to establish an off-grid AC voltage and connect them to the wind farm's AC power grid; wherein the power required for the auxiliary system startup process of the N1 grid-connected wind turbines is not higher than the available output of the energy storage system; Start N2,…,N in sequence (black) m For grid-connected wind turbines, establish off-grid AC voltage and connect them to the wind farm's AC power grid until the predetermined number of grid-connected wind turbines that have undergone black-start operation is reached, m = 2, 3, ...; where N... m The power required for the auxiliary system startup process of the grid-type wind turbine is no higher than the available output of the energy storage system at this time and the power of N1,…,N already black-started. m-1 The sum of the usable output of the platform-type wind turbine.

2. The wind farm black start method as described in claim 1, characterized in that: Once a predetermined number of grid-connected wind turbines that have already been black-started have been reached, all remaining grid-connected wind turbines in the wind farm will be started; wherein, the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

3. The wind farm black start method as described in claim 1, characterized in that: Once the predetermined number of grid-connected wind turbines that have already been started have been reached, all grid-connected wind turbines in the wind farm will be started; wherein, the grid-connected wind turbines are configured in the wind farm; the predetermined number is equal to the total number of grid-connected wind turbines in the wind farm.

4. The wind farm black start method as described in claim 1, characterized in that: After the predetermined number of grid-connected wind turbines that have already been black-started are reached, all remaining grid-connected wind turbines and all grid-following wind turbines in the wind farm will be started; wherein, the grid-following wind turbines are located in the wind farm; the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

5. The wind farm black start method as described in claim 1, characterized in that: Black-start grid-type wind turbines, including, The auxiliary system of the grid-type wind turbine, which is waiting for black start, draws energy from the AC grid of the wind farm to drive the grid-type wind turbine to accelerate to a predetermined speed and generate off-grid AC voltage. A virtual impedance is applied to synchronize the phase and frequency of the off-grid AC voltage with the phase and frequency of the AC grid voltage of the wind farm. The off-grid AC voltage is connected to the AC grid of the wind farm. After the voltage and current stabilize, the virtual impedance is removed, and the black start of the grid-connected wind turbine is completed.

6. The wind farm black start method as described in claim 5, characterized in that: The virtual impedance is applied by detecting the AC current value of the grid-connected wind turbine connected to the AC grid of the wind farm, multiplying the current value by a pre-set impedance, and then superimposing it onto the voltage reference wave.

7. A black start system for wind farms, characterized in that: include, An energy storage system startup device is configured to start the energy storage system and establish an AC power grid for the wind farm; wherein the energy storage system is located inside and / or outside the wind farm; and, A black start device for grid-connected wind turbines is configured to sequentially black start the grid-connected wind turbines in a wind farm; wherein the grid-connected wind turbines are black started in the following order: A black start is performed on N1 grid-connected wind turbines to establish an off-grid AC voltage and connect them to the wind farm's AC power grid; wherein the power required for the auxiliary system startup process of the N1 grid-connected wind turbines is not higher than the available output of the energy storage system; Start N2,…,N in sequence (black) m For grid-connected wind turbines, establish off-grid AC voltage and connect them to the wind farm's AC power grid until the predetermined number of grid-connected wind turbines that have undergone black-start operation is reached, m = 2, 3, ...; where N... m The power required for the auxiliary system startup process of the grid-type wind turbine is no higher than the available output of the energy storage system at this time and the power of N1,…,N already black-started. m-1 The sum of the usable output of the platform-type wind turbine.

8. The wind farm black start system as described in claim 7, characterized in that: It also includes, The first wind turbine starting device is configured to start all remaining grid-type wind turbines in the wind farm after a predetermined number of grid-type wind turbines that have already been black-started have been started; wherein the predetermined number is less than the total number of grid-type wind turbines in the wind farm.

9. The wind farm black start system as described in claim 7, characterized in that: It also includes, The second wind turbine starting device, after a predetermined number of grid-connected wind turbines that have already been black-started are configured, starts all grid-connected wind turbines in the wind farm; wherein, the grid-connected wind turbines are configured in the wind farm; the predetermined number is equal to the total number of grid-connected wind turbines in the wind farm.

10. The wind farm black start system as described in claim 7, characterized in that: It also includes, The third wind turbine starting device, after the number of grid-connected wind turbines that have been black-started reaches a predetermined number, starts all remaining grid-connected wind turbines and all grid-following wind turbines in the wind farm; wherein, the grid-following wind turbines are configured in the wind farm; the predetermined number is less than the total number of grid-connected wind turbines in the wind farm.

11. The wind farm black start system as described in claim 7, characterized in that: The black start device for the grid-type wind turbine is configured to black start the grid-type wind turbine, including, The auxiliary system control module is configured to control the auxiliary system of the grid-type wind turbine to be started from the AC grid of the wind farm, drive the grid-type wind turbine to accelerate to a predetermined speed, and generate off-grid AC voltage. as well as, The synchronization module is configured to synchronize the phase and frequency of the off-grid AC voltage with the phase and frequency of the AC grid voltage of the wind farm by applying a virtual impedance, and to remove the virtual impedance after the voltage and current stabilize.

12. The wind farm black start system as described in claim 11, characterized in that: The synchronization module inputs virtual impedance, including detecting the AC current value of the grid-type wind turbine connected to the wind farm's AC grid, multiplying the current value by a pre-set impedance, and then superimposing it onto the voltage reference wave.

13. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, it implements the steps of the wind farm black start method as described in any one of claims 1 to 6.

14. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it implements the steps of the wind farm black start method as described in any one of claims 1 to 6.

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