Offshore wind farm off-grid operation period operation and maintenance self-power supply system starting method

Abstract

The application discloses a kind of offshore wind farm off-grid operation period operation and maintenance self-powered system starting method, for the problem of high cost of existing diesel generator or energy storage system as operation and maintenance system main power supply, through the coordination control of wind turbine generator unit and small capacity energy storage equipment, the smooth start of off-grid operation wind farm operation and maintenance system is realized, and after starting, wind turbine can be used as the main power supply of operation and maintenance system.Compared with the existing scheme, the present application can significantly reduce the construction cost, effectively solve the off-grid wind farm operation and maintenance system power supply problem caused by the different construction of offshore wind farm and land access system line, has significant economic benefits and good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, specifically relating to a method for starting up a self-powered system for operation and maintenance during the off-grid operation period of an offshore wind farm. Background Technology

[0002] While offshore wind power is developing rapidly, some problems in the construction of wind farms have gradually emerged, one of the most significant being the asynchronous construction of wind farms and onshore grid connection lines. The completion time of offshore wind farms is often influenced by new energy power generation policies, while the construction of onshore AC power grids is mainly led by the local power grid company. This can easily lead to situations where the wind farm and its transmission cables are completed before the supporting grid connection lines are even finished. In such cases, the offshore wind farm will be unable to connect to the grid for a period of time. During this period, to ensure the environmental conditions for the wind turbine equipment, it is necessary to maintain the continuous and reliable operation of the offshore wind farm's operation and maintenance system. Therefore, the power supply for the operation and maintenance system during the off-grid operation of offshore wind farms becomes a pressing issue that needs to be addressed.

[0003] Existing solutions consider using diesel generators or energy storage devices to provide power for the self-powered operation and maintenance system of offshore wind farms during off-grid operation. However, as the scale of offshore wind farms continues to increase, the total power demand of the self-powered operation and maintenance system of offshore wind farms is also increasing, and it needs to operate continuously for a long period of time. Using diesel generators or energy storage devices as the main power source is not only uneconomical, but also faces unacceptable constraints such as insufficient land for construction.

[0004] With the continuous development of wind power technology, the flexibility of wind power control systems has significantly improved. During the off-grid operation of offshore wind farms, using wind turbine generators as the primary power source for the self-powered operation and maintenance system, while simultaneously employing small-capacity energy storage devices as the starting power source for the wind turbine generators, is a more economical and feasible solution. The biggest challenge in this system is achieving smooth startup under off-grid conditions through the coordinated control of the energy storage system and the wind turbine. Therefore, there is an urgent need to propose a startup method for the self-powered operation and maintenance system of offshore wind farms during off-grid operation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for starting up an off-grid self-powered system for offshore wind farms. This method requires only the installation of a small-capacity energy storage device on land to enable the smooth startup of offshore wind farms under off-grid conditions. After startup, the wind turbines can be used as the main power source for the operation and maintenance system, which can significantly reduce engineering construction costs.

[0006] To achieve the above-mentioned objectives, this method adopts the following technical solution:

[0007] A method for starting up an off-grid self-powered system for offshore wind farm operation and maintenance, characterized in that the off-grid self-powered system for offshore wind farm operation and maintenance includes: an energy storage battery, a bidirectional DC / DC converter, an energy storage grid-connected converter, an energy storage system step-up transformer, an energy storage system circuit breaker, an onshore AC bus, an offshore wind power transmission cable, an offshore substation, an offshore AC bus, a wind turbine circuit breaker, a wind turbine step-up transformer, a wind turbine grid-side converter, a wind turbine turbine-side converter, and a wind turbine generator; the energy storage battery is connected to the AC grid through the bidirectional DC / DC converter and the energy storage grid-connected converter, and then stepped up by the energy storage system. The voltage is stepped up to the onshore AC bus level by a step-up transformer, and then connected to the onshore AC bus via an energy storage system circuit breaker. The wind turbine is connected to the offshore AC grid via a turbine-side converter and a grid-side converter, and then stepped up to the offshore AC bus level by a turbine step-up transformer, and then connected to the offshore AC bus via a turbine circuit breaker. Multiple offshore wind turbines converge on the offshore AC bus, and then step up to the onshore AC bus level through an offshore substation, and then connect to the onshore AC bus via an offshore wind power transmission cable. The wind turbine's self-use power load is connected to the outlet of the wind turbine's grid-side converter for power intake.

[0008] During the off-grid operation of the wind farm, the system selects one wind turbine as the wind farm's self-use power source for grid-connected power generation, while the converters of the remaining wind turbines are locked out, and only the self-use power system for wind farm operation is working.

[0009] The method for starting up the self-powered system for off-grid operation and maintenance of offshore wind farms is characterized by the following:

[0010] The system startup process begins by starting the energy storage battery and the bidirectional DC / DC converter. The control strategy of the bidirectional DC / DC converter is used to adjust the DC bus voltage of the energy storage grid-connected converter to the rated value.

[0011] Start the energy storage grid-connected converter, which adopts a grid-type virtual synchronous machine control strategy.

[0012] The closed energy storage system circuit breaker, through the coordinated control of the bidirectional DC / DC converter and the energy storage grid-connected converter, charges the onshore AC bus, the offshore wind power transmission cable, the offshore substation, and the offshore AC bus, establishing the AC voltage of the self-powered operation and maintenance system;

[0013] The circuit breaker of each wind turbine in the wind farm is closed one by one to establish the AC side voltage of the grid-side converter of the wind turbine, and the power supply is provided to the wind turbine's operation and maintenance self-power system through the energy storage system.

[0014] Start the grid-side converter of the wind turbine that serves as the self-use power source for the wind farm's operation and maintenance, and adjust the DC bus voltage of the wind turbine's generator-side converter to the rated value through the constant DC bus voltage control strategy of the wind turbine's grid-side converter.

[0015] Start the turbine-side converter and wind turbine generator of the wind turbine as the self-use power source for wind farm operation and maintenance. Through the coordinated control of the turbine-side converter and the grid-side converter, gradually increase the output active power of the wind turbine to a first set value. The first set value is given based on the sum of the self-use power of all wind turbines during off-grid operation.

[0016] Since the grid-connected energy storage converter adopts a grid-type virtual synchronous machine control strategy, as the output active power of the wind turbines used as the self-use power source for wind farm operation and maintenance gradually increases, the output active power of the grid-connected energy storage converter will gradually decrease. Eventually, the power supply of the entire system will be entirely provided by the wind turbine units, and the energy storage system will only serve as a regulating power source to smooth out wind power output fluctuations and maintain the stability of the AC power grid.

[0017] Once the system startup process is complete, the entire offshore wind farm's off-grid operation and maintenance self-powered system can operate stably for a long period.

[0018] Furthermore, the bidirectional DC / DC converter adopts a constant DC bus voltage control strategy, which is responsible for establishing the DC bus voltage of the energy storage grid-connected converter during system startup and maintaining the stability of the DC bus voltage of the energy storage grid-connected converter during operation. The constant DC bus voltage control strategy of the bidirectional DC / DC converter is mainly realized through the outer loop of DC bus voltage control and the inner loop of current control.

[0019] Furthermore, the energy storage grid-connected converter adopts a grid-type virtual synchronous machine control strategy, which is responsible for establishing the AC voltage of the self-powered operation and maintenance system during system startup, providing startup power for wind turbines, and maintaining the stability of the AC grid during operation. The grid-type virtual synchronous machine control strategy of the energy storage grid-connected converter is implemented through a voltage reference value calculation module, a voltage outer loop controller, and a current inner loop controller. Among them, the voltage reference value calculation module provides voltage and frequency support for the self-powered operation and maintenance system by simulating the mechanical equations and excitation equations of a traditional synchronous generator.

[0020] In the voltage reference value calculation module, the reference voltage phase θ is calculated according to the following method. b :

[0021]

[0022]

[0023] in, The reference voltage phase for the next sampling period. The angular frequency of the next sampling period. This is the angular frequency of the current sampling period. The rated angular frequency, This is a reference value for active power. J represents the active power during this sampling period, and J represents the virtual rotor moment of inertia. This is the active damping coefficient.

[0024] In the voltage reference value calculation module, the d-axis voltage reference value u is calculated according to the following method. bdref :

[0025]

[0026] in, This serves as the d-axis voltage reference value for the next sampling period. This represents the voltage amplitude for this sampling period. This is a reference value for voltage amplitude. This is a reference value for reactive power. The reactive power for this sampling period is K, where K is the virtual excitation coefficient. This is the reactive damping coefficient.

[0027] Furthermore, the control strategies for the grid-side converters and turbine-side converters of wind turbines used as self-consumption power sources for wind farm operation and maintenance are as follows:

[0028] The wind turbine grid-side converter adopts a constant DC bus voltage and reactive power control strategy to maintain the stability of the DC bus voltage inside the wind turbine and provide necessary reactive power support to the AC grid. The control strategy of the wind turbine grid-side converter is realized through an outer loop controller for DC bus voltage and reactive power and an inner loop controller for current.

[0029] The wind turbine-side converter adopts a constant active and reactive power control strategy. Its active power command is given based on the sum of the self-consumption power of all wind turbines during off-grid operation, and it is responsible for providing active power to the self-consumption power of wind turbine operation and maintenance during the off-grid operation of the system. The control strategy of the wind turbine-side converter is realized through a power outer loop controller and a current inner loop controller.

[0030] By adopting the technical solution of this invention, only a small-capacity energy storage device needs to be installed on land to enable the smooth startup of the wind farm operation and maintenance system under off-grid operation conditions. After startup, the wind turbine can be used as the main power source for the operation and maintenance system, which can significantly reduce the engineering construction cost. It can effectively solve the startup problem of off-grid wind farm operation and maintenance system caused by the asynchronous construction of offshore wind farms and onshore grid connection lines, and has significant economic benefits and good application prospects. Attached Figure Description

[0031] Figure 1 This is a flowchart of the self-powered system startup method for off-grid operation and maintenance of offshore wind farms according to the present invention.

[0032] Figure 2This is a typical topology diagram of the off-grid operation and maintenance self-power supply system for offshore wind farms according to the present invention. In the diagram, 1-energy storage battery, 2-bidirectional DC / DC converter, 3-energy storage grid-connected converter, 4-energy storage system step-up transformer, 5-energy storage system circuit breaker, 6-onshore AC bus, 7-offshore wind power transmission cable, 8-offshore substation, 9-offshore AC bus, 10-wind turbine circuit breaker, 11-wind turbine step-up transformer, 12-wind turbine grid-side converter, 13-wind turbine generator-side converter, 14-wind turbine generator, and 15-wind turbine operation and maintenance self-consumption load.

[0033] Figure 3 This is a schematic diagram of a specific example system for the energy storage grid-connected converter control method of the present invention. In the diagram, 16 is the voltage reference value calculation module, 17 is the Park conversion module, 18 is the voltage outer loop controller, 19 is the current inner loop controller, 20 is the Park inverse conversion module, and 21 is the modulation module.

[0034] Figure 4 This is a schematic diagram of a specific example system for the wind turbine grid-side converter control method of the present invention. The modules are: 22-phase-locked loop module, 23-Park converter module, 24-DC bus voltage and reactive power outer loop controller, 25-current inner loop controller, 26-Park inverse converter module, and 27-modulation module.

[0035] Figure 5 This is a schematic diagram of a specific example system for the wind turbine-side converter control method of the present invention. In the diagram, 28 is the active power reference value calculation module, 29 is the rotor position observer, 30 is the Park conversion module, 31 is the power outer loop controller, 32 is the current inner loop controller, 33 is the Park inverse conversion module, and 34 is the modulation module. Detailed Implementation

[0036] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] In this embodiment of the invention, the off-grid operation and maintenance self-power supply system of an offshore wind farm is as follows: Figure 2 As shown, it includes energy storage battery 1, bidirectional DC / DC converter 2, energy storage grid-connected converter 3, energy storage system step-up transformer 4, energy storage system circuit breaker 5, onshore AC bus 6, offshore wind power transmission cable 7, offshore substation 8, offshore AC bus 9, wind turbine circuit breaker 10, wind turbine step-up transformer 11, wind turbine grid-side converter 12, wind turbine machine-side converter 13, wind turbine generator 14, and wind turbine operation and maintenance self-consumption load 15.

[0038] In this embodiment, the energy storage battery 1 is connected to the AC grid via a bidirectional DC / DC converter 2 and an energy storage grid-connected converter 3. The voltage is then stepped up to the onshore AC bus level via the energy storage system step-up transformer 4, and finally connected to the onshore AC bus 6 via the energy storage system circuit breaker 5. The wind turbine generator 14 is connected to the offshore AC grid via the turbine-side converter 13 and the grid-side converter 12. The voltage is then stepped up to the offshore AC bus level via the turbine step-up transformer 11, and finally connected to the offshore AC bus 9 via the turbine circuit breaker 10. Multiple offshore wind turbines converge on the offshore AC bus, and the voltage is then stepped up to the onshore AC bus level via the offshore substation 8, and finally connected to the onshore AC bus 6 via the offshore wind power transmission cable 7. The wind turbine's self-consumption load 15 is connected to the outlet of the wind turbine grid-side converter 12 for power extraction.

[0039] In this embodiment of the invention, the specific process of starting the self-powered system for off-grid operation and maintenance of an offshore wind farm is as follows: Figure 1 As shown.

[0040] The first step is to start the energy storage battery 1 and the bidirectional DC / DC converter 2, and adjust the DC-side bus voltage of the energy storage grid-connected converter to the rated value. Specifically, the bidirectional DC / DC converter 2 adopts a constant DC bus voltage control strategy, with the DC bus voltage reference value set to the rated value of the DC-side bus voltage of the energy storage grid-connected converter.

[0041] The second step is to start the energy storage grid-connected converter 3 and establish the AC voltage of the off-grid operation and maintenance self-powered system through a grid-type virtual synchronous machine control strategy. In this embodiment of the invention, the grid-type virtual synchronous machine control system adopted by the energy storage grid-connected converter 3 is as follows: Figure 3 As shown, it includes: voltage reference value calculation module 16, Park transformation module 17, voltage outer loop controller 18, current inner loop controller 19, Park inverse transformation module 20, and modulation module 21.

[0042] In the voltage reference value calculation module 16, the reference phase θ is calculated according to the following method. b :

[0043]

[0044]

[0045] in, As the reference phase for the next sampling period, The angular frequency of the next sampling period. This is the angular frequency of the current sampling period. The rated angular frequency, This is a reference value for active power. J represents the active power during this sampling period, and J represents the virtual rotor moment of inertia. This is the active damping coefficient.

[0046] The d-axis voltage reference value u is calculated using the following method. bdref :

[0047]

[0048] in, This serves as the d-axis voltage reference value for the next sampling period. This represents the voltage amplitude for this sampling period. This is a reference value for voltage amplitude. This is a reference value for reactive power. The reactive power for this sampling period is K, where K is the virtual excitation coefficient. This is the reactive damping coefficient.

[0049] The third step is to close the energy storage system circuit breaker 5 and use the energy storage system to charge the onshore AC bus 6, the offshore wind power transmission cable 7, the offshore booster station 8, and the offshore AC bus 9.

[0050] The fourth step is to close the circuit breaker 10 of each wind turbine in the wind farm one by one, and supply power to the wind turbine's self-use load 15 through the energy storage system.

[0051] Fifth, start the grid-side converter 12 of the wind turbine, which serves as the self-powered power supply for operation and maintenance, and adjust the DC bus voltage of the wind turbine to the rated value. The grid-side converter 12 adopts a constant DC bus voltage and reactive power control strategy. The DC bus voltage reference value is set to the rated DC bus voltage, and the reactive power reference value is given according to the reactive power deficit within the self-powered power supply system for operation and maintenance, providing necessary reactive power support for the self-powered power supply system during off-grid operation. The control system of the wind turbine grid-side converter is as follows: Figure 4 As shown, it includes: a phase-locked loop module 22, a Park conversion module 23, a DC bus voltage and reactive power outer loop controller 24, a current inner loop controller 25, a Park inverse conversion module 26, and a modulation module 27.

[0052] The implementation method of the DC bus voltage and reactive power outer loop controller 24 is as follows:

[0053]

[0054]

[0055] Wherein: F PI3 (s) is the transfer function of the PI controller, k p3 k is the proportionality coefficient. i3 Let i be the integral coefficient. gdref i gqref Corresponding to the current vector Igdqref d-axis and q-axis components, U dcref U is the reference value for the DC bus voltage. dc Q is the DC bus voltage. gref Q is the reactive power reference value. g This refers to reactive power.

[0056] The implementation method of the current inner loop controller 25 is as follows:

[0057]

[0058]

[0059] Wherein: F PI4 (s) is the transfer function of the PI controller, k p4 k is the proportionality coefficient. i4 U is the integral coefficient. vdref , u vqref Corresponding to voltage vector U vdqref d-axis and q-axis components, u gd , u gq Corresponding to voltage vector U gdq d-axis, q-axis components, i gd i gq Corresponding to the current vector I gdq d-axis and q-axis components, ω g L is the angular frequency of the grid voltage. g This is a filter inductor.

[0060] Step 6: Start the turbine-side converter 13 of the wind turbine, which serves as the self-use power source for operation and maintenance, and adjust the active power of the wind turbine to the first set value. The first set value is given based on the sum of the self-use power of all wind turbines during off-grid operation. The turbine-side converter 13 adopts a constant active and reactive power control strategy. The control system of the wind turbine grid-side converter is as follows: Figure 5 As shown, it includes: an active power reference value calculation module 28, a rotor position observer 29, a Park transformation module 30, a power outer loop controller 31, a current inner loop controller 32, a Park inverse transformation module 33, and a modulation module 34.

[0061] The power outer loop controller 31 is implemented as follows:

[0062]

[0063]

[0064] Wherein: F PI1 (s) is the transfer function of the PI controller, k p1 k is the proportionality coefficient. i1Let i be the integral coefficient. sdref i sqref Corresponding to the current vector I sdqref d-axis and q-axis components, P sref P is the active power reference value. s For active power, Q sref Q is the reactive power reference value. s This refers to reactive power.

[0065] The implementation method of the current inner loop controller 32 is as follows:

[0066]

[0067]

[0068] Wherein: F PI2 (s) is the transfer function of the PI controller, k p2 k is the proportionality coefficient. i2 U is the integral coefficient. sdref , u sqref Corresponding to voltage vector U sdqref d-axis, q-axis components, i sd i sq Corresponding to the current vector I sdq d-axis and q-axis components, ω r L is the rotor angular frequency. s Ψ represents the stator inductance of the wind turbine, and Ψ represents the rotor permanent magnet flux linkage.

[0069] In the seventh step, the active power output of the wind turbine gradually increases, while the active power output of the energy storage grid-connected converter gradually decreases. Ultimately, the energy storage system serves only as a regulating power source to smooth out fluctuations in wind power output and maintain the stability of the AC power grid; the system startup process ends.

[0070] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for starting up a self-powered system for operation and maintenance during the off-grid operation period of an offshore wind farm, characterized in that... The off-grid operation and maintenance self-powered system for offshore wind farms includes: energy storage batteries, bidirectional DC / DC converters, energy storage grid-connected converters, energy storage system step-up transformers, energy storage system circuit breakers, onshore AC busbars, offshore wind power transmission cables, offshore substations, offshore AC busbars, wind turbine circuit breakers, wind turbine step-up transformers, wind turbine grid-side converters, wind turbine turbine-side converters, and wind turbine generators. The energy storage batteries are connected to the AC grid via the bidirectional DC / DC converters and the energy storage grid-connected converters, and then stepped up to the onshore AC busbars via the energy storage system step-up transformers. The voltage level is connected to the onshore AC bus via the energy storage system circuit breaker; the wind turbine is connected to the offshore AC grid via the turbine-side converter and the grid-side converter, and then stepped up to the voltage level of the offshore AC bus via the wind turbine step-up transformer, and connected to the offshore AC bus via the wind turbine circuit breaker. After multiple offshore wind turbines converge on the offshore AC bus, they are stepped up to the voltage level of the onshore AC bus via the offshore substation, and then connected to the onshore AC bus via the offshore wind power transmission cable; the wind turbine's self-use power load is connected to the outlet of the wind turbine's grid-side converter for power intake; During the off-grid operation of the wind farm, the system selects one wind turbine as the wind farm's self-use power source for grid-connected power generation, while the converters of the remaining wind turbines are locked out, and only the self-use power system for wind farm operation is working. The method for starting up the self-powered system for off-grid operation and maintenance of offshore wind farms is characterized by the following: The system startup process begins by starting the energy storage battery and the bidirectional DC / DC converter. The control strategy of the bidirectional DC / DC converter is used to adjust the DC bus voltage of the energy storage grid-connected converter to the rated value. Start the energy storage grid-connected converter, which adopts a grid-type virtual synchronous machine control strategy. The closed energy storage system circuit breaker, through the coordinated control of the bidirectional DC / DC converter and the energy storage grid-connected converter, charges the onshore AC bus, the offshore wind power transmission cable, the offshore substation, and the offshore AC bus, establishing the AC voltage of the self-powered operation and maintenance system; The circuit breaker of each wind turbine in the wind farm is closed one by one to establish the AC side voltage of the grid-side converter of the wind turbine, and the power supply is provided to the wind turbine's operation and maintenance self-power system through the energy storage system. Start the grid-side converter of the wind turbine that serves as the self-use power source for the wind farm's operation and maintenance, and adjust the DC bus voltage of the wind turbine's generator-side converter to the rated value through the constant DC bus voltage control strategy of the wind turbine's grid-side converter. Start the turbine-side converter and wind turbine generator of the wind turbine as the self-use power source for wind farm operation and maintenance. Through the coordinated control of the turbine-side converter and the grid-side converter, gradually increase the output active power of the wind turbine to a first set value. The first set value is given based on the sum of the self-use power of all wind turbines during off-grid operation. As the active power output of wind turbines used as self-consumption power for wind farm operation and maintenance gradually increases, the active power output of grid-connected energy storage converters will gradually decrease. Eventually, the power supply of the entire system will be entirely provided by wind turbine units, with the energy storage system serving only as a regulating power source to smooth out fluctuations in wind power output and maintain the stability of the AC power grid.

2. The method for starting up the self-powered system for off-grid operation and maintenance of offshore wind farms according to claim 1, characterized in that: The bidirectional DC / DC converter adopts a constant DC bus voltage control strategy, which is responsible for establishing the DC bus voltage of the energy storage grid-connected converter during system startup and maintaining the stability of the DC bus voltage of the energy storage grid-connected converter during operation. The constant DC bus voltage control strategy of the bidirectional DC / DC converter is mainly realized through the outer loop of DC bus voltage control and the inner loop of current control.

3. The method for starting up the self-powered system for off-grid operation and maintenance of offshore wind farms according to claim 1, characterized in that: The energy storage grid-connected converter adopts a grid-type virtual synchronous machine control strategy, which is responsible for establishing the AC voltage of the operation and maintenance self-power supply system during system startup, providing startup power for wind turbine units, and maintaining the stability of the AC grid during operation. The grid-connected virtual synchronous machine control strategy of the energy storage grid-connected converter is implemented through a voltage reference value calculation module, a voltage outer loop controller, and a current inner loop controller. Among them, the voltage reference value calculation module provides voltage and frequency support for the operation and maintenance self-powered system by simulating the mechanical equations and excitation equations of a traditional synchronous generator. In the voltage reference value calculation module, the reference voltage phase θ is calculated according to the following method. b : in, The reference voltage phase for the next sampling period. The angular frequency of the next sampling period. This is the angular frequency of the current sampling period. The rated angular frequency, This is a reference value for active power. J represents the active power during this sampling period, and J represents the virtual rotor moment of inertia. This is the active damping coefficient; In the voltage reference value calculation module, the d-axis voltage reference value u is calculated according to the following method. bdref : in, This serves as the d-axis voltage reference value for the next sampling period. This represents the voltage amplitude for this sampling period. This is a reference value for voltage amplitude. This is a reference value for reactive power. The reactive power for this sampling period is K, where K is the virtual excitation coefficient. This is the reactive damping coefficient.

4. The method for starting up the self-powered system for off-grid operation and maintenance of offshore wind farms according to claim 1, characterized in that: The control strategies for the grid-side converters and turbine-side converters of wind turbines used as self-consumption power sources for wind farm operation and maintenance are as follows: The wind turbine grid-side converter adopts a constant DC bus voltage and reactive power control strategy to maintain the stability of the DC bus voltage inside the wind turbine and provide necessary reactive power support to the AC grid. The control strategy of the wind turbine grid-side converter is realized through an outer loop controller for DC bus voltage and reactive power and an inner loop controller for current. The wind turbine-side converter adopts a constant active and reactive power control strategy. Its active power command is given based on the sum of the self-consumption power of all wind turbines during off-grid operation, and it is responsible for providing active power to the self-consumption power of wind turbine operation and maintenance during the off-grid operation of the system. The control strategy of the wind turbine-side converter is realized through a power outer loop controller and a current inner loop controller.

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