Research On Low Voltage Ride Through Of Direct-drive Permanent Magnet Wind Turbine Based On SMES-SFCL

Wind energy is a clean and renewable energy that has developed rapidly in recent years.With the proposal of the strategic goal of carbon neutrality and carbon peaking in my country,wind power generation will usher in a wave of installed capacity.With the continuous expansion of the capacity of wind turbines and the scale of wind farms,the grid connection of large-scale wind turbines poses a threat to the stable operation of the power grid.When the grid voltage drops,if it is directly switched off,it will cause a further drop in the voltage of the grid connection point.Therefore,large-scale wind farms must have a certain low-voltage ridethrough capability,maintain grid connection in the event of a grid failure,and deliver a certain amount of reactive power to the grid to help the grid voltage recover.Due to the unique advantages of superconducting technology,the application of superconducting energy storage and current limiting technology to wind power grid connection to improve wind power failure resistance and grid stability has become a hot spot in the development of superconducting power technology and wind power,and has important cutting-edge science.and engineering application significance.This paper studies the low voltage ride-through technology of permanent magnet direct drive wind turbine based on superconducting energy storage and current limiting technology.The working principle of current limiter and back-to-back converter is established,and the corresponding mathematical model is established.A scheme of applying the superconducting energy storage-current limiting system to improve the low voltage ride-through capability of a single machine connected to the grid is proposed.When the grid voltage is normal,the SMES is used to exchange power with the DC side to smooth the output power of the unit;when the grid voltage drops,the SFCL is used to quench to reduce the impact of the fault current on the grid-side converter.The power output capacity of the generator is reduced,the power fluctuation of the DC side is reduced,and the remaining power is absorbed by the SMES,thereby enhancing the unit’s ability to resist grid faults.Aiming at the low voltage ride-through problem of multi-unit grid-connected wind farms,due to the different locations and operating conditions of different wind turbines,two evaluation indicators of low voltage ride-through capability are applied.is the reactive power output capability evaluation index grid-side converter active power Pg.A method for improving the grid-connected capability of wind farms is proposed.Different reactive power commands are allocated according to the operating conditions of each unit,which effectively improves the reactive power output capability of the entire wind farm.Through the simulation verification of the scheme,the simulation results show that the reactive power optimal allocation scheme can effectively improve the reactive power output capacity of the wind farm.The application of superconducting energy storage and resistive superconducting current limiter low-voltage ride-through method proposed in this paper can effectively improve the fault resistance of direct-drive permanent magnet wind turbines,which is useful for smoothing the output power of the grid-side converter and improving the converter current during faults.The power output capability of the device has a significant effect.The reactive power optimization control strategy can make the multi-machine system of the wind farm output more reactive power and increase the voltage of the grid connection point.It provides a new technical foundation for the stable grid connection of large-scale wind farms and wind power consumption.