Research On Low Voltage Ride-through And Frequency Regulation Of Direct-Drive Permanent Magnet Wind Power With Super Capacitor

As a strategic policy of China’s energy development and ecological civilization construction,"carbon peak and carbon neutral" has greatly promoted the development of wind power industry.But because of the random nature of wind energy,the incorporation of massive wind turbines into the grid poses a huge challenge to the secure operation of our power system,while the construction of an integrated zero-carbon green energy system of"source-grid-loadstorage" provides a new technical development idea to improve new energy consumption and grid security.Therefore,how to avoid wind turbine off-grid and even blackout accidents,solve the voltage dips caused by short circuit faults and frequency changes caused by load fluctuations,and realize wind power-friendly grid connection,has important research value.The paper proposes a low-voltage ride-through method based on energy storage and sequence component control,and a frequency adjustment method based on inertia support and primary frequency modulation for direct-drive permanent magnet wind power system with super capacitor energy storage.Firstly,the technical problems that need to be solved are summarized by combining the technical specifications of wind turbine LVRT and frequency regulation,and the mathematical module of direct-drive permanent magnet wind power system with super capacitor energy storage is built by using dq rotating coordinate system in symmetric fault and asymmetric fault cases,and the implementation of maximum power point tracking is analyzed,which lays the theoretical basis for building a precise and efficacious control strategy.Secondly,for the purpose of solving the problem of DC chain support capacitor voltage soaring due to DC link energy non-balance and power and voltage 2-frequency undulation as a result of negative sequence components during the short circuit of the grid,the machine and grid-side converter and super capacitor energy storage system are subject to improved double closedloop control respectively.The generator-side converter control considers the degree of variation of the grid-side active power output and the maximum kinetic energy storage limit of the transmitting system.The grid-side converter control considers the maximum current limitation of the converter and the principle of reactive power priority.And the control of the energy storage system considers the state-of-charge and achieves power adjustment by using a bidirectional DC-DC converter.In addition,the capacity of super capacitor is selected based on the influencing factors of super capacitor diffusion layer and end-of-life.Then,for the frequency undulation problem of power grid,inertia support based on frequency change rate and primary frequency modulation based on frequency deviation are introduced into the control strategy of generator-side converter,and frequency deviation is introduced into the control strategy of super capacitor energy storage system to realize frequency regulation.Finally,the LVRT method and frequency regulation method are integrated,and the control target is selected using logic judgment to achieve function switching,and a joint control strategy that takes into account LVRT and frequency regulation is obtained.The method of combining LVRT and frequency regulation control strategies improves the anti-fault capability of the grid-connected wind power system and provides an effective way for the wind turbine to participate in frequency regulation.Simulation results in MATLAB/SIMULINK environment indicated that the method is effective for grid-connected LVRT and frequency adjustment of direct-drive permanent magnet wind turbines.