Research On The Integrated Control Method Of Doubly-fed Induction Generator Participating In Power System Frequency Regulation

With the depletion of traditional energy sources and the intensification of environmental pollution,wind power generation is rapidly developing,and the grid-connected capacity of wind power is also gradually increasing.Doubly-Fed Induction Generator(DFIG)is the mainstream model of wind power generation.The rotor side is connected to the grid by the converter,which results in the decoupling control of the rotor speed and the grid frequency.When a large number of DFIG are connected to the grid,it will lead to the frequency modulation capability of the system is weakened,and wind energy instability also affects the stability of the DFIG grid-connected system.Therefore,it is very important and urgent to study the frequency modulation control method of DFIG participating in the power grid and the control strategy of coordinate frequency modulation with traditional synchronous generator.Based on the research of DFIG grid-connected system,this paper researches the frequency modulation control method of DFIG and the control strategy of integrated frequency modulation of flywheel energy storage device and synchronous generator.This paper combines the speeding load shedding control with the rotor inertial control to coordinate the control of the DFIG.The speeding load shedding control is used to provide the DFIG with the frequency modulation reserve capacity.The rotor inertial control response system frequency changes make the DFIG have good frequency modulation capability.The derivation formulas for the droop coefficient and inertia coefficient in the coordinated control are obtained through theoretical derivation,and a coordinated control method for variable parameter tuning is improved and designed so that the DFIG can adjust its frequency output in response to the change of wind speed when it participates in system frequency modulation.A segmented study of wind speed,combined with coordinated control of variable parameter setting and variable pitch technology,developed a control strategy for DFIG participating in system frequency tuning at multiple wind speeds,and built a 4-machine 2-area system model in the MATLAB/Simulink simulation platform.The simulation results show that the coordinated control method for variable parameter tuning can respond to the change of wind speed and participate in the adjustment of the system frequency.Moreover,the control strategy of DFIG participating in the first frequency modulation of the system at multiple wind speeds can improve the frequency regulation effect of DFIG.In order to improve the instability of wind power caused by the fluctuation of DFIG output power,a DFIG-flywheel energy storage system was built to use the charging and discharging process of the flywheel energy storage device to smooth the fluctuation of DFIG output power,assist in the regulation of the system frequency,and designed calculating method of frequency modulation capacity of flywheel energy storage device under different wind speeds.In order to match the frequency modulation capability of the synchronous generator,theoretically analyzed the frequency modulation characteristics of the DFIG grid-connected system,developed a comprehensive frequency modulation control strategy based on the DFIG grid-connected system,and built a 4-machine 2-area system model in the MATLAB/Simulink simulation platform.The simulation results show that the flywheel energy storage device can improve the instability of the DFIG output power and participate in the system frequency modulation.Moreover,the integrated frequency modulation control strategy under the DFIG grid-connection system can reduce the frequency modulation pressure of the synchronous generator,reduce the wind rejection,and the frequency modulation effect is well.