Research On Grid-connected Frequency Control Of Doubly-fed Wind Turbines Based On Flywheel Energy Storage Technology

As fossil energy shortages and environmental pollution become increasingly prominent,clean energy has gradually entered people’s horizons and has developed very rapidly.Wind energy,as a promising form of renewable clean energy,has become the third main source of power and has made great contributions to China’s sustainable development,reduction of environmental pollution,climate change,and resource depletion.Among them,Doubly Fed Induction Generator(DFIG),as the mainstream model of wind farms,can not only improve the utilization rate of wind energy,but also realize variable-speed constant-frequency operation.With the increase in the proportion of wind power access,the penetration rate of wind power continues to increase,the speed of the fan rotor is decoupled from the system frequency and does not have the frequency response nor provide the moment of inertia,which puts forward higher requirements for frequency adjustment.How to control the fan in order to smooth the power output and suppress the frequency fluctuations,while realizing the frequency adjustment while absorbing as much wind power resources as possible,reducing the issues of wind and light awaiting exploration.This article first describes the research background and significance of wind turbines and energy storage technologies,and then analyzes the current status of wind power research at home and abroad,the advantages and disadvantages of various energy storage methods,the necessity of selecting flywheel energy storage as auxiliary frequency modulation,and the importance of flywheel energy storage in other areas.Application development,and finally summarized some solutions of wind turbine frequency regulation problems,laying a theoretical foundation for the next optimization of fan frequency control strategy.The second chapter mainly introduces the composition structure,working principle,natural wind speed module of doubly-fed fan,and analyzes the virtual inertia control,load reduction control and variable pitch technology frequency modulation control method.Finally,on the MATLAB / Simulink simulation platform,the feasibility of the virtual inertia plus load shedding control frequency modulation strategy is verified under constant wind speed and natural wind speed.The third chapter is based on the second chapter to calculate the droop coefficient and the inertia coefficient with variable parameter settings and pitch angle control to make better use of wind energy.When the rated wind speed is exceeded,the pitch angle control is used,and in the case of other wind speeds,the coordinated control of Chapter 2 is used to achieve power control and maximum wind energy tracking,and the adjustment range is wider and more flexible.Finally,the optimization performance of the scheme is verified under the full wind speed step and natural wind speed on the simulation platform.Compared with the additional control method in Chapter 2,it has a better frequency modulation effect.The fourth chapter introduces the flywheel energy storage system structure,charge and discharge model and simulation analysis,and the frequency modulation characteristics of the additional control of the fan with the synchronous generator.Finally,the simulation was performed on the MATLAB / Simulink simulation platform.The simulation results show that the flywheel energy storage can smooth the DFIG output power fluctuation,play a role of auxiliary frequency modulation,and can coordinate the respective frequency modulation output well.The results show that the flywheel energy storage device can improve the instability of DFIG output power and can participate in system frequency modulation,and the integrated frequency modulation control strategy under the DFIG grid-connected system can reduce the frequency modulation pressure of the synchronous generator,reduce wind abandonment,and the frequency modulation effect is good.