Research On DFIG/Energy Storage Joint Frequency Modulation Control Strategy In Different Wind Speed Areas

With the increase of the wind power penetration rate in the power system,the "zero inertia" characteristics and output power volatility of the double-fed induction generator as the mainstream model make the frequency stability of the power system face a huge challenge.The frequency modulation capability of double-fed induction generator is greatly affected by wind speed,and the confidence of reserved reserve capacity is low,which cannot fully meet the frequency modulation requirements.Energy storage has the advantages of fast adjustment speed,accurate output power and stable reserve capacity.The joint frequency modulation of energy storage and double-fed induction generator can achieve coordination and complementarity and improve the frequency stability of the system.Therefore,this paper conducts an in-depth study on the double-fed induction generator /energy storage joint frequency regulation control strategy.First,according to the working principle of the double-fed induction generator,the mathematical model of the wind turbine,the transmission system and the doubly-fed generator is established;and the mathematical model of the lithium battery and its control system is established based on the operating characteristics of the energy storage system.Secondly,based on the analysis of the frequency characteristics of the wind power system,in the medium wind speed area,according to the frequency modulation ability of the double-fed induction generator at different wind speeds,a comprehensive inertia control strategy considering the frequency modulation ability of the double-fed induction generator is proposed based on the logistic function.The frequency modulation coefficient is used to adjust the inertia coefficient and the droop coefficient;in the high wind speed area,a pitch angle control model with the equivalent adjustment coefficient of the double-fed induction generator is established based on the pitch technology.Based on MATLAB/Simulink platform,the model of four machines and two areas is established,the simulation results show that: in the medium wind speed zone,the integrated inertia control considering the frequency modulation capability of the double-fed induction generator effectively prevents the unit from excessively participating in the frequency modulation,maintains the operating stability of the unit during the frequency modulation process,and reduces the secondary frequency drop,but the frequency modulation effect is affected by the frequency modulation ability of the wind turbine;in the high wind speed area,the pitch angle control has a good steady-state frequency support ability,but the effect of the transient frequency support is not good.Finally,according to the principle of energy storage frequency modulation,a control strategy model of energy storage frequency modulation considering the state of charge is established based on multi-input fuzzy control.In view of the insufficiency of frequency modulation of double-fed induction generator in low,medium and high wind speed areas,in low wind speed areas,energy storage alone participates in frequency modulation to solve the problem of "blind areas" in the participation of double-fed induction generator in frequency modulation;in the medium wind speed area,according to the frequency modulation coefficient of the double-fed induction generator,the energy storage is used to compensate the inertia of double-fed induction generator to prevent the secondary frequency drop when the frequency modulation is exited;in the high wind speed area,based on the principle of frequency division,it is established to consider energy storage and pitch angle wind-storage combined frequency modulation control strategy model based on system response speed.Based on MATLAB/Simulink platform,the control strategy model of double-fed induction generator/energy storage combined frequency regulation is established in low,medium and high wind speed regions,the simulation results show that the combined frequency modulation of double-fed induction generator and energy storage can provide frequency support under full wind conditions,enhance the frequency modulation capability of double-fed induction generator,suppress the secondary frequency drop,improve the frequency modulation effect,and improve the system frequency stability.