Research On Control Strategy For DFIG Participating In System Frequency Regulation Containing High Penetration Of Wind Power

As a clean,non-polluting,inexhaustible energy,Wind power is of great significance to adjust energy structure,save energy,protect ecological environment and promote sustainable economical development.As the transition of energy structure,Wind power penetration will gradually increase.So how to provide effective primary frequency regulation service in high penetration area by variable speed induction generator has become a research hotspot.According to the existing research,there are still some problems that have not been thoroughly studied.One is how to calculate the de-loaded speed of over-speed control.Because the reference speed varies with deloaded rate.Besides the relationship between wind power and rotor speed is nonlinear,which Increased the difficulty of using mathematical method to get the speed.Second is how to use pitch control to implement frequency control.Third is the lack of a coordinated control strategy for all wind conditions.To solve these problems,firstly this paper analyzes the operation principle of DFIG,establishes model of wind turbine,shaft,induction generator and pitch control in DIg SILENT 2016 and deeply researches on vector control strategy of DFIG and its converters.Then the feasibility of DFIG providing primary frequency regulation service is demonstrated in high penetration area.Both theoretical and simulation result confirm that wind power integrate into grid will reduce system's equivalent inertia and weaken frequency regulation capability.Based on the wind power data of Hainan grid,the fluctuation of wind power in different time scales are analyzed by means of qualitative and quantitative methods.So the paper conclude that during the primary frequency regulation the fluctuation of the wind power can be neglected and the double fed induction generator can provide the frequency regulation service under the appropriate control strategy.Lastly,To enhance primary frequency control ability of DFIG in all wind conditions,this paper proposes a new strategy that in maximum power tracking area coordinated inertia and over-speed control strategy is adopted while in constant speed or constant power areas,pitch angle control and auxiliary inertial control are combined.An over-speed control module is designed,which can simplify the process of obtaining rotor speed using Cp value table conresponding to different tip speed ratios and pitch angles.In addition,Aiming at the complex nonlinear relationship between pitch angle,tip speed ratio and Cp,a pitch compensation and frequency response module are conceived.The simulation results verify the effectiveness of overspeed calculation module and pitch control module,which prove that the proposed coordinated control strategy not only can take full advantage of each control measures but also can provide a powerful frequency support for system in various wind conditioons.