Research On Inertia Participation In Grid Frequency Control Strategy For Doubly-Fed Induction Generator

With the increasing seriousness of global warming and fossil energy shortage,wind power is booming as a new clean energy source.Since the rotor of Doubly-Fed Induction Generator(DFIG)is decoupled from the grid frequency,the large-scale connection of DFIG to the grid is not conducive to the stable operation of the power system.In this paper,starting from the existing inertia control strategy of DFIG,the rational use of the "hidden inertia" of DFIG is further investigated.And an improved limit torque control strategy is proposed,which is important for improving the dynamic regulation capability of the system and ensuring the safe and stable operation of the power grid.The specific research results of this paper are as follows:First,in this paper,the working principle of DFIG is introduced,the mathematicai model of DFIG is analyzed and built,and the control strategy of DFIG is studied.Then,the evaluation system of the frequency regulation performance of DFIG is established,and a simulation model is built to study the integrated inertia control of DFIG.The research results show that the frequency regulation characteristics of the system an be significantly improved by involving the integrated inertia control strategy in the system frequency regulation;The integrated inertia control parameter of the D FIG is closely related to the frequency regulation effect oft of the system.Larger integrated inertia control parameter may cause severe oscillation of the unit and lead to system instabilily,while the DFIG cannot fully play its frequency regulation ability under the condition of a lower control parameter.Secondly,for the DFIG,the control of short-time overload and limit rorque have been studied,and the control principle and implementation process of both are analyzed.Under three conditions with different wind speeds and wind power penetration rates,the system response of a DFIG turbine with three inertia control strategies involved in frequency regulation is simulated and compared.The following conclusions is drawn:Compared with the other two inertia control strategies,the control strategy of limit torque relatively fully utilizes the inertia characteristics of the fan.However,in the early stage of frequency controlling,the active power output of this strategy drops excessively fast,and its inertia characteristic still has greater potential to play.In addition,the rotor speed recovery in this strategy is rather slowly,which can hardly balance the relationship between rotor speed recovery of the wind turbine and the secondary dip of the system frequency.Finally,considering the influence of different control parameters on the limit torque controlling effect of DFIG,the frequency response and rotor speed variation of the system when the power dips are taken are analyzed,as well as the limit power control coefficient and the active reference slope are taken to different values.Based on this,the kinetic energy extraction process of the DFIG rotor is improved,and an improvement strategy is proposed and verified by simulation under different working conditions,and the results showed that:The improved control method proposed in this paper can significantly improve the transient frequency response performance and increase the frequency nadir.At the same time,it can recover the rotor speed of the wind turbine back to the maximum power tracking mode relatively quickly while alleviating the phenomenon of secondary dip in system frequency,increasing the economic efficiency of the doubly-fed wind power system,avoiding the extreme working mode of the DFIG,and improving the friendliness of the DFIG to the grid.