The Research On The Control Strategy Of The Doubly-fed Wind Turbine Participating In The System Frequency Regulation

As an environment-friendly clean energy,wind energy has a good development prospect.But because of the uncontrollability and randomness of wind energy,large-scale wind power integration will affect the frequency stability of power system.In order to reduce the impact of frequency stability caused by the grid connection of doubly fed wind power,the additional frequency control strategy of doubly fed wind turbine is proposed to participate in the primary frequency adjustment of the system.Based on this,this paper studies the primary frequency adjustment of doubly fed wind power.This paper analyzes the operation characteristics of DFIG in each operation area.When the doubly fed wind turbine operates in the start-up area,it does not participate in the system frequency adjustment;when the doubly fed wind turbine operates in the maximum power tracking area,it adopts the variable load shedding rate overspeed load shedding control;when the doubly fed wind turbine operates in the constant speed area,it adopts the integrated inertia control strategy of inertia control and droop control;when the doubly fed wind turbine operates in the constant power area,it adopts the improved pitch angle control strategy.Secondly,based on the control strategy adopted in each operation area of DFIG,a comprehensive frequency control strategy of DFIG is proposed,which is suitable for each wind speed and high and low frequency of the system.When the wind speed is greater than the cut in wind speed and less than the rated wind speed,the control strategy of overspeed load shedding control combined with integrated inertial control is adopted for the low-frequency problem caused by system disturbance;the control strategy of integrated inertial control combined with improved pitch angle control is adopted for the high-frequency problem caused by system disturbance.When the wind speed is greater than the rated wind speed and less than the cut-out wind speed,the system disturbance will cause the high and low frequency problems of the system.Finally,a simulation model is built in Matlab / Simulink to verify the effectiveness of the proposed integrated coordinated control strategy.In this paper,the phenomenon of power pit in the process of DFIG participating in low-frequency regulation in low and medium wind speed is studied.The frequency regulation process of DFIG is divided into two stages: frequency regulation stage and frequency regulation recovery stage.The two-stage operation characteristics of DFIG are analyzed,and the square method and ellipse method power pit compensation control strategy are adopted.Finally,the simulation model is built in matlab/Simulink,and the simulation results show that the square method and ellipse method have certain compensation effect on the power pit in the frequency regulation recovery stage of DFIG.According to the analysis of the frequency regulation problems after the asynchronous interconnection of Yunnan power grid,due to the large scale of hydropower units in Yunnan,and the strong rise of wind power in Yunnan in recent years.Considering the water hammer effect of hydropower units in Yunnan internal power grid,it will lead to the phenomenon of power reverse regulation at the initial stage of turbine participating in frequency regulation,which will further aggravate the frequency of power grid.Therefore,considering the water hammer effect of the turbine,this paper considers that the doubly fed wind turbine participates in frequency regulation through droop control strategy,so as to make up for the power inversion caused by the water hammer effect of the turbine.Finally,a simulation model is built in psd-bpa to verify the effectiveness of the proposed control strategy.