Research On Primary Frequency Control Strategy Of Doubly-fed Wind Turbine Based On Variable Load

Large-scale wind power grid connection poses a serious threat to system frequency stability.In order to reduce the frequency regulation burden of the conventional unit,a frequency control link can be added to the control system of the wind turbine,and the unit is subjected to load shedding to reserve standby power for the frequency division to participate in the frequency modulation.At present,most of the literature only uses the variable load shedding coefficient control to determine the power reserve under wind speed,and does not study the switching process of the unit control mode when the variable wind speed is used.Based on this,this paper takes the doubly-fed wind turbine as the object,in its power reserve and participation.The system has conducted research on frequency regulation.Firstly,the system structure of the doubly-fed wind turbine and the aerodynamic characteristics of the wind turbine are introduced.Based on the aerodynamic characteristics,the optimal power tracking characteristic curve of the unit is analyzed,and the existing three types of load shedding are compared.The basis for power backup has been laid;Secondly,the power frequency characteristic curve of the doubly-fed wind turbine is obtained by imitating the power frequency characteristic curve of the conventional unit,and the advantages and disadvantages of the two control strategies of the wind turbine participating in the system frequency regulation are compared;Then,the backup principle of the variable load shedding coefficient control is analyzed in depth,and the critical load shedding coeff-icient is introduced as the switching standard of the control mode when the wind speed is changed;Finally,a joint control frequency modulation strategy is proposed,and the frequency regulation simulation is carried out in different power standby control areas.The simulation results show that the load shedding coefficient is related to the wind speed as a piecewise function and the load shedding coefficient decreases with the increase of wind speed.When the frequency regulation is controlled based on the variable load shedding coefficient control,the frequency regulation mode can be automatically selected according to the system frequency deviation.When the joint control strategy proposed in this paper is adopted,the output power of the unit can be quickly adjusted within 6s after the frequency change,and the frequency can be changed after 40s.It provides stable power support,and its steady-state output power reaches the power variation required for droop control,which improves the friendliness of wind power grid connection.