Primary Frequency Modulation Control Strategy For Doubly-Fed Wind Turbines Based On Variable Coefficients

With the rapid development of the wind power industry,wind power has gradually become an important part of the power system.As the main model in the current market,the DFIG can realize flexible control of power,which also decouples the rotor speed from the system frequency and cannot respond to the system frequency modulation.The traditional integrated inertial control couples the system frequency with the active power output of the unit,so that it can participate in the system frequency regulation.However,because the control coefficient of this strategy adopts a fixed coefficient,the frequency regulation effect of the unit will be quite different under different conditions.In this paper,the following research work is carried out to improve the traditional integrated inertial control strategy.Firstly,the basic working principle of the doubly-fed wind turbine is introduced,the aerodynamic modeling of the wind turbine is carried out,and the relevant characteristics of the wind energy utilization coefficient are analyzed on this basis;the simplified two-mass model of the traditional system is briefly described;The mathematical model of the doubly-fed induction motor in the A-B-C three-phase static coordinate system and the d-q-0 two-phase synchronous rotating coordinate system is further analyzed for its power control strategy;the operating characteristics of the active power of the wind turbine and the doubly-fed induction motor are described.Then,in view of the shortcomings of traditional integrated inertial control,starting from its two control coefficients,the virtual inertial coefficient is combined with the rotational kinetic energy of the doubly-fed wind turbine,and the calculation formula of the virtual inertial coefficient is deduced,so that its size can be determined according to the current operating state of the turbine.Make appropriate adjustments;at the same time,considering that the unit can respond to system frequency regulation for a long time,add load shedding control,link the current active power reserve of the unit with the droop coefficient,further derive the calculation formula of the droop coefficient,and then add the improved control coefficient to the traditional control structure In,an improved integrated inertial control is proposed,and the effectiveness and rationality of the improved integrated inertial control are verified by simulation comparison.Finally,in order to improve the frequency regulation problem existing in the traditional control structure,a system frequency response model including wind power frequency regulation is established,the frequency response parameters are deduced and analyzed,and a variable coefficient control strategy based on a single droop loop is proposed.As an independent variable to control the size of the variable coefficient,the variable coefficient range is set according to the improved control coefficient,and the rationality and correctness of the integrated inertial control are verified by simulation and comparison.The simulation results show that the control strategy can allow the unit to flexibly adjust the degree of frequency adjustment of the response system according to the change of its own operating state,and at the same time,it is also excellent in improving the maximum drop depth,recovery time and static stable frequency after the system frequency is abruptly changed.for improved integrated inertial control.