Research On Control Strategy Of Doubly-fed Wind Turbine To Suppress Low-frequency Oscillation Of Power System

With the rapid development of society and the continuous improvement of productivity,people’s demand for energy is also increasing day by day.However,traditional primary energy production has its limits after all.Therefore,the development of green and pollution-free renewable energy has become the next step in various countries.Among them,wind power generation has become a green energy source all over the world due to its rapid development,mature technology and abundant resources.Therefore,the proportion of wind power in the power grid is increasing.However,as the scale of wind farm continues to increase,the impact of wind farm integration on the system is also expanding,resulting in more complex system and nonlinearity,and the low-frequency oscillation of power systems will become more prominent,appropriate control strategies are needed to suppress the effects of wind farm on the low frequency oscillations of the power systemFirstly,this paper introduces the dynamic mathematical models of doubly-fed wind turbine,which are wind turbine model,mechanical transmission system model,doubly-fed induction generator model,rotor excitation system converter and grid-side system converter and their control system model.These models are the basis for wind turbines to participate in suppressing low frequency oscillations in power systems.The design of the traditional damping controller is mainly designed based on linearization near the static point of the system operation.When the operating point of the system changes little,the damping controller works well.However,when the actual system is running,the operating point of the system is not static.When the operating point of the system changes,the controller can’t achieve the desired control effect,and may even cause the system oscillation to intensify,jeopardizing the entire power system.Therefore,in order to solve the problem that the traditional damping controller relies on the linearization of the system static point,a control method based on nonlinear control strategy is proposed.This method accurately linearizes the selected system output and system input by means of state feedback.The nonlinear system changes to a linear system to solve the problem that the traditional damping controller relies on the linearization of the system static point.In order to improve the parameters of the damping controller designed by nonlinear control,it depends on the detailed modeling parameters of the system,which is not easy to implement.A controller based on super-twisting algorithm is designed.The controller designed by this algorithm does not depend on the detailed parameters of the system,and is robust to the unmodeled part of the system,and is easy to implement in engineering.Since this control method considers the uncertainties in the model,it has a better effect than the controller proposed by the nonlinear control.The paper analyzes the simulation of the controller designed by the algorithm proposed in this paper and extends it to the multi-area system.The results show that the proposed control strategy can avoid the linearization near the equilibrium point,improve the damping of the system,and suppress the low-frequency oscillation of the power system.