Research On Doubly-fed Wind Generator Connect To The Grid Based On System Robustness

This paper takes the most popular doubly-fed generator system in the field of wind power generation as the research object,and focus on the sliding-mode control strategy of DFIG.when the stator is connected to load or not connected to the load.According to the theory of grid voltage vector orientation,the stator output voltage of the doubly-fed generator is controlled precisely by controlling the rotor current so that it can synchronize to the grid voltage.Because the PI controller is not enough to resist the internal and external interference from the system,this paper is based on the sliding mode control theory to optimize the robustness of the doublyfed variable speed constant frequency system.After studying the principle of variable-speed constant-frequency operation of a doublyfed wind power generating unit,this paper deduces the control strategies of no-load networking and load-connected networking under ideal conditions respectively.A sliding mode controller is proposed to optimize the no-load strategy that system of the doubly-fed wind power generation connect to the grid because that the dependence of the sliding mode control on the parameters of the controlled object model is not strong.The control strategy of DFIG connected to the grid with load on the stator side is also the same.And after correcting the no-load gridconnected model and the load grid-connected model of the doubly-fed wind power generation system ideally established we found that the system model of DFIG's stator side connected to load or not are highly similar.The state variables,input variables,and input matrices of the two systems are all the same.Only the system matrix has some differences;Based on the high degree of similarity of the two systems,it is proposed that the no-load and load-connected sliding mode controllers of the doubly-fed generator can be designed using the same type of sliding surface and reaching law,which stability is proved by Lyapunov function.The controller achieves smoothly connecting to the grid when the generator's stator is connected to a load or not.This paper uses MATLAB/SIMULINK platform to build a software simulation experiment.Verified the effectiveness of the control strategies of the system that the stator connected with no-load or load.A sliding mode controller is designed for the above two systems.There is a large error that between the stator output voltage of the doubly-fed generator and the grid under PI control when the disturbance exists.And the sliding mode controller improved the problem.The experimental results verify that the control effect is stable and fast when synchronized with the grid voltage under ideal working conditions and generator parameters perturbation.