Research For Low Voltage Ride-Through Of Wind Turbines With Doubly-Fed Induetion Generator

With the rapidly increase of wind power generation capacity,its influence on grid is becoming more and more remarkable.Especially grid requires that wind turbine connected to grid must be equipped with low voltage ride through(LVRT)capability for voltage dip that caused by faults in power system.Doubly fed induction generator(DFIG) wind turbine is the main type which possess advantages,for example,variable speed running,independent regulating of active and reactive power, etc.But,its weakness in dealing with grid fault is obvious.In this paper, study was made to improve low voltage ride-through ability of doubly fed wind turbines.First of all,The basic theory and control strategy of variable speed constant frequeney wind power generation system were investigated and modle of DFIG power system was established.Studies deeply on the essence and characteristics of the electric-magnetic transition,overvoltage and overcurrent of the rotor.In order to validate the validity of the views proposed here,the operating characteristics of DFIG in the low voltage condition has been simulated and analyzed by using MATLAB/Simlink.Secondly,according to the disadvantages of conventional PI and too many parameters and control rules of Takagi Sugeno(TS)fuzzy control,this paper puts forward a simplified TS fuzzy controller to improve the LVRT ability of DFIG,the basic knowledge of TS fuzzy controll was introduced,then a simplified TS fuzzy controller suitable to this study is designed.Finally,the simulation model of a practical wind farm was built,in which three-phase short circuit simulation study has been done.The simulation results show effectiveness of the TS fuzzy controller by restraining oscillations of the active power output and DC bus capacitor voltage in condition of large external voltage dip.The proposed TS-fuzzy controller can improve the fault ride through capability of DFIG compared to the conventional PI controller.