Research On Maximum Power Tracking Of Direct Drive Permanent Magnet Synchronous Wind Power Generation System

With the scarcity of fossil fuel resources,it is urgent to exploit green energy source to meet the ever-growing energy demand.The wind energy has many advantages such as abundant reserves,renewable,and non-pollution for environment,which becomes a hot research topic in the world.In order to improve the wind energy utilization,it is of great significance to implement the maximum power point tracking(MPPT)control.Taking one direct-drive permanent magnet synchronous generator(D-PMSG)as the research target,this thesis utilizes the dual PWM converter to control the maximum power point tracking of wind turbine.The working principle and topology of direct-drive permanent magnet synchronous wind power generation system are introduced.The mathematical models of wind turbine,PMSG,machine-side converter and grid-side converter are established respectively.The machine side converter obtains the optimal rotating speed under different wind speeds by using the optimal tip speed ratio method.The maximum wind energy is captured by the double close loop control system,which includes inner current loop and outer speed loop.The traditional PI control requires an accurate mathematical model,and the corresponding control parameters are fixed.However,the wind power generation system owns characteristics of time-variation and non-linear.The traditional PI control just makes response for instantaneous error,which cannot identify the error variation such as increase and decrease,so that it is impossible to track the best speed in time.Without an accurate mathematical model,the fuzzy control establishes control rules based on practical working experience,which is insensitive to parameter variation.Therefore,by combining the fuzzy control and traditional PID control,this thesis designs the fuzzy PID controller with respect to the outer speed loop at the rated wind speed.The proposed fuzzy PID controller applies a 2D fuzzy controller and triangular membership function taking the actual speed and the optimal speed as input parameters.The grid-side converter adopts the grid voltage-assisted vector control.The decoupling control of active current and reactive current is implemented by double closed loop control system with a inner current loop and a outer voltage loop.A simulation model of a 2.5 MW wind turbine is constructed in Matlab/Simulink.The numerical experiments of the simulation model are carried out by using a fuzzy PID controller and a traditional PI controller respectively.From the comparison of simulation results,it is shown that the fuzzy PID control method can better track the maximum power,and owns faster dynamic response and convergence speed.