Research On Variable Pitch Control Technology Of DFIG Wind Generation System

Under the situation of environmental pollution and the promotion of energy-saving and emission-reduction in the world,as one of the clean renewable energy,wind energy has been widely used in the world and has broad market prospects.With the development of wind power technology in many countries,pitch control technology has become one of the research hotspots.This paper takes the doubly-fed induction wind power generation system(DFIG)as the research object,and made too much theoretical analysis and simulation verification of the variable pitch control of megawatt wind turbine mainly includeing two aspects of variable pitch control strategy and variable pitch servo system.The main research work is as follows:(1)By analyzing the operation principle and control requirements of wind power generation system,the mathematical model of the important state variables,such as wind energy capture,aerodynamic power and aerodynamic torque,is established.At the same time,the mathematical model of each subsystem is established by means of mechanism modeling,including the wind turbine model and the transmission chain model.(2)The variable pitch control strategy of wind turbine in different section is proposed by analyzing of the operation principle and control requirements of wind power generation system.Then a maximum power point tracking(MPPT)algorithm and the fuzzy adaptive PID control algorithm are established for the wind speed below the rated wind speed and above the rated wind speed respectively.This paper designs a dual-model pitch controller for DFIG,and simulating in Simulink.The simulation results show that the dual-mode controller has better adaptability to the full wind speed compared to the PID controller,which can obtain better wind energy capture efficiency at low wind speed and more stable power output at high wind speed.(3)The mechanics analysis and calculation of the load of the blade provides a theoretical basis for the selection of the main components of the variable pitch actuator,then a three-closed-loop pitch servo system based on vector control is designed for PMSM.In order to solve the problem that the d-q axis current is not fully decoupled and the torque current fluctuation exists in the traditional vector control scheme,a feedforward decoupling voltage compensation scheme is proposed.The simulation results in Simulink show that the improved pitch servo system has good tracking ability to the pitch angle position and the dynamic response to the propeller load.