Research On The Double-Fed Wind Turbine Variable Pitch Control System

The appetite for energy of the world is increasing at a tremendous rate.Wind energy, a renewable form of energy becomes the most promising energy.With the rotor diameter of wind turbine enlarged,wind shear,tower shadow and turbulence effects make the asymmetric force load on wind turbine vary considerably,which has a bad influence on the safety and lifespan of wind turbine.To reduce the asymmetric force load of wind turbine and obtain high efficiency on utilizing wind energy,the control technologies of wind turbine are developing from fixed pitch control to variable pitch control.At present,the most advanced variable pitch control is electric drive individual pitch control,which is becoming a requisite control technology in large commercial wind turbines.This thesis firstly introduces the aerodynamic principle of variable pitch control and control objectives of double-fed wind turbine.Then it introduces the structure of hydromantic pitch servomechanisms and establishes the mathematical models of the rotor, drive train,double-fed generator,hydraulic drive pitch servomechanisms and wind speed. In high wind speed region,simulations of variable-pitch wind turbine adopting PID and LQG control strategies have been done,and the simulation results are compared and analyzed.Lastly,the thesis does research on the structure and model of the electric drive pitch servomechanisms.Simulations on the electric drive pitch servomechanisms under no-load and upload have been done respectively,and the simulation results show that the electric drive pitch servomechanisms have excellent tracing performance.Under existing experiment condition,the hardware and software of the electric drive pitch servomechanisms under DSP processor have been designed,and the control program of the electric pitch servomechanisms has been worked out.Since large wind turbine often has three individual electric drive pitch servomechanisms,so this thesis has done further research on the individual pitch control strategy.The aerodynamic load coefficients of individual pitch control model are confirmed by using wind turbine operation peculiarity table that is calculated by Bladed software.The concept adopting PI feedback loop control is applied to the individual pitch control,which utilizing Coleman transformation makes the decoupling of the multivariable control problem into three linear time invariant independent feedback control loops. Finally,the simulation results adopting PI feedback loop control strategy are compared to results adopting the collective pitch control.The important conclusion has been drawn is that the individual pitch control adopting the PI feedback control can reduce blade root nP frequency flap load,nacelle 0P,3P frequency tilt and yaw load that caused by wind shear, tower shadow and turbulence more obviously than the collective pitch control.