The study of variable speed variable pitch controller for wind power generation systems based on sliding mode control

Abstract

The stochastic nature of wind speed, time-varying of system parameters, system lagging and nonlinearities can lead to instability of the power generated by wind turbines. In order to improve the dynamic performance in the operation region of constant power output, multivariable control strategy using a sliding mode control technique is proposed based on analysis of the pitch-controlled system research status quo. The designed sliding mode controller is based on multivariate linear model which is linearized near the operation point of the system and is derived from exponential reaching law, thereinto, the adopted linear switching function is designed by pole assignment method. The proposed multivariable control strategy adds the generator torque as the other control variable with blade pitch angle to be controlled simultaneously above rated wind speed. The addition of generator torque control can not only guarantee generator power and generator speed at the rated value, but minimize torsional torque fluctuations in the drive train and pitch actuator activity. This can improve the quality of the electrical power and increase the life time of the mechanical parts of the system. Multivariable (variable speed variable pitch) and monovariable (variable pitch) control strategy under high wind speed are simulated on Matlab, highlight the advantages of multivariable control strategy though comparison and analysis. The performance of the proposed SMC multivariable strategy is simulated and compared with PI control method. Simulation results verify the validity of control algorithm.