Research On The Control Strategy Of The Variable Pitch System Of Wind Turbines

Due to the development of control technology,the feed-in tariffs of wind power has been trimmed constantly,the wind power has become one of the dominant forms of renewable energy generation.Variable speed variable pitch is the dominant control technology of wind power in the world with its high efficiency in tracking the best wind power capture points and flexibility in improving the power quality and conversion efficiency of the wind turbines.And the control effect of variable pitch strategy will directly affect the stability and safety of the entire wind turbines.So,how to improve the output performance of wind turbines has become the focus and the research hot of wind power practitioners.And to ameliorate variable pitch control strategy by the more mature intelligent methods is a wonderful method.The research object of this paper is the variable pitch system of wind turbines worked rated wind speed above.And the intellectualized optimization control schemes for the pitch are proposed.Firstly,with the help of MATLAB/SINMULINK simulation environment,the wind speed model and the overall model of the variable pitch wind power system are built.Then the correctness and rationality of the mathematical model of the overall wind power system are verified by PI control.Finally,in order to improve the output characteristics of wind power system with many nonlinear factors,two feasible variable pitch control strategies are proposed.The strategy of variable pitch control based on fuzzy-PI and fuzzy feedforward.Among them,the fuzzy feedforward controller gives the proper feedforward compensation angle value by live wind speed and the variation in wind speed between two sampling.Similarly,then the fuzzy-PI controller gives the proper pitch angle variation by the power error and its change rate of the wind turbines.Then the reference pitch angle of variable pitch system is combined with the feedforward compensation angle and the output pitch angle variation by fuzzy-PI controller.And the fuzzy-PI controller is a double-mode controller of fuzzy and PI.To avoid the dead area response of fuzzy-mode,a nonlinear function has been designed to achieve the smooth switching of two modes.Simulation results show that the output characteristics of the turbines are improved effectively by the strategy.The strategy of variable pitch control based on fuzzy feedforward and quasi-sliding mode.And the strategy has the same fuzzy feedforward controller as the the strategy of variable pitch control based on fuzzy-PI and fuzzy feedforward which suppressed the disturbance of the wind speed and reduced the overshoot of system.Among them,the quasi-sliding mode controller takes the wind turbine speed error and its derivative as the state variation to get the proper pitch angle variation.Then the reference pitch angle of variable pitch system is combined with the feedforward compensation angle and the output pitch angle variation by quasi-sliding mode controller.In addition,the quasi-sliding mode controller chooses a nonlinear exponential reaching law to ameliorate the smoothness of the setting process of wind power system.Simulation results show that the overshoot of system has been reduced and the response speed of system has been accelerated as well by the strategy.