Research On Hydraulic Variable Pitch System Of Megawatt Wind Turbine

Wind energy is paid more and more attention by the world since it is a kind of renewable celan energy. Variable pitch wind turbine is considered superior to other types of wind turbine due to its features such as high efficiency of utilizing wind energy and smooth output power. Variable pitch system is one of the key technologies in the megawatt wind turbine. This paper analyses the theory of hydraulic variable pitch control system of wind turbine. Furthermore, the proposed system is tested on ground.Firstly, the author briefly introduced the operating principle of wind turbine and the features of fixed pitch and variable pitch wind turbine, and overviewed the current development situation and tendency of wind turbine in China and oversea. Then, the author represented the meaning of this project and put forward the main objective of this research. The variable-speed constant-frequency theoretical basis of variable pitch wind turbine was deduced by analysis of aerodynamics. The mathematical model of variable pitch wind turbine was built and simulated. Simulation result is given to verify the reliabilities of theoretical analysis.In the traditional hydraulic driving pitch system of wind turbine, the variable pitch mechanism works with a piece of crank link connected mechanism through which the three blades are driven synchronously. In this paper, the individual hydraulic picth control was put forward and the pitch mechanism was designed. Based on the calculation of the balde driving force, the load of hydraulic system and the flux of hydraulic system, the author designed the individual hyadraulic pitch control system. Furthermore, the operating principle of the proposed hydraulic system and oil path under all kinds of working condition were explained in great detail. Since the hydraulic circuits during opening pitch and closing pitch were different, the linear mathematic models for hydraulic variable pitch mechanism among the two different operating processes were built up respectively. The closed loop control system was built up with PID controller and simulated.The designed hydraulic variable pitch control system was tested on the ground experimental bench, including normal exercise test, emergency feathering test, closed loop control test, control accuracy test and speed control test. Experimental result is given to verify the reliabilities of designed system and theoretical analysis. The designed hydraulic variable pitch system can satisfy the wind turbine's needs for accurate and fast control on pitch angle.