Research And Control Strategy To Reduce The Load Asymmetry OF Wind Turbine Rotor

With the development of energy technologies, wind power sees an increasing growth in energy utilization. Cumulative installed capacity of wind turbine in China leads the world in2012. Nowadays, the capacity, tower height and blade length have increased tremendously, as a result, torque ripple and wind turbine vibration induced by asymmetry load have caused widespread safety concerns. Thus load control and tower top displacement control becomes much more important. Once the vibration gets out of control, it will lead to fatigue damage or even falls down of tower.To study the assymetry load effect on wind turbine aerodynamic torque, this paper built wind models including wind shear and tower shadow. Based on aerodynamics technology, this paper use the wind model to simulate an effective aerodynamic torque, which proves the existence of wind shear and tower shadow induced3p oscilations and also demonstrates the effects of wind shear on the total aerodynamic torque are much smaller than those due to tower shadow. Meanwhile, torque oscilation induces tower vibration. With the knowledge of structrural dynamics, this paper studied vibration models of blade and tower, the results provides theoretical foundations for controller design.Initially, the pitch control was mainly used for the optimization of wind energy capture below rated wind speed and constant power control above rated wind speed, of which the collective pitch control algorithm could satisfy easily. However, when we want to control the load of wind turbine, the approach no longer meets our goals. Therefore, the pitch controller designed in this paper mainly contains two parts, one is collective pitch controller which is used to main rated power, the other is individual pitch controller which is used to control asymmetry load. This paper starts with basic wind turbine theory; introduced individual pitch control algorithm to eliminate the load on wind turbines based on classical equation of motion, and built the wind turbine model. According to robust control theory and optimal control theory, the paper achieved an asymmetry load controller. Simulated in Matlab, the results show that the control method applied in this paper can not only meet the basic requirements but also be able to reduce the load significantly.