Research On Robust Adaptive Control Of Large-scale Wind Turbines

Nowadays the growing environmental concerns drew much attention to the generation of renewable energy and the optimizing of the electricity structure. In order to make wind turbines more cost-effective and satisfy the exponentially growing installed capacity worldwide, the wind turbines are made larger and with higher rated powers. This type of wind turbine, however, leads to some other problems at the same time. One of the key technical issues to be addressed is to design viable and affordable control systems in support of the development in wind turbine technology, making wind energy conversion more profitable and more reliable. The wind turbine system is highly nonlinear and with uncertain system parameters. Traditional PID controller cannot satisfy such requirement. The study of advanced control theory for wind turbines is of great significance in the wind turbine technology.This thesis is focused on torque control for speed tracking of wind turbines in Region2and individual pitch control in Region3. To begin with, the aerodynamics of the wind turbines is examined. A speed tracking control that deals with the uncertainties of some system parameters, such as the inaccuracy of the wind speed measure or estimation and the drift of Cp surface, is proposed. Individual pitch control (IPC) is an advanced wind turbine control method that is able to alleviate the asymmetric rotor loads without compromising energy capture. A detailed model of individual blade positioning model of wind turbines is derived, which is more effective in describing the nonlinear relationship of individual pitch control system by considering the combined effects of all the possible moments acting on the rotor blades. A robust adaptive control strategy is proposed to avoid using the uncertain information of the system directly. A back-stepping adaptive controller is proposed to deal with the control challenge of IPC system model which considers the actuator dynamics. Both theoretical analysis and numerical simulation confirm that the proposed controllers exhibit robustness and adaptation capabilities, ensuring high precision tracking.