Sliding Mode Control of Variable Speed Wind Turbines Via Two Time Scale Theory

In this paper, maximum power point tracking problem of variable speed wind turbine systems is studied based on two time scale theory. First, the two-mass model of variable-speed wind turbine is presented, and the model is transformed into singularly perturbed form by analyzing its two time scale feature. Then, a controller composed of sliding model controller and robust $H_{\infty}$ controller is developed which offers the system the ability of precise tracking and disturbance attenuation. The singularly perturbed model is decomposed into a slow subsystem and a fast subsystem. A sliding mode controller is designed for the slow subsystem to provide wind rotor speed the capability to follow the optimal rotor speed. A robust $H_{\infty}$ controller is developed for the fast subsystem to reduce the disturbance effects and mechanical loads. The effectiveness of the new control scheme developed is shown via a verification example.