Backstepping Control of a Multimegawatt Variable-speed Wind Turbine for Maximum Power Point Tracking

Since the dynamic nonlinear characteristics and the strong inertia of the multimegawatt variable-speed wind turbine(MVWT), the conventional method on maximum power point tracking (MPPT) causes a large wind speed tracking deviation and significant power losses. Due to the ability of fast response, a backstepping control applied to MVWT is proposed. A new nonlinear dynamic model in a lower triangular form is constructed by transforming the complex system into multiple subsystems. The virtual control of each subsystem is selected from top to down of the lower triangular model. And the virtual control laws are obtained based on Lyapunov stability criterion. Until the augmentations recover the last subsystem, the control law of the last subsystem also is the actual control law. Simulation is implemented by using a FAST(Fatigue, Aerodynamic, Structure, and Turbulence) simulator based on the NREL(Nation Renewable Energy Laboratory) offshore 5-MW baseline wind turbine. The results demonstrate that the backstepping control in this paper can improve the tracking performance of rotor speed and increase the power efficiency. The asymptotic stability of the wind turbine system is also guaranteed under circumstance of uncertainties.