Voltage/pitch control for maximisation and regulation of active/reactive powers in wind turbines with uncertainties

This study addresses the problem of controlling a variable-speed wind turbine with a doubly fed induction generator (DFIG), modelled as an electromechanically coupled non-linear system with rotor voltages and blade pitch angle as its inputs, active and reactive powers as its outputs, and most of the aerodynamic and mechanical parameters as its uncertainties. Using a blend of linear and non-linear control strategies (including feedback linearisation, pole placement, uncertainty estimation and gradient-based potential function minimisation) as well as time-scale separation in the dynamics, the authors develop a controller that is capable of maximising the active power in the maximum power tracking (MPT) mode, regulating the active power in the power regulation (PR) mode, seamlessly switching between the two modes and simultaneously adjusting the reactive power to achieve a desired power factor. The controller consists of four cascaded components, uses realistic feedback signals, and operates without knowledge of the C_p-surface, air density, friction coefficient, and wind speed. Finally, the authors show the effectiveness of the controller via simulation with realistic wind profiles.