Power optimization and control in wind energy conversion systems using extremum seeking

Power optimization and control for grid-coupled wind energy conversion systems (WECS) has been extensively studied for variable speed wind turbines (VSWTs). However, existing methods are model-based, and are highly dependent on the system dynamics. We employ extremum seeking (ES), which is a non-model-based optimization approach, to perform maximum power point tracking (MPPT), i.e., extract maximum power from WECS in their sub-rated power region. Since the performance of the ES design is related to the system dynamics, we also design a nonlinear controller, based on the field oriented control concept and feedback linearization, that guarantees desired closed-loop performance. The outer ES loop tunes the wind turbine speed to maximize power capture for all wind speeds within the sub-rated power operating conditions. The inner-loop nonlinear control maintains closed-loop performance through a matrix converter, by regulating the electrical frequency and voltage amplitude of the stator of the (squirrel-cage) induction generator. Simulation results are presented to show the effectiveness of the proposed design.