Energetic Optimization of Variable Speed Wind Energy Conversion Systems by Extremum Seeking Control

Power optimization and control for grid-coupled wind energy conversion systems (WECS) has been extensively studied for variable speed wind turbines. However, existing methods widely use model-based power optimization algorithms in the outer loop along with linear control techniques in the inner loop. The transient performance of this combination is dependent on the system's operating point, especially under fast varying wind regimes. We employ extremum seeking (ES) in the outer loop, which is a non model-based optimization approach, to perform maximum power point tracking, i.e., extract maximum power from WECS in their sub rated power region. Since the convergence rate of the ES design may be limited by the speed of the system dynamics, we also design a nonlinear controller, based on the field-oriented control concept and feedback linearization that yields improvement in convergence rate by two orders of magnitude. The outer ES loop tunes the turbine speed to maximize power capture for all wind speeds within the sub rated power operating conditions.