Non-linear tip speed ratio cascade control for variable speed high power wind turbines: A backstepping approach

Abstract

This study presents a non-linear tip speed ratio (TSR) cascade controller for high power wind turbines (WTs) considering the effects of the large rotor inertia and torsional behaviour of the shafts. A model-based non-linear rotor speed controller is proposed for the inner loop. The required speed reference is provided by an outer loop. A design procedure for cascade control of WTs is based on a backstepping design. It is shown that the above two-loop control schemes lead to a nice cascade structure for the closed-loop systems. Stability result adapted for analysis of this particular kind of systems is developed. The effectiveness of the proposed control approach is evaluated on a WT by comparing with typical control strategies such as non-linear TSR control, optimal torque control, and sliding mode control. Simulation results show that the proposed two-loop controller exhibits better performance than the above typical control strategies.