Nonlinear Control of Wind Energy Conversion System Involving DFIG

Abstract

This paper presents a nonlinear control method for wind energy conversion systems (WECS), involving doubly fed induction generator (DFIG) fed by IGBT-based buck-to-buck rectifier inverter. The main control objective is to maximize wind energy extraction which cannot be achieved without letting the wind turbine rotor operate in variable speed mode. A multiloop nonlinear controller is designed to meet two main control objectives, (i) speed reference optimization in order to extract a maximum wind energy whatever the wind speed, and (ii) power factor correction (PFC) to avoid net harmonic pollution. A multiloop nonlinear controller is synthesized using the backstepping design. A formal analysis based on Lyapunov stability is carried out to describe the control system performances. In addition to closed-loop global asymptotic stability, it is proven that all control objectives (rotor speed tracking, regulation of stator flux, DC link voltage regulation and unitary power factor) are asymptotically achieved.