Optimal DFIG Flux and Speed control for Wind System in Presence of Magnetic Hysteresis

Abstract

Several works dealt with the control of the doubly fed induction generator (DFIG) integrated in a wind system. To reduce the problem complexity, the DFIG considered model is generally based on the assumption that the magnetic characteristic is linear. In coherence with this assumption, most DFIG control strategies involved rotor flux regulation around a fixed operation point (generally a nominal flux value). As a matter of fact, a constant flux reference, especially in wide range load and wind speed variations, doesn’t assure an optimal performance operation mode. Practically, without accounting for the nonlinearity of the machine magnetic characteristic, control strategies involving wide range flux reference variations cannot be reached.In this paper, based on a new DFIG model that accounts for the magnetic characteristic hysteresis and saturation, a new speed and flux optimal controller is developed. This regulator is designed using the backstepping technique. The performances of the proposed controller are formally analyzed using tools from the Lyapunov stability and averaging theory, and their supremacy with respect to standard control solutions is illustrated through simulations involving wide range variation of the wind speed.