A new control scheme for nonlinear systems with disturbances

A new learning control scheme, based on a nonlinear disturbance observer (NDO) coupled with a sliding-mode fuzzy neural network (SFNN) with a feedback-error-learning (FEL) strategy, is proposed for a class of time-varying nonlinear systems with unknown disturbances. The proposed controller, referred to as NDOFEL, involves two steps for obtaining an estimate of the time-varying lumped disturbance d(t) for improving the precision of the tracking control. The NDO is initially applied to estimate d(t), but an observer error does not converge to zero since d˙(t)≠0. The SFNN is then presented to estimate the observer error such that the output of systems follows a desired trajectory. The proposed NDOFEL has stable on-line learning ability, maintains high control performance in the presence of disturbance, and guarantees the stability of closed-loop systems on the basis of the Lyapunov theorem. The effectiveness and robustness of the proposed NDOFEL is demonstrated through simulation results obtained for the tracking control during wing rock phenomena. The results suggest that the proposed controller can significantly enhance the tracking performance of aircraft.