Title: Output Feedback Tracking for Nonlinear Systems Using Variable Structure Control *
Abstract: We consider a single-input single-output nonlinear system which can be represented by an input-output model. The system, which can be transformed into the normal form, is required to be a minimum phase system. The model contains unknown bounded disturbances. We assume that the reference signal and its derivatives are bounded. A high-gain observer is used to estimate derivatives of the tracking error while rejecting the effect of the disturbances. We design a globally bounded output feedback variable structure controller that ensures tracking of the reference signal in the presence of unknown time-varying disturbances and modeling errors. We give regional as well as semiglobal results, but we do not require exponential stability of the zero dynamics nor global growth conditions.