Output Feedback DSC Design for a Class of Nonlinear Systems with unmodelled Dynamics

An output feedback adaptive tracking control scheme is proposed for a class of uncertain nonlinear systems with unmodelled dynamics and unknown control gain sign.The unmeasurable system states are firstly estimated by using Kreisselmeier observer,then output feedback dynamic surface control system is designed in recurrent fashion,unknown control direction is counteracted by utilizing Nussbaum function.Explosion of complexity inherent in traditional backstepping control is eliminated,and the update law of the unknown parameters appears in the first step of control design procedure,therefore,simplification of controller design and realization is achieved.It is proved that the proposed scheme guarantees not only semi-global uniform ultimate boundedness of all signals in the closed-loop system,but also the tracking error to a small neighborhood of the origin by choosing design parameter appropriately.Simulation results show the effectiveness of the proposed scheme.