Differentiator-Based Output-Feedback Controller for Uncertain Nonautonomous Nonlinear Systems with Unknown Relative Degree

A novel output-feedback controller for uncertain nonautonomous nonlinear systems with unknown relative-degree is proposed in this study. With the assumption that the upper bound of the relative degree is known, the proposed control scheme is designed based on the input filter and higher-order switching differentiator(HOSD) with over dimension. Using the overestimated time-derivatives of tracking error by HOSD, the proposed controller compensates for the effects of uncertainties including an unknown relative degree in the controlled system. Assuming that the internal zero dynamics, if they exist, are stable, the asymptotic stability of the closed-loop system is guaranteed.