Output-feedback tracking for nonlinear systems with time delay and input saturation

Abstract

This paper focuses on solving the output-feedback tracking problem for a class of nonlinear time-delay systems in the presence of unmeasurable states and input saturation. A distinctive feature is that the growth assumptions imposed on system nonlinearities are proven to be unnecessary and can be removed. Based on this, by constructing a full-order state observer to handle unmeasurable states and introducing an auxiliary system to compensate for input saturation, an output-feedback controller is explicitly constructed with the help of Lyapunov-Krasovskii functional method and backstepping technique. It is proven that the designed controller can render the closed-loop system be globally uniformly ultimately bounded. Particularly, instead of converging to an arbitrarily small neighborhood of zero as in related results, the tracking error is ensured to be tuned by design parameters and input saturation error in the mean sense. Finally, a simulation example is provided to validate the effectiveness of the proposed scheme.