Robust adaptive control of a class of uncertain nonlinear systems with time-varying output constraints

Abstract

In this paper, a robust adaptive controller for single input uncertain nonlinear systems by taking parametric uncertainties and external disturbance into consideration is proposed, in which the adaptive law is synthesized to handle parametric uncertainty and a novel robust term is incorporated to attenuate lumped disturbance such as unconsidered dynamics as well as external disturbances. An asymmetric time-varying Barrier Lyapunov Function (BLF) is employed to ensure that the initial output can start from anywhere within the pre-set output constrained space. Moreover, the developed controller does not require a priori knowledge on the bound of the lumped disturbance. In addition to the stability of the whole closed-loop system is obtained, the asymptotic output tracking (i.e. the output tracking error converges to zero as time limits to infinity) can also be guaranteed. An illustrative example is provided to show the effectiveness of the proposed control scheme.