Adaptive tracking and asymptotic rejection of unknown but bounded disturbances in nonlinear MIMO systems

Abstract

The goal of this paper is global disturbance rejection in nonlinear systems. An output feed- back controller with disturbance rejection is developed for a class of nonlinear multi input-multi output (MIMO) systems. The availability of state variables and the bound of disturbances are not required to be known in advance and reference tracking will is guaranteed. By the aid of designing an adaptive ob- server, a robust adaptive nonlinear state feedback controller using the estimated states is proposed. For tracking problem, an adaptive pre-compensator is used. The control methodology is robust against both constant and time varying bounded disturbances, maintaining effective performance. The adaptive laws are derived based on the Lyapunov synthesis method, therefore closed-loop asymptotic stability is also guaranteed. Moreover, for chattering reduction we use a low-pass filter. Consequently, small gain theo- rem is adopted to prove the stability of the closed-loop system. Simulation results are employed to illu- strate the effectiveness of the proposed controller.