Disturbance characteristic information observer-based control for nonlinear systems with unknown Lipschitz constant

Abstract

This article proposes a disturbance characteristic information observer (DCIO)-based control strategy for systems with unknown Lipschitz nonlinearity. The proposed DCIO utilizes the estimated parameters of sinusoidal disturbance to generate the compensation signal. This procedure aims to remove the disturbance characteristics component in the closed-loop systems, and only the nonlinearity-related part needs to be considered. As a solving skill for the Lipschitz nonlinearity problem, the time-varying gain is constructed to attenuate for the estimation error caused by the nonlinear term, which has two important advantages over previous designs. First, the DCIO does not impose the known-Lipschitz-constant condition on the nonlinear systems, nor other structural conditions on the system dynamics as in the existing observer designs. Second, the proposed DCIO and time-varying controller are designed independently. The coupling of disturbance and nonlinearity is avoided due to the full utilization of disturbance characteristics. Simulation results on the robotic manipulator are provided to validate the effectiveness of the proposed method.