Nyquist criterion for chattering avoidance and global stability in observer-based sliding-mode control with parasitics

Abstract

A novel output-feedback sliding-mode control for linear plants is proposed. An observer-based chattering avoidance technique (OBCAT) is incorporated to counteract the effect of parasitics (unmodeled dynamics). A variable-gain unit control is designed to ensure global stability even in the presence of unmodeled dynamics. A necessary and sufficient Nyquist-like criterion for global stability is obtained, encompassing systems with time-delays, without prior assumptions about the observer gain and the characteristic parameter of the unmodeled dynamics which is not required to be sufficiently small. Numerical simulations and experimental results with a commercial robot manipulator illustrate the performance and effectiveness in chattering avoidance of the proposed control scheme and confirm its increased robustness with higher observer gain.