Fixed-time Disturbance Observer-based Sliding Mode Control for Mismatched Uncertain Systems

This paper concerns with fixed-time control for the mismatched uncertain system. We propose a fixed-time disturbance observer (DO). Then, a non-singular fixed-time sliding-mode surface and controller are designed based on the estimations of proposed DO. Existing DO-based sliding-mode control (DOSMC) and finite-time DOSMC schemes can eliminate the mismatched uncertain problem by using traditional sliding-mode control (TSMC). However, the convergence times of these DOSMC schemes are infinite or related to the initial system conditions. Unlike existing approaches, the proposed fixed-time DOSMC can guarantee the convergence time is uniformly bounded and the upper bound is independent on initial system conditions, which implies that the proposed scheme can provide similar convergence performance with the same control parameters under different initial conditions. Simulation result shows the excellent convergence performance of the proposed scheme.