Adaptive Disturbance Observer-Based Novel Fixed-Time Nonsingular Terminal Sliding-Mode Control for a Class of DoF Nonlinear Systems

In this article,we study a novel fixed-time tracking controller for a class of degree-of-freedom nonlinear systems with mismatched and matched perturbations. A modified fixed-time stable system (FTSS) is first proposed, which has an advantage in convergence rate over the existing results. Moreover, an adaptive version of fixed-time disturbance observer (DO) is established to eliminate the requirement for prior knowledge of the perturbation bounds. Based on the aforementioned FTSS and DO, a new fixed-time terminal sliding-mode surface with singularity circumvention is constructed. Then, a novel composite tracking controller is designed, which can guarantee the tracking errors to converge to zero within the fixed time. The stabilities of both the DO and the resulting closed-loop systems are rigorously proved by the Lyapunov theorem. Simulation results of two representative examples demonstrate the efficiency of the proposed approach.