Finite-time terminal sliding mode control strategy for the unmanned surface vehicle with composite disturbances

Abstract

This work investigates the trajectory tracking control problem of an unmanned surface vehicle (USV) subject to composite disturbances, including both matched and unmatched disturbances, with unmeasurable velocities. To tackle this challenging issue, a finite-time control strategy is proposed that combines unknown state estimation with terminal sliding mode control (TSMC) techniques. First, a novel dynamic system for USV trajectory tracking is formulated, allowing the simultaneous handling of composite disturbances and unknown velocities within a unified control framework. Subsequently, an extended state observer (ESO) is designed to estimate the unknown states in the dynamic system, and to provide effective approximation of the unknown complex term with the finite-time convergence of estimation errors. Building on the ESO and the sliding mode control technique, a finite-time TSMC strategy with a dual-layer adaptive update law is proposed, achieving finite-time convergence of the closed-loop system while reducing chattering. Moreover, Lyapunov functions are constructed to prove the finite-time convergence of the USV's tracking errors and the stability of the dual-layer adaptive update law. Finally, the numerical simulation on a fully-actuated USV validates the effectiveness and superiority of the proposed control strategy.