Disturbance estimator-based robust tracking control of an unmanned surface vessel with transient norm bound

This paper investigates the control problem of an unmanned surface vessel system in the presence of external disturbance. The dynamic model of an unmanned surface vessel is first introduced. Then, a nonlinear disturbance estimator is designed to estimate the external disturbance. Such an estimator ensures that the disturbance estimation error converges to zero in finite time, which means the disturbance can be compensated in finite time. Using the disturbance estimation result, a composite control technique that combines the sliding mode method and the backstepping method is developed to stabilize the position and yaw angle of the unmanned surface vessel. As a result, the tracking error is guaranteed to converge to zero asymptotically. The stability of the closed-loop system is proved based on Lyapunov theory. Furthermore, the transient norm performance of the tracking error is obtained by analyzing the selected Lyapunov function. Finally, the simulation is carried out to demonstrate the effectiveness of the proposed control scheme.