Robust adaptive control of underactuated ships with input saturation

This paper addresses the problem of practical stabilisation of arbitrary reference trajectories, including time-varying trajectories and fixed points for underactuated ships subjected to input saturation and parametric modelling uncertainties. Two novel coordinate transformations are introduced to deal with the problems caused by the non-zero off diagonal terms in the inertia matrix and the underactuation, respectively. Based on the backstepping technique, the dynamic surface control method and the Lyapunov's direct method, a saturated robust adaptive controller is designed to achieve practical convergence of tracking errors to a bounded area centred at zero. Some comparative simulations are performed to illustrate the effectiveness of the proposed control scheme.