LAUSR

This paper addresses a three-dimensional (3D) trajectory tracking problem of underactuated autonomous underwater vehicles (AUVs) subjected to input saturation and external disturbances. The proposed controller can achieve practical convergence of tracking errors for general reference trajectories, including persistently exciting (PE) time varying trajectories and fixed points. At first, a modified error state formulation is introduced to tackle the situation that desired velocities do not satisfy PE condition. Then, on the basis of the backstepping technique and a Nussbaum-type even function, a saturated controller is designed so that the tracking errors can converge to a bounded neighborhood of the origin. The stability analysis based on Lyapunov theory shows that the tracking errors are globally ultimately uniformly bounded. Finally, some simulation results illustrate the effectiveness and robustness of the proposed control strategy.