Horizontal motion tracking control for an underwater vehicle with environmental disturbances

In this paper, the trajectory tracking problem for horizontal motion of underwater vehicle with unknown environmental disturbances is solved based on the disturbance observer method. A 3-DOF nonlinear model of underwater vehicle including matched and non-matched external disturbances is developed. And then, a classical backstepping tracking controller is designed based on the established multi-input and multi-output system. In order to tackle the external disturbances, two nonlinear disturbance observers are employed to provide appropriate compensation in the system. Meanwhile, the dynamic surface control technique is used to handle the problem of explosion of terms. With the proposed control scheme, the estimated errors of the disturbance observers and the tracking errors of the closed-loop system are guaranteed to be uniformly ultimately bounded. Finally, simulation results are given to illustrate the performance of the proposed control scheme.