Output based backstepping control for trajectory tracking of an Autonomous Underwater Vehicle

This study describes the design of an output based controller for a 4-DOF (three dimensional position x-y-z as well as yaw angle) Autonomous Underwater Vehicle (AUV) using a mixed structure of a backstepping like control form and a Robust Exact Differentiator (RED). The class of AUV system allowed to control the AUV's vertical coordinate independently. To adjust the x-y plane trajectories, the angular velocity with respect to the z coordinate was used as a virtual control action. The controller was designed to solve the tracking problem of the AUV to a desired reference trajectory. The controller was originally designed under the assumption of using the whole state to construct the closed-loop structure. As the differentiator converged in finite-time, then the controller was adjusted to use the velocity information obtained by the RED. The tracking performance obtained by the proposed controller was evaluated by tracking two reference trajectories. An acceptable performance was obtained by the application of the mixed controller in terms of the mean-square error of tracking problem. A set of simulations with different reference trajectories was used to evaluate the implementation aspects of the solution suggested in this study.