Dynamic positioning for underactuated surface vessel via L1 adaptive backstepping control

This paper is concerned with the problem that fast-transient response and excellent robustness cannot be satisfied simultaneously in the process of dynamic positioning (DP) for underactuated surface vessel (USV) in shallow water. By combing the improved L1 adaptive control with backstepping method, a novel control scheme is designed, which can ensure a fast adaptation with a guaranteed smooth transient response without any overshoot and chattering phenomenon. System uncertainties and disturbances are estimated by the nonlinear observer. Moreover, the optimized extremum seeking control (ESC) is employed to reduce energy consumption under environmental disturbances. Rigorous theoretical analysis shows that all closed-loop signals are bounded-input bounded-state. Simulation and sea test results are presented to illustrate the effectiveness and the robustness of the proposed strategy under the condition of external disturbances and parametric uncertainties.