Anti-disturbance control for dynamic positioning system of ships with disturbances

A robust anti-disturbance control (RADC) strategy is investigated for the ship dynamic positioning (DP) systems with unknown time-varying disturbances. The disturbances are brought about by wind, second-order wave drift, ocean currents as well as unmodeled dynamics, which are modelled by the first-order Markov process. The disturbance observer (DO) is established to online estimate disturbances. Then, the anti-disturbance controller for the ship DP system is designed and the stability analysis of the composite system is presented by using stochastic stability theory. The DOBC and the pole placement methods are implemented to improve the robustness against ocean environmental disturbances. The unknown time-varying disturbances can be attenuated such that the yaw angle and position of the ship reach the desired value with high accuracy. Finally, simulation on a supply ship is given to illustrate the validity of the proposed control strategy. (C) 2020 Elsevier Inc. All rights reserved.