The antidisturbance control scheme for the dynamically positioned ships with ocean environmental disturbances and actuator saturation was presented. The ocean environmental disturbances comprises slowly varying disturbances and additional stochastic disturbances. The stochastic disturbance observer was constructed to online estimate the slowly varying disturbances. Based on estimation, a stochastic antidisturbance controller was proposed by combining the disturbance observer-based control with the stochastic control, where the actuator saturation was dealt with by the polytopic bounding technique. Furthermore, the optimal control allocation method was introduced to distribute control commands into each actuator. Finally, the ship's position and heading are maintained at the desired values and all signals of the closed-loop system are asymptotically mean-square bounded. And comparative simulation under different conditions demonstrates the validity and the superiority of the proposed control scheme.

There are a large number of non-harmonic disturbances generated by nonlinear exogenous systems in realistic engineering. The current disturbance observer is not applicable for estimating the non-harmonic disturbance with unknown nonlinear dynamics, thus greatly reducing the accuracy of the controller. This paper addresses a class of stochastic systems with multiple heterogeneous disturbances including white noise and non-harmonic disturbance with unknown smooth nonlinear function, which can be approximated by fuzzy logic systems. Based on the approximation of the unknown nonlinear function, an adaptive disturbance observer (ADO) is constructed to estimate non-harmonic disturbance. Combining disturbance observer-based control with fuzzy control, an elegant anti-disturbance control (EADC) scheme is proposed such that the composite system achieves asymptotically bounded in mean square. Simulation examples show that the state responses of the system gradually approache [Formula: see text] from divergence, indicating that the effectiveness of the controller is satisfactory. In addition, the anti-disturbance control accuracy of EADC approximately improves [Formula: see text] times compared with [Formula: see text] control. The simulation results demonstrate the feasibility and effectiveness of the proposed scheme.

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