Stochastic Disturbance Rejection Tracking for Surface Ships with Thruster Saturation

This article describes a composite disturbance rejection tracking control for ships with stochastic disturbances under actuator saturation. The stochastic disturbances are described by the first-order Markov process. The composite control scheme is built by incorporating the stochastic disturbance observer and the auxiliary filter with the vectorial backstepping technique. First, a stochastic disturbance observer is designed to provide stochastic disturbance on-line estimations. Second, an auxiliary filter is employed to generate filtered versions of non-achievable portions of the control derivation between commanded control signals and actual control signals, such that the stochastic anti-disturbance control performance can be preserved under actuator saturation effects. The composite stochastic disturbance rejection control achieves the ship position and heading tracking with ensuring the closed-loop stability. Simultaneous achievement of stochastic disturbance suppression and mitigation of actuator saturation is accomplished. Simulations conducted on a 1:70 scale ship model illustrate the validity of the proposed control strategy.