Practical proportional integral sliding mode control for underactuated surface ships in the fields of marine practice.

Environmental disturbances and systematical uncertainties are the main obstacles for ship motion control. This paper devotes to enhancing the control system robustness of underactuated surface ships with model uncertainties and environmental disturbances. A novel nonlinear robust adaptive scheme with sliding mode control is proposed for underactuated ships to track the desired path generated by the logical virtual ship in the presence of unknown plant parameters and environmental disturbances. Compared with the existing results, the proposed controller is designed based on the combination of PI sliding mode control and the upper bound estimation of disturbances. With the proposed design, the control scheme could not only obtain a better performance of the control system, the continuous scheme also reduce the chattering of system by a special construction of the sliding manifolds. Numerical simulations are given to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]