Robust nonlinear control for dynamic positioning system of ships based on disturbance observer

This paper presents a nonlinear robust control design for dynamic positioning system of ships with unknown disturbances using backstepping in combination with disturbance observer. By the means of Lyapunov stability theory, it is proved that the designed control law can force the position and heading of ships to the desired target value with arbitrarily small error and guarantee the uniform ultimate boundedness of all the signals of the resulting closed-loop system. Finally, simulation studies on a supply ship are included to illustrate the effectiveness of the proposed approach.