Input-output linearization designs for straight-line tracking control of underactuated ships

A nonlinear mathematical model for straight-line tracking control system of underactuated ships is established. Then, based on the input-output linearization technique, a state feedback control law, which forces an underactuated ship to asymptotically track a prescribed straight line, is developed using the idea of redefinition output variable. Meanwhile, the proposed control law can remove the constraints that the yaw rate is required to be nonzero and the convergence of the components in the redefinition output variable is not guaranteed. Numerical simulation results on an ocean-going training ship are presented to validate the proposed controller. It is shown that the proposed controller exhibits relatively high effectiveness and good transient performance.