Disturbance decoupling control based trajectory tracking for underactuated ships

To solve the trajectory tracking problem of underactuated surface ships with internal uncertainties and external disturbances, a unique dynamic disturbance decoupling control (DDC) strategy, based on Active disturbance rejection control (ADRC) frame, is introduced to track the ship trajectory/path. By requiring as little information on ship model as possible, the intention is to make the DDC method appled in ship trajectory tracking control. By use of decentralized control theory, the trajectory tracking control tasks are divided into the control over ship cross track and longitudinal position, and the inputs are defined as the rudder angle and the propeller revolutions. Drift angle compensation is added to the controller by designing a transformation equation. The cross track static error caused by wind and current is removed. Simulation results obtained on a nonlinear kinetic model of a training ship show good performance in the presence of significant unknown disturbances and unmodeled dynamics.