Semiglobal exponential output feedback control of ships

This paper describes a semiglobal exponentially stable output feedback control law for automatic heading control of ships described by a nonlinear model. Only compass (yaw angle) feedback is used. The yaw rate signal is reconstructed by a linear observer. A wave filter is included in the observer to reduce wear and tear on the rudder servo due to first-order wave-induced disturbances. Integral action is included in the control law to compensate for wave drift (second-order wave disturbances), low-frequency wind, and current disturbances. The performance and robustness of the controller are demonstrated in a simulation study of two medium-sized ships.