Control of ship replenishment by output feedback synchronization

In this paper an observer-controller scheme is presented for synchronization of two ships in a leader-follower configuration with only position/yaw angle measurements available. A new observer for ships with saturation used on some of the observer terms is presented and applied to estimate the velocity of the follower ship. The observer is shown to give globally asymptotically stable error dynamics in open-loop. For the leader ship a high gain observer is used, which will give small uniform ultimate bounds for the observer errors. Uniform ultimate boundedness of the synchronization errors is shown by using Lyapunov functions and a small gain theorem. The result is valid if the initial values are in a region of attraction and some conditions for the controller and observer gains are satisfied