Straight Line Path Following for Formations of Underactuated Marine Surface Vessels

The problem of formation control and path following for underactuated 3-degrees-of-freedom (3-DOF) marine surface vessels is considered. The proposed decentralized controller makes the vessels asymptotically constitute a desired formation that follows a given straight line path with a given forward speed profile. The controller consists of a cross-track control law, based on line-of-sight guidance, and a nonlinear synchronization control law. The closed-loop dynamics of both the cross-track errors and the synchronization errors are analyzed in detail using nonlinear cascaded systems theory and the overall cascaded system is shown to be both uniformly globally asymptotically stable and uniformly globally exponentially stable under mild assumptions. The proposed control strategy is validated in experiments in both calm water and in waves using a scale model vessel.