Line-of-Sight Path Following of an Underactuated USV Exposed to Ocean Currents using Cascaded Theorem

This paper presents a new path-following controller for an underactuated unmanned surface vessel (USV) exposed to unknown constant and irrotational ocean currents at a desired surge speed. The coordinate transformation is adopted to decouple the sway dynamic from the rudder angle and the USV model without the simplifying assumptions of having diagonal damping and inertia matrices is considered. The dynamics of the path-following errors are then expressed in a nonsingular way by using the moving Serret-Frenet (SF) frame. Next, the control strategy is designed using cascaded theorem, which comprises the line-of-sight (LOS) guidance principle, a path-variable updated law, and adaptive feedback linearizing techniques combined with a sliding mode, which guarantees that the error dynamics are uniform semiglobal exponential stable (USGES) and uniform globally asymptotic stable (UGAS). Finally, simulation results are presented to verify these theoretical results.