Path following of marine surface vessels with saturated transverse actuators

This paper presents a control technique for low speed path following applications of fully actuated marine surface vehicles with saturated transverse actuators. Path following of straight lines is considered. The control system is designed to counteract disturbances caused by ocean currents and combines the Integral Line-of-Sight guidance law (ILOS) with a nonlinear saturated sway controller. The ocean current is considered constant, irrotational and acting in any direction of the inertial frame. The control configuration is derived from controllers designed for underactuated marine vehicles and exploits both sway actuators and side-slipping to compensate for the drift and guarantee successful path following. The additional use of transverse actuators for disturbance compensation increases mission flexibility when trade-offs between path following speed, power usage and energy consumption arise. This represents an extension of the underactuated case. The vehicle dynamics are defined in terms of relative velocities only, since the ocean current is assumed irrotational. Closed loop uniform global asymptotic stability and uniform local exponential stability are achieved and explicit bounds on the guidance law parameters are given. The theoretical results are supported by simulations.