MPC-based optimal path following for underactuated vessels

In this paper we propose a control law for an underactuated vessel to follow a straight line path using a line-of-sight (LOS) guidance law. To achieve optimal performance of the closed-loop system, a parameter of the LOS guidance law, the lookahead distance, is chosen to be time-varying and updated with a model predictive control (MPC) algorithm. For the closed-loop system we prove guaranteed global asymptotic stability (convergence to the path) and demonstrate in simulations that the performance of the system (fast convergence to the path with minimal overshoot) is improved compared to what can be achieved with a constant (small or large) lookahead distance. It is shown that global asymptotic stability of the closed-loop system is preserved even in the case when the MPC solver cannot find a solution to the optimization problem within given computation time limits.