Discrete-time Sliding Mode Control for Guidance of an Unmanned Surface Vehicle

This paper discusses the Navigation, Guidance and Control (NGC) system of an Unmanned Surface Vehicle (USV) through extended numerical tests carried out with the prototype autonomous catamaran Charlie. A cascade control scheme is proposed which provides accurate straight line following performance with an USV equipped only with a GPS, a compass and an extended Kalman filter to estimate the vehicle position and speed. In the considered solution an outer Discrete-Time Sliding Mode Control (DTSMC) loop is designed for the guidance of the USV and an inner PI-based gain scheduling control loop regulates the vehicle linear and angular speed. Reported numerical tests show that the adopted control scheme produces good performance for straight lines following tasks.