Output-Feedback Control of an Underwater Vehicle Prototype: Theory and Experiments

This paper deals with the motion control problem for an underwater vehicle (UV) prototype built at the University of Cagliari. The vehicle is equipped with a special propulsion system based on hydro-jets with variable-section nozzles. To cope with the heavy uncertainties affecting the prototype dynamics, the control system has been developed by means of the second-order sliding-mode control (2-SMC) approach. Chattering is removed since the 2-SMC approach confines the high-frequency switching to the higher derivatives of the control variable. The UV velocity is estimated in real-time by means of a recently-proposed variable-structure robust differentiator, and the experimental results show that a fast and accurate response can be obtained under several operating conditions. The control system and the main implementation issues are discussed in some detail.