Nonlinear mapping for performance improvement and energy saving of underwater vehicles

This paper proposes an improvement on underwater vehicles control strategy using an adaptive sliding-mode method. This improvement is threefold. First, water current compensation is explicitly dealt within in the control law. Second, a nonlinear parameterization is developed by employing new methods for the design of the sliding surface, aiming at vehicles tracking performance. Third, parameters of the designed sliding surface in the control law are varied according to a nonlinear mapping of thruster forces aimed to energy saving of propulsion system. Three different methods are given for the design of the sliding surface. The proposed control law guarantees global asymptotic stability of the tracking error, and the stability proof is provided in the paper even in the presence of variable currents. Moreover, the tracking performance and energy saving are compared with conventional methodologies to show the effectiveness of the proposed method.