Thruster Dynamics Compensation for the Positioning of Underwater Robotic Vehicles through a Fuzzy Sliding Mode Based Approach

The dynamic behavior of underwater robotic vehicles can be greatly influenced by the nonlinear dynamics of the vehicle thrusters. In this way, the implementation of a good control strategy for the thruster subsystem is essential for the accurate control of the entire robotic vehicle. It was already shown in the literature that without compensation for thruster dynamics the closed-loop positioning system can exhibit limit cycles. This undesired behavior may compromise the overall system stability and performance. This work focuses on the problem of controlling electrically actuated bladed thrusters, that are commonly employed in the dynamically positioning of remotely operated underwater vehicles. A sliding-mode compensator with fuzzy gain is proposed to stabilize the tracking error dynamics. Numerical simulation results suggest that this approach, when compared with an uncompensated counterpart, shows a greatly improved performance.