Automatic reconfiguration and control of the MARES AUV in the presence of a thruster fault

In this paper, we address the control of a small-sized autonomous underwater vehicle (AUV), the MARES. We focus on the vertical motion of the vehicle while contemplating an alternative actuator configuration which may operate in the presence of a possible fault. We present a method to detect the occurrence of a fault and to identify the faulty thruster. In normal operation, the MARES AUV makes use of two through-hull thrusters for accurate vertical positioning. Nevertheless, the vehicle depth is still controllable with only one of these but an adequate operation requires the redefinition of the control law. Two modes of operation are made possible by deriving a new feedback control law for the configuration with only one vertical thruster. Based on the Lyapunov theory and on the backstepping method, we determine a control law that makes the vehicle tend to the reference with null error. As a demonstration of the performances of our approach, we present some results obtained from field experiments.