Actuator fault tolerance for a WAM-V catamaran with azimuth thrusters

In this chapter, we present a fault-tolerant control scheme for an over-actuated unmanned surface vehicle (USV) equipped with two azimuth thrusters. The scheme manages the most common actuator faults, i.e., loss of efficiency of the thruster and lock-in-place of the azimuth angle. The scheme is based on a three-layer architecture: a heuristic-based control policy for proper reference generation, a control law for the vehicle dynamics to achieve speed tracking of the generated reference, and a control allocation level for optimally redistributing the control efforts among the thrusters even in presence of actuator faults and failures. The control allocation and the control policies are the main focus of the chapter, since their reconfiguration capabilities allow tolerance with respect to actuator failures. On the contrary, the control law does not depend on the health status of the system. The scheme is then tested in simulation, using a nonlinear model of a wave adaptive modular vessel catamaran.