A Fault Accommodating Control of an Autonomous Underwater Vehicle Under Thruster Redundancy and Saturation

An approach to the allocation of thruster forces of an autonomous underwater vehicle (AUV) is investigated in this paper. Generally, the number of thrusters in an AUV is more than what is minimally required to produce the desired motion. This paper presents a framework that exploits the excess number of thrusters to accommodate thruster faults during operation. First, a redundancy resolution scheme is presented that takes into account the presence of excess number of thrusters along with any thruster faults, and determines the reference thruster forces to produce the desired motion. This framework is then extended to incorporate a dynamic state feedback technique to generate reference thruster forces that are within the saturation limit of each thruster. These reference thruster forces are utilized in the thruster controller to generate the required motion. This approach resolves the thruster redundancy in the Cartesian space and allows the AUV to track the task-space trajectories with asymptotic reduction of the task-space errors. Results from computer simulations are provided to demonstrate the viability of the proposed scheme.