An Optimal Control Approach for a Fault Tolerant Control Applied to an AUV for Inspection of Dams

Abstract

The main problem suffered by Autonomous Underwater Vehicles (AUV) used for research and inspection of dams environments are the fault of thrusters during the trajectory and the uncertainties of water velocity, which can compromise the mission. So in this paper we propose an optimal control approach using the Linear Quadratic Optimal Control (LQ) and a Fault Tolerant Control of an AUV, which is able of detecting the fault. First we describe the six degree-of-freedom (DOF) nonlinear equations of dynamics and kinematics of the AUV which has four horizontal thrusters and two vertical thrusters, and then we propose a Fault Tolerant Control of the AUV using an optimal control approach. If there is a solution of the optimal control problem, then it is a solution of the robust control problem. We also use an Optimal Distribution of Propulsion and Control Forces in the control system. The control performance was validated via numerical simulations of the AUV occurring fault of two horizontal thrusters in specific time during the simulation. Even with disturbance caused by variable current of the dam and fault of some AUV's thrusters, with this method we were capable of keeping good track of our AUV, enhancing the robustness, assuring asymptotic stability, and the success of the mission.