An energy efficient fault-tolerant controller for homing of underactuated AUVs

In the event of a failure that will prevent an Autonomous Underwater Vehicle (AUV) from executing a specified task, the vehicle must be recovered safely to avoid further damage to itself or to other vehicles/agents in the neighbourhood. Motivated by this operational requirement, this work presents an optimal fault-tolerant controller to drive an underactuated AUV to a recovery point (so-called automatic homing manoeuvre). The case of a critical failure that leaves only one of two stern thrusters available to drive it to the desired recovery area is considered. The control law proposed relies on the use of a Fourier series-based strategy to compute the control action as a function of the relative orientation of the vehicle with respect to the target recovery point. Energy consumption is also considered in the proposed control law, so that an appropriate trade-off can be achieved between reaching the destination faster and reducing the energy consumed as a function of mission requirements and vehicle specifications. The stability and convergence of the proposed scheme are demonstrated analytically, a comparison with MPC scheme is shown and simulation examples illustrate how the control law effectively drives the vehicle to a neighbourhood of the desired target point even in the presence of unknown constant currents.