Output Feedback Thruster Fault-Tolerant Control for Dynamic Positioning of Vessels Under Input Saturation

In this paper, an output feedback fault-tolerant control (FTC) scheme is presented for the dynamic positioning of vessels subjected to external disturbances, dynamic uncertainties, and thruster saturation constraints under thruster faults. A high-gain observer is constructed to acquire the estimates of vessel velocities. An auxiliary dynamic system is introduced to compensate the effect of the thruster faults and saturation constrains. Neural network with iterative updating laws is employed to approximate the lumped uncertainties caused by unknown environmental disturbances and dynamic uncertainties of vessels. Furthermore, the control allocation is accomplished to distribute the FTC forces and moment among individual thrusters. It is theoretically proved that the derived FTC scheme has the capability to maintain the vessel position at the desired values and guarantees that all signals in the closed-loop control system are uniformly ultimately bounded. Finally, the simulation results demonstrate the effectiveness of the proposed control scheme.