Fault-Tolerant Control for Dynamic Positioning of Ships Based on an Iterative Learning Observer

This paper develops a fault tolerant control (FTC) scheme for dynamic positioning (DP) of ships with thruster faults and environment disturbances. An iterative learning observer (ILO) is constructed to estimate the unknown thruster faults and environment disturbances. By combining the ILO with backstepping technique, an FTC law is designed for the DP control system. Furthermore, the control forces and moment computed from the FTC law are allocated to each thruster through applying the Lagrange multiplier method. By means of Lyapunov functions, it is proved that the proposed FTC law can maintain the ship's position and heading at the desired values while guaranteeing that all signals in the closed-loop DP control system are uniformly ultimately bounded. Finally, simulation studies on a model ship are carried out to demonstrate the effectiveness of the developed control scheme.