Fault-tolerant control for ships with thruster faults based on improved adaptive control allocation

Objective  In the process of marine resource development, some thrusters of over-actuated ships are prone to failures during operation, resulting in a decrease in propulsion power. This paper aims to propose a fault-tolerant control method based on improved adaptive control allocation to enhance the fault tolerance and the safety reliability of ship operations.

Methods  Firstly, an adaptive control allocation algorithm is designed to online reconstruct the configuration matrix of the faulty propulsion system based on the current propulsion capacity, reducing the thrust deviation. Additionally, a differential term is added to the adaptive update law to suppress the thrust jitter. Then, the unprocessed control allocation error is regarded as a lumped disturbance, which is estimated and compensated by a modified extended state observer. Finally, the boundedness of the error in the closed-loop control system is proved using Lyapunov theory, ensuring the theoretical feasibility of the method.

Results  Simulation and modeling experiments are carried out using a self-developed over-actuated ship experimental prototype. In terms of the upper limit of positioning error, the IACA method demonstrates a significantly lower upper limit of positioning error across all directions when compared to the ACA and QPCA methods. Furthermore, regarding system dynamic performance, the IACA method facilitates rapid stabilization of the system to a steady state following thruster failure. In the simulation experiments, the abrupt changes in disturbance estimation values, actual force, and thrust deviation associated with the IACA method were minimal post-failure, indicating a rapid recovery. Additionally, the adaptive parameter updates were both faster and more stable, exhibiting minimal jitter, effectively enhancing the system's performance in terms of jitter reduction.

Conclusion  The results show that the proposed method can effectively handle the failure of over-actuated ship thrusters. Verified by experiments, it can reduce operation errors, help the system quickly return to stability, improve the jitter, enhance the fault tolerance of the ship, provide an effective strategy for the fault-tolerant control of ship thrusters, and is of great significance for the safe and stable operation of the ship. However, further research and optimization are needed in the future.