Null-Space-Based Elegant Anti-Disturbance Control Allocation for Autonomous Berthing

To mitigate the impact of multi-source disturbances, such as environmental loads, bank effects, model uncertainties, and control allocation (CA) errors, during autonomous ship berthing, we propose an anti-disturbance control allocation method based on the null-space. This method considers the real-time and precision requirements of motion control allocation algorithms, as well as the characteristics of disturbances and their corresponding responses. The first step involves establishing models for ship berthing motion, multi-source disturbances, and control allocation. A passive elegant extended state observer (PEESO) is designed to estimate ship states and multi-source disturbances in real-time. Moreover, null-space technology is employed to develop a CA algorithm that ensures real-time and accurate results. This algorithm achieves the scheme of stabilization control outside the berth and then parallel berthing. Simulation and comparison experiments demonstrate that this method ensures the accuracy of berthing motion control and significantly reduces computation time, thereby decreasing the maximum allocation error.