Disturbance rejection control for underactuated surface vessels with input saturation

This paper presents a disturbance rejection control strategy for underactuated surface vessels (USVs) under input saturation. The proposed disturbance observer generates real-time estimates of low-frequency disturbances, which effectively compensate for the lumped disturbances encountered by the USV in dynamic environments. A theoretical analysis of the proposed observer is conducted from a complex frequency domain perspective, which reveals its response characteristics across varying frequencies. This analysis framework circumvents the stringent assumptions regarding the differentiability of disturbance signals imposed by traditional methods, which reduces the conservativeness of the approach. Furthermore, a disturbance rejection strategy is developed based on the proposed disturbance observer, which enhances the robustness of the designed USV controller. The controller incorporates an auxiliary dynamic system to ensure stable control of the USV under input saturation. Lyapunov stability analysis is employed to prove the stability of the closed-loop control system, which provides theoretical support for achieving robust control performance. Experimental results demonstrate that the proposed disturbance rejection control strategy significantly enhances control performance.