Fixed-time disturbance observer-based fractional-order dynamic surface control of autonomous surface vessel

Surface vessels, which are conventionally influenced by oceanic conditions, present significant challenges within the operational framework. Robust control of surface vessels has been a widely studied topic, with increasing attention to methods that can enhance stability and tracking performance even in the presence of complex disturbances. In this context, a fixed-time disturbance observer-based robust control is proposed for a three-degree-of-freedom surface vehicle under time-varying external disturbances. Firstly, a nonlinear disturbance observer is constructed to estimate random winds/waves and dynamic model during a predetermined interval. Leveraging the compensation capability of the fixed-time observer, a fractional-order dynamic surface control is evolved for obtaining the optimizing system responses and resolving explosion of term phenomenon simultaneously. Furthermore, the trajectory tracking error of the closed-loop system is proved to be ultimately uniformly bounded by the Lyapunov theory. Finally, the effectiveness of the proposed control approach is demonstrated via numerical simulation and comparison with the other nonlinear control methods.