Anti-disturbance trajectory tracking event-triggered control for underactuated surface vessels: A novel switching self-tuning mechanism.

Prescribed performance control has garnered significant interest for its capability to predefine system performance indicators. However, some unresolved challenges persist in prescribed performance control for underactuated surface vessels (USVs) under disturbances and input saturation. To address these issues, this paper proposes a fixed-time trajectory tracking scheme for underactuated surface vessels, where external disturbances, input saturation, and prescribed performance are considered. Specifically, the underactuated control challenge is first solved by a coordinate system transformation. A smooth saturation model addresses the actuator input saturation. Then, a dynamic event-triggering mechanism is proposed to reduce the unnecessary communication burden. Meanwhile, a non-fragile prescribed performance function is designed to avoid the serious degradation of the tracking accuracy caused by the trigger mechanism and to ensure that the tracking error converges within a prescribed range even when the desired trajectory switches. Next, we employ a command filter to avoid the "explosion of complexity" and design the compensation system for the filtering error to guarantee control accuracy. Furthermore, by designing a switching self-tuning mechanism, the negative effect of the uncertainty term on the USV can be compensated in real time, requiring no a priori knowledge of uncertainty terms. Finally, based on the Lyapunov theory, we demonstrate that our scheme is theoretically reasonable. Further simulations verify that the underactuated surface vessel can still guarantee the prescribed tracking performance under our scheme, even under external disturbances and input saturation, while significantly reducing the unnecessary communication burden.