Objectives This paper addresses the path tracking control problem for underactuated Unmanned Surface Vehicles (USVs) under the conditions of lumped disturbances, input saturation, and limited onboard energy. These factors complicate the path tracking process and hinder the effectiveness of traditional control methods. The goal is to propose an event-triggered fixed-time path tracking control strategy that improves robustness, energy efficiency, and tracking precision under these complex conditions.

Methods The proposed control strategy integrates several key components to address the challenges mentioned. First, a longitudinal speed guidance law and a fixed-time line-of-sight (SGFTLOS) guidance law are designed to provide the desired longitudinal speed and heading angle for the USV, ensuring it follows the desired trajectory with optimal speed and heading. Next, to handle model uncertainties and external disturbances (such as wind and current), a Fixed-Time Extended State Observer (FESO) is introduced. The FESO estimates and compensates for lumped disturbances, improving the system's robustness in uncertain environments. To address input saturation, where control inputs exceed actuator limits, an auxiliary dynamic system is designed to smooth the control inputs, allowing the system to maintain stable path tracking even when saturation occurs. Finally, to overcome onboard energy limitations, a periodic relative threshold event-triggered mechanism is proposed. This mechanism adjusts the frequency of control signal updates based on system states, reducing unnecessary actuator activity and minimizing energy consumption.

Results The stability of the system is proven to be fixed-time stable using Lyapunov's fixed-time stability theory, which also guarantees the elimination of Zeno behavior (infinite triggering in finite time) that could otherwise lead to instability. SimuNPS simulation results demonstrate that the tracking error converges within a fixed time, verifying the effectiveness of the proposed method.Compared to other existing methods, the proposed strategy shows faster transient response, smaller steady-state errors, and superior robustness when facing lumped disturbances. Furthermore, the introduction of the FESO provides accurate real-time disturbance estimation, allowing the controller to compensate for disturbances and ensure precise path tracking. Additionally, the event-triggered mechanism significantly reduces the number of control signal updates and actuator actions, improving the system’s energy efficiency.

Conclusions The proposed event-triggered fixed-time path tracking control strategy effectively addresses the challenges of lumped disturbances, input saturation, and limited onboard energy for underactuated USVs. By integrating event-triggered mechanisms, innovative guidance laws, and robust disturbance compensation, the strategy provides a reliable solution for path tracking in complex and uncertain environments. The fixed-time convergence property ensures that the USV achieves desired performance within a fixed time, making the strategy suitable for real-time applications where stability, precision, and energy efficiency are critical. This method offers a robust, efficient, and reliable solution for USV path tracking control in challenging operational scenarios.