Predefined-Time Globally Nonsingular Prescribed Performance Control for AUVs Under Uncertainties and Actuator Saturation

Prescribed performance control (PPC) provides an effective framework for explicitly enforcing transient and steady-state performance constraints in autonomous underwater vehicle (AUV) trajectory tracking. However, in practical underwater environments, unavoidable localization errors, model uncertainties, and actuator saturation render conventional PPC schemes unsuitable due to their inherent semi-globality and singularity issues. To address these limitations, this paper proposes a globally nonsingular PPC framework for AUV tracking control under model uncertainties and input saturation. A novel error transformation function is developed, which fundamentally eliminates semi-global and singular behaviors without imposing additional control effort or modifying the initial error. Furthermore, a predefined-time disturbance observer is designed without requiring prior knowledge of disturbance bounds, and a predefined-time saturation compensator is introduced to mitigate actuator limitations. By integrating these components into a backstepping-based control structure, all closed-loop error signals are guaranteed to converge to an arbitrarily small neighborhood of the origin within a predefined time. Numerical simulations validate the effectiveness and superiority of the proposed method.