Saturation-tolerant prescribed performance trajectory tracking control for air-cushion vehicles via auxiliary boundary adjustment

This paper addresses the trajectory tracking control problem for underactuated hovercraft subject to actuator saturation, model uncertainties, and external disturbances. To resolve the inherent conflict between strict performance constraints and limited control authority, a novel saturation-tolerant prescribed performance function is proposed. Unlike conventional fixed-boundary approaches, the proposed method introduces non-negative auxiliary signals driven by input saturation errors to dynamically expand the performance envelope. Once saturation subsides, these auxiliary signals decay to zero, seamlessly recovering the original finite-time performance boundaries. Based on this mechanism, a command-filtered backstepping controller is developed for the surge and yaw channels, incorporating nonlinear disturbance observers for lumped uncertainty compensation. Lyapunov stability analysis guarantees the uniform ultimate boundedness of the signals involved in the controlled surge–yaw subsystem and the associated controller dynamics, while the position and heading tracking errors remain within the feasible prescribed performance boundaries. Comparative simulations demonstrate that the proposed strategy achieves robust tracking performance while respecting the prescribed actuator limits under the considered numerical conditions.