Improved predefined-time robust adaptive backstepping tracking control for quadrotor with state constraints

This paper investigates the predefined-time tracking control for Quadrotor Unmanned Aerial Vehicles (QUAVs) subject to external disturbances, actuator faults, and attitude state constraints. To overcome the singularity issues and conservative parameter constraints inherent in conventional predefined-time control, a generalized predefined-time convergence theorem is proposed by introducing an improper integral method, which relaxes the Lyapunov derivative constraints and greatly improves design flexibility. On this basis, a nonsingular adaptive backstepping control scheme is developed. Specifically, an improved piecewise barrier function is embedded to transform constrained states into an unconstrained domain, achieving a better trade-off between constraint compliance and tracking precision. To compensate for the lumped disturbances, including external disturbances and actuator faults, an adaptive predefined-time disturbance observer is designed without prior boundary information. Meanwhile, a differentiator is introduced into the controller to suppress the “explosion of complexity” problem, and the adaptive compensation term is constructed to mitigate the estimation errors of the observer and filter. Lyapunov stability analysis proves that all closed-loop signals are uniformly ultimately bounded, and that the tracking errors converge to a small vicinity of the origin within a user-defined time. Finally, numerical simulations and real-world flight experiments are conducted to verify the high accuracy, strong robustness, and practical applicability of the proposed scheme.