Appointed-Time Control for Flexible Hypersonic Vehicles with Conditional Disturbance Negation

This paper investigates the anti-disturbance control design for flexible air-breathing hypersonic vehicles (FAHVs) with appointed-time prescribed tracking performances. The challenging issues include multisource disturbances, cross-coupling effects of the vehicle dynamics, and asymmetric amplitude and rate saturations. To address these issues, we propose an appointed-time prescribed performance control scheme for FAHVs via conditional disturbance negation technique. In contrast to existing disturbance rejection approaches, the proposed control scheme not only estimates the disturbances first in a fixed time, but also evaluates the estimated disturbances and selectively conducts compensation actions according to the insight of the FAHV dynamic characteristics. To further enhance convergence rate, the composite appointed-time prescribed performance controllers are designed for FAHVs via time-varying barrier Lyapunov function and nonsmooth backstepping technique, which ensure satisfactory transient response and steady-state performances. In addition, the asymmetric amplitude and rate saturation problem of actuators are dealt with by introducing unified approximation dynamics. It is rigorously proved that the practical appointed-time convergence of the tracking errors and the fixed-time convergence of all signals in the resultant FAHV closed-loop system can be achieved under the proposed control scheme. Finally, extensive comparative simulations are provided to demonstrate the feasibility and superiority of the proposed approach.