Appointed-Time Fault-Tolerant Control for Flexible Hypersonic Vehicles with Unmeasurable States Independent of Initial Errors

TL;DR

This work addresses robust trajectory tracking for flexible hypersonic vehicles with unmeasurable states and actuator faults by integrating backstepping with a practical fixed-time neural network observer and a novel error transformation. A cascaded observer reconstructs unmeasured variables, while a fixed-time neural network observer estimates lumped disturbances and faults; an appointed-time error transformation decouples initial errors from prescribed performance. The main contributions include a velocity and altitude controller designed under prescribed performance with independence from initial errors, and a stability proof ensuring practical fixed-time convergence for all closed-loop signals. Simulations demonstrate rapid convergence, reduced overshoot, and smooth control under faults, highlighting the approach’s robustness and real-time applicability for FAHVs.

Abstract

This article aims to derive a practical tracking control algorithm for flexible air-breathing hypersonic vehicles (FAHVs) with lumped disturbances, unmeasurable states and actuator failures. Based on the framework of the backstepping technique, an appointed-time fault-tolerant protocol independent of initial errors is proposed. Firstly, a new type of a state observer is constructed to reconstruct the unmeasurable states. Then, an error transformation function is designed to achieve prescribed performance control that does not depend on the initial tracking error. To deal with the actuator failures, practical fixed-time neural network observers are established to provide the estimation of the lumped disturbances. Finally, the proposed control strategy can ensure the practical fixed-time convergence of the closed-loop system, thereby greatly enhancing the transient performance. The proposed method addresses the challenges of ensuring real-time measurement accuracy for angle of attack and flight path angle in hypersonic vehicles, coupled with potential sudden actuator failures, effectively overcoming the drawback of prescribed performance control that requires knowledge of initial tracking errors. Some simulation results are provided to demonstrate the feasibility and the effectiveness of the proposed strategy

Figures (6)

• Figure 1: The reconstruction of unmeasurable state
• Figure 2: The tracking of command signals
• Figure 3: Velocity subsystem tracking error and control input
• Figure 4: Altitude subsystem tracking error and control input
• Figure 5: Comparison of velocity subsystem tracking performances