An Active Fault-Tolerant Online Control Allocation Scheme for a Dual-System UAV in Transition Flight

TL;DR

This work addresses fault tolerance for a dual-system VTOL UAV during transition flight by integrating a structured $H_{ obreakspace}\infty$ baseline controller with an online control allocation (CA) module. The baseline controller is designed via structured $H_{ obreakspace}\infty$ synthesis for altitude and attitude loops, ensuring robustness and avoiding the chattering associated with sliding-mode strategies. The online CA reallocates virtual control signals among healthy actuators using an airspeed-aware, fault-informed approach, validated through $oldsymbol{\mu}$-analysis and nonlinear 6-DOF simulations that demonstrate resilience to both symmetric and non-symmetric faults without reconfiguring the baseline law. The results indicate improved safety and reliability of transition flight for a dual-system UAV, with enhanced fault tolerance and reduced performance degradation under complex fault scenarios.

Abstract

A novel active fault-tolerant control (AFTC) scheme for a dual-system vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) during transition flight is proposed in this paper. The AFTC scheme is composed of a baseline control law and an online control reallocation module. First, the structured $H_{\infty}$ baseline control law is able to guarantee the stability of closed-loop systems without being reconfigured under simultaneous actuator fault conditions. Second, compared to the existing mainstream method of sliding mode control that is a discontinuous control strategy, the AFTC scheme can effectively avoid control chattering problem by adopting the structured $H_{\infty}$ baseline control law. Third, an online control allocation (CA) module is implemented to carry out a unified CA for all the available actuators. When actuator faults/failures occur, the CA matrix is updated according to fault information and real-time airspeed, which is able to redistribute the virtual control signals to the remaining healthy actuators, avoiding significant performance degradation. Based on the developed AFTC scheme, symmetric and non-symmetric actuator fault scenarios are simulated on a nonlinear six-degree-of-freedom simulator, where the cases of merely structured $H_{\infty}$ control and structured $H_{\infty}$ based AFTC are compared and analyzed. The results show that the proposed structured $H_{\infty}$ based AFTC system is capable of handling more complicated fault scenarios and model uncertainties with no need to reconfigure the baseline control law. The proposed AFTC scheme significantly improves the safety and reliability of the transition flight of dual-system VTOL UAVs.

Figures (13)

• Figure 1: The top view of the dual-system UAV
• Figure 2: The architecture of the AFTC system
• Figure 3: The general block diagram of a closed-loop system
• Figure 4: The structure diagram of the altitude control loop
• Figure 5: The structure diagram of the pitch control loop