A Composite Nonlinear Fault Tolerant Control Scheme for Octorotor UAV System

This paper presents an active fault-tolerant control (FTC) framework for aerial vehicles operating under system uncertainties, external disturbances, and actuator faults or failures. Specifically, we propose a nonlinear integral sliding mode-based fault-tolerant control allocation scheme to address actuator faults and failures in an octocopter system. The goal is to perform trajectory tracking control and ensure system stability under practical operating conditions while preserving nominal closed-loop performance during fault scenarios. A baseline controller is first designed using a backstepping approach and combined with a nonlinear integral sliding mode control law to achieve nominal stability. To manage actuator degradation, a control allocation strategy is developed to redistribute control efforts among healthy redundant actuators based on real-time estimates of actuator effectiveness. Key features of the proposed FTC framework include its ability to handle faults and failures online while maintaining robustness against system perturbations. The simulation results demonstrate the effectiveness of the proposed BT-ISMC-based FTC method in sustaining performance under fault and failure conditions.