Adaptive Backstepping Sliding Mode Fault-Tolerant Control of Quadrotor UAV in the Presence of External Disturbances, Uncertainties, and Simultaneous Actuator and Sensor Faults

This paper proposes a new active fault-tolerant control strategy for quadrotor unmanned aerial vehicles against simultaneous unknown external disturbances, system uncertainties, actuator faults, and sensor faults, which pose critical safety risks in autonomous flight operations. Unlike existing approaches that address these challenges separately, the proposed method provides an integrated solution for simultaneous actuator and sensor fault compensation. Based on a quadrotor’s nonlinear dynamic model, time-varying actuator and sensor faults are simultaneously estimated by a nonlinear unknown input observer. To attenuate the disturbance’s effects on fault estimation, an H∞ performance index is used. Subsequently, a robust nonlinear adaptive backstepping sliding mode controller is proposed to actively compensate for the estimated faults while maintaining stability despite the presence of uncertainties and disturbances. MATLAB simulations demonstrate successful fault estimation convergence and robust control performance across various challenging scenarios with different fault combinations and operational conditions. The proposed strategy achieves high tracking accuracy, with attitude RMSE below 10³ rad and position RMSE below 0. 2 m under concurrent actuator and sensor fault conditions.