Fault-Tolerant Control for Quadrotor Unmanned Aerial Vehicle with Nonlinearities and Unknown External Disturbances

Since an unmanned aerial vehicle (UAV) system is nonlinear, underactuated, and strongly coupled, controlling UAVs is not a trivial task. Furthermore, when actuator faults and the transient performance when disturbances change are taken into account, the control problem becomes even more challenging. This paper inserts a nonlinear control law into the conventional equivalent-input-disturbance (EID) approach for reducing the fluctuation of the system output when disturbances change. Combing the nonlinear control law with the EID approach yields an adaptive EID approach. This paper applies the adaptive EID approach to address actuator faults and improve the transient performance in nonlinear UAVs for the first time, and proposes an adaptive EID-based fault-tolerant control strategy to tackle the aforementioned challenges. Actuator faults are transformed into parameter uncertainties. Four EID estimators are then designed to suppress nonlinearities, disturbances, and actuator faults simultaneously. Furthermore, exact linearization is employed to compensate for the nonlinearities inherent in quadrotor unmanned aerial vehicle (QUAV) systems. As a result, the stability conditions are analyzed using the concept of globally uniformly ultimate boundedness (GUUB), which simplifies the tuning of controller parameters. In addition, exact linearization helps enlarge the stability region. The effectiveness of the proposed approach is demonstrated through simulation results in both way-point tracking and periodic-trajectory tracking control.