Hierarchical fault-tolerant control of a quadrotor based on fault severity

In this paper, a hierarchical Fault Tolerant Controller (FTC) for quadrotor aircrafts is developed. The proposed controller switches between suitable controllers according to the actuator fault severity. Low amplitude faults are tolerated using the inherent robustness of a regular Sliding Mode Controller (SMC). When fault magnitude increases, an Active FTC is activated. This controller uses the fault estimates provided by an Extended Kalman Filter (EKF) to recover the control loss. When a fault magnitude rises to dangerous values, an emergency controller is activated and the quadrotor continues its mission as a trirotor. Simulation results emphasize the robustness of the proposed controller in real environments where measurement noise and actuator faults affect severely the quadrotor.