Active fault tolerant control for multirotor UAVs: Controllability, design and experiment

This paper presents an active fault tolerant control approach for multirotor UAVs against motor fault/failure. A novel uniform nonlinear dynamic inversion approach is proposed for position and attitude control of multirotor UAVs no matter in the normal or in motor fault/failure cases. A new practical test criterion for positive controllability is proposed for general multirotor UAVs by considering the unidirectional and constrained motor speed under different motor failure combinations, which is easy to check in practice. Under the assumption of positive controllability, a control allocation scheme based on minimum energy is proposed to distribute the forces and moments desired by the position and attitude control loops among the working motors in the normal and motor fault/failure cases with guaranteed closed-loop system stability. Both simulation and flight test experiment results demonstrate that the proposed approach is able to maintain the flight stability and performance of the multirotor UAVs with motor faults/failures.