Fault Tolerant Control of Hexarotor UAVs against Motor Failure

This paper proposes a new approach for fault tolerant control of hexarotor UAVs against motor failure subject to maximum motor speed constraint. The proposed approach consists of two parts: sliding mode control and dynamic control allocation. The sliding mode control is designed to generate the desired forces and torques that achieve and maintain flight stability and performance. As the control design is independent of plant model parameters, it remains the same across the cases of fault-free and motor failure. The dynamic control allocation is then applied to redistribute the desired forces and moments among the remaining healthy motors subject to maximum motor speed constraint. In the proposed approach, the control allocation problem is formulated in terms of solving a nonlinear optimization problem. Then the optimization problem is transformed to a stability problem where the convergence is established by using the Lyapunov stability theory. The simulation on a hexarotor UAV demonstrates the effectiveness of the proposed approach and the advantages over existing approach in terms of motor speed limits.