Integral Sliding Mode based Model Reference FTC of an Over-Actuated Hybrid UAV using Online Control Allocation

This paper presents a novel concept for active fault-tolerant control (FTC) of dual system hybrid unmanned aerial vehicles (UAVs) based on analytical redundancy to increase the operational safety in the face of primary actuator faults. The proposed scheme exploits the inherent over-actuation property of hybrid UAVs when in addition to the aerodynamic surfaces four lift rotors are used to control the aircraft during long range fixed-wing flight mode. Fault tolerance is achieved by utilizing an integral sliding mode based model reference control law combined with control allocation techniques to reallocate control signals among healthy effectors in the face of actuator faults and maintain nominal closed-loop performance. After introducing the modelling procedure of the UAV, including the identification of aerodynamical cross-couplings between lift rotors and airframe dynamics, Hardware-in-the-loop (HIL) simulation results are presented to demonstrate the efficiency of the proposed scheme in a realistic hardware setup.