Sliding mode fault-tolerant control of an octorotor using linear parameter varying-based schemes

This study presents two fault-tolerant control (FTC) schemes for an octorotor UAV. The FTC schemes are based on an linear parameter varying system representation and utilises a combination of sliding-mode ideas and control allocation (CA) in order to take full advantage of the available redundant rotors in the octorotor configuration. A detailed synthesis procedure for the design of the two FTC schemes in the presence of uncertainty, as well as faults/failures, is presented. The first scheme is based on an online CA methodology where knowledge of the rotor effectiveness level has been used to redistribute the control signals to the healthy rotors. The second scheme assumes that this information is not available and uses a fixed CA structure even in the event of faults/failures. Although the synthesis process for the two schemes is different and they use different strategies to redistribute the control signals when faults/failures occur, both schemes involved the same ‘baseline’ (sliding-mode) controller which does not need to be reconfigured. The difference is in the final physical control law where the CA matrix is defined. Simulation results on the full non-linear octorotor model are presented for the two different schemes in the presence of uncertainty, sensor noise as well as faults/failures. The simulation results for various fault/failure scenarios show no visible degradation in state tracking performance, highlighting the potential of the proposed schemes.