Sliding Mode Fault Tolerant Control of an Octorotor Using LPV Based Schemes

This paper presents two fault tolerant control (FTC) schemes for an octorotor UAV. The FTC schemes are based on an LPV system representation and utilizes a combination of sliding mode ideas and control allocation 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 control allocation 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 control allocation 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 control allocation matrix is defined. Simulation results on the full nonlinear 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. Keyword: Fault tolerant control (FTC), multirotor UAV