An hybrid direct/functional redundancy scheme for the FDI on a small commercial aircraft

In this paper we consider the problem of detecting and isolating sensor faults on an aircraft in the presence of external disturbances. A nonlinear observer based approach is proposed which makes use of the complete nonlinear model of the aircraft. This approach exploits the so-called Unknown Input Observer (UIO) theory and guarantees disturbance decoupling with an H~ performance. A comparison between the application of the classical UIO based FDI scheme and the proposed nonlinear scheme shows the benefits of the approach provided in this paper. Finally we exploit the nonlinear UIO technique to design a mixed hardware/software FDI system to improve the performance of the classical hardware system without the replication of expensive sensors. Some numerical simulations are carried out on the model of the small commercial aircraft under consideration in the project Affordable Digital Fly-By-Wire Flight Control System (ADFCS-II) funded by the European Community.