Applications of sliding observers for FDI in aerospace systems

This paper presents applications of second order sliding mode observer schemes to three different aerospace problems. Two relate to ADDSAFE aircraft fault detection benchmark problems. Firstly, the detection and isolation problem associated with an actuator jam/ is considered and secondly an actuator oscillatory failure case is tackled. For the actuator jam scenario the actuator deflection becomes decoupled from the demand issued from the flight control computer and remains fixed at some uncommanded point. For the OFC problem, the reconstruction scheme requires an estimate of rod speed provided by a second order sliding mode observer. Ideally low gains in the observer are required because of the noisy environment associated with the physical system. An adaption scheme is therefore required to retain sliding in the presence of severe faults. A problem associated with fault detection in a formation flying scenario, associated with satellites is also discussed. This application to a relative degree two problem would be difficult to solve using linear observer methods.