A fault detection and diagnosis (FDD) method is proposed by combining transfer entropy (TE) and signed digraph (SDG). Given process historical data, transfer entropy is used to construct a SDG model to represent causal relationship between process variables. A fault severity evaluation method is then proposed based on the modified SDG model, where the nodes can take values of (0), (±1), (±3) and (±6). Then, an index named DoF is developed to measure fault severity. The application results can verify the effectiveness and feasibility of the proposed method.

This paper presents a scheme of fault diagnosis for flexible satellites during orbit maneuver. The main contribution of the paper is related to the design of the nonlinear input observer which can avoid false alarm arising from the disturbance from orbit control force. The effects of orbit control force on the fault diagnosis system for satellite attitude control systems, including the disturbing torque caused by the misalignments and the model uncertainty caused by the fuel consumed, are discussed, where standard Luenberger observer cannot work well. Then the nonlinear unknown input observer is proposed to decouple faults from disturbance. Besides, a linear matrix inequality approach is adopted to reduce the effect of nonlinear part and model uncertainties on the observer. The numerical and semi-physical simulation demonstrates the effectiveness of the proposed observer for the fault diagnosis system of the satellite during orbit maneuver.

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where H = IOJ is the angular momentum in the inertial coordinate system, OJ =[OJ x ' OJ y ' OJz]T is the attitude angular velocity vector in the inertial space, L contains all torques, I = diag{ I", I y , 1= } is the moment of inertia.

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