Frequency domain approach to optimal auxiliary input design for fault diagnosis

An optimal input design problem in frequency domain is discussed for quick fault diagnosis of dynamical systems without affecting the original system in normal mode. The optimal auxiliary input designed for detecting a specified fault mode is not always good for detection of other fault modes, i.e., it may reduce the the distance between the normal mode and the other fault modes and make harder to detect true fault mode. The max-min approach is proposed in this paper to solve this problem. The auxiliary input is designed to maximize the minimum distance measured by the Kullback discrimination information between system models corresponding to the normal and each fault mode in order to detect the true fault mode. Results of a numerical simulation result indicate the applicability of the proposed auxiliary input in fault diagnosis.