Robust FDI based on LFT BG and relative activity at junction

Abstract

It is seen that methodology for diagnosis of uncertain systems using the Bond Graph (BG) model in Linear Fractional Transformation (LFT) form is an effective way to detect the fault by systematic generation of robust adaptive thresholds over the nominal residuals. There are limitations associated, many of which are imposed due to the manner uncertain parameters can be treated. In this work, a new method of generating robust and adaptive thresholds is developed, where uncertain parameters are treated as intervals that vary between the upper and lower bounds. The developed method proposes to generate the envelopes, using the interval extension form of uncertain part of Analytic redundancy relations (ARR) that are derived from BG model in LFT form. The method is applied on an uncertain two tank system to show its viability. Issue of missed detection is discussed where not all of the considered uncertain parameters may deviate outside their allowed limits. To diagnose such a case, generation of multiple thresholds is proposed by selection of parameters based on their increasing activity. The algorithm for generation of set of robust envelopes is presented and applied over the hydraulic system to alleviate the missed alarm problem. Results are validated through simulations.