Fault Indicators and Adaptive Thresholds from Hybrid System Models

Initially, incremental bond graphs were introduced to support frequency domain sensitivity analysis of linearised time-invariant models. Subsequent publications have shown that they can be used for other purposes as well such as the determination of parameter sensitivities of analytical redundancy relations (ARRs) in symbolic form. This paper extends previous work to fault detection and isolation (FDI) from hybrid system models. In order to ensure robust FDI in the presence of parameter uncertainties and to avoid false alarms of faults reported to a diagnosis system, properly chosen thresholds for the time evolution of residuals of ARRs are needed. Hybrid systems exhibit several operation modes. Distinctive continuous time behaviour in different operation modes require adapted thresholds for fault indicators. The paper shows how an incremental bond graph can be used to set up thresholds for residuals that account for parameter uncertainties as well as for discrete mode changes. The approach is illustrated by means of an example easy to survey.