TUTORIAL SESSION

Model-based Fault Detection in Hybrid Systems Using Bond Graphs

Prof. Wolfgang Borutzky
Bonn-Rhein-Sieg University of Applied Sciences, Germany
wolfgang.borutzky@h-brs.de

Abstract

Bond graph modelling starts from considering the energy exchange between system components and possible conversions of energy from one form into another. That is, bond graphs are well suited for modelling and analysis of a wide range of engineering systems and processes, especially for the concurrent design of controlled mechatronic systems. As the exchange and transformation of energy happens to be continuous with respect to time, the methodology was initially limited to the representation of continuous time models. During the past two decades several approaches have been reported in the literature to extend the method to hybrid system models.

Beyond the purpose of analysis and simulation, bond graphs have proven useful as a tool for model-based fault detection and isolation (FDI) in engineering systems represented by continuous time models. More recently, extensions of bond graph model-based FDI have been proposed that also cover hybrid system models.

This tutorial will involve a survey of some approaches to a bond graph representation of hybrid system models. It will be shown how a set of equations for fault indicators can be derived from a bond graph that holds for all system modes of operation and can be solved numerically simultaneously along with the equations of motions.

In order to avoid that false alarms are reported to a supervisory system or that faults are overlooked, it is important that fault indicators are significantly sensitive to real faults but insensitive to parameter variations given uncertain system parameter values and are weakly sensitive to noise. The tutorial shows that adaptive mode dependent thresholds for the time evolution of fault indicators can be obtained from an incremental bond graph of switched linear time-invariant system models.

For illustration, the tutorial considers a number of small hybrid systems including switched power electronic systems and some fault scenarios.

Objectives

The tutorial welcomes all individuals, students, faculty members, practising engineers in academia and in industry who may be interested to learn about another approach to fault detection besides other existing fault diagnosis techniques and who may want to see how the bond graph methodology can also support model-based fault detection for various engineering systems represented by a hybrid model. The tutorial will be intorductory as well addressing some advanced current research issues.

Timeline

First hour:
- Introduction and motivation
- Brief recall of some essential features of the bond graph methodology
- Bond graph representations of hybrid system models illustrated by some examples

Short break

Second hour:
- Brief classification of fault diagnosis techniques
- Derivation of equations for fault indicators from bond graphs
- Incremental bond graphs and their use for the generation of adaptive mode dependent thresholds
for the time evolution of fault indicators

Short break

Third hour:
- Presentation of some case studies including the consideration of small switched power electronic
systems and some fault scenarios
- Conclusions and outlook
- Discussion

Background Knowledge Expected of the Participants

The tutorial will also briefly recall and illustrate the basic idea and some essential features of the bond graph methodology, in particular the relationship between block diagrams and bond graphs, so that some experience with physical system modelling, analysis and control of engineering systems is deemed to be sufficient to benefit from the tutorial.

Qualifications of the Instructor(s)

Prof. Wolfgang Borutzky is a Professor of Modelling and Simulation of Engineering Systems. He has published extensively in major international conferences on Modelling and Simulation and in refereed scientific journals and is author of a monograph on Bond Graph Modelling. Since 1990 he has served on many international scientific conferences in Modelling and Simulation in various positions. In 2005 he was an Assistant General Chair of the European Conference on Modelling and Simulation (EMCS) in Riga, Latvia and was General Chair of the ECMS 2006 in Sankt Augustin, Germany. Additionally he has served as a Guest Editor of Special Journal Issues on Bond Graph Modelling. The latest one is Volume 17, Issue 1, January 2009 of the Journal "Simulation Modelling Practice and Theory" published by Elsevier.He has given invited lectures as well as short courses in industry on bond graph modelling. As to dissertations on bond graph modelling, Dr. Borutzky has served has an invited external member of PhD defense committees in France and in India.