Structural Algorithms for Diagnostic System Design Using Simulink Models
Today's society depends on complex and technically advanced mechanical
systems, often containing a variety of different components. Despite
careful development andconstruction, some of these components may
eventually fail. To avoid unnecessary damage, for example
environmental or financial, there is a need to locate and diagnose
these faults as fast as possible. This can be done with a diagnostic
system, which should produce an alarm if there is a fault in the
mechanical system and, if possible, indicate the reason behind it.
In model based diagnosis, a mathematical model of a fault free system
is used to detect if the monitored system contain any faults. This is
done by constructing fault indicators, called fault tests, consisting
of equations from different parts of the model. Finding these parts is
a time-consuming and demanding task, hence it is preferable if as much
as possible of this process can be automated. In this thesis an
algorithm that finds all parts of a system that can be used to create
these fault tests is presented. To make this analysis feasible, in
industrial applications, a simplified version of a system model called
a structural model is used. Since the models considered in this thesis
are implemented in the mathematical software Simulink, a method for
transforming Simulink models into analytical equations and structural
models is described. As a way of increasing the diagnostic performance
for a model based diagnostic system, information about different
faults, called fault models, can be included in the model. However,
since the models in this thesis are implemented in Simulink, there is
no direct way in which this can be preformed. This thesis describes a
solution to this problem. The correctness of the algorithms in this
thesis are proved and they have been applied, with supreme results, to
a Scania truck engine model.
Lars Eriksson
2004
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