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Abstract |
Fault Isolation in Distributed Embedded Systems
To improve safety, reliability, and efficiency of automotive
vehicles and other technical applications, embedded systems commonly
use fault diagnosis consisting of fault detection and isolation. Since
many systems are constructed as distributed embedded systems including
multiple control units, it is necessary to perform global fault
isolation using for example a central unit. However, the drawbacks
with such a centralized method are the need of a powerful diagnostic
unit and the sensitivity against disconnections of this unit.
Two alternative methods to centralized fault isolation are
presented in this thesis. The first method performs global fault
isolation by a distributed sequential computation. For a set of
studied systems, the method gives, compared to a centralized method, a
mean reduction in maximum processor load on any unit with 40 and
70% for systems consisting of four and eight units
respectively. The second method instead extends the result of the
local fault isolation performed in each unit such that the results are
globally correct. By only considering the components affecting each
specific unit, the extended result in each agent is kept small. For a
studied automotive vehicle, the second method gives, compared to a
centralized method, a mean reduction in the sizes of the results and
the maximum processor load on any unit with 85 and 90%
respectively. To perform fault diagnosis, diagnostic tests are commonly used. If
the additional evaluation of tests can not improve the fault isolation
of a component then the component is ready. Since the evaluation of a
test comes with a cost in for example computational resources, it is
valuable to minimize the number of tests that have to be evaluated
before readiness is achieved for all components. A strategy is
presented that decides in which order to evaluate tests such that
readiness is achieved with as few evaluations of tests as
possible. Besides knowing how fault diagnosis is performed, it is also
interesting to assess the effect that fault diagnosis has on for
example safety. Since fault tree analysis often is used to evaluate
safety, this thesis contributes with a systematic method that includes
the effect of fault diagnosis in fault trees. The safety enhancement
due to the use of fault diagnosis can thereby be analyzed and
quantified.
Jonas Biteus
2007
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Senast uppdaterad: 2021-11-10
