Hans-Michael Hanisch (Otto-von-Guericke-Universität Magdeburg):
Modular Modeling of Closed Loop Systems
The contribution will focus on modeling approaches for systems in automatic
control. Such systems are characterized by the existance of at least two
subsystems, namely the system which is to be controlled (called “plant”)
and the system which performs control (called “controller”). Both systems
interact in a closed loop.
Studying (i.e. verifying or at least simulating) the behavior of the closed
loop system is of significant interest in automatic control, especially in
the emerging field of discrete event control. The main problem which arises
is that plant and controller act in different ways. The plant performs
asynchronously, driven by the laws of physics, thermodynamics, chemistry
etc. whereas the controller has a strictly time-driven, syncronous
behavior. A second problem is that a systematic way is needed to come up
with rather large models of plant and controllers.
Engineers design systems as well as models in a modular, incremental way.
The system is usually decomposed into a set of small modules with behavior
that can be overlooked, modeled and designed easily. The larger system is
than obtained by composition of modules over and over again. Composition of
models is usually performed by means of inputs and outputs of modules, not
by “glueing” their internal states.
The talk will present a formal model which supports this kind of
establishing large models. Two types of inputs and outputs are provided,
namely condition signals carrying state information of a module and event
signals carrying state transition information. These two clearly
distinguished types of signals are used for composition of modules.
Condition signals provide means for asynchronous interaction among modules
whereas event signals are a mechanism for a one-sided synchronous composition.
The contribution presents the model and the modeling methodology in an
informal, illustrative way. Examples how the methodology is applied are the
main scope of the talk. Applications covering manufacturing as well as
process systems, controller design for railway applications, and
communication systems are presented and discussed.
Some more general remarks on further development of the modeling and design
methodology and an outlook on further work conclude the talk.
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