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In this paper it is presented a study and shown
how Modelica modeling language can be used to
optimize plant behavior parameters in order to
guarantee the good and desired behavior for the
system, in the shorter time cycle, combined with
other aspects like energy consumption, for example.
To achieve the proposal goal, the section 2 is
devoted to the presentation of Modelica modeling
language and the Dymola Simulation environment;
section 3 presents the case study that is the base for
our study; section 4 discusses the mathematical
modeling of the plant. Further, section 5 presents the
Modelica model of the system (controller model
coupled with plant model); section 6 discusses the
obtained results concerning the defined plant
behavior parameters to study and, finally, section 7,
presents some conclusions and future works, in this
field.
2 MODELICA AND DYMOLA
In the few years of research in modeling and
simulation, the concept of object-oriented modeling
has achieved a big relevance. Several works have
demonstrated how objected oriented concepts can be
successfully employed to support hierarchical
structuring, reuse and evolution of large and
complex models independent from the application
domain and specialized graphical formalism.
To handle complex models, the reuse of standard
model components is a key issue. But in order to
exchange models between different packages an
unified language is needed. Modelica is an object-
oriented, general-purpose modeling language that is
under development in an international effort to
introduce an expressive standardized modeling
language, see (Elmqvist and Mattson, 1997)
(Fritzson and Vadim, 1998). Modelica supports
object-oriented modeling using inheritance concepts
taken from computer languages such as Simula and
C++. It also supports non-causal modeling, meaning
that model’s terminals do not necessarily have to be
assigned an input or output role. In fact, in the last
few years it has been proved in several cases that
non-causal simulation techniques perform much
better than the ordinary object-oriented tools.
Modelica is a powerful programming language
where equations are used for modeling of the
physical phenomena. No particular variable needs to
be solved for manually because the software Dymola
(Dymola software, 2010) has enough information to
decide that automatically. This is an important
property of Dymola to enable handling of large
models having more than hundred thousand
equations. Modelica supports several formalisms:
ordinary differential equations (ODE), differential-
algebraic equations (DAE), bond graphs, finite state
automata, Petri nets, etc.
3 CASE STUDY DESCRIPTION
The case study that is proposed as base for this work
is inspired on the benchmark system proposed by
(Kowalewski et al. 2001).
Figure 2 illustrates an example of an evaporator
system, which consists of two tanks, where an
aqueous solution suffers transformations. In the first
tank that solution should acquire a certain
concentration through the heating of the solution
using an electrical resistance (H1) which provokes
the steam formation.
Associated to the tank1 (figure 2) exist a
condenser (C) responsible for the condensation of
the steam that however it was formed. The cooling,
in that condenser, it is done through the circulation
of a cooling liquid (whose flow is measured by
sensor FIS) that passes through the cooling circuit (if
open the valve V13).
Associate to the tank1 there are a group of
sensors: level sensors (maximum (LIS1) and
minimum (LII1)), temperature sensor (acceptable
maximum (TIS1)); sensor of conductivity (QIS) that
is to indicate the desired concentration; they also
exist several actuators: filling valve of the tank1
(V12), drain valve (V16) and emptying valve (V15),
that it is also the filling valve of the tank2.
Figure 2: Scheme of the entire evaporator system.
In the normal operation mode, the system works
as follows.
The tank1 should be previously filled to its
superior level with an aqueous solution by opening
valve V12. When the tank1 is full, the heating
ICINCO 2010 - 7th International Conference on Informatics in Control, Automation and Robotics
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