Sven Erik Mattsson

Physical system modeling with Modelica

Abstract A new language, called Modelica TM , for the modeling of physical systems has been developed in an international effort. The main objective was to make it easy to exchange models and model libraries. The design approach builds on non-causal modeling with true ordinary differential and algebraic equations and the use of object-oriented constructs to facilitate the reuse of modeling knowledge. There are already several modeling languages based on these ideas, available from universities and small companies. There is also significant experience of using them in various applications. The aim of the Modelica effort was to unify the concepts and to design a new uniform language for model representation. The paper describes the effort, gives an overview of Modelica, and demonstrates how Modelica is used in real-world applications: modeling of an automatic gearbox and of a heat exchanger.

Modelica-a language for physical system modeling, visualization and interaction

Modelica is an object-oriented language for modeling of large, complex and heterogeneous physical systems. It is suited for multi-domain modeling, e.g., for modeling of mechatronics including cars, aircraft and industrial robots which typically consist of mechanical, electrical and hydraulic subsystems as well as control systems. General equations are used for modeling of the physical phenomena. No particular variable needs to be solved manually, the Modelica tools have enough information to do that automatically. The language has been designed to allow tools to generate efficient code automatically. The modeling effort is thus reduced considerably since model components can be reused and tedious and error-prone manual manipulations are not needed. The principles of object-oriented modeling and the details of the Modelica language as well as several examples are presented.

Hybrid modeling in Modelica based on the synchronous data flow principle

The unique features of the object-oriented modeling language Modelica to model combined continuous time and discrete event systems are discussed. A hybrid Modelica model is described by a set of synchronous differential, algebraic and discrete equations leading to deterministic behaviour and automatic synchronization of the continuous and discrete parts of a model. The consequences of this view are discussed and demonstrated at hand of a new method to model ideal switching elements such as ideal diodes, ideal thyristors or friction. At event instants this leads to mixed continuous/discrete systems of equations that have to be solved by appropriate algorithms.

Simulator for dynamical systems using graphics and equations for modeling

A prototype simulator for dynamical systems, called Hibliz (hierarchical block diagrams with information zooming), which explores some features of modern computer graphics, is presented. Hibliz supports hierarchical block diagrams to describe the model decomposition and interconnection structure. The user can scroll, pan, and zoom the block diagram continuously in real time. Zooming controls the amount of information displayed. Zooming in a block changes it from an annotated box to a representation showing internal structure with increasing detail. Since the block diagrams can be hierarchical, it is possible to make the description at each level simple and clear. Hibliz also simplifies model development by allowing submodels in the form or ordinary differential and algebraic equations rather than assignment statements for derivations and algebraic variables.<<ETX>>

Modelica—An international effort to design the next generation modeling language

A new language called Modelica for physical modelling is developed in an international effort. The main objective is to make it easy to exchange models and model libraries. The design approach builds on non-casual modelling with true ordinary differential and algebraic equations and the use of object-oriented constructs to facilitate reuse of modelling knowledge. There are already several modelling language based on these ideas available from universities and small companies. There is also significant experience of using them in various applications. The aim of the Modelica effort is to unify the concepts and design a new uniform language for model representation. The paper describes the effort and gives an overview of Modelica.

Modelica hybrid modeling and efficient simulation

Modelica is an object-oriented language for modeling of large and heterogeneous physical systems. Typical applications include mechatronic models in automotive and aerospace applications involving mechanical, electrical and hydraulic subsystems as well as control systems. Modeling of an ideal diode and Coulomb friction is discussed to illustrate the unique hybrid features of Modelica. The language has been designed to allow tools to generate efficient code automatically. Approaches supported by the Dynamic Modeling Laboratory Dymola from Dynasim are presented. Real-time simulation of an automatic gearbox is discussed to demonstrate the power of symbolic manipulation. A gearbox is inherently hybrid, since the structure varies during each gearshift. Friction is also an important phenomenon. It takes Dymola only a few seconds to translate a Modelica model of an automatic gearbox with 11 switching elements into efficient simulation code. A 500 MHz DEC alpha processor from dSPACE evaluates one Euler step including a possible mode switch in less than 0.18 ms.

Feasibility of Detailed Vehicle Modeling

A feasibility study is presented concerning detailed vehicle modeling, including submodels for engine, transmission mechanics and hydraulics, as well as three-dimensional chassis behavior. The study was conducted jointly by Ford Motor Company, Dynasim AB and DLR. The results demonstrate that complex behavioral models of each subsystem can be developed, used and validated independently from each other, and finally assembled together to an overall model. Therefore, this approach could be the basis to establish modeling standards that allow collaboration between model developers throughout the automotive industry.

On the Architecture Of Cace Environments

Abstract This paper discusses the objectives of an integrated interactive environment for simulation and computer aided control systems design. An integrated environment must support the userʼs work strategies and must not be based on normative work procedures. To make it easy to build such environments with customized user interface and flexible integrated tools some basic architectural issues have to be considered. The paper focuses on these issues and discusses model representation, tool integration and modularization of user interfaces. An object-oriented model representation is presented briefly and a model for tool integration is outlined

A load model for analysis and control of electric distribution networks

Power electronics result in increased harmonic distortion, but can also be used for harmonic mitigation. This requires simple, low order models for nonlinear networks. The Harmonic Norton Equivalent is a load model structure that supports aggregation of nonlinear loads, and makes nonlinear network solving (i.e. simulation) a non-iterative procedure. It is a linearized description of the relation between voltage spectrum and current spectrum. A procedure for obtaining the Equivalents from measurements is presented and shows good agreement with the validation data.

A simple model for harmonics in electrical distribution networks

A modularized approach to modeling of harmonics in electrical distribution networks at steady state is presented. It is based on harmonic balance and exploits that the loads in a distribution network are connected in parallel in such a way that their operating conditions are approximately known in advance (e.g. 230 V, 50 Hz) and the harmonic distortion of the voltage is limited. The model for a component is given by a linear relation between the Fourier coefficients of the deviations from nominal current and voltage. The linear relationship implies that aggregation of loads and network solving are a matter of solving linear equation systems. This leads to fast calculations without convergence problems.