Initialization of Equation-Based Hybrid Models within OpenModelica

Modelica is a multi-domain object-oriented modeling language designed for time-dependent systems. The timedependent part is usually described with “ordinary differential equations”. In addition to that, it is possible to express algebraic and difference equations. As a result a Modelica model will be merged to a hybrid differential algebraic equation system. The initialization process is prior to each simulation and must therefore be solved before any simulation can be started. Modelica provides high-level features to describe the initialization problem. This leads often into various problems. The initialization is usually a system-level issue. Therefore, high knowledge about the system is necessary. In OpenModelica two major methods are implemented to solve the initialization problem. Both methods are totally different and are used for different initialization issues. Both methods will be discussed within this paper.