Initialization of Hybrid Differential-Algebraic Equations in Modelica 2

Abstract

Modelica 2 provides new powerful language constructs for specifying initial conditions. Before any operation is carried out with a Modelica model, such as simulation or linearization, initialization takes place to assign consistent values for all variables, derivatives and pre-varialbles present in the model. To obtain consistent values, the initialization uses all equations and algorithms that are utilised during the simulation. Additional constraints necessary to determine the initial values of all variables can be provided as start values for any variables as well as additional constraint equations in initial equation sections. A novel feature is the possibility to have a sampled controller initialized in steady state. This tutorial paper describes and explains the new language constructs and illustrates how they in combination with Modelica's other language elements allow very flexible and powerful initialization conditions to be defined.