Model-based control with FMI and a C++ runtime for Modelica

Modelica describes physical systems on a high level, using model objects, multi-dimensional arrays and oth-er data structures as well as graphical representations. Modelica models are translated to differential-algebraic equation systems and compiled to executable code pri-or to their execution in numerical solvers. The transla-tion gives a lot of possibilities for code optimization. This is particularly important for model-based control applications. This paper investigates the exploitation of C++ for Modelica code optimization. C++ supports advanced programming concepts and at the same time aims to “leave no room for a lower-level language … (except for assembly code in rare cases)” [6]. The multitude of different requirements on arrays is treated with polymorphism. Templates keep the C++ code small and improve type safety. Built-in exception handling and destructors for memory management also contribute to smaller and more readable code. These ideas have been implemented in the OpenModel-ica C++ runtime. The paper describes its enhancement with new array features and with an FMI 2.0 interface. FMI serves as interface between modeling tools and control applications. In particular the new FMI 2.0 meets requirements of numerical optimization solvers in model-based control. A publically available application example demon-strates the achievements. CPU times obtained with the OpenModelica C++ runtime are significantly faster than CPU times obtained with the C runtime or with Dymola.