Linköping University Electronic Press

Due to the increasing complexity of technical systems, model-based engineering is getting more and more important during the development process of new products. The code generation from models and the usage of this code on hardware targets is one important feature of model-based development. To execute this code on the hardware device, a simulation runtime is additionally required, which offers numerical methods to solve the model equations. To use generated code on a controller, the simulation has to be executed in real-time, which is a huge requirement for the solver. In this work, a Modelica-based open source toolchain for model-based engineering with Rexroth controllers is presented, which is used for virtual commissioning of a typical hydromechanical system on a standard Rexroth PLC. Therefore, instead of parameterizing the controller directly on the real system, the control algorithm on the PLC is connected to the system model, which is additionally executed on the controller in parallel to the existing PLC application. Doing this, the commissioning times can be reduced significantly, as the commissioning process can already be started during the build-up of the system using a simulation model of the system. As hydro-mechanical systems are in general mathematically stiff, the choice of the solver for the system model equations is not arbitrary. In this work, five different real-time solvers, beginning with a simple explicit Euler through to more complex linearly implicit methods, are tested on a single hydraulic axis. Furthermore, typical issues like state events as well as algebraic loops are discussed in context of real-time simulation requirements.

Keywords: Real-time simulation; Modelica; Hardware-In-The-Loop; code generation; model-based engineering; real-time solver