Uncertainty Quantification in Smart Grid Co-simulation Across Heterogeneous Model Domains

The international power distribution grids are expected to undergo fundamental restructuring in the next decades, becoming Smart Grids. Smart Grids are typically defined as power grids enhanced with information and communication technology (ICT). They provide components of the power system with means to send and receive information about current states, energy requirements, load and generation predictions etc. This calls for the development of various new hardware devices and control concepts and thereby for rigorous, systematic testing of the interaction between the new components. Smart Grids are highly complex systems since their dynamics do not solely depend on classical grid components like generators and consumers anymore, but also on weather predictions, market prices, the utilization of the ICT system, and many other factors. This complexity limits the pool of possible testing procedures. Hardware experiments are too expensive and inflexible to serve as generally applicable means of testing. In the form of field tests they are even potentially dangerous since real infrastructure is involved. Software simulation is considered to be more suitable for the early stages of Smart Grid research since it is generally cheap, flexible and safe. However, monolithic simulation software easily expires in its usability since it does not consider the expendability of the Smart Grid setup. Whenever new Smart Grid components or concepts are introduced, they have to be modeled and implemented by the software developers, which requires high manual effort and sometimes simply is not possible. In order to avoid this overhead, the OFFIS – Institute for Information Technology, has developed the modular Smart Grid simulation tool mosaik (Rohjans et al., 2013). Mosaik is an event-based co-simulation framework that allows the integration of existing Smart Grid component models with the help of a flexible API. The implemented models exchange data with one another via mosaik and may be instantiated and orchestrated to form large-scale simulation scenarios (i.e. scenarios with thousands of model instances). The extensive scenario size is enabled at reasonable computational costs by employing steady-state calculation of the grid utilization in the frequency domain (e.g. PyPower, a port of the MATPOWER package (Zimmerman et al., 2011)). This means that shortterm dynamic behavior like electro-magnetic transients is not resolved. Due to its flexible design, mosaik supports various kinds of simulation processes, e.g. hardware emulation. This is the concept of the Smart Energy Simulation and Automation Laboratory (SESA-Lab) that has been set up at the OFFIS. The central component of the laboratory is the real-time simulator eMEGAsim developed by the company OPAL-RT. This high performance computer allows the simulation of network models with μs resolution and provides digital and analogue I/O capabilities that make it a ready-to-use hardware-in-the-loop framework (HIL, see (de Jong et al., 2011)). By combining mosaik and eMEGAsim, the SESA-Lab enables analysis of dynamic transients in precise subsystems of otherwise steady-state largescale scenarios. The main challenge of this approach is to ensure accuracy of results for this heterogeneous co-simulation system. A schematic overview of the SESA-Lab setup is given in Figure 1.