Analysis of the efficacy of RMS-EMT co-simulation in capturing the response of IBR-rich grids

Hybrid electromagnetic transient (EMT)/three-phase phasor (RMS) domain co-simulation can be a practical alternative to full EMT studies for converter-interfaced grids. However, its efficacy primarily depends on the selection of interface/boundary parameters. While prior works focus on improving the efficacy of co-simulation for transmission grids, this paper investigates the accuracy of co-simulation in comparison with EMT analysis for a converter-rich, transmission-distribution grid in DIgSILENT PowerFactory. Using a modified IEEE 9-Bus system, this paper examines the impacts of boundary configuration and the region of fault modeling on the accuracy of co-simulation responses. The results demonstrate that transformers adjacent to the interface element and the region of fault representation can influence co-simulation responses. This study also recommends potential ranges of boundary region and co-simulation transformation settings for obtaining reliably accurate results under different conditions.