Benchmarking Hybrid EMT-Phasor Simulations for Studying the Impacts of Grid-Forming Inverters in the Bulk Power System

With the increasing penetration of grid-forming inverters (GFMs) and inverter-based resources in general across the bulk power system, the need for high-fidelity simulations to accurately study their interactions is compelling. While electromagnetic transient (EMT) simulations provide the required fidelity, they are computationally burdensome for large-scale systems. In this context, EMT-phasor hybrid simulations are a promising alternative providing the right balance between computational burden and simulation fidelity by appropriately choosing the portion of the system that needs to be modeled in the EMT domain. To validate the fidelity and suitability of hybrid EMT-phasor simulations, this work describes an approach for hybrid simulations and benchmarks the performance of the hybrid EMT-phasor simulation with corresponding phasor domain and full EMT domain simulations for the standard IEEE 39 bus system with a generic GFM inverter model (REGFM_A1) integrated into it. Specific cases such as an under-frequency event and a 3-phase to ground fault were studied and the error between the various simulation fidelities (phasor, phasor-EMT vs. EMT) was analyzed. Our case study showed that hybrid EMT-phasor simulations offer reasonable accuracy improvement over just phasor simulations and definitely have a role to play in studying the integration and impacts of GFMs accurately and efficiently.