Equivalent Circuit Modeling of Grid-Forming Inverters in (Sub)-Transient Time-Frame

Researchers have proposed a systematic method to quantify the effective impedance of grid-forming (GFM) inverters from black-box models using frequency-domain admittance plots. The work addresses a key gap where system operators mandate impedance ranges but lack clear definitions. Using NREL's standard PSCAD GFM models, they demonstrated their equivalent impedance model accurately captures sub-transient response and static voltage stability limits, which is crucial for integrating renewable energy sources into the power grid.