A: It is important to note that there are some scenarios for which a phasor domain solution cannot be obtained. One such example would be a 3LG POI fault where an grid-following IBR model loses its reference quantity.
Another example would be where the MVA rating of the installed grid-following IBR plant at a location in the System approaches or exceeds the short circuit MVA capability of the System at that location without the IBR plant. In this case, the grid-following IBR model would also be the primary influence on its own terminal voltage, which leads to an unstable solution.
It may be necessary to supplement phasor-domain studies with time-domain studies (such as electromagnetic transient studies) that can account for the detailed time-domain response for certain faults.