  Time-domain simulations are a critical tool for power system operators.
Depending on the instability mechanism under consideration and the system
characteristics, such as the time constants of controllers, either phasor or
Electro-Magnetic Transient (EMT) models should be employed. On the one hand,
EMT models provide a detailed-modeling of the system dynamics, thus increase
the reliability of stability analysis; on the other end, using these models
increase the computational times of simulations, slowing down the security
assessment process. To decrease computational time, system operators could
resort to phasor-mode simulations for a (hopefully large) subset of
disturbances. This paper investigates the appropriateness of
phasor-approximation models on simulating events related to power supply and
balance stability in zero-inertia systems. First, the stability boundaries,
which each model is able to identify, are analyzed; then sufficient conditions
for control parameters are derived, which allow using phasor-approximation
models to monitor power sharing among grid-forming converter-based resources.
Time-domain simulations are performed in PowerFactory DigSilent to verify the
results.
