  Time-varying phasor-based analysis of subsynchronous oscillations (SSOs)
involving grid-following converters (GFLCs) and its benchmarking with
electromagnetic transient (EMT) models have so far been restricted to highly
simplified grid models with constant voltage sources behind series R-L
circuits. In this paper, modeling adequacy of bulk power systems with
synchronous generators (SGs), transmission systems, loads, and GFLCs are
considered. To this end, we revisit the notions of time-varying phasor
calculus, highlighting the distinction between space-phasor-calculus (SPC) and
two often interchangeably used frameworks namely baseband-abc and generalized
averaging. We present the models of grids in SPC framework that include
transmission line dynamics, load dynamics, and SG stator transients. Next, we
propose a generic approach to study modeling adequacy in small-signal sense by
(a) identifying critical modes through eigenvalue and singular value analysis
followed by (b) using weighted maximum singular value error magnitudes as
metrics, and (c) further cross-validation. Using a modified 4-machine IEEE
benchmark model with up to 3 GFLCs we show that SPC framework can be used for
analysis of SSOs. Further, we consider the quasistationary phasor calculus
(QPC) framework that neglects transmission line, load, and SG stator dynamics
to show its adequacy in SSO modeling and analysis. Time-domain and
frequency-domain results with EMT models are also presented.
