  This paper explores the modal analysis of power systems with high
Converter-Interfaced Generation (CIG) penetration utilizing an impedance-based
modeling approach. Traditional modal analysis based on the state-space model
(MASS) requires comprehensive control structures and parameters of each system
element, a challenging prerequisite as converters increasingly integrate into
power systems and their internal specifics remain largely inaccessible.
Conversely, the proposed modal analysis based on the impedance model (MAI)
leverages only the impedance port characteristics to pinpoint system elements
significantly influencing unstable modes. This study is the first to confirm
the theoretical equivalency between MASS and MAI in terms of transfer
functions, eigenvalues, and sensitivities, thus bridging the gap between
detailed theoretical modeling and practical, accessible analyses. We further
provide enhancements to the MAI method, including a revised element
participation index, a transformer ratio-based admittance sensitivity
adjustment, and an impedance splitting-based sensitivity analysis considering
parameter variations. Validation through numerical simulations on a modified
IEEE 14-bus system underscores the efficacy of our approach. By examining the
interplay between different elements and system modes in high CIG environments,
this study offers insights and a foundational framework for delineating the
oscillatory modes' participation and stability characteristics of power systems
with substantial CIG integration.
