Abstract
<jats:p>A method is introduced to quantitatively identify oscillatory modes in power systems using only frequency-domain impedance data. In contrast to state-space-based eigenvalue analysis and transfer-function-based pole/zero analysis, the proposed approach enables the graphical extraction of critical dynamic modes directly from Bode plots of modal impedances, without requiring detailed analytical models: 1) mode frequency is identified at impedance magnitude peak; 2) damping sign is determined through impedance real and imaginary parts and their slopes, which is further mathematically equivalent to phase-angle slope; 3) damping ratio is obtained from resonance bandwidth with an adaptive scheme. Validation on benchmark grids (such as IEEE 5-, 14-, and 39-bus systems) and a simplified MMC-HVDC system shows close agreement with the eigenvalue and pole/zero analysis as well as Prony analysis to EMT simulations. The results demonstrate accurate and analytically tractable identification of poorly damped and unstable oscillatory modes (|ζ|≤0.1) using a straightforward and simple approach, enabling practical stability assessment in converter-dominated AC/DC networks.</jats:p>