A Dynamic Phasor Framework for Analysis of IBR-Induced SSOs in Multi-Machine Systems

Researchers from Penn State University—Fiaz Hossain, Nilanjan Ray Chaudhuri, and Constantino M. Lagoa—have introduced a generalized dynamic phasor (DP) framework to analyze and mitigate subsynchronous oscillations (SSOs) caused by inverter-based resources (IBRs) in multi-machine power systems. Published on arXiv (April 2026), the framework models grid-following (GFL) IBRs in dq-frame DPs and synchronous generators (SGs) with dynamic transmission networks in pnz-frame DPs. This linear, time-invariant structure allows eigen decomposition, a powerful tool for root-cause analysis of SSO modes and designing damping controllers. The work addresses a critical challenge as renewable energy sources and data center loads increase, threatening grid stability with oscillations in the 10-50 Hz range.

The team validated their framework on the modified IEEE two-area benchmark system, replacing 2 SGs with GFL IBRs and comparing results with EMTDC/PSCAD simulations. Key contributions include a robust decentralized H∞ damping controller based on local GFL IBR signals, which effectively damps oscillations after unbalanced faults. Additionally, the framework analyzes SSO excitation from data center (DC) loads, quantifying their locational impact. This enables utilities to predict and prevent instability from high-power DC loads, which are growing rapidly with AI and cloud computing. The approach offers a practical tool for grid operators to design controllers and assess risks without costly hardware testing.