New Voltage Index Reveals Hidden Weaknesses in Inverter-Dominated Power Grids

As inverter-based resources (IBRs) increasingly dominate bulk power systems, traditional short-circuit capacity (SCC) metrics are proving inadequate for assessing post-disturbance voltage stability. A bus with high SCC can still experience deep voltage dips, delayed recovery, or transient overvoltage that violates operating criteria. To address this, researchers from Iowa State University have introduced the Short-Term Voltage Performance Index (STVPI), a criteria-aware, electromagnetic-transient (EMT)-based metric that quantifies the quality of voltage waveforms after disturbances.

The STVPI processes voltage signals at the half-cycle level by computing a weighted log-amplitude ratio between the actual waveform and an ideal half-sine reference. Monotonic recovery envelopes on overvoltage and undervoltage sides are compared against half-normal reference distributions using Kullback-Leibler (KL) divergence, normalized by the critical voltage envelope. This yields two directional indices — STVPI+ and STVPI- — whose combination produces a baseline-corrected scalar severity score. Bus-level and event-level aggregation derive BSTVPI and ESTVPI, enabling simultaneous identification of dynamically weak buses and critical fault contingencies. The framework was validated on the IEEE 9-bus and 39-bus test systems with IBR integration, demonstrating its ability to capture vulnerabilities that SCC metrics overlook.