Monitoring Effective Inertia via Ambient Synchronized Phasor Measurements

This paper proposes a non-intrusive methodology for continuous estimation of effective system inertia using ambient synchronized phasor measurements. The approach exploits natural power and frequency fluctuations and applies system identification techniques, enabling inertia estimation without major disturbances or probing signals. Effective inertia is treated as an operational quantity that reflects the combined contributions of synchronous machines, rotating loads, and fast control responses, and therefore varies with operating conditions and network topology.

The proposed framework includes data preprocessing, system identification, inertia extraction, and time-domain post-processing. It is first calibrated using the IEEE 39-bus test system under constant and time-varying inertia conditions, demonstrating accurate tracking of inertia changes under ambient operation. The method is then applied to real PMU data from the Brazilian

Interconnected Power System, where it successfully tracks known inertia variations associated with generator disconnections, achieving mean absolute percentage errors below 6%.

Overall, the results indicate that ambient data-based inertia estimation is feasible and operationally attractive for real-time situational awareness in power systems with high IBR penetration.