Strategies and limitations for the detection of sub-synchronous oscillations in power systems
Stefano Lodetti, Frederick Wilkins, Alex Mitroi, Peter Davis, Deborah Ritzmann, Paul Wright National Physical Laboratory, Hampton Road, Teddington, United Kingdom 2026-02-15

Abstract

Sub-synchronous oscillations pose a significantchallenge in modern power systems, particularly in networks with high penetration of power electronic converters. While phasor measurement units (PMUs) are generally used for grid monitoring, their ability to detect sub-synchronous oscillations is being challenged. This paper discusses PMU limitations in measuring sub-synchronous oscillations, introducing a novel algorithm to detect their occurrence by leveraging PMU phasor data and rate-of-change-of-frequency analysis to trigger high-resolution voltage waveform recordings. This approach enables direct comparison between PMU-reported events and raw waveform data, which paves the way to analysing discrepancies and limitations in PMU-based detection.

Key words: Measurement techniques, power grids, phasor measurement units, oscillations, power quality.

References

[1] CIGRE JWG C4/B4.52, “CIGRE TB 909 - Guidelines for Subsynchronous Oscillation Studies in Power Electronics Dominated Power Systems,” 2023.

[2] National Grid ESO, “GC0077: Sub-Synchronous Oscillations (SSO),” 2016.

[3] Y. Cheng et al., “Real-World Subsynchronous Oscillation Events in Power Grids With High Penetrations of Inverter-Based Resources,” IEEE Transactions on Power Systems, vol. 38, no. 1, 2023.

[4] S. Choi, “Massive Wildfires in Korean Eastern Area and Sub-Synchronous Oscillation Events,” in IEEE PES General Meeting, PES 2023, 2023.

[5] S. Lodetti, P. Davis, D. Ritzmann, and P. Wright, “Measurement and Detection of Sub-synchronous Oscillations in Power Electronics Dominated Power Systems,” in Conference on Precision Electromagnetic Measurements (CPEM), Denver, Colorado, USA, 2024.

[6] C. Wang, C. Mishra, K. D. Jones, R. M. Gardner, and L. Vanfretti, “Identifying Oscillations Injected by Inverter-Based Solar Energy Sources,” in IEEE Power and Energy Society General Meeting, 2022.

[7] H. Liu et al., “Impacts of subsynchronous and supersynchronous frequency components on synchrophasor measurements,” Journal of Modern Power Systems and Clean Energy, vol. 4, no. 3, pp. 362–369, 2016.

[8] AEMO, “West Murray Zone Power System Oscillations 2020-2021 [report],” no. February, 2023.

[9] T. Rauhala, A. M. Gole, and P. Jarventausta, “Detection of Subsynchronous Torsional Oscillation Frequencies Using Phasor Measurement,” IEEE Transactions on Power Delivery, vol. 31, no. 1, pp. 11–19, Feb. 2016, doi: 10.1109/TPWRD.2015.2436814.

[10] F. Zhang, L. Cheng, W. Gao, and R. Huang, “Synchrophasors-based identification for subsynchronous oscillations in power systems,” IEEE Trans Smart Grid, vol. 10, no. 2, pp. 2224–2233, 2019.

[11] H. Liu, Y. Qi, J. Zhao, and T. Bi, “Data-Driven Subsynchronous Oscillation Identification Using Field Synchrophasor Measurements,” IEEE Transactions on Power Delivery, vol. 37, no. 1, pp. 165–175, Feb. 2022, doi: 10.1109/TPWRD.2021.3054889.

[12] C. Canizares et al., “Benchmark Models for the Analysis and Control of Small-Signal Oscillatory Dynamics in Power Systems,” IEEE Transactions on Power Systems, vol. 32, no. 1, pp. 715–722, Jan. 2017, doi: 10.1109/TPWRS.2016.2561263.

[13] Y. He, W. Du, Q. Fu, and H. F. Wang, “A model-free method to detect the risk and locate the sources of sub-synchronous oscillations in a large-scale renewable power system,” International Journal of Electrical Power & Energy Systems, vol. 165, p. 110460, Apr. 2025, doi: 10.1016/J.IJEPES.2025.110460.

[14] IEC/IEEE 60255-118-1, “Measuring relays and protection equipment – Part 118-1: Synchrophasor for power systems – Measurements,” 2018.

[15] “Power System Oscillations,” Aemo.com.au, 2024. https://aemo.com.au/energy-systems/electricity/national-electricity-market-nem/system-operations/power-system-oscillations (accessed March. 25, 2025).

[16] National Grid ESO, “Sub-synchronous oscillations in GB - Current state and plans for future management”, May 2024.