Understanding Power System Oscillation and Stability: An Interharmonic Perspective and Its Practical Applications
Aug 21, 2025 • Virtual - Webex
Power system oscillation is a significant stability concern for system operators and planners. In recent years, there has been a noticeable increase of oscillation events due to the interconnection of inverter-based resources (IBRs). Traditionally, oscillations are investigated using phasor data. This presentation takes a different approach by analyzing the actual voltage and current waveforms underlying the phasors. It is found that oscillations are the appearance of beating waveforms in the phasor domain. The beating waveforms, in turn, are caused by interharmonics (defined per IEC 61000-4-30). Notably, it can be proven that the presence of interharmonics is both a necessary and sufficient condition for power system oscillations, and synchronous generator oscillations can be easily explained using interharmonics. Multiple field measurement results will be used to substantiate these findings. The interharmonic insights could lead to many innovative applications. Two of them will be shared in this webinar: One for locating oscillation sources and another for identifying components that amplify oscillations.It is useful to note that interharmonics are well known in the power quality community. Establishing the link between power system oscillations and interharmonics marks significant progress in power quality data analytics. As a result, power quality engineers, with their expertise on interharmonics monitoring and analysis, can provide unique support to power system oscillation and stability monitoring.Speaker Bio:The presenter, Dr. Wilsun Xu, received Ph.D. from the University of British Columbia, Canada, in 1989. He worked at BC Hydro in Vancouver, Canada for seven years before joining the University of Alberta in Edmonton, Canada, in 1996, where he is currently a professor. Dr. Xu has been engaged in power quality research, education, and consulting for over 30 years, and he was elevated to IEEE Fellow for contributions to power system harmonics analysis in 2005. In recent years, Dr. Xu has been advocating for the application of waveform (and power quality) data to support equipment condition and system stability monitoring. His research work on voltage flicker source location has led to the findings shared in this presentation.