Advancing Power System Oscillation & Stability Analysis Based on the Concept of Interharmonics

Abstract: Power system oscillation has been a stability concern for many years. The problem has grown due to the interconnection of inverter-based resources (IBRs). Traditionally, oscillations are investigated using phasor data. This research 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 form. The beating waveforms, in turn, are caused by interharmonics (defined per IEC 61000-4-30). It can be proven that the presence of interharmonics is both a necessary and sufficient condition for phasor oscillations. Multiple field measurement results have confirmed these findings.

The above new insights have led to several applications. One of them is the s-domain based small-disturbance stability assessment tool. Compared to the traditional state space model-based methods, the s-domain methods offer greater flexibility for integrating impedance-based IBR models and are more scalable for large systems. However, the method cannot reveal participation information and other dynamic characteristics of the study system. There are also challenges in finding the critical eigenvalues. Utilizing the interharmonic concept, this presentation will show that participation factors can be determined with a clear physical meaning, and they can be applied to rank oscillation-causing generators and oscillation-amplifying capacitors. The critical eigenvalues can be determined using a simple 2D frequency scan. These advancements pave the way for a comprehensive s-domain stability assessment tool that are both simpler and more powerful than the traditional state-space model-based tools.