Applicability and Limitation Analysis of PMU Data and Phasor Concept for Low- and High- Frequency Oscillations

TL;DR

This paper analyzes the limitations of PMU data and phasor concepts in detecting high-frequency oscillations in power systems, proposing a new signal model and estimation method to improve waveform representation and highlighting the need for waveform data analysis.

Contribution

It introduces a general signal model and multi-step estimation method that outperform existing approaches in representing oscillatory signals, and clarifies the limitations of PMU phasors for high-frequency oscillations.

Findings

PMU phasors are effective only for low-frequency oscillations.

The proposed model and methods improve waveform signal estimation.

Phasor concept may be invalid for high-frequency oscillations.

Abstract

Phasor Measurement Units (PMUs) convert high-speed waveform data into low-speed phasor data, which are fundamental to wide-area monitoring and control in power systems, with oscillation detection and localization among their most prominent applications. However, representing electrical waveform signals with oscillations using PMU phasors is effective only for low-frequency oscillations. This paper investigates the root causes of this limitation, focusing on errors introduced by Discrete Fourier Transform (DFT)-based signal processing, in addition to the attenuation effects of anti-aliasing filters, and the impact of low reporting rates. To better represent and estimate waveform signals with oscillations, we propose a more general signal model and a multi-step estimation method that leverages one-cycle DFT, the Matrix Pencil Method, and the Least Squares Method. Numerical experiments demonstrate the superior performance of the proposed signal model and estimation method. Furthermore, this paper reveals that the phasor concept, let alone PMU phasors, can become invalid for waveform signals with high-frequency oscillations characterized by asymmetric sub- and super-synchronous components. These findings highlight the fundamental limitations of PMU data and phasor concept, and emphasize the need to rely on waveform data for analyzing high-frequency oscillations in modern power systems.