Frequency Response of Windowed DFT Phasor Estimation: Impact on Oscillation Observability

TL;DR

This paper analyzes how windowed DFT-based phasor estimation affects the detection of oscillations in power systems, revealing frequency-dependent distortions and proposing a correction method to improve measurement accuracy.

Contribution

It derives the complete frequency response of windowed DFT phasor estimators and introduces a recovery method to correct amplitude and phase distortions.

Findings

Windowed DFT introduces frequency-dependent magnitude attenuation.

Phase shifts caused by the window affect oscillation observability.

Proposed correction restores true oscillation amplitude and phase.

Abstract

Phasor measurement units (PMUs) are widely used for sub-synchronous oscillation monitoring, yet the effect of windowed discrete Fourier transform (DFT)-based phasor estimation on oscillation observability is not fully characterized. This letter derives the complete complex-valued frequency response of the windowed DFT phasor estimator under both magnitude and phase modulation. The analysis shows that the estimation window introduces both frequency-dependent magnitude attenuation and phase shift to oscillation components, governed by the complex gain. A simple recovery method is also proposed to restore the true oscillation amplitude and phase from PMU data using the analytically known complex gain. The results are validated through time-domain simulations and provide guidance for industry practitioners on interpreting PMU-based oscillation measurements and selecting appropriate window lengths.