A Phase Locked Loop-Based Approach to Real-Time Modal Analysis on Synchrophasor Measurements

This paper presents a phase locked loop-based approach for real-time estimation of electro-mechanical modal properties of slow-frequency oscillations in a power grid. The approach utilizes a closed-loop feedback control system to automatically adjust a locally generated signal to optimally fit the targeted signal from real-time measurements in order to obtain modal properties directly from the local signal. The paper tests the approach on a variety of datasets including simulated and real synchrophasor data. Compared to a traditional spectral analysis based approach, this new approach has better adaptability and accuracy especially when the length of a measured signal is limited, or the signal contains modes with close frequencies or has floating modal properties, which is not unusual in a power grid due to its nonlinearity. Applied to wide-area synchrophasor measurements, the new approach may help system operators monitor slow-frequency oscillations, especially inter-area modes, which is important for a smart grid to maintain angular stability under disturbances.