Frequency Retrieval from PMU Data Corrupted with Pseudo-Oscillations during Off-Nominal Operation

Phasor measurement units are widely used for enhancing awareness of the operation of transmission and distribution networks. Their synchronized measurements enable the development of multiple near-real-time applications that are unattainable with SCADA data only. However, the accuracy of PMU measurements is highly dependent on the chosen algorithms. This paper illustrates that a certain PMU model is unable to accurately estimate system frequency as it drifts away from its nominal value (the estimated frequency profile is contaminated with pseudo-oscillations). Moreover, three devices connected at the same location produce divergent estimates during off-nominal frequency operation. Then, a technique is proposed for directly estimating frequency from phase angle measurements through numerical derivatives. It is shown to accurately estimate the system frequency regardless of nominal or off-nominal frequency operation, and it eliminates the two issues presented previously.