Accuracy Comparison of Frequency and ROCOF Dynamic Estimators under Contingencies

The measurement of frequency and Rate of Change of Frequency (ROCOF) is essential for power system monitoring and control. As known, the Phasor Measurement Units (PMUs), especially those based on dynamic estimators, can perform high-rate frequency and ROCOF measurements, thus improving system observability. Indeed, many monitoring and control applications rely on the comparison or aggregation of such measurements, but do not consider their inherent uncertainty. However, the actual accuracy of existing algorithms under contingencies, as well as the accuracy requirements in such conditions are often unclear. In this paper we present a thorough comparison of frequency and ROCOF estimation accuracy of three dynamic PMU algorithms just before and after the occurrence of a contingency. Extensive simulation results in two realistic scenarios confirm that, with a minimum Signal-to-Noise Ratio (SNR) of 60 dB and a four-cycle data record length, the measurement results are rather consistent. Under stable conditions, the frequency and ROCOF errors generally lie within the limits of the IEEE/IEC Standard 60255-118-1:2018, while after contingency, the measurement uncertainty may grow by about one order of magnitude. The presented results pave the way to the use of data fusion techniques to aggregate frequency and ROCOF values over a given area.