The amended standard C37.118.1a and its implications for frequency-tracking m-class Phasor Measurement Units (PMUs)

The new amendment to the Phasor Measurement Unit (PMU) standard C37.118.1a makes several significant changes, compared to the standard C37.118.1a (2011). This paper highlights some of the most important changes, with a particular emphasis applied to how those changes relate to the way that a frequency-tracking PMU (Phasor Measurement Unit) algorithm needs to be designed. In particular, there is a delicate trade-off between passband flatness (the bandwidth test) and stopband rejection in the Out-Of-Band (OOB) test. For a PMU algorithm using frequency-tracking and adaptive filters, it is shown that passband flatness can be relaxed to about 2.5dB, but that the stopband needs to begin up to 14.8% closer to 0 Hz than for a fixed-filter PMU. This is partly due to the exact procedures of the C37.118.1a “OOB” testing, and partly due to the adaptive nature of a frequency-tracking PMU filter section.