Design criteria of digital filters for synchrophasor estimation

In the near future electrical waveforms in power networks are expected to exhibit strong amplitude and phase fluctuations caused by dynamic network topology changes and variable energy flows between loads and generators. Such fluctuations need to be constantly and accurately monitored both to optimize energy distribution and for safety and protection reasons. Nowadays, this task is typically accomplished by the so called Phasor Measurement Units (PMU), which measure the phasor of voltage and current waveforms on a common timescale synchronized to the Coordinated Universal Time (UTC). One of the most typical techniques for phasor estimation is based on digital down-conversion and filtering. This approach, although not explicitly recommended, is described in Annex C of Standard IEEE C37.118.1-2011, namely one of the main reference document for synchrophasor measurement in power systems. The same standard also reports two possible examples of filters for P-class and M-class phasor estimation. However, no specific filter design methods are provided. In this paper some guidelines for filter design are proposed on the basis of a model describing the behavior of a power waveform in both static and dynamic conditions. The reported design criteria are supported by some simulation results.