A Lightweight Sampling Time Error Correction Technique for Micro Phasor Measurement Units

Abstract

In this paper, we deal with enhancing the accuracy of the sampling instant of Micro Phasor Measurement Units (μPMUs) used in distribution grids. The pulse per second (PPS) signal of the GPS synchronizes the start of each second of all μPMUs in the grid. The internal clock of each μPMUs then takes over and determines the sampling instants till the next PPS. Due to the inaccuracy and drift of the clock and the unavoidably needed fractional count of the clock pulses, accumulation of error leads to excessive phase error. A lightweight algorithm is proposed for the correction of the sampling period. The algorithm fine tunes the timer count used to determine the sampling instant. As the proposed algorithm aims at correcting the sampling instant, it can be applied by any other platform, but it needs an accurate time reference like that of the 1PPS (1 pulse per second) of the GPS. The performance evaluation shows that, the maximum phase error is lower than the accepted phase error by about two orders of magnitude. The theoretical results are confirmed by implementing the algorithm on a prototype μPMU.