Improving Synchrophasor Estimation at Off-Nominal Power System Conditions using Discrete Fourier Transformations

Abstract

Phasor Measurement Units (PMU) provide time-synchronized measurements of magnitude, phase angle, frequency, and rate of change of frequency at higher reporting rate in comparison with the conventional remote terminal unit (RTU) used by SCADA. Discrete Fourier Transformation (DFT) used by PMUs, usually designed at system frequency for phasor computation. As a result, leakage effect increases at large off-nominal frequency of the grid, which degrades the estimation from DFT. In order to enhance the accuracy of DFT during wide frequency deviations, two types of method based on frequency information were proposed in this research. The first approach is known as variable sampling time (VST) and the second is sample value adjustment (SVA). For frequency information, two estimators such as Biased Jacobsen and recursive least square (RLS), were used in VST and SVA methods, respectively. The combination of frequency and phasor estimators constitute an enhanced version of DFT, suitable for PMUs. The MATLAB model of the proposed PMU designs were tested with various types of input signals as specified in the IEEE C37.118.1-2011 standard. The compliance of the designs with the standard were evaluated for steady and dynamic state by help of indices such as Total vector error (TVE), frequency error (FE), and rate of change of frequency error (RFE). Both the design demonstrated TVEs less than 1% and 3% at steady and dynamic states, respectively. Furthermore, the second design using SVA performed better than VST in terms of TVE and reporting rate. Because of this, the second design was implemented in prototype PMU and the measurements from it were visualized and recorded by LabVIEW. The recorded measurements were validated by determining the TVE and were in compliance with the standard.

Date of Award	May 2015
Original language	American English
Supervisor	Jimmy Peng (Supervisor)