Distribution Level Phasor Measurement Accuracy Limits
What is the maximum accuracy a distribution level measurement of frequency and phase angle can reach? This is discovered by analyzing the contribution of different measurement error sources. The main error sources include:
a) Algorithm error: error brought by frequency and phase angle estimation algorithms.
b) GPS error: pulse per second (PPS) signal from GPS is utilized as the time reference.
c) ADC error: error sourced from the inaccuracy and limited resolution of ADC.
d) White noise: the white noise mixed in the fed-in signal.
e) Harmonic distortion: the harmonic distortions mixed in the fed-in signal.
By analyzing and simulation, the theoretical accuracy of each error is obtained. The accuracy limits of phasor measurement is essential for both instrument development and the measurement-based applications. It helps to evaluate the performance of an instrument, and the main error sources the developers should take care of. For measurement-based power system applications, this knowledge provides references to evaluate their applicability. If its required accuracy is near or beyond the theoretical accuracy limitation, the application is not likely to be used successfully.
Figure 1. Different errors of frequency and phase angle estimation
 J. Zhao, L. Zhan, Y. Liu, H. Qi, J. R. Garcia, P. D. Ewing, "Measurement accuracy limitation analysis on synchrophasors" (under review).
 J. Chen, "Accurate Frequency Estimation with Phasor Angles," Master of Science, Electrical Engineering, Virginia Plytechnic Institue and State University, Blacksburg, VA, 1994.
 X. Zhang, "High Precision Dynamic Power System Frequency Estimation Algorithm Based on Phasor Approach," Master of Science, Electrical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, 2004.