On–line Instantaneous Frequency Estimation and Voltage/current Coherent Resampling Method

An innovatory on–line method of power system frequency estimation and voltage/current signals resampling is presented. The method is designed to increase the accuracy of power system equivalent harmonic impedance estimation using simple DAQ systems. Estimation of instantaneous frequency uses 5–th degree polynomial interpolation of filtered signal zero crossings time positions. Final resampling uses cubic splines interpolation for the calculation of output signal values. The details of resampling algorithm are described. The results of simulation tests demonstrating the typical behavior of a power system were shown as well as results of real voltage signal resampling. The method shows good capabilities of tracking varying harmonic phase angles in reference to the fundamental one while phase/frequency of fundamental harmonic varies too. The computational complexity allows to implement the method as a realtime version on DSP. Comparison of the amount of math operations used in this and another method [1] is shown too.