Comparative Analysis of Digital Frequency Measurement Methods for Power Networks

Currently, frequency measurement is one of the most popular tasks in power engineering. The voltage and current of real power networks are different from sinusoidal ones: there are harmonics, supraharmonics, noise and flicker. For this reason, the application of measurement methods designed to measure the frequency of a sinusoidal voltage results in larger measurement errors. This paper discusses two most popular frequency measurement methods applied in power engineering: zero crossing technique and a method based on the amplitude spectrum analysis. The paper provides a description of each method, indicates the main advantages and disadvantages, considers the features for the practical implementation. Analytical relations are obtained which allows to estimate the methodological error of all the methods under consideration. In the paper main modification directions for the considered methods are shown, aimed mainly at simplifying the implementation and reducing the methodological error. The influence of the parameters of the input signals, namely the sample time and the measurement time, on the frequency measurement error is considered. A comparative analysis of the methodological error of the considered methods for the cases of sinusoidal signal, polyharmonic signal and combined signals (sinusoidal signal and sinusoidal flicker) was made by simulation modeling in Matlab and Simulink software. The influence of supraharmonics on the measurement error for the case of considered methods is researched. The reliability of the obtained analytical relations is confirmed by comparison of the results of analytical and simulation modeling at check points.