Zero-Crossing Technique Modification for the Frequency Measurements of Real Power Grids

Abstract

Currently, the most popular method of the frequency measurement of electric power grids signals is the zero-crossing technique. The main disadvantage of this method is associated with the sensitivity of this method to harmonics, noise and flicker of the measured signal. The existing methods of reducing the measurement error results to an increase of the measurement time, which is a significant disadvantage for a number of practical tasks. This paper discusses a method of reducing the frequency measurement error when applying the zero-crossing technique. The proposed method is based on the determination of the moments of signal transition through the level which corresponds to signal maximum derivative. To clarify the moments of signal transition through a given level, a piecewise-linear approximation of the signal in the vicinity of its transition through a given level was applied. To determine the value of the derivative, a seventh-order digital differentiator is proposed. Analytical expressions for the frequency measurement error estimation for the proposed measurement method are obtained. The effectiveness of the proposed method of reducing the measurement error in comparison with the “traditional” zero-crossing technique has been evaluated. By using the Simulink software package, a model of simulation modeling of a frequency measurement transducer that implements the proposed measurement method has been proposed. The reliability of the obtained analytical expressions is confirmed by the coincidence of the results of simulation modeling and analytical expressions at check points.