APPLICATION OF THE zero crossing technique for the FREQUENCY MEASURement OF the REAL POWER NETWORK SIGNALS
In solving modern problems of the electric power industry, when measuring the signal frequency, the most common method is based on determining the zero crossings of a given signal. The advantage of the method is the simplicity of the analysis and implementation of measurement algorithms, which makes it possible to impose lower requirements on the element base used in the implementation. The disadvantage of this method is the significant influence of harmonics and noise on the frequency measurement error. In this article, a new version of the modification of this method for measuring the signal frequency is proposed. The analysis carried out in the article shows that the proposed modification to reduce the dependence of the metrological characteristics of the method on the minor spectral components of the measured signal and noise. The essence of the modification consists in the additional use of another value instead of the zero level, for which the application of the method for signal zero crossings will be more effective. The signal level is determined by calculating the torque that will correspond to the maximum derivative of the measured signal, i.e. its maximum tilt angle. The derivative value of the signal is determined using a first-order digital differentiator. The paper considers options for constructing digital differentiators and their influence on the frequency measurement error. The moments of signal transition through the level corresponding to the maximum derivative are refined using piecewise linear approximation of the signal in the vicinity of the transition. In the course of the work, a computer simulation of the zero-crossing method and its modifications was carried out using the Simulink software package, and analytical expressions were obtained that characterize the frequency measurement error. As a result of the simulation, a comparison was made between the metro-logical characteristics of the “classical” zero-crossing method and the proposed modification.