Measuring method of alternating current voltage frequency

Abstract

The invention discloses a simple and practical method for measuring frequency of alternating current voltage with software. The method comprises the following steps: acquiring a voltage value with a sampling time interval, carrying out discrete Fourier transform on the acquired voltage value, calculating a phase real part and a phase imaginary part of voltage, taking a product of the phase real part and the phase imaginary part as an input value of an interpolation fitting method, searching same direction zero crossing of the product of the phase real part and the phase imaginary part, and calculating frequency of the product of the phase real part and the phase imaginary part according to the zero crossing, wherein the frequency is the frequency of the alternating current voltage. According to the method, a filtering function of the discrete Fourier transform is fully utilized, influence of harmonic wave and direct current component on frequency measurement is eliminated, anti-interference capability is strong, a calculated value has high precision and small discrete, measurement precision is high, the method is simple and practical, high precision can be achieved both in stable state and transient state processes of a power system, realization of frequency measurement in a protection apparatus with a DSP as a core CPU is facilitated, and a requirement of the power system automatic field is satisfied.

Description

technical field [0001] The invention relates to a method for measuring AC voltage frequency, which belongs to the field of electrotechnical technology. Background technique [0002] In power systems, it is often necessary to measure the frequency of AC voltage. The method of measuring the period and frequency of the AC voltage by finding the zero-crossing moment with the same direction of change adjacent to it, because of its clear concept and simple method, is widely used in software and hardware frequency measurement. However, the real-time sampling value of AC voltage is greatly affected by harmonics and DC components, and the sampling value of the voltage near the zero-crossing point is small, and the calculation results are more discrete. The application of the software frequency measurement algorithm based on the voltage zero-crossing point has been limited. Certain restrictions, when the harmonic content of the power grid is large or the frequency deviation is large,...

AI Technical Summary

Problems solved by technology

However, the real-time sampling value of AC voltage is greatly affected by harmonics and DC components, and the sampling value of the voltage near the zero-crossing point is small, and the calculation results are more discrete. The application of the software frequency measurement algorithm based on the voltage zero-crossing point has been limited. Certain restrictions, when the harmonic content of the power grid is large or the frequency deviation is large, the calculation accuracy is difficult to meet the site requirements

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