Frequency measuring method and frequency measuring circuit

Abstract

The invention discloses a frequency measuring method and a frequency measuring circuit. The method comprises the steps that a voltage zero crossing signal is subjected to voltage lifting to obtain a voltage no-zero-crossing signal with the same frequency as the voltage zero crossing signal; the voltage no-zero-crossing signal is compared with high level reference voltage and low level reference voltage to obtain a square wave signal with the same frequency as the voltage no-zero-crossing signal; and the rising edge and / or falling edge of the square wave signal is captured, the frequency of thesquare wave signal is computed according to the time interval between the captured rising edge and / or falling edge, and the computed frequency of the square wave signal serves as the frequency of thevoltage zero crossing signal. The frequency measuring method and frequency measuring circuit accurately extracts the fundamental wave frequency of the voltage zero crossing signal by conducting voltage lifting on the voltage zero crossing signal and arranging the high level reference voltage and the low level reference voltage, effectively reduces the complexity and the calculated quantities of the software, and meanwhile improves measuring real-time performance.

Description

technical field [0001] Embodiments of the present invention relate to but are not limited to the technical field of power metering, and particularly relate to a frequency measurement method and a frequency measurement circuit. Background technique [0002] In the power system, the system frequency is a very important parameter. Accurately measuring the frequency of the fundamental wave of the system is of great significance to the control and regulation of the power system, especially in some relay protection and safety automatic devices, which require not only real-time Measuring power system frequency also requires high measurement accuracy. The relay protection devices of some manufacturers also need to adjust the sampling frequency in real time according to the measured frequency, so as to achieve the purpose of fixed sampling points per cycle. However, the existence of fundamental frequency fluctuations, harmonics and noise in the actual power grid or traction network ...

AI Technical Summary

Problems solved by technology

[0004] Among the many software frequency measurement methods, most methods cannot be widely used in power system relay protection or safety automatic devices due to complex algorithms, large amount of calculation, poor real-time performance or high sampling frequency requirements.

At present, the software frequency measurement methods that are widely used include zero-crossing method and discrete Fourier transform method. Among them, the zero-crossing method is the basic method of low-frequency sinusoidal frequency measurement. It is similar to the zero-crossing detection method of hardware frequency measurement and is easily affected by harmonics. and noise interference; the discrete Fourier transform method is a basic mathematical method for sinusoidal frequency calculation, which has the characteristics of strong anti-interference ability and high measurement accuracy, and is most widely used in microcomputer protection and some measurement and control devices, but it is also There are certain limitations, among which the spectrum leakage problem caused by the non-integer cycle truncation of the signal is the main cause of the algorithm error, and the spectrum leakage problem is objectively unavoidable

[0005] The zero-crossing detection method of hardware frequency measurement is similar to the zero-crossing method. It calculates the period of the sine wave by detecting the time of the two zero-crossing points of the sine wave, which is easily affected by harmonics and noise interference.

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