Inter-harmonics measuring method for power grid

Abstract

The invention discloses an inter-harmonics measuring method for the power grid. The inter-harmonics measuring method includes: 1) sampling three-phase current and three-phase voltage of the power grid by sampling frequency fs and sampling points N in real time, and transmitting sampled signals to a DSP (digital signal processor) processing module; and 2) detecting inter-harmonics by means of FFT (fast fourier transform algorithm) according to the current and voltage signals sampled in the step 1). The step 2) includes: 21) utilizing the sampled signals obtained in the step 1) as original signals; 22) calculating amplitude, phase and frequency of fundamental harmonics and harmonics; 23) calculating frequency domain signals of the fundamental harmonics and harmonics; 24) subtracting frequency signals of the fundamental harmonics and harmonics obtained in the step 23) from the original signals to obtain windowed frequency domain signals of the inter-harmonics; and 25) calculating amplitude, phase and frequency of the inter-harmonics obtained in the step 24). On the basis of results obtained by conventional integral subharmonics measuring method, a Hanning window is selected as window function, and inter-harmonics measuring instantaneity is improved by filtering components of fundamental harmonics and integral subharmonics by frequency domain.

Description

technical field [0001] The invention relates to an online detection of electric energy quality, in particular to a method for measuring harmonics among power grids. Background technique [0002] Non-integral harmonics of the fundamental frequency, ie interharmonics, may also be generated by non-linear loads in the power system in addition to the integral harmonics of the fundamental frequency. According to IEC-61000-2-1, interharmonic (Interharmonic) is defined as: between the harmonic components of voltage and current signals, there is a signal whose frequency is not an integer multiple of the fundamental frequency, which is manifested as a discrete spectrum or broadband spectrum. The main interharmonic sources in the power system include: frequency conversion speed control device; high voltage direct current transmission; motor and electric arc furnace, etc. Similar to harmonics, inter-harmonics will not only affect the operation of passive filters and cause flicker prob...

AI Technical Summary

Problems solved by technology

However, due to the inherent non-stationarity of inter-harmonics, the frequency is difficult to predict, and the amplitude is often much smaller than the fundamental wave and harmonic components, the improved FFT method and the AR model power spectrum based on second-order statistics are currently used. It is difficult to accurately detect inter-harmonics, and there are deficiencies such as spectrum leakage and poor anti-interference

However, the more accurate measurement method based on high-order cumulants has a large amount of calculation, and it is difficult to meet the real-time requirements of online power quality detection.

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