Constant-frequency variable dot power grid harmonic wave detection method and admeasuring apparatus thereof

A technology of harmonic detection and power grid cycle, applied in spectrum analysis/Fourier analysis, etc., can solve the problem of difficulty in reducing synchronization error, and achieve the effect of reducing harmonic measurement error, improving real-time performance, and no delay.

Inactive Publication Date: 2011-04-20
HOHAI UNIV
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Problems solved by technology

[0008] The purpose of the present invention is to solve the problem that the synchronization error of the existing harmonic measuring instrument is difficult to reduce, and propose a harmonic measuring instrument structure - fixed frequency variable point harmonic measuring instrument

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  • Constant-frequency variable dot power grid harmonic wave detection method and admeasuring apparatus thereof
  • Constant-frequency variable dot power grid harmonic wave detection method and admeasuring apparatus thereof
  • Constant-frequency variable dot power grid harmonic wave detection method and admeasuring apparatus thereof

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Embodiment Construction

[0026] Below in conjunction with accompanying drawing, the technical scheme of invention is described in detail:

[0027] like figure 1 As shown, the fixed-frequency variable-point harmonic measuring instrument includes two special components: (1) fixed-frequency full cycle sampler: with a constant sampling frequency f S The grid voltage (current) waveform is sampled, and each data window is controlled by a zero-crossing detector to be very close to S full cycles; (2) Variable point DFT calculator: when the grid frequency fluctuates, the number of sampling points of each data window is variable , designed a 'change point DFT calculator'.

[0028] like figure 2 As shown, the fixed-frequency full-cycle sampler includes an analog / digital converter, a zero-crossing detector and a DSP, the variable-point DFT calculator includes a programmable on-chip system and memory, and the fixed-frequency variable-point harmonic measuring instrument also includes three voltage mutual inducta...

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Abstract

The invention discloses a constant-frequency variable dot power grid harmonic wave detection method and an admeasuring apparatus thereof. The admeasuring apparatus comprises two special members, i.e. a constant-frequency complete cycle sampler and a variable dot DFT calculator. The detection method comprises the following steps: (1) constant-frequency complete cycle sampling: the waveform of power grid voltage (current) is sampled at constant sampling frequency fS and a zero passage detector controls each data window to infinitely approach to S complete cycle waves; and (2) variable dot DFT calculation: the sampling dot number of each data window is variable when the power grid frequency fluctuates, DFTs of different dots can be calculated at high speed and the high speed is mainly ensured by executing a trigonometric function type DFT by adopting high-speed DSP, acquiring DFT coefficients of different dots by a table lookup method and only calculating 500 frequency dots required by IEC61000-4-30 standard. The invention realizes the synchronization by a constant-frequency variable dot method; the synchronism deviation is guaranteed to be less than 1 / L0(L0 is equal to S*fS / 55); andas long as selected fS and S are large enough, the synchronism deviation for sampling can be guaranteed to be small enough, no time delay exists and the synchronization error for harmonic wave measurement can be reduced.

Description

technical field [0001] The invention relates to a harmonic measuring instrument and a harmonic measuring method of a power system, and belongs to the technical field of power quality monitoring. Background technique [0002] Power system harmonic measurement is an important part of power system power quality monitoring. The common method of harmonic measurement in power system is FFT (Fast Fourier Transform) method. Its basic principle is: first, sample the power grid waveform and ADC (analog-to-digital conversion) to obtain a sampling sequence, and then perform FFT on the sampling sequence to obtain each harmonic, Amplitude and phase information of interharmonics. FFT is a fast algorithm of DFT (Discrete Fourier Transform). When there are many data points, FFT is much faster than standard DFT, but FFT requires that the number of data points must be an integer power of 2. [0003] Theoretically, the FFT method requires 'synchronous sampling', that is, 'equal interval full-...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01R23/16
Inventor 梅永王柏林
Owner HOHAI UNIV
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