CN117330834A - Dual-sampling-based power grid harmonic content testing method and system - Google Patents
Dual-sampling-based power grid harmonic content testing method and system Download PDFInfo
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- CN117330834A CN117330834A CN202311296703.9A CN202311296703A CN117330834A CN 117330834 A CN117330834 A CN 117330834A CN 202311296703 A CN202311296703 A CN 202311296703A CN 117330834 A CN117330834 A CN 117330834A
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- 238000012360 testing method Methods 0.000 title claims abstract description 20
- 238000000034 method Methods 0.000 claims abstract description 24
- 238000012545 processing Methods 0.000 claims abstract description 22
- 238000012952 Resampling Methods 0.000 claims abstract description 16
- 238000004364 calculation method Methods 0.000 claims abstract description 16
- 238000013500 data storage Methods 0.000 claims abstract description 13
- 238000004458 analytical method Methods 0.000 claims description 15
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- 238000005311 autocorrelation function Methods 0.000 claims description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
- G01R23/163—Spectrum analysis; Fourier analysis adapted for measuring in circuits having distributed constants
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
- G01R23/06—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage by converting frequency into an amplitude of current or voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
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Abstract
The invention relates to a method and a system for testing harmonic content of a power grid based on double sampling, wherein the method comprises the following steps: setting the fixed sampling frequency as Z kHz, and carrying out first resampling and obtaining first resampled data; the first resampled data is subjected to autocorrelation calculation, and the alternating current signal is converted into a pure sinusoidal signal; acquiring the period and the frequency of a pure sinusoidal signal, and performing second resampling on the alternating current signal according to the fixed sampling frequency and the fundamental frequency of the power grid to acquire second resampling data; and carrying out FFT calculation by adopting the second resampling data to obtain the contents of fundamental waves and harmonic waves. The system comprises a battery module, an electric parameter acquisition module, a data processing module, a display module and a data storage module. The invention solves the problems of large calculation amount required by the harmonic testing method and the problem of cost improvement caused by the enlarged volume of the testing device in the prior art, and can improve the calculation efficiency and miniaturize the testing device.
Description
Technical Field
The invention belongs to the technical field of power grid electric energy metering, and particularly relates to a power grid harmonic content testing method and system based on double sampling.
Background
At present, a plurality of photovoltaic power generation devices are distributed in a power supply district in a part of areas, and after the photovoltaic power generation devices are integrated into a power grid, the power quality output by a photovoltaic inverter, particularly the harmonic content of the alternating current side of the inverter, needs to be tested.
In the prior art, common methods for harmonic analysis include a frequency scanning method, a wavelet analysis method, a mutation theory method and an FFT (fast Fourier transform) method, and the FFT method is currently more common. When the FFT method is used for sampling the electric signal, if the sampling frequency is fixed, the tiny change of the sampled signal frequency can lead to the fact that the data window can not record an integer number of periods, and then frequency spectrum leakage and errors of harmonic analysis data occur. In order to solve the above problems, a method is often adopted, in which a window function is adjusted, the length of a fourier time window is lengthened, or a frequency adaptive algorithm is adopted, but the calculation amount is increased in the above method, so that the requirement on the hardware level is increased, and the volume and the cost of the testing device are further increased.
Disclosure of Invention
The invention provides a double sampling-based power grid harmonic content testing method and system, which solve the problems of large calculated amount required by a harmonic testing method in the prior art and cost improvement caused by the large size of a testing device.
A method for testing harmonic content of a power grid based on double sampling comprises the following steps:
setting the fixed sampling frequency as Z kHz; performing first resampling on the alternating current signal at the fixed sampling frequency and obtaining first resampled data;
performing autocorrelation calculation on the first resampled data to convert the alternating current signal into a pure sinusoidal signal;
acquiring the period and the frequency of the pure sinusoidal signal, and respectively recording the period and the frequency as the period of the fundamental wave of the power gridT 0 And the fundamental frequency of the power gridf 0 ；
The alternating current signal is subjected to second resampling according to the fixed sampling frequency and the fundamental frequency of the power grid to obtain second resampled data
And carrying out FFT calculation by adopting the second resampling data to obtain the contents of fundamental waves and harmonic waves.
Further, the calculation formula of the first resampled data is:
；
wherein,s(n) For the first resampled data the second data,x(n) As the fundamental component of the wave,h(n) Is a harmonic component.
Further, the first resampled data hasNA sampling period, the fundamental component is a periodic signal, and hasMA sampling period, and。
further, the autocorrelation function calculation formula of the first resampled data is:
；
wherein,r(m) Is the pure sinusoidal signal.
A system for implementing the method of claim 1, the system comprising a battery module, an electrical parameter acquisition module, a data processing module, a display module, and a data storage module.
Further, the power module adopts a lithium battery to supply power for the electric parameter acquisition module, the data processing module, the display module and the data storage module.
Further, the electrical parameter acquisition module is used for converting an output signal of the current transformer into a voltage signal, performing amplitude limiting processing on the voltage signal and then transmitting the voltage signal to the data processing module.
Further, the data processing module is configured to receive an output signal of the electrical parameter acquisition module, and perform analog-to-digital conversion on the output signal to obtain digital quantity signals corresponding to voltages and currents in the first resampled data and the second resampled data; the data processing module can carry out harmonic analysis through the digital quantity signal by utilizing an FFT method, and transmits a harmonic analysis result to the display module and the data storage module.
Further, the display module is used for displaying the harmonic analysis result of the data processing module and setting parameters of the system.
Further, the data storage module is used for storing harmonic analysis results.
Due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. compared with the traditional FFT harmonic measurement method, the harmonic measurement method has higher precision and smaller calculated quantity compared with the improved FFT harmonic measurement method in the prior art.
2. The system can realize an accurate harmonic measurement method with smaller calculated amount based on double sampling without upgrading the system, is beneficial to miniaturization of measurement equipment and contributes to saving equipment transformation cost.
Drawings
FIG. 1 is a flow chart of a method for testing harmonic content of a power grid based on double sampling;
fig. 2 is a system frame diagram of the power grid harmonic content test for double sampling provided in the present application.
Detailed Description
As shown in fig. 1, a method for testing harmonic content of a power grid based on double sampling comprises the following steps:
setting the fixed sampling frequency as 12.8kHz, carrying out first resampling on the alternating current signal at the fixed sampling frequency and obtaining first resampled data, and recording the first resampled data ass(n)（n0 to 12799),s(n) Comprising a fundamental componentx(n) Harmonic componenth(n) The method comprises the steps of carrying out a first treatment on the surface of the That is to say,
；
periodic signal of power gridIs about 50Hz, the sampling frequency is 12.8kHz, so each sampling frequency comprises about 256 sampling periods, so the fundamental component hasMA number of sampling periods of time,Mis 256. Continuous sampling 1sThereafter, shareNA sampling period, thusThe first resampled data can be subjected to autocorrelation calculation to determine the fundamental frequency of the acquired voltage signal or current signal, wherein the fundamental frequency is the real frequency of the power grid;
；
after the alternating current signal is converted into the pure sinusoidal signal through autocorrelation calculation, the period and the frequency of the pure sinusoidal signal are obtained, and the period and the frequency are respectively recorded as the period of the fundamental wave of the power gridT 0 And the fundamental frequency of the power gridf 0 The method comprises the steps of carrying out a first treatment on the surface of the At 128×f 0 Performing second resampling on the alternating current signal for the sampling frequency according to the specified sampling frequency and the fundamental frequency of the power grid to obtain second resampling data, and continuously sampling 128 points at the sampling rate;
and carrying out FFT calculation by adopting the second resampled data, and calculating a direct current component, a fundamental wave and 2-63 times of harmonic waves.
As shown in fig. 2, the system for testing the harmonic content of the power grid based on double sampling comprises a battery module, an electric parameter acquisition module, a data processing module, a display module and a data storage module.
The power module adopts a lithium battery to supply power for the electric parameter acquisition module, the data processing module, the display module and the data storage module.
The electric parameter acquisition module is used for converting the output signal of the current transformer into a voltage signal, carrying out amplitude limiting processing on the voltage signal and then transmitting the voltage signal to the data processing module.
The data processing module is used for receiving the output signal of the electric parameter acquisition module and carrying out analog-to-digital conversion on the output signal so as to acquire digital quantity signals corresponding to the voltage and the current in the first resampling data and the second resampling data; the data processing module can carry out harmonic analysis through the digital quantity signal by utilizing an FFT method, and transmits a result of the harmonic analysis to the display module and the data storage module.
The display module is used for displaying the harmonic analysis result of the data processing module and setting parameters of the system.
The data storage module is used for storing harmonic analysis results.
The foregoing description is only of the basic principles and preferred embodiments of the present invention, and modifications and alternatives thereto will occur to those skilled in the art to which the present invention pertains, as defined by the appended claims.
Claims (10)
1. The method for testing the harmonic content of the power grid based on double sampling is characterized by comprising the following steps of:
setting the fixed sampling frequency as Z kHz; performing first resampling on the alternating current signal at the fixed sampling frequency and obtaining first resampled data;
performing autocorrelation calculation on the first resampled data to convert the alternating current signal into a pure sinusoidal signal;
acquiring the period and the frequency of the pure sinusoidal signal, and respectively recording the period and the frequency as the period of the fundamental wave of the power gridT 0 And the fundamental frequency of the power gridf 0 ；
Carrying out second resampling on the alternating current signal according to the fixed sampling frequency and the fundamental frequency of the power grid to obtain second resampling data;
and carrying out FFT calculation by adopting the second resampling data to obtain the contents of fundamental waves and harmonic waves.
2. The method for testing harmonic content of a power grid based on double sampling according to claim 1, wherein,
the calculation formula of the first resampled data is as follows:
；
wherein,s(n) For the first resampled data the second data,x(n) As the fundamental component of the wave,h(n) Is a harmonic component.
3. A method for testing harmonic content of a power grid based on double sampling as recited in claim 2, wherein,
the first resampled data hasNA sampling period, the fundamental component is a periodic signal, and hasMA sampling period, and。
4. a method for testing harmonic content of a power grid based on double sampling as claimed in claim 3, wherein,
the autocorrelation function calculation formula of the first resampled data is as follows:
；
wherein,r(m) Is the pure sinusoidal signal.
5. A system for implementing the method of claim 1,
the system comprises a battery module, an electric parameter acquisition module, a data processing module, a display module and a data storage module.
6. The system of claim 5, wherein the system further comprises a controller configured to control the controller,
the power module adopts a lithium battery to supply power for the electric parameter acquisition module, the data processing module, the display module and the data storage module.
7. The system of claim 5, wherein the system further comprises a controller configured to control the controller,
the electric parameter acquisition module is used for converting the output signal of the current transformer into a voltage signal, carrying out amplitude limiting processing on the voltage signal and then transmitting the voltage signal to the data processing module.
8. The system of claim 5, wherein the system further comprises a controller configured to control the controller,
the data processing module is used for receiving the output signal of the electric parameter acquisition module and performing analog-to-digital conversion on the output signal so as to acquire digital quantity signals corresponding to voltage and current in the first resampled data and the second resampled data; the data processing module can carry out harmonic analysis through the digital quantity signal by utilizing an FFT method, and transmits a harmonic analysis result to the display module and the data storage module.
9. The system of claim 8, wherein the system further comprises a controller configured to control the controller,
the display module is used for displaying the harmonic analysis result of the data processing module and setting parameters of the system.
10. The system of claim 9, wherein the system further comprises a controller configured to control the controller,
the data storage module is used for storing harmonic analysis results.
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