CN103969507A - Power quality harmonic analysis method - Google Patents
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Abstract
The invention discloses a power quality harmonic analysis method which is realized through improvement on the basis of quasi-synchronous DFT (discrete fourier transform). The harmonic analysis method comprises the following steps: sampling an electrical signal X needing harmonic analysis in a power grid, and sampling the data of W+2 sampling points at an equal interval; changing the sampling position of a frequency domain according to the drift micron of signal frequency when the quasi-synchronous DFT is applied to harmonic analysis, namely the sampling position of the frequency domain as a micron2pai/N; calculating the amplitude and initial phase angle of harmonic waves of the electric signal X; and finally, respectively calculating the percentage of amplitude P<k> and amplitude of first harmonic P1, and phase angle difference of higher harmonic and first harmonic P1 of a voltage signal V and a current signal I, and outputting and displaying.
Description
The application is that application number is: 201110322629.4, and invention and created name is " a kind of harmonic analysis method of electric energy quality harmonic analyser ", the applying date is: the divisional application of the application for a patent for invention on October 21st, 2011.
Technical field
The present invention relates to the technical field that electric energy quality harmonic is analyzed, specifically a kind of high-precision harmonic analysis method.
Background technology
Frequency analysis technology is widely used in various fields such as electric energy quality monitoring, electronic product production testing, electric equipment monitoring, is the important technical of carrying out power system monitor, quality inspection, monitoring of tools.
In power supply grid, the generation of harmonic phenomena is mainly due to large-capacity power equipment, cause with electric rectification or converter and other nonlinear-loads.Along with the develop rapidly of Power Electronic Technique, many industrial enterprises introduce a large amount of impact load, asymmetric load and nonlinear load in recent years, and they inevitably occur harmonic pollution phenomenon in the time of access electrical network.Therefore, voltage, current signal to power supply grid carry out frequency analysis, can observe better electric network pollution situation, and then provide theoretical foundation for power network compensation and purification.
The most widely used technology of frequency analysis is discrete Fourier transformation (DFT) and Fast Fourier Transform (FFT) (FFT) at present.The frequency analysis technology (that is: accurate synchronous DFT frequency analysis technology) that accurate synchronous sampling technique and DFT technology combine can improve the precision of frequency analysis, and its formula is:
，
In formula: k is the number of times (as first-harmonic k=1,3 subharmonic k=3) that needs the harmonic wave obtaining; Sin and cos are respectively sine and cosine functions; And a
kand b
kbe respectively real part and the imaginary part of k subharmonic; N is iterations; W determines by integration method, while adopting complexification trapezoidal integration method, and W=nN;
it is a weighting coefficient;
, be all weighting coefficient sums; I the sampled value that f (i) is analysis waveform; N is sampling number in the cycle.
In engineering application, frequency analysis is always carried out the sampling of finite point and is difficult to accomplish the synchronized sampling of stricti jurise.Like this, in the time that the accurate synchronous DFT of application carries out frequency analysis, the short scope leakage that will exist the long scope causing due to truncation effect to leak and cause due to fence effect, makes analysis result precision not high, even not credible.
Summary of the invention
The technical problem to be solved in the present invention is to provide the harmonic analysis method of the electric energy quality harmonic analyser that a kind of precision is higher, effectively to improve the analytical error of accurate synchronous DFT frequency analysis technology, obtain high-precision frequency analysis result, thereby improve the reliability of the electric energy quality monitoring equipment based on frequency analysis theory and the validity of state judgement.
For solving the problems of the technologies described above, the invention provides a kind of harmonic analysis method of electric energy quality harmonic analyser, described electric energy quality harmonic analyser comprises successively and to be connected: sensor, signal conditioning circuit, data acquisition circuit and CPU element; Described harmonic analysis method comprises the steps:
(1) in described CPU element sampling electrical network, need the electric signal X of frequency analysis, and equal interval sampling W+2 sampling number is according to { f (i), i=0,1, w+1}(W is determined by selected integration method, the present invention does not specify a certain integration method, conventional integration method has complexification trapezoidal integration method W=nN, complexification rectangular integration method W=n (N-1), iterative Simpson integration method W=n (N-1)/2 etc., and the actual conditions that can apply according to the present invention are selected suitable integration method.Generally more satisfactory with complexification trapezoidal integration method effect);
(2) CPU element starts the accurate synchronous DFT formula of application from the sampled point i=0 of described electric signal X:
Analyze W+1 data acquisition first-harmonic information
with
;
Then, CPU element starts the accurate synchronous DFT formula of application from the sampled point i=1 of described electric signal X:
Analyze W+1 data acquisition first-harmonic information
;
Application of formula
calculate the frequency drift of described electric signal X
;
Application of formula
, draw respectively the first-harmonic of described electric signal X and higher hamonic wave
;
(3), CPU element calculates respectively the first-harmonic of described electric signal X and the amplitude of higher hamonic wave
and initial phase angle
;
(5), CPU element calculates respectively the amplitude P of the higher hamonic wave of described electric signal X
kwith first-harmonic P
1amplitude number percent
and phase angle difference
, and output display (the general LCD unit being connected with this CPU element that adopts shows).
Described electric signal X is generally grid ac voltage signal or grid alternating current stream signal.
Accurate synchronous DFT frequency analysis can effectively suppress long scope and leak, the main cause of its spectrum leakage is that the short scope that signal frequency drift causes is leaked, and signal frequency drift causes principal character that short scope leaks is spectrum peak-to-peak value occurs position along with signal frequency drift synchronous change, so variable fence frequency domain sample can effectively catch according to signal drift the position that spectrum peak-to-peak value occurs, thereby obtains high-precision harmonic information.
Equal interval sampling is cycle T and the frequency f (if power frequency component frequency f is 50Hz, the cycle is 20mS) that basis is carried out the ideal signal of frequency analysis, the N point of sampling in one-period, and sample frequency is f
s=Nf, and N>=64.
Described sampling W+2 sampling number is according to being to do corresponding selection according to selected integration method, if adopt complexification trapezoidal integration method, W=nN; If adopt complexification rectangular integration method, W=n (N-1); If adopt iterative Simpson integration method, W=n (N-1)/2.Then according to sample frequency f
s=Nf, acquisition sampled point data sequence f (i), and i=0,1 ..., w+1}, n>=3, finally carry out frequency analysis to this data sequence.
An iteration coefficient
determined by integration method, ideal period sampled point N and iterations n, concrete derivation referring to document [Dai Xianzhong. the some problems [J] in accurate synchronized sampling application. electrical measurement and instrument, 1988, (2): 2-7.].
for all weighting coefficient sums.
for imaginary part and the real part of k subharmonic, according to
just can obtain harmonic amplitude and initial phase angle.
The drift of signal frequency
to obtain according to the fixed relationship of sampling number N in neighbouring sample point first-harmonic phase angle difference and ideal period, the drift of signal frequency
also can be used for revising the frequency f of first-harmonic and higher hamonic wave
1frequency f with higher hamonic wave
k.
The present invention is mainly used in the analysis software of electric energy quality harmonic analyser, for improvement of with improve the quality of frequency analysis, obtain amplitude, phase angle and the frequency of high-precision first-harmonic and higher hamonic wave.Analyzed signal is carried out sampling and analyzing by the present invention, and analysis result (amplitude, phase angle and frequency etc.) is exported according to the requirement of electric energy quality harmonic analyser.The harmonic analysis method that electric energy quality harmonic analyser of the present invention adopts, is the frequency analysis technology based on variable fence thought, has following technical advantage:
(1) high-precision frequency analysis result.No matter the analysis result that frequency analysis technology of the present invention obtains is that amplitude or phase angle error improve 4 more than the order of magnitude.
(2) frequency analysis technology of the present invention has fundamentally solved the low problem of accurate synchronous DFT analysis precision, and without carrying out complicated inverting and correction, algorithm is simple.
(3) with respect to the synchronous DFT of standard, frequency analysis technology of the present invention only need to increase a sampled point and just solve the large problem of accurate synchronous DFT analytical error, is easy to realize.
(4) application the present invention improves existing instrument and equipment, and technical is feasible, and does not need to increase any hardware spending and just can make analysis result can improve 4 more than the order of magnitude.
(5) variable fence thought is also applicable to carry out repeatedly iteration and the frequency analysis process of non-once iteration too, now only an iteration need to be resolved into repeatedly to iteration and realize just passable.Iteration is the same with iteration repeatedly in essence, and just in the time calculating, repeatedly iteration is carried out substep calculating, and iteration is that the process of iteration is repeatedly merged to iteration coefficient
in once calculated, so the present invention is equally applicable to repeatedly iterative process.
(6) the present invention applies the position that accurate synchronous DFT carries out the sampling of frequency analysis time-frequency domain and changes according to the drift of signal frequency, and described frequency domain sampling position is μ 2 π/N, wherein:
for the drift of signal frequency, during without drift
be 1.The thought of harmonic analysis method of the present invention based on variable fence, realizes by 5 analytical procedures.The thought of variable fence: the main cause of accurate synchronous DFT analytical error is position and the ideal position generation deviation that the drift of signal frequency causes spectrum peak to occur, if the analysis result still obtaining to sample in frequency domain according to 2 π/N is extremely incorrect.Variable fence refers to: the position of frequency domain sampling be not the 2 π/N fixing, but change according to the drift of signal frequency, frequency sampling position is the drift that μ 2 π/N(μ is signal frequency).Frequency domain sampling fence changes along with the drift of signal frequency can accurately estimate the position that higher hamonic wave peak value occurs, and then obtains high-precision amplitude and phase angle information.
Embodiment
Electric energy quality harmonic analyser is mainly made up of sensor, signal conditioning circuit, data acquisition circuit, CPU, LCD unit and corresponding analysis software.Sensor generally adopts voltage transformer (VT) and current transformer, and the high voltage of tested electrical network and large current signal are changed by a certain percentage; Voltage, the current signal that signal conditioning circuit is sent sensor here is transformed to the voltage signal that is applicable to data acquisition circuit sampling; By data acquisition circuit, the signal after conditioning is sampled, then complete analysis and the detection to harmonic wave by CPU by analysis software.
The harmonic analysis method of electric energy quality harmonic analyser of the present invention, comprises the following steps:
First, in CPU element sampling electrical network, need the electric signal X of frequency analysis, and an equal interval sampling W+2 sampled point, with obtain described electric signal X discrete series f (k), k=0,1 ..., w+1}.W is determined jointly by sampling number N in integration method, iterations n and ideal period.Equal interval sampling refers to according to the frequency f (if power frequency component frequency is 50Hz, the cycle is 20mS) of the ideal signal that carries out frequency analysis determines sample frequency f
s=Nf, at sample frequency f
seffect under the N point of sampling equably in one-period.Usually, periodic sampling point N=64 or just can obtain good frequency analysis result above, and iterations n=3-5 just can obtain comparatively ideal frequency analysis result.Integration method has complexification trapezoidal integration method W=nN, complexification rectangular integration method W=n (N-1), Simpson's integration method W=n (N-1)/2 etc. multiple, can select according to actual conditions.
Secondly, CPU element starts the accurate synchronous DFT formula of application from the sampled point i=0 of described electric signal X:
analyze W+1 data acquisition first-harmonic information
with
.Wherein, an iteration coefficient
determined by integration method, ideal period sampled point N and iterations n, and
for all weighting coefficient sums.
Then, CPU element starts the accurate synchronous DFT formula of application from the sampled point i=1 of described electric signal X:
analyze W+1 data acquisition first-harmonic information
.
Then, application of formula
calculate the frequency drift of described electric signal X
.Obtain frequency drift
after, can be according to sample frequency f
scalculate and obtain the first-harmonic of analyzed signal and the frequency f of higher hamonic wave with sampling number N in ideal period.
Then, application of formula
, calculate respectively the first-harmonic of described electric signal X and the real part of higher hamonic wave
and imaginary part
;
CPU element and then according to formula:
calculate respectively the first-harmonic of described electric signal X and the amplitude of higher hamonic wave
and initial phase angle:
.
Finally, CPU element calculates respectively the amplitude P of the higher hamonic wave of described electric signal X
kwith first-harmonic P
1amplitude number percent
and phase angle difference
, and output display (the general LCD unit being connected with this CPU element that adopts shows).
Those skilled in the art will be appreciated that, above embodiment is only for the present invention is described, and not as limitation of the invention, the present invention can also be varied to more mode, as long as within the scope of connotation of the present invention, variation, modification to the above embodiment all will drop within the scope of claims of the present invention.
Claims (1)
1. an electric energy quality harmonic analytical approach, is characterized in that comprising the following steps:
(1), need the electric signal X of frequency analysis equal interval sampling W+2 sampling number certificate in the CPU element of electric energy quality harmonic analyser sampling electrical network: f (i), i=0,1 ..., w+1}; Described equal interval sampling is cycle T and the frequency f that basis is carried out the ideal signal of frequency analysis, the N point of sampling in one-period, and sample frequency is f
s=Nf, and N>=64;
(2), CPU element starts the accurate synchronous DFT formula of application from the sampled point i=0 of described electric signal X:
analyze W+1 data acquisition first-harmonic information
with
;
Then, CPU element starts the accurate synchronous DFT formula of application from the sampled point i=1 of described electric signal X:
, analyze W+1 data acquisition first-harmonic information
;
Application of formula:
,
Calculate the frequency drift of described electric signal X
; Frequency drift
to obtain according to the fixed relationship of sampling number N in neighbouring sample point first-harmonic phase angle difference and ideal period, frequency drift
for revising the frequency f of first-harmonic
1frequency f with higher hamonic wave
k;
Application of formula:
, draw respectively the first-harmonic of described electric signal X and higher hamonic wave
;
(3), CPU element calculates respectively the first-harmonic of described electric signal X and the amplitude of higher hamonic wave
and initial phase angle
(4), CPU element calculates respectively the amplitude P of the higher hamonic wave of described electric signal X
kwith first-harmonic P
1amplitude number percent
and phase angle difference
, and output display.
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| CN201110322629.4A CN102508026B (en) | 2011-10-21 | 2011-10-21 | Harmonic wave analysis method for electric energy quality harmonic wave analyzer |
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| CN113358930A (en) * | 2021-08-09 | 2021-09-07 | 南京派格测控科技有限公司 | Harmonic wave test system, device and method based on signal deviation |
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