CN101949974A - Field tester of alternating current electric energy meter - Google Patents

Abstract

The invention discloses a field tester of an alternating current electric energy meter, comprising an input unit, a digital-to-analogue conversion unit, a digital filtering unit, a reactive power calculating unit and an output unit, wherein the digital-to-analogue conversion unit is connected to the input unit and used for respectively sampling an analogue voltage signal and an analogue current signal and converting the analogue voltage signal and the analogue current signal into a digital voltage signal and a digital current signal; the digital filtering unit is connected to the digital-to-analogue conversion unit and used for filtering the digital voltage signal and the digital current signal according to a predetermined Hilbert filter to respectively acquire a filtering voltage signal and a filtering current signal; the reactive power calculating unit is connected to the digital filtering unit and used for calculating according to the acquired two filtering signals and a reactive power calculation formula to acquire reactive power of a non-sine circuit; and the output unit is connected to the reactive power calculating unit and used for outputting the reactive power. The field tester dephases -90 degrees to the digital voltage signal and the digital current signal through the digital filtering unit, and correctly calculates and measures the reactive power under the non-sine condition through the reactive power calculation formula.

Description

The AC energy meter on-spot tester

Technical field

The present invention relates to a kind of AC energy meter on-spot tester.

Background technology

At present, the metering of reactive energy becomes extremely important, it is not only the needs that improve the reactive energy metering accuracy, also is the needs of safeguarding for electricity consumption both sides legitimate interests, still strengthens the needs of harmonic management, raising electric system ground energy quality management and security of operation.In correlation technique, the definition of the notion of reactive power and computing formula exists bigger difference in the non-sinusoidal circuit, and physical significance neither be very clear, use AC energy meter on-spot tester (hereinafter to be referred as on-spot tester) when alternating current is measured, can't measure accurately the reactive power in the non-sinusoidal circuit.

Summary of the invention

In view of this, the present invention proposes a kind of AC energy meter on-spot tester, in order to solve the problems referred to above that exist in the correlation technique.

According to an aspect of the present invention, provide a kind of AC energy meter on-spot tester.

AC energy meter on-spot tester according to the present invention comprises: input block is used for obtaining the analog voltage signal u (t) and the analog current signal i (t) of non-sinusoidal circuit; D/A conversion unit is connected to input block, is used for u (t) and i (t) are sampled respectively, converts u (t) and i (t) to digital voltage signal u (n) and digital current signal i (n); The digital filtering unit is connected to D/A conversion unit, is used for according to predetermined hilbert filter H _d(e ^{J ω}) u (n) and i (n) are carried out filtering, obtain respectively filtering signal u ' (n) and i ' (n), wherein,

$H_d\left(e^{\mathrm{j\&omega;}}\right)=\begin{array}{}\end{array}\left\{\begin{array}{c}{e}^{-j(\mathrm{\&tau;\&omega;}+\mathrm{\&pi;}/2)},{\mathrm{\&omega;}}_{\mathrm{cl}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{ch}}\\ e^{-j(\mathrm{\&tau;\&omega;}-\mathrm{\&pi;}/2)},-{\mathrm{\&omega;}}_{\mathrm{ch}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{cl}}\\ 0,\left|\mathrm{\&omega;}\right|<{\mathrm{\&omega;}}_{\mathrm{cl}},\left|\mathrm{\&omega;}\right|>{\mathrm{\&omega;}}_{\mathrm{cl}}\end{array}\right.,$

τ is a sampling delay, τ=(N-1)/2, ω _ClFor descending by frequency ω _ChFor last by frequency; Reactive power is calculated the unit, is connected to the digital filtering unit, be used for according to filtering signal u ' (n) and i ' (n) and reactive power calculating formula Q calculate the reactive power Q of non-sinusoidal circuit, wherein, Output unit is connected to reactive power and calculates the unit, is used for reactive power Q is exported.

By means of technical scheme provided by the invention, with digital voltage signal u (n) and digital current signal i (n) phase shift-90 °, and calculate formula by reactive power by the digital filtering unit

Can measure the reactive power under the nonsinusoidal condition accurately.

Other features and advantages of the present invention will be set forth in the following description, and, partly from instructions, become apparent, perhaps understand by implementing the present invention.Purpose of the present invention and other advantages can realize and obtain by specifically noted structure in the instructions of being write, claims and accompanying drawing.

Description of drawings

Accompanying drawing is used to provide further understanding of the present invention, and constitutes the part of instructions, is used from explanation the present invention with embodiments of the invention one, is not construed as limiting the invention.In the accompanying drawings:

Fig. 1 is the structured flowchart according to the AC energy meter on-spot tester of the embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing embodiments of the invention are described, should be appreciated that embodiment described herein only is used for description and interpretation the present invention, and be not used in qualification the present invention.

In the electric energy meter field tester, reactive power mainly contains four kinds of methods under the measurement harmonic condition: power trigonometry (striding the phase method), (the current signal time domain phase shift of time delay method

), low-pass filter method and Hilbert digital filter method.The metering method of reactive power is all used power trigonometry or time delay method in most of like products, but the power trigonometry must depend on (the three-phase voltage angle strictness of three-phase voltage balance , the voltage assignment is strict to be equated) ideal conditions, and the electrical network situation of actual field is really not so, therefore can introduce bigger error; The time delay method is utilized time domain voltage or electric current phase shift

, but this method is in fact only carried out phase shift according to the first-harmonic phase angle, lacks the consideration to the harmonic wave phase angle, and the actual field signal can not be the sine wave of desirable single-frequency, so also can cause the inaccurate of wattless power measurement.In theory, Hilbert digital filter method can satisfy the actual measurement of reactive power more accurately.

The present invention adopts the Hilbert wave filter that voltage signal and current signal are carried out filtering, keeps each time voltage harmonic amplitude constant, with all harmonic components phase shifts of voltage

, adopt the measuring method of active power to measure reactive power then.

The AC energy meter on-spot tester that Fig. 1 shows according to the embodiment of the invention comprises: input block 2 is used for obtaining the analog voltage signal u (t) and the analog current signal i (t) of non-sinusoidal circuit; D/A conversion unit 4 is connected to input block 2, is used for u (t) and i (t) are sampled respectively, converts u (t) and i (t) to digital voltage signal u (n) and digital current signal i (n); Digital filtering unit 6 is connected to D/A conversion unit 4, is used for according to predetermined hilbert filter H _d(e ^{J ω)}U (n) and i (n) are carried out filtering, obtain respectively filtering signal u ' (n) and i ' (n),

$H_d\left(e^{\mathrm{j\&omega;}}\right)=\begin{array}{}\end{array}\left\{\begin{array}{c}{e}^{-j(\mathrm{\&tau;\&omega;}+\mathrm{\&pi;}/2)},{\mathrm{\&omega;}}_{\mathrm{cl}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{ch}}\\ e^{-j(\mathrm{\&tau;\&omega;}-\mathrm{\&pi;}/2)},-{\mathrm{\&omega;}}_{\mathrm{ch}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{cl}}\\ 0,\left|\mathrm{\&omega;}\right|<{\mathrm{\&omega;}}_{\mathrm{cl}},\left|\mathrm{\&omega;}\right|>{\mathrm{\&omega;}}_{\mathrm{cl}}\end{array}\right.$

Wherein,

τ is a sampling delay, τ=(N-1)/2, ω _ClFor descending by frequency ω _ChFor last by frequency; Reactive power is calculated unit 8, is connected to digital filtering unit 6, be used for according to filtering signal u ' (n) and i ' (n) and reactive power calculating formula Q calculate the reactive power Q of non-sinusoidal circuit,

Wherein,

Output unit 10 is connected to reactive power and calculates unit 8, is used for reactive power Q is exported.

Below the principle of work according to the AC energy meter on-spot tester of the embodiment of the invention is described.

Desirable Hilbert conversion is defined as:

$H_d\left(\mathrm{\&omega;}\right)=\left\{\begin{array}{cc}-j& 0<\mathrm{\&omega;}<\mathrm{\&pi;}\\ j& -\mathrm{\&pi;}<\mathrm{\&omega;}<0\end{array}\right.$

Being respectively of its amplitude and phase angle:

$H_d\left(e^{\mathrm{j\&omega;}}\right)=\begin{array}{}\end{array}\left\{\begin{array}{c}{e}^{-j(\mathrm{\&tau;\&omega;}+\mathrm{\&pi;}/2)},{\mathrm{\&omega;}}_{\mathrm{cl}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{ch}}\\ e^{-j(\mathrm{\&tau;\&omega;}-\mathrm{\&pi;}/2)},-{\mathrm{\&omega;}}_{\mathrm{ch}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{cl}}\\ 0,\left|\mathrm{\&omega;}\right|<{\mathrm{\&omega;}}_{\mathrm{cl}},\left|\mathrm{\&omega;}\right|>{\mathrm{\&omega;}}_{\mathrm{ch}}\end{array}\right.---\left(1\right)$

By (1) formula, the amplitude characteristic of Hilbert digital filter is 1, and signal is by behind the Hilbert digital filter, and its negative composition frequently carries out phase shift

, positive composition frequently carries out phase shift

As seen, the Hilbert digital filter can be used to realize the calculating or the measurement of aforesaid reactive power.

The design uses the window function method to design the Hilbert digital filter.

The ideal frequency response function of Hilbert digital filter is:

$H_d\left(e^{\mathrm{j\&omega;}}\right)=\begin{array}{}\end{array}\left\{\begin{array}{c}{e}^{-j(\mathrm{\&tau;\&omega;}+\mathrm{\&pi;}/2)},{\mathrm{\&omega;}}_{\mathrm{cl}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{ch}}\\ e^{-j(\mathrm{\&tau;\&omega;}-\mathrm{\&pi;}/2)},-{\mathrm{\&omega;}}_{\mathrm{ch}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{cl}}\\ 0,\left|\mathrm{\&omega;}\right|<{\mathrm{\&omega;}}_{\mathrm{cl}},\left|\mathrm{\&omega;}\right|>{\mathrm{\&omega;}}_{\mathrm{ch}}\end{array}\right.$

τ in the formula=be sampling delay (N-1)/2, ω _ClFor descending by frequency ω _ChFor last by frequency.Its unit impact response h _d(n) be:

$h_d\left(n\right)=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_{-\mathrm{\&pi;}}^{\mathrm{\&pi;}}{H}_d\left(e^{\mathrm{j\&omega;}}\right)e^{\mathrm{j\&omega;n}}\mathrm{d\&omega;}$

$=\left\{\begin{array}{c}{\&Integral;}_{-{\mathrm{\&omega;}}_{\mathrm{ch}}}^{-{\mathrm{\&omega;}}_{\mathrm{cl}}}{e}^{-j(\mathrm{\&omega;\&tau;}+2/\mathrm{\&pi;})}{e}^{\mathrm{j\&omega;n}}\mathrm{d\&omega;}\\ +{\&Integral;}_{{\mathrm{\&omega;}}_{\mathrm{cl}}}^{{\mathrm{\&omega;}}_{\mathrm{ch}}}{e}^{-j(\mathrm{\&omega;\&tau;}-2/\mathrm{\&pi;})}{e}^{\mathrm{j\&omega;n}}\mathrm{d\&omega;}\end{array}\right\}$

$=\frac{\cos [{\mathrm{\&omega;}}_{\mathrm{ch}}(n-\mathrm{\&tau;})-{\mathrm{\&omega;}}_{\mathrm{cl}}(n-\mathrm{\&tau;})]}{\mathrm{\&pi;}(n-\mathrm{\&tau;})}$

So have:

h ₁(n)＝h _d(n)ω(n)

ω in the formula (n) is the window function sequence of a finite length.

For the fundamental frequency signal of 50Hz, if consider that higher harmonics number of times is 21 times, the frequency range design that then this Hilbert digital filter can be concerned about is at 40～1300Hz.According to being Qwest's sampling thheorem, sample frequency Fs is not less than 2 times higher hamonic wave frequency, and the design gets 256 points each primitive period, the value of 100 subharmonic that can survey in theory, but consider actual conditions, we only are concerned about the situation of 1～21 subharmonic.

Consider that there is truncation effect in the THE DESIGN OF WINDOW FUNCTION wave filter, the design adopts the Hamming window to intercept, and carries out emulation with MATLAB, experimental results show that its passband ripple characteristic of Hilbert wave filter of Hamming THE DESIGN OF WINDOW FUNCTION is improved obviously.

The embodiment of the invention is when specific implementation, and the part that the effect in the AC energy meter on-spot tester is associated comprises signal sampling, and signal Processing is calculated, and they all need powerful hardware to do support, and the precision prescribed height requires speed fast on the one hand on the one hand.The design uses the parallel A/D sampling A of the high speed 16bit of AD company aspect signal sampling, the sample rate of 500KSPS, guaranteed the real-time requirement of 256 of samplings in per 0.02 second, and do not had the 16bit parallel transmission of error code, guaranteed that signal does not have drop-out when carrying out analog to digital conversion.Aspect signal Processing, the design has selected the dsp chip of TI company 5000 series for use, and the speed of 100M bar VAX Instructions Per Second VAX is guaranteed the real time measure of tester, and the advantage of the digital signal processing aspect that DSP is powerful is put to good use fully.

The method of using the Hilbert digital filter to measure reactive power can effectively be measured the reactive power under nonsinusoidal condition.It is with all harmonic componentss of voltage all phase shifts-90 ° and keep the each harmonic amplitude constant, adopts the wattful power messurement method to measure reactive power, has obtained very high measuring accuracy.

The above is the preferred embodiments of the present invention only, is not limited to the present invention, and for a person skilled in the art, the present invention can have various changes and variation.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (1)

1. an AC energy meter on-spot tester is characterized in that, comprising:

Input block is used for obtaining the analog voltage signal u (t) and the analog current signal i (t) of non-sinusoidal circuit;

D/A conversion unit is connected to described input block, is used for described u (t) and described i (t) are sampled respectively, converts described u (t) and described i (t) to digital voltage signal u (n) and digital current signal i (n);

The digital filtering unit is connected to described D/A conversion unit, is used for according to predetermined hilbert filter H _d(e ^{J ω}) described u (n) and described i (n) are carried out filtering, obtain respectively filtering signal u ' (n) and i ' (n), wherein, $H_d\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{c}{e}^{-j(\mathrm{\&tau;\&omega;}+\mathrm{\&pi;}/2)},{\mathrm{\&omega;}}_{\mathrm{cl}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{ch}}\\ e^{-j(\mathrm{\&tau;\&omega;}-\mathrm{\&pi;}/2)},-{\mathrm{\&omega;}}_{\mathrm{ch}}\&le;\left|\mathrm{\&omega;}\right|\&le;{\mathrm{\&omega;}}_{\mathrm{cl}}\\ 0,\left|\mathrm{\&omega;}\right|<{\mathrm{\&omega;}}_{\mathrm{cl}},\left|\mathrm{\&omega;}\right|>{\mathrm{\&omega;}}_{\mathrm{cl}}\end{array}\right.,$ τ is a sampling delay, τ=(N-1)/2, ω _ClFor descending by frequency ω _ChFor last by frequency;

Reactive power is calculated the unit, is connected to described digital filtering unit, be used for according to described filtering signal u ' (n) and i ' (n) and reactive power calculating formula Q calculate the reactive power Q of described non-sinusoidal circuit, wherein,

Output unit is connected to described reactive power and calculates the unit, is used for described reactive power Q output.

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