CN100454026C - Cycle sampling method in quality of power supply in electrical network - Google Patents

Abstract

The present invention relates to a cycle sampling method in the quality of the power supply in an electrical network, which aims at the method that the frequency of the current cycle is predicted though the calculation of the frequency of a plurality of front cycles of the current cycles of a system, and thereby, the defects of effective sampling point loss and a larger measure error in a sampling process are caused. One constant sampling frequency for sampling is adopted and then is restored to waveform through a waveform fitting technique; a least square method is utilized for finding out a zero crossing point of the waveform for obtaining one complete cycle; double sampling can be carried out on the fitted waveform; the quality index of the power supply in the system is analyzed according to the points. The sampling precision of the method of the present invention is increased, which provides more accurate and reliable data for the quality index of the electric energy of the effective value of current, harmonic, power, etc. The method of the present invention has an obvious effect in practice.

Description

The cycle method of sampling in the electrical network quality of power supply

(1) technical field:

The present invention relates to the measuring method of power quality index in a kind of electric system, the cycle method of sampling in especially a kind of electrical network quality of power supply.

(2) background technology:

Along with expanding economy, electric power is played the part of more and more important role in economic life.The fine or not direct relation of the quality of power supply the overall benefit of national economy.Impact, nonlinear-load are on the increase in the electrical network at present, cause power quality problem severe exacerbations such as mains by harmonics, voltage fluctuation flickering, three-phase imbalance; And in a large number make temporary overvoltage and transient overvoltage, voltage sag and short time some former economic losses that do not caused by the power quality problem that people paid attention to such as be interrupted also in continuous increase based on the appearance of class sensitive loads such as the opertaing device of computer system and electronic installation, imperative to the improvement work of the management of the quality of power supply and electric pollution.

Along with science and technology development, realize that the robotization of electrical network has become the trend of power system development.Measurement to power quality index in the electric system has become an element task.For grid automation management, measure very important accurately to its power quality index in service.This is to guarantee power grid security, economy, the basic premise of operation reliably.Because accurately carrying out the cycle sampling is the basis of accurately measuring other power quality index, therefore, the cycle method of sampling becomes the determinative of power quality index.

Common practice to the sampling of the cycle in the electrical network quality of power supply is, at first the AC signal such as voltage and current in the electrical network are carried out AC sampling, according to certain linear transformation, propose corresponding algorithm then, thereby calculate effective value, frequency, phase angle, power and the electric energy etc. of voltage and current.Wherein, the method majority of AC sampling is: by the next voltage (or electric current) in secondary system loop, after the suitable voltage of A/D is delivered in changes such as (or current transformer CT) through secondary voltage mutual inductor PT, A/D carries out analog to digital conversion with certain sample frequency by CPU control, obtains discrete sampled data.Then, through discrete Fourier transform (DFT) (DFT), calculate first-harmonic effective value, each harmonic value and other index of correlation.

The condition of each parameter value is to rely on said method can obtain accurately: the real-time frequency of the system of current sampling cycle is known, in view of the above, could determine that suitable sample frequency samples.The power frequency of sample frequency and electric system, the two one of change, all can influence the calculating of sampling back effective value.Obviously, the current cycle of system can't learn.The most original method is that the viewing system frequency is constant, samples with a fixing sample frequency, and still, system frequency is constantly to change in the reality, certainly will cause and lose effective sampled point in sampling process, causes measuring error.

In order to address the above problem, prior art is numerous and confused to be adopted by the frequency of preceding several cycles of the current cycle of system being calculated and doped the method for current all wave frequencies.At this, various theories, technology and algorithm are arranged, as zero passage technology, level cross technology, least square difference technology or the like, and measure in view of the above, wherein, tool extensively and representational be PHASE-LOCKED LOOP PLL TECHNIQUE.

The principle of PHASE-LOCKED LOOP PLL TECHNIQUE is as follows: on the basis of typical A/D translation interface, increased the phaselocked loop loop, this phaselocked loop loop is a feedback system, usually by phase detector (PhaseDetector, abbreviation P D), loop filter (Loop Filter, abbreviation LPF), voltage controlled oscillator (Voltage Control Oscillator is called for short VCO) is formed.The function of phase detector can be decomposed into two effects, at first is two phase of input signals are subtracted each other, and promptly obtains the phase differential between these two input signals; And phase differential is converted to error voltage output, so the device of its to be phase differential be converted to voltage.Loop filter can filter high fdrequency component.Voltage controlled oscillator is a kind of frequency to voltage converter.In the phaselocked loop loop, the frequency of voltage controlled oscillator signal is subjected to the control of filter output voltage, and the phase place of its output signal changes with phaselocked loop loop phase of input signals, thereby keeps Phase Tracking.

PHASE-LOCKED LOOP PLL TECHNIQUE since realized to the measured signal frequency change from motion tracking and phase locking, improved the automatization level of measuring system and the accuracy of measurement effectively.But because it is to be undertaken from motion tracking and phase locking by the frequency to preceding several cycles of the current cycle of system, it can not equate fully that with current all wave frequencies still can lose effective sampled point in sampling process, measuring error is still bigger.

(3) summary of the invention:

The present invention aims to provide the cycle method of sampling in the higher electrical network quality of power supply of a kind of accuracy.

Technical solution of the present invention is as follows:

1, gathers secondary side voltage, electric current according to fixing sample frequency, gather n ₁Individual point (n ₁=2 ⁿ, n 〉=6)

2, by waveform fitting technique with the n that collects ₁Individual point is reduced to waveform

3, find out the zero crossing of this waveform, and determine a complete cycle in view of the above

4, according to a fixing sample frequency (f=2 ⁿ* 50Hz, n=6,7,8,9 ...), the match waveform of above-mentioned acquisition is carried out double sampling, gather n ₂Individual point

5, according to n ₂The AC signal values such as voltage and current of individual point calculate each the power quality index value in the electric system.

In the said method, way is in detail:

By the voltage (or electric current) that the secondary system loop is come, after the suitable voltage of A/D was delivered in changes such as (or current transformer CT) through voltage transformer pt, A/D carried out analog to digital conversion with certain sample frequency by CPU control, obtains discrete sampled data.

As:

Adopt fixedly crystal oscillator 10.245MHz and NAND gate circuit composition oscillatory circuit, through 74F393, adopt 8 fractional frequency signals to obtain the signal of 1.28MHz, by becoming the square-wave signal of 12.8KHz after the secondary 74F390 chip 2-4 decoding, form the switching signal that pulse width is the AD sampling of 10uS by monostable circuit.Like this AD7874 can every 0.000078125s analog to digital conversion once.

Sampled signal is owing to be the AC sinusoidal voltage waveform of high voltage 100V, for high-voltage signal exerts an influence to the low pressure digital circuit, can adopt the isolating transmitter of high-precision 100v/5v, thereby the 100v signal can be formed the low-voltage signal that amplitude has only 5v, again by the ∏ mode filter, filtering is harmonic signal and noise signal more than 50 times, can well remove the external disturbance that the technological process owing to hardware circuit or printed board quality causes like this.Signal after the filtering was through 1: 1 amplifier, can play the impedance matching effect like this, make sampling A consistent, make the signal of delivering to the AD7874 analog to digital conversion circuit through the signal of amplifier, can can't not sample because of decay with the signal circuit impedance of front.

The discrete sampled data that above-mentioned sampling obtains being delivered among the CPU, by numerical analysis method, as least square method, linear interpolation method etc., utilized the data that collect in CPU, is example with the least square method, according to the following formula of least square method

f(x)＝a ₀+a ₁x+a ₂x ²+Λ+a _mx ^m

Simulate the most approaching real waveform, calculate the correlation parameter of this waveform, parameter is stored among the RAM.Then,

Data are compared with zero, find out the point (zero crossing of collection) of zero passage,

Again by various technology, the linear interpolation method that detects as least square method, Wavelet Transform, based on zero crossing etc. are example with the least square method, according to following formula:

y＝ax+b

$\frac{\∂\mathrm{\ϵ}}{\∂a}=2\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(y_i-{\mathrm{ax}}_i-b)\left({-x}_i\right)=0$

$\frac{\∂\mathrm{\ϵ}}{\∂b}=2\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(y_i-{\mathrm{ax}}_i-b)\left(-1\right)=0$

$a=\frac{n\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i{y}_i-\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i\right)\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{y}_i\right)}{n\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x_i}^2-{\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i\right)}^2},$ $b=\frac{\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{y}_i\right)\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x_i}^2\right)-\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i\right)\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x_{i}y}_i\right)}{n\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x_i}^2-{\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{x}_i\right)}^2},$

Find out spaced apart by a distance less than the zero crossing in 1/4 cycle, utilize these zero crossings, calculate the data of approaching true zero crossing spaced apart by a distance less than 1/4 cycle, as real zero crossing,

And with this data storage in RAM.

According to true zero crossing, CPU compares, and judges the waveform that is in in one-period,

Then, carry out again on the basis of complete cycle sampling second time obtaining, promptly CPU on the waveform that simulates again according to (f=2 ⁿ* 50Hz, n=6,7,8,9 ...) speed adopt again a little,

And the point that will gather for the second time is stored among the RAM, stays and does the data source of analyzing power quality index.

The present invention adopts a fixing sample frequency (f=2 ⁿ* 50Hz, n=6,7,8,9 ...) sampling, be reduced to waveform by waveform fitting technique, utilize least square method to find out the zero crossing of this waveform again, as a cycle, so can obtain a complete cycle with the waveform in the middle of hithermost two zero crossings that possess the identical change direction, obtain its cycle, and by that analogy, the error that produces with regard to avoiding mains frequency to change like this, real-time tracking system frequency.Simultaneously, on the waveform of match, be starting point with a certain zero crossing, according to certain sample frequency, carry out double sampling, gather n ₂Individual, then according to this n ₂Power quality indexs such as the harmonic wave in the individual point analysis system, three-phase imbalance.Owing to adopted the mathematical measure of waveform fitting, the most approaching real voltage and current waveform of waveform after the match, therefore, carry out the also the most approaching real point of point that double sampling collected on this basis, sampling precision is improved, and this provides more accurate and reliable data for power quality index analyses such as voltage and current effective value afterwards, harmonic wave, power.

The inventive method has obvious superiority than PHASE-LOCKED LOOP PLL TECHNIQUE, and it be the reasons are as follows:

PHASE-LOCKED LOOP PLL TECHNIQUE is to be undertaken from motion tracking and phase locking by preceding several cycles that system is just pass by, the all wave widths that obtain in view of the above are to represent cycle period in the past the cycle, PHASE-LOCKED LOOP PLL TECHNIQUE but replaces periodic width on the horizon with this cycle, obtain sampling interval divided by the sampled point number with this cycle, sample.And in the reality cycle of former and later two cycles be different length, this just must bring error, this is the fatal defective of PHASE-LOCKED LOOP PLL TECHNIQUE, itself has no idea to overcome.The method that the present invention narrated has fundamentally solved this problem, does not have error in theory.

The inventive method has obtained obvious effects in practice, as stated above, is example with power frequency 50Hz, gathers secondary side voltage, electric current according to the sample frequency of n/0.02s, then by waveform fitting technique with the n that collects ₁Individual point is reduced to waveform, finds out the zero crossing of this waveform by least square method, thereby determines a complete cycle, again according to f=2 ⁶* the sample frequency of 50Hz is carried out double sampling to the match waveform of above-mentioned acquisition, at last analyze every power quality index in the electric system according to the AC signal values such as voltage and current that double sampling obtained, the accuracy of its measurement obviously improves than the measurement accuracy of prior art.

Further scheme is:

1, be (f=2 according to frequency ⁿ* sample frequency 50Hz, n 〉=7) is gathered secondary side voltage, electric current, gathers n ₁Individual point (n ₁=2 ⁿ, n 〉=7)

2, carry out waveform fitting with least square method, with the n that collects ₁Individual point is reduced to waveform,

3, find out the zero crossing of this waveform with least square method, and determine a complete cycle,

4, according to a fixing sample frequency (f=2 ⁿ* 50Hz, n 〉=7), the match waveform of above-mentioned acquisition is carried out double sampling, gather n ₂It is individual,

5, according to n ₂The AC signal values such as voltage and current of individual point are analyzed each the power quality index value in the electric system.

Further scheme has increased the collection point owing to adopted higher sample frequency, makes that the waveform of match is more accurate, and the accuracy of measured value is also higher.

(4) description of drawings:

Below with reference to drawings and Examples the present invention is described in further details:

Accompanying drawing 1 is the functional-block diagram of related hardware in the first embodiment of the invention.

Accompanying drawing 2 is the process flow diagram of related software in the foregoing description.

(5) embodiment:

Referring to accompanying drawing 1, hardware device that first embodiment of the invention is relied on comprises: storage inside have the program that realizes the inventive method common computer, be plugged in capture card on this computing machine expansion card slot, 16 voltage-types and current mode transmitter, above-mentioned 16 transmitters link to each other with secondary side PT, the CT of electrical network, and its signal output part links to each other with the signal input part of capture card.Can gather ten six road voltages, current signal simultaneously, this capture card is made up of following each module section, now is described below respectively:

The oscillatory circuit that the sampling clock source circuit partly adopts fixedly crystal oscillator 10.245MHz and NAND gate circuit to form, through 74F393, adopt 8 fractional frequency signals to obtain the signal of 1.28MHz, again by becoming the square-wave signal of 12.8KHz after the secondary 74F390 chip 2-4 decoding, form the switching signal that pulse width is the AD sampling of 10uS by monostable circuit, like this AD7874 can every 0.000078125s analog to digital conversion once.

AD oneself has internal clock circuit in addition, but also can add clock, and the benefit that adds clock is to coordinate outside sample frequency when high frequency sampling.Among this embodiment, taked to carry the 2.56MHz frequency of external timing signal, directly given the clock pin of each road AD7874 by 10.245MHz crystal oscillator four frequency divisions.

Sampled signal is owing to be the AC sinusoidal voltage waveform of high voltage 100V, for high-voltage signal exerts an influence to the low pressure digital circuit, we have selected the isolating transmitter of high-precision 100v/5v for use, thereby the 100v signal can be formed the low-voltage signal that amplitude has only 5v, again by the ∏ mode filter, filtering is harmonic signal and noise signal more than 50 times, can well remove the external disturbance that the technological process owing to hardware circuit or printed board quality causes like this.Signal after the filtering can play the impedance matching effect like this through 1: 1 amplifier, makes sampling A consistent with the signal circuit impedance of front, when making the signal that passes through amplifier deliver to the AD7874 analog to digital conversion circuit, can can't not sample because of decay.

In the data memory module, every AD can adopt four road signals, 16 the tunnel need 4 AD altogether, in own corresponding RAM, be divided into four road RAM through the data storing after the AD7874 sampling altogether, the write signal of each partial RAM is provided by AD sampling end signal, after AD adopts end, can send sampling automatically and finish the pulse sign, thereby can offer RAM, as the write pulse sign of RAM.

Because the plug and play module of this capture card system, computer, can be inserted in the middle of arbitrary the computing machine with PCI slot, thereby can use slot central positive and negative 12V and 5V direct supply, on this capture card, add power supply chip 7909 in addition again, 7809, can conversion return ± direct supply of 9V, the amplifier in the power supply road uses, and the 5V direct voltage source is for uses such as RAM, AD7874, oscillation sources.

Because hardware circuit self does not have management function, as long as under the power supply stable case, can use safely, if but supply voltage shakiness, hardware runs non-phenomenon and happens occasionally, so added voltage monitoring circuit MAX706 among this embodiment, it works between the 4.75-5.25V, during normal operation in normal, its control pin makes all chip operate as normal corresponding to all pin that enables that need monitor chip.If voltage exceeds this scope, its monitoring voltage pin will be exported the level "0" signal, and it monitors that pin will stop the pin that enables of all chips, quit work it.

Referring to accompanying drawing 2, after AD sampling module sampling by above-mentioned capture card finishes and its data (256 points) is offered RAM, image data is read in a certain storage address of computer system from RAM, data are sent among the CPU, data are compared with zero, find out the point of zero passage, find out again spaced apart by a distance less than the zero crossing in 1/4 cycle, store among the RAM, then, in CPU according to the formula of least square method, utilize these zero crossings spaced apart by a distance less than 1/4 cycle, calculate the data of approaching true zero crossing, as real zero crossing, with this data storage in RAM.In CPU,, utilize the data that collect, go out the most approaching real waveform, calculate the correlation parameter of this waveform, parameter is stored among the RAM according to formula fitting by least square method.In addition, according to true zero crossing, CPU compares, and judges the waveform that is in in one-period, then, on the basis that obtains complete cycle, carry out the sampling second time again, be CPU on the waveform that simulates again the speed according to 6.4kHz adopt again a little, obtain the data of 128 points, make that like this point of secondary acquisition can be farthest near real point, also guaranteed simultaneously the complete of waveform, thus for after power quality analysis more accurate and reliable data are provided.The point of gathering is stored among the RAM for the second time, stays and does the data source of analyzing power quality index.

The above-mentioned program in order to realization the inventive method that is stored in the computing machine for common intermediate programmer, relies on above-mentioned guidance, utilizes current computerese such as VC, Delphi to work out out.

Embodiment 2:

Carry out following step successively:

1, be 6.4KHz (f=2 according to frequency ⁿ* 50Hz, sample frequency n=7) is gathered secondary side voltage, electric current, gathers 128 points

2, carry out waveform fitting with least square method, 128 points that collect be reduced to waveform,

3, find out the zero crossing of this waveform with least square method, and determine a complete cycle,

4, according to the sample frequency of f=128*50Hz, the match waveform of above-mentioned acquisition is carried out double sampling, gather 128 points,

5, according to each the power quality index value in AC signal values such as the voltage and current analysis electric system of 128 points.

The principle of the hardware of embodiment 2 and the flow process of software are similar to embodiment 1, wherein, transmitter adopts 16 voltage-types and current mode transmitter, and those skilled in the art needn't pay creative work according to above-mentioned guidance and disclosed prior art and can realize, have not just given unnecessary details at this.

Embodiment 3:

Carry out following step successively:

1, be f=2 according to frequency ⁿ* 50Hz, the sample frequency of n=8 is gathered secondary side voltage, electric current, gathers 256 points

2,256 somes match that will collect with linear interpolation method is reduced to waveform

3, the zero crossing of finding out this waveform with Wavelet Transform is determined a complete cycle,

4, according to f=2 ⁿ* 50Hz, the sample frequency of n=6 is carried out double sampling to the match waveform of above-mentioned acquisition, gathers 64 points,

5, according to each the power quality index value in AC signal values such as the voltage and current analysis electric system of 64 points.

The principle of the hardware of embodiment 3 and the flow process of software are similar to embodiment 1.

Embodiment 4:

Carry out following step successively:

According to frequency is f=2 ⁿ* 50Hz, the sample frequency of n=9 is gathered secondary side voltage, electric current, gathers n1 point

With least square method n1 the point that collects fitted to waveform,

Find out the zero crossing of this waveform with least square method and determine a complete cycle,

According to f=2n*50Hz, the sample frequency of n=8 is carried out double sampling to the match waveform of above-mentioned acquisition, gathers n2 point,

According to each the power quality index value in AC signal values such as the voltage and current analysis electric system of n2 point.

The principle of the hardware of embodiment 4 and the flow process of software are similar to embodiment 1.

The above embodiment of the present invention has all obtained adopting in practice, and has obtained the good technical effect.The accuracy of measuring each power quality index value with the inventive method obviously improves than the measurement accuracy of prior art.

Certainly, under inventive concept of the present invention, the present invention has multiple form of implementation, and those skilled in the art read and need not pay creative work behind this instructions and can reveal again, have not just given unnecessary details at this.

Claims (2)

1, the cycle method of sampling in a kind of electrical network quality of power supply may further comprise the steps:

(1) gathers secondary side voltage, electric current according to fixing sample frequency, gather n ₁Individual, wherein, n ₁=2 ⁿ, n 〉=6,

(2) by waveform fitting technique with the n that collects ₁Individual point is reduced to waveform,

(3) find out the zero crossing of this waveform, and determine a complete cycle in view of the above,

(4) according to a fixing sample frequency f=2 ⁿ* 50Hz, wherein, n=6,7,8,9 ..., the match waveform of above-mentioned acquisition is carried out double sampling, gather n ₂It is individual,

(5) according to n ₂The voltage and current signal value of individual point calculates each the power quality index value in the electric system.

2, the cycle method of sampling in the electrical network quality of power supply according to claim 1, it is characterized in that: it may further comprise the steps:

(1) be f=2 according to frequency ⁿ* 50Hz, wherein, the sample frequency of n 〉=7 is gathered secondary side voltage, electric current, gathers n ₁Individual, wherein, n ₁=2 ⁿ, n 〉=7,

(2) carry out waveform fitting with least square method, with the n that collects ₁Individual point is reduced to waveform,

(3) find out the zero crossing of this waveform with least square method, and determine a complete cycle,

(4) according to a fixing sample frequency f=2 ⁿ* 50Hz, wherein, double sampling is carried out to the match waveform of above-mentioned acquisition in n 〉=7, gathers n ₂It is individual,

(5) according to n ₂The voltage and current signal value of individual point is analyzed each the power quality index value in the electric system.

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