CN102749488A - Power grid harmonic wave real-time on-line monitor and method for detecting harmonic wave using same - Google Patents

Abstract

The invention discloses a power grid harmonic wave real-time on-line monitor and a method for detecting harmonic wave using the power grid harmonic wave real-time on-line monitor, belonging to the technical field of a high-precision apparatus. The method comprises the following steps of: measuring an alternating current signal, sampling the alternating current signal, carrying out windowing DFT (discrete fourier transformation) treatment to obtain harmonic wave parameter information, and correcting the harmonic wave parameter information by an offset correction formula deducted from a matrix inversion theorem. By adopting a time domain deviation correction algorithm, the invention selects the deviation correction times according to the precision requirement, and under the condition that the grid frequency is small in change, and the frequency test precision is higher, the harmonic wave algorithm can provide the precision which is very approximate to that of the FFT (fast fourier transform algorithm) algorithm under the condition of ideal synchronous sampling.

Description

Mains by harmonics real time on-line monitoring appearance and utilize this monitor to detect the method for harmonic wave

Technical field

The invention discloses mains by harmonics real time on-line monitoring appearance and utilize this monitor to detect the method for harmonic wave, belong to the technical field of high precision exact instrument.

Background technology

The harmonic monitoring appearance is of long duration in the application of electric system, but the monitor of ability real time on-line monitoring harmonic wave is more few.Along with the raising that the quality of power supply is required; The intellectuality of electrical network, greenization are the contents that work about electric power person need study and solve; Power system harmonic measurement is one of important content of electric power quality monitoring, and the monitoring harmonic information of real-time online can find effectively that power system state also is the foundation of effectively carrying out harmonic wave control.IEC61000-4-7 standard and most harmonic measuring instrument still prolong with adding Hanning window FFT method the measurement of harmonic wave.It is more more accurately under the less situation of synchronous error that the FFT method is measured the whole subharmonic of electrical network; If but it is just not too rationally not too accurate to exist big synchronous error to measure mains by harmonics with traditional windowing FFT method; But with regard to practical applications; It is a kind of practical method that the FFT method is measured harmonic wave, if so we can on the FFT method, improve and correction for drift a kind of more satisfactory method of still can yet be regarded as.FFT post-processing approach scholar studies already: interpolation, frequency spectrum are proofreaied and correct, and frequency spectrum is proofreaied and correct and comprised peak value searching method, three-point convolution method, the correction method of frequency spectrum center of gravity etc. again.Traditional frequency spectrum correcting algorithm is frequency domain method mostly, and the present invention then derives a kind of according to the algebraically mechanism method of DFT

Summary of the invention

Technical matters to be solved by this invention is the deficiency to the above-mentioned background technology, mains by harmonics real time on-line monitoring appearance is provided and has utilized this monitor to detect the method for harmonic wave.

The present invention adopts following technical scheme for realizing the foregoing invention purpose:

Mains by harmonics real time on-line monitoring appearance; Comprise real-time measurement module harmonic computing module, said real-time measurement module comprises threephase potential transformer, threephase current transformer, signal condition module, analog to digital converter, dsp chip, frequency measurement unit, synchronous control unit;

The input end reception survey time road electric wire of said voltage transformer (VT), current transformer; The output terminal of voltage transformer (VT), current transformer is connected with the input end of signal condition module; The output terminal of said signal condition module is connected with analog to digital converter; The input end of said frequency measurement module is connected with the output terminal of voltage transformer (VT); Two output terminals of said frequency measurement module are connected with analog to digital converter, DSP chip respectively, and the two ends of said synchronous control unit are connected with dsp chip, analog to digital converter respectively; Wherein, said frequency measurement unit comprises zero-crossing detector and phase-locked loop circuit.

Utilize mains by harmonics real time on-line monitoring appearance to detect the method for harmonic wave, comprise the steps:

Step 1, phase-locked loop circuit obtain the ac frequency that three-phase voltage zero passage number of times that the sampled clock signal, dsp chip of analog to digital converter record according to zero-crossing detector calculates current time according to the three-phase voltage of current time;

Step 2, the ac signal that signal conditioning circuit records mutual inductor are done peak value and are handled, and analog to digital converter obtains the current time processing sampling sequence signals according to sampled clock signal to going the ac signal sampling behind the peak value and doing analog to digital conversion;

Step 3, dsp chip obtains the sample sequence of current time cycle through synchronous control unit, and a windowing DFT who puts in order subharmonic calculates harmonic parameters information;

Step 4 is handled the harmonic parameters information obtain according to step 3, utilizes following expression formula that the result of harmonic wave is carried out offset correction:

$\mathrm{\θ}=[I+(-A_0^{-1}\mathrm{\ΔA})+{(-A_0^{-1}\mathrm{\ΔA})}^2+{(-A_0^{-1}\mathrm{\ΔA})}^3+......+{(-A_0^{-1}\mathrm{\ΔA})}^n]{\mathrm{\θ}}_0$

Wherein, I is a unit matrix, and θ is the harmonic parameters information after proofreading and correct, θ ₀Be that line voltage or current sampling data are carried out windowing DFT result, A one time ₀Be parameter matrix, Δ A is the running parameter matrix,

Be that a DFT result is carried out an offset correction,

Be that current windowing DFT result is carried out n offset correction.

The present invention adopts technique scheme; Has following beneficial effect: adopt time domain offset correction algorithm; According to accuracy requirement Select Error number of corrections; Under mains frequency small variations, frequency-measurement accuracy condition with higher, the harmonic wave algorithm can provide very the precision near fft algorithm under ' ideal synchronisation sampling ' situation.

Description of drawings

Fig. 1 is the block diagram of mains by harmonics real time on-line monitoring appearance.

Fig. 2 is the block diagram of real-time measurement module.

Fig. 3 is the experiment effect figure in the specific embodiment.

Embodiment

Be elaborated below in conjunction with the technical scheme of accompanying drawing to invention:

Mains by harmonics real time on-line monitoring appearance as shown in Figure 1 comprises real-time measurement module harmonic computing module (ARM unit).Measurement module is as shown in Figure 2 in real time, comprises threephase potential transformer, threephase current transformer, signal condition module, analog to digital converter, dsp chip, frequency measurement unit, synchronous control unit.The input end reception survey time road electric wire of voltage transformer (VT), current transformer; The output terminal of voltage transformer (VT), current transformer is connected with the input end of signal condition module; The output terminal of signal condition module is connected with analog to digital converter; The input end of frequency measurement module is connected with the output terminal of voltage transformer (VT), and two output terminals of frequency measurement module are connected with analog to digital converter, DSP chip respectively, and the two ends of synchronous control unit are connected with dsp chip, analog to digital converter respectively.The input end of frequency measurement unit also can be connected with the output terminal of current transformer.Frequency measurement unit comprises zero-crossing detector and phase-locked loop circuit.

The harmonic monitoring appearance adopts the DSP+ARM framework, makes full use of the powerful digital signal processing capability of DSP and control and management and the communication function of ARM.This device is made up of 1 " Harmonics Calculation module " and 1 to 6 " real-time measurement module ", can directly generate the power quality data of PQDIF form and uploads onto the server through the FTP mode.Wherein: " measurement module in real time " is core with 32 High Performance DSP TMS320F2812, and the main completion power quality index of being responsible for calculates in real time, and each " measurement module in real time " links to each other with " administration module " through high speed SPI interface; " Harmonics Calculation module " adopts the ARM9 processor and implants embedded OS Windows CE6.0, functions such as calling of the real-time computational data of main completion each " measurement module " and ASSOCIATE STATISTICS analysis, PQDIF format conversion, man-machine interaction, network service.In order to satisfy the requirement can monitor a plurality of loops simultaneously, that " measurement module in real time " and " Harmonics Calculation module " adopt is independent, the back of the body is inserted the formula design, can on the device mainboard, plug easily, installs multipotency and inserts 6 measurement modules.

The number of measurement module depends on the number of loop (or monitoring point) in real time, 1 corresponding 1 loop (or monitoring point) of measurement module.Three-phase voltage, electric current and the harmonic electric energy mass parameter thereof in each " measurement module in real time " 1 loop of independent measurement.Generally speaking, the input quantity of each " in real time measurement module " all is three-phase voltage and corresponding with it three-phase current, guarantees that like this each phase voltage in each loop and electric current all sample simultaneously---this is that accurately to measure power necessary.The strict IEC61000-4-30:2003 that presses of " measurement module in real time " algorithm carries out, and measuring accuracy is the A level.Mutual inductor is 3 pairs of high-precision micro voltage transformer (VT) (PT) and micro-transformer of current (CT).Analog to digital converter has been selected 16 ∑s-Δ type ADC---the AD73360L of U.S. ADI company.DSP adopts 32 bit DSPs---the TMS320F2812 of American TI Company, and its frequency of operation is 150MHz.

Three-phase voltage and electric current u _a, i _a, u _b, i _b, u _c, i _cDeliver to 6 tunnel 16 ADC through voltage transformer (VT) (PT) summation current transformer (CT) respectively, ADC is converted into 6 way word signals (sample sequence) and delivers to 32 bit DSPs and carry out data processing; Three-phase voltage signal also will be delivered to PLL (phase-locked loop circuit), follows the tracks of mains frequency by PLL, and the output of PLL circuit makes sampling must approach synchronized sampling as far as possible as the sampling clock of ADC.The zero passage detection signal is delivered to DSP and is used for accurate frequency measurement.

Utilize mains by harmonics real-time online detector to detect the method for harmonic wave, comprise the steps:

Step 1; The electrical network three-phase voltage is delivered to 16 A/D converters through voltage transformer (VT) and signal conditioning circuit respectively; The electrical network three-phase current is delivered to the frequency measurement link through current transformer respectively, and the electrical network three-phase voltage is delivered to A/D converter through voltage transformer (VT) and signal conditioning circuit respectively;

Step 2, frequency measurement link are with zero passage detection method detection of grid real-time frequency, thus the current sampling frequency of definite voltage current waveform, and the real-time frequency according to the electrical network of measuring refreshed SF one time in per 3 seconds;

Step 3, dsp chip are according to real-time 10 cycle sampled datas, and a windowing DFT who puts in order subharmonic calculates;

Step 4 is handled the harmonic information that obtains according to step 3, in conjunction with the requirement to mains by harmonics real-time and precision, utilizes the updating formula that is derived by the inverse matrix theorem that harmonic information is carried out offset correction and proofreaies and correct:

$\mathrm{\θ}=[I+(-A_0^{-1}\mathrm{\ΔA})+{(-A_0^{-1}\mathrm{\ΔA})}^2+{(-A_0^{-1}\mathrm{\ΔA})}^3+......+{(-A_0^{-1}\mathrm{\ΔA})}^n]{\mathrm{\θ}}_0---\left(1\right)$

Wherein, I is a unit matrix, and θ is the harmonic parameters information after proofreading and correct, θ ₀Be that line voltage or current sampling data are carried out windowing DFT result one time,

Be that a DFT result is carried out an offset correction, Be that current windowing DFT result is carried out n offset correction, number of corrections is big more, and the measuring accuracy of harmonic wave is sampled near ideal synchronisation more.

Updating formula (1) inverse matrix theorem capable of using is derived:

1) 10 cycles of sampling obtain N point sampling sequences y;

2) obtain the mains frequency f of notebook data window;

3) obtain A and Δ A according to the mains frequency of notebook data window;

4) carry out windowing DFT: θ one time ₀=Fy (2)

Wherein, F is a windowing DFT matrix of coefficients,

5) carry out the subsynchronous correction of n (n generally gets 3,4 and gets final product).

Said detection side's ratio juris proves as follows:

Suppose that actual electric network voltage (electric current) signal description is:

$y\left(t\right)=a_0+\underset{m=1}{\overset{M}{\mathrm{\Σ}}}[a_m\mathrm{Cos}\left(\mathrm{M\ω\; t}\right)+b_m\mathrm{Sin}\left(\mathrm{M\ω\; t}\right)]---\left(3\right),$ Be A θ=y (4).

Make θ ^T=[a ₀a ₁b ₁A _Mb _M],

y ^T=[y(t ₁)y(t ₂)…y(t _N)] (5)

$A=\left[\begin{array}{cccccc}1& \cos \left({\mathrm{\ω}}_k{t}_1\right)& \sin \left({\mathrm{\ω}}_k{t}_1\right)& \·\·\·& \cos \left(M{\mathrm{\ω}}_k{t}_1\right)& \sin \left(M{\mathrm{\ω}}_k{t}_1\right)\\ 1& \cos \left({\mathrm{\ω}}_k{t}_2\right)& \sin \left({\mathrm{\ω}}_k{t}_2\right)& \·\·\·& \cos \left(M{\mathrm{\ω}}_k{t}_2\right)& \sin \left(M{\mathrm{\ω}}_k{t}_2\right)\\ \·\·\·& \·\·\·& \·\·\·& \·\·\·& \·\·\·& \·\·\·\\ 1& \cos \left({\mathrm{\ω}}_k{t}_N\right)& \sin \left({\mathrm{\ω}}_k{t}_N\right)& \·\·\·& \cos \left(M{\mathrm{\ω}}_k{t}_N\right)& \sin \left(M{\mathrm{\ω}}_k{t}_N\right)\end{array}\right]---\left(6\right)$

Accurately find the solution the method for θ: θ=A ^-1Y (7),

The windowing DFT of y is equivalent to: $\widehat{\mathrm{\θ}}=\mathrm{Fy}={\left[\begin{array}{cccccc}{\hat{a}}_0& {\hat{a}}_1& {\hat{b}}_1& \·\·\·& {\hat{a}}_M& {\hat{b}}_M\end{array}\right]}^T---\left(8\right)$

When N=2M+1, A, F are square matrixes,

During synchronized sampling, make A=A ₀

Can prove

Wherein $A_0=\left[\begin{array}{cccccc}1& \mathrm{Cos}\left(\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(\frac{2\mathrm{\&pi;}}{N}\right)& \&CenterDot;\&CenterDot;\&CenterDot;& \mathrm{Cos}\left(\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="120627122146.png"\; state="\{\{state\}\}">M</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="120627122146.png"\; state="\{\{state\}\}">M</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)\\ 1& \mathrm{Cos}\left(2\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(2\frac{2\mathrm{\&pi;}}{N}\right)& \&CenterDot;\&CenterDot;\&CenterDot;& \mathrm{Cos}\left(2\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="120627122146.png"\; state="\{\{state\}\}">M</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(2\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="120627122146.png"\; state="\{\{state\}\}">M</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)\\ \&CenterDot;\&CenterDot;\&CenterDot;& \&CenterDot;\&CenterDot;\&CenterDot;& \&CenterDot;\&CenterDot;\&CenterDot;& \&CenterDot;\&CenterDot;\&CenterDot;& \&CenterDot;\&CenterDot;\&CenterDot;& \&CenterDot;\&CenterDot;\&CenterDot;\\ 1& \mathrm{Cos}\left(\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="120627122146.png"\; state="\{\{state\}\}">N</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="120627122146.png"\; state="\{\{state\}\}">N</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)& \&CenterDot;\&CenterDot;\&CenterDot;& \mathrm{Cos}\left(\mathrm{NM}\frac{2\mathrm{\&pi;}}{N}\right)& \mathrm{Sin}\left(\mathrm{<figure-callout\; id="2"\; label="NM"\; filenames="120627122146.png"\; state="\{\{state\}\}">NM</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\right)\end{array}\right]---\left(9\right)$

When non-synchronous sampling, A=A ₀+ Δ A, θ=(A ₀+ Δ A) ^-1y

If can obtain (A ₀+ Δ A) ^-1, just can accurately obtain θ, utilize the inverse matrix theorem to find the solution.Prove as follows: the inverse matrix theorem: establish Λ, C and Λ+RCD are nonsingular matrix, then

(Λ+BCD) ^-1=Λ ^-1-Λ ^-1B(C ^-1+DΛ ^-1B) ^-1DΛ ^-1

Make Λ=A ₀, B=Δ A, C=D=I has:

${(A_0+\mathrm{\&Delta;A})}^{-1}=A_0^{-1}-A_0^{-1}\mathrm{\&Delta;A}{(I+A_0^{-1}\mathrm{\&Delta;A})}^{-1}{A}_0^{-1}$

$=A_0^{-1}-A_0^{-1}\mathrm{\&Delta;A}{(A_0+\mathrm{\&Delta;A})}^{-1}$

Once get with following formula ' from generation ':

${(A_0+\mathrm{\&Delta;A})}^{-1}=A_0^{-1}-\left(A_0^{-1}\mathrm{\&Delta;A}\right)A_0^{-1}+{\left(A_0^{-1}\mathrm{\&Delta;A}\right)}^2{(A_0+\mathrm{\&Delta;A})}^{-1}$

${(A_0+\mathrm{\&Delta;A})}^{-1}=A_0^{-1}-A_0^{-1}\mathrm{\&Delta;A}{(A_0+\mathrm{\&Delta;A})}^{-1}$

${(A_0+\mathrm{\&Delta;A})}^{-1}=A_0^{-1}-\left(A_0^{-1}\mathrm{\&Delta;A}\right)A_0^{-1}+{\left(A_0^{-1}\mathrm{\&Delta;A}\right)}^2{(A_0+\mathrm{\&Delta;A})}^{-1}$

' from generation ' is infinite repeatedly:

${(A_0+\mathrm{\&Delta;A})}^{-1}=A_0^{-1}+\underset{i=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{(-A_0^{-1}\mathrm{\&Delta;A})}^i{A}_0^{-1}---\left(10\right)$

Accurate θ expression formula is: $\mathrm{\&theta;}={(A_0+\mathrm{\&Delta;\; A})}^{-1}y=A_0^{-1}y+\underset{i=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{(-A_0^{-1}\mathrm{\&Delta;\; A})}^i{A}_0^{-1}y---\left(11\right)$

Notice: $F=A_0^{-1}$ The substitution following formula gets: $\mathrm{\&theta;}=\mathrm{Fy}+\underset{i=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{(-A_0^{-1}\mathrm{\&Delta;\; A})}^i\mathrm{Fy}---\left(12\right)$

Notice that Fy carries out DFT exactly one time, makes θ ₀=Fy substitution following formula gets:

$\mathrm{\&theta;}={\mathrm{\&theta;}}_0+(-A_0^{-1}\mathrm{\&Delta;A}){\mathrm{\&theta;}}_0+{(-A_0^{-1}\mathrm{\&Delta;A})}^2{\mathrm{\&theta;}}_0+{(-A_0^{-1}\mathrm{\&Delta;A})}^3{\mathrm{\&theta;}}_0+......{(-A_0^{-1}\mathrm{\&Delta;A})}^n{\mathrm{\&theta;}}_0$

Promptly obtain the offset correction formula.

DSP timer frequency of operation is 150MHz; Get fs=60kHz; S=10; The used AC signal

of emulation is got M=7, gets sample-synchronous error 3%, and graph of errors is as shown in Figure 3.The timing error does not improve through precision after the error correction between 2% to 10% greatly, and when number of corrections I=3, the error of each harmonic parameters is all less than 4%; When I=5, the error of each harmonic parameters is all less than 2%, and when I=7, the error of each harmonic parameters is all less than 0.5%, and number of corrections is many more, and result calculated is accurate more, can number of corrections be set according to the requirement of precision.It is thus clear that the precision of this algorithm is very high, real-time also is extraordinary.

In sum; The on-line calculation of this algorithm is suitable with the DFT algorithm, and the surface sees that its calculated amount is big, but under the situation of ubiquity synchronism deviation; The result of calculation of this algorithm is very accurate, does not need to increase type loaded down with trivial details computing such as ' compensation ', ' interpolation ' again; This algorithm only needs N=2M+1 point of sampling in one-period, and N is less; In the stable period of mains frequency, this computing need not to calculate new (A ₀+ Δ A) ^-1, can prolong and use result calculated last time.

Claims (2)

1. mains by harmonics real time on-line monitoring appearance; Comprise real-time measurement module harmonic computing module, it is characterized in that said real-time measurement module comprises threephase potential transformer, threephase current transformer, signal condition module, analog to digital converter, dsp chip, frequency measurement unit, synchronous control unit;

The input end reception survey time road electric wire of said voltage transformer (VT), current transformer; The output terminal of voltage transformer (VT), current transformer is connected with the input end of signal condition module; The output terminal of said signal condition module is connected with analog to digital converter; The input end of said frequency measurement module is connected with the output terminal of voltage transformer (VT); Two output terminals of said frequency measurement module are connected with analog to digital converter, dsp chip respectively, and the two ends of said synchronous control unit are connected with dsp chip, analog to digital converter respectively; Wherein, said frequency measurement unit comprises zero-crossing detector and phase-locked loop circuit.

2. utilize the described mains by harmonics real time on-line monitoring of claim 1 appearance to detect the method for harmonic wave, it is characterized in that comprising the steps:

Step 1, phase-locked loop circuit obtain the ac frequency that three-phase voltage zero passage number of times that the sampled clock signal, dsp chip of analog to digital converter record according to zero-crossing detector calculates current time according to the three-phase voltage of current time;

Step 2, the ac signal that signal conditioning circuit records mutual inductor are done peak value and are handled, and analog to digital converter obtains the current time processing sampling sequence signals according to sampled clock signal to going the ac signal sampling behind the peak value and doing analog to digital conversion;

Step 3, dsp chip obtains the sample sequence of current time cycle through synchronous control unit, and a windowing DFT who puts in order subharmonic calculates harmonic parameters information;

Step 4 is handled the harmonic parameters information obtain according to step 3, utilizes following expression formula that the result of harmonic wave is carried out offset correction:

$\mathrm{\&theta;}=[I+(-A_0^{-1}\mathrm{\&Delta;A})+{(-A_0^{-1}\mathrm{\&Delta;A})}^2+{(-A_0^{-1}\mathrm{\&Delta;A})}^3+......+{(-A_0^{-1}\mathrm{\&Delta;A})}^n]{\mathrm{\&theta;}}_0$

Wherein, I is a unit matrix, and θ is the harmonic parameters information after proofreading and correct, θ ₀Be that line voltage or current sampling data are carried out windowing DFT result, A one time ₀Be parameter matrix, Δ A is the running parameter matrix,

Be that a DFT result is carried out an offset correction,

Be that current windowing DFT result is carried out n offset correction.

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