CN102279300A - All-fiber current transformer open loop signal detection method and apparatus thereof - Google Patents

Abstract

The invention discloses an all-fiber current transformer open loop signal detection method which comprises the following steps: employing an asymmetric square wave with a period of 2t and an amplitude of Vpi/2 as a modulation signal, carrying out phase modulation on an optical signal, wherein the t is a transit time of the all-fiber current transformer; after the optical signal after phase modulation is subjected to interference, converting the optical signal into an electric signal; subjecting the electric signal to a sampling treatment; in a period 2t, calculating difference between sampling sum of electric signal positive half cycle and sampling sum of electric signal negative half cycle, defining a difference result as S1, defining sampling sum of the electric signal as S2, dividing S1 by S2, and defining a divide resultant as an open loop signal detection result of the all-fiber current transformer. An embodiment of the invention also discloses an all-fiber current transformer open loop detection apparatus. Since the asymmetric square wave is employed as a modulation signal, in a demodulation process, factors related to light source power and circuit gain in an interference output result are eliminated through a specific algorithm, thus the open loop signal detection result is only related to Faraday phase shift, and accuracy of a measuring result is raised.

Description

A kind of open loop signal detection method and device of all-fiber current transformator

Technical field

The present invention relates to the photoelectricity technical field, relate in particular to a kind of open loop signal detection method and device of all-fiber current transformator.

Background technology

All-fiber current transformator is based on Faraday (faraday) effect, and with the New type of current sensing device of optical fiber as sensitive element and transport element.The structure of all-fiber current transformator as shown in Figure 1, its principle of work is as follows: light that light source sends becomes linearly polarized light partially through being risen by fibre optic polarizer behind the circulator; The tail optical fiber of above-mentioned polarization of light device and the tail optical fiber of phase-modulator are with 45 ° of weldings, linearly polarized light is with the polarization maintaining optical fibre of 45 ° of injection fibre polarizers, be decomposed into the linearly polarized light of two bundle orthogonal modess, transmit along the X-axis and the Y-axis of polarization maintaining optical fibre respectively, and be subjected to phase modulation (PM) at the phase-modulator place; Behind the linearly polarized light process quarter wave plate through the bundle of two after phase modulation (PM) orthogonal modes, become the left-handed circularly polarized light and the circularly polarized light of dextrorotation respectively, and enter sensor fibre; The action of a magnetic field that exchange current produces makes the transmission speed of two bundle circularly polarized lights change in sensor fibre, produces phase differential; When two bundle circularly polarized lights are transferred to sensor fibre terminal, produce direct reflection; Through after the direct reflection, it (is that left-handed circularly polarized light becomes the dextrorotation pattern that the polarization mode of two bundle circularly polarized lights exchanges, the circularly polarized light of dextrorotation becomes left-handed pattern) return along original optical path, pass sensor fibre once more, under the effect of Faraday effect, the phase differential between the two bundle circularly polarized lights doubles; And this two bundles circularly polarized light is once more by becoming linearly polarized light behind the quarter wave plate, and polarization mode exchanges (linearly polarized light that is original X polarization mode becomes the Y polarization mode, and originally the linearly polarized light of Y polarization mode becomes the X polarization mode); The linearly polarized light of two bundle orthogonal modess interferes at the fibre optic polarizer place; The interference light that carries current information enters photodetector by circulator.Accordingly, the light signal that receives of photodetector is formulated as follows:

I _D=I ₀(1+cos 4F) (formula 1)

Wherein, I ₀For arriving the luminous power of photodetector, F is the Faraday phase shift that exchange current causes.

The open loop of existing all-fiber current transformator detects adopts the sinusoidal phase modulation method to realize that the equation expression of its modulation signal is as follows usually:

Φ _m(t)=Φ ₀Sin ω _mT (formula 2)

Wherein, Φ ₀And ω _mBe respectively modulated amplitude and modulating frequency.The equation expression of the nonreciprocal phase shift that becomes when then, introducing between the two bundle coherent lights is as follows:

ΔΦ (t)=2 Φ ₀Sin (ω _mτ/2) cos[ω _m(t-τ/2)] (formula 3)

Wherein, τ is the transit time of light in the all-fiber current transformator light path.

Above-mentioned formula (3) in the above-mentioned formula of people (1), and is pressed Bessel's function and is launched, following formula is then arranged:

$I_D=I_0\left\{\begin{array}{c}1+[J_0\left({\mathrm{\η}}_{\mathrm{\φ}}\right)+2\mathrm{\Σ}{(-1)}^n{J}_{2n}\left({\mathrm{\η}}_{\mathrm{\φ}}\right)\cos 2n{\mathrm{\ω}}_m(t-\mathrm{\τ}/2)]\cos 4F\\ +2\mathrm{\Σ}{(-1)}^{2n+1}{J}_{2n-1}\left({\mathrm{\η}}_{\mathrm{\φ}}\right)\sin \left[(2n-1){\mathrm{\ω}}_m(t-\mathrm{\τ}/2)\right]\sin 4F\end{array}\right.$ (formula 4)

This formula is the mutual inductor output light signal through sinusoidal phase modulation.Wherein, n gets positive integer, J _nBe η _φFirst kind n rank Bessel's function; η _φ=2 Φ ₀Sin (ω _mτ/2).When not having electric current, output only has the even-order harmonic of modulating frequency; When having electric current, then produce the odd harmonic of modulating frequency.Utilize lock-in amplifier to detect first harmonic, the output result that can get the open loop signal detection is:

I ₁(F)=2KI ₀J ₁(η _φ) sin4F (formula 5)

Wherein, K is the amplification coefficient of circuit.Work as η _φDuring=1.8rad, J ₁(1.8)=0.58 be maximal value, can obtain peak response.

According to above-mentioned formula 5 as can be known, the no-load voltage ratio of all-fiber current transformator gains relevant with the light intensity that arrives photodetector, signal deteching circuit.Light source goes out the fluctuation of luminous power, the drift of signal deteching circuit gain all can cause ratio error, thereby reduce the measurement accuracy of all-fiber current transformator.

Summary of the invention

The open loop signal detection method and the device that the purpose of this invention is to provide a kind of all-fiber current transformator.

The objective of the invention is to be achieved through the following technical solutions:

A kind of open loop signal detection method of all-fiber current transformator comprises:

The employing cycle is 2 τ, and amplitude is V _π/ 2, and dutycycle be not 1: 1 asymmetrical square wave as modulation signal, light signal is carried out phase modulation (PM), described τ is the transit time of described all-fiber current transformator;

After interfering, the light signal after interfering is converted to electric signal through the light signal after the phase modulation (PM);

Described electric signal is carried out sampling processing;

In each τ modulation periods 2, the sampling sum of described electric signal positive half period and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described electric signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of described all-fiber current transformator.

A kind of open loop signal pick-up unit of all-fiber current transformator comprises:

Pre-amplifier unit is connected with A/D converter with photodetector respectively, is used for that electric signal with the output of described photodetector amplifies, after the Filtering Processing, sends to A/D converter;

A/D converter, be connected with digital signal processing unit with described pre-amplifier unit respectively, be used under the control of the sampling clock that described digital signal processing unit produces, after the analog electrical signal of described pre-amplifier unit output is converted to digital signal, send to described digital signal processing unit;

Digital signal processing unit is connected with the square wave generation unit with A/D converter respectively, is used to produce sampling clock and sends to A/D converter; The generation cycle is that 2 τ, amplitude are V _π/ 2 and dutycycle be not 1: 1 asymmetric digital square wave and send to described square wave generation unit; In each τ modulation periods 2, the sampling sum of the digital signal positive half period of described A/D converter output and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described digital signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of all-fiber current transformator and output;

The square wave generation unit, phase-modulator with described digital signal processing unit and described all-fiber current transformator is connected respectively, exports to described phase-modulator after being used for the asymmetric digital square wave that described digital signal processing unit produces is converted to asymmetric simulation square wave.

As seen from the above technical solution provided by the invention, the open loop signal detection method and the device of a kind of all-fiber current transformator that the embodiment of the invention provides, owing to adopt asymmetrical square wave as modulation signal, and in demodulating process, eliminate and interfere among the output result and light source power, the factor that circuit gain is relevant by specific algorithm, make that the testing result of open loop signal is only relevant with the Faraday phase shift, improved the accuracy of measurement result.

Description of drawings

In order to be illustrated more clearly in the technical scheme of the embodiment of the invention, the accompanying drawing of required use is done to introduce simply in will describing embodiment below, apparently, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite of not paying creative work, can also obtain other accompanying drawings according to these accompanying drawings.

Fig. 1 is the structural representation of all-fiber current transformator;

The apparatus structure synoptic diagram that Fig. 2 provides for the embodiment of the invention

The digital signal processing unit structural representation that Fig. 3 provides for the embodiment of the invention;

The oscillogram that Fig. 4 provides for the embodiment of the invention.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on embodiments of the invention, those of ordinary skills belong to protection scope of the present invention not making the every other embodiment that is obtained under the creative work prerequisite.

Below in conjunction with accompanying drawing the embodiment of the invention is described in further detail.

In the prior art, the open loop signal detection scheme of all-fiber current transformator is based on the realization of sinusoidal phase modulation signal, the testing result of open loop signal and the light intensity of photodetector, signal deteching circuit gain are relevant, have reduced the accuracy of the open loop signal detection of mutual inductor.In order to address this problem, the embodiment of the invention discloses a kind of open loop signal detection method of all-fiber current transformator, this method comprises following operation:

Step 1, employing cycle are 2 τ, and amplitude is V _π/ 2, and dutycycle be not 1: 1 asymmetrical square wave as modulation signal, light signal is carried out phase modulation (PM), described τ is the transit time of described all-fiber current transformator;

After step 2, the light signal after passing through phase modulation (PM) interfere, the light signal after interfering is converted to electric signal;

Step 3, described electric signal is carried out sampling processing;

Step 4, in each τ modulation periods 2, the sampling sum of described electric signal positive half period and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described electric signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of described all-fiber current transformator.

The open loop signal detection method that the embodiment of the invention provides, adopt asymmetrical square wave as modulation signal, and in demodulating process, eliminate and interfere among the output result and light source power, the factor that circuit gain is relevant by specific algorithm, make that the testing result of open loop signal is only relevant with the Faraday phase shift, improved the accuracy of measurement result.

In the said method that the embodiment of the invention provides, can determine that as the dutycycle of the asymmetrical square wave of modulation signal for example and without limitation, its dutycycle can be 1: 3 according to sampling rate.

If the cycle as the asymmetrical square wave of modulation signal is 2 τ, amplitude is V _π/ 2, dutycycle is 1: 3, then in circuit, introduce this asymmetrical square wave after, the equation expression of the light signal after above-mentioned the interfering is:

$I_d(F,\mathrm{\π}/2)=\frac{I_0}{2}(1-\sin 4F);$ (formula 6)

$I_d(F,0)=\frac{I_0}{2}(1+\cos 4F);$ (formula 7)

$I_d(F,-\mathrm{\π}/2)=\frac{I_0}{2}(1+\sin 4F).$ (formula 8)

Wherein, when formula 6 is pi/2 for this asymmetrical square wave is incorporated into the nonreciprocal phase shift amplitude between two bundle coherent lights, the expression formula of light signal; Formula 7 is 0 o'clock for this asymmetrical square wave is incorporated into the nonreciprocal phase shift amplitude between two bundle coherent lights, the expression formula of light signal; When formula 8 is incorporated into the nonreciprocal phase shift amplitude for-pi/2 for this asymmetrical square wave between two bundle coherent lights, the expression formula of light signal; I ₀Luminous power for the photodetector place, its value size is by light source power and whole optical path loss decision, F is the Faraday phase shift that exchange current causes, after introducing asymmetrical square wave, this phase shift is that asymmetrical square wave is incorporated into nonreciprocal phase shift between two bundle coherent lights.Accordingly, before above-said current signal is carried out sampling processing, also to this electric signal amplify, Filtering Processing.Described processing and amplifying is meant amplifies according to amplification coefficient K described electric signal; Described Filtering Processing is meant the DC component filtering in the electric signal.Equation expression through the electric signal after amplification, the Filtering Processing is:

$V_d({\mathrm{\Φ}}_F,\mathrm{\π}/2)=-\frac{K{I}_0}{2}\sin 4F;$ (formula 9)

$V_d({\mathrm{\Φ}}_F,0)=\frac{{\mathrm{KI}}_0}{2}\cos 4F;$ (formula 10)

$V_d({\mathrm{\Φ}}_F,-\mathrm{\π}/2)=\frac{{\mathrm{KI}}_0}{2}\sin 4F.$ (formula 11)

Wherein, K is amplification coefficient, i.e. circuit gain.Accordingly, after the comb filter that to above-said current signal by amplitude is 1 is carried out sampling processing, respectively sampled signal is carried out correlation demodulation and accumulation process.Above-mentioned S1 is the correlation demodulation result, and its equation expression is: S ₁=MKI ₀Sin 4F; Above-mentioned S2 is the accumulation process result, and its equation expression is: S ₂=2MKI ₀Cos4F, wherein M is that 1/4 periodic sampling is counted.

The embodiment of the invention also provides a kind of open loop signal pick-up unit of all-fiber current transformator, can realize said method by this device, its structure as shown in Figure 2, the specific implementation structure is as follows:

Pre-amplifier unit 201 is connected with A/D converter 202 with photodetector 200 respectively, is used for that electric signal with photodetector 200 output amplifies, after the Filtering Processing, sends to A/D converter 202;

Wherein, pre-amplifier unit 201 comprises every straight filtering circuit and two-stage amplifying circuit.Because all-fiber current transformator output signal and faint, and there is the direct current biasing of a hundreds of millivolt in the output signal of photodetector, therefore adopts the method for R-C coupling to make the DC component in the prime output signal can not be coupled to next stage; Adopt the series connection of two-stage amplifying circuit, it is excessive to gain in the time of can avoiding only with the one-level amplifying circuit, limited by the operational amplifier gain bandwidth product, causes that bandwidth descends.For example and without limitation, amplifying circuit can be selected amplifier OPA627 chip for use.

A/D converter 202, be connected with digital signal processing unit 203 with pre-amplifier unit 201 respectively, be used under the control of the sampling clock that digital signal processing unit 203 produces, after the analog electrical signal of pre-amplifier unit 201 output is converted to digital signal, send to digital signal processing unit 203;

Wherein, mould/number (A/D) converting unit 202 is interfaces of mimic channel and digital circuit, and the continuous analog electric signal with pre-amplifier unit 201 outputs is converted to discrete digital signal, offers digital signal processing unit 203.For example and without limitation, can adopt 10 A/D converter TLV1571.

Digital signal processing unit 203 is connected with square wave generation unit 204 with A/D converter 202 respectively, is used to produce sampling clock and sends to A/D converter 202; The generation cycle is that 2 τ, amplitude are V _Pi/2, and dutycycle be not 1: 1 asymmetric digital square wave and send to square wave generation unit 204; In each τ modulation periods 2, the sampling sum of the digital signal positive half period of A/D converter 202 outputs and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described digital signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of all-fiber current transformator and output;

For example and without limitation, digital signal processing unit 203 can be realized by FPGA and DSP.Wherein, FPGA can choose the TMS320F206 chip, and DSP can choose the EPF10K10TC144 chip.

Square wave generation unit 204, phase-modulator 205 with digital signal processing unit 203 and described all-fiber current transformator is connected respectively, exports to phase-modulator 205 after being used for the asymmetric digital square wave that digital signal processing unit 203 produces is converted to asymmetric simulation square wave.

Wherein, square wave generation unit 204 is made of modulation methods wave generation circuit and frequency dividing circuit.For example and without limitation, the constant voltage circuit of modulation methods wave generation circuit is selected the Max873 chip for use, and frequency dividing circuit is selected 4/8 simulation multiplexer ADG509FBRN chip for use.

The apparatus structure that the invention described above embodiment provides is simple, and use this device and can realize above-mentioned open loop detecting method, thus the accuracy of raising measurement result.

In the device that the invention described above embodiment provides, digital signal processing unit 203 is cores of whole device, its structure comprises as shown in Figure 3: time schedule controller 2031, square-wave generator 2032, correlation demodulation device 2033, peak detctor 2034, divider 2035 etc.Wherein, time schedule controller 2031 is used for the work schedule of each functional module of control detection device; Square-wave generator 2032 is used to produce asymmetric digital square wave, and offers square wave generation unit 204; The digital signal that 2033 couples of A/D of correlation demodulation device are converted to is carried out the digital correlation demodulation, the spike that peak detctor 2034 extracts in the result of interference, divider 2035 provides the numeral output of mutual inductor by predetermined algorithm elimination and light source power, the factor that circuit gain is relevant.

The present invention is based on the open loop signal detection method of asymmetrical square wave below with a concrete Application Example explanation.

Should be with among the embodiment, the employing cycle be that the asymmetrical square wave of 2 τ carries out phase modulation (PM) and handles on the phase-modulator of all-fiber current transformator.This asymmetrical square wave is produced by above-mentioned open loop pick-up unit, and its dutycycle specifically can be adjusted according to the sampling rate of A/D converter, for example and without limitation, should use among the embodiment, and the dutycycle of asymmetrical square wave is 1: 3, and its amplitude is V _Pi/2, the phase modulation of corresponding pi/2, then the nonreciprocal phase shift introduced between the coherent lights at two bundles of this asymmetrical square wave is

And this nonreciprocal phase shift pi/2,0 ,-pi/2,0 between periodically the upset, each state duration is τ/2.

After introducing the asymmetrical square wave modulation, all-fiber current transformator interferes the light signal of output to be:

$I_d(F,\mathrm{\π}/2)=\frac{I_0}{2}(1-\sin 4F)$

$I_d(F,0)=\frac{I_0}{2}(1+\cos 4F)$

$I_d(F,-\mathrm{\π}/2)=\frac{I_0}{2}(1+\sin 4F)$

The interference output of above-mentioned all-fiber current transformator becomes electric signal through photodetector 200, and by after pre-amplifier unit 201 amplifications, the filtering, the electric signal of output is again:

$V_d({\mathrm{\Φ}}_F,\mathrm{\π}/2)=-\frac{K{I}_0}{2}\sin 4F$

$V_d({\mathrm{\Φ}}_F,0)=\frac{{\mathrm{KI}}_0}{2}\cos 4F$

$V_d({\mathrm{\Φ}}_F,-\mathrm{\π}/2)=\frac{{\mathrm{KI}}_0}{2}\sin 4F$

Wherein, K is the gain of testing circuit.

Becoming digital quantity after the A/D conversion of above-said current signal through A/D converting unit 203 enters digital signal processing unit 204 and carries out correlation demodulation.

In oscillogram shown in Figure 4,

Be the phase modulation that asymmetrical square wave is introduced, V _dBe the output signal of pre-amplifier unit 201, h (n) is used to select the sampled data of AD for amplitude is 1 comb filter waveform, avoids the hopping edge of data as far as possible, and its pulse width can be regulated.According to the coherent detection theory, correlation demodulation is output as V _dThe sample difference of sum of positive half period (c section among Fig. 4) sampling sum and negative half-cycle (a section among Fig. 4) if the semiperiod sampling number is M, can gets the correlation demodulation result and is:

S ₁=MKI ₀Sin4F formula 12

Simultaneously, gather V _dPeak value (b, d section among Fig. 4) and add up, if sampling number is M, can gets the accumulation process result and be:

S ₂=2MKI ₀Cos4F formula 13

Formula 12 and 13 liang of formulas of formula are divided by, can get:

$S_{\mathrm{out}}=\frac{S_1}{S_2}=\frac{1}{2}\tan 4F\≈2F$ Formula 14

With the output as mutual inductor of the value of formula 14, the output result that detects of open loop is only relevant with the Faraday phase shift that electric current causes as can be seen, has eliminated the error that light intensity, circuit gain drift about and cause.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.

Claims (6)

1. the open loop signal detection method of an all-fiber current transformator is characterized in that, comprising:

The employing cycle is that 2 τ, amplitude are V _Pi/2, and dutycycle be not 1: 1 asymmetrical square wave as modulation signal, light signal is carried out phase modulation (PM), described τ is the transit time of described all-fiber current transformator;

After interfering, the light signal after interfering is converted to electric signal through the light signal after the phase modulation (PM);

Described electric signal is carried out sampling processing;

In each τ modulation periods 2, the sampling sum of described electric signal positive half period and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described electric signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of described all-fiber current transformator.

2. method according to claim 1 is characterized in that, this method also comprises:

Determine the dutycycle of described asymmetrical square wave according to sampling rate.

3. method according to claim 1 and 2 is characterized in that, if the dutycycle of described asymmetrical square wave is 1: 3, the equation expression of the light signal after then described the interfering is:

When the phase shift of described light signal after phase modulation (PM) is pi/2,

The phase shift of described light signal after phase modulation (PM) is 0 o'clock,

The phase shift of described light signal after phase modulation (PM) is-during pi/2,

Wherein, I ₀Be the luminous power at photodetector place, F is the described phase shift of light signal after phase modulation (PM).

4. method according to claim 3 is characterized in that, before described electric signal was carried out sampling processing, this method also comprised:

To described electric signal amplify, Filtering Processing, through amplification, the equation expression of electric signal after the Filtering Processing is:

When the phase shift of described light signal after phase modulation (PM) is pi/2,

The phase shift of described light signal after phase modulation (PM) is 0 o'clock,

The phase shift of described light signal after phase modulation (PM) is-during pi/2,

Wherein, K is an amplification coefficient.

5. method according to claim 4 is characterized in that the equation expression of described S1 is: S ₁=MKI ₀Sin4F; Described S ₂Equation expression be: S ₂=2MKI ₀Cos4F, wherein, M is the sampling number in τ/2.

6. the open loop signal pick-up unit of an all-fiber current transformator is characterized in that, comprising:

Pre-amplifier unit is connected with A/D converter with photodetector respectively, is used for that electric signal with the output of described photodetector amplifies, after the Filtering Processing, sends to A/D converter;

A/D converter, be connected with digital signal processing unit with described pre-amplifier unit respectively, be used under the control of the sampling clock that described digital signal processing unit produces, after the analog electrical signal of described pre-amplifier unit output is converted to digital signal, send to described digital signal processing unit;

Digital signal processing unit is connected with the square wave generation unit with A/D converter respectively, is used to produce sampling clock and sends to A/D converter; The generation cycle is that 2 τ, amplitude are V _Pi/2, and dutycycle be not 1: 1 asymmetric digital square wave and send to described square wave generation unit; In each τ modulation periods 2, the sampling sum of the digital signal positive half period of described A/D converter output and the sampling sum of negative half-cycle are got difference, difference result is designated as S ₁, the peak value sampling sum of described digital signal is designated as S ₂, get S ₁Divided by S ₂The result as the open loop signal testing result of all-fiber current transformator and output;

The square wave generation unit, phase-modulator with described digital signal processing unit and described all-fiber current transformator is connected respectively, exports to described phase-modulator after being used for the asymmetric digital square wave that described digital signal processing unit produces is converted to asymmetric simulation square wave.

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