CN102628884B - Closed-loop optical fiber current transformer - Google Patents
Closed-loop optical fiber current transformer Download PDFInfo
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- CN102628884B CN102628884B CN201210087601.1A CN201210087601A CN102628884B CN 102628884 B CN102628884 B CN 102628884B CN 201210087601 A CN201210087601 A CN 201210087601A CN 102628884 B CN102628884 B CN 102628884B
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Abstract
The invention provides a closed-loop optical fiber current transformer, which comprises a light source, a light source control unit, a photoelectric detector, an optical device integrated assembly and a sensing head. An optical path system of the transformer is simple in structure and convenient in integration and modularization; a used optical element is small in volume and light in weight and free of electromagnetic interference, and has no interference on measured amount; and a reflection type optical path and a simple optical device are used for achieving mode interchange of orthogonal polarized light so as to form a reciprocity optical path and improve anti-interference capacity of the optical path. The multi-closed-loop technology is adopted, system measurement error caused by light source power attenuation and half-wave voltage drift of an optical is overcome, and stability and reliability of the transformer are improved.
Description
Technical field
The present invention relates to a kind of optical fiber current mutual inductor, the Current Mutual Inductance of all -fiber scheme of more particularly, to a kind of closed loop
Device, its sensing element and optical signal carrying components are all optical fiber, and its signal processing adopts a kind of coherent detection scheme
Many technology of closed loop.
Background technology
Current transformer is one of most basic, most important testing equipment in electric power power transmission and transformation network, and its effect is main
Including: one, the high current numerical value in high voltage environment on transmission line of electricity is dropped to and can use secondary meter numerical value measured directly,
In order to be measured with general instrument；2nd, be various monitoring and protection equipment provides electric signal, to monitor the peace of power system
Complete and stable operation；3rd, the secondary device of high voltage primary equipment and low-voltage is isolated.
Therefore, the performance of current transformer is closely related with the safe and reliable of power system and Economic Status.Electric power
In system, conventional current detecting equipment is the current transformer adopting based on undesirable mutual electromagnetic inductance principle.In high voltage, greatly electricity
In stream and superpower power system, this conventional current transformer exposes a series of serious shortcomings: potentially loses suddenly
Effect danger, insulation difficulty, iron core magnetic saturation, secondary side load open circuit etc..
Optical fiber current mutual inductor possesses the incomparable advantage of conventional electromagnetic current transformer due to its inherent characteristics.
With the continuous improvement of its reliability, optical fiber current mutual inductor will become the main choosing of power domain electric energy metrical and protection use
With equipment, progressively become domestic and international industry common recognition.
Ampere's law is pointed out, when there being electric current to flow through in conductor, can produce closed magnetic field about, using Faraday magneto-optical
The method of effect is measured this magnetic field and just can be obtained flowing through the size of electric current in conductor.Optical fiber current mutual inductor typically arrives external
Optical fiber around a upper fixing turn forms a Fibre Optical Sensor unit.When there being electric current to flow through in conductor, according to Faraday effect, its
The magnetic field of surrounding will make one angle of change of polarization of transmission light in sensor fibre, and the variable quantity measuring angle is with regard to energy
Obtain the size of current flowing through in conductor.Due to this angle very little, direct measurement angle is very low to determine size of current precision, because
This adopts the method for interferometry, polarised light angle is transformed into the phase changing capacity of light, then applies base after interfering
Weak Signal Processing method in associated modulation demodulation is extracted.
But, there are following some shortcomings: 1, light path system complex structure in existing optical fiber current mutual inductor, be unfavorable for be
System is integrated；2nd, the element in light path is easily affected by conditions of work such as temperature, and measure error is big it is impossible to realize closed loop anti-
Feedback.Existing optical fiber current mutual inductor technology referring to cn100575959c, cn101299147b, cn101364475b,
cn101521104b、cn101692401b、cn101915866a、cn101957395a、cn102087307a、cn102082606a
Deng.
Content of the invention
It is an object of the invention to the following aspects: one, light path system structure is simple, be easy to integrated and modularization；2nd,
Optical element volume used is little, lightweight, and is not subject to electromagnetic interference, does not also interfere with to measured；3rd, utilize reflection type optical path
Realize the modes swap of crossed polarized light with simple optical device, form reciprocity light path, improve light path antijamming capability；4th, adopt
Use multiple technology of closed loop, effectively overcome the systematic survey that light source power decay, the drift of optical phase modulator half-wave voltage cause by mistake
Difference, improves transformer operation stability and reliability.
In order to simplify system and effectively improve system reliability it is necessary to the signal processing unit data for sensing is adopted
Collection unit carries out integrated design.
In view of the foregoing, the present invention provide a kind of closed-loop optical fiber current transformer, comprising: light source, light source driving units,
Photodetector, optics integrated package, sensing head, wherein, optics integrated package, for by the light of light source output
It is polarized and is decomposed into two bunch polarised lights of orthogonal mode, then described two bunch polarizations are optically coupled in same polarization maintaining optical fibre
Two orthogonal modes on and transmit to sensing head；Receive the light returning at sensing head and make the light returning described
Interfere in optics integrated package；Result of interference is exported photodetector；Receive from signal processing unit
Feedback modulation information, superposition bias modulation phase place and feedback modulation phase place between two bunch polarised lights；Closed signal processing unit,
Receive the output signal of photodetector, this signal is processed, and signal processing results are anti-as feedback modulation information
Feed optical device integrated package and light source driving units；Light source driving units, for providing constant current and temperature control information to light source, with
When receipt signal processing unit feedback signal input, make the light intensity that light source output is stable.
According to an aspect of the present invention, described optics integrated package includes: light splitting optics, polarization maintaining optical fibre,
Optical phase modulator, light delay device.
According to an aspect of the present invention, described optical device integrated package includes: light splitting optics, polarization maintaining optical fibre, light
The polarizer, optical phase modulator, light delay device.
According to an aspect of the present invention, described optical device integrated package includes: the first light splitting optics, guarantor's polarisation
Fibre, y type optical phase modulator, the second light splitting optics, light delay device.
According to an aspect of the present invention, described closed signal processing unit includes: Simulation scale-up filter unit, modulus turn
Change unit, major loop Digital Logical Circuits, D/A conversion unit, 2 π voltage control units and filter unit.
According to an aspect of the present invention, using square wave bias modulation mode, introducing ± pi/2 between two bundle cross polarization light
Bias modulation phase difference；The method being formed at introducing between two bundle cross polarization light with sensing head using staircase waveform feedback modulation mode
Draw phase information phase difference equal in magnitude, in opposite direction；Method using associated modulation demodulation carries out signal demodulation.
According to an aspect of the present invention, Simulation scale-up filter unit, receives the electric signal from photodetector, carries out
It is input to AD conversion unit after amplifying filtering；AD conversion unit, for receiving the output of Simulation scale-up filter unit, will be through
The analog signal crossing amplification filtering is converted to data signal, is then output to major loop Digital Logical Circuits；Major loop numeral is patrolled
Collect circuit, receive AD conversion unit output, AD conversion unit output signal is demodulated, therewith demodulation result is carried out
Integration forms digital staircase shoulder height, and the formation digital staircase that adds up further；Receive 2 π voltage control unit outputs
Integrated signal, detected whether periodic demodulating error, with to 2 π feed back driving voltages adjust automatically；Described major loop
Being superimposed of digital staircase and bias modulation square wave is also realized, stack result exports digital-to-analogue conversion list in Digital Logical Circuits
Unit；The integral result of demodulating information is also directly output to wave filter by described major loop Digital Logical Circuits；2 π voltages control single
Unit, for receiving the output of major loop Digital Logical Circuits, the signal after demodulation is integrated, and obtains characterizing with the presence or absence of 2 π
The signal of voltage amplitude error, and by described signal output to major loop Digital Logical Circuits；D/A conversion unit, for receiving
The output of major loop Digital Logical Circuits, the stack result of digital staircase and bias modulation square-wave signal is converted to simulation letter
Number, then output analog signal to optical phase modulator, drive optical phase modulator introducing ± pi/2 between two bunch polarised lights
Bias modulation phase place and feedback modulation phase difference；Filter unit, for receiving the output of integral unit, filters to integrated signal
Ripple, filter result is as transformer numeral output.
According to the hereafter detailed description to preferred forms, these and other purposes disclosed by the invention, feature and excellent
Point will become apparent from.
Brief description
Fig. 1 is the theory structure schematic diagram of one embodiment of optical fiber mutual inductor of the present invention；
Fig. 2 is the structure chart of a specific embodiment of closed signal processing unit in Fig. 1；
Fig. 3 is the structure chart of multiple specific embodiments of optics integrated package in Fig. 1；
Fig. 4 is the waveform diagram of square-wave frequency modulation；
Fig. 5 is the waveform diagram of staircase waveform feedback phase relation.
Specific embodiment
Fig. 1 is the principle assumption diagram of an embodiment of optical fiber mutual inductor involved in the present invention.According to this embodiment, should
Optical fiber mutual inductor includes: light source driving units, light source, optics integrated package, sensor fibre, speculum, quarter wave plate, light
Electric explorer, closed signal processing unit, power supply.These three parts of sensor fibre, speculum, quarter wave plate constitute sensing head.By
Belong to prior art in sensing head, therefore do not indicated with word in FIG.
Additionally, sensing head can also have multiple ways of realization, it is not belonging to present disclosure, therefore repeat no more.
Light source, for exporting the light beam of certain power under the control of light source driving units.
Optics integrated package, for receiving the light of light source output, and plays this light of light source output and is biased into line
Polarised light, is decomposed into this linearly polarized light two bunch polarised lights of orthogonal mode immediately again；In optics integrated package, upper
State two bunch to shake in two orthogonal modes being optically coupled in same polarization maintaining optical fibre, that is, optics integrated package sends two
The linearly polarized light of bundle orthogonal mode along same polarization maintaining optical fibre two orthogonal modes fl transmission to sensing head, and with being followed by
The light beam returning along original optical path modes swap after receiving this two bunch polarised light sensitive Faraday magnetooptical effect at sensing head, returns
Two-beam line interfere in optics integrated package；Optics integrated package is additionally operable to two bunch polarised lights
Result of interference passes through optical fiber output to photodetector；Additionally, optics integrated package accepts to process list from closed signal
Unit feedback modulation information, with superposition ± pi/2 bias modulation phase place between two bunch polarised lights and with faraday's phase differencefGreatly
Little feedback modulation phase equal, in opposite directionr.
Sensing head, including quarter wave plate, sensor fibre, speculum, for the magnetic field around sensitive ampere wires to be measured, that is,
According to Faraday magnetooptical effect, between two bundle crossed polarized lights, introduce Faraday magnetooptical effect phase differencef.
In sensing head, quarter wave plate is used for light beam from linearly polarized light to circularly polarized light, or circularly polarized light is to linear polarization
Mode conversion between light.In the present embodiment, quarter wave plate is used for two bundle orhtogonal linear polarizaiton light of fl transmission to be changed into a left side
Rotation and two bundle orthogonal mode circularly polarized lights of dextrorotation, and the two bundle circularly polarized lights returning from sensor fibre are transformed back into orthogonal simultaneously
Linearly polarized light.Afterwards, the two bunch polarised lights transforming back into return along original optical path.
In sensing head, speculum is used for reflection light, makes light reverse transfer.In the present embodiment, speculum is used for
Make two bundle circularly polarized light beam modes swap reverse transfer, that is, so that being originally that left-handed and dextrorotation two bundle circularly polarized lights change
Return for dextrorotation and left-handed two bundle circularly polarized lights and along sensor fibre.
Photodetector, the optical signal for receiving optics integrated package exports, using photoelectric effect by optical signal
Be converted to electric signal, by the amplification filter unit in closed signal processing unit for the electric signal output.Photodetector belongs to existing
There is technology, those skilled in the art is fully able to learn its specific implementation, hereafter no longer describes in detail.
Closed signal processing unit, receives the signal input of photodetector, realizes the digital control of signal and processes, and
Signal processing results are fed back to optics integrated package and light source driving units.
Power supply, the available light current of the circuit board for the direct currents such as 110v, 220v or electric main are changed in transformer,
I.e. power supply effect is to power to light source driving units and closed signal processing unit.
Light source driving units, for providing constant current and temperature control information to light source, receive closed signal processing unit simultaneously
Feedback signal input is so that light source exports stable intensity signal all the time.
As shown in figure 1, under in working order, power supply is powered to light source driving units, closed signal processing unit, light source drives
Moving cell works, and controls light source luminescent.The light that light source sends, enters optics integrated package by optical fiber, through optics device
The adjustment of part integrated package, is divided into the two-beam line of orthogonal mode again after forming linearly polarized light, i.e. x, y two restraint orthogonal mode
Linearly polarized light.Then this two bundles polarised light is protected inclined Transmission Fibers along same and is transferred to sensing head.
At sensing head, x, y two restraint orthogonal mode linearly polarized light first pass through quarter wave plate be converted into respectively left-handed and
(or) circularly polarized light of dextrorotation.When described left-handed and (or) dextrorotation circularly polarized light reaches the speculum of sensor fibre end,
Both circularly polarized lights produce modes swap, return (i.e. left-handed change dextrorotation, dextrorotation become left-handed) after modes swap.
This two-beam sensitive Faraday magnetooptical effect pass through sensor fibre arrival quarter wave plate, through quarter wave plate transformation again
Loop line polarised light (also being exchanged with linear polarization pattern before) is simultaneously returned along original optical path.
Two-beam interferes after reaching optics integrated package, and result of interference carries out photoelectricity through photodetector
Enter closed signal processing unit after conversion and carry out signal resolving and extraction.
Closed signal processing unit is processed according to the signal that photodetector inputs, and the result obtaining is exported
To optics integrated package, thus forming the signal feedback to light path devices, it is easy to accurately, stably detect current carrying conductor
Middle passed through electric current.
Additionally, closed signal processing unit is carried out instead to light source driving units always according to the input signal of photodetector
Feedback, forms the closed-loop control that light source drives.As shown in figure 1, by the extraction to DC component in photodetector output result
The change of reflection light source power, and this DC component information (i.e. i0 hereinafter) Real-time Feedback, to light source driving units, is repaiied
Positive light source drive current size is so that light source exports stable luminous power all the time.
In said process, the two bundle polarised lights phase difference size that sensitive Faraday effect is formed twice respectively is: φf=
4nvi
Wherein, n be the sensor fibre number of turns, v be the verdet constant of sensor fibre, i be size of current to be measured.φfIt is method
Draw phase shift.
Afterwards, two bunch polarised lights are passed back in optics integrated package, and interfere wherein, and result of interference is delivered to
Photodetector, turns and Wei not enter follow-up signal processing links after power information, the phase difference to the two bundle polarised lights interfering
Information is extracted.Because the interference light intensity information of transformer is faraday's phase shift φfCosine function, that is,
id=i0(1+cosφf)
Wherein, i0It is the light intensity of two bundle correlation light.
From property near zero phase for the cosine function: (1) interference light intensity can not reflect the symbol of faraday's phase shift,
No matter φfPositive and negative all export same numerical value, thus the flow direction of electric current to be measured can not be reflected；(2) small current measurement sensitivity
Low, because cosine function first derivative at zero phase is zero.But in most application scenario, faraday's phase shift very little；
(3) in optical fiber current mutual inductor, limited by the optics basic parameter being used, determine the output electricity of photodetector
Pressure is the Weak Information of microvolt level, and noise is usually millivolt magnitude, that is, be difficult to from above formula extracting directly phase information.
Poor by introducing phase modulation in optics integrated package in the present invention, reach extraction faraday's phase shift φf
Purpose.I.e. by introduce square wave bias modulation and staircase waveform feedback technique so that transformer system always work in the sensitiveest
Region, and be easy to extract faraday's phase shift information using the method for correlation demodulation.
In the present invention, optical phase modulator is set in optics integrated package, its objective is to restraint coherent light two
Between introducing ± pi/2 bias modulation phase place and closed loop feedback phase modulation φr, wherein feedback modulation phaserIn order to offset farad
Phase differencefSo that system always works in sensitive area.
Light splitting closing light mainly realized by optics integrated package, light is polarized, polarised light decomposes, optical coupling, light phase modulation
Etc. several functions.Optics integrated package can have multiple specific embodiments.
Fig. 3 is the structure chart of multiple specific embodiments of optics integrated package in Fig. 1.
As shown in Fig. 3 (a), optics integrated package include light splitting optics 1, polarization maintaining optical fibre, optical phase modulator,
Light delay device.Except sensing head part in the program, the light path scheme of optical fiber current mutual inductor is all risk insurance folk prescription case, i.e. all light
Fine and device tail optical fiber is all polarization maintaining optical fibre.The linearly polarized light that high polarisation source sends is after light splitting optics through tail optical fiber
Two bunch polarised light x, y that 45° angle is divided into orthogonal mode to axle welding transmit, through light phase in same polarization maintaining optical fibre
After modulator and light delay device (light delay device is one section of polarization maintaining optical fibre of a hop count rice to thousands of meters in itself), then along same
Two orthogonal modes of polarization maintaining optical fibre are transmitted to sensing head.After returning at sensing head, this two-beam modes swap, again pass by
Optical phase modulator, reaches and meets interference condition at 45 ° of fusion points, interfere, and result of interference is through light splitting optics 1 coupling
Close into photodetector.
As shown in Fig. 3 (b), optics integrated package includes light splitting optics 1, polarization maintaining optical fibre, the light polarizer, light phase
Position modulator, light delay device.The light that light source sends after light splitting optics and the light polarizer, through protecting 45 ° of inclined tail optical fiber
Two bunch polarised light x, y that angle is divided into orthogonal mode to axle welding transmit in same polarization maintaining optical fibre, adjust through light phase
After device processed and light delay device (light delay device is one section of polarization maintaining optical fibre of a hop count rice to thousands of meters in itself), then protect along same
Two fine orthogonal modes of polarisation are transmitted to sensing head.After returning at sensing head, this two-beam modes swap, again pass by light
Phase-modulator, reaches and meets interference condition at 45 ° of fusion points, interfere, and result of interference is closed through the light polarizer and light splitting
Optical Device Coupling enters photodetector.
As shown in Fig. 3 (c), optics integrated package includes the first light splitting optics (i.e. light splitting optics 1), protects
Polarisation fibre, y type optical phase modulator, the second light splitting optics (i.e. light splitting optics 2), light delay device.Light source sends
Light reaches y type optical phase modulator after the first light splitting optics.Y type optical phase modulator has light to be polarized, light beam splitting, light adjust
The function of system.Y type optical phase modulator belongs to prior art, no longer describes in detail.At y type optical phase modulator, light is polarized simultaneously
After being divided into two bundle polarization mode identical linearly polarized lights, reach the second light splitting splicer along its two tail optical fiber propagated forward respectively
Part.Before this, by a tail optical fiber of y type optical phase modulator and 90 ° of angles pair of a tail optical fiber of the second light splitting optics
Axle welding so that above-mentioned two bunch polarised lights from the second light splitting optics out after pattern orthogonally protect partially along same
Optical fiber propagated forward.Similarly, this two bundle orthogonal mode polarised light at sensing head back through the second light splitting splicer
After part, and because above-mentioned 90 ° of angles are changed into pattern identical two bunch polarised light to axle welding, and in y type optical phase modulator
Place interferes, and result of interference is coupled into photodetector through the first light splitting optics.
As shown in Fig. 3 (d), optics integrated package includes the first light splitting optics (i.e. light splitting optics 1), protects
Polarisation fibre, y type optical phase modulator, the second light splitting optics (i.e. light splitting optics 2), light delay device.Light source sends
Light reaches y type optical phase modulator after the first light splitting optics, and at y type optical phase modulator, light is polarized and divides equally
After two bundle polarization mode identical linearly polarized lights, reach the second light splitting optics along its two tail optical fiber propagated forward respectively.
Second light splitting optics can become the mode the linearly polarized light set of the identical polarization mode in two tail optical fibers of forward path
Two orthogonal bunch polarised lights and protect inclined tail optical fiber along same and continue propagated forward additionally it is possible to one in backward channel be protected inclined
In tail optical fiber, two bunch polarised lights of orthogonal mode are changed into two bunch polarised lights of model identical, and anti-respectively along its two
Propagate to passage tail optical fiber, you can so that the polarization angle of a branch of polarised light in the two bundle polarised lights propagated wherein is rotated 90 °.
Above-mentioned two bunch polarised lights from the second light splitting optics out after pattern orthogonally along before same polarization maintaining optical fibre to biography
Broadcast.Similarly, after the polarised light of this two bundles orthogonal mode is at sensing head back through the second light splitting optics, change again
For pattern identical two bunch polarised light, and interfere at y type optical phase modulator, result of interference is through the first light splitting closing light
Device is coupled into photodetector.
It is enumerated above the several specific embodiments with regard to optics integrated package that can realize in this patent, but
Any design that can realize above-mentioned functions is all within the protection domain of this patent.
As shown in Fig. 2 according to an embodiment of the invention, it is single that closed signal processing unit includes Simulation scale-up filtering
Unit, AD conversion unit (a/d), major loop Digital Logical Circuits, D/A conversion unit (d/a), 2 π voltage control units and
Filter unit.
Wherein, Simulation scale-up filter unit, for receive from photodetector electric signal, be amplified filter in order to
Input as analog-to-digital conversion link.
AD conversion unit, for receiving the output of Simulation scale-up filter unit, by the analog signal through amplifying filtering
Be converted to data signal, be then output to major loop Digital Logical Circuits, carry out logical operation.
Major loop Digital Logical Circuits, receives AD conversion unit output, AD conversion unit output signal is solved
Adjust, demodulation result is integrated forming the shoulder height of feedback staircase waveform, afterwards with time τ for step-length to above-mentioned step therewith
Highly added up, formed digital staircase.Step-length τ is transmission time in transformer light path for the light.According to follow-up link number
The digit of mould converting unit, digital staircase can overflow zero automatically, realizes automatically reseting of feedback modulation.If when automatically
When reset occurs, staircase waveform total height corresponds to feedback modulation 2 π phase difference, then this automatically reseting will not be to the survey of transformer
Accuracy of measurement produces impact.Further, since the half-wave voltage of light phase modulation produces drift such as the change of environment and time
Move, in the present embodiment, demodulated signal is delivered simultaneously in 2 π voltage control units；Additionally, this logic circuit also receives
The integrated signal of 2 π voltage control unit outputs, has detected whether periodic demodulating error, in order to feed back driving voltage to 2 π
Adjust automatically；In addition being superimposed of digital staircase and bias modulation square wave, superposition are also realized in major loop Digital Logical Circuits
Result exports D/A conversion unit；Additionally, major loop Digital Logical Circuits also directly exports to the integral result of demodulating information
To wave filter, filter result as transformer numeral output, to characterize size of current to be measured.
2 π voltage control units, for receiving the output of major loop Digital Logical Circuits, the signal after demodulation are amassed
Point, obtain characterizing the signal with the presence or absence of 2 π voltage amplitude errors, and by this signal output to major loop Digital Logic electricity
Road, in order to be automatically adjusted to 2 π resetting voltages.
D/A conversion unit, for receiving the output of major loop Digital Logical Circuits, by digital staircase and bias modulation
The stack result of square-wave signal is converted to analog signal, then outputs analog signal to optical phase modulator, thus driving light
Phase-modulator is with introducing ± pi/2 bias modulation phase place and φ between two bunch polarised lightsrFeedback modulation phase difference.
Filter unit, for receiving the output of integral unit, is filtered to integrated signal, filter result is as transformer
Numeral output, to characterize size of current to be measured.
According to an embodiment of the invention, in this embodiment, major loop Digital Logical Circuits at least includes signal
Demodulating unit, integral unit and summing elements.
According to an embodiment of the invention, in this embodiment, 2 π voltage control units include 2 π voltage error letters
Number demodulating unit and digital integrator.
Signal demodulation unit receives the output of AD conversion unit, and the output signal of AD conversion unit is demodulated.
Demodulation method be: to AD conversion unit output periodic signal adjacent before and after the half period separately sampled do cumulative, add up
Result is subtracted each other again, and subtracting each other result is demodulation result.Then demodulation result is sent to 2 π voltages in 2 π voltage control units
Error signal demodulating unit.
2 π voltage error signal demodulating units are demodulated to the signal receiving judging, judge whether periodically
Control information, and form demodulation judged result and be sent in digital integrator, further form update information, and feed back to master
Loop Digital Logical Circuits, in order to be automatically adjusted to 2 π feedback voltages.
Integral unit exports integral result to filter unit, and integral result is transferred in accumulator by accumulator
Carry out cumulative formation digital staircase, as shown in Figure 5.The digital staircase being formed is sent to after being superimposed with bias modulation square wave
In D/A conversion unit.Bias modulation square wave is as shown in Figure 4.Transformation result is input to optical phase modulator by D/A conversion unit
In, thus introducing corresponding bias modulation phase place and feedback modulation phase difference in the middle of light path.
According to a specific embodiment of the present invention, Fig. 4 describes a kind of embodiment of square-wave frequency modulation.Fig. 4 can be divided into,
Under, right three parts.On Fig. 4, the sinogram longitudinal axis of part represents the later light intensity of two bundle polarized light interferences, and transverse axis represents two bundles
Cross polarization light phase is poor.It is partly the modulated square wave that two bundle cross polarization light are carried out with ± pi/2 bias modulation under Fig. 4, it
Vertical pivot is the time, and transverse axis represents square wave amplitude, and just can introduce between two bundle cross polarization light during square wave amplitude modulation
± pi/2 bias modulation phase difference.Fig. 4 right half is output waveform after square-wave frequency modulation for the two bundle polarized light interference results, its
In partially left part be waveform when measured physical quantity=0, inclined right part is the ripple when measured physical quantity is not equal to 0
Shape, the flat part in bottom represents when being in square wave amplitude modulation, spike be then two bundles in square wave peak-peak amplitude jump partially
Shake what interference of light result was formed through peak.
The interference light intensity information of transformer is faraday's phase shift φfCosine function, that is,
id=i0(1+cosφf)
In above formula, i0It is the light intensity of two bundle correlation light, φf=4nvi is the sensitive method at sensing head of two bunch polarised lights
Draw phase shift, wherein n be sensor fibre be wound around the number of turns, v be sensor fibre verdet constant, i be size of current to be measured.
As shown in figure 4, modulation pull-in frequency is driven by square wave by optical phase modulator first at optical phase modulator
Square wave phase bias modulation (wherein τ is that two bunch polarised lights form the time difference finally interfering) for 1/ (2 τ),
Between two bunch polarised lights, superposition ± pi/2 phase is poor, improves the sensitivity of transformer system；Pass through to introduce square wave biasing tune simultaneously
Output signal spectrum is moved to high frequency by low frequency range on frequency domain, avoids the 1/f noise of low frequency range, decreases low frequency and make an uproar by system
The impact of sound.At this moment interfere and be output as
By bias modulation, it is superimposed upon direct current i interfering output to be modulated into one0On amplitude be i0sinφfSquare wave
Signal, square wave amplitude reflects faraday's phase shift size.In order to reduce system output nonlinear error further and increase dynamic
Measurement range, introduces one and faraday's phase shift by optical phase modulator by staircase waveform feedback modulation at optical phase modulator
Feedback compensation phase shift φ equal in magnitude, in opposite directionr, form closed-loop control system.Now, the interference of two-beam is output as
Due to φf+φr≈ 0, so now transformer system always works in the best zero phase near zone of the linearity,
Therefore measurement sensitivity highest；Simultaneously because realizing closed loop detection, have also been enlarged the measurement range of system.At this moment the correlation of system
Demodulation result is (before and after the periodic signal that above formula represents, the half period subtracts each other result):
δ=n i0·sin(φf+φr)≈n·i0·(φf+φr)
Wherein, δ is that signal demodulates the intermediate quantity that link occurs, and it represents demodulation result, is a small quantity, leads to
Cross the integration to this small quantity and form digital staircase shoulder height.It results from the signal solution in major loop Digital Logical Circuits
Adjust unit, export integral unit and 2 π voltage control units.
According to one embodiment of present invention, Fig. 5 gives the embodiment of staircase waveform feedback phase relation.As shown in figure 5,
Fig. 5 is divided into upper and lower two parts.Wherein in the top half of Fig. 5, the longitudinal axis is phase difference, and transverse axis is the time.Solid line therein
Staircase waveform represents the feedback staircase waveform of t, and dotted line staircase waveform represents the feedback staircase waveform in t+ τ moment, and the step of staircase waveform is high
The size of degree actual feedback amount.The latter half of Fig. 5 is corresponding with top half, is subtracted each other by the solid line and dotted line of top half
Arrive, it actual characterize be staircase waveform shoulder height.In periodic recessed portion, sign be equally staircase waveform height
Value, simply staircase waveform is phase-accumulated herein forms and resets to 2 π, highly low 2 π therefore at its aspect ratio non-reset.
Staircase waveform feedback modulation is adopted to produce feedback phase difference φ in the present embodimentr.Demodulation result described in above formula is made
Cumulative integration, forms shoulder height so (so is intermediate quantity, does not indicate in Figure 5) of digital staircase.So mono- aspect is through number
Mould converting unit drives optical phase modulator after forming analogue step ripple, compensates difference φ to introduce between two-beamr, so simultaneously
The numeral output as transformer after further filtering process, the size and Orientation of reflection transformer input current.
If the analogue step ripple being formed through digital-to-analogue conversion is δ vr(t)=vr(t)-vr(t- τ), its codomain be (- ∞ ,+
∞), then the additional phase shift producing between two bunch polarised lights is:
φr=kfpvr(t)-kfpvr(t-τ)
=kfp(vr(t)-vr(t-τ))
=lfpδvr(t)
In above formula, τ is the transition time in fibre delay line for the light beam, and kfp is phase modulator modulation coefficient.Above formula is said
Bright, the phase difference that Staircase wave produces is directly proportional to staircase waveform shoulder height.In Fig. 5, fw (solid line) represents the feedback of t
Staircase waveform, bw (dotted line) represents the feedback staircase waveform in t+ τ moment；vrT () represents the absolute altitude of analogue step ripple step.
But it is clear that codomain scope is impossible in (- ∞ ,+∞) upper staircase waveform constantly rising.Due to interfering
Output signal, with 2 π as cycle, so in this closed loop policy, is the ladder of (0,2 π) using shape codomain scope as shown in Figure 5
Ripple come to replace codomain be (- ∞ ,+∞) staircase waveform, that is, when Staircase wave phase place kfp·vrAutomatically reset during (t)=2 π.
Realize the closed signal detection of optical fiber current mutual inductor by above method.But in transformer long-term work process
In, the half-wave voltage of optical phase modulator can be drifted about, i.e. kfp·vrT () ≠ 2 π, is at this moment accomplished by designing 2 π resetting voltages
Automatic corrective loop, as shown in Figure 2.
Firstly the need of the error signal extracting 2 π resetting voltage corrective loops, point kfp·vr(t) ＞ 2 π, kfp·vr(t) ＜ 2
π、kfp·vrTri- kinds of situations of (t)=2 π.Work as kfp·vrT, during () ≠ 2 π, photo-detector power output can produce a transient, should
Transient can obtain according to system correlation demodulation result in the staircase waveform reset moment, and this demodulation result is returned as the 2nd closed loop
Road, that is, in Fig. 2 the signal circuit of major loop Digital Logical Circuits and both 2 π voltage control units input error signal, then
With processing to it by digital integrator, then the data signal after integration is transformed into analog signal by digital-to-analogue, goes to control
The gain of D/A conversion unit processed or the digital to analog converter reference voltage of transformer major loop Digital Logical Circuits generation staircase waveform,
Thus defining 2 π resetting voltage corrective loops, real-time control is carried out to 2 π resetting voltages so as to accurate 2 can be produced all the time
π phase place, thus ensure the no-load voltage ratio performance of transformer.
According to an aspect of the present invention, closed signal processing unit can be realized by technology such as fpga, dsp.Said units
In the case that function determines, integrated device or single module can be designed as, be designed as integrated device according to demand
In the case of, light path, the device of circuit are easy to modularization and integrated, and reciprocity is good, is easy to Networking Design.
It will be understood by those of skill in the art that in scope of the following claims and its equivalency range, according to design
Require and other factors, various modifications, merging, subitem merging can occur and change.
Claims (1)
1. a kind of closed-loop optical fiber current transformer, comprising: light source, light source driving units, photodetector, optics collection are in groups
Part, sensing head it is characterised in that:
Optics integrated package, for the light of light source output being polarized and being decomposed into two bunch polarised lights of orthogonal mode,
Then described two bunch polarizations are optically coupled in two orthogonal modes of same polarization maintaining optical fibre and are transmitted to sensing head；Receive
At sensing head return light and make return light interfere in described optics integrated package；Knot will be interfered
Fruit exports photodetector；Receive the feedback modulation information from signal processing unit, be superimposed partially between two bunch polarised lights
Put phase modulation and feedback modulation phase place；
Closed signal processing unit, receives the output signal of photodetector, this signal is processed, and signal transacting is tied
Fruit is as feedback modulation feedback of the information to optical device integrated package and light source driving units；
Light source driving units, for providing constant current and temperature control information, the feedback signal of receipt signal processing unit simultaneously to light source
Input, makes the light intensity that light source output is stable；
Described optical device integrated package includes: the first light splitting optics, polarization maintaining optical fibre, y type optical phase modulator, the second light splitting
Optics, light delay device；
A piece tail optical fiber of a piece tail optical fiber of y type optical phase modulator and the second light splitting optics is with 90 ° of angles to axle welding；Light source
The light sending reaches y type optical phase modulator after the first light splitting optics, and at y type optical phase modulator, light is polarized
And after being divided into two bundle polarization mode identical linearly polarized lights, propagate along two tail optical fibers of described y type optical phase modulator respectively
Reach the second light splitting optics；At sensing head return two-beam line after the second light splitting optics, in y type light phase
Interfere at the modulator of position, result of interference is coupled to photodetector through the first light splitting optics；
The linearly polarized light set of the identical polarization mode in two tail optical fibers of forward path is just become the mode by the second light splitting optics
Propagate wherein two bunch are also polarized by the two bunch polarised lights handed over and protect inclined tail optical fiber along same and continue propagated forward
The polarization angle of a branch of linearly polarized light in light rotates 90 °；The light that light source sends reaches y type light after the first light splitting optics
Phase-modulator, at y type optical phase modulator, after light is polarized and is divided into two bundle polarization mode identical linearly polarized lights,
Reach the second light splitting optics along two tail optical fibers propagation of described y type optical phase modulator respectively；Return at sensing head
Two-beam line, after the second light splitting optics, is changed into pattern identical two bunch polarised light, in y type optical phase modulator
Place interferes, and result of interference is coupled into photodetector through the first light splitting optics；
Described closed signal processing unit includes: Simulation scale-up filter unit, AD conversion unit, major loop Digital Logic electricity
Road, D/A conversion unit, 2 π voltage control units and filter unit；
Using square wave bias modulation mode, introducing ± pi/2 bias modulation phase difference between two bundle cross polarization light；Using staircase waveform
Faraday's phase information that feedback modulation mode is formed at introducing between two bundle cross polarization light with sensing head is equal in magnitude, direction
Contrary phase difference；Method using associated modulation demodulation carries out signal demodulation；
Simulation scale-up filter unit, receives the electric signal from photodetector, is input to analog-to-digital conversion after being amplified filtering
Unit；
AD conversion unit, for receiving the output of Simulation scale-up filter unit, by the analog signal conversion through amplifying filtering
For data signal, it is then output to major loop Digital Logical Circuits；
Major loop Digital Logical Circuits, receives AD conversion unit output, AD conversion unit output signal is demodulated, with
Demodulation result is integrated formed digital staircase shoulder height, and further add up formed digital staircase；Receive 2 π
Voltage control unit output integrated signal, detected whether periodic demodulating error, with to 2 π feed back driving voltages from
Dynamic adjustment；Being superimposed of digital staircase and bias modulation square wave, stack result is also realized in described major loop Digital Logical Circuits
Export D/A conversion unit；The integral result of demodulating information also is directly output to filter by described major loop Digital Logical Circuits
Device；
2 π voltage control units, for receiving the output of major loop Digital Logical Circuits, the signal after demodulation are integrated, obtain
To the signal characterizing with the presence or absence of 2 π voltage amplitude errors, and by described signal output to major loop Digital Logical Circuits；
D/A conversion unit, for receiving the output of major loop Digital Logical Circuits, by digital staircase and bias modulation square wave
The stack result of signal is converted to analog signal, then outputs analog signal to optical phase modulator, drives light phase modulation
Device introducing ± pi/2 bias modulation phase place and feedback modulation phase difference between two bunch polarised lights；
Filter unit, for receiving the output of integral unit, is filtered to integrated signal, and filter result is as transformer numeral
Output.
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