WO2014127654A1

WO2014127654A1 - Quasi-reciprocal reflective optical voltage sensing unit and sensing system thereof

Info

Publication number: WO2014127654A1
Application number: PCT/CN2013/087784
Authority: WO
Inventors: 张朝阳; 荆平; 雷林绪; 温海燕; 孙海江; 侯继彪; 刘占元; 叶志奇
Original assignee: 国家电网公司; 国网智能电网研究院
Priority date: 2013-02-20
Filing date: 2013-11-25
Publication date: 2014-08-28
Also published as: CN103197113B; CN103197113A

Abstract

A quasi-reciprocal reflective optical voltage sensing unit and a sensing system thereof. The sensing unit includes a sensing head and two polarization-maintaining circulators (1, 2). A first tail fiber (a, a'), a second tail fiber (b, b') and a third tail fiber (c, c') are provided in each of the polarization-maintaining circulator (1, 2). Two cross linear polarized light beams are transmitted to the sensing unit through the second tail fiber (b) of the first polarization-maintaining circulator (1). 0-degree angle welding is performed on the third tail fiber (c) of the first polarization-maintaining circulator (1) and the first tail fiber (a') of the second polarization-maintaining circulator (2) so as to form a branch I , 90-degrees angle welding is performed on the first tail fiber (a) of the first polarization-maintaining circulator (1) and the third tail fiber (c') of the second polarization-maintaining circulator (2) so as to form a branch II, and the second tail fiber (b') of the second polarization-maintaining circulator (2) and the tail fiber of the sensing head is welded. The sensing system includes the sensing unit, an optical path portion and a circuit portion. The sensing unit and the system thereof utilizes the two polarization-maintaining circulators (1, 2) to implement the mode exchange of the two cross linear polarized light beams and the ability of anti-interference of the optical path is improved.

Description

Quasi-reciprocal reflective optical voltage sensing unit and sensing system thereof

The invention belongs to the field of voltage transformers, and in particular relates to a quasi-reciprocal reflective optical voltage sensing unit for an optical voltage transformer and a sensing system thereof. Background technique

An optical voltage transformer is a transformer that uses an optical signal to induce a voltage and is subjected to signal processing to obtain an output voltage. Compared with traditional electromagnetic induction and capacitive voltage transformers, it has many incomparable advantages. It has become a hot research topic in the field of voltage transformers, and is the future development trend of voltage transformers. Among them, the voltage sensing unit is a key part of photoelectric sensing. At present, the voltage sensing unit of the optical voltage transformer based on the Pockels effect mostly needs two photoelectric detecting devices to receive the two optical output signals carrying the modulation information, so that the structure of the entire optical voltage transformer is complicated. Summary of the invention

In order to overcome the above-mentioned drawbacks of the prior art, one of the objects of the present invention is to provide a quasi-reciprocal reflective optical voltage sensing unit having strong anti-interference ability and simple structure.

The quasi-reciprocal reflective optical voltage sensing unit of the present invention is realized by the following technical solutions: a quasi-reciprocal reflective optical voltage sensing unit, the sensing unit comprising a sensing head, and further comprising two polarization maintaining rings a first pigtail, a second pigtail and a third pigtail on each of the polarization maintaining circulators;

Two orthogonal linearly polarized lights are transmitted to the sensing unit through the second pigtail of the first polarization maintaining circulator, the third pigtail of the first polarization maintaining circulator and the second polarization maintaining circulator The first pigtail is welded at 0° to form a branch I, and the first pigtail of the first polarization maintaining circulator and the third pigtail of the second polarization maintaining circulator are welded at a 90° angle to form a branch Π; The second pigtail of the second polarization maintaining circulator is welded to the pigtail of the sensing head.

Further, the sensing head includes a collimator and an electro-optical crystal, and the light incident surface of the electro-optic crystal is plated with an anti-reflection film, and the other surface opposite to the light incident surface is plated with a reflective film, the collimator The electro-optic crystal is fixed on one side of the antireflection film, and the pigtail of the sensor head is connected to the light incident surface of the collimator; and the upper and lower end faces of the electro-optic crystal are respectively mounted with electrodes.

Further, the sensing head is encapsulated in a shielding case. Further, the two orthogonal linearly polarized lights sequentially pass through the first polarization maintaining circulator, the branch I and the second polarization maintaining circulator, and then enter the sensing head to obtain a total phase difference of 2φ and then output from the sensing head; The two orthogonal linearly polarized lights output by the sensor head are sequentially output through the second polarization maintaining circulator, the branch Π and the first polarization maintaining circulator; when passing through the branch Π, the polarization of the two orthogonal linear polarized lights is made The direction is rotated by 90 degrees to realize the mode interchange of two orthogonal linearly polarized lights.

Further, the sensing head generates a phase difference φ after the two orthogonal linearly polarized lights pass through the sensing head under the action of the electric field, and the two phase-polarized light passes through the sensing head again after reflection, and the total phase difference is 2φ.

The phase difference produced by the two linearly polarized lights passing through the sensing head is:

π / ₃

λ a

Where Z is the length of the electro-optic crystal in the direction of light propagation, is the thickness of the electro-optic crystal in the direction of the applied electric field, "is the refractive index of the electro-optic crystal, and γ ₄₁ is the electro-optic coefficient of the electro-optic crystal, which is the voltage applied to the electro-optic crystal.

Further, the first pigtail, the second pigtail and the third pigtail of the two polarization maintaining circulators and the pigtail of the sensing head are both polarization-maintaining fibers.

Another object of the present invention is to provide a quasi-reciprocal reflective optical voltage sensing system, comprising the sensing unit of any of the above, further comprising an optical path portion and a circuit portion disposed in the secondary chassis; The light emitted by the light source is divided into two orthogonal linearly polarized lights through the optical path portion and transmitted to the sensing unit through the polarization maintaining optical fiber; the sensing unit generates a total phase difference of 2 ^ under the action of the electric field and is reflected, and two The vibration directions of the beam-polarized light are respectively rotated by 90° to realize the mode interchange; the two linearly polarized lights returned from the sensing unit are transmitted back to the optical path portion through the polarization-maintaining optical fiber for interference, and the interference light is detected by the circuit portion. After a strong signal and signal processing, a digital signal output is formed.

Further, the optical path portion includes a light source, a circulator, a Υ waveguide modulator, and a polarization beam splitter, and the light emitted from the light source passes through the circulator into the Υ waveguide modulator to split the light into two polarized lights, one of which After the beam is rotated by 90°, it enters the polarizing beam splitter together with the other beam, and the two polarized lights are adjusted into two orthogonal linearly polarized lights and transmitted to the sensing unit through the polarization maintaining fiber; the two beams returned by the sensing unit The orthogonal linearly polarized light carries the voltage information to be measured, and then enters the Υ waveguide modulator through the polarizing beam splitter to interfere. After the interference, the interfering light intensity signal passes through the circulator and enters the circuit part for signal processing.

Further, the circuit part includes: a photoelectric converter for detecting an interference light intensity signal emitted by the optical path portion, and converting the signal into an analog voltage signal, and sending the signal to an analog to digital converter;

An analog-to-digital converter for converting an analog voltage signal into a discrete digital signal and sending it to a digital signal processing unit;

a digital-to-analog converter that converts a digital staircase wave generated by a digital signal processing unit into an analog staircase wave; a driving circuit that drives a Y-waveguide modulator that applies an analog staircase wave to the optical path portion; and a digital signal processing unit that is used for a digital signal Data demodulation is performed, and after the integral processing, the stepped step height is generated, and the digital staircase wave is accumulated and sent to the digital-to-analog converter to be converted into an analog staircase wave, which is applied to the Y-waveguide modulator of the optical path portion by the driving circuit. Closed-loop control; the digital signal processing unit is further configured to generate a modulated square wave, which is converted into an analog square wave by a square wave driving circuit, and then superimposed with the analog step wave, and then applied to the Y-waveguide of the optical path portion The digital signal processing unit is further configured to perform smoothing filtering on the digital signal to form a digital signal output.

Further, the digital signal processing unit includes a digital signal processor (DSP) and a field programmable gate array (FPGA).

The beneficial effects of the invention are:

1. The invention realizes the mode interchange of two orthogonally polarized lights by using two polarization maintaining circulators, forms a quasi-reciprocal reflective optical path, and improves the anti-interference ability of the optical path.

2. The optical component used in the invention is small in size, light in weight, simple in structure, and free from electromagnetic interference, and has little disturbance to the electric field to be measured. DRAWINGS

1 is a schematic structural view of a quasi-reciprocal reflective optical voltage sensing unit of the present invention;

2 is a structural schematic diagram of an optical path portion of a quasi-reciprocal reflective optical voltage sensing system of the present invention; FIG. 3 is a structural schematic diagram of a circuit portion of a quasi-reciprocal reflective electrical voltage sensing system of the present invention; - first polarization maintaining circulator, 2-second polarization maintaining circulator, 3-collimator, 4-electro-optical crystal, 5-antireflection coating, 6-reflecting film, 7-electrode, 8-light source, 9-ring , 10-Y Waveguide Modulator, 11-Polarizing Beam Splitter (hereinafter referred to as PBS), 12-to-Optical Converter, 13-Analog-to-Digital Converter, 14-Digital Signal Processing Unit, 15-Digital-to-Analog Converter, 16 - Drive circuit, 17-square wave drive circuit. detailed description

The quasi-reciprocal reflective optical voltage sensing unit of the present invention and its sensing system will be further described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the quasi-reciprocal reflective optical voltage sensing unit of this example includes two polarization maintaining circulators (ie, the first polarization maintaining circulator 1 and the second polarization maintaining circulator 2) and the sensing head. . The first polarization maintaining circulator 1 is provided with a first pigtail & a second pigtail b and a third pigtail c, and the first pigtail a and the second pigtail b are symmetrically connected to the first polarization maintaining circulator 1 On both sides, the third pigtail c is connected to the lower end of the first polarization maintaining circulator 1 and disposed at 90° to the pigtails a, b. Similarly, the second polarization maintaining circulator 2 is provided with the first pigtail a ', the second pigtail b' and the third pigtail c', the first pigtail a' and the second pigtail b' are symmetrically connected to both sides of the second polarization maintaining circulator 2, and the third pigtail c' is connected At the lower end of the second polarization maintaining circulator 2 and at 90° with the pigtails a', b'; two orthogonal linearly polarized lights are transmitted along the second pigtail b of the first polarization maintaining circulator 1 to the transmission In the sensing unit, the third pigtail c of the first polarization maintaining circulator 1 and the first pigtail a' of the second polarization maintaining circulator 2 are welded at an angle of 0° to form a branch I, the first polarization maintaining circulator 1 The first pigtail a and the third pigtail c' of the second polarization maintaining circulator 2 are welded at a 90° angle to form a branch II, and the second pigtail b' of the second polarization maintaining circulator 2 and the tail of the sensing head Fiber fusion. The pigtail of the above sensing head and the first pigtail, the second pigtail and the third pigtail of the two polarization maintaining circulators are all polarization-maintaining fibers.

The optical transmission direction of this example is as follows: When two polarization-maintaining circulators with the same structure are connected, only the connection mode as shown in Fig. 1 can realize the transmission mode and function of this example, namely: the first polarization-maintaining circulator The third pigtail c of 1 is welded to the first pigtail a' of the second polarization maintaining circulator 2, the first pigtail a of the first polarization maintaining circulator 1 and the third tail of the second polarization maintaining circulator 2 The fiber c' 90° is welded, so that the light transmission of b→c→a,→b,→c,→a→b can be realized.

The sensing head can be made of an insulating material and has good insulation performance, and includes a collimator 3 (a collimating lens can be used) and an electro-optic crystal 4, and the front end surface (ie, the light incident surface) of the electro-optic crystal 4 is plated with antireflection. The film 5, the rear end surface of the electro-optic crystal 4 (ie, the side opposite to the light incident surface) is plated with a reflective film 6, and the collimator 3 is fixed to the side of the electro-optical crystal 4 coated with the antireflection film, and the light of the collimator A pigtail that is welded to the second pigtail of the second polarization maintaining circulator 2 is connected to the incident surface; the upper and lower end faces of the electro-optic crystal 4 are also respectively mounted with electrodes 7. The electrode is for sensing the potential in the electric field and adopts lateral modulation, i.e., the direction of the electric field applied to the electro-optic crystal 4 is perpendicular to the direction of light propagation.

The working principle of the quasi-reciprocal reflective optical voltage sensing unit is: The two orthogonal linearly polarized lights emitted from the optical path structure are respectively transmitted along the X-axis and the Y-axis of the polarization-maintaining fiber, and pass through the first polarization-maintaining circulator 1 to enter the second polarization-maintaining circulator 2 after the branch I, and then pass through the sensor. The collimator 3 undergoes collimation and beam expansion and enters the electro-optic crystal 7; in the electric field, the electro-optical crystal induces a potential difference through the upper and lower surfaces of the gas. The electro-optical crystal 7 generates an electro-optical effect under the action of an electric field, introducing a phase difference φ = 丄³ γ ₄₁ ί/ between the two orthogonal linearly polarized lights, wherein the length of the crystal in the direction of light propagation is the applied electric field λ d

The thickness of the crystal in the direction, ". is the refractive index of the crystal, γ ₄₁ is the electro-optic coefficient of the crystal, and is the voltage applied to the crystal. The two orthogonal linearly polarized lights are reflected by the reflective film 7 on the surface of the electro-optical crystal and then passed through the electro-optic Crystal 4, the total phase difference of 2φ is obtained cumulatively. After output from the collimator 3 of the sensor, it enters the second polarization maintaining circulator 3, and propagates along the branch II. Since the optical fiber in the branch II is 90° welded, two When the orthogonal linearly polarized light passes through the branch, the respective polarization directions are rotated by 90°. At this time, the orthogonal linearly polarized light propagating along the X-axis of the polarization-maintaining fiber is propagated along the paraxial axis of the polarization-maintaining fiber. The orthogonal linearly polarized light propagating along the paraxial axis of the polarization-maintaining fiber becomes the X-axis propagation along the polarization-maintaining fiber, that is, the mode interchange of two orthogonal linearly polarized lights is realized; the two orthogonal linear polarizations undergoing mode interchange The light is then output through the first polarization maintaining circulator 1 and then passed through the optical path structure, and finally detected by the photoelectric converter. Since the length of each pigtail is not long, the phase difference introduced by the pigtail is small, in this example, Ignore (ie adjust the length of the polarization-maintaining fiber Two orthogonal linearly polarized beams so that the optical path difference before and after the mode interchange is zero), the light thus returned only carries electro-optical effect a phase difference caused by the electro-optic crystal.

This example also proposes a quasi-reciprocal reflective optical voltage sensing system that can be introduced into a mature digital closed-loop detection technique (through the circuit portion shown in Figure 3) through a quasi-reciprocal reflective optical path. The detection of the signal improves the dynamic range and response sensitivity of the sensing unit and the entire system. The detailed structure is as follows:

The sensing system includes, in addition to the sensing unit as described above, an optical path portion and a circuit portion disposed in the secondary chassis; the light emitted from the light source is divided into two orthogonal linearly polarized lights through the optical path portion, and the polarization maintaining is performed. The optical fiber is transmitted to the sensing unit; the sensing unit generates a total phase difference of 2 under the action of the electric field, and the vibration directions of the two linearly polarized lights are respectively rotated by 90° to realize the mode interchange; returning from the sensing unit The two bundles of linearly polarized light are transmitted back to the optical path portion through the polarization maintaining fiber for interference, and then the circuit portion detects the interference light intensity signal and performs signal processing to form a digital signal output.

As shown in FIG. 2, the optical path portion is mainly composed of a light source 8, a circulator 9, a Υ waveguide modulator 10, and a PBS 11 composition. The working principle is as follows: The light emitted by the light source 8 passes through the circulator 9 and enters the Y-waveguide modulator 10; the Y-waveguide modulator, also known as the integrated optical phase modulator, is a multifunctional device, consisting of a Y-beam splitter and The two phase modulators are used, and the Y-waveguide modulator can make the mechanism of the optical path portion more compact, reduce the volume of the secondary chassis, and operate more conveniently; the light entering the Y-waveguide modulator 10 is divided into two polarized lights, one of which After the beam is rotated by 90°, it enters the PBS together with the other beam. The two polarized lights are adjusted into two orthogonal linearly polarized lights and then passed through the polarization maintaining fiber (the polarization maintaining fiber is the second of the first polarization maintaining circulator 1). The pigtail b) is transmitted to the sensing unit; after passing through the sensing unit, the two orthogonal linearly polarized lights carrying the voltage information to be tested are returned along the original optical path, interference occurs in the Y-waveguide modulator 10, and then enters through the circulator The circuit part performs signal processing.

As shown in Fig. 3, the circuit portion is mainly composed of a photoelectric converter 12, an analog-to-digital converter 13, a digital signal processing unit 14, a digital-to-analog converter 15, and a corresponding driving circuit 16. The signal processing process is: the photoelectric converter 12 detects the interference light intensity signal carrying the voltage information to be tested from the optical path portion, and converts the signal into a voltage signal, and then transmits the signal to the analog-to-digital converter 13 to convert the voltage signal into discrete signals. The digital signal is sent to a digital signal processing unit 14, which is implemented by a DSP and an FPGA. The FPGA demodulates the discrete digital signal, integrates the demodulation result, generates a stepped step height, and then accumulates to form a digital staircase wave, which is sent to the digital-to-analog converter 15 to be converted into an analog staircase wave, and passes through the driving circuit 16 The Y-waveguide modulator 10 applied to the optical path portion implements closed-loop control; the FPGA also generates a modulated square wave, which is converted into an analog square wave by the square wave drive circuit 17, and superimposed and mixed with the analog square wave, and then applied to Y-waveguide modulator 10; In addition, the DSP smoothes the demodulated data of the FPGA, and forms a digital signal output by the FPGA. After that, the existing measurement equipment can be used to measure the voltage information to be measured, that is, the electric field size, by measuring the output digital signals of the two beams.

The quasi-reciprocal reflective optical voltage sensing unit of this example uses lateral modulation to induce an electric field signal by an electro-optic effect of an electro-optical crystal under an external electric field, and realizes two orthogonal linearly polarized lights by using two polarization maintaining circulators. The modes are interchanged, thereby forming a quasi-reciprocal reflective optical path structure, and the two orthogonal linearly polarized lights that are emitted only carry the phase modulation information of the electro-optical crystals. The optical voltage sensing unit has few optical components, simple structure, small volume and light weight; it is composed of an insulating material and has good insulation performance; the quasi-reciprocal reflective optical path can greatly improve the anti-interference ability in the long optical path transmission process, and The digital closed-loop signal detection technology in the optical current transformer can be utilized to improve the dynamic range and response sensitivity of the system. Finally, it should be noted that the above embodiments are only for explaining the technical solutions of the present invention and are not limited thereto, although the present invention will be described in detail with reference to the above embodiments, and those skilled in the art should understand that the present invention can still be The invention is to be construed as being limited by the scope of the appended claims.

Claims

Rights request

1. A quasi-reciprocal reflective optical voltage sensing unit. The sensing unit includes a sensing head, which is characterized in that: it also includes two polarization-maintaining circulators, each polarization-maintaining circulator is provided with a first tail fiber, second pigtail and third pigtail;

Two beams of orthogonal linearly polarized light are transmitted to the sensing unit through the second pigtail of the first polarization-maintaining circulator, and the third pigtail of the first polarization-maintaining circulator and the second pigtail of the second polarization-maintaining circulator. The first pigtail is welded at an angle of 0° to form branch I, and the first pigtail of the first polarization-maintaining circulator and the third pigtail of the second polarization-maintaining circulator are welded at an angle of 90° to form branch II; so The second pigtail of the second polarization-maintaining circulator is welded to the pigtail of the sensing head.

2. The quasi-reciprocal optical voltage sensing unit according to claim 1, characterized in that: the sensing head includes a collimator and an electro-optical crystal, and the light incident surface of the electro-optical crystal is plated with anti-reflection film, and the other side opposite to the light incident surface is coated with a reflective film, the collimator is fixedly connected to the side of the electro-optical crystal coated with an anti-reflection film, and the light incident surface of the collimator is connected to the sensor The pigtail of the head; electrodes are respectively installed on the upper and lower end surfaces of the electro-optical crystal.

3. The quasi-reciprocal reflective optical voltage sensing unit according to claim 1 or 2, characterized by:

The sensing head is enclosed in a shielded housing.

4. The quasi-reciprocal reflective optical voltage sensing unit according to claim 1, characterized in that: two beams of orthogonal linearly polarized light pass through the first polarization-maintaining circulator, branch I and the second polarization-maintaining circulator in sequence. Then enters the sensor head, obtains a total phase difference of 2 Φ and then outputs it from the sensor head;

The two beams of orthogonal linearly polarized light output from the sensor head pass through the second polarization-maintaining circulator, branch II and the first polarization-maintaining circulator in sequence and then are output; when passing through branch II, the two beams of orthogonal linearly polarized light are The polarization direction is rotated 90 degrees to achieve mode exchange of two orthogonal linearly polarized lights.

5. The quasi-reciprocal optical voltage sensing unit according to claim 4, characterized in that: under the action of the electric field, the sensing head causes two beams of orthogonal linearly polarized light to generate phases after passing through the sensing head. Difference

Φ, after the two beams of linearly polarized light pass through the sensor head again after reflection, the total phase difference is 2 Φ, and the phase difference is calculated by the following formula: Among them, Z is the length of the electro-optic crystal in the direction of light propagation, is the thickness of the electro-optic crystal in the direction of the external electric field, "." is the refractive index of the electro-optic crystal, γ ₄₁ is the electro-optic coefficient of the electro-optic crystal, and is the voltage applied to the electro-optic crystal.

6. The quasi-reciprocal optical voltage sensing unit according to claim 1, characterized in that: the first pigtail, the second pigtail and the third pigtail of the two polarization-maintaining circulators and the sensing The pigtails at the head are all made of polarization-maintaining optical fiber.

7. A quasi-reciprocal reflective optical voltage sensing system, characterized in that the sensor includes the sensing unit according to any one of claims 1-6, and also includes an optical path part and a circuit part placed in a secondary chassis ; The light emitted from the light source is divided into two bundles of orthogonal linearly polarized light through the optical path part, and is transmitted to the sensing unit through the polarization-maintaining fiber; The sensing unit generates a total phase difference of 2^ under the action of the electric field and reflection, And the vibration directions of the two linearly polarized lights are rotated by 90% respectively to realize their mode interchange; the two linearly polarized lights returned from the sensing unit are transmitted back to the optical path part through the polarization-maintaining fiber for interference, and then the interference is detected by the circuit part After receiving the light intensity signal and performing signal processing, a digital signal output is formed.

8. The quasi-reciprocal optical voltage sensing system according to claim 7, characterized in that: the optical path part includes a light source, a circulator, a Y waveguide modulator and a polarizing beam splitter, emitted from the light source The light enters the Υ waveguide modulator through the circulator, which splits the light into two beams of polarized light. One beam is rotated 90° and then enters the polarizing beam splitter together with the other beam. The two beams of polarized light are adjusted into two orthogonal lines. The polarized light is then transmitted to the sensing unit through the polarization-maintaining optical fiber; the two orthogonal linearly polarized lights returned by the sensing unit carry the voltage information to be measured, pass through the polarizing beam splitter again, and then enter the Υ waveguide modulator to interfere. After the interference light intensity signal passes through the circulator, it enters the circuit part for signal processing.

9. The quasi-reciprocal reflective optical voltage sensing system according to claim 7 or 8, characterized in that the circuit part includes:

A photoelectric converter is used to detect the interference light intensity signal emitted by the optical path part, convert the signal into an analog voltage signal, and send it to the analog-to-digital converter;

Analog-to-digital converter, used to convert analog voltage signals into discrete digital signals and then send them to the digital signal processing unit;

The digital-to-analog converter converts the digital step wave generated by the digital signal processing unit into the analog step wave; the driving circuit drives the analog step wave to be applied to the Υ waveguide modulator of the optical path part; and The digital signal processing unit is used for data demodulation of digital signals. After integration processing, the step height of the step wave is generated, which is accumulated to form a digital step wave, and is sent to the digital-to-analog converter to be converted into an analog step wave through the drive circuit. The Y waveguide modulator is applied to the optical path part to achieve closed-loop control; the digital signal processing unit is also used to generate a modulated square wave, which is converted into an analog square wave through the square wave drive circuit, and then superimposed with the analog step wave , and then applied to the Y waveguide modulator of the optical path part; the digital signal processing unit is also used to smooth and filter the digital signal to form a digital signal output.

10. The quasi-reciprocal optical voltage sensing system according to claim 9, wherein the digital signal processing unit includes a digital signal processor (DSP) and a field programmable gate array (FPGA).