Optical Current Sensor Stress Line Birefringence Compensation Method Based on Crystal Split Interference and Peak Detection Circuit

Abstract

The present invention proposes a stress line birefringence compensation method for an optical current sensor based on crystal cleavage interference and peak detection circuit, aiming at the problem that stress line birefringence is generated in the magneto-optical thin film and transmission optical fiber due to temperature change and vibration, and it is difficult to separate and compensate because it is aliased with the Faraday magneto-optical rotation angle. The present invention realizes that the optical current sensor can linearly demodulate the Faraday magneto-optical rotation angle based on crystal cleavage interference; when there is stress line birefringence, the output of the optical current sensor is the linear superposition of the Faraday magneto-optical rotation angle and the stress line birefringence; the peak detection circuit is used to determine the peak value of the alternating current to be measured. At this time, the Faraday magneto-optical rotation angle is 90°. The difference between the output signal of the optical current sensor and the Faraday magneto-optical rotation angle is the stress line birefringence, which can be detected and compensated.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage measurement, and particularly relates to a stress line birefringence compensation method for an optical current sensor based on crystal cleavage interference and a peak detection circuit. Background Art

[0002] An optical current sensor is a type of electronic current transformer. Compared with traditional electromagnetic current transformers, it has advantages such as fast response speed, no transient magnetic saturation, good insulation performance, and wide operating frequency band, and has good application prospects. Existing optical current sensors mostly achieve indirect measurement of primary current based on Malus' law. Affected by factors such as temperature drift and vibration, random stress line birefringence occurs in magneto-optical materials and transmission optical fibers, which is aliased with the Faraday magneto-optic rotation angle, seriously damaging the measurement accuracy and stability of the sensor.

[0003] To solve the problem of stress linear birefringence in optical current sensors, some scholars have proposed heating the optical fiber to a high temperature and then slowly cooling it to eliminate the line birefringence in the sensitive optical fiber; or using the matrix optics method to establish a mathematical model of stress line birefringence, analyzing the influence of line birefringence through simulation experiments, and realizing intelligent analysis of error influence; there are also scholars who have introduced a BP neural network compensation method with generalization ability, strong universality, and high precision to compensate for the stress line birefringence effect of optical current transformers. However, the effects of the above methods are not ideal, and stress line birefringence is still one of the key problems restricting the practical application of optical current sensors for many years. Summary of the Invention

[0004] Aiming at the problem that temperature changes and vibration generate stress line birefringence in magneto-optical thin films and transmission optical fibers, which is aliased with the Faraday magneto-optic rotation angle and difficult to separate and compensate.

[0005] Based on crystal cleavage interference, the present invention enables an optical current sensor to linearly demodulate the Faraday magneto-optic rotation angle; when stress line birefringence exists, the output of the optical current sensor is a linear superposition of the Faraday magneto-optic rotation angle and stress line birefringence; a peak detection circuit is used to determine the peak value of the alternating current to be measured. At this time, the Faraday magneto-optic rotation angle is 90°, and the difference between the output signal of the optical current sensor and the Faraday magneto-optic rotation angle is the stress line birefringence, which can be detected and compensated.

[0006] In the solution of the present invention, the optical current sensor is based on a linear measurement mode, and can extract and compensate the stress-induced birefringence at the peak moment of the alternating current. The optical current sensor can linearly demodulate the Faraday magneto-optical rotation angle. When there is stress-induced birefringence, its output result is the linear superposition of the Faraday magneto-optical rotation angle and the stress-induced birefringence. According to the Faraday magneto-optical effect, when the measured alternating current reaches the peak, the Faraday magneto-optical rotation angle of the magneto-optical material is a fixed value (90°). At this time, the difference between the output signal of the optical current sensor and the Faraday magneto-optical rotation angle is the stress-induced birefringence. By using the peak detection circuit to determine the peak moment of the measured alternating current, the stress-induced birefringence can be detected and eliminated.

[0007] The technical solution adopted by the present invention to solve its technical problems is:

[0008] A method for compensating stress-induced birefringence of an optical current sensor based on crystal cleavage interference and peak detection circuit, characterized in that: based on crystal cleavage interference, the optical current sensor linearly demodulates the Faraday magneto-optical rotation angle; when there is stress-induced birefringence, the output of the optical current sensor is the linear superposition of the Faraday magneto-optical rotation angle and the stress-induced birefringence; using the peak detection circuit to determine the peak of the measured alternating current, at this time the Faraday magneto-optical rotation angle is 90°, and the difference between the output signal of the optical current sensor and the Faraday magneto-optical rotation angle is the stress-induced birefringence, which is detected and compensated.

[0009] The specific implementation scheme includes: after the primary wire (1) passes through the measured alternating current, a magnetic field is generated in the magnetic collecting ring (2). The laser (3) passes through the first magnetic conductive plate (4), and then passes through the polarizer (5) to obtain linearly polarized light. The linearly polarized light passes through the magneto-optical thin film (6), and under the action of the magnetic field, the polarization plane of the polarized light rotates, and the rotation angle is the Faraday magneto-optical rotation angle;

[0010] Temperature changes and vibrations generate stress-induced birefringence in the magneto-optical thin film and the transmission optical fiber, and are superimposed on the Faraday magneto-optical rotation angle; the linearly polarized light becomes circularly polarized light after passing through the quarter-wave plate (7), and is decomposed into two linearly polarized lights: o light and e light; after passing through the crystal cleavage (8) and the analyzer (9), an interference fringe image (11) with alternating bright and dark fringes is obtained; using the peak detection circuit (12) to determine the peak moment of the measured alternating current, according to the Faraday magneto-optical effect, at this time the Faraday magneto-optical rotation angle is 90°, which corresponds to the first spot image (13); the difference between the output result of the optical current sensor and the Faraday magneto-optical rotation angle is the stress-induced birefringence, which corresponds to the second spot image (14).

[0011] The present invention and its preferred solution specifically solve the problem that temperature changes and vibrations generate stress-induced birefringence in the magneto-optical thin film and the transmission optical fiber, and are difficult to separate and compensate when mixed with the Faraday magneto-optical rotation angle. Brief Description of the Drawings

[0012] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0013] Figure 1 It is the schematic diagram of the implementation of the stress line birefringence compensation method for the optical current sensor based on crystal cleavage interference and peak detection circuit in the embodiment of the present invention;

[0014] Figure 2 It is the interference image diagram with alternating bright and dark fringes in the embodiment of the present invention;

[0015] Figure 3 It is different in the embodiment of the present invention It is the simulation image diagram of bright and dark interference fringes at

[0016] Figure 4 It is the schematic diagram of the peak detection circuit in the embodiment of the present invention.

[0017] Among them, 1 is the primary wire, 2 is the magnetic flux concentrator, 3 is the laser, 4 is the first magnetic conductive plate, 5 is the polarizer, 6 is the magneto-optical thin film, 7 is the quarter-wave plate, 8 is the crystal cleavage, 9 is the analyzer, 10 is the second magnetic conductive plate, 11 is the bright and dark fringe spot output by the optical current sensor, 12 is the peak detection circuit, 13 is the bright and dark fringe spot corresponding to the Faraday magneto-optical rotation angle of 90°, and 14 is the bright and dark fringe spot corresponding to the stress line birefringence. Specific Embodiments

[0018] To make the features and advantages of this patent more obvious and understandable, specific embodiments are given below and described in detail as follows:

[0019] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0020] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] The following further specifically introduces the solution of this embodiment in conjunction with the drawings:

[0022] As Figure 1As shown. After the primary wire (1) passes through the alternating current to be measured, a magnetic field is generated in the magnetic flux concentrating ring (2). The laser (3) passes through the first magnetic conductive plate (4), and then passes through the polarizer (5) to obtain linearly polarized light. The linearly polarized light passes through the magneto-optical thin film (6), and under the action of the magnetic field, the polarization plane of the polarized light rotates, and the rotation angle is the Faraday magneto-optical rotation angle. However, temperature changes and vibrations generate stress-induced birefringence in the magneto-optical thin film and the transmission optical fiber, and are superimposed on the Faraday magneto-optical rotation angle. The linearly polarized light becomes circularly polarized light after passing through the quarter-wave plate (7), and it can be decomposed into two linearly polarized lights: o-light and e-light. After passing through the crystal cleavage (8) and the analyzer (9), an interference fringe image (11) with alternating bright and dark fringes is obtained. The peak detection circuit (12) can be used to determine the peak moment of the alternating current to be measured. According to the Faraday magneto-optical effect, at this time, the Faraday magneto-optical rotation angle is 90°, and the corresponding spot image is (13). The difference between the output result of the optical current sensor and the Faraday magneto-optical rotation angle (90°) is the stress-induced birefringence, and the corresponding spot image is (14).

[0023] Verify the compensation principle of stress-induced birefringence in this embodiment based on the Jones matrix.

[0024] The included angle between the optical axis directions of the polarizer and the analyzer is 90°; the slow axis direction of the quarter-wave plate is consistent with the optical axis direction of the polarizer, and the fast axis direction is consistent with the optical axis direction of the analyzer; the fast and slow axis directions of the crystal cleavage are both at an angle of 45° with the fast axis direction of the quarter-wave plate

[0025] The linearly polarized light formed after the laser is polarized passes through the magneto-optical thin film, and its polarization plane rotates under the action of the magnetic field by angle, which is expressed by the Jones matrix E as:

[0026]

[0027] Taking into account the stress-induced birefringence γ generated by temperature drift and vibration in the magneto-optical thin film and the transmission optical fiber, the above formula becomes:

[0028]

[0029] The linearly polarized light then passes through the quarter-wave plate, and the Jones matrix is:

[0030]

[0031] At this time, the linearly polarized light becomes circularly polarized light, which can be decomposed into o-light and e-light. There is a fixed phase difference between the two beams of light, and the vibration planes are perpendicular to each other. Assuming that the cleavage angle of the crystal cleavage is Taking the tip of the crystal cleavage as the coordinate origin, the thickness d at x is:

[0032]

[0033] Due to the birefringence of the crystal, the optical path difference introduced by the o-ray (refractive index n o ) and the e-ray (refractive index n e ) at the x position of the crystal cleavage is:

[0034]

[0035] Then the displacement Δx of the interference fringes can be calculated as:

[0036]

[0037] Let the change in optical path difference Δδ be equal to the wavelength λ of the incident light, and the full-wave travel Δx λ is:

[0038]

[0039] Calculate the phase difference ρ according to the optical path difference in Equation (5):

[0040]

[0041] It can be seen from the optical path design that the fast and slow axes of the crystal cleavage form an angle of 45° with the vertical direction, then:

[0042]

[0043] After passing through the analyzer with an azimuth angle of 90°, the Jones matrix is:

[0044]

[0045] At this time, the light intensity distribution is:

[0046]

[0047] In summary, the outgoing light intensity distribution is related to the value of ρ + 2θ + 2γ. When the value of ρ + 2θ + 2γ is an even multiple of π, the cosine function value is 1, and the calculated outgoing light intensity is 0; when the value of ρ + 2θ + 2γ is an odd multiple of π, the cosine function value is -1, then the calculated maximum light intensity value is 1, and the outgoing light intensity is distributed according to this rule, forming an interference image with alternating bright and dark fringes, as Figure 2 shown. The distance between adjacent two interference fringes is the full-wave travel length.

[0048] Taking the tip of the crystal cleavage as an example (here ρ = 0), when changes, in order to satisfy the condition that ρ + 2θ + 2γ is 0, the position of the first dark fringe will shift. At this time the relationship between

[0049]

[0050] It can be seen that it satisfies a linear relationship with the displacement of the light spot image. Therefore, the first dark fringe is taken as the analysis object. By measuring its displacement and performing conversion, direct and linear measurement can be achieved. A mathematical model of the crystal split optical path is established by the Jones matrix, and the interference fringes under different Faraday rotation angles are simulated. The results are as Figure 3 shown. As changes, the light spot image undergoes linear translation. By measuring the real-time offset Δx of the bright fringe with a four-quadrant detector,

[0051] the result of the linear measurement of the optical current sensor can be calculated as a linear superposition of and γ. According to the Faraday magneto-optical effect, the measured magnetic field H and satisfy:

[0052] θ = VHL (13) where V is the Verdet constant and L is the optical path length of the magneto-optical material along the magnetic field direction. When H reaches the peak Since is known, γ can be detected and compensated at this moment.

[0053] In this embodiment, a peak detection circuit is used to determine the peak moment of the measured alternating current. The preferred peak detection circuit is as Figure 4 shown. The principle is as follows: Before the peak of the alternating current arrives, the amplitude of the input signal rises, controlling the sample-and-hold circuit to work in the sampling mode, and the output follows the input; after the peak arrives, the input signal starts to decline, controlling the sample-and-hold circuit to work in the hold mode, and the output holds the peak; the peak is maintained until the trough, and the input signal starts to rise again, and the circuit switches from the hold mode to the sampling mode again, waiting to detect the next peak.

[0054] Combined with the above design, this embodiment provides a specific test example:

[0055] The laser uses a single transverse mode frequency-stabilized laser light source with a light wave wavelength of 808 nm, a wavelength stability of ±0.02 nm, a power of 30 mW, and a light intensity stability of ±1%; the magneto-optical thin film is of the Bi-Gd-YIG type; the cleavage angle of the crystal used is 1°; a four-quadrant detector is used to collect and calculate the displacement of the spot image; a high and low temperature alternating damp heat test chamber is used to provide different temperature environments with a temperature range of -40°C to 85°C and a temperature fluctuation of ±0.5°C. In the example, the optical path of the optical current sensor is placed in the inner chamber of the temperature chamber, and a temperature cycle experiment is carried out in the range of -40°C to 85°C. A peak detection circuit is used to determine the peak value of the current to be measured in each cycle, so as to calculate the stress line birefringence and perform compensation. Finally, a calibrator is used to record the basic accuracy of the optical current sensor, as shown in Table 1. Under the temperature cycle condition, the optical current sensor can meet the accuracy requirement of class 0.5.

[0056] Table 1 Experimental data of basic accuracy

[0057] Rated current percentage / % Ratio error / % Phase angle error / (′) 80 0.354 －21.97 100 0.415 －26.72 120 0.438 21.81

[0058] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0059] As described above, it is only a preferred embodiment of the present invention, and it is not a limitation of the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention shall still fall within the protection scope of the technical solution of the present invention.

[0060] This patent is not limited to the above best implementation manner. Anyone inspired by this patent can obtain various other forms of the stress line birefringence compensation method of the optical current sensor based on crystal cleavage interference and peak detection circuit. All equal changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by this patent.

Claims

1. An optical current sensor stress line birefringence compensation method based on crystal cleavage interference and peak detection circuit, characterized in that: Based on crystal cleavage interference, linear demodulation of the Faraday magneto-optic rotation angle can be achieved; when there is stress-induced birefringence, the output of the optical current sensor is a linear superposition of the Faraday magneto-optic rotation angle and the stress-induced birefringence; the peak detection circuit is used to determine the peak value of the alternating current to be measured. At this time, the theoretical value of the Faraday magneto-optic rotation angle is 90°. The difference between the output signal of the optical current sensor and the Faraday magneto-optic rotation angle is the stress-induced birefringence, which is detected and compensated. After the primary wire (1) passes through the alternating current to be measured, a magnetic field is generated in the magnetic flux concentrator (2); the laser (3) passes through the first magnetic plate (4), and then passes through the polarizer (5) to obtain linearly polarized light; the linearly polarized light passes through the magneto-optic thin film (6), and under the action of the magnetic field, the polarization plane of the polarized light rotates, and the rotation angle is the Faraday magneto-optic rotation angle. Temperature changes and vibrations generate stress-induced birefringence in the magneto-optic thin film and the transmission optical fiber, which is superimposed on the Faraday magneto-optic rotation angle; the linearly polarized light becomes circularly polarized light after passing through the quarter-wave plate (7), and it is decomposed into two linearly polarized lights: the o-light and the e-light; after passing through the crystal cleavage (8) and the analyzer (9), an interference fringe image (11) with alternating bright and dark fringes is obtained; the peak detection circuit (12) is used to determine the peak moment of the alternating current to be measured. According to the Faraday magneto-optic effect, the Faraday magneto-optic rotation angle is 90° at this time, which corresponds to the first spot image (13); the difference between the output result of the optical current sensor and the Faraday magneto-optic rotation angle is the stress-induced birefringence, which corresponds to the second spot image (14).

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