An AC zero-crossing compensation method for stress line birefringence of optical current sensor

Abstract

The present invention provides an AC zero-crossing compensation method for stress line birefringence in an optical current sensor. The method comprises the following steps: Step S1: Light emitted by a light source passes through a polarizer to form linearly polarized light. Under the action of a magnetic field to be measured, the linearly polarized light passes through a magneto-optical film and forms a Faraday magneto-rotation angle, which is then analyzed by a Newton circular polarization grating. Step S2: When the environment in which the optical current sensor is located experiences temperature drift or vibration, the Newton circular polarization grating converts the Faraday magneto-rotation angle and the stress line birefringence generated by the optical element and the magneto-optical film into synchronous rotation of a light spot image, and outputs a linear superposition result of the Faraday magneto-rotation angle and the stress line birefringence. Step S3: When an AC current passes through zero, the current magnetic field is zero, causing the Faraday magneto-rotation angle to be zero. At this time, the output of the Newton circular polarization grating is the interference value corresponding to the stress line birefringence caused by the current temperature drift or vibration. The present invention can extract and compensate for the stress line birefringence when the AC current passes through zero.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage measurement, in particular to an AC zero-crossing compensation method for stress line birefringence of an optical current sensor. Background Art

[0002] Optical current sensors based on the Faraday magneto-optical effect offer advantages such as passive operation, excellent insulation performance, wide response bandwidth, and strong anti-interference capabilities. They meet the development needs of my country's smart grid and hold promising prospects. However, temperature drift and vibration can easily cause stress line birefringence in the magneto-optical materials and transmission fibers of optical current sensors. This stress line birefringence, often several or even dozens of times greater than the Faraday magneto-optical rotation angle, significantly quenches the optical rotation angle, degrading the measurement accuracy and long-term reliability of optical current sensors. This has been a bottleneck restricting their practical application for many years, and has been dubbed a "world problem" by the industry.

[0003] Existing optical current sensors, based on Malus's law, achieve approximately linear measurement of the Faraday magneto-optical rotation angle by detecting the output light intensity. This measurement mode suffers from optical power dependence and nonlinear measurement, leading to the mixing of stress line birefringence and the Faraday magneto-optical rotation angle, making separation and compensation difficult. This is the crux of the problem of stress line birefringence, which has not been effectively solved. Summary of the Invention

[0004] The present invention provides an AC zero-crossing compensation method for stress line birefringence of an optical current sensor, which can extract and compensate for the stress line birefringence when the AC current passes through zero.

[0005] The present invention adopts the following technical solutions.

[0006] An AC zero-crossing compensation method for stress line birefringence in an optical current sensor is disclosed. The method is used to detect interference corresponding to stress line birefringence caused by temperature drift or vibration of an optical fiber or magneto-optical film in an optical current sensor based on the Faraday magneto-optical effect. The compensation method comprises the following steps:

[0007] Step S1: Light emitted by a light source passes through a polarizer to form linearly polarized light. Under the action of a magnetic field to be measured, the linearly polarized light passes through a magneto-optical film, and its polarization plane rotates, which is the Faraday magneto-optical rotation angle. The linearly polarized light is then analyzed by a Newton circular polarization grating.

[0008] Step S2: When the environment where the optical current sensor is located experiences temperature drift or vibration, the Newton circular polarization grating converts the Faraday magneto-optical rotation angle and the stress line birefringence generated by the optical element and the magneto-optical film into a synchronous rotation of the spot image, and outputs a linear superposition result of the Faraday magneto-optical rotation angle and the stress line birefringence;

[0009] Step S3: When the AC current passes through zero, the current magnetic field is zero, causing the Faraday magneto-rotation angle to be zero. At this time, the output result of the Newton circular polarization grating is the interference amount corresponding to the stress line birefringence caused by the current temperature drift or vibration.

[0010] In step S3, the zero-crossing detection circuit (7) is used to detect the zero-crossing of the alternating current.

[0011] The zero-crossing detection circuit includes a dual-input four-AND gate circuit 7408N and an integrated circuit LM339. The two comparators of the integrated circuit LM339 are U2A and U2B. V i As the input signal of the zero-crossing detection circuit, V o is the output signal of the zero-crossing detection circuit, V2 and V3 are the upper limit and lower limit of the comparator reference voltage respectively; when the zero-crossing detection circuit is working, within one cycle, when V i >V2, V o Is low level; when V3<V i <V2,V o is high level; when V i <V3, V o It is at low level, and the zero-crossing point detection of AC current is achieved by adjusting the values of V2 and V3.

[0012] The compensation method compensates for the interference measured in step S3.

[0013] The linearly polarized light is generated by a laser (1) and a polarizer.

[0014] In step S2 and step S3, the separation effect of stress line birefringence is calculated based on the Jones matrix. The method is as follows: Assume that the incident light from the laser source passes through the polarizer to obtain linearly polarized light E in , the formula is as follows;

[0015]

[0016] Where A represents the input light intensity;

[0017] When linearly polarized light passes through the magneto-optical film, the polarization plane of the linearly polarized light rotates under the action of the magnetic field to be measured. The rotation angle is the Faraday magneto-optical rotation angle α. The transmission matrix J E It can be expressed as:

[0018]

[0019] Affected by temperature changes and vibrations, stress line birefringence γ is generated in the magneto-optical film and the transmission optical fiber. E Rewrite as J r :

[0020]

[0021] Where α' = α + γ is the rotation angle of the polarization plane of linearly polarized light when taking into account stress linear birefringence;

[0022] The Jones vector of linearly polarized light after passing through the magneto-optical film is:

[0023]

[0024] After the vibration components of the output light vector E1 in the x and y directions are synthesized, a beam of linearly polarized light is obtained, whose amplitude is still A and the polarization azimuth θ is:

[0025]

[0026] The θ and α' of E1 satisfy the linear relationship: θ = α' Formula 6;

[0027] After being demodulated by a Newton circular polarization grating, E1 is converted into an annular light spot. The center of the dark pattern corresponds to the polarization plane of E1 and rotates synchronously with the change of α'. By measuring the rotation angle of the dark pattern center of the annular light spot, θ can be directly measured.

[0028] Since: θ=α′=α+γFormula 7;

[0029] Therefore, the result of the linear measurement of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the magnetic field H to be measured and α satisfy:

[0030] α=VHL M Formula 8;

[0031] Where V is the Verdet constant, L M is the length of the optical path of the magneto-optical material along the direction of the magnetic field;

[0032] When H=0, α=0, that is, when the AC current passes through zero, the output signal of the optical current sensor is α'=γ, and the angle corresponding to the dark pattern position of the annular light spot is γ. The AC zero-crossing compensation method detects γ and compensates for it by positioning the light spot at this moment.

[0033] In the method, the rotation angle of the annular light spot is detected by a four-quadrant detector (5), so as to realize direct measurement and linear measurement of the rotation angle of the polarization plane of linearly polarized light.

[0034] To address the problem of stress line birefringence generated in the magneto-optical film and transmission optical fiber of an optical current sensor due to temperature changes and vibrations, which has a harmful quenching effect on the Faraday magneto-optical rotation angle of the optical current sensor, the present invention is based on a linear measurement mode. It can extract and compensate for the stress line birefringence when the AC current passes through zero, thereby improving the measurement accuracy and long-term reliability of the optical current sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0036] Attachment Figure 1 It is a schematic diagram of the principle of the present invention;

[0037] Attachment Figure 2 Schematic diagram of the experiment of the optical current sensor outputting a light spot under the method of the present invention;

[0038] Attachment Figure 3 This is a schematic diagram of the principle of the zero-crossing detection circuit;

[0039] Attachment Figure 4 It is a schematic diagram of the structure of Newton's circular polarization grating;

[0040] In the figure: 1 is a laser, 2 is a polarizer, 3 is a magneto-optical film, 4 is a Newton circular polarization grating, 5 is a four-quadrant detector, 6 is an annular light spot output by an optical current sensor, 7 is a zero-crossing detection circuit, 8 is an annular light spot corresponding to when the Faraday magneto-optical rotation angle is zero, and 9 is an annular light spot corresponding to stress line birefringence. DETAILED DESCRIPTION

[0041] As shown in the figure, an AC zero-crossing compensation method for stress line birefringence of an optical current sensor is used for detecting the interference corresponding to stress line birefringence caused by temperature drift or vibration of the optical fiber and magneto-optical film of the optical current sensor. The compensation method includes the following steps:

[0042] Step S1: Light emitted by a light source passes through a polarizer to form linearly polarized light. Under the action of a magnetic field to be measured, the linearly polarized light passes through a magneto-optical film, and its polarization plane rotates, which is the Faraday magneto-optical rotation angle. The linearly polarized light is then analyzed by a Newton circular polarization grating.

[0043] Step S2: When the environment where the optical current sensor is located experiences temperature drift or vibration, the Newton circular polarization grating converts the Faraday magneto-optical rotation angle and the stress line birefringence generated by the optical element and the magneto-optical film into a synchronous rotation of the spot image, and outputs a linear superposition result of the Faraday magneto-optical rotation angle and the stress line birefringence;

[0044] Step S3: When the AC current passes through zero, the current magnetic field is zero, causing the Faraday magneto-rotation angle to be zero. At this time, the output result of the Newton circular polarization grating is the interference amount corresponding to the stress line birefringence caused by the current temperature drift or vibration.

[0045] In step S3, the zero-crossing detection circuit 7 is used to detect the zero-crossing of the AC power.

[0046] The zero-crossing detection circuit includes a dual-input four-AND gate circuit 7408N and an integrated circuit LM339. The two comparators of the integrated circuit LM339 are U2A and U2B. V i As the input signal of the zero-crossing detection circuit, V o is the output signal of the zero-crossing detection circuit, V2 and V3 are the upper limit and lower limit of the comparator reference voltage respectively; when the zero-crossing detection circuit is working, within one cycle, when V i >V2, V o Is low level; when V3<V i <V2,V o is high level; when V i <V3, V o It is at low level, and the zero-crossing point detection of AC current is achieved by adjusting the values of V2 and V3.

[0047] The compensation method compensates for the interference measured in step S3.

[0048] The linearly polarized light is generated by the laser 1 and the polarizer.

[0049] In step S2 and step S3, the separation effect of stress line birefringence is calculated based on the Jones matrix. The method is as follows: Assume that the incident light from the laser source passes through the polarizer to obtain linearly polarized light E in , the formula is as follows;

[0050]

[0051] Where A represents the input light intensity;

[0052] When linearly polarized light passes through the magneto-optical film, the polarization plane of the linearly polarized light rotates under the action of the magnetic field to be measured. The rotation angle is the Faraday magneto-optical rotation angle α. The transmission matrix J E It can be expressed as:

[0053]

[0054] Affected by temperature changes and vibrations, stress line birefringence γ is generated in the magneto-optical film and the transmission optical fiber. E Rewrite as J r :

[0055]

[0056] Where α' = α + γ is the rotation angle of the polarization plane of linearly polarized light when taking into account stress linear birefringence;

[0057] The Jones vector of linearly polarized light after passing through the magneto-optical film is:

[0058]

[0059] After the vibration components of the output light vector E1 in the x and y directions are synthesized, a beam of linearly polarized light is obtained, whose amplitude is still A and the polarization azimuth θ is:

[0060]

[0061] The θ and α' of E1 satisfy the linear relationship: θ = α' Formula 6;

[0062] After being demodulated by a Newton circular polarization grating, E1 is converted into an annular light spot. The center of the dark pattern corresponds to the polarization plane of E1 and rotates synchronously with the change of α'. By measuring the rotation angle of the dark pattern center of the annular light spot, θ can be directly measured.

[0063] Since: θ=α′=α+γFormula 7;

[0064] Therefore, the result of the linear measurement of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the magnetic field H to be measured and α satisfy:

[0065] α=VHL M Formula 8;

[0066] Where V is the Verdet constant, L M is the length of the optical path of the magneto-optical material along the direction of the magnetic field;

[0067] When H=0, α=0, that is, when the AC current passes through zero, the output signal of the optical current sensor is α'=γ, and the angle corresponding to the dark pattern position of the annular light spot is γ. The AC zero-crossing compensation method detects γ and compensates for it by positioning the light spot at this moment.

[0068] In the method, the rotation angle of the annular light spot is detected by the four-quadrant detector 5 to achieve direct and linear measurement of the rotation angle of the polarization plane of linearly polarized light.

[0069] Example:

[0070] An AC zero-crossing compensation method for stress line birefringence of an optical current sensor is provided. Figure 1 As shown in Figure 1, the optical signal emitted by laser source 1 passes through polarizer 2 to produce linearly polarized light. This linearly polarized light passes through magneto-optical film 3, where the magnetic field causes the plane of polarization to rotate by an angle known as the Faraday magneto-optical rotation angle α. However, temperature fluctuations and vibrations generate stress linear birefringence γ in the magneto-optical film and transmission fiber. This is superimposed on α, causing the polarization plane of the output linearly polarized light to rotate by a total of α+γ.

[0071] In this method, linearly polarized light is demodulated by a Newton circular polarization grating 4 and converted into an annular light spot, which rotates synchronously with the change of α+γ. Finally, the rotation angle of the annular light spot is detected by a four-quadrant detector 5, thereby achieving direct and linear measurement of the rotation angle of the polarization plane of the linearly polarized light. According to the Faraday magneto-optical effect, when the AC current to be measured passes through zero, α is zero, and the output signal of the sensor is γ. The zero-crossing point of the current to be measured can be determined using the zero-crossing detection circuit 7. The center position of the dark pattern of the annular light spot 8 corresponding to α=0 is on the y-axis. At this time, the angle 9 corresponding to the dark pattern position of the annular light spot of the optical current sensor is γ. By positioning the light spot, γ can be detected and compensated, thereby achieving the purpose of eliminating γ.

[0072] In this example, the laser used is a single longitudinal mode laser with a wavelength of 808 nm; the magneto-optical film is of Bi-Gd-YIG type; the period of the Newton circular polarization grating is 150 nm, the height is 100 nm, the duty cycle is 0.5, the inner radius of the grating ring area is 3.2 mm, and the outer radius is 4 mm.

[0073] As attached Figure 4 As shown in the figure, a position sensitive detector is used to detect the displacement of the light spot. Its model is S3932, with a photosensitive area of 1×12mm, a wavelength response range of 760~1100nm, and a peak wavelength of 960nm.

[0074] Zero Crossing Detection Circuit Reference Figure 3 ; A high and low temperature alternating humidity test chamber is used to provide different temperature environments, with a temperature range of -40℃ to 85℃ and a temperature fluctuation of ±0.5℃.

[0075] In this embodiment, the optical path of the optical current sensor is placed in an incubator, and a temperature cycle experiment is performed within a range of -40°C to 85°C.

[0076] The zero-crossing point is detected by a zero-crossing detection circuit to determine the stress line birefringence introduced in each cycle and compensate for it. Finally, the basic accuracy of the optical current sensor is recorded by a calibrator, as shown in Table 1.

[0077] The data in the table show that the optical current sensor of this method can meet the accuracy requirement of level 0.5 under temperature cycling conditions.

[0078] Table 1 Basic accuracy experimental data

[0079]

[0080] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. An AC zero-crossing compensation method for stress line birefringence in an optical current sensor based on the Faraday magneto-optical effect is used to detect the interference corresponding to stress line birefringence caused by temperature drift or vibration in the optical fiber or magneto-optical film of the optical current sensor. The method is characterized by: The compensation method comprises the following steps: Step S1: Light emitted by a light source passes through a polarizer to form linearly polarized light. Under the action of a magnetic field to be measured, the linearly polarized light passes through a magneto-optical film, and its polarization plane rotates, which is the Faraday magneto-optical rotation angle. The linearly polarized light is then analyzed by a Newton circular polarization grating. Step S2: When the environment where the optical current sensor is located experiences temperature drift or vibration, the Newton circular polarization grating converts the Faraday magneto-optical rotation angle and the stress line birefringence generated by the optical element and the magneto-optical film into a synchronous rotation of the spot image, and outputs a linear superposition result of the Faraday magneto-optical rotation angle and the stress line birefringence; Step S3: When the AC current passes through zero, the current magnetic field is zero, causing the Faraday magneto-rotation angle to be zero. At this time, the output result of the Newton circular polarization grating is the interference amount corresponding to the stress line birefringence caused by the current temperature drift or vibration; the compensation method compensates for the interference amount measured in step S3; The linearly polarized light is generated by a laser and a polarizer; In step S2 and step S3, the separation effect of stress line birefringence is calculated based on the Jones matrix. The method is as follows: the incident light of the laser source is obtained by passing through the polarizer (2) to obtain linearly polarized light E in , the formula is as follows; Where A represents the input light intensity; When linearly polarized light passes through the magneto-optical film, the polarization plane of the linearly polarized light rotates under the action of the magnetic field to be measured. The rotation angle is the Faraday magneto-optical rotation angle α. The transmission matrix J E It can be expressed as: Affected by temperature changes and vibrations, stress line birefringence γ is generated in the magneto-optical film and the transmission optical fiber. E Rewrite as J r : Where α' = α + γ is the rotation angle of the polarization plane of linearly polarized light when taking into account stress linear birefringence; The Jones vector of linearly polarized light after passing through the magneto-optical film is: After the vibration components of the output light vector E1 in the x and y directions are synthesized, a beam of linearly polarized light is obtained, whose amplitude is still A and the polarization azimuth θ is: The θ and α' of E1 satisfy the linear relationship: θ = α' Formula 6; After being demodulated by a Newton circular polarization grating, E1 is converted into an annular light spot. The center of the dark pattern corresponds to the polarization plane of E1 and rotates synchronously with the change of α'. By measuring the rotation angle of the dark pattern center of the annular light spot, θ can be directly measured. Since: θ=α′=α+γ Formula 7; Therefore, the result of the linear measurement of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the magnetic field H to be measured and α satisfy: α=VHL M Formula 8; Where V is the Verdet constant, L M is the length of the optical path of the magneto-optical material along the direction of the magnetic field; When H=0, α=0, that is, when the AC current passes through zero, the output signal of the optical current sensor is α'=γ, and the angle corresponding to the dark pattern position of the annular light spot is γ. The AC zero-crossing compensation method detects γ and compensates for it by locating the light spot.

2. The AC zero-crossing compensation method for stress line birefringence of an optical current sensor according to claim 1, characterized in that: In step S3, the zero-crossing detection circuit (7) is used to detect the zero-crossing of the alternating current.

3. The AC zero-crossing compensation method for stress line birefringence of an optical current sensor according to claim 2, characterized in that: The zero-crossing detection circuit includes a dual-input four-AND gate circuit 7408N and an integrated circuit LM339. The two comparators of the integrated circuit LM339 are U2A and U2B. V i As the input signal of the zero-crossing detection circuit, V o is the output signal of the zero-crossing detection circuit, V2 and V3 are the upper and lower limits of the comparator reference voltage respectively; When the zero-crossing detection circuit works, within one cycle, when V i >V2, V o Is low level; when V3<V i <V2,V o is high level; when V i <V3, V o It is at low level, and the zero-crossing point detection of AC current is achieved by adjusting the values of V2 and V3.

4. The AC zero-crossing compensation method for stress line birefringence of an optical current sensor according to claim 1, characterized in that: In the method, the rotation angle of the annular light spot is detected by a four-quadrant detector (5), so as to realize direct measurement and linear measurement of the rotation angle of the polarization plane of linearly polarized light.

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