Stress line birefringence compensation method for optical voltage sensor based on S-wave plate and model-free adaptive iterative learning

Abstract

The present invention proposes a method for compensating stress line birefringence of an optical voltage sensor based on an S-wave plate and model-free adaptive iterative learning. The method addresses the problem that temperature changes and vibrations generate stress line birefringence in electro-optical crystals and transmission optical fibers, introduce additional phase delay, and are difficult to separate and compensate for together with the aliasing of electro-optical phase delay. The optical voltage sensor implemented based on the S-wave plate can linearly demodulate the electro-optical phase delay. When stress line birefringence exists, the output of the optical voltage sensor is a linear superposition of the electro-optical phase delay and the additional phase delay. The zero-point theorem is used to determine the zero-crossing moment of the AC voltage to be measured. At this time, the electro-optical phase delay is zero, and the output signal of the optical voltage sensor is the stress line birefringence. Based on the stress line birefringence of the previous several cycles, a model-free adaptive iterative learning method is used to obtain the learning rate of the stress line birefringence, which is used to calculate the additional phase delay of the next cycle and compensate for it.

Description

Technical Field

[0001] The present invention belongs to the technical field of high voltage measurement, and in particular relates to a stress line birefringence compensation method for an optical voltage sensor based on an S-wave plate and model-free adaptive iterative learning. Background Art

[0002] Voltage transformers are a crucial component of smart grid construction. Their safety, reliability, and accuracy are crucial for dispatching, metering, monitoring, and relay protection. Currently, electromagnetic and capacitive voltage transformers are widely used in power systems, but they suffer from high insulation costs, a narrow dynamic measurement range, and issues such as magnetic saturation and ferromagnetic resonance, posing a threat to the safety and reliability of power systems.

[0003] Optical voltage sensors use electro-optical crystals as their sensitive elements, eliminating the need for ferromagnetic materials and, in principle, avoiding problems such as ferromagnetic resonance and magnetic saturation. They utilize optical fiber to transmit voltage signals, achieving optical isolation between high and low voltages. These sensors offer advantages such as compact size, light weight, safety, and reliability, demonstrating promising application prospects. However, in engineering applications, electro-optical crystals and transmission optical fibers are susceptible to stress line birefringence due to factors such as temperature drift and vibration. This introduced additional phase delay, combined with electro-optical phase delay aliasing, is difficult to separate and compensate for, severely compromising the accuracy and stability of optical voltage sensor measurements and hindering their practical application. Summary of the Invention

[0004] Temperature changes and vibrations generate stress line birefringence in electro-optic crystals and transmission optical fibers, which introduces additional phase delays and is difficult to separate and compensate for together with the electro-optical phase delay aliasing.

[0005] The optical voltage sensor implemented using an S-wave plate can linearly demodulate electro-optical phase delay. When stress line birefringence is present, the output of the optical voltage sensor is a linear superposition of the electro-optical phase delay and the additional phase delay. The zero-point theorem is used to determine the zero-crossing moment of the AC voltage to be measured, at which point the electro-optical phase delay is zero, and the output signal of the optical voltage sensor is the stress line birefringence. Based on the stress line birefringence of the previous several cycles, a model-free adaptive iterative learning method is used to obtain the learning rate of the stress line birefringence, which is used to calculate and compensate for the additional phase delay in the next cycle.

[0006] Its main design points include:

[0007] The optical voltage sensor is based on a linear measurement mode and can extract and compensate for stress line birefringence at the zero-crossing moment of the AC voltage. The optical voltage sensor is implemented based on an S-wave plate, which achieves linear demodulation of the electro-optical phase delay. When stress line birefringence exists, its output result is a linear superposition of the electro-optical phase delay and the stress line birefringence. According to the Pockels effect, when the AC voltage to be measured passes through zero, the electro-optical phase delay of the electro-optical crystal is also zero. At this time, the output signal of the optical voltage sensor is the stress line birefringence. The zero-crossing moment of the AC voltage to be measured is determined by the zero-point theorem, and based on the stress line birefringence of the previous several cycles, a model-free adaptive iterative learning method is used to obtain the learning rate of the stress line birefringence, calculate the stress line birefringence of the next cycle, and compensate for it.

[0008] The technical solution adopted by the present invention to solve the technical problem is:

[0009] A method for compensating stress line birefringence in an optical voltage sensor based on an S-wave plate and model-free adaptive iterative learning is characterized in that: the optical voltage sensor is implemented based on the S-wave plate, and based on a linear measurement mode, the zero-crossing moment of the AC voltage to be measured is determined by the zero-point theorem, and based on the stress line birefringence of several previous cycles, a model-free adaptive iterative learning method is used to obtain a learning rate of the stress line birefringence, and the stress line birefringence of the next cycle is calculated and compensated; thereby, the additional phase delay is detected and eliminated.

[0010] Furthermore, the specific implementation method is as follows: the laser light emitted by the light source (1) is passed through the polarizer (2) to obtain linearly polarized light, and the linearly polarized light is passed through the electro-optical crystal (3) to generate phase delay, wherein the phase delay includes the electro-optical phase delay generated by the crystal under the action of the AC electric field to be measured and the additional phase delay introduced by the stress line birefringence;

[0011] The light vector emitted from the electro-optical crystal (3) passes through a quarter wave plate (4), and is synthesized from elliptically polarized light into linearly polarized light, and the phase delay is converted into the rotation angle of the polarization plane of the linearly polarized light; the polarization plane rotation angle is converted into the horizontal movement of the strip light spot (7) through an S wave plate (5) and a polarizer (6); according to the Pockels electro-optic effect, when the AC voltage to be measured passes through zero, the electro-optical phase delay of the crystal is zero; the zero-crossing moment of the AC voltage to be measured is determined using the zero point theorem, at which moment the dark fringe position (8) of the light spot corresponding to the electro-optical phase delay is at zero, and the output signal of the optical voltage sensor is the dark fringe position (9) of the light spot corresponding to the additional phase delay; thereby, the stress line birefringence is detected; based on the stress line birefringence of the previous several cycles, the learning rate of the stress line birefringence is obtained using a model-free adaptive iterative learning method, and the stress line birefringence of the next cycle is calculated and compensated.

[0012] The present invention and its preferred solution specifically solve the problem that temperature changes and vibrations generate stress line birefringence in electro-optic crystals and transmission optical fibers, introduce additional phase delay, and are difficult to separate and compensate together with electro-optical phase delay aliasing. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0014] Figure 1 This is a schematic diagram of the process and optical path of a method for compensating for stress line birefringence of an optical voltage sensor based on an S-wave plate and model-free adaptive iterative learning according to an embodiment of the present invention;

[0015] Figure 2 1 is a diagram showing simulation results of the output light spot of an optical voltage sensor based on an S-wave plate according to an embodiment of the present invention;

[0016] Figure 3 This is a flow chart of a stress line birefringence compensation method based on model-free adaptive iterative learning in an embodiment of the present invention.

[0017] Among them, 1 is the laser, 2 is the polarizer, 3 is the electro-optic crystal, 4 is the 1 / 4 wave plate, 5 is the S wave plate, 6 is the analyzer, 7 is the stripe light spot output by the optical voltage sensor, 8 is the stripe light spot when the electro-optical phase delay angle is zero, and 9 is the stripe light spot corresponding to the stress line birefringence. DETAILED DESCRIPTION

[0018] To make the features and advantages of this patent more clearly understood, the following embodiments are specifically 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 skilled in the art 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 form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0021] The following is a further detailed description of this embodiment with reference to the accompanying drawings:

[0022] like Figure 1As shown, to implement the solution designed by the present invention, in this embodiment, laser light emitted by light source 1 is converted into linearly polarized light through polarizer 2. The linearly polarized light is subjected to phase delay by electro-optical crystal 3, where the phase delay includes the electro-optical phase delay generated by the crystal under the action of the AC electric field to be measured and the additional phase delay introduced by stress linear birefringence.

[0023] After passing through a quarter-wave plate 4, the light vector emitted from the crystal is synthesized from elliptically polarized light into linearly polarized light, and the phase delay is converted into the rotation angle of the linearly polarized light's polarization plane. This polarization plane rotation angle is converted into the horizontal movement of a stripe light spot 7 by an S-wave plate 5 and an analyzer 6. According to the Pockels electro-optic effect, when the AC voltage to be measured passes through zero, the electro-optical phase delay of the crystal is zero. The zero-point theorem is used to determine the zero-crossing moment of the AC voltage to be measured. At this moment, the electro-optical phase delay equals 0°, and the corresponding dark spot position 8 is at zero. The output signal of the optical voltage sensor is the dark spot position 9 corresponding to the additional phase delay, thereby detecting stress line birefringence. Based on the stress line birefringence of the previous several cycles, a model-free adaptive iterative learning method is used to obtain the learning rate of stress line birefringence, and the stress line birefringence of the next cycle is calculated and compensated.

[0024] The feasibility of the principle of the solution of this embodiment is demonstrated below based on the Jones matrix.

[0025] like Figure 1 As shown, the azimuth angles of the polarizer, electro-optic crystal, quarter wave plate, S wave plate, and analyzer are 0°, 45°, 0°, 0°, and 90°, respectively.

[0026] The transmission axis of the polarizer is in the x-direction. The laser light becomes linearly polarized light after passing through the polarizer, which can be expressed as follows using the Jones matrix:

[0027]

[0028] Where A represents the light intensity.

[0029] Linearly polarized light passes through an electro-optical crystal to generate phase delay, where the phase delay includes the electro-optical phase delay under the action of the electric field to be measured. And the additional phase delay δ caused by stress line birefringence, at this time the Jones matrix J of the electro-optical crystal is E for:

[0030]

[0031] The Jones matrix of the quarter wave plate is:

[0032]

[0033] Therefore, the Jones vector of linearly polarized light after passing through the electro-optical crystal and the quarter-wave plate is:

[0034]

[0035] The Jones matrix of the S wave plate is (1) :

[0036]

[0037] Where x represents the center position of the dark fringe of the output light spot; l represents the length of the S wave plate window. The Jones matrix of the polarization analyzer is:

[0038]

[0039] Therefore, after the Jones vector E passes through the S wave plate and the analyzer, we get:

[0040]

[0041] Then the output light intensity distribution is:

[0042]

[0043] The measurement is achieved by locating the center of the dark pattern of the light spot. Satisfies the linear relationship:

[0044]

[0045] Where △x is the displacement of the light spot. When △x=0, the center of the dark pattern is at the center of the S wave plate window. Based on Matlab simulation, the output light intensity distribution after S wave plate polarization is obtained, as shown in the figure: Figure 2 As shown, the center of the visible light spot dark pattern By measuring the translation of the center of the dark pattern of the light spot, the polarization angle of the incident polarized light can be directly and linearly measured.

[0046] Therefore, the measurement result of the optical voltage sensor is The linear superposition of δ and δ, according to the Pockels electro-optic effect, the voltage to be measured U is satisfy:

[0047]

[0048] Among them U π is the half-wave voltage of the crystal. Therefore, when U=0 When the AC voltage passes through zero, the output signal of the optical voltage sensor is δ, which can be detected and compensated at this moment.

[0049] The zero-crossing moment of the AC voltage is determined using the zero-point theorem by collecting the discrete output data of the optical voltage sensor. Determine 2 adjacent data and Whether the rotation angle symbols are the same (k < n). If the symbols are the same, it is considered that there is no zero crossing of voltage between the two points; if the symbols are different, it is considered that there is a zero crossing point between the two points, and t k and t k+1 The average value of is determined as the zero crossing time.

[0050] Finally, according to δ in the previous several cycles i , the learning rate of δ is obtained by using the model-free adaptive iterative learning method, and δ in the next cycle is calculated for compensation. The principle of the model-free iterative error algorithm is:

[0051] com k (t) = com k-1 (t) + k p δ k-1 (11)

[0052] where com k (t) is the error compensation value at the t-th moment of the k-th iteration; k p is the learning law.

[0053] Adding an adaptive algorithm to the model-free iterative learning to achieve model-free adaptive iterative learning. Mainly, the fixed learning law in the iterative learning is replaced by the pseudo partial derivative in the adaptive algorithm to realize the real-time modification of the learning law, so that the system can better adapt to the disturbance signal and error. The process of the δ compensation method based on model-free adaptive iterative learning is referred to Figure 3 .

[0054] The reference documents for the above verification scheme are:

[0055] Xie N, Zhu D, Xu Q, et al. Linear phase delay detection method for optical voltage transformer based on S-wave plate[J]. Measurement Science and Technology, 2021, 32(8): 085107.

[0056] Combined with the above design, this embodiment provides a specific test example:

[0057] The laser used is a distributed feedback semiconductor light source with a wavelength of 980 nm. The length and width of the S-wave plate operating window are 2l = 20 mm and m = 4 mm, respectively. A dual-image detector is used to detect the light spot displacement. A high-low temperature alternating humidity test chamber provides a variable temperature environment ranging from -40°C to 85°C with a temperature fluctuation of ±0.5°C. In this example, the main optical components are placed in the chamber's inner chamber and temperature cycling experiments are performed within the -40°C to 85°C range. The zero-point theorem and a model-free adaptive iterative learning method are used to determine and compensate for the stress line birefringence in each cycle. Finally, the basic accuracy of the optical voltage sensor is recorded using a calibrator, as shown in Table 1. Under temperature cycling conditions, the optical voltage sensor meets the Class 0.5 accuracy requirement.

[0058] Table 1 Basic accuracy experimental data

[0059] Rated voltage percentage / % Ratio difference / % Angular difference / (′) 80 0.378 16.54 100 0.34 －20.09 120 0.329 －18.31

[0060] 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.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

[0062] This patent is not limited to the above-mentioned optimal implementation method. Anyone can derive various other forms of stress line birefringence compensation methods for optical voltage sensors based on S-wave plates and model-free adaptive iterative learning under the inspiration of this patent. All equal changes and modifications made within the scope of the patent application of this invention should be covered by this patent.

Claims

1. A method for compensating stress line birefringence in an optical voltage sensor based on an S-wave plate and model-free adaptive iterative learning, characterized by: The optical voltage sensor is implemented using an S-wave plate. Based on a linear measurement mode, the zero-crossing moment of the AC voltage to be measured is determined using the zero-point theorem. A model-free adaptive iterative learning method is used to obtain the learning rate of the stress line birefringence based on the stress line birefringence of the previous several cycles. The stress line birefringence of the next cycle is calculated and compensated for. This allows the additional phase delay to be detected and eliminated. The laser light emitted by the light source (1) is passed through the polarizer (2) to obtain linearly polarized light, and the linearly polarized light is passed through the electro-optical crystal (3) to generate phase delay, wherein the phase delay includes the electro-optical phase delay generated by the crystal under the action of the AC electric field to be measured and the additional phase delay introduced by the stress line birefringence; The light vector emitted from the electro-optical crystal (3) passes through a quarter wave plate (4), and is synthesized from elliptically polarized light into linearly polarized light, and the phase delay is converted into the rotation angle of the polarization plane of the linearly polarized light; the polarization plane rotation angle is converted into the horizontal movement of the strip light spot (7) through the S wave plate (5) and the analyzer (6); according to the Pockels electro-optic effect, when the AC voltage to be measured passes through zero, the electro-optical phase delay of the crystal is zero; the zero-crossing moment of the AC voltage to be measured is determined using the zero point theorem, at which moment the dark fringe position (8) of the light spot corresponding to the electro-optical phase delay is at zero, and the output signal of the optical voltage sensor is the dark fringe position (9) of the light spot corresponding to the additional phase delay; thereby, the stress line birefringence is detected; based on the stress line birefringence of the previous several cycles, the learning rate of the stress line birefringence is obtained using a model-free adaptive iterative learning method, and the stress line birefringence of the next cycle is calculated and compensated.

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