Optical voltage transformer for realizing harmonic measurement and working method thereof

Abstract

The invention provides an optical voltage transformer for realizing harmonic measurement and a working method thereof. The optical voltage transformer comprises a polarizer, a BGO crystal, a wave plate, a radial polarization grating, an image sensor and a light source emitter. Based on a linear demodulation mode of phase delay, rotation of a polarization plane of linearly polarized light is converted into synchronous translation of a light spot by using a radial polarization grating, and the light spot is positioned by an image sensor to obtain a displacement difference, so that linear measurement of the phase delay is realized. And when the voltage modulation signal contains the harmonic component, the translation amount of the light spot image in the linear demodulation result is the superposition result of the action of the fundamental wave and each harmonic component. And the linear demodulation mode also belongs to a linear time-invariant mode, so that the harmonic measurement capability without distortion is realized. In addition, compensation of thermal stress birefringence is achieved through a square wave difference method, and the temperature drift problem of the optical voltage transformer in harmonic measurement is solved.

Description

TECHNICAL FIELD

[0001] The application provides an optical voltage transformer for realizing harmonic measurement and a working method thereof, and relates to the technical field of electrical measurement. BACKGROUND

[0002] With the rapid development of power electronic technology and the wide access of distributed renewable energy, the structure of power grid is increasingly complex, and the generated harmonics gradually become a key factor affecting power quality. These harmonic problems not only cause power grid signal waveform distortion, metering error, equipment aging, but also may cause serious equipment failure and even personal safety accidents, which poses a serious challenge to the stable operation of the power grid. Therefore, as a key data acquisition device of the power system, the voltage transformer has the ability to accurately and stably measure harmonics, which has become an important foundation for ensuring the smooth operation of the new power system, improving power quality and ensuring power supply safety. SUMMARY

[0003] The optical voltage transformer (OVT) is based on the Pockels electro-optic effect principle, which has the advantages of high measurement sensitivity, wide frequency band and no magnetic hysteresis effect. Therefore, OVT represents the development direction of measuring harmonic voltage. The biggest challenge faced by current OVT is the non-linear demodulation and temperature drift problem, which has always been unable to effectively solve the non-linear time-varying phenomenon, becoming a bottleneck restricting its practicalization. The linear time-invariant mode avoids the non-linear demodulation based on Malus law and realizes the compensation of thermal stress birefringence caused by temperature drift, which is used for distortionless harmonic measurement.

[0004] Therefore, in order to make up for the gaps and deficiencies of the prior art, the application provides an optical voltage transformer for realizing harmonic measurement and a working method thereof, which includes the following contents:

[0005] The application provides an optical voltage transformer for realizing harmonic measurement, which is characterized in that the optical voltage transformer realizes distortionless measurement of harmonic voltage based on radial polarization grating detection and square wave difference method.

[0006] The optical voltage transformer includes a polarizer, a BGO crystal, a λ / 4 wave plate, a radial polarization grating, an image sensor and a light source emitter.

[0007] The light source emitter outputs omnidirectional light, and the light path of the omnidirectional light sequentially passes through the polarizer, the BGO crystal, the λ / 4 wave plate and the radial polarization grating.

[0008] The polarizer is used for receiving the omnidirectional light from the light source emitter and outputting linearly polarized light.

[0009] Wherein after receiving linearly polarized light, the BGO crystal outputs a polarized light signal used to express the harmonic voltage measurement result;

[0010] Wherein the quarter-wave plate and the radial polarization grating receive the polarized light signal from the BGO crystal in turn and convert it into the light spot synchronous translation amount of the polarized light signal;

[0011] Wherein the image sensor measures the light spot translation amount and obtains the voltage value to be measured.

[0012] Further, the BGO crystal has a Pockels linear superposition effect; the BGO crystal outputs a polarized light signal used to express the harmonic voltage measurement result through the Pockels linear superposition effect, and the crystal direction of the BGO crystal in operation forms a 45° angle with the y-axis of the light path of the omnidirectional light.

[0013] Further, the image sensor filters out the thermal stress birefringence δ T The light spot translation amount is measured.

[0014] The present application provides a working method of an optical voltage transformer for harmonic measurement, which is applied to the optical voltage transformer for harmonic measurement as described in any one of the present application, and characterized in that the working method of the optical voltage transformer for harmonic measurement comprises the following contents:

[0015] Step S1: the omnidirectional light emitted by the light source emitter is first converted into linearly polarized light by the polarizer, the electric field generated by the voltage superposition of different frequencies acts on both ends of the BGO crystal and produces Pockels effect, so that the linearly polarized light is split into fast and slow axes, based on the linear superposition property of different harmonic components, and then an electro-optic phase delay ∑ i δ i is formed, which is a polarized light signal used to express the harmonic voltage measurement result and emitted from the BGO;

[0016] Step S2: the polarized light signal is processed, and then the light signal polarization plane sequentially passes through the quarter-wave plate and the radial polarization grating of the sensor, so that the electro-optic phase delay is converted into the rotation amount of the polarization plane and then converted into the light spot synchronous translation amount of the polarized light signal;

[0017] Step S3: the phase difference is obtained by the image sensor positioning the light spot, and then the thermal stress birefringence is filtered out through the square wave difference algorithm, and the voltage to be measured is obtained.

[0018] Further, step S1 comprises the following contents:

[0019] Step S11: ignore the undesired phase delay caused by the thermal stress birefringence; the light emitted by the light source emitter forms linearly polarized light through the polarizer, and the Jones vector is:

[0020] E in = A [1 0] T

[0021] where E in is the Jones vector of the polarizer, and A is the incident light intensity.

[0022] Further, step S1 further includes the following content:

[0023] Step S12: Polarized light is incident on the BGO, and the single-frequency voltage U i induced electro-optic phase delay is δ i The expression is:

[0024]

[0025] where γ 41 represents the electro-optic coefficient, n o represents the refractive index of the crystal, L represents the length of the crystal, and V π is the half-wave voltage of the crystal.

[0026] Step S12: Based on the optical isolation principle of the Pockels effect, the BGO crystal presents independent linear superposition to voltage components of different frequencies when it is not saturated. Therefore, the total electro-optic phase delay ∑ i δ i can be expressed as:

[0027]

[0028] Step S12: The Jones vector of the light emitted by the BGO crystal is:

[0029]

[0030] where J BGO is the Jones matrix of the BGO.

[0031] Further, step S2 includes the following content:

[0032] Step S21: The polarized light signal emitted by the BGO to express the harmonic voltage measurement result enters the radial polarization grating, and ∑ i δ i is converted into linear translation of the bar light spot image; the expression of the Jones vector E out of the light emitted by the radial polarization grating is:

[0033]

[0034] where J SAPG , J 1 / 4 , and J BGO represent the Jones matrices of the SAPG, the λ / 4 wave plate, and the BGO, respectively, The angle of the grid strips on the SAPG is represented by , and i represents the phase factor, which can be ignored.

[0035] At this time, the emitted light intensity I out for:

[0036]

[0037] Where t TM It is the diffraction efficiency of the TM wave. E out This is the Jones vector of the light emitted from the radially polarized grating.

[0038] Furthermore, step S2 also includes the following:

[0039] Step S22: When I out When taking the minimum value, we have:

[0040]

[0041] As δ changes, the dark fringes translate linearly along the grating.

[0042] At this time, the measurement range of the radial polarization grating is -50° to +50°;

[0043] The measurement range of δ is -100° to +100°.

[0044] The range of dark fringe translation is the length of the grating, and the range of dark fringe translation is: 0~1;

[0045] The relationship between the dark fringe displacement Δx and δ satisfies:

[0046]

[0047] After simplification, we get:

[0048]

[0049] Finally, the linear measurement of the electro-optic phase delay δ is achieved by detecting the dark fringe displacement Δx of the emitted light spot from the LIT-OVS.

[0050] Further, step S3 includes the following:

[0051] Step S31: The image sensor calculation process includes:

[0052] Step S311: Introduce the undesirable phase delay δ caused by thermal stress T , Σ i δ i With δ T Each step is independent, and the final measured phase delay δ is:

[0053]

[0054] Step S312: Based on the periodicity of the alternating voltage, by comparing the maximum dark stripe displacement amount of different dark stripe directions in each period, the following is obtained:

[0055]

[0056] Wherein ∑ i δ i，1 = -∑ i δ i，2 .

[0057] Further, step S3 further comprises the following contents:

[0058] Step S313: By difference, separate δ T And realize time-invariant measurement, the following is obtained:

[0059]

[0060] Wherein the crystal direction of BGO is 45° angle with the light path y axis, when the harmonic voltage transformer is used for measuring less than 1kV level, 10kV level half-wave voltage BGO crystal is adopted;When the harmonic voltage transformer is used for measuring high voltage level, BGO crystal greater than 10kV level half-wave voltage is adopted.

[0061] The present application has the following advantages:

[0062] The device of the present application realizes harmonic distortionless measurement, compensates thermal stress birefringence, and has distortionless harmonic measurement capability. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 It is a schematic diagram of the present application.

[0064] Figure 2 It is a working principle diagram of the present application.

[0065] Figure 3 It is a test result diagram of the present application.

[0066] Figure 4 It is a step flowchart of the present application. DETAILED DESCRIPTION

[0067] The technical solutions of the present application will be specifically described below in combination with the drawings.

[0068] It should be pointed out that the following detailed description is exemplary, and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0069] It is to be noted that the terms used herein are merely for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise, and it should be further understood that the terms "comprise" and / or "include" when used in this specification, specify the presence of stated features, steps, operations, devices, components and / or combinations thereof.

[0070] As shown in Figures 1 to 4 The present application provides an optical voltage transformer for harmonic measurement and a working method thereof, comprising the following contents:

[0071] As shown in Figures 1 to 3 The present application provides an optical voltage transformer for harmonic measurement, characterized in that the optical voltage transformer realizes distortionless measurement of harmonic voltage based on radial polarization grating detection and square wave difference method.

[0072] The optical voltage transformer comprises a polarizer, a BGO crystal, a λ / 4 wave plate, a radial polarization grating, an image sensor and a light source emitter.

[0073] The light source emitter outputs omnidirectional light, and the light path of the omnidirectional light sequentially passes through the polarizer, the BGO crystal, the λ / 4 wave plate and the radial polarization grating.

[0074] The polarizer is used to receive the omnidirectional light from the light source emitter and output polarized light.

[0075] The BGO crystal outputs a polarized light signal for expressing the harmonic voltage measurement result after receiving the polarized light.

[0076] The λ / 4 wave plate and the radial polarization grating sequentially receive the polarized light signal from the BGO crystal and convert it into a light spot synchronous translation amount of the polarized light signal.

[0077] The image sensor measures the light spot translation amount and obtains the voltage value to be measured.

[0078] Further, the BGO crystal has Pockels linear superposition effect; the BGO crystal outputs the polarized light signal for expressing the harmonic voltage measurement result through the Pockels linear superposition effect, and the crystal direction of the BGO crystal in operation forms a 45° angle with the y-axis of the light path of the omnidirectional light.

[0079] Further, the image sensor filters out thermal stress birefringence δ T The light spot translation amount is measured.

[0080] As shown in Figures 1 to 4As shown, the application provides a working method of an optical voltage transformer for harmonic measurement, which is applied to the optical voltage transformer for harmonic measurement as described in any one of the application, and characterized in that the working method of the optical voltage transformer for harmonic measurement comprises the following contents:

[0081] Step S1: the omnidirectional light emitted by the light source emitter is first converted into linearly polarized light by a polarizer, an electric field generated by voltage superposition of different frequencies acts on both ends of the BGO crystal and produces Pockels effect, so that the linearly polarized light is split into fast and slow axes, based on the linear superposition property of different harmonic components, and then an electro-optic phase delay Σ i δ i is generated, forming a polarized light signal emitted from the BGO to express the harmonic voltage measurement result;

[0082] Step S2: the polarized light signal is processed, and the light polarization plane of the light signal is sequentially passed through the λ / 4 wave plate and the radial polarized grating of the sensor, so as to convert the rotation amount of the light polarization plane into the synchronous translation amount of the light spot of the polarized light signal;

[0083] Step S3: the phase difference is obtained by positioning the light spot by the image sensor, and then the thermal stress birefringence is filtered out by the square wave difference algorithm to obtain the measured voltage.

[0084] Further, step S1 comprises the following contents:

[0085] Step S11: ignoring the undesired phase delay caused by thermal stress birefringence; the light emitted by the light source emitter forms linearly polarized light through the polarizer, and the Jones vector is:

[0086] E in =A[1 0] T

[0087] wherein E in is the Jones vector of the polarizer, and A is the incident light intensity.

[0088] Further, step S1 further comprises the following contents:

[0089] Step S12: the polarized light is incident on the BGO, and the electro-optic phase delay caused by the single-frequency voltage U i is δ i , and the expression is:

[0090]

[0091] wherein γ 41 represents the electro-optic coefficient, n o represents the refractive index of the crystal, L represents the length of the crystal, and V π is the half-wave voltage of the crystal.

[0092] Step S12: Based on the principle of optical isolation of Pockels effect, BGO crystal presents independent linear superposition to voltage components of different frequencies when working in unsaturated state, so the total electro-optical phase delay Σ i δ i Can be expressed as:

[0093]

[0094] Step S12: The Jones vector of the BGO crystal exit light is:

[0095]

[0096] Where J BGO is the Jones matrix of BGO.

[0097] Further, step S2 includes the following content:

[0098] Step S21: After the polarization light signal expressing the harmonic voltage measurement result of BGO exit enters the radial polarization grating, Σ i δ i Is converted into linear translation of bar spot image; the expression of the Jones vector E out of the radial polarization grating exit light is:

[0099]

[0100] Where J SAPG , J 1 / 4 , J BGO respectively represent the Jones matrix of SAPG, λ / 4 wave plate, BGO, represents the grating angle on SAPG, i represents the phase factor, which can be ignored.

[0101] At this time, the exit light intensity I out is:

[0102]

[0103] Where t TM is the diffraction efficiency of TM wave. E out is the Jones vector of the radial polarization grating exit light.

[0104] Further, step S2 also includes the following content:

[0105] Step S22: When I out takes the minimum value, there is:

[0106]

[0107] When δ changes, the dark lines translate linearly along the grating lines;

[0108] The measurement range of the radial polarization grating is -50°~+50° at this time;

[0109] The measurement range of δ is -100°~+100°;

[0110] Wherein the range of the dark stripe translation is the length of the grating, and the range of the dark stripe translation is 0~l;

[0111] The relationship between the dark stripe displacement amount Δx and δ satisfies:

[0112]

[0113] After simplification, we get:

[0114]

[0115] Finally, by detecting the dark stripe displacement amount Δx of the LIT-OVS exit light spot, the linear measurement of the electro-optical phase delay δ is realized.

[0116] Further, step S3 includes the following contents:

[0117] Step S31: The image sensor calculation process includes:

[0118] Step S311: Introducing the undesirable phase delay δ caused by thermal stress T ,∑ i δ i and δ T are each independent, and finally the measured phase delay δ is obtained as:

[0119]

[0120] Step S312: Based on the periodicity of the alternating voltage, by comparing the maximum dark stripe displacement amounts Δx1 and Δx2 of different dark stripes in each period, we get:

[0121]

[0122] Wherein ∑ i δ i，1 = -∑ i δ i，2 .

[0123] Further, step S3 also includes the following contents:

[0124] Step S313: By difference, δ T is separated and time-invariant measurement is realized, and we get:

[0125]

[0126] The crystal direction of the BGO is at an angle of 45 degrees with the y-axis of the light path, when the harmonic voltage transformer is used to measure a level less than 1kV, the BGO crystal of the kV level half-wave voltage is adopted; when the harmonic voltage transformer is used to measure a high voltage level, the BGO crystal of the dozens of kV level half-wave voltage is adopted.

[0127] In an embodiment of the present application, the relationship between the output interference fringe of the transformer and delta is obtained based on MATLAB simulation, as shown in the following figure: Figure 3 The figure shows the interference fringe results generated by the electro-optical phase delay of-30°, 0° and 30° respectively.

[0128] In addition to the above, the present application also has related embodiments, including the following:

[0129] The omnidirectional light emitted by the light source is converted into linearly polarized light by the polarizer, and the linearly polarized light is split into the fast axis and the slow axis by the Pockels linear superposition effect of the voltage, that is, different frequencies of the voltage generate electro-optical phase delay superposition, and then the linearly polarized light is converted into linearly polarized light by the λ / 4 wave plate, the phase difference between the fast and slow axes of the elliptically polarized light is converted into the rotation angle of the polarization plane, and then the rotation of the linearly polarized light polarization plane is converted into the synchronous translation of the light spot by the radial polarization grating, and the displacement difference is obtained by positioning the light spot by the image sensor, and the compensation of thermal stress birefringence is realized by the square wave difference method.

[0130] This embodiment realizes the distortionless measurement of the harmonic voltage and realizes the compensation of the thermal stress birefringence.

[0131] The optical voltage transformer for realizing harmonic measurement in the present application realizes the distortionless measurement of the harmonic voltage based on the radial polarization grating detection method and the square wave difference algorithm.

[0132] Specifically, the light emitted by the light source transmitter is converted into polarized light by the polarizer, and the linearly polarized light is split into the fast axis and the slow axis by the BGO, that is, electro-optical phase delay is generated, the linearly polarized light is converted into linearly polarized light by the λ / 4 wave plate, and the phase difference between the fast and slow axes of the elliptically polarized light is converted into the rotation angle of the polarization plane. The rotation of the linearly polarized light polarization plane is converted into the synchronous translation of the dark fringe by the radial polarization grating, the phase difference is obtained by positioning the light spot by the image sensor, and the compensation of the thermal stress birefringence is realized by the square wave difference algorithm of the image sensor, and the measured harmonic voltage is obtained.

[0133] The above is the preferred embodiment of the present application, and any changes made according to the technical solutions of the present application, as long as the generated function does not exceed the scope of the technical solutions of the present application, belong to the protection scope of the present application.

Claims

1. An optical voltage transformer for harmonic measurement, characterized in that, The optical voltage transformer described above achieves distortion-free measurement of harmonic voltage based on radial polarization grating polarization detection and square wave differential method; The optical voltage transformer mentioned above includes a polarizer, a BGO crystal, a λ / 4 waveplate, a radial polarization grating, an image sensor, and a light source emitter. The light source emitter outputs omnidirectional light, and the optical path of the omnidirectional light passes through a polarizer, a BGO crystal, a λ / 4 waveplate, and a radial polarization grating in sequence. The polarizer is used to receive omnidirectional light from the light source emitter and output linearly polarized light. After receiving polarized light, the BGO crystal outputs a linearly polarized light signal to represent the harmonic voltage measurement results. The λ / 4 waveplate and the radial polarization grating sequentially receive polarized light signals from the BGO crystal and convert them into the synchronous shift amount of the polarized light signal; The image sensor measures the amount of light spot shift and obtains the voltage value to be measured.

2. The optical voltage transformer for harmonic measurement according to claim 1, characterized in that, The BGO crystal described therein exhibits the Pockels linear superposition effect; the BGO crystal outputs a polarized light signal to represent the harmonic voltage measurement results through the Pockels linear superposition effect, and the crystal orientation of the BGO crystal during operation forms a 45° angle with the y-axis of the omnidirectional light path.

3. An optical voltage transformer for harmonic measurement according to claim 1, characterized in that, The image sensor described above uses a square wave differential algorithm to filter out thermal stress birefringence δ. T It enables the measurement of the light spot translation.

4. A method for operating an optical voltage transformer for harmonic measurement, applied to an optical voltage transformer for harmonic measurement as described in any one of claims 1 to 3, characterized in that, The operating method of the optical voltage transformer for harmonic measurement includes the following: Step S1: The omnidirectional light emitted by the light source emitter is first converted into linearly polarized light by a polarizer. The electric field generated by the superposition of voltages of different frequencies acts on both ends of the BGO crystal and produces the Pockels effect, causing the linearly polarized light to split into a fast axis and a slow axis. Based on the linear superposition property of different harmonic components, an electro-optic phase delay ∑ is then generated. i δ i This forms a polarized light signal emitted from the BGO to represent the harmonic voltage measurement results; Step S2: Process the polarized light signal, and then make the polarization plane of the light signal pass through the λ / 4 waveplate and radial polarization grating of the sensor in sequence, converting the electro-optic phase delay into the rotation amount of the polarization plane, and then into the synchronous translation amount of the light spot of the polarized light signal. Step S3: Use an image sensor to locate the light spot and obtain the phase difference, then use a square wave differential algorithm to filter out thermal stress birefringence to obtain the voltage to be measured.

5. The operating method of an optical voltage transformer for harmonic measurement according to claim 4, characterized in that, Step S1 includes the following: Step S11: Ignore the undesirable phase delay caused by thermal stress birefringence; the light emitted from the light source emitter is polarized by a polarizer to form linearly polarized light, whose Jones vector is: AND in =A[1 0] T Where E in Let be the Jones vector of the polarizer, and A be the incident light intensity.

6. The operating method of an optical voltage transformer for harmonic measurement according to claim 5, characterized in that, Step S1 also includes the following: Step S12: Polarized light is incident on the BGO, and is controlled by a single-frequency voltage U i The resulting electro-optic phase delay is δ i The expression is: Where, γ 41 Represents the electro-optic coefficient, n o V represents the refractive index of the crystal, L represents the crystal length, and V represents the crystal length. π This is the half-wave voltage of the crystal; Step S12: Based on the optical isolation principle of the Pockels effect, the BGO crystal exhibits independent linear superposition of voltage components at different frequencies when operating in unsaturated mode, therefore the total electro-optic phase delay ∑ i δ i It can be represented as: Step S12: The Jones vector of the light emitted from the BGO crystal is: J BGO E in The Jones matrix of the BGO crystal.

7. The operating method of an optical voltage transformer for harmonic measurement according to claim 4, characterized in that, Step S2 includes the following: Step S21: After the polarized light signal emitted from the BGO to represent the harmonic voltage measurement result enters the radial polarization grating, the ∑ i δ i Linear translation into a stripe-shaped light spot image; E of the Jones vector of the radially polarized grating output light. out The expression is: J SAPG J 1 / 4 J BGO These represent the Jones matrices for the SAPG, λ / 4 waveplate, and BGO, respectively. The grating angle on the SAPG is represented by i, and the phase factor is represented by i. At this time, the emitted light intensity I out for: Where t TM It is the diffraction efficiency of the TM wave, E out This is the Jones vector of the light emitted from the radially polarized grating.

8. The operating method of an optical voltage transformer for harmonic measurement according to claim 7, characterized in that, Step S2 also includes the following: Step S22: When I out When taking the minimum value, we have: As δ changes, the dark fringes translate linearly along the grating. At this time, the measurement range of the radial polarization grating is: -50° to +50°; The measurement range of δ is -100° to +100°. The range of dark fringe translation is the length of the grating, and the range of dark fringe translation is: 0~1; The relationship between the dark fringe displacement Δx and δ satisfies: After simplification, we get: Finally, the linear measurement of the electro-optic phase delay δ is achieved by detecting the dark fringe displacement Δx of the emitted light spot from the LIT-OVS.

9. The operating method of an optical voltage transformer for harmonic measurement according to claim 4, characterized in that, Step S3 includes the following: Step S31: The image sensor calculation process includes: Step S311: Introduce the undesirable phase delay δ caused by thermal stress T , ∑ i δ i With δ T Each step is independent, and the final measured phase delay δ is: Step S312: Based on the periodicity of the AC voltage, the maximum dark fringe displacement Δx1 and Δx2 in different dark fringe directions in each period are obtained by comparison, resulting in: among them i d i，1 =-∑ i d i，2 。 10. The operating method of an optical voltage transformer for harmonic measurement according to claim 9, characterized in that, Step S3 also Includes the following: Step S313: Separate δ by difference T And by implementing time-invariant measurements, we obtain: The crystal orientation of the BGO crystal forms a 45° angle with the y-axis of the optical path. When the harmonic voltage transformer is used to measure voltages below 1kV, a BGO crystal with a half-wave voltage of 10kV is used; when the harmonic voltage transformer is used to measure voltages above 1kV, a BGO crystal with a half-wave voltage of more than 10kV is used.

Images