Crystal type AC voltage sensor and sensing signal processing method thereof

Abstract

The invention discloses a crystal type AC voltage sensor and a sensing signal processing method thereof, and belongs to the technical field of optical sensing and signal processing thereof. The invention mainly solves the problems that the optical bias of the existing crystal type voltage sensor is influenced by the inherent birefringence effect of a sensing crystal and the optical power in an optical path is unstable, and provides a method for reasonably selecting and designing the sensing crystal to enable the optical sensing signal of the sensing crystal to contain the harmonic component of the measured voltage. And through a signal processing mode of carrying out reasonable operation on different harmonic components, the adverse effect of the optical bias instability on the voltage sensing signal is effectively inhibited. The main technical advantage of the invention is that the influence of the inherent birefringence temperature, the elasto-optical effect and the like in the voltage sensing crystal on the voltage sensing signal can be effectively inhibited. The invention is mainly applied to optical sensing and measurement of various alternating voltages.

Description

Technical Field

[0001] This invention belongs to the field of optical sensor and signal processing technology, and mainly relates to optical voltage sensing technology and signal processing methods, particularly to a sensing signal processing method that can remove the influence of optical bias instability in voltage sensors. Background Technology

[0002] Currently, the main method for measuring power frequency voltage in power systems and smart grids is using electromagnetic voltage transformers. In addition, there are optical or electronic voltage sensors currently in the grid-connected trial operation phase. Optical or electronic voltage sensors generally have advantages such as excellent electrical insulation performance, wide response bandwidth, large measurement range, small size, light weight, excellent safety performance, and ease of connection to power communication networks, thus attracting widespread attention. (See: Xiao Zhihong. Principles and Practical Technology of Electronic Instrument Transformers [M]. Beijing: China Electric Power Press. 2018.)

[0003] Optical voltage sensors generally achieve voltage sensing and measurement based on the linear electro-optic effect of electro-optic crystals, the elasto-optic effect of optical fibers combined with the inverse piezoelectric effect of piezoelectric materials, and the electroluminescence effect. Most electro-optic crystal voltage sensing mechanisms are based on obtaining the measured voltage through light polarization and intensity modulation. Therefore, fluctuations in the sensor's optical bias caused by factors such as temperature changes and stress strain will affect the stability of the voltage sensing signal, requiring corresponding signal drift suppression and compensation measures. Although various methods exist for suppressing or compensating for optical bias instability, these methods all have various shortcomings. (See: Li Changsheng, Cui Xiang. A Review of Optical Electric Field Sensor Research [J]. Electrical Applications, 2008, 27(16), 8-13.)

[0004] For crystal-type optical voltage sensors, the temperature effect and elasto-optic effect of the natural or inherent birefringence of the sensing crystal are among the main causes of optical bias drift. Various compensation methods have been proposed to address this. For example, a compensation scheme using two electro-optic crystals with identical geometric dimensions and orthogonal birefringence principal axes connected in series can theoretically compensate for the temperature drift of the voltage sensing signal. However, this requires the two crystals to be of strictly equal length; otherwise, a large phase deviation will be introduced. (See: Yang Qing, Sun Shangpeng, Sima Wenxia, ​​et al. Temperature-compensated strong electric field sensor and its measurement method [P]. Chinese Invention Patent: CN 105182093 A, 2015-12-23.)

[0005] For example, with commonly used potassium dihydrogen phosphate (KDP) crystals, if the length error between two crystals in the light transmission direction is 0.1 mm, then for every 1 °C change in temperature, the phase change of the light wave at a wavelength of 632.8 nm can reach 0.6 °C. This will directly lead to temperature drift in the static optical bias of the voltage sensor. Since it is generally difficult to fabricate two electro-optic crystals with identical geometric dimensions, this limits the practical application of this scheme. (See: Jiang Minhua. Crystal Physics [M]. Jinan: Shandong Science and Technology Press, 1980: 354-356.)

[0006] To address the stress-induced linear birefringence phase delay problem in electro-optic crystals and transmission fibers caused by environmental temperature changes and vibrations, some scholars have proposed a birefringence error compensation method based on S-wave plates and adaptive iterative learning. (See: Xu Qifeng. Stress Line Birefringence Compensation Method for Optical Voltage Sensors Based on S-Wave Plates and Model-Free Adaptive Iterative Learning [P]. Chinese Invention Patent: CN115792780A, 2023-03-14.) However, the voltage sensing unit structure and signal processing of this scheme are relatively complex, and a special S-wave plate is required.

[0007] Optical voltage sensors are also a type of electro-optic modulator. Some scholars have proposed a method to improve the temperature stability of electro-optic modulators by optimizing the deflection angle between the crystal optical axis and the sensing beam, which can also be applied to optical voltage sensors. (See: Chen Haibo, She Weilong. Temperature characteristics and optimal design of electro-optic modulators [J]. Acta Optica Sinica, 2004, 24(10), 1353-1357.) However, the drawback of this compensation method is that its compensation effect heavily depends on the orientation accuracy of the crystal deflection angle.

[0008] In summary, the problem of unstable optical bias and sensing signal caused by the birefringence temperature and photoelastic effect of the sensing crystal remains one of the main reasons affecting the performance of crystal voltage sensors, and it has not yet been completely solved.

[0009] In the research on optical current sensing signal processing methods, some scholars have proposed a method to obtain the current sensing signal under test by dividing the second harmonic component of the current sensing signal with its fundamental frequency component, while effectively suppressing the influence of light source power fluctuations on the sensing signal. (See: Ferrari JA, Perciante CD, Dubra A, et al. Alternating current sensor with second-harmonic detection[J]. Applied Optics,2000,39(25),4638-4640.) However, this sensing scheme does not address the temperature instability problem of the current sensing signal.

[0010] In the research on signal modulation, demodulation, and detection methods for open-loop fiber optic gyroscopes, for open-loop fiber optic gyroscopes using sinusoidal modulation, the Sagnac effect phase difference related to the measured angular velocity can be calculated by separating, detecting, and processing the harmonic components of the gyroscope output signal, thereby achieving demodulation of the gyroscope signal. (See: Zhang Weixu. Fiber Optic Gyroscopes and Their Applications [M]. Beijing: National Defense Industry Press, 2008: 90-97.) This method can also suppress the influence of unstable light source power on the gyroscope signal, but it still cannot effectively suppress the temperature drift of the fiber optic gyroscope output signal.

[0011] The signal processing methods for harmonic analysis in the existing literature have not been applied to optical voltage sensors, and are limited to obtaining sensing signals through calculations, but have not been used to suppress or compensate for optical bias drift problems in optical voltage sensors. Summary of the Invention

[0012] This invention addresses the technical problem of unstable optical bias in conventional crystal voltage sensors caused by birefringence temperature effects and photoelasticity, proposing a drift suppression method based on harmonic analysis of the output sensing signal. Previous methods for generating static optical bias in typical crystal voltage sensors included using various quarter-wave plates or utilizing a deflection angle between the principal axis of the sensing crystal and the beam. However, these methods all suffer from drift caused by birefringence temperature effects and photoelasticity, and their influence exists in all harmonic components of the output sensing signal. This invention employs a signal processing method that separates and rationally calculates different harmonic components of the sensing signal, effectively solving the optical bias and sensing signal drift problems of such crystal voltage sensors.

[0013] In order to solve the technical problem that the stability of optical voltage sensing signals is affected by the instability of light source and optical power in sensing optical path, this invention effectively suppresses the adverse effects of optical power instability on voltage sensing signals by using a method of division operation on different harmonic components of the output voltage sensing signal.

[0014] This invention proposes an optical voltage sensor and a signal processing method based on harmonic analysis, as shown in the appendix. Figure 1 As shown, the voltage sensor system mainly consists of a light source 101, an optical carrier transmission fiber 102, a voltage sensing head 103, an optical sensing signal transmission fiber 104, a photoelectric signal detection and amplification unit 105, an electronic filtering unit 106, a division operation unit 107, and an information display unit 108. The characteristic requirements for the light source 101, transmission fibers 102 and 104, photoelectric signal detection and amplification unit 105, and information display unit 108 are basically the same as those for conventional optical polarization or optical intensity modulation type voltage sensors.

[0015] As attached Figure 1 The optical voltage sensor system shown in the figure has a voltage sensing crystal in the voltage sensing head 103 that can generate a voltage sensing signal containing harmonics within the range of the AC voltage to be measured. The electronic filtering unit 106 should be able to perform electronic filtering of the voltage sensing signal and separation of different harmonic components. The division operation unit 107 can perform division operation on the different harmonic components output by the above filter to obtain the voltage signal to be measured.

[0016] The technical solution of the optical voltage sensor and its signal processing method described in this invention is as follows: (See attached diagram) Figure 1 As shown, the voltage sensing head is assembled from a fiber optic collimator (e.g., a self-focusing lens), two prism polarizers, an electro-optic crystal, and a support base. According to the attached... Figure 1 After the various units and devices shown are assembled into a voltage sensing system, the AC voltage to be measured is introduced into the electro-optic crystal through wires and electrodes. The AC voltage sensing signal containing nonlinear harmonics can then be obtained through a photodetector and an amplifier circuit. Different harmonic components can then be separated using an analog electronic filter or a data acquisition card and its LabVIEW software. The separated harmonic components can be divided using an analog divider or LabVIEW software program to obtain the amplitude of the AC voltage being measured. Furthermore, the voltage sensing signal can eliminate the adverse effects of light source power fluctuations, crystal birefringence temperature, and photoelastic effects.

[0017] The light source 101 with a pigtail in the voltage sensing system of the present invention should be a broadband incoherent light source, such as a superluminescent light-emitting diode (SLED), whose working light wavelength is generally in the near-infrared spectrum range, such as a broadband light source with a center wavelength of 850nm, 1310nm or 1550nm, and whose output light power is about 1 to 2mW.

[0018] In the voltage sensing system described in this invention, the incident optical fiber 102 is generally a single-mode optical fiber, and the output optical fiber 104 is generally a multimode optical fiber.

[0019] The electro-optic crystal in the voltage sensing head 103 of the present invention should be a crystal with linear electro-optic effect and a large electro-optic coefficient, such as lithium niobate (LN) crystal, potassium titanium oxyphosphate (KTP) crystal, rubidium titanium oxy arsenate (RTA) crystal, etc. It adopts a transverse electro-optic modulation method, that is, the direction of the voltage to be measured applied to the crystal is perpendicular to its light transmission direction. The crystal shape can be rectangular, and its quarter-wave voltage value is required to be approximately the minimum measured voltage amplitude, so as to ensure that a sensing signal containing nonlinear harmonics can be generated within the measured voltage range.

[0020] The photodetector in the photoelectric signal detection and amplification unit 105 of the present invention should be a photodetector sensitive in the near-infrared spectral range, such as a heterojunction photodiode; at the same time, the signal amplification circuit accompanying the photodetector should be able to amplify the optical sensing signal with an optical power of about a few μW to a voltage sensing signal with an amplitude of about 1 to 5V.

[0021] The electronic filtering unit 106 described in this invention is used to filter and separate different harmonic components in the output voltage sensing signal. It can be implemented using an analog electronic filter or an electronic filtering function module in the auxiliary software of a data acquisition card.

[0022] The division operation unit 107 of the present invention is used to perform division operations between the third harmonic component and the fundamental frequency component separated by the above filtering, or between the fourth harmonic component and the second harmonic component. It can be implemented by an electronic analog divider or the division operation function module in the LabVIEW software program attached to the data acquisition card.

[0023] The total phase delay Γ of the sensing crystal in the voltage sensing head 103 of the present invention for the two linear intrinsic polarization components of the incident light wave can be expressed as: Γ=Γ0+Γ e (1) Where Γ0 represents the phase retardation caused by the crystal's natural birefringence or other inherent birefringence, it is easy to see that its value will drift due to the temperature shift in the crystal's refractive index. e This represents the electro-optic phase delay of the crystal.

[0024] Based on the Pockels effect of electro-optic crystals, Γ in the above equation (1) can be... e Represented as, Γ e =Ku(t)=KU m sin(ωt), (2) In the formula, K is the coefficient related to the Pockels effect, u(t) is the instantaneous value of the measured voltage, and U m Let ω be its amplitude, ω be its angular frequency, and t be time.

[0025] The voltage sensing head 103 of this invention can employ typical optical polarization and optical intensity modulation methods, and its structure is shown in the attached figure. Figure 2 As shown, in the laboratory coordinate system o-xyz, when the azimuth angles of the polarizer 201 and analyzer 203 are set to 0° and 90° respectively, and the azimuth angle of the principal axis of the electro-optic birefringence of the electro-optic crystal 202 is 45°, the output light intensity sensing signal I2 can be expressed as follows: In the formula, I1 is the incident light intensity of the electro-optic crystal 202.

[0026] In the above equation (3), let KU m =β, ωt =γ, it is easy to see that the expression contains function terms of the form cos(βsinγ) and sin(βsinγ). According to relevant mathematical handbooks, it can be expressed as the following Bessel function expansion. In the formula J n (β) is the nth-order Bessel function of the first kind. According to relevant mathematical handbooks, its series expression is:

[0027] Substituting equations (4) and (5) into equation (3), we obtain the following expression for the optical sensing signal:

[0028] The amplitudes of the DC component and each harmonic component in equation (7) above can be expressed as follows: A1=I1sinΓ0J1(KU m (9) A2=-I1cosΓ0J2(KU m (10) A3=I1sinΓ0J3(KU m (11) A4=-I1cosΓ0J4(KU m (12)

[0029] After passing through the photoelectric detection and amplification circuit, the above-mentioned optical sensing signal can be proportionally converted into a voltage sensing signal. Considering that the general sensing signal detection and processing unit is in an indoor temperature environment, it can be assumed that the linear proportional transformation coefficients involved in the photoelectric detection and amplification circuit, as well as subsequent electronic filtering and division operations, can remain stable. Therefore, only the amplitudes of the harmonic components of the above-mentioned optical sensing signal are considered.

[0030] Based on the characteristics of equations (9)-(12) above, in order to remove the adverse effects of unstable light intensity I1 and the temperature and photoelastic effects of the inherent phase delay Γ0 on the sensing signal, this invention proposes to perform the following division operation on the amplitudes of the harmonic components of different orders above. According to the above formulas (13) and (14), the present invention uses the optoelectronic detection signal proportional to S1 and S2 as the voltage sensing signal, which can effectively remove the drift of the voltage sensing signal caused by factors such as the instability of the optical power I1, and the temperature and elasto-optic effects of the phase delay Γ0.

[0031] To illustrate the feasibility of using the signal proportional to S1 and S2 as the voltage sensing signal, according to the above formulas (13), (14) and the Bessel function expression (6), a mathematical software can be used to simulate and draw the non-linear function relationship curves of the functions S1 and S2 changing monotonically with the independent variable β. For example: within the range of 0 < β < 2.6, the non-linear relationship curves of S1 and S2 changing with β are as shown in the appendix Figure 3 shown, corresponding to the ratio value ranges of 0 < S1 < 0.5 and 0 < S2 < 0.18 respectively. It can be seen that S1 and S2 change monotonically with β or the measured voltage amplitude U m monotonically.

[0032] Further simulation results show that the value range of the function S1 changing monotonically with β is approximately 0 < β < 3.8, and the value range of the function S2 changing monotonically with β is approximately 0 < β < 5.1 respectively. According to the above relational formula β = KU m , when the coefficient K related to the Pockels effect of the sensing crystal is known, the theoretically monotonic measurement range of the measured voltage amplitude can be estimated, that is, 0 < U m < (3.8 / K) and 0 < U m < (5.1 / K).

[0033] Compared with the conventional crystal-type voltage sensors, the voltage sensor of the present invention has the following technical advantages and beneficial effects: 1) According to the above formulas (9)-(14), theoretically, the output voltage sensing signal S1 or S2 is not affected by the temperature effect of the inherent birefringence phase delay Γ0 of the crystal itself, thereby effectively suppressing the optical bias drift caused by the crystal birefringence effect in the conventional typical optical voltage sensors. 2) The electro-optic crystal used for sensing is usually subjected to additional stress or strain during the assembly of the voltage sensing unit and the voltage sensing application process. According to the elasto-optic effect of the crystal, this will also cause an additional birefringence phase delay Γ0 of the crystal to the light wave. Therefore, according to the above formulas (9)-(14), theoretically, when using S1 or S2 as the output voltage sensing signal, the influence of the additional stress or strain on the voltage sensing performance can also be effectively removed. 3) According to the above formulas (9)-(14), the output voltage sensing signal S1 or S2 does not contain the incident light intensity I1 of the sensing crystal, thereby effectively removing the adverse influence of the instability of the light intensity I1 in the optical path on the output voltage sensing signal.

[0034] The main shortcomings of this invention include: 1) As can be seen from the above equations (13)-(14), the relationship between the output voltage sensing signal S1 or S2 and the measured voltage is a nonlinear response function. 2) According to the appendix Figure 3 When the measured voltage amplitude is low, the corresponding ratio S1 or S2 is very small because the harmonic components in the output voltage sensing signal are very small at this time. This limits the measured voltage range of the present invention. Therefore, it is recommended that the measured voltage be greater than the quarter-wave voltage of the crystal in the design of the sensing unit.

[0035] The voltage sensor and signal processing method described in this invention can be applied to the sensing and measurement of power frequency voltage in power systems or smart grids, or to the sensing and measurement of AC voltage in other similar situations. Attached Figure Description

[0036] Appendix Figure 1 Block diagram of the optical voltage sensor system described in this invention.

[0037] Appendix Figure 2 Schematic diagram of the structure of a crystal-type optical voltage sensor head.

[0038] Appendix Figure 3 The curves showing the functional relationship between the output voltage sensing signals S1 and S2 and β.

[0039] Appendix Figure 4 A schematic diagram of the support base structure for a crystal-type optical voltage sensing unit.

[0040] Appendix Figure 5 The flowchart of the LabVIEW software program used in the experiment to implement digital filtering and division operations.

[0041] Appendix Figure 6 A typical voltage sensing signal waveform output from an oscilloscope.

[0042] Appendix Figure 7 A typical voltage sensing signal waveform output by a data acquisition card.

[0043] Appendix Figure 8 Typical experimental data graphs showing the variation of output voltage sensing signals S1 and S2 with the measured voltage under room temperature conditions.

[0044] Appendix Figure 9 A set of typical experimental data graphs showing the variation of voltage sensing signal S1 with the measured voltage under different temperature conditions.

[0045] Appendix Figure 10 A set of typical experimental data graphs showing the variation of the total effective value of the voltage sensing signal with the measured voltage under different temperature conditions. Detailed Implementation

[0046] The inventors have conducted experimental research on AC voltage sensing based on the above-mentioned invention. The voltage sensor system used in the experiment is shown in the attached figure. Figure 1 As shown in the figure. The following describes a specific embodiment of the present invention based on relevant experimental results and accompanying drawings.

[0047] As attached Figure 2 As shown, the electro-optic crystal 202 of this invention can be a lithium niobate crystal. For example, the specific parameters of the lithium niobate crystal used in the experiment are as follows: its actual dimensions in the x1, x2, and x3 directions of its own principal axis are 2 mm, 4 mm, and 36 mm, respectively. Among them, two (100) crystal planes are gold-plated electrodes, two (001) crystal planes are polished, and the other two crystal planes (010) are finely ground. According to the known relevant parameters of this crystal, its half-wave voltage for incident light with a wavelength of 633 nm can be estimated to be about 240 V (see: Li Changsheng. Optical voltage sensor based on the self-angle light bias of lithium niobate crystal [J]. Journal of Sensor Technology, 2007, 20(7), 1494-1497.). In addition, Figure 2 The polarizer 201 and analyzer 203 shown can be prism-type polarizers, such as Glan-Thompson prisms, with an extinction ratio of up to 10. 5 .

[0048] The schematic diagram of the sensor head support base structure in the voltage sensing unit 103 mentioned above is attached. Figure 4 As shown in the diagram. Position 401 is used to fix the self-focusing rod lens connected to the end of the incident single-mode fiber, used to generate a collimated parallel beam; positions 402 and 404 are for placing prism polarizers P1 and P2, respectively; position 403 is used to place and fix the sensing crystal and electrodes; position 405 is for placing the adjustable clamp of the output fiber, which can be laterally adjusted along the direction perpendicular to the beam to better couple the sensing beam into the output fiber; position 406 shows two screws used to fix the clamp.

[0049] As attached Figure 1In the voltage sensing system shown, the other components and their parameters used in the specific experiment are as follows: 1) The light source 101 is a superluminescent diode (SLED) with a center wavelength of 1304 nm, a spectral half-width of 38 nm, an average wavelength of 1307 nm, and an output optical power of 1 mW. 2) The operating wavelength of the input single-mode fiber 102 is 1310 nm, and the fiber length is 1.5 m. 3) The collimated beam spot diameter generated by the self-focusing rod lens connected to the single-mode fiber 102 is approximately 0.5 mm. 4) The output receiving fiber 104 is a quartz core multimode fiber with a core diameter of 0.6 mm and a fiber length of approximately 2 m. Other similar multimode fibers can also be used, such as plastic fibers with a core diameter of 1 mm. 5) The photoelectric detection and amplification unit 105 includes a photodetector and an analog electronic amplification circuit. The photodetector is made of indium gallium arsenide (InGaAs), and its normal detection wavelength range is 1100-1650nm. Its responsivity at a wavelength of 1310nm is greater than 0.85A / W. The analog amplification circuit is mainly a transimpedance amplifier circuit using an integrated operational amplifier of model CA3140.

[0050] As attached Figure 1 In the voltage sensing system shown, the voltage sensing signal output from the photodetector and amplification unit 105 is connected to an oscilloscope (model TDS-1062) and a data acquisition card (model USB-6210, manufactured by NI). The connection to the acquisition card uses a differential input and measurement method. Then, the acquisition card is connected to a computer via its USB interface, and the LabVIEW software program on the computer processes, stores, and displays the voltage sensing signal, thus achieving the desired signal transmission. Figure 1 The functions of the filtering unit 106, the division unit 107, and the information display unit 108 are described below. The LabVIEW software flowchart for implementing digital filtering and division operations is attached. Figure 5 As shown.

[0051] As attached Figure 5The diagram shows the data acquisition card and its LabVIEW software program. The data acquisition card 501 receives the voltage sensing signal output by the photoelectric detection and amplification unit 105 and transmits it to various LabVIEW software program modules in the computer, including the total effective voltage value calculation module 502, the 50Hz filtering module 503, the 150Hz filtering module 504, the 100Hz filtering module 506, and the 200Hz filtering module 507. Then, the fundamental frequency and third harmonic component signals output by the filtering modules 503 and 304 are input to the division operation module 505 to obtain a voltage sensing signal proportional to S1. The second harmonic and fourth harmonic component signals output by the filtering modules 506 and 307 are input to the division operation module 508 to obtain a voltage sensing signal proportional to S2.

[0052] First, the power frequency voltage, with an effective value of approximately 50–260V, was experimentally measured at room temperature. A typical output voltage sensing signal waveform observed using an oscilloscope during the experiment is recorded below. Figure 6 As shown, the horizontal axis represents time (s), and the vertical axis represents the output voltage amplitude (V). In the figure, channel 2 is the original photoelectric detection signal (1V / division), and channel 1 is its amplified AC component (5V / division). Figure 6 The effective value of the measured voltage during sampling was 220V, indicating that the output signal waveform contained obvious harmonic signals.

[0053] In the experiment, it is necessary to ensure that the voltage sensing signal sampled by the data acquisition card is consistent with the signal displayed synchronously on the oscilloscope. For example, with the attached... Figure 6 The waveform of the sensing signal corresponding to the AC voltage sensing signal shown in channel 1, which is sampled and acquired by the data acquisition card, is shown in the attached figure. Figure 7 As shown, the waveform is taken from the LabVIEW software block diagram. Figure 5 Waveform diagram output by module 502.

[0054] Using the aforementioned data acquisition card and its corresponding LabVIEW data processing program, voltage sensing signals proportional to S1 and S2 as shown in equations (13) and (14) can be obtained. A set of typical experimental data showing the variation of the voltage sensing signals corresponding to S1 and S2 with the effective value of the measured voltage is attached. Figure 8 As shown in the figure, the vertical axis represents the output signal obtained by the LabVIEW data processing program.

[0055] To verify the effectiveness of the voltage sensing scheme described in this invention in suppressing the birefringence phase delay Γ0 temperature effect of the sensing crystal, the voltage sensing system and a temperature test chamber (model T-40 / 25) manufactured by CTS were used to experimentally measure the power frequency voltage with an effective value of 50 to 260V within a temperature range of -40 to 60℃.

[0056] In the above temperature experiment, a set of typical experimental data on the variation of S1 with the measured voltage under six typical temperature conditions at intervals of 20°C is attached. Figure 9 As shown, the voltage sensing signal exhibits good consistency within the temperature range of -40 to 60℃. Meanwhile, a set of typical experimental data showing the total effective value of the output voltage sensing signal varying with the measured voltage is attached. Figure 10 As shown, the consistency of the corresponding voltage sensing signal is poor. Comparison reveals that using different harmonic component ratios as the voltage sensing signal can effectively suppress temperature drift of the sensing signal.

Claims

1. A crystal-type AC voltage sensor and its sensing signal processing method, characterized in that: Its voltage sensor system mainly includes a light source, transmission optical fiber, voltage sensing unit, photoelectric detection and signal processing unit. The electro-optic crystal in the voltage sensing unit can enable the optical carrier to generate an optical sensing signal containing the harmonic components of the measured voltage. In the signal processing unit, by separating different harmonic components and performing division operations, the measured AC voltage sensing signal can be obtained and the influence of its optical bias drift can be effectively suppressed.

2. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The light source is a broadband, low-coherence light source, and its output optical power is generally in the milliwatt range. Its center wavelength and spectral half-width are consistent with the parameters of commonly used light sources for optical sensing on the market.

3. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The voltage sensing unit can generate optical bias by reasonably setting the deflection angle between the principal optical axis of the uniaxial electro-optic crystal and the beam, or by selecting a biaxial electro-optic crystal as the voltage sensing crystal to generate optical bias. The selection of the optical bias value should enable the sensing crystal to easily generate an optical sensing signal containing harmonics under the action of the AC voltage being measured.

4. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The electro-optic crystal used for sensing can generate an optical sensing signal containing harmonic components of the measured voltage by the optical carrier under the modulation of the measured AC voltage. Therefore, it is required to reasonably select and design the type, shape and size of the electro-optic crystal according to the amplitude range of the measured voltage to ensure that the optical sensing signal contains each harmonic component of the measured voltage, and that these harmonic components simultaneously contain the influence of the measured voltage signal and the inherent birefringence of the sensing crystal.

5. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The photoelectric detection and signal processing unit can proportionally detect, amplify, and simultaneously separate different harmonic components in the photovoltage sensing signal, such as the fundamental frequency, second harmonic, third harmonic, and fourth harmonic components. The filtering and separation of different harmonic components can be achieved by using the digital filtering function module in the data acquisition card and its LabVIEW software program.

6. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The signal processing unit can perform reasonable calculations on different harmonic components in the sensing signal described in claim 4, thereby effectively removing or suppressing the influence of inherent birefringence instability in the sensing crystal on the voltage sensing signal. For example, the division operation function module in LabVIEW software can be used to realize the division operation between the third harmonic and the fundamental frequency component, or the division operation between the fourth harmonic and the second harmonic component.

7. The AC voltage sensor and its sensing signal processing method according to claim 1, characterized in that: The signal processing unit can perform reasonable calculations on different harmonic components in the sensing signal described in claim 4, thereby effectively removing or suppressing the adverse effects of unstable optical power in the sensing optical path on the voltage sensing signal. For example, the division operation method described in claim 6 can be used.

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