A grating light valve type current sensor based on a micro-power optical control signal source

Abstract

The present invention discloses a grating light valve type current sensor based on a micro-power optical control signal source, which includes a signal processing unit and a sensing unit. The sensing unit is a three-beam grating light valve temperature-current sensing unit based on micro-optoelectromechanical system technology. The signal processing unit adopts a closed-loop demodulation algorithm to obtain the detected current by demodulating the output compensation phase shift. In the closed-loop demodulation algorithm, error correction is performed according to the temperature information measured by the sensing unit to correct the influence of ambient temperature change on the measurement accuracy of the sensing unit. At the same time, the micro-power optical control signal source technology is used to realize the closed-loop optical feedback control of the grating light valve, improve the measurement linearity of the grating light valve in the closed-loop demodulation algorithm, and increase the dynamic measurement range.

Description

Technical Field

[0001] The present invention relates to an optical fiber current sensor. Background Art

[0002] In the production and transmission of electric power and the operation of electric power equipment, it is necessary to monitor various physical quantities, and current is one of the most important parameters. At present, a series of problems exist in the traditional electromagnetic current transformers widely used in the power system, such as magnetic saturation, large electromagnetic interference, small dynamic range, narrow frequency band range, flammability, explosiveness, etc. Moreover, with the increase of the operating voltage level of the power grid, the design of the insulation structure of the traditional transformer will become extremely complicated, and its cost and volume will increase sharply accordingly.

[0003] With the in-depth development of substation automation technology, new intelligent primary equipment with the mutual penetration and integration of primary and secondary equipment has emerged. Replacing the traditional electromagnetic transformer with an electronic transformer, transmitting digital signals through optical fibers, integrating relay protection and measurement and control functions in-situ, and combining with a circuit breaker or a gas-insulated switchgear to form a new generation of intelligent primary equipment can enhance the reliability and flexibility of real-time monitoring and control of the substation automation system, reduce construction and operation investment, and facilitate maintenance.

[0004] The optical current transformer (OCT) uses an optical medium as the medium for current sensing and / or signal transmission, can overcome the shortcomings of traditional current transformers, and has the advantages of good insulation performance, small volume, no magnetic saturation and ferromagnetic resonance, wide frequency response range, good electromagnetic compatibility, etc. And it can be seamlessly connected with the existing communication network, meeting the development direction of the power system towards networking and intelligence. However, high cost and great influence by environmental disturbances such as temperature and vibration are still the main problems faced in the mass production process of OCT. Summary of the Invention

[0005] Object of the Invention: A grating light valve type current sensor based on a micro-power optical control signal source is proposed for the above-mentioned existing technology, which can eliminate the influence of environmental temperature change on the measurement accuracy of the fiber optic direct current sensor, and enables the measurement to have a high linearity and a large dynamic measurement range.

[0006] Technical Solution: A grating light valve type current sensor based on a micro-power optical control signal source includes a signal processing unit and a sensing unit;

[0007] The sensing unit is a three-beam grating light valve temperature-current sensing unit based on micro-optical electromechanical system technology, including a first polarization-maintaining fiber collimator, a second polarization-maintaining fiber collimator, a third polarization-maintaining fiber collimator, a current-sensitive beam, a feedback control beam, a temperature-sensitive beam, and a substrate; reflective films are plated on the surfaces of the current-sensitive beam, the feedback control beam, and the temperature-sensitive beam, and they are respectively arranged opposite to the output ends of the first polarization-maintaining fiber collimator, the second polarization-maintaining fiber collimator, and the third polarization-maintaining fiber collimator. There are air gaps between the bottom surfaces of the current-sensitive beam, the feedback control beam, and the temperature-sensitive beam and the substrate; the current-sensitive beam and the feedback control beam are made of permanent magnetic materials, and the temperature-sensitive beam is made of temperature-sensitive materials;

[0008] The signal processing unit adopts a closed-loop demodulation algorithm. In the closed-loop demodulation algorithm, a micro-power laser outputs a laser signal composed of a square wave signal, a first stepped wave signal, and a second stepped wave signal under the control of a signal processor. The laser signal is transmitted through a single-mode fiber and converted into an electrical signal by a photodiode. The electrical signal is amplified by a transformer and then loaded onto the feedback control beam of the sensing unit; among them, the square wave signal corresponds to generating a non-reciprocal π / 2 modulation phase shift, the first stepped wave signal corresponds to generating a compensation phase shift φ l , and the second stepped wave signal corresponds to generating a compensation phase shift Ф f ; the signal processor demodulates the compensation phase shift Ф f to obtain temperature information, calculates a temperature error correction coefficient according to the temperature information, and introduces the temperature error correction coefficient into the process of the signal processor demodulating the compensation phase shift φ l to obtain current information.

[0009] Furthermore, the reflective film adopts aluminum or a dielectric material with an emissivity greater than 92%.

[0010] Furthermore, the signal processing unit further includes a broadband light source, a depolarizer, a 1×3 beam splitter, a first circulator, a first polarizer, a first polarization-maintaining transmission fiber, a Faraday rotator, a first polarization beam splitter, a 1×2 beam splitter, a second circulator, a second polarizer, a second polarization-maintaining transmission fiber, and a second polarization beam splitter;

[0011] The output end of the broadband light source is connected to the input end of the depolarizer, the output end of the depolarizer is connected to the input end of the 1×3 beam splitter, the first output end of the 1×3 beam splitter is connected to the first end of the first circulator, the second end of the first circulator is connected to the input end of the first polarizer, the output end of the first polarizer is connected to the input end of the Faraday rotator through the first polarization-maintaining transmission fiber, the output end of the Faraday rotator is connected to the input end of the first polarization beam splitter, and the two output ends of the first polarization beam splitter are respectively connected to the first polarization-maintaining fiber collimator and the first output end of the 1×2 beam splitter; the third end of the first circulator is connected to the first input end of the signal processor;

[0012] The second output end of the 1×3 beam splitter is connected to the first end of the second circulator. The second end of the second circulator is connected to the input end of the second polarizer. The output end of the second polarizer is connected to the input end of the second polarization beam splitter through a second polarization-maintaining transmission optical fiber. The two output ends of the second polarization beam splitter are respectively connected to the third polarization-maintaining optical fiber collimator and the second output end of the 1×2 beam splitter. The input end of the 1×2 beam splitter is connected to the second polarization-maintaining optical fiber collimator. The third end of the second circulator is connected to the second input end of the signal processor; the first output end of the signal processor is connected to the input end of the micro-power laser.

[0013] Further, the third output end of the 1×3 beam splitter is connected to the third input end of the signal processor. The second output end of the signal processor is connected to the control end of the broad-spectrum light source; the signal processor performs feedback control on the output wavelength of the broad-spectrum light source according to the wavelength signal obtained by demodulation.

[0014] Beneficial effects: A grating light valve type current sensor based on a micro-power optical control signal source of the present invention uses a three-beam grating light valve based on micro-optical electro-mechanical system (MOEMS) technology to sense temperature and current signals. The signal processing unit performs closed-loop demodulation of temperature and current signals and generates micro-power optical control signals. The present invention corrects the self-temperature error of current acquisition through the temperature information collected by the three-beam grating light valve, improving the environmental adaptability of the sensor. The closed-loop optical feedback control of the system is realized by using the micro-power optical control signal source technology to improve the measurement linearity and dynamic measurement range of the sensor. Description of the Drawings

[0015] Figure 1 It is a structural diagram of a grating light valve type current sensor based on a micro-power optical control signal source of the present invention;

[0016] Figure 2 It is a schematic diagram of the superposition of a square wave and a stepped wave in the present invention. Detailed Embodiments

[0017] The following further explains the present invention with reference to the drawings.

[0018] As Figure 1 shown, a grating light valve type current sensor based on a micro-power optical control signal source includes a signal processing unit and a sensing unit.

[0019] The sensing unit includes a first polarization-maintaining fiber collimator 9, a second polarization-maintaining fiber collimator 12, a third polarization-maintaining fiber collimator 14, a current-sensitive beam 10, a feedback control beam 13, a temperature-sensitive beam 15, and a substrate 16. Reflective films are plated on the surfaces of the current-sensitive beam 10, the feedback control beam 13, and the temperature-sensitive beam 15, and they are respectively arranged opposite to the output ends of the first polarization-maintaining fiber collimator 9, the second polarization-maintaining fiber collimator 12, and the third polarization-maintaining fiber collimator 14. An air gap with a thickness of about 1 μm is provided between the bottom surfaces of the current-sensitive beam 10, the feedback control beam 13, and the temperature-sensitive beam 15 and the substrate 16. Among them, the current-sensitive beam 10 and the feedback control beam 13 are made of permanent magnetic materials, the temperature-sensitive beam 15 is made of temperature-sensitive materials, and the dimensions of the three beams are all 1 - 10 μm in width, 100 - 1000 μm in length, and 200 - 300 nm in thickness; the reflective film uses aluminum or dielectric materials with an emissivity greater than 92%; the substrate 16 is made of semiconductor Si and electromagnetic materials.

[0020] The signal processing unit includes a broadband light source 1, a depolarizer 2, a 1×3 beam splitter 3, a first circulator 4, a first polarizer 5, a first polarization-maintaining transmission fiber 6, a Faraday rotator 7, a first polarization beam splitter 8, a 1×2 beam splitter 11, a signal processor 17, a micro-power laser 18, a single-mode fiber 19, a photodiode 20, a transformer 21, a second circulator 22, a second polarizer 23, a second polarization-maintaining transmission fiber 24, and a second polarization beam splitter 25.

[0021] The output end 11 of the broadband light source 1 is connected to the input end of the depolarizer 2, the output end of the depolarizer 2 is connected to the input end of the 1×3 beam splitter 3, the first output end of the 1×3 beam splitter 3 is connected to the first end of the first circulator 4, the second end of the first circulator 4 is connected to the input end of the first polarizer 5, the output end of the first polarizer 5 is connected to the input end of the Faraday rotator 7 through the first polarization-maintaining transmission fiber 6, the output end of the Faraday rotator 7 is connected to the input end of the first polarization beam splitter 8, and the two output ends of the first polarization beam splitter 8 are respectively connected to the first polarization-maintaining fiber collimator 9 and the first output end of the 1×2 beam splitter 11; the third end of the first circulator 4 is connected to the first input end of the signal processor 17.

[0022] The second output end of the 1×3 beam splitter 3 is connected to the first end of the second circulator 22, the second end of the second circulator 22 is connected to the input end of the second polarizer 23, the output end of the second polarizer 23 is connected to the input end of the second polarization beam splitter 25 through the second polarization-maintaining transmission fiber 24, the two output ends of the second polarization beam splitter 25 are respectively connected to the third polarization-maintaining fiber collimator 14 and the second output end of the 1×2 beam splitter 11, the input end of the 1×2 beam splitter 11 is connected to the second polarization-maintaining fiber collimator 12, and the third end of the second circulator 22 is connected to the second input end of the signal processor 17.

[0023] The first output terminal of the signal processor 17 is connected to the input terminal of the micro-power laser 18. The output terminal of the micro-power laser 18 is connected to the input terminal of the photodiode 20 through a single-mode optical fiber 19. The output terminal of the photodiode 20 is connected to the input terminal of the transformer 21. The output terminal of the transformer 21 is connected to the feedback control beam 13.

[0024] The third output terminal of the 1×3 beam splitter 3 is connected to the third input terminal of the signal processor 17. The second output terminal of the signal processor 17 is connected to the control terminal of the broad-spectrum light source 1.

[0025] In the above structure, the light emitted by the broad-spectrum light source 1 passes through the depolarizer 2, the 1×3 optical splitter 3, the first circulator 4, and the first polarizer 5 to form linearly polarized light. The linearly polarized light enters the first polarization-maintaining transmission optical fiber 6 at an angle of 45°, and then is divided into two orthogonal linearly polarized lights that are transmitted along the fast and slow axes of the first polarization-maintaining transmission optical fiber 6 respectively. After passing through the first polarization-maintaining transmission optical fiber 6, it reaches the Faraday rotator 7, and then the two orthogonal linearly polarized modes are rotated by 45°. After being split by the first polarization beam splitter 8, one of the outputs passes through the first polarization-maintaining optical fiber collimator 9 and then enters the current-sensitive beam 10, and the other output passes through the 1×2 beam splitter 11 and the second polarization-maintaining optical fiber collimator 12 and then enters the feedback control beam 13.

[0026] When the two orthogonal linearly polarized lights are reflected by the reflecting surfaces of the current-sensitive beam 10 and the feedback control beam 13, they return along the original path and pass through the Faraday rotator 7 again. At this time, the two orthogonal linearly polarized modes are rotated by 45° again and the mode conversion occurs. Finally, equal-path interference occurs at the first polarizer 5. The interference signal passes through the first circulator 4 and then is sent into the signal processor 17.

[0027] The current to be measured is converted into the voltage to be measured U through a sampling resistor or a Rogowski coil. When it acts on the current-sensitive beam 10, under the action of the electrostatic force, the current-sensitive beam 10 undergoes a small deformation. At this time, a high and low reflecting surface is formed between the current-sensitive beam 10 and the feedback control beam 13, which causes a change in the phase difference between the surface reflected lights. Therefore, the output interference signal also changes with the change of the current to be measured.

[0028] Specifically, after the two polarized lights reflected by the current-sensitive beam 10 and the feedback control beam 13 interfere, they pass through the first circulator 4 and then are sent into the optical signal processor 17. The received optical wave interference signal is:

[0029]

[0030] Wherein, P0 is the input light intensity, λ is the wavelength of the incident light, d = y1 - y2 is the displacement difference between the current-sensitive beam 10 and the feedback control beam 13. Here, y1 is the displacement generated by the current-sensitive beam 10 under the action of the voltage to be measured, which is linearly related to the voltage to be measured within the elastic deformation range, and y2 is the displacement generated by the feedback control beam 13, and the magnitude of the displacement is related to the feedback control voltage applied to the feedback control beam 13. Therefore, by detecting the magnitude of the interference signal intensity, the position of the feedback control beam 13 can be inferred, and further the magnitude of the direct current to be measured can be inferred.

[0031] For the grating light valve, the difference in the thermal expansion coefficients of the two materials, namely the aluminum reflective film and the silicon substrate, on the surfaces of the sensitive beam and the feedback beam will cause the optical loss coefficient and the optical path difference of the grating light valve to change with temperature, thereby causing errors in the optical wave interference signal received by the photoelectric receiver. Using δ to represent the equivalent error coefficient, the optical wave interference signal received by the photoelectric receiver is:

[0032]

[0033] It can be seen from Equation (2) that the interference output result is a cosine function, with low response sensitivity near the zero phase difference, limited measurement range, and the interference result cannot reflect the directionality of the input current and other defects. In order to solve the problems of cosine sensitivity and directionality, improve the linearity of the detection system, and increase the dynamic range, the present invention adds a closed-loop optical feedback control structure based on a micro-power optical control signal source to the closed-loop demodulation algorithm.

[0034] The signal processor 17 drives the 980nm micro-power laser 18 to output a modulated optical signal composed of a square wave and a first stepped wave in a pulse code modulation manner. The optical signal is sent to the high-voltage end through a single-mode optical fiber 19. The high-voltage end uses a Si-based photodiode 20 to convert the optical energy into a current signal proportional thereto, and after being stepped up by a transformer 21, it is applied to the feedback control beam 13. Among them, the square wave modulation introduces a non-reciprocal phase bias φ s , and the first stepped wave introduces a compensation phase shift φ l . Under the combined action of the two, the non-reciprocal phase shift caused by the current can be offset, so that the system output operates near the operating point with a non-zero response slope and zero phase difference.

[0035] At this time, the optical wave interference signal P D received by the signal processor 17 is:

[0036]

[0037] Taking φ s = ±π / 2, the output signals of the positive and negative half-cycles of the square wave modulation signal are:

[0038]

[0039] Subtracting the output signals of the positive and negative half-cycles of the square-wave modulation signal, we can obtain:

[0040]

[0041] According to the closed-loop demodulation algorithm, the signal processor generates a first stepped-wave to feedback and compensate for the phase shift φ l , such that P diff = 0, and we can obtain:

[0042]

[0043] In the closed-loop case, The value is small, satisfying the small-angle approximation condition, and we can obtain:

[0044]

[0045] Therefore,

[0046]

[0047] As Figure 2 shown, at this time, the compensation phase shift φ l is both the step height of the stepped-wave signal and the demodulation output. It can be seen that φ l is related to δ, where the environmental temperature change is the key factor introducing δ. For this reason, the present invention designs a three-beam grating light valve and uses its temperature-sensitive beam 15 to detect temperature information. The principle is as follows:

[0048] The light emitted by the broadband light source 1 passes through the depolarizer 2, 1×3 beam splitter 3, second circulator 22, and second polarizer 23 to form linearly polarized light. The linearly polarized light enters the second polarization-maintaining transmission fiber 24 at an angle of 45°, and then is divided into two orthogonal linearly polarized lights that are respectively transmitted along the fast and slow axes of the second polarization-maintaining transmission fiber 24. After passing through the second polarization-maintaining transmission fiber 24, it reaches the second polarization beam splitter 25. After being split by the second polarization beam splitter 25, one of the outputs passes through the third polarization-maintaining fiber collimator 14 and then enters the temperature-sensitive beam 15, and the other output passes through the 1×2 beam splitter 11 and the second polarization-maintaining fiber collimator 12 and then enters the feedback control beam 13.

[0049] When the two orthogonal linearly polarized lights are reflected by the reflecting surfaces of the temperature-sensitive beam 15 and the feedback control beam 13, they return along the original path and finally interfere at the second polarizer 23. The interference signal is sent into the signal processor 17 after passing through the second circulator 22.

[0050] When temperature acts on the temperature-sensitive beam 15, due to thermal expansion and contraction, the temperature-sensitive beam 15 undergoes a slight deformation, resulting in a reflective surface with different heights between it and the feedback control beam 13. This causes the phase difference between the reflected lights on its surface to change with the temperature, and further causes the interference output light intensity to also change with the temperature.

[0051] The interference output light intensity P caused by temperature T is expressed as:

[0052]

[0053] where d T is the micro-displacement of the temperature-sensitive beam 15 relative to the feedback control beam 13, and φ f is the second-order step wave feedback compensation phase shift introduced due to temperature change.

[0054] Taking the square wave modulation phase shift φ s = ±π / 2, the output signals of the positive and negative half-cycles of the square wave modulation signal are,

[0055]

[0056] Subtracting the output signals of the positive and negative half-cycles of the square wave modulation signal, we can obtain:

[0057]

[0058] According to the closed-loop demodulation algorithm, the signal processor generates the second-order step wave feedback compensation phase shift φ f , such that P T-diff = 0, and we can obtain:

[0059]

[0060] where k′ is the temperature coefficient, and φ f is also used as the temperature demodulation output at the same time.

[0061] The signal processor 17 obtains information based on the temperature measurement, calculates the error correction coefficient (1 - δ), and multiplies it with Equation (8), and we can obtain:

[0062]

[0063] In the present invention, the sensing head of the grating light valve type fiber optic direct current sensor is pre-placed in an environmental test chamber to obtain the variation law of the system output with temperature, and the error correction coefficient (1 - δ) can be determined according to the previously obtained variation law. Thus, the influence of temperature on the measurement accuracy of the system can be eliminated.

[0064] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A grating light valve type current sensor based on a micro-power optical control signal source, characterized in that, It includes a signal processing unit and a sensing unit; The sensing unit is a three-beam grating light valve temperature-current sensing unit based on micro-optical electro-mechanical system technology, including a first polarization-maintaining fiber collimator (9), a second polarization-maintaining fiber collimator (12), a third polarization-maintaining fiber collimator (14), a current-sensitive beam (10), a feedback control beam (13), a temperature-sensitive beam (15), and a substrate (16); reflective films are plated on the surfaces of the current-sensitive beam (10), the feedback control beam (13), and the temperature-sensitive beam (15), and they are respectively arranged opposite to the output ends of the first polarization-maintaining fiber collimator (9), the second polarization-maintaining fiber collimator (12), and the third polarization-maintaining fiber collimator (14). Air gaps are provided between the bottom surfaces of the current-sensitive beam (10), the feedback control beam (13), and the temperature-sensitive beam (15) and the substrate (16); the current-sensitive beam (10) and the feedback control beam (13) are made of permanent magnetic materials, and the temperature-sensitive beam (15) is made of temperature-sensitive materials; The signal processing unit adopts a closed-loop demodulation algorithm. In the closed-loop demodulation algorithm, the micro-power laser (18) outputs a laser signal formed by superimposing a square wave signal, a first stepped wave signal, and a second stepped wave signal under the control of the signal processor (17). The laser signal is transmitted to the photodiode (20) through the single-mode optical fiber (19) and converted into an electrical signal. The electrical signal is amplified by the transformer (21) and then loaded onto the feedback control beam (13) of the sensing unit. Among them, the square wave signal correspondingly generates a non-reciprocal π / 2 modulation phase shift, and the first stepped wave signal correspondingly generates a compensation phase shift φ l , and the second stepped wave signal correspondingly generates a compensation phase shift Ф f ; the signal processor (17) demodulates the compensation phase shift Ф f to obtain temperature information, calculates a temperature error correction coefficient according to the temperature information, and introduces the temperature error correction coefficient into the process of the signal processor (17) demodulating the compensation phase shift φ l to obtain current information.

2. The grating light valve type current sensor based on a micro-power optical control signal source according to claim 1, wherein The reflective film uses aluminum or a dielectric material with an emissivity greater than 92%.

3. The grating light valve type current sensor based on a micro-power light control signal source according to claim 1, wherein The signal processing unit further includes a broadband light source (1), a depolarizer (2), a 1×3 beam splitter (3), a first circulator (4), a first polarizer (5), a first polarization-maintaining transmission fiber (6), a Faraday rotator (7), a first polarization beam splitter (8), a 1×2 beam splitter (11), a second circulator (22), a second polarizer (23), a second polarization-maintaining transmission fiber (24), and a second polarization beam splitter (25); The output end (11) of the broadband light source (1) is connected to the input end of the depolarizer (2), the output end of the depolarizer (2) is connected to the input end of the 1×3 beam splitter (3), the first output end of the 1×3 beam splitter (3) is connected to the first end of the first circulator (4), the second end of the first circulator (4) is connected to the input end of the first polarizer (5), the output end of the first polarizer (5) is connected to the input end of the Faraday rotator (7) through the first polarization-maintaining transmission fiber (6), the output end of the Faraday rotator (7) is connected to the input end of the first polarization beam splitter (8), and the two output ends of the first polarization beam splitter (8) are respectively connected to the first polarization-maintaining fiber collimator (9) and the first output end of the 1×2 beam splitter (11); the third end of the first circulator (4) is connected to the first input end of the signal processor (17); The second output end of the 1×3 beam splitter (3) is connected to the first end of the second circulator (22), the second end of the second circulator (22) is connected to the input end of the second polarizer (23), the output end of the second polarizer (23) is connected to the input end of the second polarization-maintaining transmission fiber (24), and the two output ends of the second polarization beam splitter (25) are respectively connected to the third polarization-maintaining fiber collimator (14) and the second output end of the 1×2 beam splitter (11). The input end of the 1×2 beam splitter (11) is connected to the second polarization-maintaining fiber collimator (12), and the third end of the second circulator (22) is connected to the second input end of the signal processor (17); the first output end of the signal processor (17) is connected to the input end of the micro-power laser (18).

4. The grating light valve type current sensor based on a micro-power optical control signal source according to claim 3, characterized in that, The third output end of the 1×3 beam splitter (3) is connected to the third input end of the signal processor (17), and the second output end of the signal processor (17) is connected to the control end of the broadband light source (1); the signal processor (17) performs feedback control on the output wavelength of the broadband light source (1) according to the demodulated wavelength signal.

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