A grating light valve type current sensor based on temperature compensation

Abstract

The present invention discloses a grating light valve type current sensor based on temperature compensation, 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 grating light valve based on micro-optoelectromechanical system technology is used to measure the two parameters of temperature and current, and according to the detected temperature information, the current measurement error introduced by the change of the grating light valve with temperature is corrected to meet the accurate current measurement requirements in the outdoor engineering application process. At the same time, a closed-loop control modulation and demodulation algorithm based on square wave + stepped wave is adopted to improve the linearity and dynamic measurement range of current measurement.

Description

Technical Field

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

[0002] For a long time, electromagnetic transformers have played an important role in the operation monitoring of power systems. With the continuous increase of the voltage level of transmission lines, traditional electromagnetic transformers have gradually revealed their own disadvantages. In the context of power digitization, the replacement of traditional transformers by electronic transformers has become an inevitable trend. Among them, compared with active electronic current transformers, passive electronic transformers have the advantages of being passive, having a simple structure, reliable operation, strong anti-interference ability, and a wide frequency response range, and have become a research hotspot.

[0003] As a representative technical solution of passive electronic transformers, all-fiber current transformers (FOCT) have been widely used in the past decade. However, high cost and large influence by environmental disturbances such as temperature and vibration are still the main problems faced in the mass production process of FOCT.

[0004] Currently, micro-optoelectromechanical systems (MOEMS) technology is becoming increasingly mature, and its advantages such as low cost and good process consistency provide a new research direction for passive current transformers. Among them, the grating light valve (GLV) based on MOEMS technology has high optical efficiency, fast modulation rate, and low mass production cost, and can meet the current measurement requirements of power systems.

[0005] Since the surfaces of the GLV sensitive beam and the reference beam are generally coated with a reflective film, the difference in the thermal expansion coefficients of the two materials of the reflective film and the substrate will cause the optical loss coefficient and optical path difference of the GLV to change with temperature. In addition, the material and manufacturing process differences between different beams will also result in different temperature sensitivity coefficients between different beams. The above reasons will cause the accuracy of the GLV to be affected by temperature when measuring current. Summary of the Invention

[0006] Object of the Invention: Aiming at the above-mentioned existing technologies, a grating light valve type current sensor based on temperature compensation is proposed, which can eliminate the influence of environmental temperature changes on the measurement accuracy of optical fiber direct current sensors, and make the measurement have high linearity and a large dynamic measurement range.

[0007] Technical Solution: A grating light valve type current sensor based on temperature compensation includes a signal processing unit and a sensing unit;

[0008] The sensing unit is a three-beam grating light valve temperature-current sensing unit based on micro-opto-electro-mechanical system technology, and includes a first polarization-maintaining fiber collimator, a second polarization-maintaining fiber collimator, a third polarization-maintaining fiber collimator, a current-sensitive beam, a reference beam, a temperature-sensitive beam, and a substrate; reflective films are plated on the surfaces of the current-sensitive beam, the reference 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 reference beam, and the temperature-sensitive beam and the substrate; the current-sensitive beam is made of a permanent magnetic material, the reference beam is made of a non-magnetic material, and the temperature-sensitive beam is made of a temperature-sensitive material;

[0009] The signal processing unit adopts a closed-loop demodulation algorithm; in the closed-loop demodulation algorithm, the feedback signal loaded onto the current-sensitive beam through the phase modulator is a superimposed signal of a square wave signal and a staircase wave signal. The square wave signal introduces a non-reciprocal phase bias φ s , and the staircase wave signal introduces a compensation phase shift φ l , and the detection current is obtained by demodulating and outputting the compensation phase shift φ l ; among them, when the demodulated output compensation phase shift is φ l , error correction is performed according to the temperature information measured by the temperature-sensitive beam to correct the influence of ambient temperature change on the measurement accuracy of the sensing unit.

[0010] Furthermore, the reflective film adopts aluminum or a dielectric material with an emissivity greater than 92%.

[0011] Furthermore, the signal processing unit further includes: feedback control of the output power of the broadband light source according to the output wavelength of the broadband light source to stabilize the output wavelength of the broadband light source.

[0012] 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 signal processor, a second circulator, a second polarizer, a second polarization-maintaining transmission fiber, and a second polarization beam splitter;

[0013] 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 first input end of the phase modulator, the output end of the phase modulator is connected to the input end of the Faraday rotator through the first polarization-maintaining transmission optical 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;

[0014] 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 the second polarization-maintaining transmission optical fiber, the two output ends of the second polarization beam splitter are respectively connected to the third polarization-maintaining 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 fiber collimator, and 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 second input end of the phase modulator;

[0015] The third output end of the 1×3 beam splitter is connected to the third input end of the signal processor, and the second output end of the signal processor is connected to the control end of the broadband light source.

[0016] Beneficial effects: A grating light valve type current sensor based on temperature compensation of the present invention uses a three-beam grating light valve based on micro-optoelectromechanical system (MOEMS) technology to sense temperature and current signals. Through the temperature information collected by the three-beam grating light valve, the self-correction of the temperature error of current acquisition is carried out to improve the environmental adaptability of the sensor. At the same time, the micro-power optical control signal source technology is used to realize the closed-loop optical feedback control of the system to improve the measurement linearity and dynamic measurement range of the sensor. Description of the Drawings

[0017] Figure 1 It is a structural diagram of a grating light valve type current sensor based on temperature compensation of the present invention. Detailed Embodiments

[0018] The present invention will be further explained below with reference to the drawings.

[0019] As Figure 1 shown, a grating light valve type current sensor based on temperature compensation includes a signal processing unit and a sensing unit.

[0020] 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 10, a second polarization-maintaining fiber collimator 13, a third polarization-maintaining fiber collimator 15, a current-sensitive beam 11, a reference beam 14, a temperature-sensitive beam 16, and a substrate 17. Reflective films are plated on the surfaces of the current-sensitive beam 11, the reference beam 14, and the temperature-sensitive beam 16, and they are respectively arranged opposite to the output ends of the first polarization-maintaining fiber collimator 10, the second polarization-maintaining fiber collimator 13, and the third polarization-maintaining fiber collimator 15. An air gap with a thickness of about 1 μm is provided between the bottom surfaces of the current-sensitive beam 11, the reference beam 14, and the temperature-sensitive beam 16 and the substrate 17. The current-sensitive beam 11 is made of a permanent magnetic material, the reference beam 14 is made of a non-magnetic material, and the temperature-sensitive beam 15 is made of a temperature-sensitive material. 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 a dielectric material with an emissivity greater than 92%; the substrate 17 is made of semiconductor Si and electromagnetic materials.

[0021] 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 phase modulator 6, a first polarization-maintaining transmission fiber 7, a Faraday rotator 8, a first polarization beam splitter 9, a 1×2 beam splitter 12, a signal processor 18, a second circulator 19, a second polarizer 20, a second polarization-maintaining transmission fiber 21, and a second polarization beam splitter 22.

[0022] 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 31 of the 1×3 beam splitter 3 is connected to the first end 41 of the first circulator 4, the second end 42 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 first input end 61 of the phase modulator 6, the output end 62 of the phase modulator 6 is connected to the input end of the Faraday rotator 8 through the first polarization-maintaining transmission fiber 7, the output end of the Faraday rotator 8 is connected to the input end of the first polarization beam splitter 9, and the two output ends of the first polarization beam splitter 9 are respectively connected to the first polarization-maintaining fiber collimator 10 and the first output end of the 1×2 beam splitter 12; the third end 43 of the first circulator 4 is connected to the first input end 181 of the signal processor 18.

[0023] The second output end 33 of the 1×3 beam splitter 3 is connected to the first end 191 of the second circulator 19. The second end 192 of the second circulator 19 is connected to the input end of the second polarizer 20. The output end of the second polarizer 20 is connected to the input end of the second polarization beam splitter 22 through the second polarization-maintaining transmission optical fiber 21. The two output ends of the second polarization beam splitter 22 are respectively connected to the third polarization-maintaining optical fiber collimator 15 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 optical fiber collimator 13. The third end 193 of the second circulator 19 is connected to the second input end 183 of the signal processor 18. The first output end 184 of the signal processor 18 is connected to the second input end 63 of the phase modulator 6.

[0024] The third output end 32 of the 1×3 beam splitter 3 is connected to the third input end 182 of the signal processor 18. The second output end 185 of the signal processor 18 is connected to the control end 12 of the broadband light source 1.

[0025] In the above structure, the light emitted by the broadband light source 1 passes through the depolarizer 2, the 1×3 optical splitter 3, the first circulator 4, and the first polarizer 5, and then forms linearly polarized light. After the linearly polarized light enters the phase modulator 6 at an angle of 45°, it is divided into two orthogonal linearly polarized lights and transmitted along the fast and slow axes of the first polarization-maintaining transmission optical fiber 7 respectively. After passing through the first polarization-maintaining transmission optical fiber 7, it reaches the Faraday rotator 8. Then, the two orthogonal linearly polarized modes rotate by 45°. After being split by the first polarization beam splitter 9, one path of the output passes through the first polarization-maintaining optical fiber collimator 10 and then enters the current-sensitive beam 10, and the other path of the output passes through the 1×2 beam splitter 12 and the second polarization-maintaining optical fiber collimator 13 and then enters the reference beam 14.

[0026] When the two orthogonal linearly polarized lights are reflected by the reflecting surfaces of the current-sensitive beam 11 and the reference beam 14, they return along the original path and pass through the Faraday rotator 8 again. At this time, the two orthogonal linearly polarized modes rotate 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 18.

[0027] The current to be measured is converted into the voltage to be measured U through the sampling resistor or the Rogowski coil. When it acts on the current-sensitive beam 11, under the action of the electrostatic force, the current-sensitive beam 11 undergoes a small deformation, while the reference beam 14 is made of non-magnetic material and is not affected by the electrostatic force. At this time, a reflecting surface with different heights is formed between the current-sensitive beam 11 and the reference beam 14, so that the phase difference between the surface-reflected lights changes. 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 11 and the reference beam 14 interfere, they pass through the first circulator 4 and then are sent into the optical signal processor 18. The received optical wave interference signal is:

[0029]

[0030] Wherein, P0 is the input light intensity, λ is the wavelength of the incident light, and d is the displacement of the current-sensitive beam 11 relative to the reference beam 14 under the action of the voltage to be measured, which is linearly related to the voltage to be measured within the elastic deformation range.

[0031] Due to the difference in the thermal expansion coefficients of the two materials, the reflective film and the substrate, on the surfaces of the sensitive beam and the reference beam, the optical loss coefficient and the optical path difference of the grating light valve will change with temperature. In addition, the differences in materials and manufacturing processes between different beams will also result in different temperature sensitivity coefficients between different beams. The above reasons will cause the accuracy of the grating light valve to be affected by temperature during current measurement. 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 zero phase difference, limited measurement range, and the interference result cannot reflect the directionality of the input current and other defects. To solve the problems of cosine sensitivity and directionality, improve the linearity of the detection system, and increase the dynamic range, the feedback signal loaded onto the current-sensitive beam 11 by the phase modulator 6 in the closed-loop demodulation algorithm of the present invention is a superimposed signal of a square wave signal and a staircase wave signal. The square wave signal introduces a non-reciprocal phase bias φ s , and the staircase wave signal 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 cancelled, so that the system output operates near the operating point where the response slope is not zero and the phase difference is zero.

[0034] Specifically, the photodetector PD in the signal processor 18 converts the optical signal entering the signal processor 18 into an electrical signal. The electrical signal is sent to the A / D after pre-amplification. The A / D samples the electrical signal respectively in the positive and negative half-cycles of the square wave modulation signal, and sends the sampling results to the FPGA. The FPGA mainly establishes each timing. The phase-locked loop is used to generate a reference clock for frequency division to obtain timings such as the D / A clock, the modulation square wave, the demodulation square wave, and the staircase wave respectively. The FPGA generates the square wave and the staircase wave, and at the same time realizes the superposition of the square wave and the staircase wave. The superimposed signal passes through the D / A and the drive circuit and is applied to the phase modulator 6 to generate φ s and φ l .

[0035] At this time, the optical wave interference signal P D received by the signal processor 18 is:

[0036]

[0037] Take φs = ±π / 2, the output signals of the positive and negative half - cycles of the square - wave modulation signal are as follows:

[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 the first stepped - wave to feedback and compensate for the phase shift φ l , such that P diff = 0, we can obtain:

[0042]

[0043] In the closed - loop case, the values of φ l and are small, satisfying the small - angle approximation condition, we can obtain:

[0044]

[0045] Therefore,

[0046]

[0047] At this time, the compensation phase shift φ l is the demodulation output. It can be seen that φ l is related to δ, and the change of environmental temperature 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 16 to detect temperature information.

[0048] Specifically, the light emitted by the broadband light source 1 passes through the depolarizer 2, 1×3 beam splitter 3, second circulator 19, and second polarizer 20, and then forms linearly polarized light. The linearly polarized light enters the second polarization - maintaining transmission fiber 21 at an angle of 45°, and is divided into two orthogonal linearly polarized lights, which are transmitted along the fast and slow axes of the second polarization - maintaining transmission fiber 21 respectively. After passing through the second polarization - maintaining transmission fiber 21, it reaches the second polarization beam splitter 22. After being split by the second polarization beam splitter 22, one of the output paths enters the temperature - sensitive beam 16 after passing through the third polarization - maintaining fiber collimator 15, and the other output path enters the reference beam 14 after passing through the 1×2 beam splitter 12 and the second polarization - maintaining fiber collimator 13.

[0049] When two beams of orthogonally linearly polarized light are emitted through the reflecting surfaces of the temperature-sensitive beam 16 and the reference beam 14, they return along the original path and finally interfere at the second polarizer 20. The interference signal is sent into the signal processor 18 after passing through the second circulator 19. When temperature acts on the temperature-sensitive beam 16, due to thermal expansion and contraction, the temperature-sensitive beam 16 undergoes a small deformation, resulting in a reflecting surface with different heights between it and the reference beam 14, causing the phase difference between the reflected lights on its surface to change with the change of temperature, and further causing the interference output light intensity to also change with temperature.

[0050] The interference output light intensity P caused by temperature T is expressed as:

[0051]

[0052] where d T is the micro-displacement of the temperature-sensitive beam 16 relative to the reference beam 14. Performing polynomial fitting on the cosine response output P T can obtain the linear temperature output.

[0053] Based on the measured temperature information, the signal processor 18 calculates the error coefficient (1 - δ) and multiplies it with Equation (8) to obtain:

[0054]

[0055] 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 pre-obtained variation law. Thus, the influence of temperature on the measurement accuracy of the system can be eliminated.

[0056] Due to the influence of factors such as temperature and aging, the output power of the broadband light source 1 will change. As can be seen from Equation (4), the output power of the light source can be obtained by the following formula:

[0057] P0 = P D+ + P D- (11)

[0058] Therefore, according to this value, the drive current I of the broadband light source 1 can be adjusted within the safe range of the core temperature of the broadband light source 1 D to stabilize the output power and thus stabilize the output wavelength.

[0059] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still 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 temperature compensation, 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, and includes a first polarization-maintaining fiber collimator (10), a second polarization-maintaining fiber collimator (13), a third polarization-maintaining fiber collimator (15), a current-sensitive beam (11), a reference beam (14), a temperature-sensitive beam (16), and a substrate (17); Reflective films are coated on the surfaces of the current-sensitive beam (11), the reference beam (14), and the temperature-sensitive beam (16), and they are respectively arranged opposite to the output ends of the first polarization-maintaining fiber collimator (10), the second polarization-maintaining fiber collimator (13), and the third polarization-maintaining fiber collimator (15). Air gaps are provided between the bottom surfaces of the current-sensitive beam (11), the reference beam (14), and the temperature-sensitive beam (16) and the substrate (17); The current-sensitive beam (11) is made of a permanent magnetic material, the reference beam (14) is made of a non-magnetic material, and the temperature-sensitive beam (16) is made of a temperature-sensitive material; The signal processing unit adopts a closed-loop demodulation algorithm; in the closed-loop demodulation algorithm, the feedback signal loaded onto the current-sensitive beam (11) through the phase modulator (6) is a superimposed signal of a square wave signal and a staircase wave signal, and the square wave signal introduces a non-reciprocal phase bias ϕ s , and the staircase wave signal introduces a compensation phase shift ϕ l , and the compensation phase shift is demodulated and output ϕ l to obtain the detected current; wherein, when the compensation phase shift is demodulated and output ϕ l , error correction is performed according to the temperature information measured by the temperature-sensitive beam (16) to correct the influence of environmental temperature change on the measurement accuracy of the sensing unit; 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 (7), a Faraday rotator (8), a first polarization beam splitter (9), a 1×2 beam splitter (12), a signal processor (18), a second circulator (19), a second polarizer (20), a second polarization-maintaining transmission fiber (21), and a second polarization beam splitter (22); 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 (31) of the 1×3 beam splitter (3) is connected to the first end (41) of the first circulator (4), the second end (42) 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 first input end (61) of the phase modulator (6), the output end (62) of the phase modulator (6) is connected to the input end of the Faraday rotator (8) through the first polarization-maintaining transmission fiber (7), the output end of the Faraday rotator (8) is connected to the input end of the first polarization beam splitter (9), and the two output ends of the first polarization beam splitter (9) are respectively connected to the first polarization-maintaining fiber collimator (10) and the first output end of the 1×2 beam splitter (12); The third end (43) of the first circulator (4) is connected to the first input end (181) of the signal processor (18); The second output end (33) of the 1×3 beam splitter (3) is connected to the first end (191) of the second circulator (19). The second end (192) of the second circulator (19) is connected to the input end of the second polarizer (20). The output end of the second polarizer (20) is connected to the input end of the second polarization-maintaining transmission optical fiber (21), and the input end of the second polarization beam splitter (22). The two output ends of the second polarization beam splitter (22) are respectively connected to the third polarization-maintaining fiber collimator (15) and the second output end of the 1×2 beam splitter (12). The input end of the 1×2 beam splitter (12) is connected to the second polarization-maintaining fiber collimator (13). The third end (193) of the second circulator (19) is connected to the second input end (183) of the signal processor (18). The first output end (184) of the signal processor (18) is connected to the second input end (63) of the phase modulator (6). The third output end (32) of the 1×3 beam splitter (3) is connected to the third input end (182) of the signal processor (18). The second output end (185) of the signal processor (18) is connected to the control end (12) of the broadband light source (1).

2. The grating light valve type current sensor based on temperature compensation according to claim 1, wherein The reflective film is made of aluminum or a dielectric material with an emissivity greater than 92%.

3. The grating light valve type current sensor based on temperature compensation according to claim 1, characterized in that, The signal processing unit further includes: feedback controlling the output power of the broadband light source (1) according to the output wavelength of the broadband light source (1) to stabilize the output wavelength of the broadband light source (1).

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