Device and method for monitoring gas concentration in transformer based on optical interference demodulation

Abstract

The invention relates to the technical field of optical interference demodulation, and discloses a device and a method for monitoring gas concentration in a transformer based on optical interference demodulation.The method comprises the steps of generating narrow-band laser with a preset wavelength, dividing the narrow-band laser into two paths to be output, modulating one path through an acousto-optic modulator to generate a frequency-shift optical signal, and outputting the frequency-shift optical signal; in one path, a low-frequency phase modulation signal sensed by the optical fiber gas sensor is modulated to generate a sensing optical signal with low-frequency phase change; performing photoelectric conversion on the frequency shift optical signal and the sensing optical signal, and outputting an optical interference beat frequency signal; performing frequency mixing and fusion on the optical interference beat frequency signal and a difference frequency signal which differs from the optical interference beat frequency signal by a preset low-frequency carrier frequency, and outputting a first fusion frequency reduction signal and a second fusion frequency reduction signal; the first fusion frequency reduction module is filtered to serve as a reference signal; and demodulating the second fusion underclocking signal based on the reference signal by using a lock-in amplifier to obtain a low-frequency phase modulation signal representing the gas concentration in the to-be-monitored transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of optical interference demodulation, and in particular to a device and method for monitoring gas concentration in a transformer based on optical interference demodulation. Background Art

[0002] As the operating hub equipment of power transmission and distribution, transformer is one of the most important components of power system. Once a failure occurs, it will pose a great threat to the stable operation of power system and social production. Therefore, the safe and stable operation of transformer is of far-reaching significance for ensuring the safety of power grid. Traditional transformer status monitoring methods mainly rely on electrical sensors and electronic equipment, which may be affected by electromagnetic interference and may have reliability problems during long-term operation. Fiber optic sensing technology has gradually become an important means of transformer status monitoring due to its advantages of anti-electromagnetic interference, high reliability and ability to realize distributed measurement.

[0003] Common fiber optic sensing technologies include fiber Bragg grating (FBG) sensor technology and Brillouin optical time domain reflectometry (BOTDR) technology.

[0004] The FBG sensor in the fiber Bragg grating (FBG) sensor technology is based on the grating structure in the optical fiber. When the light wave passes through the grating, the light of a specific wavelength will be reflected and the rest of the light will be transmitted. The reflected wavelength is directly related to the strain and temperature changes in the optical fiber, and is widely used to monitor the temperature and strain of the transformer; by embedding the FBG sensor in the transformer oil or fixing it on the transformer winding, the temperature change and mechanical strain inside the transformer can be monitored in real time. However, the demodulation and processing of the FBG sensor signal requires high-precision optical equipment and complex signal processing algorithms.

[0005] Brillouin optical time-domain reflectometry (BOTDR) technology is based on the principle of Brillouin scattering. It obtains strain and temperature information distributed along the optical fiber by measuring the Brillouin scattering frequency shift in the optical fiber. BOTDR technology can realize distributed measurement of temperature and strain inside the transformer. By arranging optical fibers inside the transformer, it can continuously monitor the transformer windings and the inside of the oil tank over long distances. However, BOTDR systems usually require expensive optical equipment and complex signal processing algorithms, with high system costs and relatively long measurement times, which are not suitable for real-time and rapidly changing monitoring needs.

[0006] In summary, the existing transformer internal gas concentration detection device based on optical fiber sensing technology is not suitable for real-time monitoring because of the complex signal processing method, high device cost and relatively long measurement time when demodulating the collected transformer internal signal. It has the problems of low detection efficiency and high cost. Summary of the invention

[0007] To this end, the technical problem to be solved by the present invention is to overcome the problems of low detection efficiency and high cost when the prior art demodulates the collected internal signal of the transformer to obtain the corresponding detection result.

[0008] In order to solve the above technical problems, the present invention provides a gas concentration monitoring device in a transformer based on optical interference demodulation, comprising: A light source module is used to generate narrow-band laser light of a preset wavelength and output it in two paths; an acousto-optic modulator, the input end of which is connected to the output end of the light source module, for frequency-shifting a narrow-band laser to obtain a frequency-shifted optical signal; The optical fiber gas sensor has a sensing probe placed inside the transformer to be monitored to obtain a low-frequency phase modulation signal; the sensing optical fiber input end is connected to the sensing probe and the output end of the light source module, and the other narrow-band laser output by the light source module is modulated by the low-frequency phase modulation signal, and a sensing optical signal carrying a low-frequency phase change is output through the sensing optical fiber output end; A balanced photoelectric detector, whose input end is connected to the acousto-optic modulator and the sensing optical fiber output end of the optical fiber gas sensor, performs photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputs an optical interference beat frequency signal; A signal generating module, used for generating a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes and fuses the optical interference beat frequency signal and the difference frequency signal, and outputs a first fused down-conversion signal and a second fused down-conversion signal; A filtering module, whose input end is connected to the output end of the mixing module, and outputs the first fusion down-conversion module as a reference signal after filtering; A phase-locked amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulates the second fused down-conversion signal based on the reference signal to obtain a low-frequency phase modulation signal representing the gas concentration inside the transformer to be monitored.

[0009] Preferably, the frequency mixing module comprises: A first power divider, whose input end is connected to the output end of the balanced photodetector, divides the optical interference beat frequency signal into two output paths; A second power divider, whose input end is connected to the output end of the signal generating module, divides the difference frequency signal into two output paths; A first mixer, whose input end is connected to the first output end of the first power divider and the first output end of the second power divider, mixes one optical interference beat frequency signal with one difference frequency signal to output as a first fused down-conversion signal; The second mixer, whose input end is connected to the second output end of the first power divider and the second output end of the second power divider, mixes another optical interference beat frequency signal with another difference frequency signal to output as a second fused down-conversion signal.

[0010] Preferably, the frequency mixing module comprises: A mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes the optical interference beat frequency signal with the difference frequency signal, and outputs the mixed down-conversion signal as a fused down-conversion signal; The power divider has an input end connected to the output end of the mixer, and divides the fused down-conversion signal into a first fused down-conversion signal and a second fused down-conversion signal for output.

[0011] Preferably, the light source module comprises: A narrow-band laser, used for outputting narrow-band laser light of a preset wavelength; The optical coupler has an input end connected to the output end of the narrow-band laser and divides the narrow-band laser of a preset wavelength into two output paths.

[0012] Preferably, the optical fiber gas sensor comprises: The sensing probe is placed inside the transformer to be monitored, and the gas sensing layer inside the sensing probe generates a low-frequency phase modulation signal by interacting with the gas inside the transformer to be monitored; The sensing optical fiber modulates the narrowband laser based on the low-frequency phase modulation signal and outputs a sensing light signal carrying a low-frequency phase change.

[0013] Preferably, the preset low-frequency carrier frequency is greater than 80KHz.

[0014] This embodiment provides a monitoring method for a gas concentration monitoring device in a transformer based on optical interferometry demodulation as described above, comprising: Acquire a low-frequency phase-modulated signal containing the concentration of the gas to be measured in the transformer to be monitored; The narrowband laser of the preset wavelength is divided into two paths, one path is frequency-shifted by acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying a low-frequency phase change; Performing photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat frequency signal; Acquire a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; Mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-conversion signal and a second fused down-conversion signal; Filtering the first fused down-converted signal to obtain a reference signal; Based on the reference signal, a phase-locked amplification operation is performed on the second fused down-frequency signal, and the phase amplitude of the low-frequency phase modulation signal in the second fused down-frequency signal is demodulated to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

[0015] Preferably, the phase amplitude of the low-frequency phase modulation signal in the second fused down-frequency signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

[0016] Preferably, mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal comprises: dividing the optical interference beat signal into a first optical interference beat signal and a second optical interference beat signal; dividing the difference frequency signal into a first difference frequency signal and a second difference frequency signal; Mixing the first optical interference beat frequency signal with the first difference frequency signal and outputting the mixed signal as a first fused down-conversion signal; The second optical interference beat frequency signal is mixed with the second difference frequency signal and output as a second fused down-conversion signal.

[0017] Preferably, mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-converted signal and a second fused down-converted signal comprises: Mixing the optical interference beat frequency signal with the difference frequency signal to obtain a fused down-conversion signal; The fused down-converted signal is divided into a first fused down-converted signal and a second fused down-converted signal for output.

[0018] The above technical solution of the present invention has the following beneficial effects compared with the prior art: The device and method for monitoring gas concentration in a transformer based on optical interference demodulation described in the present invention use an optical fiber gas sensor to sense the gas concentration inside the transformer to be monitored, generate a corresponding low-frequency phase modulation signal, modulate a narrowband laser, and obtain a sensing light signal carrying a low-frequency phase change; perform photoelectric conversion on the sensing light signal and the frequency-shifted light signal generated by frequency shifting to generate an optical interference beat signal; mix and fuse the optical interference beat signal to generate two identical signals; filter one of the signals to remove the influence of the low-frequency phase modulation signal and use it as a reference signal, and use the other signal as a signal to be measured, and use a phase-locked amplifier for demodulation to obtain a low-frequency phase modulation signal that characterizes the gas concentration inside the transformer to be monitored; based on the relationship that the phase amplitude of the low-frequency phase modulation signal is proportional to the gas concentration, the gas concentration inside the transformer to be monitored is analyzed without the need for complex processing algorithms. The present invention uses optical interference to obtain a low-frequency phase modulation signal of the gas concentration sensed inside the transformer to be monitored, and uses a mixer to down-convert the optical interference beat frequency signal, thereby reducing the frequency of the signal and greatly reducing the time required for signal processing and demodulation, thereby achieving rapid detection of the gas concentration inside the transformer to be monitored. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 It is a structural schematic diagram of a gas concentration monitoring device in a transformer based on optical interference demodulation provided by the present invention; Figure 2 It is a schematic diagram of a mixing module provided by the present invention that performs power division followed by frequency mixing; Figure 3 It is a schematic diagram of a mixing module for mixing first and then power dividing provided by the present invention; Figure 4 It is a flow chart of the steps of the method for monitoring gas concentration in a transformer based on optical interference demodulation provided by the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0021] Reference Figure 1 As shown, the structural schematic diagram of the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention, the specific device includes: A light source module is used to generate narrow-band laser light of a preset wavelength and output it in two paths; an acousto-optic modulator, the input end of which is connected to the output end of the light source module, for frequency-shifting a narrow-band laser to obtain a frequency-shifted optical signal; The optical fiber gas sensor has a sensing probe placed inside the transformer to be monitored to obtain a low-frequency phase modulation signal; the sensing optical fiber input end is connected to the sensing probe and the output end of the light source module, and the other narrow-band laser output by the light source module is modulated by the low-frequency phase modulation signal, and a sensing optical signal carrying a low-frequency phase change is output through the sensing optical fiber output end; A balanced photoelectric detector, whose input end is connected to the acousto-optic modulator and the sensing optical fiber output end of the optical fiber gas sensor, performs photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputs an optical interference beat frequency signal; A signal generating module, used for generating a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes and fuses the optical interference beat frequency signal and the difference frequency signal, and outputs a first fused down-conversion signal and a second fused down-conversion signal; A filtering module, whose input end is connected to the output end of the mixing module, and outputs the first fusion down-conversion module as a reference signal after filtering; A phase-locked amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulates the second fused down-conversion signal based on the reference signal to obtain a low-frequency phase modulation signal representing the gas concentration inside the transformer to be monitored.

[0022] Specifically, in an embodiment of the present invention, two connection methods of the mixing module are provided according to the attenuation effect of the mixer and the power divider used; since the power divider attenuates high frequencies more than low frequencies, power division followed by mixing will attenuate the signal amplitude and reduce sensitivity. In this case, the method of mixing first and then dividing is required; but when the performance of the power divider is good enough and will not attenuate the target frequency, both connection methods are applicable.

[0023] ①Reference Figure 2 As shown, it is a schematic diagram of a mixing module with power division followed by mixing. In this case, the mixing module includes: A first power divider, whose input end is connected to the output end of the balanced photodetector, divides the optical interference beat frequency signal into two output paths; A second power divider, whose input end is connected to the output end of the signal generating module, divides the difference frequency signal into two output paths; A first mixer, whose input end is connected to the first output end of the first power divider and the first output end of the second power divider, mixes one optical interference beat frequency signal with one difference frequency signal to output as a first fused down-conversion signal; The second mixer, whose input end is connected to the second output end of the first power divider and the second output end of the second power divider, mixes another optical interference beat frequency signal with another difference frequency signal to output as a second fused down-conversion signal.

[0024] ②Reference Figure 3 As shown, it is a schematic diagram of a mixing module that mixes first and then divides the power. In this case, the mixing module includes: A mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes the optical interference beat frequency signal with the difference frequency signal, and outputs the mixed down-conversion signal as a fused down-conversion signal; The power divider has an input end connected to the output end of the mixer, and divides the fused down-conversion signal into a first fused down-conversion signal and a second fused down-conversion signal for output.

[0025] Specifically, the light source module includes: A narrow-band laser, used for outputting narrow-band laser light of a preset wavelength; The optical coupler has an input end connected to the output end of the narrow-band laser and divides the narrow-band laser of a preset wavelength into two output paths.

[0026] Specifically, the optical fiber gas sensor comprises: The sensing probe is placed inside the transformer to be monitored, and the gas sensing layer inside the sensing probe generates a low-frequency phase modulation signal by interacting with the gas inside the transformer to be monitored; The sensing optical fiber modulates the narrowband laser based on the low-frequency phase modulation signal and outputs a sensing light signal carrying a low-frequency phase change.

[0027] In the embodiment of the present invention, the preset low-frequency carrier frequency that differs between the difference frequency signal and the optical interference beat frequency signal is greater than 80 KHz, which can avoid low-frequency noise interference and effectively realize phase carrier.

[0028] Based on the above description, the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention can be divided into two parts, the first part is used to generate an optical interference beat frequency signal, and the second part is used to demodulate the optical interference beat frequency signal to obtain the corresponding parameter to be measured. In the first part, the source module emits a narrowband laser of a specific wavelength through an optical fiber, and uses an optical coupler to transmit the generated laser to the acousto-optic modulation module and the optical fiber gas sensor respectively; the optical signal is frequency-shifted in the acousto-optic modulation module, and the parameter to be measured inside the transformer is measured in the optical fiber gas sensor, which has a relatively low-frequency change compared to the frequency shift amount in the acousto-optic modulation module. Finally, the two beams of light are transmitted into the balanced photoelectric detection module; the balanced photoelectric detection module processes the two input lights to obtain a beat frequency signal carrying a low-frequency change in the optical fiber gas sensor at the frequency of the frequency shift amount in the acousto-optic modulation module, that is, an optical interference beat frequency signal; in the second part, the generated optical interference beat frequency signal is The frequency signal is input into the first power divider module, and the signal generating module generates a signal with the required low-frequency carrier frequency which is different from the interference beat frequency signal and inputs it into the second power divider module; after the first power divider module and the second power divider module distribute the input signal, they are respectively output to the first mixer module and the second mixer module for mixing; the signal output by the first mixer module is input into the filtering module, the low-frequency variation in the interference signal is filtered out, and only the signal with the required low-frequency carrier frequency is retained as the reference signal, which is input into the phase-locked amplifier module together with the measured signal output by the second mixer module, and the phase-locked amplification function is used to realize the real-time demodulation processing of the low-frequency variation in the optical interference signal. The optical interference demodulation system based on mixer frequency reduction proposed by the present invention solves the problem that the optical interference signal is difficult to demodulate and process in real time and requires complex signal processing algorithms.

[0029] The present invention performs optical interference demodulation based on mixer frequency reduction. By using the mixer frequency reduction method to reduce the low-frequency information contained in the high-frequency optical interference beat frequency signal, the function of real-time demodulation of the low-frequency variation generated by the internal state monitoring of the transformer is realized, thereby improving the real-time performance of the state monitoring.

[0030] In this embodiment, after using the gas concentration monitoring device in the transformer based on optical interference demodulation provided by the present invention to obtain a low-frequency phase modulation signal representing the gas concentration inside the transformer to be monitored, the phase-locked amplifier transmits the demodulated signal to the acquisition card through the BNC data line for storage and analysis. The gas concentration inside the transformer to be monitored includes the concentration of hydrocarbon gases (methane, ethane, ethylene, acetylene) dissolved in the transformer oil to be monitored.

[0031] Based on the above embodiment, in an embodiment of the present invention, a monitoring method for a gas concentration monitoring device in a transformer based on optical interference demodulation as described above is also provided, referring to Figure 4As shown, it is a flow chart of the steps of the method for monitoring gas concentration in a transformer based on optical interferometric demodulation, and the specific steps include: S101: Acquire a low-frequency phase modulation signal including the concentration of a gas to be measured in a transformer to be monitored; S102: Split a narrowband laser of a preset wavelength into two paths, one path is frequency-shifted by acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying a low-frequency phase change; S103: performing photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat frequency signal; S104: Acquire a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; S105: Mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-conversion signal and a second fused down-conversion signal; S106: Filter the first fused down-converted signal to obtain a reference signal; S107: performing a phase-locked amplification operation on the second fused down-frequency signal based on the reference signal, and demodulating to obtain the phase amplitude of the low-frequency phase modulation signal in the second fused down-frequency signal, so as to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

[0032] The phase amplitude of the low-frequency phase modulation signal in the second fused frequency-reduced signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

[0033] Specifically, in step S105, the optical interference beat frequency signal and the difference frequency signal are mixed and merged in two ways: mixing first and then centrifuging, and power division first and then mixing, which are respectively: ① Power division before mixing: dividing the optical interference beat signal into a first optical interference beat signal and a second optical interference beat signal; dividing the difference frequency signal into a first difference frequency signal and a second difference frequency signal; Mixing the first optical interference beat frequency signal with the first difference frequency signal and outputting the mixed signal as a first fused down-conversion signal; The second optical interference beat frequency signal is mixed with the second difference frequency signal and output as a second fused down-conversion signal.

[0034] ② Mix first and then divide the power: Mixing the optical interference beat frequency signal with the difference frequency signal to obtain a fused down-conversion signal; The fused down-converted signal is divided into a first fused down-converted signal and a second fused down-converted signal for output.

[0035] The device and method for monitoring gas concentration in a transformer based on optical interference demodulation described in the present invention use an optical fiber gas sensor to sense the gas concentration inside the transformer to be monitored, generate a corresponding low-frequency phase modulation signal, modulate a narrowband laser, and obtain a sensing light signal carrying a low-frequency phase change; perform photoelectric conversion on the sensing light signal and the frequency-shifted light signal generated by frequency shifting to generate an optical interference beat signal; mix and fuse the optical interference beat signal to generate two identical signals; filter one of the signals to remove the influence of the low-frequency phase modulation signal and use it as a reference signal, and use the other signal as a signal to be measured, and use a phase-locked amplifier for demodulation to obtain a low-frequency phase modulation signal that characterizes the gas concentration inside the transformer to be monitored; based on the relationship that the phase amplitude of the low-frequency phase modulation signal is proportional to the gas concentration, the gas concentration inside the transformer to be monitored is analyzed without the need for complex processing algorithms. The present invention uses optical interference to obtain a low-frequency phase modulation signal of the gas concentration sensed inside the transformer to be monitored, and uses a mixer to down-convert the optical interference beat frequency signal, thereby reducing the frequency of the signal and greatly reducing the time required for signal processing and demodulation, thereby achieving rapid detection of the gas concentration inside the transformer to be monitored.

[0036] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0037] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0038] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0039] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0040] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A gas concentration monitoring device in a transformer based on optical interference demodulation, characterized in that: include: A light source module is used to generate narrow-band laser light of a preset wavelength and output it in two paths; an acousto-optic modulator, the input end of which is connected to the output end of the light source module, for frequency-shifting a narrow-band laser to obtain a frequency-shifted optical signal; The optical fiber gas sensor has a sensing probe placed inside the transformer to be monitored to obtain a low-frequency phase-modulated signal; The input end of the sensing optical fiber is connected to the sensing probe and the output end of the light source module, and another narrow-band laser output by the light source module is modulated by a low-frequency phase modulation signal, and a sensing light signal carrying a low-frequency phase change is output through the output end of the sensing optical fiber; A balanced photoelectric detector, whose input end is connected to the acousto-optic modulator and the sensing optical fiber output end of the optical fiber gas sensor, performs photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal, and outputs an optical interference beat frequency signal; A signal generating module, used for generating a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; A mixing module, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes and fuses the optical interference beat frequency signal and the difference frequency signal, and outputs a first fused down-conversion signal and a second fused down-conversion signal; A filtering module, whose input end is connected to the output end of the mixing module, and outputs the first fusion down-conversion module as a reference signal after filtering; A phase-locked amplifier, whose input end is connected to the output end of the mixing module and the output end of the filtering module, demodulates the second fused down-conversion signal based on the reference signal to obtain a low-frequency phase modulation signal representing the gas concentration inside the transformer to be monitored.

2. The gas concentration monitoring device in a transformer based on optical interference demodulation according to claim 1 is characterized in that: The mixing module comprises: A first power divider, whose input end is connected to the output end of the balanced photodetector, divides the optical interference beat frequency signal into two output paths; A second power divider, whose input end is connected to the output end of the signal generating module, divides the difference frequency signal into two output paths; A first mixer, whose input end is connected to the first output end of the first power divider and the first output end of the second power divider, mixes one optical interference beat frequency signal with one difference frequency signal to output as a first fused down-conversion signal; The second mixer, whose input end is connected to the second output end of the first power divider and the second output end of the second power divider, mixes another optical interference beat frequency signal with another difference frequency signal to output as a second fused down-conversion signal.

3. The gas concentration monitoring device in a transformer based on optical interference demodulation according to claim 1 is characterized in that: The mixing module comprises: A mixer, whose input end is connected to the output end of the balanced photodetector and the output end of the signal generating module, mixes the optical interference beat frequency signal with the difference frequency signal, and outputs the mixed down-conversion signal as a fused down-conversion signal; The power divider has an input end connected to the output end of the mixer, and divides the fused down-conversion signal into a first fused down-conversion signal and a second fused down-conversion signal for output.

4. The gas concentration monitoring device in a transformer based on optical interference demodulation according to claim 1 is characterized in that: The light source module comprises: A narrow-band laser, used for outputting narrow-band laser light of a preset wavelength; The optical coupler has an input end connected to the output end of the narrow-band laser and divides the narrow-band laser of a preset wavelength into two output paths.

5. The gas concentration monitoring device in a transformer based on optical interference demodulation according to claim 1, characterized in that: The optical fiber gas sensor comprises: The sensing probe is placed inside the transformer to be monitored, and the gas sensing layer inside the sensing probe generates a low-frequency phase modulation signal by interacting with the gas inside the transformer to be monitored; The sensing optical fiber modulates the narrowband laser based on the low-frequency phase modulation signal and outputs a sensing light signal carrying a low-frequency phase change.

6. The method for monitoring gas concentration in a transformer based on optical interference demodulation according to claim 1, characterized in that: The preset low-frequency carrier frequency is greater than 80KHz.

7. A monitoring method for a gas concentration monitoring device in a transformer based on optical interference demodulation as claimed in any one of claims 1 to 6, characterized in that: include: Acquire a low-frequency phase-modulated signal containing the concentration of the gas to be measured in the transformer to be monitored; The narrowband laser of the preset wavelength is divided into two paths, one path is frequency-shifted by acousto-optic modulation to obtain a frequency-shifted optical signal, and the other path is modulated based on the low-frequency phase modulation signal to obtain a sensing optical signal carrying a low-frequency phase change; Performing photoelectric conversion on the frequency-shifted optical signal and the sensing optical signal to generate an optical interference beat frequency signal; Acquire a difference frequency signal having a preset low-frequency carrier frequency difference from the optical interference beat frequency signal; Mixing and fusing the optical interference beat frequency signal and the difference frequency signal to output a first fused down-conversion signal and a second fused down-conversion signal; Filtering the first fused down-converted signal to obtain a reference signal; Based on the reference signal, a phase-locked amplification operation is performed on the second fused down-frequency signal, and the phase amplitude of the low-frequency phase modulation signal in the second fused down-frequency signal is demodulated to obtain the gas concentration in the transformer to be monitored based on the phase amplitude.

8. The method for monitoring gas concentration in a transformer based on optical interference demodulation according to claim 7, characterized in that: The phase amplitude of the low-frequency phase modulation signal in the second fused frequency-reduced signal is proportional to the concentration of the corresponding gas in the transformer to be monitored.

9. The method for monitoring gas concentration in a transformer based on optical interference demodulation according to claim 7, characterized in that: The mixing and fusing of the optical interference beat frequency signal and the difference frequency signal to output a first fused down-conversion signal and a second fused down-conversion signal comprises: dividing the optical interference beat signal into a first optical interference beat signal and a second optical interference beat signal; dividing the difference frequency signal into a first difference frequency signal and a second difference frequency signal; Mixing the first optical interference beat frequency signal with the first difference frequency signal and outputting the mixed signal as a first fused down-conversion signal; The second optical interference beat frequency signal is mixed with the second difference frequency signal and output as a second fused down-conversion signal.

10. The method for monitoring gas concentration in a transformer based on optical interference demodulation according to claim 7, characterized in that: The mixing and fusing of the optical interference beat frequency signal and the difference frequency signal to output a first fused down-conversion signal and a second fused down-conversion signal comprises: Mixing the optical interference beat frequency signal with the difference frequency signal to obtain a fused down-conversion signal; The fused down-converted signal is divided into a first fused down-converted signal and a second fused down-converted signal for output.

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