Tdlas-based detection system and method for dissolved gases in oil

Abstract

The present application discloses a TDLAS-based detection system and method for dissolved gases in oil, comprising: selecting four lasers with different central wavelengths for detection of six different dissolved gases in oil, and using an optical switch to control the light emission timing and duration of the lasers; configuring a characteristic absorption cell and a reference absorption cell; obtaining weak useful signals by means of dual-channel lock-in amplification; and dynamically adjusting parameters of a gas detection system to obtain an optimal second harmonic peak value for concentration inversion. The TDLAS-based detection system for dissolved gases in oil provided by the present application ensures the detection precision of the system after long-term operation, improves the economy and long-term stability of the system, and provides auxiliary decision-making for health condition monitoring of transformers.

Description

A TDLAS-based dissolved gas detection system and method for oil

[0001] Related applications

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 27, 2023, with application number 202311821651.2 and application name “A system and method for detecting dissolved gas in oil based on TDLAS”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of online monitoring of electrical equipment in intelligent substations, and in particular to a TDLAS-based dissolved gas detection system in oil. Background Art

[0004] Power transformers are essential equipment in the transmission, transformation, and distribution of power in power grids. They perform critical tasks in converting voltage levels and distributing electrical energy. Their proper operation is crucial for ensuring the safety and stability of power systems. Currently, large power transformers, both domestically and internationally, are primarily oil-immersed transformers, with a composite insulation structure composed of insulating oil and paper. Long-term transformer operation can lead to faults such as oil overheating, oil sparkover, and oil arcing. These faults accelerate the decomposition of materials such as the insulating oil and paper, generating gases. Monitoring the concentration of gases such as alkanes provides effective feedback on the current health of the transformer.

[0005] Currently, common methods for detecting dissolved gases in transformer oil include electrochemical detection, gas chromatography, photoacoustic spectroscopy, and tunable diode laser absorption spectroscopy (TDLAS). Electrochemical detection relies on chemical reactions to detect gases, offering low cost and high sensitivity, but is limited by response time and lifespan. Gas chromatography utilizes the varying adsorption capacities of chromatographic columns for different samples to separate and detect gases. It can simultaneously detect multiple gas components, but requires frequent replacement of the carrier gas and chromatographic column. Photoacoustic spectroscopy, based on the photoacoustic effect, detects gases, offering fast response speed and high measurement accuracy, but the system is complex and susceptible to environmental noise. TDLAS detects gas content by detecting changes in the intensity of light absorbed and transmitted by the gas to obtain the spectral characteristics of the gas. It offers advantages such as high sensitivity and non-contact measurement, making it widely used in the field of gas detection.

[0006] However, current TDLAS technology for detecting multi-component gases dissolved in oil often requires multiple corresponding lasers. For example, measuring N different dissolved gases in oil requires N equal lasers, resulting in a complex optical path, poor flexibility, and low economic efficiency. Furthermore, after long-term operation, the laser center wavelength drifts, making it impossible to obtain the corresponding signal waveform at low concentrations, resulting in poor gas detection accuracy.

[0007] Summary of the Invention

[0008] In response to the defects of the existing technology, the purpose of this application is to provide a TDLAS-based dissolved gas detection system in oil, which realizes the rapid detection of 6 different dissolved gases in oil using lasers with 4 different central wavelengths, ensures the detection accuracy after long-term operation of the system, improves the economy and long-term stability of the system, and provides auxiliary decision-making for transformer health status monitoring.

[0009] In order to achieve the above objectives, the technical solutions adopted in this application are:

[0010] A first aspect of the present application provides a TDLAS-based dissolved gas detection system in oil, comprising: N2 lasers with different central wavelengths, a reference absorption cell 7, a characteristic absorption cell 8, a photodetector, a lock-in amplifier 11, a signal processing circuit 12, and a control module;

[0011] The reference absorption cell 7 is filled with N1 known oil-dissolved gases of set concentrations, and the characteristic absorption cell 8 is filled with a test gas of unknown concentration and type, where the test gas is at least one of the N1 known oil-dissolved gases. The N1 known oil-dissolved gases are divided into N2 groups, each containing one or two oil-dissolved gases. If the difference between the gas absorption spectra of two oil-dissolved gases is less than a set value, they are grouped together.

[0012] The N2 lasers with different central wavelengths are used to emit laser light to detect N1 different gases dissolved in oil, where N1>N2; the gas absorption spectra of the N2 groups of gases to be tested correspond to the central wavelengths of the N2 lasers respectively;

[0013] The control module controls the emission sequence and emission time of N2 lasers with different central wavelengths. After the transmission light is split, it is divided into two and enters the characteristic absorption cell 8 and the reference absorption cell 7. The photoelectric detector performs photoelectric conversion to obtain the electrical signal after the gas molecules absorb it; the electrical signal is input into the phase-locked amplifier and signal processing circuit 12 for extracting weak useful signals from the electrical signal and performing concentration inversion.

[0014] Preferably, if there is only one type of dissolved gas in oil in the group, after rounding off the gas absorption spectral line to an integer, it is used as the center wavelength of the corresponding laser; if there are two types of dissolved gases in oil in the group, when selecting a laser, it is necessary to consider the measurement of both gases. After averaging the absorption spectral lines of the two gases and rounding off to an integer, it is used as the center wavelength of the corresponding laser.

[0015] Preferably, for the gas absorption spectral lines of 6 different types of dissolved gases in oil in the near-infrared region, select lasers with 4 different center wavelengths to emit light. The gas absorption spectral lines of 6 different types of dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO, and CO2, in the near-infrared region are 1522.0nm, 1653.1nm, 1681.8nm, 1680.2nm, 1580.8nm, and 1579.1nm respectively;

[0016] Classify C2H2 into the first group, CH4 into the second group, C2H4 and C2H6 into the third group, and CO and CO2 into the fourth group. Then select distributed feedback lasers with 4 different center wavelengths of 1522nm, 1653nm, 1680nm, and 1579nm respectively.

[0017] Preferably, the dissolved gas in oil detection system further includes: the optical switch 5. The optical switch 5 switches N2 lasers with different center wavelengths, the switching time is less than or equal to 15ms, and the switching channels are greater than or equal to 4 channels.

[0018] Preferably, the characteristic absorption cell and the reference absorption cell are White cells, the effective optical path range is 3 - 20m, and the cell volume range is 50 - 300ml.

[0019] The second aspect of the present application provides a method for detecting dissolved gases in oil based on TDLAS. Based on the above-mentioned dissolved gas in oil detection system based on TDLAS, it includes the following steps:

[0020] Step 1, according to the gas absorption spectral lines of N1 types of dissolved gases in oil in the near-infrared region, merge them into N2 groups, where N2 < N1, and determine the different center wavelengths of N2 lasers;

[0021] Step 2, control the emission timing and emission time of N2 lasers with different center wavelengths, use the fiber optic coupler 6 to split the transmitted light, the transmitted light is split into two parts and enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system. The first photodetector 9 and the second photodetector 10 detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after gas molecule absorption; input the electrical signal into the lock-in amplifier;

[0022] Step 3, dynamically adjust the gas detection system parameters so that the peak value of the waveform output by the reference absorption cell 7 after phase-locked amplification is maximized;

[0023] Step 4: Fix the gas detection system parameters when the waveform peak in step 3 is the largest, obtain the waveform corresponding to the characteristic absorption cell, and perform peak value and concentration inversion.

[0024] Preferably, step 1 comprises:

[0025] Step 1.1, obtaining the gas absorption spectrum of the dissolved gas in the N1 oil in the near-infrared region;

[0026] Step 1.2, sorting the gas absorption spectra of each dissolved gas in the oil obtained in step 1.1 in the near-infrared region. If the adjacent gas absorption spectra are less than a set value, they are grouped together. If the adjacent gas absorption spectra are not less than the set value, they are grouped separately, and the total number of groups is divided into N2;

[0027] Step 1.3: Determine the laser center wavelength for each group of dissolved oil gases. If there is only one dissolved oil gas in the group, round the gas absorption spectrum to the nearest integer and use it as the laser center wavelength. If there are two dissolved oil gases in the group, select a laser that can measure both gases. Take the average of the two gas absorption spectra and round it to the nearest integer to use as the laser center wavelength.

[0028] Preferably, the gas absorption spectra of the six gases dissolved in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2, in the near-infrared region are obtained, which are 1522.0nm, 1653.1nm, 1681.8nm, 1680.2nm, 1580.8nm, and 1579.1nm, respectively; C2H2 is divided into the first group, CH4 is divided into the second group, C2H4 and C2H6 are divided into the third group, and CO and CO2 are divided into the fourth group; and four lasers with different central wavelengths are selected as distributed feedback lasers, with central wavelengths of 1522nm, 1653nm, 1680nm, and 1579nm, respectively.

[0029] Preferably, step 2 includes: using the optical switch 5 to switch N2 lasers with different central wavelengths, with a switching time less than or equal to 15ms and a switching channel greater than or equal to 4 channels, so that the lasers are connected to the gas detection system in a timed manner to emit light, and the light emission time lasts for 10 to 60 seconds.

[0030] Preferably, step 3 includes: dynamically adjusting the laser operating temperature, minimum drive current and maximum drive current so that the waveform peak generated by the high-concentration gas in the reference absorption cell 7 after absorbing light is maximized, and the waveform peak is the second harmonic peak generated by gas absorption.

[0031] Preferably, in step 3, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured respectively; the high-frequency components are filtered out through a low-pass filter, and the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summing up to extract the waveform peak.

[0032] The beneficial effects of the present application are: by using the TDLAS-based dissolved gas detection system in oil described in the present application, rapid detection of six different dissolved gases in oil is achieved using lasers with four different central wavelengths, ensuring the detection accuracy after long-term operation of the system, improving the economy and long-term stability of the system, and providing auxiliary decision-making for transformer health status monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic structural diagram of a TDLAS-based dissolved gas detection system in oil provided in an embodiment of the present application;

[0034] In Figure 1: 1-1522nm central wavelength laser, 2-1653nm central wavelength laser, 3-1680nm central wavelength laser, 4-1579nm central wavelength laser, 5-optical switch, 6-fiber coupler, 7-reference absorption cell, 8-characteristic absorption cell, 9-first photodetector, 10-second photodetector, 11-lock-in amplifier, 12-signal processing circuit. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0036] In response to the defects or improvement needs of the existing technology, this application provides a TDLAS-based dissolved gas detection system in oil, which realizes the rapid detection of 6 different dissolved gases in oil using lasers with 4 different central wavelengths, ensures the detection accuracy after long-term operation of the system, improves the economy and long-term stability of the system, and provides auxiliary decision-making for transformer health status monitoring.

[0037] Example 1 of the present application provides a TDLAS-based dissolved gas detection system in oil, comprising: N2 lasers with different central wavelengths, an optical switch 5, a fiber coupler 6, a reference absorption cell 7, a characteristic absorption cell 8, a first photodetector 9, a second photodetector 10, a lock-in amplifier 11, a signal processing circuit 12 and a control module.

[0038] The N2 lasers, each with different central wavelengths, are used to emit laser light to detect N1 different dissolved gases in oil, with N1 > N2. Specifically, the N1 known dissolved gases in oil can be divided into N2 groups, each containing one or two dissolved gases. If the difference between the gas absorption lines of two dissolved gases in oil is less than a set value, they are grouped together. The gas absorption lines of the N2 groups of gases to be tested correspond to the central wavelengths of the N2 lasers.

[0039] Preferably, the gas absorption spectra of N1 known dissolved gases in oil are sorted in the near-infrared region, and the following formula is used to determine whether to group adjacent gas absorption spectra. If formula (1) holds, the adjacent gas absorption spectra are grouped together, otherwise a single gas is grouped together. δ i+1 =|s i -s i+1 |≤S TH (1)

[0040] Where:

[0041] δ i+1 Indicates the relative difference between the i+1th gas absorption line and the ith gas absorption line in the gas absorption line sequence;

[0042] s i represents the i-th gas absorption line, i∈[1,N1];

[0043] S TH Indicates the set grouping threshold, preferably but not limited to, S TH ≤2nm.

[0044] Determine the laser center wavelength for each group of dissolved gases in oil. If there is only one dissolved gas in the group, round off the gas absorption spectrum and use it as the corresponding laser center wavelength. If there are two dissolved gases in the group, select a laser to measure both gases. Take the average of the two gas absorption spectra and round off the average to use it as the corresponding laser center wavelength.

[0045] N2 lasers with different central wavelengths are distributed feedback lasers with an operating temperature range of 25 to 35°C and a drive current range of 20 to 110 mA.

[0046] In a preferred but non-limiting embodiment of the present application, four lasers with different central wavelengths are selected to emit light for gas molecule absorption in the near-infrared region, targeting six different gas absorption lines of dissolved gases in oil, i.e., N1 = 6 and N2 = 4. Specifically, the four lasers with different central wavelengths include: a 1522nm central wavelength laser 1, a 1653nm central wavelength laser 2, a 1680nm central wavelength laser 3, and a 1579nm central wavelength laser 4, for absorbing C2H2, CH4, C2H4 and C2H6, and CO and CO2 gas molecules, respectively.

[0047] Among them, the gas absorption spectra of 6 different dissolved gases in oil, C2H2, CH4, C2H4, C2H6, CO and CO2 in the near-infrared region are 1522.0nm, 1653.1nm, 1681.8nm, 1680.2nm, 1580.8nm and 1579.1nm respectively; according to formula (1), C2H2 is divided into the first group, CH4 is divided into the second group, C2H4 and C2H6 are divided into the third group, CO and CO2 are divided into the fourth group, and then distributed feedback lasers with four different central wavelengths of 1522nm, 1653nm, 1680nm and 1579nm are selected.

[0048] The optical switch 5 is used to control the emission timing and emission time of N2 lasers with different central wavelengths. Specifically, the control module uses the optical switch 5 to switch N2 lasers with different central wavelengths. The switching time is less than or equal to 15ms, and the switching channels are greater than or equal to 4 channels. Therefore, the lasers are connected to the gas detection system in a timely manner to emit light, and the emission time lasts for 10 to 60 seconds.

[0049] The optical fiber coupler 6 is used to split the transmitted light, and the transmitted light is divided into two and enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system. Preferably, the splitting ratio of the optical fiber coupler is 1:1.

[0050] Reference absorption cell 7 is used for signal waveform comparison to identify and determine gas detection system parameters. It is filled with N1 known dissolved oil gases of set concentrations, with N1 > N2. Characteristic absorption cell 8 is used for oil dissolved gas concentration detection. It is filled with a test gas of unknown concentration and type, at least one of the N1 known dissolved oil gases. Transmitted light passes through fiber coupler 6, entering characteristic absorption cell 8 and reference absorption cell 7. Within these cells, gas molecules absorb the light, causing the light intensity signal to attenuate slightly and be converted into a useful electrical signal by the photodetector.

[0051] In a preferred but non-limiting embodiment of the present application, the characteristic absorption cell and the reference absorption cell of the gas detection system are White cells, with an effective optical path range of 3 to 20 m and a cell volume range of 50 to 300 ml.

[0052] The first photodetector 9 and the second photodetector 10 are used to detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after the absorption of gas molecules.

[0053] The lock-in amplifier 11 is used to receive the electrical signals obtained by the first photodetector 9 and the second photodetector 10, and perform lock-in amplification using two reference signals with the same frequency as the signal to be measured.

[0054] The signal processing circuit 12 is used to receive the signal amplified by lock-in by the lock-in amplifier 11, and perform cross-correlation operations on the signal to be measured respectively using two reference signals with the same frequency as the signal to be measured. Subsequently, the high-frequency components are filtered out through a low-pass filter, and the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summation. Preferably, the frequencies of the two reference signals are twice the high-frequency driving frequency of the laser, and the phases of the two reference signals differ by 90°. The cut-off frequency of the low-pass filter is 100 Hz.

[0055] The control module is used to dynamically adjust the parameters of the gas detection system, including: switching the optical switch 5, adjusting the operating temperature of the laser, the minimum driving current and the maximum driving current to make the waveform peak value of the final signal generated by the reference absorption cell 7 the largest. The waveform peak value is the second harmonic peak value generated by gas absorption, which is used for inversion with the concentration.

[0056] Embodiment 2 of the present application provides a method for detecting dissolved gases in oil based on TDLAS, including the following steps:

[0057] Step 1, according to the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region, merge them into N2 groups, N2 < N1, and determine the different central wavelengths of N2 lasers.

[0058] In a preferred but non-limiting embodiment of the present application, Step 1 specifically includes:

[0059] Step 1.1, obtain the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region.

[0060] In a preferred but non-limiting embodiment of the present application, obtain the gas absorption spectral lines of 6 kinds of dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2, in the near-infrared region, which are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, and 1579.1 nm respectively.

[0061] Step 1.2, sort the gas absorption spectra of each dissolved gas in the oil in the near-infrared region obtained in step 1.1. If the adjacent gas absorption spectra are less than the set value, they are divided into one group. If the adjacent gas absorption spectra are not less than the set value, they are grouped separately, and the total number is divided into N2 group.

[0062] It is worth noting that among the gases dissolved in the N1 oil in this application, the gas absorption spectra of at least two gases are smaller than the set value, so there is N2 <N1。

[0063] Preferably, the following formula (1) is used to determine whether to group adjacent gas absorption spectra. If formula (1) holds true, the adjacent gas absorption spectra are grouped together. Otherwise, a single gas is grouped together. δ i+1 =|s i -s i+1 |≤S TH (1)

[0064] Where:

[0065] δ i+1 Indicates the relative difference between the i+1th gas absorption line and the ith gas absorption line in the gas absorption line sequence;

[0066] s i represents the i-th gas absorption line, i∈[1,N1];

[0067] S TH Indicates the set grouping threshold, preferably but not limited to, S TH ≤2nm.

[0068] Similarly, it is preferred to use the following formula to determine whether to group adjacent gas absorption spectra into one group. If formula (2) holds true, then the adjacent gas absorption spectra are grouped into one group. Otherwise, a single gas is grouped into one group.

[0069] Where:

[0070] δ i+1 Indicates the relative difference between the i+1th gas absorption line and the ith gas absorption line in the gas absorption line sequence;

[0071] s i represents the i-th gas absorption line, i∈[1,N1];

[0072] S TH Indicates the set grouping threshold.

[0073] For the above 6 gases to be tested, C2H2 is divided into the first group, CH4 is divided into the second group, C2H4 and C2H6 are divided into the third group, and CO and CO2 are divided into the fourth group.

[0074] In step 1.3, determine the laser center wavelength for each group of dissolved oil gases. If there is only one dissolved oil gas in the group, round the gas absorption spectrum to the nearest integer and use it as the laser center wavelength. If there are two dissolved oil gases in the group, select a laser that can measure both gases. Take the average of the two gas absorption spectra and round it to the nearest integer to use as the laser center wavelength. It can be understood that step 1.3 will result in N2 different center wavelengths.

[0075] According to the gas absorption spectra of the above six different gases dissolved in oil in the near-infrared region, four lasers with different central wavelengths are selected as distributed feedback lasers, and the central wavelengths are 1522nm, 1653nm, 1680nm, and 1579nm respectively.

[0076] Step 2: Using the N2 different central wavelengths obtained in step 1, select N2 lasers with different central wavelengths to emit light, control the emission sequence and emission time of the N2 lasers with different central wavelengths, and use the optical fiber coupler 6 to split the transmitted light. The transmitted light enters the reference absorption cell 7 and the characteristic absorption cell 8 of the gas detection system in two parts. The first photodetector 9 and the second photodetector 10 detect the laser passing through the reference absorption cell 7 and the characteristic absorption cell 8, perform photoelectric conversion, and obtain the electrical signal after the gas molecules absorb it; the electrical signal is input into the phase-locked amplifier to realize the extraction of weak useful signals in the electrical signal.

[0077] In a preferred but non-limiting embodiment of the present application, step 2 specifically includes: the control module uses the optical switch 5 to switch N2 lasers with different central wavelengths, the switching time is less than or equal to 15ms, and the switching channel is greater than or equal to 4 channels, so that the laser is connected to the gas detection system in a timed manner to emit light, and the light emission time lasts for 10 to 60s.

[0078] Step 3: Dynamically adjust the gas detection system parameters so that the peak value of the waveform output by the reference absorption cell 7 after phase-locked amplification is maximized.

[0079] In a preferred but non-limiting embodiment of the present application, step 3 includes: dynamically adjusting the laser operating temperature, minimum drive current and maximum drive current so that the waveform peak generated by the high-concentration gas in the reference absorption cell 7 after absorbing light is maximized, and the waveform peak is the second harmonic peak generated by gas absorption.

[0080] Specifically, the lock-in amplifier 11 receives the electrical signals obtained by the first photodetector 9 and the second photodetector 10, and performs phase-locked amplification using two reference signals with the same frequency as the signal to be measured. More preferably, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured. Subsequently, the high-frequency component is filtered out through a low-pass filter, and the DC component containing the amplitude of the signal to be measured is retained, and the final signal is summed to obtain. Preferably, the frequency of the two reference signals is twice the high-frequency drive frequency of the laser, and the phase difference between the two reference signals is 90°. The cutoff frequency of the low-pass filter is 100 Hz.

[0081] Step 4: Fix the gas detection system parameters when the waveform peak in step 3 is the largest, obtain the waveform corresponding to the characteristic absorption cell, and perform peak value and concentration inversion.

[0082] In a preferred but non-limiting embodiment of the present application, step 4 comprises:

[0083] Fix the laser operating temperature, minimum drive current, and maximum drive current at step 3, obtain the waveform peak generated by the gas with the measured concentration absorbing light, and invert it with the concentration.

[0084] It is worth noting that the present application sets up a reference absorption pool 7, which contains six gases with known high concentrations. If there is only a characteristic absorption pool 8, when the concentration of the gas to be measured is very low, when the center wavelength drift occurs, it is impossible to obtain a useful waveform or the waveform degrades under the set laser operating temperature and driving current, causing the gas detection accuracy to deteriorate or even become abnormal; the present application sets up a reference absorption pool containing six gases with known high concentrations, and the transmitted light will enter it after passing through the optical fiber coupler. Since the gas concentration in the reference absorption pool is high, the absorption waveform and the corresponding position of its peak value can be clearly seen. Therefore, by recording the peak position and its change law to perform program correction, adjust the laser temperature and driving current, and restore the waveform peak to the initial position. This solves the impact of the center wavelength drift.

[0085] The above shows and describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. These changes and improvements are intended to fall within the scope of the present application. The scope of protection claimed in this application is defined by the appended claims and their equivalents.

Claims

1. A dissolved gas in oil detection system based on TDLAS, comprising: N2 lasers with different central wavelengths, a reference absorption cell (7), a characteristic absorption cell (8), a photodetector, a lock-in amplifier (11), a signal processing circuit (12) and a control module; The reference absorption cell (7) is filled with N1 kinds of known dissolved gases in oil with set concentrations, and the characteristic absorption cell (8) is filled with a to-be-detected gas with an unknown concentration and an unknown type, and the to-be-detected gas is at least one of the N1 kinds of known dissolved gases in oil; the N1 kinds of known dissolved gases in oil are divided into N2 groups, and each group contains one or two dissolved gases in oil. If the difference between the gas absorption spectra of two dissolved gases in oil is less than a set value, they are divided into one group; The N2 lasers with different central wavelengths are used to emit laser light to detect N1 different dissolved gases in oil, where N1 > N2; the gas absorption spectra of the N2 groups of to-be-detected gases respectively correspond to the central wavelengths of the N2 lasers; The control module controls the light emission timing and light emission time of the N2 lasers with different central wavelengths. After the transmitted light is split, it enters the characteristic absorption cell (8) and the reference absorption cell (7) in two parts, and is subjected to photoelectric conversion by the photodetector to obtain the electrical signal after gas molecule absorption; The electrical signal is input into the lock-in amplifier and the signal processing circuit (12) for extracting weak useful signals in the electrical signal and performing concentration inversion.

2. A dissolved gas in oil detection system based on TDLAS according to claim 1, wherein: If there is only one dissolved gas in oil in the group, after rounding off the gas absorption spectrum, it is used as the central wavelength of the corresponding laser; if there are two dissolved gases in oil in the group, when selecting a laser, both gas measurements need to be considered. After averaging the two gas absorption spectra and rounding off, it is used as the central wavelength of the corresponding laser.

3. A dissolved gas in oil detection system based on TDLAS according to claim 3, wherein: For the gas absorption spectra of 6 different dissolved gases in oil in the near-infrared region, 4 lasers with different central wavelengths are selected to emit light. The gas absorption spectra of the 6 different dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2 in the near-infrared region are 1522.0nm, 1653.1nm, 1681.8nm, 1680.2nm, 1580.8nm, 1579.1nm respectively; C2H2 is classified into the first group, CH4 is classified into the second group, C2H4 and C2H6 are classified into the third group, and CO and CO2 are classified into the fourth group. Furthermore, 4 distributed feedback lasers with different central wavelengths of 1522nm, 1653nm, 1680nm, and 1579nm are selected.

4. A dissolved gas in oil detection system based on TDLAS according to any one of claims 1 to 3, wherein: The dissolved gas in oil detection system further includes: the optical switch (5), and the optical switch (5) switches the N2 lasers with different central wavelengths, and the switching time is less than or equal to 15ms, and the switching channels are greater than or equal to 4 channels.

5. A dissolved gas in oil detection system based on TDLAS according to any one of claims 1 to 3, wherein: The characteristic absorption cell and the reference absorption cell are White cells, with an effective optical path range of 3 to 20 m and a cell volume range of 50 to 300 ml.

6. A method for detecting dissolved gases in oil based on TDLAS, based on a system for detecting dissolved gases in oil based on TDLAS according to any one of claims 1-5, comprising the following steps: Step 1, according to the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region, merge them into N2 groups, N2 < N1, and determine the different central wavelengths of N2 lasers; Step 2, control the emission timing and emission time of N2 lasers with different central wavelengths, use an optical fiber coupler (6) to split the transmitted light, and the transmitted light enters the reference absorption cell (7) and the characteristic absorption cell (8) of the gas detection system in two equal parts. The first photodetector (9) and the second photodetector (10) detect the laser passing through the reference absorption cell (7) and the characteristic absorption cell (8), perform photoelectric conversion, and obtain the electrical signal after gas molecule absorption; input the electrical signal into a lock-in amplifier; Step 3, dynamically adjust the parameters of the gas detection system so that the peak value of the waveform output from the reference absorption cell (7) after lock-in amplification is the largest; Step 4, fix the parameters of the gas detection system when the peak value of the waveform in Step 3 is the largest, obtain the corresponding waveform of the characteristic absorption cell, and perform peak and concentration inversion.

7. A method for detecting dissolved gases in oil based on TDLAS according to claim 6, wherein: Step 1 includes: Step 1.1, obtain the gas absorption spectral lines of N1 kinds of dissolved gases in oil in the near-infrared region; Step 1.2, sort the gas absorption spectral lines of each dissolved gas in oil obtained in Step 1.1 in the near-infrared region. If the adjacent gas absorption spectral lines are less than the set value, divide them into one group. If the adjacent gas absorption spectral lines are not less than the set value, make each one a separate group, and a total of N2 groups are divided; Step 1.3, determine the laser center wavelength for each group of dissolved gases in oil. If there is only one kind of dissolved gas in oil in the group, round the gas absorption spectral line to the nearest integer as the laser center wavelength; if there are two kinds of dissolved gases in oil in the group, when selecting a laser, it is necessary to take both gases into account. After averaging the two gas absorption spectral lines, round to the nearest integer as the laser center wavelength.

8. A method for detecting dissolved gases in oil based on TDLAS according to claim 7, wherein: Obtain the gas absorption spectral lines of 6 kinds of dissolved gases in oil, namely C2H2, CH4, C2H4, C2H6, CO and CO2, in the near-infrared region, which are 1522.0 nm, 1653.1 nm, 1681.8 nm, 1680.2 nm, 1580.8 nm, 1579.1 nm respectively; divide C2H2 into the first group, CH4 into the second group, C2H4 and C2H6 into the third group, and CO and CO2 into the fourth group; select 4 lasers with different central wavelengths as distributed feedback lasers, and the central wavelengths are 1522 nm, 1653 nm, 1680 nm, and 1579 nm respectively.

9. A method for detecting dissolved gases in oil based on TDLAS according to claim 6 or 7, wherein: Step 2 includes: using an optical switch (5) to switch N2 lasers with different central wavelengths, the switching time being less than or equal to 15 ms and the number of switching channels being greater than or equal to 4 channels, so that the lasers access the gas detection system to emit light in sequence, and the light emission time lasts for 10 to 60 s.

10. A method for detecting dissolved gases in oil based on TDLAS according to claim 6 or 7, wherein: Step 3 includes: dynamically adjusting the operating temperature, minimum drive current, and maximum drive current of the laser so that the peak value of the waveform generated after the high-concentration gas in the reference absorption cell (7) absorbs light is the largest, and the waveform peak value is the peak value of the second harmonic generated by gas absorption.

11. A method for detecting dissolved gases in oil based on TDLAS according to claim 10, wherein: In step 3, two reference signals with the same frequency as the signal to be measured are used to perform cross-correlation operations with the signal to be measured respectively; The high-frequency components are filtered out through a low-pass filter, the DC component containing the amplitude of the signal to be measured is retained, and the final signal is obtained by summation, and the waveform peak is extracted.

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