Method and device for detecting dynamic bias current of transformer based on magnetoelectric coupling sensing

Abstract

The present invention relates to the technical field of sensors, specifically a method and device for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing. The detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit is used to measure the DC bias current. The working principle of the magnetoelectric coupling sensing element is based on the stress coupling between magnetostrictive materials and piezoelectric materials, and then an output signal is generated on the piezoelectric material. By utilizing the resonance amplification effect of the magnetoelectric coupling sensing element, the sensitivity is significantly improved. It can achieve non-contact current detection by detecting the magnetic field generated by the bias current of the neutral point grounding wire of the transformer, without the need for direct physical contact with power equipment, which not only improves the safety of the system but also avoids the problem of difficult installation of contact sensors, realizing high-sensitivity, high-precision, anti-interference, and real-time monitoring of the DC bias current of the transformer, and having the characteristics of easy installation and deployment and miniaturization.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and specifically to a method and device for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing. Background Art

[0002] With the rapid development of urban rail transit, the problem of stray current generated by the DC traction power supply system of rail transit has become increasingly serious. The stray current of urban rail transit leaks into the ground through the rails and then enters the transformer of the substation through the grounding grid. Since the rails and the ground are not completely insulated, when urban rail transit accelerates or decelerates, the traction current cannot completely return to the negative pole of the DC traction system through the rails, and part of the current will flow into the ground through the rails to form stray current. This part of the stray current flows into the grounding grid of the substation, thus affecting the potential of the transformer neutral point and forming a bias current on its neutral line. This bias current is superimposed on the main magnetic field of the transformer, resulting in the offset of the magnetization curve and the occurrence of DC bias phenomenon. This phenomenon will exacerbate the vibration, noise and overheating of the equipment. The high-frequency and low-frequency harmonics in the stray current will further increase the influence of bias magnetization, affect the stability of the system and accelerate the aging of the equipment. Therefore, it is necessary to detect the bias current on the neutral line of the transformer to determine whether the DC bias of the transformer exceeds the threshold.

[0003] Currently, the following methods are mainly used to detect the DC bias of transformers: Hall-type neutral point current detection method; flat steel-type neutral point current detection method; deep learning algorithm to predict the insulation resistance value of the anti-corrosion layer of the grounding grid.

[0004] For example, Chinese Patent No. CN116322272A discloses a magnetoelectric sensor for realizing vibration cancellation and its manufacturing method, which includes a first magnetostrictive material layer, a first piezoelectric material layer, a second piezoelectric material layer, and a second magnetostrictive material layer arranged in sequence from top to bottom; wherein, the upper and lower surfaces of the first piezoelectric material layer and the second piezoelectric material layer are adhered with interdigital electrode flexible circuit boards, and two wires for electrode polarization and signal output of the first piezoelectric material layer and the second piezoelectric material layer are led out from the electrode flexible circuit boards.

[0005] Another example is Chinese Patent No. CN118534178A, which discloses a magnetoelectric sensor for characteristic current identification and its manufacturing method, including a magnetostrictive material, a piezoelectric material, a base, two permanent magnets, and a magnetic concentrating material; the piezoelectric material is adhered to the surface of the magnetostrictive material to form a magnetoelectric composite material. One end of the magnetoelectric composite material is fixed by the base to form a cantilever beam structure. The two permanent magnets are respectively adhered to the upper and lower surfaces of the free end of the cantilever beam, and the magnetization direction is perpendicular to the length direction of the cantilever beam; the magnetic concentrating material is arranged outside the magnetoelectric composite material to collect the alternating magnetic field generated by the characteristic current on the energized wire.

[0006] For example, Chinese patent publication number CN110672906A discloses a differential current sensor for measuring a straight AC conductor, which includes two sensitive units and a fixed block; the sensitive unit includes a magnetostrictive / piezoelectric composite material, a height adjustment frame, a base plate, a bias plate, a spacer, a signal output line, and a conductor.

[0007] For example, Chinese patent publication number CN117120861A discloses a magnetic field sensor for detecting a magnetic field, comprising: a magnetoelectric sensor element capable of mechanical oscillation, the sensor element having at least one first layer made of a magnetostrictive material, a second layer made of a piezoelectric material, and at least one electrode made of a conductive material, more specifically a metal; and an electronic device. The magnetic field sensor, more specifically the electronic device, is designed to induce mechanical oscillations in the sensor element by means of an excitation signal, receive the mechanical oscillations of the sensor element and convert them into a received signal, generate an excitation signal from the received signal, and determine a variable related to the magnetic field based on the received signal.

[0008] For example, Chinese patent publication number CN114706025A discloses a resonant DC magnetic sensor based on magnetoelectric effect, which includes a sensor package, a permanent magnet, an excitation coil, a magnetoelectric sensitive unit, and a peripheral signal processing circuit.

[0009] Finally, Chinese patent publication number CN116430097A discloses a current sensor and current measurement method based on a magnetoelectric composite material. The current sensor includes: a sensing element comprising a magnetoelectric composite material for sensing a measured current and outputting an induced electrical signal; a bias magnet for providing a bias magnetic field for the sensing element; a magnetic winding comprising a first core, a second core, a first coil wound on the first core, and a second coil wound on the second core; an AC signal connected to the first coil to drive the first coil to generate an AC excitation magnetic field for the sensing element; a processing module connected to the sensing element to obtain the induced electrical signal; the processing module also receives the AC signal and the second coil, and based on the induced electrical signal and the AC signal, adjusts the feedback current output to the second coil to drive the second coil to compensate for the bias magnetic field; the processing module obtains the feedback current that compensates for the bias magnetic field and determines the measured value of the measured current.

[0010] In summary and in combination with existing technologies, the current technology for detecting DC bias magnetic field of transformers has many drawbacks, which are summarized as follows:

[0011] ① The disadvantages of the Hall-type neutral point current detection method are that the Hall sensor has low sensitivity, is easily affected by complex working conditions, and is highly dependent on the magnetic concentrator structure for current detection;

[0012] ②The flat steel type neutral point current detection method requires collecting data on-site for analysis, with poor real-time performance of the data, high labor costs, inconvenient portability of detection equipment, and low measurement accuracy. Traditional measuring instruments, such as DC clamp meters, have great limitations. The clamp is small and cannot adapt to a wide grounding bar;

[0013] ③In addition, the main board of the existing measuring instrument is installed inside the measuring box. To repair or replace the main board, the entire measuring box must be removed, which is time-consuming and troublesome, and has a certain impact on actual use;

[0014] ④Furthermore, by relying on deep learning algorithms to predict the insulation resistance value of the anti-corrosion layer of the grounding grid, and thus predict the intrusion status of stray current, this method requires collecting a large amount of training data and is highly dependent on surrounding environmental variables, making it difficult to carry out universal promotion;

[0015] ⑤In actual application scenarios, in the stray current in the neutral grounding wire of the transformer caused by urban rail transit operation, in addition to the DC component, there is also a stray AC component below 1 Hz, and currently, it is still impossible to detect the stray AC component. Summary of the Invention

[0016] In view of the deficiencies of the prior art, the present invention provides a method and device for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing to solve the above problems.

[0017] To achieve the above objectives, the present invention is realized through the following technical solutions.

[0018] A method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing, the method comprising the following steps:

[0019] Step S1. When the magnetoelectric coupling sensing element detects the AC stray current signal, an AC excitation magnetic field is applied for modulation. The excitation coil is connected through the backend processing circuit to generate an AC excitation magnetic field, and the magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, so that the magnetoelectric coupling sensing element operates in a resonance state with high sensitivity;

[0020] Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensing element. After the output signal of the magnetoelectric coupling sensing element is amplified and filtered, phase-locked detection is performed, the phase information is read out, the direction of the DC bias current is obtained, and then the polarity of the DC bias current in the transformer is judged;

[0021] Then, the current is converted by the backend processing circuit, and the signal is converted into a DC output form to obtain the amplitude information of the bias magnetic current. The DC component and AC component in the output signal of the magnetoelectric coupling sensing element are separated by using the time-averaging method and the frequency-domain decoupling method to complete the detection of the DC bias magnetic current under the AC background current;

[0022] Step S3. In addition, when detecting the stray current in urban rail transit, the resonance amplification mechanism of the magnetoelectric coupling sensing element and the nonlinear strain characteristics of the magnetostrictive material can be utilized. Through the carrier modulation technology, the low-frequency stray current signal below 1 Hz is modulated to the resonance frequency of the magnetoelectric coupling sensing element, and the resonance amplification effect is used to improve the response output to the low-frequency stray current signal, thereby enhancing the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

[0023] Preferably, the output signal of the magnetoelectric coupling sensing element at the resonance frequency in step S1 and the output signal of the magnetoelectric coupling sensing element at the non-resonance frequency satisfy the following equation:

[0024] (1)

[0025] where is the mechanical quality factor, is the magneto-mechanical conversion coefficient of the magnetostrictive material, is the electromechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensing element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is the imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensing element at the non-resonance frequency, and the output signal of the magnetoelectric coupling sensing element is increased by nearly 0.8 times relative to the output signal at the non-resonance frequency. The formula (1) is the voltage-magnetic field conversion relationship.

[0026] Preferably, in step S2, when detecting the DC bias magnetic field, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously and are separated by the time-averaging method and the frequency-domain decoupling method. Let the total magnetic field be:

[0027] (2)

[0028] where is the DC magnetic field component, is the AC magnetic field component,

[0029] Eliminating the alternating magnetic field component through time averaging:

[0030] (3)

[0031] wherein, is the starting time, and the integration time is greater than the period of the alternating excitation signal,

[0032] The alternating magnetic field component can be obtained by subtracting the DC magnetic field component from the total magnetic field. The calculation steps are as follows:

[0033] (4)

[0034] The frequency domain decoupling method separates the spectrum through Fourier transform to obtain the total output amplitude:

[0035] (5)

[0036] wherein, the DC component is the spectrum value at, and the AC component is the spectrum value at, is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the AC magnetic field, is the AC output amplitude, is the total magnetic field;

[0037] By eliminating the alternating magnetic field component through time averaging, a relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensing element is obtained. The DC bias current generates a DC magnetic field and acts on the magnetoelectric coupling sensing element. By measuring the change of the output voltage of the magnetoelectric coupling sensing element with the DC bias current and combining the sensing model, the magnitude of the DC bias current can be inversely deduced.

[0038] Preferably, the sensing model is used to describe the non-linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. The model establishes the relationship between the piezomagnetic coefficient of the magnetic material and the DC magnetic field:

[0039] (6)

[0040] (7)

[0041] (8)

[0042] wherein, is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetization, is the saturation magnetostriction coefficient, is the saturation Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the permeability of vacuum, is the effective initial magnetic induction intensity, is the magnetic susceptibility at is the magnetic susceptibility at is the effective magnetic field; According to back-calculate the magnitude of the DC bias current, including the following steps:

[0043] Step S2.1. When the magnetoelectric coupling sensing element detects the AC stray current signal, an AC excitation magnetic field is applied for modulation. An AC excitation magnetic field is generated through the excitation coil connected by the backend processing circuit. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, so that the magnetoelectric coupling sensing element works in a resonant state with high sensitivity (this is actually the same as step S1, but for the sake of explanation, it is cited here);

[0044] Step S2.2. When detecting the DC bias, the AC excitation magnetic field and the DC magnetic field to be measured coexist. They are separated by the time-averaging method and the frequency-domain decoupling method. According to formulas (2), (3), (4), and (5), the AC magnetic field component is eliminated by time averaging;

[0045] Step S2.3. The sensing model is used to describe the non-linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. After eliminating the AC magnetic field component, calculate the magnitude of the DC magnetic field;

[0046] Step S2.4. According to the Biot-Savart law, convert the DC magnetic field obtained in step S2.3 into the magnitude of the DC current.

[0047] Preferably, for the magnetostrictive material, the effective magnetic field is the sum of the externally applied DC magnetic field and the demagnetizing field [[ID=५१]]generated by the magnetostrictive material under the externally applied magnetic field :

[0048] (9)

[0049] Wherein, , is the demagnetization factor. For a magnetic material with a certain structure, the demagnetization factor is a constant value. The non-linear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula:

[0050] (10)

[0051] Where, is the magnetostrictive strain under DC bias. is the AC magnetic field intensity at the point to be determined.

[0052] is described by the following formula:

[0053] (11)

[0054] Where, is the low-frequency stray AC magnetic field intensity to be measured. is the AC modulation magnetic field intensity provided by the excitation coil. is the amplitude of the low-frequency stray AC magnetic field. is the amplitude of the AC modulation magnetic field provided by the excitation coil. is time. is the frequency of the AC modulation magnetic field provided by the excitation coil. is the frequency of the low-frequency stray AC magnetic field to be measured.

[0055] Thus, the following output voltage signal is obtained:

[0056] (12)

[0057] Where, is a constant determined by the material of the magnetoelectric coupling sensing element. is the maximum piezomagnetic coefficient of the magnetostrictive material under zero bias. is the amplitude of the low-frequency stray AC magnetic field. is the amplitude of the AC modulation magnetic field provided by the excitation coil, and the amplitude is a certain value within the range. is the frequency of the AC modulation magnetic field provided by the excitation coil, and the frequency is a certain value within the range. is the frequency of the low-frequency stray AC magnetic field to be measured. is time.

[0058] According to the non-linear strain characteristics of the magnetostrictive material, the low-frequency stray current signal will be modulated into the excitation signal in the form of a carrier wave. The output voltage signal includes the AC modulation magnetic field signal and the low-frequency stray AC magnetic field signal to be measured.

[0059] According to formula (1), the output voltage signal is converted into a magnetic field. The relationship between the current and the magnitude of the magnetic field is expressed by the Biot-Savart law, and its direction relationship is judged by the right-hand rule. For an infinitely long current-carrying straight wire, it can be expressed as:

[0060] (13)

[0061] Wherein, is the distance from the point to be measured to the center of the wire, is the current passing through the wire, is the magnetic permeability of vacuum, and its value is ; is the alternating magnetic field strength at the point to be measured. According to formula (13), there is a linear correspondence between the current to be measured and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength shows a linear attenuation with the increase of the distance Thereby, the magnitude of the current is calculated according to the magnetic field strength.

[0062] Device implemented by the method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing:

[0063] The detection device includes a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit. The excitation coil used is wound along the length direction of the magnetoelectric coupling sensing element;

[0064] The backend processing circuit is provided with a signal driving circuit, a filtering and amplifying circuit, a phase-locked detection circuit, a conversion circuit, and the signal driving circuit is connected to the excitation coil.

[0065] Preferably, the magnetoelectric coupling sensing element is provided with a piezoelectric material and a magnetostrictive material, and the piezoelectric material and the magnetostrictive material are connected by an adhesive.

[0066] Preferably, the piezoelectric material includes an upper electrode surface and a lower electrode surface. The upper electrode surface and the lower electrode surface are externally connected with wires. The piezoelectric material is in a sheet structure, and the number of piezoelectric materials is 1.

[0067] Preferably, the input end of the magnetoelectric coupling sensing element is connected to the signal driving circuit, and the output end of the magnetoelectric coupling sensing element is connected to the filtering and amplifying circuit.

[0068] Preferably, the input end of the phase-locked detection circuit is respectively connected to the output ends of the signal driving circuit and the filtering and amplifying circuit, and is used for detecting the phase information of the signal source and the output signal of the magnetoelectric coupling sensing element. By comparing the phase information of the two, the true output signal of the magnetoelectric coupling sensing element can be extracted from the output signal of the filtering and amplifying circuit.

[0069] The output end of the phase-locked detection circuit is connected to The input end of the conversion circuit is used to convert the AC signal waveform into a DC output form and output a stable amplitude signal.

[0070] The output end of the signal driving circuit is connected to the input end of the magnetoelectric coupling sensing element to provide a signal source for the magnetoelectric coupling sensing element.

[0071] The filtering and amplifying circuit is connected to the output end of the magnetoelectric coupling sensing element and is used to amplify the signal output by the magnetoelectric coupling sensing element and perform filtering and zero adjustment processing on the amplified output signal.

[0072] Compared with the prior art, the present invention discloses a method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing. The method measures the DC bias current using a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit. The working principle of the magnetoelectric coupling sensing element is based on the stress coupling between magnetostrictive material and piezoelectric material, and then an output signal is generated on the piezoelectric material. This output signal changes significantly with the DC bias. Using this phenomenon, high-precision detection of the DC bias can be completed. By using the backend processing circuit, the signal is converted into a DC output form to obtain the amplitude information of the DC bias current. Different from the traditional contact detection method, the present invention adopts magnetoelectric coupling sensing technology and utilizes the resonance amplification effect of the magnetoelectric coupling sensing element, so the sensitivity is significantly improved. It can realize non-contact current detection by detecting the magnetic field generated by the bias current of the neutral point grounding wire of the transformer without directly physically contacting the power equipment. In this way, not only the safety of the system is improved, but also the problem of difficult installation of contact sensors is avoided. At the same time, it can realize high-sensitivity, high-precision, anti-interference, and real-time monitoring of the DC bias current of the transformer, and has the characteristics of easy installation and deployment and miniaturization, solving the deficiencies existing in the prior art.

[0073] Utilizing the high sensitivity and high precision of its device, it can realize the accurate detection of the bias current caused by stray current in the transformer. At the same time, the synchronous detection method of the dynamic bias current of the transformer based on magnetoelectric coupling can monitor the dynamic changes inside the transformer in real time, improving the comprehensiveness and accuracy of the monitoring. Using this technology, the DC bias phenomenon caused by stray current can be detected in time, avoiding problems such as equipment overheating, increased mechanical vibration, and increased noise caused by the interference of the bias current on the magnetic field of the transformer.

[0074] At the same time, the magnetoelectric coupling sensor can operate stably in a complex electromagnetic environment, overcoming the problem that traditional current sensors are easily affected by electromagnetic interference.

[0075] Through efficient signal processing technology, external noise can be removed, ensuring the accuracy of monitoring results. A real-time monitoring and high-precision fault warning system can provide more reliable operation data for the power system, detect potential fault hazards early, thus effectively preventing equipment damage, reducing the frequency of outages and repairs, and significantly extending the service life of transformers;

[0076] Moreover, by adopting non-contact detection methods, the problems of contact resistance, mechanical wear, and electrical interference faced by traditional contact sensors are effectively avoided. In addition, the non-contact detection method greatly improves the reliability and long-term stability of the system;

[0077] The magnetoelectric coupling sensing element has higher sensitivity compared to existing Hall sensors, can achieve non-contact current monitoring, and has the advantage of being easy to deploy; Using a model to describe the non-linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element can significantly improve the accuracy of the sensing element and reduce measurement errors;

[0078] Utilizing the resonance enhancement effect of the magnetoelectric coupling sensing element, when the AC excitation frequency is close to the resonance frequency of the magnetoelectric coupling sensing element, the output signal of the magnetoelectric coupling sensing element is increased by nearly 0.8 times compared to the output signal at non-resonant frequencies. For non-contact current measurement, the magnetoelectric coupling sensing element, excitation coil, and backend processing circuit form a detection device. The signal drive circuit is connected to the excitation coil to generate an excitation magnetic field, and the magnetic field frequency generated by the excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, enabling the output signal of the magnetoelectric coupling sensing element to produce a resonance amplification effect, thereby improving the detection sensitivity of the magnetoelectric coupling sensing element and significantly enhancing the output signal, so non-contact measurement can be achieved;

[0079] The output signal of the magnetoelectric coupling sensing element at the resonance frequency is increased by more than 230 times compared to the output signal at non-resonant frequencies. Using this resonance enhancement mechanism, the sensitivity of the magnetoelectric coupling sensing element is significantly improved;

[0080] Utilize the resonance amplification effect to improve the response output to low-frequency stray current signals, thereby enhancing the signal-to-noise ratio of low-frequency stray current and completing the detection of low-frequency stray current;

[0081] Compared to the non-modulated direct measurement method, the magnetic field resolution can reach levels, and the signal-to-noise ratio is increased by nearly 2 orders of magnitude. This detection method compared to Hall sensors ( level magnetic field resolution), magnetoresistive sensors ( For sensors with linear outputs such as 0-level magnetic field resolution, they are more suitable for non-contact measurement of currents in the typical amplitude range of several hundred milliamperes to several amperes in the DC bias magnetic field scenario of the neutral point grounding wire of a transformer. Brief Description of the Drawings

[0082] Figure 1 It is a schematic structural diagram of the method for detecting dynamic bias magnetic current of a transformer based on magnetoelectric coupling sensing of the present invention;

[0083] Figure 2 It is a schematic structural diagram of the magnetoelectric coupling sensing element of the present invention;

[0084] Figure 3 It is a graph of the experimental results of the present invention, where A is the output voltage graph of the magnetoelectric coupling sensing element for the DC magnetic field, B is the voltage phase change graph of the magnetoelectric coupling sensing element for the DC magnetic field, and C is the graph of the output voltage varying with the AC excitation frequency;

[0085] Figure 4 It is the non-linear sensing model of the method for detecting dynamic bias magnetic current of a transformer based on magnetoelectric coupling sensing of the present invention;

[0086] Figure 5 It is the deployment scenario of the method for detecting dynamic bias magnetic current of a transformer based on magnetoelectric coupling sensing of the present invention;

[0087] Figure 6 It is a schematic diagram of the module composition of the backend processing circuit of the present invention. Detailed Embodiments

[0088] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0089] The detection method in the method for detecting dynamic bias magnetic current of a transformer based on magnetoelectric coupling sensing uses a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit;

[0090] The excitation coil is wound along the length direction of the magnetoelectric coupling sensing element;

[0091] The backend processing circuit is provided with a signal driving circuit, a filtering and amplifying circuit, a phase-locked detection circuit, A conversion circuit, the signal driving circuit is connected to the excitation coil. Inside the magnetoelectric coupling sensing element, there are piezoelectric materials and magnetostrictive materials. The piezoelectric material and the magnetostrictive material are connected by an adhesive. The piezoelectric material includes an upper electrode surface and a lower electrode surface. The upper electrode surface and the lower electrode surface are externally connected to wires for conducting and outputting signals. The piezoelectric material is in a sheet structure, and the number of piezoelectric materials is 1. The input end of the magnetoelectric coupling sensing element is connected to the signal driving circuit, and the output end of the magnetoelectric coupling sensing element is connected to the filter amplification circuit.

[0092] The input end of the phase-locked detection circuit is respectively connected to the output ends of the signal driving circuit and the filter amplification circuit, and is used to detect the phase information of the signal source and the output signal of the magnetoelectric coupling sensing element. By comparing the phase information of the two, the true output signal of the magnetoelectric coupling sensing element can be extracted from the output signal of the filter amplification circuit.

[0093] The output end of the phase-locked detection circuit is connected to the input end of the conversion circuit, so as to convert the AC signal waveform into a DC output form and output a stable amplitude signal.

[0094] The output end of the signal driving circuit is connected to the input end of the magnetoelectric coupling sensing element to provide a signal source for the magnetoelectric coupling sensing element.

[0095] The filter amplification circuit is connected to the output end of the magnetoelectric coupling sensing element, and is used to amplify the signal output by the magnetoelectric coupling sensing element and perform filtering and zero adjustment processing on the amplified output signal.

[0096] The magnetoelectric coupling sensing element is composed of a sheet material in a multi-layer form. The upper and lower layers are magnetostrictive materials, which are used to receive magnetic signals in a magnetic field and generate deformations caused by magnetostriction. The middle layer is a piezoelectric material, which is used to receive the strains generated by the upper and lower layers due to magnetostriction and generate a piezoelectric effect to convert the magnetic signal into an electrical signal. The layers are bonded with epoxy resin to fix and transfer the strains between the materials. The magnetoelectric coupling sensing element is more sensitive in the length direction and has a more significant magnetostrictive effect than other directions, and can exhibit a better magnetoelectric coupling coefficient.

[0097] The piezoelectric material is a single crystal or polycrystalline ceramic material, specifically , quartz, , , , , , or one of them.

[0098] The magnetostrictive material is an alloy or oxide with magnetostrictive effect, or a magnetostrictive composite material formed by the composite of them and a polymer, and is in the shape of long strip multi-layer thin flakes; the alloy or oxide with magnetostrictive effect includes Terfenol-D Nickel-iron oxide Cobalt-iron oxide Nickel-manganese-gallium alloy etc., or a magnetostrictive composite material formed by the composite of the above magnetostrictive material and a polymer, and the magnetostrictive material is in a single-layer structure or a multi-layer structure.

[0099] Regarding the method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing, the main steps are as follows:

[0100] ① Provide a piezoelectric material, process the piezoelectric material into the required size and shape, and ultrasonically clean it with ultrapure water;

[0101] ② Electrodes are plated on the upper and lower ends of the surface of the piezoelectric material by annealing, evaporation or magnetron sputtering;

[0102] ③ The piezoelectric material is polarized along the thickness direction after the electrodes are made;

[0103] ④ Wires are respectively attached to the two electrode end faces of the two piezoelectric materials for conducting electrical signals;

[0104] ⑤ Provide a magnetostrictive material, process the magnetostrictive material into the required size and shape, and clean it with alcohol;

[0105] ⑥ Bond the magnetostrictive material to the surface of the piezoelectric material with an adhesive to form a magnetoelectric coupling sensing element;

[0106] ⑦ Lead out signals from the wires on both sides of the magnetoelectric coupling sensing element to produce a magnetoelectric coupling sensing element.

[0107] ⑧ Wind an excitation coil around the periphery of the magnetoelectric coupling sensing element, and its sensitive axis direction is along the length direction of the magnetoelectric coupling sensing element.

[0108] ⑨ The two ends of the coil are connected to the signal drive circuit module, and the two electrodes of the magnetoelectric coupling sensing element are connected to the filter amplification circuit module for preliminary signal processing.

[0109] ⑩ The output signal of the signal drive circuit module is simultaneously connected to the reference signal terminal of the phase-locked detection circuit module for subsequent operation to read the phase information of the current.

[0110] ⑪ Reasonably assemble the excitation coil, the magnetoelectric coupling sensing element and the backend processing circuit module, and debug to realize the synchronous detection function of the dynamic bias current of the transformer.

[0111] ⑫ Install the proposed bias current synchronous detection device near the wire to be measured, and assemble a complete detection device according to the actual working conditions.

[0112] A method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing uses a detection device composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit to measure the DC bias current.

[0113] Step S1. When the magnetoelectric coupling sensing element detects the AC stray current signal, an AC excitation magnetic field is applied for modulation. The excitation coil is connected through the backend processing circuit to generate an AC excitation magnetic field. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, so that the magnetoelectric coupling sensing element works in a resonant state with high sensitivity.

[0114] Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensing element. After the output signal of the magnetoelectric coupling sensing element is amplified and filtered, phase-locked detection is performed, the phase information is read out, the direction of the DC bias current is obtained, and then the polarity of the DC bias current in the transformer is judged.

[0115] Then, the current is converted through the backend processing circuit, and the signal is converted into a DC output form to obtain the amplitude information of the bias current. Using the time-averaging method and the frequency-domain decoupling method, the DC component and the AC component in the output signal of the magnetoelectric coupling sensing element are separated to complete the detection of the DC bias current under the AC background current.

[0116] Step S3. In addition, when detecting the stray current of urban rail transit, the resonance amplification mechanism of the magnetoelectric coupling sensing element and the non-linear strain characteristics of the magnetostrictive material can be used. Through the carrier modulation technology (that is, formulas (11) and (12) are the descriptions for carrier modulation), the low-frequency stray current signal below 1 Hz is modulated to the resonance frequency of the magnetoelectric coupling sensing element, and the resonance amplification effect is used to improve the response output to the low-frequency stray current signal, thereby improving the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

[0117] The working principle of the magnetoelectric coupling sensing element is based on the stress coupling between the magnetostrictive material and the piezoelectric material, and then an output signal is generated on the piezoelectric material. Utilizing the high-sensitivity response characteristic of the magnetostrictive material in the magnetoelectric coupling sensing element to DC bias magnetization, when the DC bias magnetization is zero, the magnetostrictive material is not magnetized, so the output of the magnetoelectric coupling sensing element is close to zero. When the DC bias magnetization is not zero, the magnetostrictive material is magnetized, and the output signal of the magnetoelectric coupling sensing element is significantly enhanced. When the direction of the DC magnetic field around the center line of the transformer changes, the phase of the output voltage of the magnetoelectric coupling sensing element changes, and thus the direction of the current on the center line can be judged.

[0118] Meanwhile, the present invention also utilizes the resonance enhancement effect of the magnetoelectric coupling sensing element. The variation of the output voltage of the magnetoelectric coupling sensing element with the AC excitation frequency is as Figure 3 shown in C of . When the AC excitation frequency is close to the resonance frequency of the magnetoelectric coupling sensing element, the output signal of the magnetoelectric coupling sensing element is increased by nearly 0.8 Figure 3 times compared with the output signal at non-resonance frequencies. For non-contact current measurement, the magnetoelectric coupling sensing element, the excitation coil, and the backend processing circuit form a detection device. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field, and the magnetic field frequency generated by the excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, so that the output signal of the magnetoelectric coupling sensing element generates a resonance amplification effect, thereby improving the detection sensitivity of the magnetoelectric coupling sensing element, and the output signal is significantly enhanced. Therefore, non-contact measurement can be realized. According to the comparison of the experimental result diagrams of A, B, and C in , the output signal of the magnetoelectric coupling sensing element at the resonance frequency is increased by more than 230 times compared with the output signal at non-resonance frequencies. Utilizing this resonance enhancement mechanism, the sensitivity of the magnetoelectric coupling sensing element is significantly improved. The output signal of the magnetoelectric coupling sensing element at the resonance frequency in step S1

[0119] (1)

[0120] wherein, is the mechanical quality factor, is the magneto-mechanical conversion coefficient of the magnetostrictive material, is the electro-mechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensing element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is the imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensing element at the non-resonant frequency. The output signal of the magnetoelectric coupling sensing element is increased by nearly 0.8 times relative to the output signal at the non-resonant frequency. The formula (1) is the voltage-magnetic field conversion relationship. The magnetoelectric coupling sensing element of the present invention has higher sensitivity than the existing Hall sensor, can realize non-contact current monitoring, and has the advantage of being easy to deploy.

[0121] In the step S2, a model is used to describe the non-linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. The model establishes the relationship between the piezomagnetic coefficient of the magnetic material and the DC magnetic field. The piezomagnetic coefficient in the piezomagnetic coefficient of the magnetic material and the response voltage are linearly related:

[0122] (6)

[0123] (7)

[0124] (8)

[0125] Among them, [[ID= 26]] is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetic susceptibility, is the saturation magnetostriction coefficient, is the saturation Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the vacuum permeability, is the effective initial magnetic induction intensity, is the magnetic susceptibility at is the magnetic susceptibility at is the effective magnetic field,

[0126] For the magnetostrictive material, the effective magnetic field is the sum of the externally applied DC magnetic field and the demagnetizing field generated by the magnetostrictive material under the action of the externally applied magnetic field :

[0127] (5)

[0128] Among them, . is the demagnetization factor. For a magnetic material with a certain structure, the demagnetization factor is a fixed value. Using the model to describe the nonlinear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element can significantly improve the accuracy of the sensing element and reduce the measurement error.

[0129] The method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing includes two closed loops. The first closed loop: time averaging eliminates the AC magnetic field component to complete the detection of the DC bias current appearing on the neutral point grounding wire of the transformer. The second closed loop: carrier modulation technology is used to detect the stray current in urban rail transit.

[0130] In step S2, when detecting the DC bias, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously and can be separated by the time averaging method and the frequency domain decoupling method. Let the total magnetic field be:

[0131] (2)

[0132] where is the DC magnetic field component, is the AC magnetic field component,

[0133] Eliminate the AC magnetic field component by time averaging:

[0134] (3)

[0135] where is the starting time, and the integration time is greater than the period of the AC excitation signal,

[0136] Subtracting the DC magnetic field component from the total magnetic field can obtain the AC magnetic field component. The calculation steps are as follows:

[0137] (4)

[0138] The frequency domain decoupling method separates the spectrum through Fourier transform to obtain the total output amplitude:

[0139] (5)

[0140] where the DC component is the spectrum value at and the AC component is the spectrum value at , is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the AC magnetic field, is the AC output amplitude, is the total magnetic field;

[0141] such asFigure 4 As shown in the experimental result diagram, the AC magnetic field component is eliminated by time averaging to obtain the relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensing element. The DC bias current generates a DC magnetic field, which acts on the magnetoelectric coupling sensing element. By measuring the change in the output voltage of the magnetoelectric coupling sensing element with respect to the DC bias current and combining with the sensing model, the magnitude of the DC bias current can be deduced inversely.

[0142] According to To deduce inversely the magnitude of the DC bias current, the following steps are included:

[0143] Step S2.1. When the magnetoelectric coupling sensing element detects the AC stray current signal, an AC excitation magnetic field is applied for modulation. The AC excitation magnetic field is generated through the excitation coil connected by the backend processing circuit. The magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, so that the magnetoelectric coupling sensing element operates in a resonance state with high sensitivity (this is actually the same as step S1, but for the sake of explanation, it is cited here);

[0144] Step S2.2. When detecting the DC bias magnetic field, the AC excitation magnetic field and the DC magnetic field to be measured coexist simultaneously. They can be separated by the time averaging method and the frequency domain decoupling method. According to formulas (2), (3), (4), and (5), the AC magnetic field component is eliminated by time averaging;

[0145] Step S2.3. The sensing model is used to describe the non - linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. After eliminating the AC magnetic field component, the magnitude of the DC magnetic field is calculated;

[0146] Step S2.4. According to the Biot - Savart law, based on the DC magnetic field obtained in step S2.3, the magnitude of the DC current is calculated.

[0147] For the non - contact measurement of the magnetoelectric coupling sensing element, Figure 5 as shown, the magnetoelectric coupling sensing element is close to the wire to be measured, and the DC magnetic field can be applied to the device. The total signal contains DC and AC. After eliminating the AC component, only the DC component remains, and the detection of the DC bias magnetic field can be carried out.

[0148] For the measurement of DC bias current, a device composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field, and the magnetic field frequency generated by the excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element. When a bias current appears in the neutral grounding wire of the transformer, this DC bias will magnetize the magnetostrictive material in the magnetoelectric coupling sensing element. After the output signal of the magnetoelectric sensor is amplified and filtered, phase-locked detection is performed to read out the phase information and obtain the direction of the current; then through converting the current, the signal is converted into a DC output form to obtain the amplitude information of the bias current; in terms of the backend processing circuit, by using the time-averaging method and the frequency-domain decoupling method, the DC component and the AC component in the output signal of the sensing element can be effectively separated, realizing the detection of the DC bias current under the AC background current. In the actual application scenario, in the stray current in the neutral grounding wire of the transformer caused by the operation of urban rail transit, in addition to the DC component, there is also a stray AC component below 1 Hz. By using the time-averaging method and the frequency-domain decoupling method, the DC component and the AC component can be separated, the AC component is eliminated, and the DC component is obtained, completing the detection of the DC bias and realizing the detection of the DC bias current. To detect the stray AC component below 1 Hz, a carrier modulation technique needs to be adopted.

[0149] For the detection of stray current in urban rail transit, the device proposed by the present invention can utilize the resonance amplification mechanism of the magnetoelectric coupling sensing element and the non-linear strain characteristics of the magnetostrictive material. Through the carrier modulation technique, the low-frequency stray current signal below 1 Hz is modulated to the frequency of the excitation coil, which is the resonance frequency of the magnetoelectric coupling sensing element, realizing a significant improvement in the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current.

[0150] The non-linear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula:

[0151] (10)

[0152] Where is the magnetostrictive strain under DC bias, is the AC magnetic field strength at the point to be determined, which can be described by the following formula:

[0153] (11)

[0154] Where is the stray AC magnetic field strength to be measured, is the AC modulation magnetic field strength provided by the excitation coil, is the amplitude of the stray AC magnetic field, The amplitude of the alternating current modulated magnetic field provided for the excitation coil, is time, the frequency of the alternating current modulated magnetic field provided for the excitation coil, the frequency of the low-frequency stray alternating current magnetic field to be measured. It should be noted that in formula (2), is the alternating current magnetic field component, which is used by the time-averaging method to measure the direct current magnetic field, while in formula (11), the intensity of the alternating current modulated magnetic field provided for the excitation coil, which is used by the carrier modulation technique to measure the stray current.

[0155] The following output voltage signal is thus obtained:

[0156] (12)

[0157] Wherein, is a constant determined by the material of the magnetoelectric coupling sensing element, the maximum piezomagnetic coefficient of the magnetostrictive material under zero bias magnetic field, the amplitude of the low-frequency stray alternating current magnetic field, the amplitude of the alternating current modulated magnetic field provided for the excitation coil ( a certain value within the range), the frequency of the alternating current modulated magnetic field provided for the excitation coil ( a certain value within the range), the frequency of the low-frequency stray alternating current magnetic field to be measured, is time. For the measurement of low-frequency stray current, a detection device is composed of a magnetoelectric coupling sensing element, an excitation coil, and a backend processing circuit. The signal driving circuit is connected to the excitation coil to generate an excitation magnetic field, and the magnetic field frequency generated by the excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, enabling the magnetoelectric coupling sensing element to operate in a resonant state with high sensitivity.

[0158] Due to the non-linear strain characteristics of the magnetostrictive material, the low-frequency stray current signal will be modulated into the excitation signal in the form of a carrier, and the output voltage signal contains the alternating current modulated magnetic field signal and the low-frequency stray alternating current magnetic field signal to be measured. In terms of the backend processing circuit, the frequency domain signal is obtained by using the fast Fourier transform, and then the signal frequency and amplitude of the low-frequency stray alternating current magnetic field are obtained to realize the detection of the low-frequency stray current. Based on the conversion relationship between the dynamic bias current and the magnetic field of the transformer, and using the non-linear strain of the magnetostrictive material, we can also measure the low-frequency stray signal in the dynamic bias current of the transformer. Compared with the non-modulated direct measurement method, the magnetic field resolution can reach level, and the signal-to-noise ratio is improved by nearly two orders of magnitude. This modulation test method compared with Hall sensors ( level magnetic field resolution), For sensors with linear outputs such as magnetoresistive sensors ( level magnetic field resolution), it is more suitable for non-contact measurement of typical currents ranging from several hundred milliamperes to several amperes in the DC bias magnetic field scenario of the grounding wire of the transformer neutral point. In step S1, the signal driving circuit is connected to the excitation coil to generate an excitation magnetic field. The magnetic field frequency generated by the excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element, enabling the magnetoelectric coupling sensing element to operate in a resonant state with high sensitivity. Then, according to the non-linear strain characteristics of the magnetostrictive material, the low-frequency stray current signal will be modulated into the excitation signal in the form of a carrier. The output voltage signal includes an AC modulated magnetic field signal and the low-frequency stray AC magnetic field signal to be measured. In the backend processing circuit, by using the fast Fourier transform, the frequency domain signal is obtained, and then the signal frequency and amplitude of the low-frequency stray AC magnetic field are obtained to complete the detection of the low-frequency stray current.

[0159] Figure 5 This is the deployment scenario of the device. In the actual application scenario, the proposed dynamic bias current synchronous detection device is deployed near the neutral line of the transformer, and the sensitive axis direction of the magnetoelectric coupling sensing element is perpendicular to the bias current direction. Since the rail and the ground are not completely insulated, when the urban rail transit accelerates or decelerates, the traction current cannot completely return to the negative pole of the DC traction system through the rail, and part of the current will flow into the ground through the rail to form stray current. This part of the stray current flows into the grounding grid of the substation, thus affecting the potential of the transformer neutral point and forming a bias current on its neutral line. This bias current is superimposed on the main magnetic field of the transformer, resulting in the deviation of the magnetization curve and the occurrence of the DC bias phenomenon. A voltage signal with the resonance frequency of the magnetoelectric coupling sensing element is generated by the signal driving circuit and applied to the coil to generate an excitation magnetic field. This excitation magnetic field is used to drive the magnetoelectric coupling sensing element to operate in a resonant state to obtain the highest detection sensitivity. In step S2, when there is a DC bias current on the transformer neutral line, a surrounding magnetic field is generated around the flat steel. The relationship between the current and the magnetic field can be expressed by the Biot-Savart law, and its direction relationship can be judged by the right-hand rule. For an infinitely long current-carrying straight wire, it can be expressed as:

[0160] (13)

[0161] Among them, is the distance from the point to be measured to the center of the wire, is the current passing through the wire, is the vacuum permeability, and its value is , There is a linear correspondence between the measured current and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength decreases with the distance It shows a linear attenuation, and the magnitude of the current can be calculated based on the magnetic field strength. During implementation and deployment, the influence of distance and position needs to be considered. By utilizing the inverse attenuation relationship of the magnetic field strength with distance, calibration is performed for different types of grounding wires, and the operating parameters for installation are given.

[0162] On this basis, when there is a bias magnetic current on the neutral line, according to the Biot - Savart law, the magnetoelectric coupling sensing element will sense the corresponding DC magnetic field. Under the action of this magnetic field, the amplitude of the resonant signal output by the magnetoelectric coupling sensing element will change synchronously. After the signal is preliminarily processed by an amplification and filtering circuit, the phase information is read out through a phase - locked detection circuit, and then the conversion circuit reads out the amplitude information of the resonant signal, forming a standard current output form, thereby realizing the synchronous detection of the dynamic bias magnetic current of the transformer.

[0163] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0164] It should be noted that the terms "first", "second", etc. in the description, claims, and above - mentioned drawings of the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order different from those illustrated or described herein.

[0165] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing, characterized in that: The method includes the following steps: Step S1. When the magnetoelectric coupling sensing element detects the AC stray current signal, an AC excitation magnetic field is applied for modulation. An AC excitation magnetic field is generated through the excitation coil connected by the backend processing circuit, and the magnetic field frequency generated by the AC excitation magnetic field is consistent with the resonance frequency of the magnetoelectric coupling sensing element; Step S2. When a DC bias current appears on the neutral point grounding wire of the transformer, the DC bias current will magnetize the magnetostrictive material in the magnetoelectric coupling sensing element. After the output signal of the magnetoelectric coupling sensing element is amplified and filtered, phase-locked detection is performed, the phase information is read out, the direction of the DC bias current is obtained, and then the polarity of the DC bias current in the transformer is judged; Then, the current is converted through the backend processing circuit, the signal is converted into a DC output form, the amplitude information of the bias current is obtained, and the DC component and AC component in the output signal of the magnetoelectric coupling sensing element are separated by using the time averaging method and the frequency domain decoupling method to complete the detection of the DC bias current under the AC background current; Step S3. In addition, when detecting the stray current of urban rail transit, the resonance amplification mechanism of the magnetoelectric coupling sensing element and the non-linear strain characteristics of the magnetostrictive material can be utilized. Through carrier modulation, the low-frequency stray current signal below 1 Hz is modulated to the resonance frequency of the magnetoelectric coupling sensing element, and the resonance amplification effect is used to improve the response output to the low-frequency stray current signal, thereby improving the signal-to-noise ratio of the low-frequency stray current and completing the detection of the low-frequency stray current. The AC magnetic field component is eliminated by the time-averaging method to obtain the relationship curve between the DC magnetic field and the output voltage of the magnetoelectric coupling sensing element. The DC bias current generates a DC magnetic field, which acts on the magnetoelectric coupling sensing element. By measuring the change of the output voltage of the magnetoelectric coupling sensing element with the DC bias current and combining with the sensing model, the magnitude of the DC bias current can be deduced inversely. The above-mentioned sensing model is used to describe the non-linear relationship between the magnitude of the DC magnetic field and the response voltage of the magnetoelectric coupling sensing element. The model establishes the relationship between the piezomagnetic coefficient of the magnetic material and the DC magnetic field: (6) (7) (8) in, is the piezomagnetic coefficient of the magnetostrictive material, is the compliance coefficient, is the magnetic susceptibility, is the saturation magnetic susceptibility, is the saturation magnetostriction coefficient, is the saturated Young's modulus, is the stress of the magnetostrictive layer, is the saturation stress of the magnetostrictive layer, is the vacuum permeability, is the effective initial magnetic induction intensity, for The magnetic susceptibility at for The magnetic susceptibility at is the effective magnetic field, and the output signal of the magnetoelectric coupling sensor element at the resonant frequency in step S1 is Output signal of magnetoelectric coupling sensor element at non-resonant frequency Satisfies the following equation: (1) Among them, is the mechanical quality factor, is the magneto-mechanical conversion coefficient of the magnetostrictive material, is the electromechanical conversion coefficient of the piezoelectric material, is the angular frequency, is the static capacitance of the piezoelectric material, is the mechanical impedance of the magnetoelectric coupling sensing element, is the AC magnetic field strength at the point to be determined, d is the thickness of the piezoelectric material, j is the imaginary number related to the phase, is the output signal of the magnetoelectric coupling sensing element at the non-resonant frequency. Formula (1) is the voltage-magnetic field conversion relationship. When detecting the DC bias magnetic field in step S2, the AC excitation magnetic field and the DC magnetic field to be measured exist simultaneously and are separated by the time-averaging method and the frequency-domain decoupling method. Let the total magnetic field be: (2) Among them, is the DC magnetic field component, is the AC magnetic field component, Eliminate the AC magnetic field component through time averaging: (3) Among them, is the starting time, the integration time is greater than the period of the AC excitation signal, The AC magnetic field component can be obtained by subtracting the DC magnetic field component from the total magnetic field. The calculation steps are as follows: (4) The frequency domain decoupling method separates the spectrum through Fourier transform to obtain the total output amplitude: (5) Among them, the DC component is the spectral value at , and the AC component is the spectral value at . is the total output amplitude, is the DC magnetic field, is the frequency-dependent sensitivity, is the AC magnetic field, is the AC output amplitude, is the total magnetic field.

2. The method for detecting the dynamic bias current of a transformer based on magnetoelectric coupling sensing according to claim 1, wherein: Effective magnetic field is the externally applied DC magnetic field and the demagnetizing field generated by the magnetostrictive material under the externally applied magnetic field action: sum: (9) Among them, , is the demagnetizing field, is the demagnetization factor. For a magnetic material with a certain structure, the demagnetization factor is a fixed value. The non-linear strain of the magnetostrictive material in step S3 is expressed by the following Taylor series formula: （10） Among them, is the magnetostrictive strain under DC bias magnetic field, the AC magnetic field intensity at the point to be solved, described by the following formula: （11） Among them, is the intensity of the low-frequency stray alternating magnetic field to be measured, is the intensity of the alternating modulation magnetic field provided by the excitation coil, is the amplitude of the low-frequency stray alternating magnetic field, is the amplitude of the alternating modulation magnetic field provided by the excitation coil, is time, is the frequency of the alternating modulation magnetic field provided by the excitation coil, is the frequency of the low-frequency stray alternating magnetic field to be measured, The following output voltage signal is obtained therefrom: （12） wherein, is a constant determined by the magnetoelectric coupling sensing element material, is the maximum piezomagnetic coefficient of the magnetostrictive material under zero bias magnetic field, is the amplitude of the low-frequency stray alternating magnetic field, is the amplitude of the alternating modulation magnetic field provided by the excitation coil, and the amplitude is a certain value within the range, is the frequency of the alternating modulation magnetic field provided by the excitation coil, and the frequency is a certain value within the range, is the frequency of the low-frequency stray alternating magnetic field to be measured, is time, According to the non-linear strain characteristics of the magnetostrictive material, the low-frequency stray current signal will be modulated into the excitation signal in the form of a carrier. The output voltage signal includes an AC modulated magnetic field signal and a low-frequency stray AC magnetic field signal to be measured. According to formula (1), the output voltage signal is converted into a magnetic field. The magnitude relationship between the current and the magnetic field is expressed by the Biot-Savart law, and its direction relationship is judged by the right-hand rule. For an infinitely long current-carrying straight wire, it can be expressed as: (13) Among them, is the distance from the point to be determined to the center of the wire, is the current passing through the wire, is the magnetic permeability of vacuum, and its value is , is the AC magnetic field strength at the point to be determined. According to formula (13), there is a linear correspondence between the current to be measured and the magnetic field. The larger the current, the larger the magnetic field, and the magnetic field strength shows a linear attenuation as the distance increases, so that the magnitude of the current can be calculated based on the magnetic field strength.

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