Iron core residual magnetism measurement method based on maximum value of irreversible differential magnetic susceptibility

Abstract

The invention discloses an iron core residual magnetism measurement method based on an irreversible differential magnetic susceptibility maximum value, and belongs to the technical field of electromagnetic parameter measurement. Aiming at the problems of low measurement precision and complex system of the existing iron core residual magnetism measurement method, the invention provides an innovative solution which comprises the following steps of: firstly, deducing an expression of the maximum value of the irreversible differential magnetic susceptibility when the residual magnetization exists or not by utilizing an expression of the irreversible differential magnetic susceptibility and combining a # imgabs0 # hysteresis model; establishing a physical model relational expression between the residual magnetization intensity and the maximum irreversible differential magnetic susceptibility; then, the maximum value of the irreversible differential magnetic susceptibility is obtained by measuring a hysteresis loop of # imgabs 1 #, and the residual magnetism value in the iron core is calculated through the maximum value of the irreversible differential magnetic susceptibility according to the constitutive relation # imgabs 2 #; the method is easy and convenient to operate, reliable in result and clear and novel in principle, is widely applied to measurement and calculation of transformer iron core residual magnetism in power equipment, and has great significance in improving the operation efficiency and stability of a power system.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic parameter measurement, and in particular to a method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility. Background Art

[0002] The hysteresis property of ferromagnetic materials is an important phenomenon in the field of electromagnetism. It causes the magnetic induction intensity of the material to be non-zero when the external magnetic field strength is zero. This non-zero magnetic induction intensity is called residual magnetic induction intensity, or remanence for short. In the power system, most inductive devices such as transformers, reactors, and current transformers use ferromagnetic materials as their core components. When these devices are powered off, the iron core inside them often retains a certain amount of remanence. If the remanence in the iron core is high, when the device is closed again, a significant excitation inrush current will occur. The overcurrent value generated by this excitation inrush current can be as high as 6 to 8 times the rated current value, posing a serious threat to the mechanical stability and insulation strength of the transformer winding, and thus affecting the safety and stability of the transformer in power grid applications.

[0003] In order to accurately measure and evaluate the residual magnetism in the iron core, the prior art has proposed a variety of methods, but all of them have limitations to varying degrees. For example, Chinese patent CN116593947A discloses a transformer core residual magnetism detection method based on magnetization time. This method determines the direction of residual magnetism by the changing trend of magnetization time under positive and negative short-term small DC excitation, and obtains the empirical formula of residual magnetism and positive magnetization time through data fitting. However, under different excitations, the coefficients of the empirical formula fitted by this method are different, resulting in the empirical formula being non-unique and lacking clear physical meaning.

[0004] In addition, the article "Evaluation and Experimental Verification of Residual Magnetism of Power Transformers Based on External DC Excitation" published in the 10th issue of "Power System Technology" in 2022 proposed a measurement method based on real-time tracking of magnetic flux; this method applies an external current excitation of known magnitude to the transformer winding and records the changes in magnetic flux to obtain the magnitude and direction of the residual magnetism; however, this method has high requirements on the performance of the measuring instrument and requires that the external excitation magnetization process be reversible, so it is mainly suitable for residual magnetism measurement of soft magnetic materials.

[0005] The article "Estimation of Transformer Core Residual Magnetism" in the 2011 issue 2 of "Power System Technology" uses the voltage and current data detected on the primary side of the transformer after the transformer is closed at no-load to find the core saturation moment to estimate the residual magnetism; however, this method needs to record the time when the core reaches saturation during measurement, and the excitation surge current generated when the core is saturated will cause harm to the equipment, and demagnetization processing is required after the measurement.

[0006] The article "Research on Residual Magnetism Measurement Method of Power Transformer" in the 15th issue of "Power System Protection and Control" in 2019 analyzed the generation principle of excitation surge current of power transformers and concluded that the peak value of excitation surge current is uniquely determined by residual magnetism, and then reversely inferred the residual magnetism from the closing angle of voltage and the first peak value of excitation surge current; however, this method cannot calculate the residual magnetism value in the iron core before closing, and cannot effectively suppress the generation of excitation surge current, and the excitation surge current generated during the measurement process will also cause damage to the equipment.

[0007] In summary, the existing iron core remanence measurement methods have problems such as low measurement accuracy, complex measurement system, and harm to equipment, and a simpler, more reliable and clear-principle measurement method is urgently needed. Based on this demand, the present invention proposes an iron core remanence measurement method based on the maximum value of irreversible differential susceptibility, aiming to achieve accurate measurement and evaluation of iron core remanence by constructing a physical model relationship between the maximum value of irreversible differential susceptibility and remanence. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility, so as to solve the problems of low measurement accuracy and complex measurement system of the existing method for measuring the residual magnetism of an iron core.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for measuring the remanence of an iron core based on the maximum value of irreversible differential magnetic susceptibility, comprising the following steps: Step 1: Use the expression of irreversible differential magnetic susceptibility and combine The theory of hysteresis model derives the expressions of the maximum value of irreversible differential susceptibility with and without residual magnetization respectively; Step 2: Combine the expressions of irreversible differential susceptibility with and without residual magnetization in Step 1 to establish the physical model relationship between residual magnetization and the maximum value of irreversible differential susceptibility; Step 3: Establish irreversible differential susceptibility and The relationship between the hysteresis loop and the The maximum value of irreversible differential susceptibility is obtained from the hysteresis loop, which is substituted into the physical model relationship between the residual magnetization intensity and the maximum value of irreversible differential susceptibility in Step 2 to obtain the residual magnetism value in the iron core; Step 4: Build the core The hysteresis loop measurement platform uses DC excitation to preset different remanence values ​​and obtains the maximum value of the irreversible differential susceptibility under different preset remanence values, which is used to verify the correctness of the theoretical model expression proposed for remanence measurement.

[0010] In the preferred embodiment, the Step 1 is combined with The specific steps of deriving the maximum expression of irreversible differential susceptibility with and without residual magnetization intensity from the theory of hysteresis model include: Step 1.1: According to the theory of JA hysteresis model, the calculation formula of irreversible differential magnetic susceptibility can be expressed as: (1) In the formula, is the strength of the external magnetic field, is the containment coefficient, is the directivity coefficient, is the coupled average magnetic field parameter within the magnetic domain, is the hysteresis-free magnetization, is the irreversible magnetization, is the irreversible differential susceptibility; Step 1.2: From Step 1.1, we know that the irreversible differential susceptibility is The slope of the hysteresis curve, so the maximum value of the irreversible differential susceptibility appears at the coercivity point , expressed as: (2) In the formula, is the maximum value of irreversible differential susceptibility; Step 1.3: The relationship between irreversible magnetization and hysteresis-free magnetization is expressed as: (3) In the formula, is the reversible susceptibility, is the total magnetization; Step 1.4: Combining Step 1.2 and Step 1.3, when there is no residual magnetization and only AC excitation is applied, the maximum value of irreversible differential susceptibility is expressed as: (4) In the formula, is the residual magnetization, is the magnetization intensity produced by AC excitation; Step 1.5: When there is residual magnetization, It can be divided into the AC action part and the residual magnetic action part, which can be expressed as: (5) Step 1.6: When calculating the maximum irreversible differential susceptibility value, The AC part of is 0. According to Step 1.1, the maximum value of irreversible differential susceptibility with residual magnetization is expressed as: (6).

[0011] In a preferred embodiment, the specific steps of establishing the physical model relationship between the residual magnetization and the maximum value of the irreversible differential susceptibility in Step 2 include: Step 2.1: Considering that when the applied AC excitation is small, use The model identifies the internal coupling mean field parameters of the magnetic domains The order of magnitude is very small, so the maximum value of irreversible differential susceptibility with or without residual magnetism can be simplified to: (7) (8) Step 2.2: Due to According to Step 2.1, the physical model relationship between the residual flux density and the maximum value of the irreversible differential susceptibility is expressed as: (9) In the formula, is the residual magnetic density, is the magnetic permeability of vacuum.

[0012] In the preferred embodiment, the irreversible differential magnetic susceptibility and The specific steps of the relationship of the hysteresis loop include: Step 3.1: According to JA magnetization theory, the differential magnetic susceptibility can be expressed as: (10) In the formula, is the differential magnetic susceptibility, is the hysteresis-free differential susceptibility; Step 3.2: In the absence of hysteresis, due to the conservation of energy, can be expressed as: (11); Step 3.3: Due to According to Step 3.1 and Step 3.2, the irreversible differential susceptibility can be B - H The hysteresis loop is expressed as: (12) In the formula, is the magnetic induction intensity, yes The slope of the hysteresis loop, yes The first derivative of the slope of the hysteresis loop.

[0013] In the preferred solution, by measuring different preset residual magnetism The hysteresis loop can be used to obtain the maximum value of the irreversible differential susceptibility under different remanent magnetization. The physical model relationship between the maximum value of the irreversible differential susceptibility and the remanent magnetic flux density is , the residual magnetism value in the iron core can be detected.

[0014] The present invention provides a method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility, which has the following beneficial effects: 1. The present invention solves the problems of low measurement accuracy, complex measurement system, high dependence on complex experimental equipment and unclear physical meaning of traditional empirical formula in existing iron core residual magnetism measurement methods; 2. The present invention uses irreversible differential magnetic susceptibility as a detection medium to construct a relationship between the maximum value of irreversible differential magnetic susceptibility and residual magnetic flux density, providing a new method and idea for the measurement and evaluation of iron core residual magnetism; 3. The core remanence measurement equation provided by the present invention has a clear physical meaning. Based on a clear physical model and experimental verification, the measurement principle is simple and clear, and the obtained remanence measurement result has high credibility and accuracy. 4. The method of the present invention is generally applicable and can be widely used in the measurement and calculation of the residual magnetism of the transformer core in power equipment, which plays a significant role in suppressing and eliminating the influence of residual magnetism in power equipment; 5. The present invention combines The magnetization theory innovatively constructs the physical model relationship between the maximum value of irreversible differential magnetic susceptibility and remanence. The introduction of this theoretical model provides a new theoretical basis for remanence measurement, which is different from the previous methods that rely on empirical formulas or complex experimental measurements. 6. The present invention has achieved a breakthrough in theory. By deeply analyzing the relationship between the maximum value of irreversible differential susceptibility and remanence, an innovative remanence measurement method based on the maximum value of irreversible differential susceptibility is proposed, and a corresponding theoretical model is constructed. This theoretical innovation brings new perspectives and thinking to the field of remanence measurement. 7. The present invention successfully The fusion of magnetization theory is applied to the remanent magnetization measurement, and the theoretical model relationship between the maximum value of irreversible differential susceptibility and remanent magnetization is derived. The application of this technology fusion not only improves the reliability of the measurement, but also broadens the application scope of the theoretical model. 8. The present invention measures The maximum value of irreversible differential magnetic susceptibility is obtained from the hysteresis loop, and the remanence is calculated using the physical model relationship. The entire measurement process is simple and easy. 9. The present invention improves the measurement accuracy of the iron core remanence through theoretical model derivation and experimental verification; simplifies the measurement process, reduces the requirements for the measurement equipment, and makes the measurement method more popular and practical; 10. The method of the present invention accurately measures the residual magnetism of the iron core, avoids the influence of the residual magnetism on the safety and stability of the power equipment, and improves the operating efficiency and reliability of the power system. 11. The invention brings new perspectives and thinking to the field of residual magnetism measurement and promotes the progress and development of related technologies; 12. The measurement method of the present invention has a wide range of practical application value and can be applied to the measurement and evaluation of the residual magnetism of various ferromagnetic equipment in the power system. By accurately measuring the residual magnetism, the influence of the residual magnetism on the safety and stability of the equipment can be effectively avoided, and the operating efficiency and reliability of the power system can be improved. The creativity of this practical application has contributed to the technological progress and development of the power industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below in conjunction with the accompanying drawings and implementation examples: Figure 1 This is a schematic block diagram of the operation flow of Embodiment 3 of the present invention; Figure 2 The circular iron core of embodiment 3 of the present invention Schematic diagram of hysteresis loop experimental detection; Figure 3 The same preset residual magnetic value in different directions detected in Example 3 of the present invention Magnetic hysteresis loop diagram; Figure 4 The same direction but different preset residual magnetic values ​​detected in Example 3 of the present invention Magnetic hysteresis loop diagram; Figure 5 This is a trend diagram of the relationship between the preset remanence value and the detected maximum value of the irreversible differential magnetic susceptibility in Example 3 of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below in conjunction with the embodiments and drawings: Example 1 A method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility comprises the following steps: Step 1: Use the expression of irreversible differential magnetic susceptibility and combine (Jiles-Atherton, hysteresis model) The theory of the hysteresis model derives expressions for the maximum value of the irreversible differential susceptibility with and without residual magnetization; Step 2: Combine the expressions of irreversible differential susceptibility with and without residual magnetization in Step 1 to establish the physical model relationship between residual magnetization and the maximum value of irreversible differential susceptibility; Step 3: Establish irreversible differential susceptibility and The relationship between the hysteresis loop and the The maximum value of irreversible differential susceptibility is obtained from the hysteresis loop, which is substituted into the physical model relationship between the residual magnetization intensity and the maximum value of irreversible differential susceptibility in Step 2 to obtain the residual magnetism value in the iron core; Step 4: Build the core The hysteresis loop measurement platform uses DC excitation to preset different remanence values ​​and obtains the maximum value of the irreversible differential susceptibility under different preset remanence values, which is used to verify the correctness of the theoretical model expression proposed for remanence measurement.

[0017] In this embodiment, the Step 1 is combined with The specific steps of deriving the maximum expression of irreversible differential susceptibility with and without residual magnetization intensity from the theory of hysteresis model include: Step 1.1: According to the theory of JA hysteresis model, the calculation formula of irreversible differential magnetic susceptibility can be expressed as: (1) In the formula, is the strength of the external magnetic field, is the containment coefficient, is the directivity coefficient, is the coupled average magnetic field parameter within the magnetic domain, is the hysteresis-free magnetization, is the irreversible magnetization, is the irreversible differential susceptibility; Step 1.2: From Step 1.1, we know that the irreversible differential susceptibility is The slope of the hysteresis curve, so the maximum value of the irreversible differential susceptibility appears at the coercivity point , expressed as: (2) In the formula, is the maximum value of irreversible differential susceptibility; Step 1.3: The relationship between irreversible magnetization and hysteresis-free magnetization is expressed as: (3) In the formula, is the reversible susceptibility, is the total magnetization; Step 1.4: Combining Step 1.2 and Step 1.3, when there is no residual magnetization and only AC excitation is applied, the maximum value of irreversible differential susceptibility is expressed as: (4) In the formula, is the residual magnetization, is the magnetization intensity produced by AC excitation; Step 1.5: When there is residual magnetization, It can be divided into the AC action part and the residual magnetic action part, which can be expressed as: (5) Step 1.6: When calculating the maximum irreversible differential susceptibility value, The AC part of is 0. According to Step 1.1, the maximum value of irreversible differential susceptibility with residual magnetization is expressed as: (6).

[0018] Furthermore, the specific steps of establishing the physical model relationship between the residual magnetization and the maximum value of the irreversible differential magnetic susceptibility in Step 2 include: Step 2.1: Considering that when the applied AC excitation is small, use The model identifies the internal coupling mean field parameters of the magnetic domains The order of magnitude is very small, so the maximum value of irreversible differential susceptibility with or without residual magnetism can be simplified to: (7) (8) Step 2.2: Due to According to Step 2.1, the physical model relationship between the residual flux density and the maximum value of the irreversible differential susceptibility is expressed as: (9) In the formula, is the residual magnetic density, is the magnetic permeability of vacuum.

[0019] Furthermore, in Step 3, the irreversible differential magnetic susceptibility is established. The specific steps of the relationship of the hysteresis loop include: Step 3.1: According to JA magnetization theory, the differential magnetic susceptibility can be expressed as: (10) In the formula, is the differential magnetic susceptibility, is the hysteresis-free differential susceptibility; Step 3.2: In the absence of hysteresis, due to the conservation of energy, can be expressed as: (11); Step 3.3: Due to According to Step 3.1 and Step 3.2, the irreversible differential susceptibility can be B - H The hysteresis loop is expressed as: (12) In the formula, is the magnetic induction intensity, yes The slope of the hysteresis loop, yes The first derivative of the slope of the hysteresis loop.

[0020] Furthermore, by measuring the different preset residual magnetism The hysteresis loop can be used to obtain the maximum value of the irreversible differential susceptibility under different remanent magnetization. The physical model relationship between the maximum value of the irreversible differential susceptibility and the remanent magnetic flux density is , the residual magnetism value in the iron core can be detected.

[0021] Example 2 In another preferred embodiment, based on the above-mentioned embodiment 1, a method for measuring the core remanence based on the maximum value of irreversible differential magnetic susceptibility of the present invention comprises the following steps: Step 1: Establish irreversible differential susceptibility and The relationship between the hysteresis loop and the The maximum value of irreversible differential susceptibility is calculated indirectly from the hysteresis loop; Step 1.1: According to JA magnetization theory, the differential magnetic susceptibility can be expressed as: (10) In the formula, is the differential magnetic susceptibility, is the hysteresis-free differential susceptibility; Step 1.2: In the absence of hysteresis, due to the conservation of energy, can be expressed as: (11) Step 1.3: Due to According to Step 3.1 and Step 3.2, the irreversible differential susceptibility can be expressed by the BH hysteresis loop as: (12) In the formula, is the magnetic induction intensity, yes B - H The slope of the hysteresis loop, yes The first derivative of the slope of the hysteresis loop.

[0022] Step 2: Establish The relationship between the hysteresis loop and the maximum value of irreversible differential susceptibility and residual magnetic flux density is expressed as follows: Combined with the above Magnetization theory and The relationship between the hysteresis loop and the irreversible differential magnetic susceptibility can be used to obtain the physical model relationship for core remanence detection: (13) Thus, the physical model relationship of the core remanence detection is obtained, and the The hysteresis loop can be used to calculate the maximum value of the irreversible differential susceptibility, and then the residual magnetism in the core can be calculated through the maximum value of the irreversible differential susceptibility and the residual flux density.

[0023] Example 3 In another preferred embodiment, based on the above embodiments 1 and 2, as Figures 1 to 5 As shown, a core remanence measurement method based on the maximum value of irreversible differential susceptibility and its implementation process are further explained below in conjunction with the accompanying drawings.

[0024] use Figure 1 The measurement process shown in the figure uses the AC demagnetization method to eliminate the residual magnetism in the iron core, and applies a sinusoidal voltage with a frequency of 50Hz and an amplitude of 0.2V to obtain the residual magnetism when there is no residual magnetism. curve, and then use the particle swarm algorithm to combine Model identification calculates the model formula Parameter values ​​and identification calculation results of parameter values ​​are shown in the following table:

[0025] As can be seen from Table 1, The value is very small, so formula (7) and formula (8) can be satisfied, so the residual flux density can be calculated using formula (9); finally, the mathematical expression for the core residual magnetism measurement based on the maximum value of the irreversible differential magnetic susceptibility can be obtained: (14) use Figure 2 The shown circular core Schematic diagram of hysteresis loop test. By changing the direction of DC voltage, a flux meter is used to detect the residual magnetism in different preset directions. The voltage probe and current sampling resistor on the coil detect the magnetic induction intensity respectively With magnetic field strength ,draw The hysteresis loop is collected and plotted at the same value of residual magnetic flux density of 0.61T in different directions. Magnetic hysteresis loop.

[0026] use Figure 3 Remanence in different directions The different directions of residual magnetism obtained from the hysteresis loop will affect the detected Curved shape, so you can use The shape of the curve determines the direction of residual magnetism detection. At the same time, considering that the residual magnetism values ​​in the positive and negative directions are the same, this paper presets different positive residual magnetism and measures the residual magnetism under different residual magnetisms. curve.

[0027] use Figure 4 In different positive remanence values The maximum value of irreversible differential susceptibility is obtained by curve calculation, and the maximum value of irreversible differential susceptibility and preset remanence are plotted on Figure 5 In, from Figure 5 It can be seen that the relationship between the residual magnetic flux density and the maximum value of the irreversible differential susceptibility has the same linear trend as the established theoretical model relationship.

[0028] Finally, the obtained theoretical formula was used to calculate the 5 sets of preset residual magnetism, and the relative error between the residual magnetic flux obtained by the theoretical formula and the preset residual magnetic flux was calculated, as shown in the following table:

[0029] It can be seen from the table that the residual magnetic flux calculated according to the theoretical formula is close to the preset residual magnetic flux value, the maximum relative error does not exceed 10%, and the larger the residual magnetic flux, the more accurate the calculated value.

[0030] In summary, the present invention provides a method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility, which solves the problem of the complexity of the existing method and system for measuring the residual magnetism of an iron core; The hysteresis model is combined with the theory of irreversible differential susceptibility to derive the maximum expression of irreversible differential susceptibility with or without residual magnetization. This method is not only rigorous in theory, but also has high reliability in practical applications. It establishes the relationship between irreversible differential susceptibility and The relationship between the hysteresis loop is measured by The hysteresis loop is used to indirectly calculate the maximum value of the irreversible differential susceptibility. This step simplifies the measurement process and improves the measurement efficiency. By combining the irreversible differential susceptibility expressions with and without residual magnetization, a physical model relationship between residual magnetization and the maximum value of irreversible differential susceptibility is constructed. This relationship provides a theoretical support for the accurate calculation of residual magnetism. The present invention innovatively combines the JA magnetization theory, proposes a residual magnetism measurement method based on the maximum value of irreversible differential susceptibility, and constructs a corresponding theoretical model relationship. This theoretical innovation brings new perspectives, thinking and theoretical basis to the field of residual magnetism measurement. The present invention measures The hysteresis loop is used to indirectly calculate the maximum value of the irreversible differential susceptibility, and then the residual magnetism is calculated in combination with the physical model relationship. This method innovatively avoids the reliance of traditional residual magnetism measurement methods on complex measuring equipment and reversible excitation processes, thereby improving the convenience and practicality of the measurement. The present invention is based on a clear physical model and theoretical derivation, and the measurement results have high credibility and accuracy, providing a strong guarantee for the safe and stable operation of the power system. The method of the present invention has universal applicability and can be widely used in the measurement and calculation of the residual magnetism of transformer cores in power equipment, which is of great help in suppressing and eliminating the influence of residual magnetism in power equipment and has a high practical application value. In addition, the promotion and use of this technology is expected to promote the improvement of relevant industry standards and specifications, promote the overall progress of power detection technology, and contribute important technical support to the construction and development of smart grids.

Claims

1. A method for measuring the residual magnetism of an iron core based on the maximum value of irreversible differential magnetic susceptibility, characterized in that: The method comprises the following steps: Step 1: Use the expression of irreversible differential magnetic susceptibility and combine The theory of hysteresis model derives the expressions of the maximum value of irreversible differential susceptibility with and without residual magnetization respectively; Step 2: Combine the expressions of irreversible differential susceptibility with and without residual magnetization in Step 1 to establish the physical model relationship between residual magnetization and the maximum value of irreversible differential susceptibility; Step 3: Establish irreversible differential susceptibility and The relationship between the hysteresis loop and the The maximum value of irreversible differential susceptibility is obtained from the hysteresis loop, which is substituted into the physical model relationship between the residual magnetization intensity and the maximum value of irreversible differential susceptibility in Step 2 to obtain the residual magnetism value in the iron core; Step 4: Build the core The hysteresis loop measurement platform uses DC excitation to preset different remanence values ​​and obtains the maximum value of the irreversible differential susceptibility under different preset remanence values, which is used to verify the correctness of the theoretical model expression proposed for remanence measurement.

2. The method for measuring the iron core remanence based on the maximum value of irreversible differential magnetic susceptibility according to claim 1, characterized in that: In Step 1, The specific steps of deriving the maximum expression of irreversible differential susceptibility with and without residual magnetization intensity from the theory of hysteresis model include: Step 1.1: According to the theory of JA hysteresis model, the calculation formula of irreversible differential magnetic susceptibility can be expressed as: （1）； In the formula, is the strength of the external magnetic field, is the containment coefficient, is the directivity coefficient, is the coupled average magnetic field parameter within the magnetic domain, is the hysteresis-free magnetization, is the irreversible magnetization, is the irreversible differential susceptibility; Step 1.2: From Step 1.1, we know that the irreversible differential susceptibility is The slope of the hysteresis curve, so the maximum value of the irreversible differential susceptibility appears at the coercivity point , expressed as: （2）； In the formula, is the maximum value of irreversible differential susceptibility; Step 1.3: The relationship between irreversible magnetization and hysteresis-free magnetization is expressed as: （3）； In the formula, is the reversible susceptibility, is the total magnetization; Step 1.4: Combining Step 1.2 and Step 1.3, when there is no residual magnetization and only AC excitation is applied, the maximum value of irreversible differential susceptibility is expressed as: （4）； In the formula, is the residual magnetization, is the magnetization intensity produced by AC excitation; Step 1.5: When there is residual magnetization, It can be divided into the AC action part and the residual magnetic action part, which can be expressed as: （5）； Step 1.6: When calculating the maximum irreversible differential susceptibility value, The AC part of is 0. According to Step 1.1, the maximum value of irreversible differential susceptibility with residual magnetization is expressed as: （6）。 3. The method for measuring the iron core remanence based on the maximum value of irreversible differential magnetic susceptibility according to claim 1, characterized in that: The specific steps of establishing the physical model relationship between the residual magnetization and the maximum value of the irreversible differential susceptibility in Step 2 include: Step 2.1: Considering that when the applied AC excitation is small, use The model identifies the internal coupling mean field parameters of the magnetic domains The order of magnitude is very small, so the maximum value of irreversible differential susceptibility with or without residual magnetism can be simplified to: （7）； （8）； Step 2.2: Due to According to Step 2.1, the physical model relationship between the residual flux density and the maximum value of the irreversible differential susceptibility is expressed as: （9）； In the formula, is the residual magnetic density, is the magnetic permeability of vacuum.

4. The method for measuring the iron core remanence based on the maximum value of irreversible differential magnetic susceptibility according to claim 1, characterized in that: In Step 3, the irreversible differential magnetic susceptibility is established. The specific steps of the relationship of the hysteresis loop include: Step 3.1: According to JA magnetization theory, the differential magnetic susceptibility can be expressed as: （10）； In the formula, is the differential magnetic susceptibility, is the hysteresis-free differential susceptibility; Step 3.2: In the absence of hysteresis, due to the conservation of energy, can be expressed as: （11）； Step 3.3: Due to According to Step 3.1 and Step 3.2, the irreversible differential susceptibility can be B - H The hysteresis loop is expressed as: （12）； In the formula, is the magnetic induction intensity, yes The slope of the hysteresis loop, yes The first derivative of the slope of the hysteresis loop.

5. A method for measuring the iron core remanence based on the maximum value of irreversible differential magnetic susceptibility according to any one of claims 1 to 4, characterized in that: By measuring different preset residual magnetism The hysteresis loop can be used to obtain the maximum value of the irreversible differential susceptibility under different remanent magnetization. The physical model relationship between the maximum value of the irreversible differential susceptibility and the remanent magnetic flux density is , the residual magnetism value in the iron core can be detected.

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