Transformer residual magnetism measuring method and device based on variable frequency power supply

Abstract

The invention relates to the technical field of residual magnetism detection, in particular to a transformer residual magnetism measuring method and device based on a variable-frequency power supply. The method comprises the following steps: applying a multi-frequency excitation signal to a tested transformer; acquiring a voltage signal and a current signal of a winding of the tested transformer; processing the voltage signal and the current signal to obtain the magnetic flux density and the magnetic field intensity of the iron core; and judging whether the iron core has residual magnetism based on the magnetic flux density and the magnetic field intensity. The method can solve the problems that in the prior art, the residual magnetism detection precision is limited, the data dimension is low, local magnetic characteristic information is prone to being lost, and equipment needs to be disassembled in part of methods.

Description

Technical Field

[0001] This invention relates to the field of residual magnetism detection technology, and in particular to a method and apparatus for measuring residual magnetism in transformers based on a variable frequency power supply. Background Technology

[0002] Transformers and other ferromagnetic components are widely used in power systems, and their core remanence and core losses directly affect the safety, stability, and energy efficiency of the equipment. Remanence can lead to core saturation and distortion of the excitation current, while core losses result in energy waste. Therefore, accurately measuring the remanence state is a key aspect of power equipment operation, maintenance, and design.

[0003] Current methods for detecting residual magnetism mostly employ power frequency excitation or DC bias, determining residual magnetism by observing the shift of the hysteresis loop B (Magnetic Induction) - H (Magnetic Field Strength).

[0004] Existing technologies have obvious limitations: the accuracy of residual magnetism detection is limited, the data dimension is low, local magnetic characteristic information is easily lost, and some judgment methods require disassembly of the equipment. Summary of the Invention

[0005] This invention provides a method and apparatus for measuring residual magnetism in transformers based on a variable frequency power supply, which solves the problems of limited accuracy, low data dimensionality, easy loss of local magnetic characteristic information, and the need to disassemble equipment in some methods in the prior art.

[0006] In a first aspect, embodiments of the present invention provide a method for measuring the residual magnetism of a transformer based on a variable frequency power supply, comprising: Apply multi-frequency excitation signals to the transformer under test; The voltage and current signals of the windings of the transformer under test are collected; The voltage and current signals are processed to obtain the magnetic flux density and magnetic field strength of the iron core; Based on the magnetic flux density and the magnetic field strength, determine whether the iron core has residual magnetism.

[0007] One possible implementation also includes: Calculate the core loss at different frequencies based on the voltage signal and the current signal; Based on the core loss at different frequencies, the core loss at the power frequency is calculated.

[0008] In one possible implementation, the multi-frequency excitation signal is a superposition signal of multiple sine waves of different frequencies, wherein the frequencies of the sine waves are selected from multiple frequency points between 10Hz and 1kHz, and the expression of the multi-frequency excitation signal is: ; in, Indicates the first The voltage signal corresponding to the time. Indicates the first The amplitude of the second harmonic. , This indicates the total number of harmonic terms. Indicates the first Second harmonic Indicates the first The initial phase of the subharmonic.

[0009] In one possible implementation, the voltage and current signals are processed to obtain the magnetic flux density and magnetic field strength of the iron core, including: according to The magnetic flux density of the iron core is obtained; according to The magnetic field strength of the iron core is obtained; in, Indicates the first The magnetic flux density of the iron core at that moment. Indicates the number of turns in the iron core winding. This represents the effective cross-sectional area of ​​the iron core. Indicates the first The magnetic field strength of the iron core at that moment. Indicates the first The current signal in the iron core winding at the corresponding moment.

[0010] In one possible implementation, determining whether the iron core has residual magnetism based on the magnetic flux density and the magnetic field strength includes: Based on the magnetic flux density and the magnetic field strength, draw the hysteresis loop; If the hysteresis loop deviates along the H-axis or B-axis and the residual magnetic induction intensity is not equal to zero, it is determined that the iron core has residual magnetism. The residual magnetic induction intensity is calculated as follows: determine the maximum and minimum magnetic induction intensity in the hysteresis loop; and take the average value of the maximum and minimum magnetic induction intensity as the residual magnetic induction intensity.

[0011] In one possible implementation, under the no-load measurement scenario of the iron core, the current signal in the winding of the transformer under test is the excitation current signal. Calculate the core loss at different frequencies based on the voltage and current signals, including: according to Calculate the core loss at different frequencies; in, Indicates core loss. , This indicates the period of the excitation current or voltage signal. This represents the excitation current signal. express The effective value, This indicates the DC resistance of the windings of the iron core.

[0012] In one possible implementation, the core loss at the power frequency is calculated based on the core loss at different frequencies, including: Keep the peak magnetic flux of the iron core equal at different frequencies, and simultaneously collect iron core loss data corresponding to multiple different frequencies; Based on the core loss data, the average no-load input power at each frequency is calculated. After removing the copper loss of the core winding, the core loss corresponding to each frequency is obtained. Based on the relationship model between core loss and frequency, the unit hysteresis loss and unit eddy current loss are solved by using each frequency and the corresponding core loss. Substituting the power frequency into the aforementioned relationship model, the core loss at the power frequency is calculated.

[0013] In one possible implementation, the relationship between the core loss and frequency is modeled as follows: ; in, This represents the unit hysteresis produced per magnetization cycle. This represents the eddy current loss generated in each magnetization cycle. Indicates the test frequency; The method of using each frequency and the corresponding core loss to solve for unit hysteresis loss and unit eddy current loss includes: An overdetermined set of equations is constructed, and the unit hysteresis loss and unit eddy current loss are solved by the least squares method using each frequency and the corresponding iron core loss. The overdetermined equation set is: ;in, Represents the frequency matrix, express , The constructed parameter vector to be solved This represents the core loss vector.

[0014] In one possible implementation, while substituting the power frequency into the relationship model to calculate the core loss at the power frequency, the method also includes: calculating the excitation current and excitation voltage at the power frequency. The calculation method for the excitation current converted to power frequency is as follows: ; The calculation method for the excitation voltage converted to power frequency is as follows: ; in, This represents the excitation current at power frequency. This represents the instantaneous value of the magnetizing current in the iron core. This represents the instantaneous value of the eddy current loss current at power frequency. This represents the instantaneous value of the excitation current at the test frequency. This represents the instantaneous value of the eddy current loss current at the test frequency. Indicates the power frequency. This represents the excitation voltage at power frequency. This represents the instantaneous value of the induced electromotive force at the test frequency. This indicates the leakage inductance of the winding.

[0015] Secondly, embodiments of the present invention provide a transformer residual magnetism measuring device based on a variable frequency power supply, comprising: The variable frequency excitation source module is used to apply multi-frequency excitation signals to the transformer under test; The signal acquisition module is used to acquire the voltage and current signals of the windings of the transformer under test; The processing module is used to process the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the iron core. The determination module is used to determine whether the iron core has residual magnetism based on the magnetic flux density and the magnetic field strength.

[0016] This invention provides a method and apparatus for measuring residual magnetism in transformers based on a variable frequency power supply. The method involves applying multi-frequency excitation signals to the transformer under test; acquiring voltage and current signals from the transformer windings; processing the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the core; and determining the presence of residual magnetism in the core based on the magnetic flux density and magnetic field strength. This invention overcomes the limitations of traditional power frequency excitation or DC bias methods by applying multi-frequency excitation signals and acquiring voltage and current signals from the transformer windings for subsequent determination of core residual magnetism. Furthermore, multi-frequency excitation can be directly applied through the existing windings of the transformer under test without disassembling the transformer structure or altering the original installation state. This reduces the complexity and workload of core residual magnetism measurement and avoids potential damage to the transformer windings and insulation structure during disassembly, ensuring equipment operational safety. The wide frequency range excitation design makes it applicable to different types and specifications of transformer cores, unrestricted by core material or structural dimensions, solving the problem of poor adaptability to specific types of transformers in traditional methods and improving the versatility of the measurement method. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the implementation of the transformer residual magnetism measurement method based on a variable frequency power supply provided in this embodiment of the invention. Figure 2 This is a schematic diagram of the no-load equivalent circuit of the ferromagnetic element provided in the embodiment of the present invention; Figure 3 This is a circuit diagram of the variable frequency excitation source generator provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the signal acquisition module provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the hysteresis loop provided in an embodiment of the present invention; Figure 6 This is a flowchart illustrating the implementation of a transformer residual magnetism measurement method based on a variable frequency power supply, provided in another embodiment of the present invention. Figure 7 This is a schematic diagram of the transformer residual magnetism measuring device based on a variable frequency power supply provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the terminal provided in an embodiment of the present invention. Detailed Implementation

[0019] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0021] Figure 1 A flowchart illustrating the implementation of a transformer residual magnetism measurement method based on a variable frequency power supply, provided in this embodiment of the invention, is detailed below: Step 101: Apply a multi-frequency excitation signal to the transformer under test.

[0022] This step is the excitation application stage of the transformer residual magnetism measurement method based on variable frequency power supply provided in this embodiment. Its execution needs to match the no-load operating state of the transformer under test and is controlled by specific signal forms and parameters to provide effective input for subsequent signal acquisition, residual magnetism judgment and loss calculation.

[0023] First, perform circuit preparation before applying the stimulus.

[0024] One winding of the transformer under test is opened, leaving only the other winding as the excitation terminal, putting the transformer in an unloaded operating state. In this unloaded operating state, only the excitation current exists in the transformer windings, with no load current interference. This matches the analysis scenario of the unloaded equivalent circuit of ferromagnetic components, avoiding the influence of load components on subsequent magnetic flux and loss calculations. Figure 2 The diagram shows the equivalent circuit of the ferromagnetic element under no-load conditions. DC resistance of winding, For leakage inductance of this side winding, The equivalent resistance for eddy current losses is a nonlinear inductor with a hysteresis loop. For magnetizing inductance, hysteresis loss Included middle. For excitation current, For flow magnetizing current, This is the equivalent current for eddy current losses. To induce electromotive force. This is the excitation voltage applied to the winding.

[0025] Secondly, generate and apply multi-frequency excitation signals.

[0026] In this step, the multi-frequency excitation signal is specifically a superposition signal of multiple sine waves of different frequencies. The frequency selection needs to cover multiple frequency points between 10Hz and 1kHz (in actual applications, adjacent power frequency points can be added in the range of 1Hz to 60Hz according to test requirements).

[0027] The expression for the multi-frequency excitation signal is: ; in, Indicates the first The voltage signal corresponding to the time. Indicates the first The amplitude of the second harmonic. , This indicates the total number of harmonic terms. Indicates the first Second harmonic Indicates the first The initial phase of the subharmonic.

[0028] The multi-frequency excitation signal is generated and output by a variable frequency excitation source, such as... Figure 3 The circuit diagram of the variable frequency excitation source generator shown is for illustrative purposes only. The excitation source first passes through a programmable sine wave generator, which is programmed by a microcontroller unit (MCU) to output multiple sine waves with adjustable frequency and amplitude, and then superimposes them. Subsequently, the driving capability of the signal is enhanced by a signal follower, and electrical isolation is achieved by a precision transformer to protect the front-end equipment. Then, the power is amplified by an electronic frequency and voltage regulating power supply, and finally, the signal is boosted to the rated voltage level of the transformer under test by a step-up transformer and input to the excitation winding.

[0029] Finally, the key parameter control during the excitation process: when applying multi-frequency excitation signals, it is necessary to control the peak value of the transformer core magnetic flux corresponding to different frequency components to remain consistent.

[0030] Specifically, through the formula of induced electromotive force Calculate the induced electromotive force in the winding; where, This represents the instantaneous value of the induced electromotive force at the test frequency. Indicates the first The voltage signal corresponding to that moment, i.e., the winding terminal voltage signal. This represents the instantaneous value of the excitation current at the test frequency; Integrating the induced electromotive force yields the core flux linkage: ,in, Indicates iron core magnetic flux. , This indicates the period of the excitation current or voltage signal.

[0031] Due to magnetic flux ,in Indicates the number of turns in the iron core winding. Indicates the peak value of the core magnetic flux. This represents the effective cross-sectional area of ​​the iron core. Therefore, by adjusting the signal amplitude of each frequency component to make the flux linkage values ​​consistent at different frequencies, the peak magnetic flux of the iron core can be guaranteed. Stability provides a unified physical benchmark for subsequent extraction of remanent magnetization features and calculation of loss parameters at multiple frequencies.

[0032] The core function of this step is to provide multi-dimensional excitation input for the transformer under test, which covers the operating frequency band of traditional power frequency excitation and supplements the low-frequency signal components. It can simultaneously support the accurate detection of core residual magnetism and the multi-frequency conversion analysis of core loss.

[0033] Step 102: Collect the voltage and current signals of the windings of the transformer under test.

[0034] This step is the raw data acquisition stage, which needs to be executed synchronously with the application of the multi-frequency excitation signal in step 101. Valid electrical signals are collected through a dedicated sampling module to provide accurate input for subsequent calculations of magnetic flux density, magnetic field strength, and core loss analysis.

[0035] First, clarify the synchronization requirements for data acquisition: the signal acquisition in this step must be synchronized in real time with the output of the multi-frequency excitation signal in step 101. That is, the signal acquisition should start synchronously from the moment the multi-frequency excitation signal is applied to the excitation end of the transformer under test, to ensure that the time dimensions of the voltage signal and the current signal are completely aligned, and to avoid subsequent integration and product calculation errors caused by signal delay.

[0036] Secondly, data acquisition is completed through a dedicated signal sampling module, such as... Figure 4 The diagram shows a signal acquisition module. The signal sampling module consists of a sampling front-end, an isolation chip, and a high-precision digital-to-digital converter (ADC) connected sequentially. The functions and roles of each component are as follows: 1) Sampling front end: directly connected to the excitation winding of the transformer under test, and collects two types of electrical signals: one is the instantaneous voltage signal at both ends of the winding, which reflects the voltage input state of the excitation end; the other is the instantaneous excitation current signal in the winding, that is, the winding current under no-load condition, which includes magnetizing current and eddy current loss current components. 2) Isolation chip: Performs electrical isolation processing on the electrical signal acquired by the sampling front end to prevent the high voltage signal of the transformer under test from being transmitted in reverse to the sampling device, and at the same time eliminates the influence of electromagnetic interference on the signal; 3) High-precision ADC: Converts isolated analog electrical signals into digital signals with a resolution of no less than 16 bits to ensure accurate identification of weak components in multi-frequency signals and meet the needs of subsequent high-precision calculations.

[0037] Simultaneously, the acquisition duration and data integrity must be controlled. For multi-frequency excitation signals of each frequency component, the acquisition duration must include at least one complete signal cycle. ( ), The frequency value of this frequency component is used to ensure that the signal waveform characteristics within one cycle are fully covered. If the multi-frequency excitation signal contains multiple frequency components, the acquisition duration must meet the requirement of "covering the longest cycle among all components" to ensure that the signal data of each frequency component is complete and valid.

[0038] Finally, signal transmission after acquisition: The digital signal converted by the high-precision ADC will be directly transmitted to the host (such as an industrial computer) and temporarily stored in the storage module, providing raw data support for subsequent steps such as "calculating magnetic flux density and magnetic field strength based on voltage and current signals" and "calculating the average power of no-load input".

[0039] The core function of this step is to accurately capture the electrical signal response of the transformer under multi-frequency excitation. The voltage and current signals acquired are the basis for all subsequent physical quantity calculations. The synchronization, integrity, and accuracy of the signals directly determine the accuracy of the final residual magnetism judgment and loss calculation.

[0040] Step 103: Process the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the iron core.

[0041] This step is the core data processing stage. By preprocessing, theoretically calculating and correcting the voltage and current signals collected in step 102, the magnetic flux density and magnetic field strength of the iron core are accurately derived, providing core physical quantity support for subsequent remanence judgment.

[0042] After acquiring voltage and current signals, preprocessing is performed to eliminate interference factors.

[0043] Because electromagnetic interference and signal delay may occur during the acquisition process, it is necessary to use timestamp alignment to achieve synchronous calibration of voltage and current signals to ensure that voltage and current signals at the same time correspond one-to-one. At the same time, a finite impulse response (FIR) low-pass filter (passband frequency is 1.2 to 1.5 times the highest frequency of the test signal) is used to filter out high-frequency noise, retain the effective components in the signal related to the electromagnetic response of the iron core, and avoid calculation deviations caused by noise.

[0044] The voltage signal is corrected by subtracting non-inductive components. Based on the no-load equivalent circuit of a ferromagnetic element, the winding terminal voltage... It consists of three parts: induced electromotive force, resistance voltage drop, and leakage inductance voltage drop. This is to obtain the pure induced electromotive force corresponding to the magnetic flux of the iron core. It needs to be corrected using the following formula: .

[0045] No. The magnetic flux density of the iron core at that moment The calculation is based on the law of electromagnetic induction and the relationship between magnetic flux and magnetic linkage. The steps are as follows: For the revised e ( t By performing time integration, the instantaneous value of the magnetic flux is obtained: in, The initial flux linkage is 0 (taken as 0 in the initial unloaded state).

[0046] Iron core magnetic linkage With magnetic flux density satisfy The formula for calculating magnetic flux density is obtained after deformation: .

[0047] in the formula The number of winding turns can be confirmed through transformer design drawings or by directly counting the transformer design drawings. The effective magnetic field area is obtained by using a geometric measurement method, which involves measuring the actual dimensions (length × width) of the core laminations and deducting the gaps between the laminations. If the core has a regular structure (such as a toroidal or EI type), it can be directly calculated using standard geometric formulas to ensure that the parameter accuracy is not less than 0.1%.

[0048] In one embodiment, according to The magnetic field strength of the iron core is obtained; Indicates the first The magnetic field strength of the iron core at that moment. Indicates the first The current signal in the iron core winding at the corresponding moment.

[0049] magnetic flux density With magnetic field strength satisfy ,in, The permeability of free space, The relative permeability of the core material can be used to cross-validate the calculation results. If the deviation exceeds ±3%, the parameter measurement or signal preprocessing steps need to be rechecked.

[0050] After processing, the output is synchronized with the timeline. and The time-series data should be sampled at the same frequency as the electrical signal acquisition frequency in step 102 (ensuring each signal cycle contains a sufficient number of sampling points). The physical units of the output data must be clearly specified. The unit is Tesla (T). The unit is amperes per meter (A / m), and it is temporarily stored in the host storage module for subsequent "based on and The process of "plotting hysteresis loops and determining the remanence of the iron core" provides direct data support. The core value of this step lies in converting electrical signals (voltage signals and current signals) into physical quantities that reflect the magnetic properties of the iron core. Its calculation accuracy directly depends on the completeness of signal preprocessing, the accuracy of parameter measurement, and the rationality of the integration algorithm. It is a key link to ensure the reliability of the subsequent remanence determination results.

[0051] Step 104: Determine whether the iron core has residual magnetism based on the magnetic flux density and magnetic field strength.

[0052] This step is the core judgment process. Based on the time series data of core magnetic flux density and magnetic field strength obtained in step 103, the presence of residual magnetism in the core is accurately determined by drawing hysteresis loops, offset analysis and calculation of residual magnetic induction intensity.

[0053] In one embodiment, determining whether the iron core has residual magnetism based on magnetic flux density and magnetic field strength may include: Based on magnetic flux density and magnetic field strength, draw the hysteresis loop; If the hysteresis loop deviates along the H-axis or B-axis and the residual magnetic induction intensity is not equal to zero, it is determined that the iron core has residual magnetism. The residual magnetic induction intensity is calculated as follows: determine the maximum and minimum magnetic induction intensity in the hysteresis loop; take the average value of the maximum and minimum magnetic induction intensity as the residual magnetic induction intensity.

[0054] Optionally, the hysteresis loop is the core curve reflecting the magnetization characteristics of ferromagnetic materials. Its plotting requires synchronous and complete magnetic flux density and magnetic field strength. The specific process is as follows: The magnetic flux density and magnetic field strength obtained in step 103 are calibrated and filtered to ensure that the timestamps of the two sets of data are perfectly aligned, and outlier sampling points (such as extreme points caused by integral drift) are removed to ensure data continuity. A two-dimensional rectangular coordinate system is established with the magnetic field strength H-axis as the horizontal axis (unit: A / m) and the magnetic flux density B-axis as the vertical axis (unit: T). The range of the coordinate system must cover the extreme value range of the measured data to ensure that the closed shape of the hysteresis loop is fully represented. The synchronized magnetic flux density and magnetic field strength data points are mapped to the coordinate system in chronological order and connected to form a closed curve, i.e., the hysteresis loop. Figure 5 As shown, due to the irreversible magnetization of ferromagnetic materials, it is necessary to ensure that the plotted hysteresis loop is a stable closed curve after "magnetic training" (it no longer changes after multiple alternating magnetizations), which conforms to the basic law of the hysteresis characteristics of ferromagnetic materials. This curve intuitively reflects the nonlinear relationship between B and H in the entire process of magnetization-demagnetization-reverse magnetization-reverse demagnetization of the iron core, and its shape is directly related to the remanent magnetization state of the iron core. Figure 5 middle, Residual magnetic flux density For coercivity, This represents the peak value of the magnetic field strength.

[0055] Figure 5 In a non-residual iron core, the hysteresis loop is symmetrically distributed along the H-axis and B-axis with the origin as the center; however, when residual magnetism is present, the hysteresis loop will shift due to the asymmetry of the magnetization state. The specific criteria for judgment are as follows: Offset along the B-axis (core offset): When the magnetic field strength is 0 (excitation current is zero), the magnetic flux density is not zero, and the positive and negative half-cycles of the hysteresis loop are asymmetrically distributed relative to the B-axis. This offset originates from the residual magnetic flux in the iron core, causing the magnetization starting point to deviate from the origin, which is a typical characteristic of residual magnetism.

[0056] Offset along the H-axis (auxiliary offset form): When the magnetic flux density is 0 (the core magnetic flux is zero), the magnetic field strength is not 0, and a reverse magnetic field needs to be applied to completely demagnetize it. The positive and negative half-cycles of the hysteresis loop are asymmetrical with respect to the H-axis. This offset is usually related to the change in coercivity accompanying remanence, and also reflects that the core has an incompletely demagnetized state.

[0057] The physical nature of the offset: The offset of the hysteresis loop is essentially a DC bias phenomenon caused by the "volt-second product imbalance" during the magnetization process of the iron core. Residual magnetism is the long-term residual result of DC bias, which will significantly increase the amplitude of the inrush current when the transformer is closed under no-load conditions, exacerbating the risk of winding insulation damage. Therefore, offset judgment is a key link in residual magnetism detection.

[0058] Remanent magnetic flux density is the core quantitative indicator for determining the existence of remanent magnetization. It is calculated as follows: determine the maximum and minimum magnetic flux density in the hysteresis loop; and take the average of the maximum and minimum magnetic flux density as the remanent magnetic flux density.

[0059] Optionally, the maximum magnetic flux density can be accurately identified and extracted from the plotted hysteresis loop. (The peak value of the positive half-cycle of the loop corresponds to the positive magnetization saturation point) and the minimum magnetic flux density. (The valley value of the negative half-cycle of the loop corresponds to the reverse magnetization saturation point). When extracting, local extrema caused by curve noise need to be excluded, and the positive and negative vertices of the overall closed contour of the loop should be used as the reference.

[0060] Through formula The core logic of the formula for calculating remanent magnetic flux density is: when there is no remanent magnetization, and The absolute values ​​are equal but opposite in sign, and the average value is 0. When there is residual magnetism, the symmetry between the two is broken, and the average value is the magnitude of the residual magnetic flux density.

[0061] Based on the combined characteristics of the hysteresis loop offset and the calculation results of the residual magnetic induction, the following judgment rules are formed: If the hysteresis loop has a significant offset along the H-axis or B-axis, and the residual magnetic induction intensity is not equal to zero, then it is determined that the iron core has residual magnetism. If the hysteresis loop is symmetrical and has no offset, and the residual magnetic induction is equal to zero, then the iron core is determined to have no residual magnetism.

[0062] It should be noted that in actual measurements, the presence of residual magnetism in the iron core can be determined as long as the residual magnetic induction intensity is within the allowable error range. For example, the absolute value of the residual magnetic induction intensity can be set to be greater than 0.01T. If the hysteresis loop shows a significant offset along the H-axis or B-axis, the iron core is considered to have residual magnetism. Here, 0.01T is a preset threshold that can be adjusted according to the transformer model. Similarly, if the residual magnetic induction intensity is approximately zero and the hysteresis loop is symmetrical and without offset, the iron core is considered to have no residual magnetism.

[0063] The core value of this step lies in transforming abstract magnetic characteristic data into intuitive loop shapes and quantified remanence indicators, thereby achieving accurate determination of core remanence. Compared with traditional remanence assessment methods, the transformer remanence measurement method based on variable frequency power supply provided in this invention can determine remanence without disassembling the equipment or making significant modifications. Furthermore, it has a stronger ability to capture changes in weak magnetic response and can comprehensively reflect the magnetic characteristics of the material, making it suitable for different types of cores and transformer models.

[0064] Residual magnetism can lead to core saturation and excitation current distortion, while core losses result in energy waste. Therefore, accurately measuring the residual magnetism state and core losses is a crucial aspect of power equipment operation, maintenance, and design. Existing technologies primarily use power frequency measurement methods for core loss measurement, utilizing no-load loss testing at rated frequency and combining Steinmetz's formula to calculate hysteresis and eddy current losses. In some scenarios, measurement results under non-standard conditions require correction. However, power frequency measurement methods for core losses are insufficient for capturing low-frequency magnetic characteristics, require complex corrections for non-standard temperatures and waveform distortions, and have limited measurement efficiency and applicability, making it difficult to fully adapt to the needs of different types of cores and complex operating scenarios. Therefore, this invention also provides a method for calculating core losses. In one embodiment, such as... Figure 6 As shown, it also includes: Step 105: Calculate the core loss at different frequencies based on voltage and current signals, and then calculate the core loss at the power frequency based on the core loss at different frequencies.

[0065] This section is the core of the energy consumption analysis of the transformer residual magnetism measurement method based on variable frequency power supply. By accurately calculating the core loss at different frequencies and combining multi-frequency data modeling and conversion, the core loss and corresponding excitation parameters at the power frequency (50Hz / 60Hz) are obtained, providing a key basis for transformer energy efficiency assessment.

[0066] In the no-load measurement scenario of the iron core, only one winding of the transformer under test is energized, while the other side is open-circuited. There is no load current in the winding, only the excitation current exists. (including magnetizing current) With eddy current loss current Core loss is the sum of hysteresis loss and eddy current loss in the core, and is obtained by subtracting winding copper loss from the average no-load input power. Core loss at different frequencies is calculated based on voltage and current signals, including: according to Calculate the core loss at different frequencies; in, Indicates core loss. , This indicates the period of the excitation current or voltage signal. This represents the excitation current signal acquired in step 102. express The effective value, This indicates the DC resistance of the windings of the iron core. The instantaneous voltage signal at both ends of the winding is acquired in step 102. The average no-load input power at each frequency is calculated based on the core loss data. After removing the copper loss of the core windings, the core loss corresponding to each frequency is obtained, which may include: according to The no-load input average power is calculated, which includes core loss and winding copper loss. The integral operation adopts the trapezoidal integration method to reduce numerical error. according to The calculation of winding copper loss is based on the derivation of Joule's law. Although the excitation current is small under no-load conditions, resulting in a low proportion of copper loss, it must be strictly deducted in order to ensure the accuracy of core loss calculation. Obtain pure iron core loss It can average multiple sets of continuously collected data to suppress random errors.

[0067] The core of power frequency loss conversion is to use the "linear-quadratic function relationship between core loss and frequency" to solve for key parameters through multiple sets of loss data at different frequencies, and finally extrapolate to the power frequency.

[0068] The conversion is based on the consistent control of the magnetic flux peak value.

[0069] The relationship between core loss and frequency is modeled as follows: ; in, This represents the unit hysteresis produced per magnetization cycle. This represents the eddy current loss generated in each magnetization cycle. Indicates the test frequency; Only when the peak magnetic flux of the iron core is at different frequencies When they remain equal, and Since the value is constant (independent of frequency), it needs to be implemented in the following way. Consistent, through the formula of induced electromotive force Calculate the induced electromotive force of the winding; then... Integration yields the iron core flux linkage: Due to magnetic flux By adjusting the excitation voltage amplitude at each test frequency, the voltage at different frequencies can be adjusted. Consistent values ​​guarantee equal.

[0070] Select multiple test frequency points within the range of 1Hz to 60Hz (covering adjacent power frequency intervals, such as 15Hz, 30Hz, 45Hz, and 50Hz). Calculate the core loss for each frequency point using the steps described above, obtaining multiple sets of "frequency-core loss" data pairs (e.g., ...). This ensures that the data covers the different influence weights of hysteresis loss and eddy current loss, thereby improving modeling accuracy.

[0071] In one embodiment, solving for the unit hysteresis loss and unit eddy current loss using each frequency and the corresponding core loss can include: An overdetermined set of equations is constructed, and the unit hysteresis loss and unit eddy current loss are solved by the least squares method using each frequency and the corresponding iron core loss. The overdetermined system of equations is ;in, Represents the frequency matrix, express , The constructed parameter vector to be solved This represents the core loss vector.

[0072] Optionally, the core loss of the ferromagnetic element at different frequencies is obtained as follows: ; Write it in matrix form as follows: ; in, , , ; For the above overdetermined system of equations, the least squares method is used to minimize the error, and the solution formula is as follows: This method can effectively offset the random errors of single-frequency data and obtain stable results. , ; power frequency (50Hz or 60Hz, depending on the application region) Substitute into the relational model The core loss at the power frequency can then be calculated.

[0073] This result is equivalent to the core loss measured directly under power frequency excitation, without the need for complex waveform distortion correction and temperature correction, thus solving the accuracy defects of traditional power frequency measurement methods under non-standard conditions.

[0074] While obtaining the core loss at power frequency, the excitation current and excitation voltage at power frequency are further calculated based on the frequency characteristics of the core loss current.

[0075] In one embodiment, while substituting the power frequency into the relational model to calculate the core loss at the power frequency, the method also includes: calculating the excitation current and excitation voltage at the power frequency. The calculation method for the excitation current converted to power frequency is as follows: ; The calculation method for the excitation voltage converted to power frequency is as follows: ; in, This represents the excitation current at power frequency. This represents the instantaneous value of the magnetizing current in the iron core. This represents the instantaneous value of the eddy current loss current at power frequency. This represents the instantaneous value of the excitation current at the test frequency. This represents the instantaneous value of the eddy current loss current at the test frequency. Indicates the power frequency. This represents the excitation voltage at power frequency. This represents the instantaneous value of the induced electromotive force at the test frequency. This indicates the leakage inductance of the winding.

[0076] Optionally, the sum of hysteresis loss and eddy current loss in the iron core is called the core loss, which can usually be expressed by the Steinmetz formula (…). ) is calculated. For the same ferromagnetic element, its core volume Silicon steel sheet thickness Hysteresis loss coefficient Hysteresis loss coefficient All are constant values.

[0077] based on , , Therefore, it can be seen that when When the (saturation level) remains constant, the magnetizing current It is stable; while the electromotive force With frequency Proportional.

[0078] Because the voltage drop across the leakage inductance and DC resistance is very small under no-load conditions, the excitation voltage... Approximately equal to electromotive force Therefore, excitation voltage It is roughly proportional to the frequency.

[0079] Eddy current It decreases as the frequency decreases, but It is much smaller than Therefore, the excitation current It has only decreased slightly.

[0080] Test power supply capacity Basic and power frequency Proportional – this means that reducing the frequency can significantly reduce the capacity of the test power supply.

[0081] Therefore, iron loss can be divided into hysteresis loss current and eddy current loss current: ; In the formula, These are the effective values ​​corresponding to the core loss current, hysteresis loss current, and eddy current loss current.

[0082] From the above equation, it can be seen that the eddy current loss current It is proportional to the first power of the frequency, while the hysteresis loss current It is independent of frequency. However, because at different frequencies... They are equal, therefore They are equal, therefore the excitation current converted to the power frequency is: ; The calculation method for the excitation voltage converted to power frequency is as follows: ; This allows us to obtain the excitation voltage converted to the power frequency. With power frequency loss The correspondence.

[0083] This invention provides a method for measuring residual magnetism in transformers based on a variable frequency power supply. The method involves applying multi-frequency excitation signals to the transformer under test; acquiring voltage and current signals from the transformer windings; processing the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the core; and determining whether residual magnetism exists in the core based on the magnetic flux density and magnetic field strength. This invention overcomes the frequency limitations of traditional power frequency excitation or DC bias methods by applying multi-frequency excitation signals and acquiring voltage and current signals from the transformer windings for subsequent core residual magnetism determination. Furthermore, multi-frequency excitation can be applied directly to the existing windings of the transformer under test without disassembling the transformer structure or altering the original installation state. This reduces the complexity and workload of the measurement operation and avoids potential damage to the transformer windings and insulation structure during disassembly, ensuring equipment operational safety. The wide frequency range excitation design makes it applicable to different types and specifications of transformer cores, unrestricted by core material or structural dimensions, solving the problem of poor adaptability to specific types of transformers in traditional methods and improving the versatility of the measurement method.

[0084] This invention calculates the magnetic flux density and magnetic field strength of the iron core and plots a hysteresis loop, allowing for direct observation of whether the loop deviates along the H-axis or B-axis. Simultaneously, it combines this with quantitative calculation of remanent magnetic induction to achieve dual verification of "qualitative judgment + quantitative analysis," avoiding the misjudgments and omissions caused by traditional methods relying solely on experience or a single indicator. The hysteresis loop under multi-frequency excitation amplifies the asymmetric characteristics caused by remanence, enabling accurate identification even of weak remanence through loop deviation and quantitative values. This overcomes the deficiency of traditional power frequency excitation methods in capturing weak magnetic responses.

[0085] This invention can also calculate the core loss at different frequencies based on the collected voltage and current signals, and convert the core loss at different frequencies to the core loss at the power frequency. This allows for accurate elimination of winding copper loss interference, obtaining pure core loss data, and adaptability to multi-frequency scenarios. It comprehensively captures the core loss characteristics, providing a reliable basis for power frequency conversion; reduces the test power supply capacity requirement; avoids the complex correction process of traditional power frequency measurements; and improves measurement efficiency and accuracy. It is also compatible with different types of transformers and 50 / 60Hz power frequency standards, simultaneously acquiring power frequency excitation current and voltage, and improving energy efficiency evaluation parameters.

[0086] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0087] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0088] Figure 7 The diagram shows a schematic of a transformer residual magnetism measuring device based on a variable frequency power supply according to an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 7 As shown, the transformer residual magnetism measurement device based on variable frequency power supply includes: a variable frequency excitation source module 71, a signal acquisition module 72, a processing module 73, and a judgment module 74.

[0089] The variable frequency excitation source module 71 is used to apply multi-frequency excitation signals to the transformer under test; The signal acquisition module 72 is used to acquire the voltage and current signals of the windings of the transformer under test; Processing module 73 is used to process voltage and current signals to obtain the magnetic flux density and magnetic field strength of the iron core; The determination module 74 is used to determine whether there is residual magnetism in the iron core based on the magnetic flux density and magnetic field strength.

[0090] In one possible implementation, processing module 73 is further configured to: Calculate core loss at different frequencies based on voltage and current signals; Based on the core loss at different frequencies, the core loss at the power frequency is calculated.

[0091] In one possible implementation, the multi-frequency excitation signal is a superposition of multiple sine waves of different frequencies. The frequencies of the sine waves are selected from multiple frequency points between 10Hz and 1kHz. The expression for the multi-frequency excitation signal is: ; in, Indicates the first The voltage signal corresponding to the time. Indicates the first The amplitude of the second harmonic. , This indicates the total number of harmonic terms. Indicates the first Second harmonic Indicates the first The initial phase of the subharmonic.

[0092] In one possible implementation, when processing the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the iron core, the processing module 73 is used for: according to The magnetic flux density of the iron core is obtained; according to The magnetic field strength of the iron core is obtained; in, Indicates the first The magnetic flux density of the iron core at that moment. Indicates the number of turns in the iron core winding. This represents the effective cross-sectional area of ​​the iron core. Indicates the first The magnetic field strength of the iron core at that moment. Indicates the first The current signal in the iron core winding at the corresponding moment.

[0093] In one possible implementation, when the determination module 74 determines whether the iron core has residual magnetism based on magnetic flux density and magnetic field strength, it is used for: Based on magnetic flux density and magnetic field strength, draw the hysteresis loop; If the hysteresis loop deviates along the H-axis or B-axis and the residual magnetic induction intensity is not equal to zero, it is determined that the iron core has residual magnetism. The residual magnetic induction intensity is calculated as follows: determine the maximum and minimum magnetic induction intensity in the hysteresis loop; take the average value of the maximum and minimum magnetic induction intensity as the residual magnetic induction intensity.

[0094] In one possible implementation, under the no-load measurement scenario of the iron core, the current signal in the winding of the transformer under test is the excitation current signal. When processing module 73 calculates core losses at different frequencies based on voltage and current signals, it is used for: according to Calculate the core loss at different frequencies; in, Indicates core loss. , This indicates the period of the excitation current or voltage signal. Indicates the excitation current signal. express The effective value, This indicates the DC resistance of the windings of the iron core.

[0095] In one possible implementation, when processing module 73 calculates the core loss at the power frequency based on the core loss at different frequencies, it is used for: Keep the peak magnetic flux of the iron core equal at different frequencies, and simultaneously collect iron core loss data corresponding to multiple different frequencies; The average no-load input power at each frequency is calculated based on the core loss data. After removing the copper loss of the core winding, the core loss corresponding to each frequency is obtained. Based on the relationship model between core loss and frequency, the unit hysteresis loss and unit eddy current loss are solved by using each frequency and the corresponding core loss. By substituting the power frequency into the relational model, the core loss at the power frequency can be calculated.

[0096] In one possible implementation, the relationship between core loss and frequency is modeled as follows: ; in, This represents the unit hysteresis produced per magnetization cycle. This represents the eddy current loss generated in each magnetization cycle. Indicates the test frequency; Processing module 73, when calculating unit hysteresis loss and unit eddy current loss using each frequency and its corresponding core loss, is used for: An overdetermined set of equations is constructed, and the unit hysteresis loss and unit eddy current loss are solved by the least squares method using each frequency and the corresponding iron core loss. The overdetermined system of equations is ;in, Represents the frequency matrix, express , The constructed parameter vector to be solved This represents the core loss vector.

[0097] In one possible implementation, while processing module 73 substitutes the power frequency into the relational model to calculate the core loss at the power frequency, it is also used to: calculate the excitation current and excitation voltage at the power frequency. The calculation method for the excitation current converted to power frequency is as follows: ; The calculation method for the excitation voltage converted to power frequency is as follows: ; in, This represents the excitation current at power frequency. This represents the instantaneous value of the magnetizing current in the iron core. This represents the instantaneous value of the eddy current loss current at power frequency. This represents the instantaneous value of the excitation current at the test frequency. This represents the instantaneous value of the eddy current loss current at the test frequency. Indicates the power frequency. This represents the excitation voltage at power frequency. This represents the instantaneous value of the induced electromotive force at the test frequency. This indicates the leakage inductance of the winding.

[0098] The above embodiments provide a transformer residual magnetism measurement device based on a variable frequency power supply. A variable frequency excitation source module applies multi-frequency excitation signals to the transformer under test; a signal acquisition module acquires the voltage and current signals of the transformer windings; a processing module processes the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the core; and a judgment module determines whether residual magnetism exists in the core based on the magnetic flux density and magnetic field strength. This invention, by applying multi-frequency excitation signals and acquiring the voltage and current signals of the transformer windings for subsequent determination of core residual magnetism, overcomes the single-frequency limitation of traditional power frequency excitation or DC bias methods. Furthermore, multi-frequency excitation can be directly applied through the existing windings of the transformer under test without disassembling the transformer structure or changing the original installation state of the equipment. This reduces the complexity and workload of the measurement operation and avoids potential damage to the transformer windings and insulation structure during disassembly, ensuring the safety of equipment operation. The wide frequency range excitation design makes it applicable to different types and specifications of transformer cores, unrestricted by core material or structural dimensions, solving the problem of poor adaptability of traditional methods to specific types of transformers and improving the versatility of the measurement method.

[0099] This invention calculates the magnetic flux density and magnetic field strength of the iron core and plots a hysteresis loop, allowing for direct observation of whether the loop deviates along the H-axis or B-axis. Simultaneously, it combines this with quantitative calculation of remanent magnetic induction to achieve dual verification of "qualitative judgment + quantitative analysis," avoiding the misjudgments and omissions caused by traditional methods relying solely on experience or a single indicator. The hysteresis loop under multi-frequency excitation amplifies the asymmetric characteristics caused by remanence, enabling accurate identification even of weak remanence through loop deviation and quantitative values. This overcomes the deficiency of traditional power frequency excitation methods in capturing weak magnetic responses.

[0100] This invention can also calculate the core loss at different frequencies based on the collected voltage and current signals, and convert the core loss at different frequencies to the core loss at the power frequency. This allows for accurate elimination of winding copper loss interference, obtaining pure core loss data, and adaptability to multi-frequency scenarios. It comprehensively captures the core loss characteristics, providing a reliable basis for power frequency conversion; reduces the test power supply capacity requirement; avoids the complex correction process of traditional power frequency measurements; and improves measurement efficiency and accuracy. It is also compatible with different types of transformers and 50 / 60Hz power frequency standards, simultaneously acquiring power frequency excitation current and voltage, and improving energy efficiency evaluation parameters.

[0101] Figure 8 This is a schematic diagram of a terminal provided in an embodiment of the present invention. Figure 8As shown, the terminal 8 in this embodiment includes a processor 80, a memory 81, and a computer program 82 stored in the memory 81 and executable on the processor 80. When the processor 80 executes the computer program 82, it implements the steps in the various embodiments of the transformer residual magnetism measurement method based on variable frequency power supply described above, for example... Figure 1 Steps 101 to 104 are shown. Alternatively, when processor 80 executes computer program 82, it implements the functions of each module / unit in the above-described device embodiments, for example... Figure 7 The functions of each module / unit are shown.

[0102] For example, computer program 82 can be divided into one or more modules / units, one or more of which are stored in memory 81 and executed by processor 80 to complete the present invention. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 82 in terminal 8. For example, computer program 82 can be divided into... Figure 7 The modules / units shown are shown.

[0103] Terminal 8 may include, but is not limited to, a processor 80 and a memory 81. Those skilled in the art will understand that... Figure 8 This is merely an example of terminal 8 and does not constitute a limitation on terminal 8. It may include more or fewer components than shown, or combine certain components, or different components. For example, the terminal may also include input / output devices, network access devices, buses, etc.

[0104] The processor 80 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0105] The memory 81 can be an internal storage unit of the terminal 8, such as a hard disk or RAM. The memory 81 can also be an external storage device of the terminal 8, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory 81 can include both internal and external storage units of the terminal 8. The memory 81 is used to store computer programs and other programs and data required by the terminal. The memory 81 can also be used to temporarily store data that has been output or will be output.

[0106] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0107] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0108] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0109] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0110] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0111] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0112] If integrated modules / units are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various embodiments of the transformer residual magnetism measurement method based on a variable frequency power supply. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0113] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for measuring the residual magnetism of a transformer based on a variable frequency power supply, characterized in that, include: Apply multi-frequency excitation signals to the transformer under test; The voltage and current signals of the windings of the transformer under test are collected; The voltage and current signals are processed to obtain the magnetic flux density and magnetic field strength of the iron core; Based on the magnetic flux density and the magnetic field strength, determine whether the iron core has residual magnetism.

2. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 1, characterized in that, Also includes: Calculate the core loss at different frequencies based on the voltage signal and the current signal; Based on the core loss at different frequencies, the core loss at the power frequency is calculated.

3. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 1, characterized in that, The multi-frequency excitation signal is a superposition of multiple sine waves of different frequencies. The frequencies of the sine waves are selected from multiple frequency points between 10Hz and 1kHz. The expression of the multi-frequency excitation signal is: ； in, Indicates the first The voltage signal corresponding to the time. Indicates the first The amplitude of the second harmonic. , This indicates the total number of harmonic terms. Indicates the first Second harmonic Indicates the first The initial phase of the subharmonic.

4. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 3, characterized in that, The voltage and current signals are processed to obtain the magnetic flux density and magnetic field strength of the iron core, including: according to The magnetic flux density of the iron core is obtained; according to The magnetic field strength of the iron core is obtained; in, Indicates the first The magnetic flux density of the iron core at that moment. Indicates the number of turns in the iron core winding. This represents the effective cross-sectional area of ​​the iron core. Indicates the first The magnetic field strength of the iron core at that moment. Indicates the first The current signal in the iron core winding at the corresponding moment.

5. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 4, characterized in that, Based on the magnetic flux density and the magnetic field strength, determining whether the iron core has residual magnetism includes: Based on the magnetic flux density and the magnetic field strength, draw the hysteresis loop; If the hysteresis loop deviates along the H-axis or B-axis and the residual magnetic induction intensity is not equal to zero, it is determined that the iron core has residual magnetism. The residual magnetic induction intensity is calculated as follows: determine the maximum and minimum magnetic induction intensity in the hysteresis loop; and take the average value of the maximum and minimum magnetic induction intensity as the residual magnetic induction intensity.

6. The method for measuring transformer residual magnetism based on a variable frequency power supply according to any one of claims 2-5, characterized in that, In the scenario of core no-load measurement, the current signal in the winding of the transformer under test is the excitation current signal; Calculate the core loss at different frequencies based on the voltage and current signals, including: according to Calculate the core loss at different frequencies; in, Indicates core loss. , This indicates the period of the excitation current or voltage signal. This represents the excitation current signal. express The effective value, This indicates the DC resistance of the windings of the iron core.

7. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 6, characterized in that, Based on the core losses at different frequencies, the core losses at the power frequency are calculated, including: Keep the peak magnetic flux of the iron core equal at different frequencies, and simultaneously collect iron core loss data corresponding to multiple different frequencies; Based on the core loss data, the average no-load input power at each frequency is calculated. After removing the copper loss of the core winding, the core loss corresponding to each frequency is obtained. Based on the relationship model between core loss and frequency, the unit hysteresis loss and unit eddy current loss are solved by using each frequency and the corresponding core loss. Substituting the power frequency into the aforementioned relationship model, the core loss at the power frequency is calculated.

8. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 7, characterized in that, The relationship model between core loss and frequency is as follows: ； in, This represents the unit hysteresis produced per magnetization cycle. This represents the eddy current loss generated in each magnetization cycle. Indicates the test frequency; The method of using each frequency and the corresponding core loss to solve for unit hysteresis loss and unit eddy current loss includes: An overdetermined set of equations is constructed, and the unit hysteresis loss and unit eddy current loss are solved by the least squares method using each frequency and the corresponding iron core loss. The overdetermined equation set is: ;in, Represents the frequency matrix, express , The constructed parameter vector to be solved This represents the core loss vector.

9. The method for measuring transformer residual magnetism based on a variable frequency power supply according to claim 8, characterized in that, In addition to substituting the power frequency into the aforementioned relationship model to calculate the core loss at the power frequency, the model also includes: calculating the excitation current and excitation voltage at the power frequency. The calculation method for the excitation current converted to power frequency is as follows: ； The calculation method for the excitation voltage converted to power frequency is as follows: ； in, This represents the excitation current at power frequency. This represents the instantaneous value of the magnetizing current in the iron core. This represents the instantaneous value of the eddy current loss current at power frequency. This represents the instantaneous value of the excitation current at the test frequency. This represents the instantaneous value of the eddy current loss current at the test frequency. Indicates the power frequency. This represents the excitation voltage at power frequency. This represents the instantaneous value of the induced electromotive force at the test frequency. This indicates the leakage inductance of the winding.

10. A transformer residual magnetism measuring device based on a variable frequency power supply, characterized in that, include: The variable frequency excitation source module is used to apply multi-frequency excitation signals to the transformer under test; The signal acquisition module is used to acquire the voltage and current signals of the windings of the transformer under test; The processing module is used to process the voltage and current signals to obtain the magnetic flux density and magnetic field strength of the iron core. The determination module is used to determine whether the iron core has residual magnetism based on the magnetic flux density and the magnetic field strength.

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