A direct current bias magnetic resistance method based on magnetic permeability feedback compensation and a current transformer

Abstract

The application discloses a kind of anti DC bias magnetic methods and current transformers based on magnetic permeability feedback compensation, comprising: the magnetic permeability of current transformer core is acquired in real time by magnetic permeability measuring unit;According to the relationship model of magnetic permeability and DC component established in advance, the DC component of invading current transformer is determined based on the magnetic permeability acquired;DC bias compensation unit generates reverse DC counter-biasing according to the DC component determined on compensation winding.The application realizes real-time monitoring and dynamic compensation adjustment to the magnetization state of transformer core by introducing magnetic permeability measuring unit and magnetic permeability feedback control, compared with traditional open-loop compensation or simple current feedback, can more accurately judge the saturation degree of magnetic core, adjusts compensation strategy in time according to the change of magnetic core state, effectively avoids compensation lag or overcompensation problem, improves the adaptability and measurement stability of transformer in complex current environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current transformers, in particular to a DC bias magnetic field resisting method based on magnetic permeability feedback compensation and a current transformer. BACKGROUND

[0002] With the construction of ultra-high voltage direct current and alternating current projects, the Chinese power grid presents a form of AC / DC hybrid large power grid. When the direct current transmission operates in a single pole ground return or bipolar unbalanced operation mode, up to thousands of amperes of direct current will flow into the ground, and part of the direct current will flow through the neutral point grounded power transformer to form a loop in the alternating current system, thereby generating a direct current bias in the transformer and the current transformer. The electromagnetic current transformer, as an important electric energy metering instrument in the power system, works based on the principle of electromagnetic induction, and realizes the transformation of primary current to secondary current through the magnetic coupling of the core. When the primary current has a direct current component, a direct current component also appears in the excitation current; when measuring the current containing a direct current component, the non-linear excitation characteristics of the core will cause the operating point of the current transformer to change, and local magnetic saturation is easy to occur, resulting in a decrease in measurement accuracy. In the prior art, although bias compensation measures are adopted, they mostly rely on open-loop control or simple feedback, and it is difficult to adapt to the dynamic changes of the magnetic core state, and there are problems of delayed compensation or overcompensation.

[0003] A production process for a DC-resistant nanocrystalline double magnetic core current transformer is disclosed in Chinese patent literature, with publication number CN117153549A and publication date 20231201, which includes nanocrystalline strip preparation: nanocrystalline strip is prepared by rapid solidification method, and heat treatment is performed to obtain nanocrystalline strip with high magnetic permeability and low remanence; magnetic core shearing and magnetic optimization treatment: the nanocrystalline strip is sheared into magnetic core pieces of the required size, and the magnetic core pieces are subjected to magnetic optimization treatment; double magnetic core assembly: two pieces of nanocrystalline magnetic core pieces subjected to magnetic optimization treatment are assembled into a double magnetic core structure; winding production and assembly: the double magnetic core structure and the winding are assembled together to form a complete current transformer structure; current transformer shell production and packaging: the shell of the current transformer is made and packed into the shell; this technology improves the current transformer itself to enhance the performance of DC bias magnetic field resistance, but the DC bias magnetic field resistance performance of the current transformer itself has a limit and only offsets or reduces the partial influence of the DC bias magnetic field, and the existing bias compensation measures mostly rely on simple or preset fixed feedback methods, which are difficult to adapt to the dynamic changes of the magnetic core state, and there are problems of delayed compensation or overcompensation. SUMMARY

[0004] The application provides a DC bias magnetic field resisting method based on permeability feedback compensation and a current transformer.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A DC bias magnetic field resisting method based on permeability feedback compensation comprises:

[0007] The permeability of the current transformer core is acquired in real time by a permeability measuring unit;

[0008] According to a pre-established relationship model between the permeability and the DC component, the DC component invading the current transformer is determined based on the acquired permeability.

[0009] A DC bias magnetic field compensation unit generates a reverse DC offset magnetic field on the compensation winding according to the determined DC component.

[0010] In the application, the permeability measuring unit and the permeability feedback control are introduced, so that the magnetization state of the current transformer core is monitored and dynamically compensated, compared with the traditional open-loop compensation or simple current feedback, the saturation degree of the magnetic core can be more accurately judged, the compensation strategy is adjusted in time according to the change of the magnetic core state, the problems of compensation lag or overcompensation are effectively avoided, and the adaptability and measurement stability of the current transformer in a complex current environment are greatly improved; the saturation state of the magnetic core is reflected by the change of the permeability, when the permeability feedback signal indicates that the magnetic core is in a normal working state, the compensation current is maintained at a normal level; when the permeability is detected to start to decrease, the corresponding compensation current amplitude is timely increased, the compensation strength is strengthened, and the magnetic core is prevented from further saturation; when the permeability is detected to return to a normal level, the compensation current is gradually reduced until the normal compensation state is restored, and the measurement accuracy is prevented from being affected by overcompensation.

[0011] Preferably, the permeability input into the relationship model is a first permeability, and the corresponding DC component is acquired.

[0012] The permeability of the current transformer core considering the DC component is calculated as a second permeability.

[0013] When the deviation between the first permeability and the second permeability is greater than a deviation threshold, the first permeability is corrected based on the deviation, the DC component and the second permeability are recalculated until the deviation is less than or equal to the deviation threshold, and the corresponding DC component is the DC component invading the current transformer.

[0014] Preferably, the establishment process of the relationship model between the permeability and the DC component comprises:

[0015] A fundamental current is applied to the primary winding of the transformer, while a DC component is superimposed and the magnitude of the DC component is changed;

[0016] The permeability of the core of the current transformer corresponding to the DC component is measured, and each set of DC component and permeability is a data point; the data points are fitted to obtain a relationship model of the permeability and the DC component.

[0017] Preferably, the calculation considering the permeability of the core of the current transformer of the DC component includes:

[0018] Based on the basic parameters of the current transformer, the basic magnetic flux without magnetic bias is calculated;

[0019] The total magnetic flux of the DC magnetic flux considering the DC component, the sum of the basic magnetic flux and the DC magnetic flux, and the excitation current is iteratively calculated;

[0020] The excitation inductance is obtained by differentiating the magnetization curve fitted by the total magnetic flux and the excitation current;

[0021] The permeability is calculated based on the proportional relationship between the excitation inductance and the permeability.

[0022] Preferably, the process of obtaining the permeability of the core of the current transformer in real time includes:

[0023] A voltage with constant amplitude is applied to the auxiliary winding wound on the core of the current transformer, and the current of the loop and the voltage across the auxiliary winding are detected;

[0024] The excitation inductance of the core is calculated based on the voltage across the auxiliary winding, the current passing through, and the phase difference between the two;

[0025] The permeability is calculated based on the proportional relationship between the excitation inductance and the permeability.

[0026] Preferably, the process of iterative calculation includes: considering the DC component i d c,

[0027] S1, calculating the excitation current i m，k , the DC component i dc，k and the maximum value of the excitation current i max at the kth iteration;

[0028] S2, if |i dc -i dc，k | is less than a preset deviation, go to S5;

[0029] S3, calculating the DC magnetic flux at the k+1th iteration, and letting k=k+1;

[0030] S4, returning to S1 when k is less than an iteration threshold;

[0031] S5, stop iteration, take k-1 times iteration in |i dc -i dc，k | The minimum direct current magnetic flux and the maximum value of the excitation current are calculated to obtain the total magnetic flux.

[0032] As a preferred, the DC bias compensation unit generates reverse DC on the compensation winding according to the determined DC component, generates magnetic field opposite to the DC bias to offset the bias.

[0033] A DC bias resistant current transformer based on permeability feedback compensation, comprising a core and a primary winding and a secondary winding wound on the core; an auxiliary winding and a compensation winding are also wound on the core; the auxiliary winding is connected to a permeability measurement unit, and the compensation winding is connected to a DC bias compensation unit, and the result detected by the permeability measurement unit is transmitted to the DC bias compensation unit.

[0034] As a preferred, the permeability measurement unit obtains the permeability of the current transformer core in real time through the auxiliary winding; the DC bias compensation unit determines the DC component invading the current transformer according to the received permeability data, and generates reverse DC on the compensation winding to offset the bias.

[0035] As a preferred, the DC bias compensation unit comprises:

[0036] A DC component calculation unit that saves a relationship model of permeability and DC component;

[0037] A compensation correction unit that calculates the permeability of the current transformer core considering the DC component, corrects the permeability and the DC component, and obtains the DC component that needs to be compensated.

[0038] The present application has the following beneficial effects: by introducing the permeability measurement unit and the permeability feedback control, the real-time monitoring and dynamic compensation adjustment of the magnetization state of the transformer core are realized, compared with the traditional open-loop compensation or simple current feedback, the saturation degree of the magnetic core can be more accurately judged, the compensation strategy is adjusted in time according to the change of the magnetic core state, the problems of compensation lag or overcompensation are effectively avoided, and the adaptability and measurement stability of the transformer in complex current environment are greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is the flowchart of the DC bias resistant method based on permeability feedback compensation of the present application.

[0040] Figure 2 It is the flowchart of the correction of the permeability and the DC component of the present application.

[0041] Figure 3 It is the flowchart of the calculation of the permeability of the current transformer core considering the DC component of the present application.

[0042] Figure 4 is a schematic diagram of the DC bias current transformer of the present application. DETAILED DESCRIPTION

[0043] The present application will be further described below in conjunction with the drawings and specific embodiments.

[0044] As shown in the drawings, Figure 1 a DC bias magnetic resistance method based on magnetic permeability feedback compensation, comprising:

[0045] The magnetic permeability of the current transformer core is obtained in real time by a magnetic permeability measurement unit;

[0046] According to the pre-established magnetic permeability and DC component relationship model, the DC component of the invaded current transformer is determined based on the obtained magnetic permeability;

[0047] The DC bias compensation unit generates an opposite DC offset magnetic field on the compensation winding according to the determined DC component.

[0048] It should be noted that in the present application, by introducing the magnetic permeability measurement unit and the magnetic permeability feedback control, the real-time monitoring and dynamic compensation adjustment of the transformer core magnetization state are realized. Compared with the traditional open-loop compensation or simple current feedback, the saturation degree of the magnetic core can be more accurately judged, the compensation strategy can be adjusted in time according to the change of the magnetic core state, the problems of compensation lag or overcompensation are effectively avoided, and the adaptability and measurement stability of the transformer in complex current environment are greatly improved. The saturation state of the magnetic core is reflected by the change in the size of the magnetic permeability. When the magnetic permeability feedback signal indicates that the magnetic core is in a normal working state, the compensation current is maintained at a normal level. When the magnetic permeability is detected to start to decrease, the corresponding compensation current amplitude is increased in time to strengthen the compensation effort and prevent the magnetic core from further saturation. When the magnetic permeability is detected to return to the normal level, the compensation current is gradually reduced until the normal compensation state is restored, avoiding the influence on the measurement accuracy caused by overcompensation.

[0049] It is worth mentioning that with the increase of the DC component of the invaded current transformer, the ratio difference curve of the current transformer as a whole shifts to the negative direction, and the phase difference curve as a whole shifts to the positive direction, so that the conclusion that the magnetic permeability of the current transformer will decrease to cause the error to increase is obtained against the increase of the DC component; When the load of the current transformer is larger, the influence of the DC bias is larger. Meanwhile, the characteristic that the magnetic permeability of the core decreases with the increase of the saturation degree of the magnetic circuit does not change under the condition of the DC bias, but only speeds up or slows down the saturation of the current transformer under the condition of the DC bias, causing the magnetic hysteresis distortion of the current transformer and thus causing the measurement error of the current transformer. The present application accurately reflects the saturation degree and working state of the magnetic core by monitoring and measuring the magnetic permeability, infers the actual DC bias condition, and thus compensates for the DC bias in time, effectively avoiding the problems of compensation lag or overcompensation.

[0050] As a specific embodiment, the establishment process of the relationship model of the magnetic permeability and the DC component includes:

[0051] The fundamental wave current is applied to the primary coil of the transformer, and the DC component is superimposed and the size of the DC component is changed;

[0052] The magnetic permeability of the current transformer core corresponding to the DC component is measured, and each group of DC component and magnetic permeability is a data point; the data points are fitted to obtain the relationship model of the magnetic permeability and the DC component.

[0053] It should be noted that the relationship model of the magnetic permeability and the DC component is obtained based on the fixed fundamental wave current, and in normal circumstances, the operating current without DC bias during normal operation of the transformer is used as the fundamental wave current, and different sizes of DC components are added to simulate the influence of various DC components on the current transformer; For each DC component size, the magnetic permeability of the current transformer under the condition of superimposing the DC component on the fundamental wave current is measured; The DC component is taken as the x-axis coordinate data, and the corresponding magnetic permeability is taken as the y-axis coordinate to form a data point; A plurality of discrete data points are obtained by using different DC component sizes, and these data points are fitted to obtain the relationship model of the magnetic permeability and the DC component under a certain fundamental wave current. Correspondingly, the relationship model of the magnetic permeability and the DC component corresponding to different fundamental wave currents can be established.

[0054] It is worth mentioning that it is difficult to directly measure the magnetic permeability of the transformer, so the inductance of the transformer can be measured, and then the magnetic permeability of the current transformer can be indirectly obtained according to the proportional relationship between the inductance and the magnetic permeability; For data point fitting, the obtained data points can be directly input into existing software (such as matlab or excel) for fitting analysis.

[0055] Further, the relationship model of the magnetic permeability and the DC component can also be obtained through learning training of the neural network model; the magnetic permeability in the simulation data acquisition process is taken as input, and the DC component is taken as output to form a training group, a set of several training groups obtained under different DC components is taken as a training sample, the constructed neural network model is trained, and the relationship model of the magnetic permeability and the DC component after training is obtained; if necessary, the fundamental current and the magnetic permeability can also be taken as input, and the DC component is taken as output to form a training group for training.

[0056] As an optional embodiment, the process of obtaining the magnetic permeability of the current transformer core in real time comprises:

[0057] A voltage with a constant amplitude is applied to the auxiliary winding wound on the current transformer core, the current of the detection loop and the voltage across the auxiliary winding are detected;

[0058] The excitation inductance of the core is calculated based on the voltage across the auxiliary winding, the current passing through and the phase difference between the two;

[0059] The magnetic permeability is calculated based on the proportional relationship between the excitation inductance and the magnetic permeability.

[0060] It should be noted that the inductance of the current transformer depends on the physical properties (such as geometric size and number of turns) of the core and the magnetic permeability of the material; because the magnetic permeability of the current transformer core can be derived by measuring the inductance value of the core coil, the influence of the DC bias magnetization on the current transformer can be reflected.

[0061] It should be noted that the present application refers to the way of measuring inductance by LCR meter to detect the inductance of the core of the current transformer, and then the magnetic permeability is obtained based on the proportional relationship between the inductance and the magnetic permeability. The auxiliary winding is wound on the core and is used for the detection of the inductance of the current transformer by the magnetic permeability measurement unit. A voltage V m with a constant amplitude is applied to the auxiliary winding to simulate the detection in constant voltage mode, and the current I m passing through the auxiliary winding can be detected at this time; the total impedance of the auxiliary winding at this time can be calculated as the ratio of the voltage V m to the current I m , |Z x | = V m / I m . Because of the total impedance of the auxiliary winding, the detected current is in phase with the voltage by θ. Based on the physical knowledge of the total impedance, the equivalent circuit of the auxiliary winding at this time is equivalent to a series connection of a resistor Rs and an inductor Ls, and the total impedance can be represented in complex form: Z x = R s +jωL s , ω = 2πf, f represents the frequency of the constant voltage alternating current.

[0062] Based on the orthogonal vector relationship of the series inductance and the resistance, the two are combined into the total impedance, the angle between the resistance Rs and the total impedance is the phase θ of the six-point relative to the voltage, and thus R s = |Z x |cosθ, ωL s = |Z x |sinθ; thus the total impedance of the auxiliary winding is calculated by the ratio of the detected voltage and current, and the inductance of the auxiliary winding is calculated according to the phase difference between the voltage and the current and the total impedance, and the inductance result of the excitation is finally obtained based on the frequency of the constant voltage current. According to the relationship between the inductance and the magnetic permeability:

[0063]

[0064] where L is the inductance; N is the number of turns, which is the number of turns of the auxiliary winding here; Rs is the resistance component of the auxiliary winding in the measurement loop; l F is the magnetic path length; A F is the cross-sectional area; μ0 is the magnetic permeability in vacuum; μ m is the relative magnetic permeability, and the product of the rest of the magnetic permeability in vacuum is the magnetic permeability that needs to be calculated.

[0065] As a specific embodiment, as shown in Figure 2 , the magnetic permeability of the input magnetic permeability and the relationship model of the direct current component is taken as the first magnetic permeability, and the corresponding direct current component is obtained;

[0066] The magnetic permeability of the current transformer core considering the direct current component is calculated as the second magnetic permeability;

[0067] When the deviation between the first magnetic permeability and the second magnetic permeability is greater than the deviation threshold, the first magnetic permeability is corrected based on the deviation, the direct current component and the second magnetic permeability are recalculated, until the deviation is less than or equal to the deviation threshold, and the corresponding direct current component is the direct current component of the invaded current transformer.

[0068] It should be noted that the magnetic permeability measured by the magnetic permeability measuring unit has errors due to the influence of the direct current bias magnetic field and other factors of the current transformer itself, and thus the direct current component calculated by the magnetic permeability has errors, and the compensation of the direct current bias magnetic field will not be sufficient or overcompensated, which will still affect the measurement accuracy. In this case, the magnetic permeability and the direct current component need to be continuously corrected, and the final direct current component obtained after correction is taken as the direct current component of the invaded power circuit transformer for compensation.

[0069] It is worth noting that in the initial correction process, the permeability obtained through measurement is the first permeability, which is then input into the permeability-DC component relationship model to obtain its corresponding DC component. Assuming that this DC component is accurate, the permeability of the current transformer core considering the DC component is calculated and used as the second permeability. If the deviation between the first and second permeability is less than or equal to the deviation threshold, it indicates that the results of the first permeability and the corresponding DC component are relatively accurate, and this DC component is used as the DC component of the intruding current transformer.

[0070] If the deviation between the first and second permeability exceeds a deviation threshold, it indicates that the first permeability and its corresponding DC component are inaccurate. Therefore, the first permeability needs to be corrected based on the deviation to obtain a new first permeability. The updated first permeability = first permeability + weighting coefficient multiplied by (second permeability - first permeability), where the weighting coefficient is a number greater than 0 and less than 1, determined according to the actual situation. That is, if the second permeability is too large, the first permeability needs to be increased for correction; if the second permeability is too small, the first permeability needs to be decreased for correction. The calculation is then repeated using the corrected first permeability until the deviation between the first and second permeability is less than or equal to the deviation threshold. At this point, the DC component corresponding to the first permeability is taken as the DC component of the intrusion current transformer.

[0071] Specifically, the process of calculating the permeability of a current transformer core that takes into account the DC component includes:

[0072] Based on the basic parameters of the current transformer, the basic magnetic flux under no magnetic bias condition is calculated. The basic parameters of the current transformer include its factory-issued volt-ampere characteristic data set: voltages U1, U2, U3 to Um, currents I1, I2, I3 to Im, number of turns N of the secondary coil, average cross-sectional area S of the iron core, average magnetic circuit length I of the iron core, and leakage coefficient α, etc.

[0073] According to Faraday's law of electromagnetic induction, the acquired voltage Ui is converted into magnetic flux density Bi: Where i∈[1,m], f is the AC frequency; according to Ampere's circuital law, the obtained current Ii is converted into magnetic field strength Hi: H i =NI i / I; Using the least squares method, the data sets of magnetic induction intensity Bi and magnetic field intensity Hi are fitted to a hyperbola H = xsinh(yB), where sinh represents the hyperbolic function, x and y are the fitting coefficients, and the values ​​of x and y should both be greater than 1. Simultaneously, the fundamental magnetic flux under no magnetic deflection condition is calculated using the voltage Ui. Using the least squares method to determine the fundamental magnetic flux The obtained current Ii was fitted to a curve. And on Differentiating the curve, with f-1 represents the derivative of the curve f.

[0074] Iterative calculation of the DC component i dc under the alternating voltage Ui and the sum of the DC magnetic flux, the basic magnetic flux and the DC magnetic flux m，i ; fitting (least squares method or other fitting methods can be used) the total magnetic flux and the excitation current i m，i , to obtain the DC component i dc intrusion into the current transformer core of the magnetization curve, and the derivative of the magnetization curve to obtain the DC component i dc intrusion into the current transformer under the condition of excitation inductance; based on the proportional relationship between the excitation inductance and the magnetic permeability, the magnetic permeability is calculated. The process of calculating the magnetic permeability based on the proportional relationship between the excitation inductance and the magnetic permeability is the same as the process of calculating the magnetic permeability by inductance in the previous process of real-time acquisition of the magnetic permeability of the current transformer core, so it is not repeated here.

[0075] Through the method of iterative calculation, the problem of inaccurate calculation of the excitation inductance value of the current transformer under the condition of DC bias, which leads to inaccurate calculation of the current transformer transient transfer characteristic index such as the initial saturation time, is solved, so that the excitation inductance value of the current transformer under the condition of DC bias is closer to the actual value, and more accurate magnetic permeability results can be obtained, and then more accurate DC component results are obtained for DC bias compensation.

[0076] Further, as shown in Figure 3 , the specific iterative calculation process includes: considering the DC component i dc , setting the DC magnetic flux of the DC component i dc to be any value less than the basic magnetic flux in the first iteration calculation.

[0077] S1, calculate the excitation current i m，k , the DC component i dc，k and the maximum excitation current i max of the kth iteration.

[0078] The excitation current of the kth iteration calculation is:

[0079]

[0080] Where is the DC magnetic flux of the current transformer in the kth iteration calculation, k=1, 2, 3, …; x and y are the fitting coefficients of the magnetic field strength and the magnetic induction strength, the number of turns N of the secondary coil, the average cross-sectional area S of the core, the average magnetic path length 1 of the core and the leakage coefficient α.

[0081] The DC component calculated in the k-th iteration is:

[0082]

[0083] Where T is one cycle of alternating current. Taking 50Hz alternating current as an example, T corresponds to 20ms.

[0084] The maximum excitation current during the k-th iteration is i max =max(i m，k (t)).

[0085] The total magnetic flux of the current transformer during the k-th iteration is:

[0086] S2, if |i dc -i dc，k If |i is less than the preset deviation, the preset deviation can be 0.00001 or other values ​​selected according to the actual situation, proceed to S5. Before proceeding to S5, first set k = k + 1; if |i dc -i dc，k If the deviation is greater than or equal to the preset deviation, proceed to step S3.

[0087] S3. Calculate the DC flux in the (k+1)th iteration, and let k = k+1; the DC flux calculated in the (k+1)th iteration is:

[0088] Where sign() is the sign function, if i dc If i is positive, then the sign function takes the value 1; if i dc If the value is negative, the sign function takes the value -1; f -1 This is a function used to differentiate the fitted curve of the fundamental magnetic flux and current values.

[0089] S4. When k is less than the iteration threshold, return to S1. The iteration threshold limits the upper limit of the number of iterations and can be 10000 or other values ​​determined according to the actual situation. When k is greater than or equal to the iteration threshold, proceed to S5.

[0090] S5. Stop iteration, and take |i from k-1 iterations. dc -i dc，k Minimum DC flux and the maximum value of excitation current i max And calculate the total magnetic flux. and the excitation current i fitted with the total magnetic flux m，i =i max .

[0091] As a specific embodiment, the DC bias compensation unit generates a reverse DC on the compensation winding according to the determined DC component, generates a magnetic field opposite to the DC bias to offset the DC bias. The DC bias is because there is a DC component in the current of the input primary winding, and the corresponding magnetic field is generated in the process of the winding, which affects the operation of the current transformer, so the purpose of the DC bias compensation is to inject a reverse DC current to generate a magnetic field opposite to the DC bias to offset the influence of the DC bias.

[0092] Based on the anti-DC bias current transformer based on the permeability feedback compensation of the application, there is an anti-DC bias current transformer based on the permeability feedback compensation, as shown in Figure 4 The core T1 and the primary winding N1 and the secondary winding N2 wound on the core are included; the auxiliary winding Nf and the compensation winding Nb are also wound on the core; the auxiliary winding Nf is connected to the permeability measurement unit, the compensation winding Nb is connected to the DC bias compensation unit, and the result detected by the permeability measurement unit is transmitted to the DC bias compensation unit.

[0093] In the operation process of the current transformer, the AC current and the mixed DC component pass through the primary winding N1; in order to measure the permeability of the current transformer to obtain the result of the DC component, the permeability measurement unit injects a voltage V m with constant amplitude into the auxiliary winding Nf to simulate the detection of constant voltage mode, and the current I m passing through the auxiliary winding can be detected at this time; the total impedance of the auxiliary winding at this time can be calculated as the ratio of the voltage V m to the current I m |Z x |=V m / I m . Because of the existence of the total impedance of the auxiliary winding, the detected current is behind the phase of the voltage θ. Based on the physical knowledge of the total impedance, the equivalent circuit of the auxiliary winding at this time is equivalent to a series connection of a resistor Rs and an inductor Ls, and its total impedance can be represented in complex form: Z x =R s +jωL s , ω=2πf, f represents the frequency of the constant voltage AC.

[0094] Based on the orthogonal vector relationship of the series inductance and resistance, the total impedance is synthesized, and the angle between the resistance Rs and the total impedance is the θ phase of the six-point voltage, so R s =|Z x |cosθ, ωL s =|Z x| sinθ; thus the total impedance of the auxiliary winding is calculated by the ratio of the detected voltage and current, and the inductance of the auxiliary winding is calculated according to the phase difference between the voltage and current and the total impedance, and the excitation inductance is finally obtained based on the frequency of the constant voltage current. According to the relationship between inductance and magnetic permeability:

[0095]

[0096] Where L is the inductance; N is the number of turns, here the number of turns of the auxiliary winding; Rs is the resistance component of the auxiliary winding in the measurement circuit; l F is the magnetic path length; A F is the cross-sectional area; μ0 is the magnetic permeability in vacuum; μ m is the relative magnetic permeability, and the product of the magnetic permeability in vacuum is the magnetic permeability to be calculated.

[0097] The magnetic permeability measuring unit obtains the magnetic permeability of the current transformer core in real time through the auxiliary winding Nf; the DC bias compensation unit determines the DC component of the intruded current transformer according to the received magnetic permeability data, and generates an opposite DC offset bias on the compensation winding Nb.

[0098] The DC bias compensation unit includes: a DC component calculation unit, which stores a relationship model of magnetic permeability and DC component; a compensation correction unit, which calculates the magnetic permeability of the current transformer core considering the DC component, corrects the magnetic permeability and the DC component, and obtains the DC component to be compensated.

[0099] In the initial correction process, the measured magnetic permeability is the first magnetic permeability, which is input into the relationship model of magnetic permeability and DC component to obtain the corresponding DC component; under the assumption that the DC component is accurate, the magnetic permeability of the current transformer core considering the DC component is calculated as the second magnetic permeability. If the deviation between the first magnetic permeability and the second magnetic permeability is less than or equal to the deviation threshold, it means that the first magnetic permeability and the corresponding DC component are relatively accurate, and the DC component is taken as the DC component of the intruded current transformer.

[0100] If the deviation of the first magnetic permeability and the second magnetic permeability is greater than the deviation threshold, it indicates that the first magnetic permeability and the corresponding DC component are not accurate, and thus the first magnetic permeability needs to be corrected by the deviation to obtain a new first magnetic permeability. The updated first magnetic permeability = the first magnetic permeability + a weight coefficient multiplied by (the second magnetic permeability - the first magnetic permeability), the weight coefficient being a number greater than 0 and less than 1, which is determined according to actual conditions. That is, if the second magnetic permeability is too large, the first magnetic permeability needs to be increased for correction, and if the second magnetic permeability is too small, the first magnetic permeability needs to be reduced for correction. The first magnetic permeability is corrected and then recalculated again, until the deviation of the first magnetic permeability and the second magnetic permeability is less than or equal to the deviation threshold, and the DC component corresponding to the first magnetic permeability is taken as the DC component of the invasive current transformer.

[0101] The above embodiments are further elaborations and explanations of the present application, so as to facilitate understanding, and are not any limitation of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A DC bias magnetic field compensation method based on magnetic permeability feedback compensation, characterized in that, The method comprises the following steps: Real-time acquisition of the magnetic permeability of the current transformer core by a magnetic permeability measurement unit; Based on the acquired magnetic permeability, the DC component of the invaded current transformer is determined according to a pre-established relationship model between the magnetic permeability and the DC component; The magnetic permeability input into the relationship model is taken as the first magnetic permeability, and the corresponding DC component is acquired; The magnetic permeability of the current transformer core considering the DC component is calculated as the second magnetic permeability; When the deviation between the first magnetic permeability and the second magnetic permeability is greater than a deviation threshold, the first magnetic permeability is corrected based on the deviation, and the DC component and the second magnetic permeability are recalculated until the deviation is less than or equal to the deviation threshold, and the corresponding DC component is the DC component of the invaded current transformer; The DC bias compensation unit generates a reverse DC to offset the bias magnetic field according to the determined DC component on the compensation winding.

2. The DC bias compensation method based on permeability feedback according to claim 1, wherein, The establishment process of the relationship model between the magnetic permeability and the DC component comprises the following steps: A fundamental wave current is applied to the primary winding of the transformer, and a DC component is superimposed while changing the size of the DC component; The magnetic permeability of the current transformer core corresponding to the DC component is measured, and each set of DC component and magnetic permeability is a data point; The data points are fitted to obtain the relationship model between the magnetic permeability and the DC component.

3. The DC bias compensation method based on permeability feedback according to claim 1, wherein, The process of calculating the magnetic permeability of the current transformer core considering the DC component comprises the following steps: Based on the basic parameters of the current transformer, the basic magnetic flux without magnetic bias is calculated; The DC magnetic flux considering the DC component, the total magnetic flux which is the sum of the basic magnetic flux and the DC magnetic flux, and the excitation current are iteratively calculated; The excitation inductance is obtained by deriving the magnetization curve fitted by the total magnetic flux and the excitation current; The magnetic permeability is calculated based on the proportional relationship between the excitation inductance and the magnetic permeability.

4. The DC bias compensation method based on magnetic permeability feedback according to claim 1 or 3, characterized in that, The process of real-time acquisition of the magnetic permeability of the current transformer core comprises the following steps: A voltage with constant amplitude is applied to the auxiliary winding wound on the current transformer core, and the current of the detection loop and the voltage across the auxiliary winding are detected; The excitation inductance of the core is calculated based on the voltage across the auxiliary winding, the current passing through, and the phase difference between the two; The excitation inductance and the magnetic permeability are proportional to each other, and the magnetic permeability is calculated based on the proportional relationship.

5. The DC bias compensation method based on permeability feedback according to claim 3, wherein, The process of the iterative calculation comprises: the direct current component i considered dc , S1, calculate the field current i at the kth iteration m,k , the direct current component i dc,k and the field current maximum i max ; S2, if |i dc -i dc,k | is less than a preset deviation, go to S5; S3, calculate the DC magnetic flux at the k+1th iteration, and let k=k+1; S4, when k is less than the iteration threshold, return to S1; S5, stop iteration, take k-1 iteration in |i dc -i dc,k | minimum direct current magnetic flux and excitation current maximum value, and calculate the total magnetic flux.

6. The DC bias compensation method based on magnetic permeability feedback according to claim 1 or 3 or 5, characterized in that, The DC bias compensation unit generates a reverse DC on the compensation winding according to the determined DC component, generating a magnetic field opposite to the DC bias to offset the bias.

7. A DC bias compensating current transformer based on permeability feedback compensation, suitable for the DC bias compensating method according to any one of claims 1 to 6, characterized in that It comprises a core and a primary winding and a secondary winding wound on the core; the core is also wound with an auxiliary winding and a compensation winding; the auxiliary winding is connected with a magnetic permeability measurement unit, and the compensation winding is connected with a DC bias compensation unit; the result detected by the magnetic permeability measurement unit is transmitted to the DC bias compensation unit.

8. The DC bias compensation magnetic current transformer based on permeability feedback according to claim 7, characterized in that, The magnetic permeability measurement unit acquires the magnetic permeability of the current transformer core in real time through the auxiliary winding; The DC bias compensation unit determines the DC component of the invaded current transformer according to the received magnetic permeability data, and generates a reverse DC on the compensation winding to offset the bias magnetic field.

9. The DC bias compensation magnetic current transformer based on permeability feedback according to claim 7 or 8, characterized in that, The DC bias compensation unit comprises: A DC component calculation unit which stores a relationship model between the magnetic permeability and the DC component; The compensation correction unit calculates the permeability of the current transformer core considering the DC component, performs correction of the permeability and the DC component, and obtains the DC component that needs to be compensated.

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