A direct current resistance mutual inductor and method based on temperature compensation

Abstract

The present application relates to the technical field of anti-DC current transformer, and discloses an anti-DC current transformer and method based on temperature compensation, which comprises a shell, an iron core is installed on the inner side of the shell, and a transformer coil is wound on the outer side of the iron core, and further comprises a negative temperature resistance compensation system connected in series with the transformer coil, the negative temperature resistance compensation system comprises a NTC negative temperature thermistor R1 and a parallel resistance system composed of a common resistance R3 and a common resistance R2 connected in parallel, and a parallel loop connected in series with the transformer coil, and the equivalent resistance value of the negative temperature resistance compensation system decreases with the increase of ambient temperature.The present application solves the problem of large phase difference / bias difference variation of traditional single-iron-core anti-DC transformer caused by changes in working environment temperature, reduces the phase difference variation caused by temperature from about 15% of the traditional value to 1-2%, and reduces the bias difference variation to within 0.1%, greatly reducing the temperature drift error and improving the transformer precision.

Description

Technical Field

[0001] This invention relates to the field of DC current transformer technology, and specifically to a temperature-compensated DC current transformer and method. Background Technology

[0002] DC-DC transformers are mainly used in power metering equipment. As a current signal acquisition element, they are a key component for the accuracy of power metering equipment. The application of DC-DC transformers in power metering equipment can significantly improve the accuracy of power metering. The accuracy of the transformer directly affects the accuracy of the metering. There are two main types of DC-DC transformers on the market: the first is the double-core DC-DC transformer, and the second is the single-core DC-DC transformer. Both types of DC-DC transformers have certain disadvantages.

[0003] For example, a dual-core DC-resistant transformer (high permeability core superimposed with low permeability core) has the advantages of high AC accuracy, ratio error ≤0.2%, and phase difference ≤10′, but poor DC resistance. When there is a half-wave DC input, the ratio error changes by about 3%, and the phase difference is 300′-600′. Compared with sinusoidal AC, the phase difference between the two is several hundred parts (radian angle), so it cannot achieve the true DC resistance function of the transformer.

[0004] Single-core DC-resistant transformers (single low-permeability iron core) have good DC resistance. During sinusoidal AC and half-wave DC tests, the phase difference between the two is similar, reaching only 10-30′. Although the original phase difference is large, generally designed to be 200′-500′, the change in the full-range measurement range at different current points is very small. It can be compensated to within 10′ error in one go through phase shifting. However, since single-core DC-resistant transformers must be designed and manufactured with low-permeability soft magnetic cores, the original phase difference is relatively large. When the ambient operating temperature changes, the phase difference changes significantly across the entire operating temperature range, reaching about ±15% of the original phase difference at room temperature. At the same time, the ratio difference also changes significantly. Therefore, it is necessary to optimize its accuracy consistency under different temperature environments through technical means. Summary of the Invention

[0005] This invention provides a temperature-compensated DC current transformer and method. It utilizes a series-connected negative temperature resistance system, which decreases as the ambient temperature rises, to counteract the increase in coil internal resistance caused by temperature rise, thereby ensuring measurement accuracy, reducing errors, and improving precision.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] Firstly, a temperature-compensated DC current transformer includes a housing, an iron core mounted inside the housing, and a transformer coil wound around the outside of the iron core. It also includes a negative temperature resistance compensation system connected in series with the transformer coil. The negative temperature resistance compensation system includes a negative temperature thermistor (NTC thermistor), an NTC negative temperature thermistor R1, and a series resistor R3 with a zero resistance value, and a parallel resistor R2 with a non-zero resistance value. The system adjusts the resistance values ​​of R1, R2, and R3 to fit a curve of the negative temperature resistance compensation system, thus adapting it to different transformer coils.

[0008] A method for an anti-DC current transformer, applied to the anti-DC current transformer, includes: a negative temperature resistance compensation system and an equivalent resistance unit composed thereof, wherein the negative temperature thermistor is disposed inside the negative temperature resistance compensation system, and the negative temperature resistance compensation system includes at least one negative temperature thermistor and at least one conventional resistor in parallel.

[0009] Furthermore, the parallel circuit is connected in series with the transformer coil. The equivalent resistance value of the negative temperature resistance compensation system decreases as the ambient temperature rises, in order to offset the effect of the increase in coil internal resistance caused by the temperature rise, so that the ratio difference change caused by temperature is reduced to ≤1-2% and the ratio difference change is ≤0.1%.

[0010] Furthermore, the error calculation formula for the negative temperature resistance compensation system (4) is as follows:

[0011] Difference:

[0012] ;

[0013] Angular difference:

[0014] ;

[0015] in, The total impedance of the current transformer after compensation. ; It is the internal resistance of the transformer coil. It is the load resistance of the current transformer. It is the equivalent resistance of the negative temperature resistance compensation system. It is the magnetic permeability of the magnetic core.

[0016] Furthermore, the negative temperature resistance compensation system uses an NTC thermistor, whose temperature coefficient satisfies the requirement that the resistance changes with the ambient temperature.

[0017] Furthermore, the formula for calculating the equivalent resistance unit is as follows:

[0018] The equivalent resistance of R_complement = (R1+R3)×R2 / (R1+R3+R2;

[0019] Where: R1: NTC is a negative temperature thermistor, R2: is a conventional resistor, R3: is a conventional resistor with a resistance value of zero to a few ohms, used to fine-tune the negative temperature compensation curve of the negative temperature resistance compensation system, Rb: load resistance, Rcu: current transformer coil resistance.

[0020] Furthermore, after the current transformer coil is connected in series with a negative temperature resistance compensation system, the Z′ value will remain basically unchanged with temperature changes.

[0021] The above-described solution of the present invention has at least the following beneficial effects:

[0022] This invention solves the problem of large phase difference / ratio difference variations in single-core DC current transformers caused by changes in ambient temperature. The phase difference variation caused by temperature is reduced from approximately 15% to 1-2%, and the ratio difference variation is reduced to less than 0.1%, significantly reducing the temperature drift error of the transformer and improving its accuracy. Attached Figure Description

[0023] The invention will now be further described with reference to the accompanying drawings.

[0024] Figure 1 This is a schematic diagram of the overall structure of the DC current transformer provided in an embodiment of the present invention;

[0025] Figure 2 The embodiment of the present invention provides a schematic diagram of the temperature change curve of the coil resistance;

[0026] Figure 3 A schematic diagram of the temperature change curve of the magnetic permeability of the transformer core provided in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the equivalent resistance curve of the negative temperature resistance compensation system provided in the embodiment of the present invention;

[0028] Figure 5 A schematic diagram of a typical temperature change curve of an NTC negative temperature thermistor R1 (taking 20 ohms as an example) provided in an embodiment of the present invention;

[0029] Figure 6 This is a schematic diagram of the data for the NTC negative temperature thermistor R1 provided in an embodiment of the present invention;

[0030] Figure 7 A schematic diagram of high and low temperature test angle difference data for a conventional single-core DC current transformer product (German VAC sample) provided for an embodiment of the present invention;

[0031] Figure 8A schematic diagram of high and low temperature test ratio difference data of a conventional single-core DC current transformer product (German VAC sample) provided for embodiments of the present invention;

[0032] Figure 9 A schematic diagram of the high and low temperature ratio difference test data of the single-core DC current transformer product designed according to the present invention, provided for an embodiment of the present invention;

[0033] Figure 10 A schematic diagram of high and low temperature angle difference test data for a single-core DC current transformer product designed according to the present invention, provided for an embodiment of the present invention;

[0034] Figure 11 This is a schematic diagram of angular difference comparison provided in an embodiment of the present invention;

[0035] Figure 12 This is a schematic diagram of the comparison of the ratio provided in an embodiment of the present invention;

[0036] Figure 13 This is a schematic diagram of a negative temperature resistance compensation system provided in an embodiment of the present invention;

[0037] Figure 14 This is a schematic diagram of the internal cross-section of the outer shell provided for an embodiment of the present invention.

[0038] In the diagram: 1. Outer casing; 2. Iron core; 3. Current transformer coil; 4. Negative temperature resistance compensation system. Detailed Implementation

[0039] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0040] like Figures 1 to 14 As shown, a temperature-compensated DC current transformer and method includes a housing 1, an iron core 2 installed inside the housing 1, and a transformer coil 3 wound around the outside of the iron core 2. It also includes a negative temperature resistance compensation system 4 connected in series with the transformer coil 3. The negative temperature resistance compensation system 4 includes: an NTC negative temperature thermistor R1 inside the negative temperature resistance compensation system (4), and a parallel resistance system consisting of at least one negative temperature thermistor (NTC thermistor) and at least one conventional resistor.

[0041] A method for using an anti-DC current transformer, applied to the aforementioned anti-DC current transformer, includes: a negative temperature resistance compensation system 4 and its generated equivalent resistance unit, wherein a negative temperature thermistor (NTC thermistor) is disposed inside the negative temperature resistance compensation system 4, and the negative temperature resistance compensation system 4 consists of at least one negative temperature thermistor and at least one conventional resistor in a parallel circuit.

[0042] The parallel circuit is connected in series with the transformer coil. The equivalent resistance value of the negative temperature resistance compensation system 4 decreases as the ambient temperature increases, in order to offset the effect of the increase in coil internal resistance caused by the increase in temperature; so that the change in angle difference caused by temperature is reduced to 1-2%, and the change in ratio difference is ≤0.1%.

[0043] Specifically, the phase difference of an anti-DC transformer refers to the phase difference between the AC current waveforms on the primary side (measured current) and the secondary side (output signal), usually expressed in degrees (°): 1° = 60′.

[0044] Ideally, the primary and secondary current waveforms should be exactly the same (phase difference of 0°).

[0045] However, in reality, there is a phase shift due to the electromagnetic characteristics and losses of the current transformer;

[0046] Mathematical expression:

[0047] If the primary current is ;

[0048] Secondary current is The phase difference is (Unit: degrees or minutes).

[0049] Specifically It is the instantaneous current expression of the primary side of the current transformer; where i represents current (physical quantity symbol), and the subscript "1" represents "primary side" (i.e., the input terminal of the current transformer, usually connected to the main circuit of the circuit being measured). This indicates that the current is a function of time (i.e., the instantaneous value of the alternating current changes with time), and the entire expression describes the changing characteristics of the primary current:

[0050] It is the peak value (maximum value) of the primary side current. It is angular frequency. This indicates that the current changes sinusoidally with time, which is a typical form of current change in AC circuits.

[0051] This is the expression for the instantaneous current on the secondary side of the current transformer;

[0052] In this context, the subscript "2" represents the "secondary side" (i.e., the output terminal of the current transformer, which is usually connected to measuring instruments or protection devices). This also indicates that the current is a function of time;

[0053] It is the peak value of the secondary current; This indicates that the secondary current also changes according to a sinusoidal law, but there is a phase shift between it and the primary current, with the shift amount being... (i.e., the phase difference between the two);

[0054] Phase difference This is the core source of the phase difference in the transformer (which, in essence, is the phase deviation between the primary and secondary currents, according to the error formula).

[0055] In practical application, the negative temperature resistance compensation system 4 is first installed inside the transformer. The output terminals S1 and S2 are connected to the external load sampling resistor Rb, which is connected to the smart meter metering module. The equivalent resistance value of the negative temperature resistance compensation system 4 decreases as the ambient temperature rises, thereby offsetting the effect of the increase in coil internal resistance caused by the temperature rise, so as to ensure measurement accuracy, reduce errors, and improve the metering accuracy of the smart meter.

[0056] Furthermore, the error calculation formula for the negative temperature resistance compensation system 4 is as follows:

[0057] Difference:

[0058] ;

[0059] Angular difference:

[0060] ;

[0061] The phase difference / ratio difference changes with temperature, as shown in the above transformer error calculation formula, mainly due to the significant change in the resistance RCU of the transformer coil 3 with temperature. For example, the temperature change rate of copper resistivity is approximately 0.0039% / ℃. Assuming a single-core DC inductor coil resistance is 60 ohms at 25℃, and the phase difference is approximately 300′ at 25℃, when the transformer temperature rises from 25℃ to 85℃, the coil resistance will increase to approximately 75Ω (see...). Figure 2 This has a significant impact on the accuracy error of the current transformer. At this time, the angle difference may become about 340′, which is several tens of degrees larger.

[0062] When the DC current transformer coil 3RCU increases in temperature, its resistance increases. However, the NTC negative temperature thermistor R1, connected in series with the negative temperature resistance compensation system 4, adjusts its resistance based on the temperature change and works with R2 and R3 to reduce the R-compensation resistance. A negative temperature resistance "R-compensation" system (with a suitable resistance value) is connected in series with the original current transformer coil 3. When the coil resistance RCU increases in temperature, the resistance increases, but the connected "R-compensation" resistance decreases. The two almost cancel each other out, achieving the principle that the total impedance remains basically unchanged. This ensures that the phase difference / ratio difference error of the current transformer remains almost constant with temperature. Similarly, when the temperature decreases, the coil resistance RCU decreases, and the "R-compensation" resistance increases.

[0063] Coil resistance Rcu high and low temperature test data table:

[0064]

[0065] Inductance (permeability) high and low temperature test data table:

[0066]

[0067] Equivalent resistance values ​​of the R-complement system at different temperatures:

[0068]

[0069] Comparison table of the differences between the present invention's solution and the traditional solution:

[0070] temperature Invention solution comparison German VAC difference -40℃ 0.0600 0.16 -25℃ 0.0542 0.15 -15℃ 0.0533 0.14 0℃ 0.0531 0.11 10℃ 0.0521 0.09 25℃ 0.0568 0.05 40℃ 0.0589 0.06 55℃ 0.0589 0 70℃ 0.0511 0.01 85℃ 0.0494 -0.05

[0071] like Figures 2 to 4 As shown, the error calculation formula for the negative temperature resistance compensation system (4) is as follows:

[0072] Difference:

[0073] ;

[0074] Angular difference:

[0075] ;

[0076] in, The total impedance of the current transformer after compensation. ; It is the internal resistance of the transformer coil. It is the load resistance of the current transformer. It is the equivalent resistance of the negative temperature resistance compensation system 4. It is the magnetic permeability of the magnetic core.

[0077] In the implementation and application of this embodiment,

[0078] I. Physical meaning and core variables of the error formula:

[0079] Ratio error: measures the error in the ratio of the magnitude of the current (or voltage) on the primary side to the secondary side of the transformer, and the result is expressed as a percentage;

[0080] Phase difference: measures the phase deviation between the primary and secondary currents (or voltages), and the result is expressed in minutes (′).

[0081] Key variables and temperature-sensitive parameters in the formula:

[0082] Z2 (total impedance): Z2 = Rcu (internal resistance of coil) + Rb (load resistance), where Rcu changes significantly with temperature (positive temperature coefficient of copper conductor).

[0083] μ (core permeability): The permeability of the core material changes with temperature, affecting the excitation characteristics of the core;

[0084] I2 (secondary current): When the load or primary current changes, I2 changes accordingly, and is indirectly affected by temperature (such as Rcu changes causing loop current fluctuations).

[0085] Lc is the average magnetic path length of the current transformer core, that is, the average path length of the magnetic field lines when they are closed inside the core. It is one of the core's core geometric parameters and directly affects the distribution of the magnetic field strength in the core. According to Ohm's law for magnetic circuits, the magnetomotive force (related to the winding current and number of turns) must overcome the magnetic reluctance caused by the magnetic path length in order to generate effective magnetic flux in the core. Therefore, the magnitude of Lc indirectly affects the strength of the magnetic flux in the core, and thus affects the error of the current transformer through electromagnetic induction.

[0086] The denominator in the formula is mainly a "benchmark term" composed of multiple core physical parameters. Its magnitude directly determines the benchmark for error calculation. The meaning and function of each parameter are as follows:

[0087] 2πf: Angular frequency (f is the power supply frequency), reflecting the rate of change of the electromagnetic field in an AC circuit. Current transformers operate based on electromagnetic induction; frequency directly affects the rate of change of magnetic flux, and consequently, the accuracy of the transformation of induced electromotive force and current. Therefore, angular frequency is a fundamental parameter for error calculation.

[0088] μ: Permeability of the magnetic core, a physical quantity that measures the magnetic permeability of the core (the larger the μ, the stronger the magnetic permeability). Permeability is significantly affected by temperature: temperature changes will cause changes in the magnetic properties of the core material (e.g., high temperature may cause μ to decrease), which in turn affects the establishment of magnetic flux in the core and is one of the key factors in the variation of error with temperature.

[0089] Ac: The effective cross-sectional area of ​​the magnetic core, that is, the cross-sectional area of ​​the magnetic core perpendicular to the direction of the magnetic circuit. It, together with the length of the magnetic circuit Lc, determines the "magnetic permeability" of the magnetic core (similar to the electrical conductance in a circuit). The larger Ac is, the more magnetic flux can pass through under the same magnetic field, and the stronger the "carrying capacity" of electromagnetic induction. It is the core geometric parameter affecting the magnitude of the magnetic flux.

[0090] N2: The number of turns in the secondary winding is a core parameter for current transformation (the transformer ratio is directly related to the ratio of primary to secondary turns). The accuracy of the secondary turns directly affects the proportional relationship of current transformation, and thus affects the error.

[0091] n: This usually refers to the turns ratio of the primary winding to the secondary winding (n=N1 / N2, where N1 is the number of turns in the primary winding), reflecting the "turn ratio coefficient" of the instrument transformer. The accuracy of the turns ratio is the foundation for ensuring the turn ratio accuracy of the instrument transformer; its deviation will directly amplify the error.

[0092] (I n 1. Primary rated current, i.e., the rated operating current on the primary side of the instrument transformer (the reference current during design). Error calculation must be based on the rated operating conditions; therefore, the primary rated current is the benchmark value for measuring the "relative magnitude" of the error.

[0093] The numerator in the formula includes "Z2" (Z2 = Rcu + Rb, where Rcu is the coil internal resistance and Rb is the load resistance), and temperature changes affect the error through two core paths:

[0094] The change of Z2: When the temperature rises, the internal resistance Rcu of the coil increases (positive temperature coefficient of conductor resistance), which leads to an increase in Z2, making the numerator larger, and the error (specific error, angle error) changes accordingly;

[0095] Changes in μ: Temperature changes alter the magnetic core permeability μ (e.g., high temperatures may cause μ to decrease), leading to changes in the denominator and further amplifying error fluctuations.

[0096] The previously mentioned "negative temperature resistance compensation system 4" reduces the amplitude of molecular changes by compensating for changes in Z2 (making Z2 fluctuate less with temperature), thereby ultimately reducing the drift of specificity and angle difference with temperature.

[0097] The effect of temperature on Z2 and the error coupling mechanism: The temperature characteristics of Rcu directly affect Z2. The resistance of the copper coil Rcu increases linearly with increasing temperature (α≈+0.004% / ℃), which leads to Z2=Rcu+Rb increasing with increasing temperature.

[0098] If Rb is a fixed resistance, Z2 increases linearly with temperature, thus affecting the numerator (I2Z2Lc) in the formulas for specific difference f% and angle difference δ′. The propagation path of error due to Z2 changes: When Z2 increases, with the secondary current I2 remaining constant, the product of I2Z2 increases, leading to a proportional increase in the calculated results of specific difference f% and angle difference δ′. For example, if the temperature increases Rcu from 100Ω to 120Ω (ΔT=50℃), Z2 increases from (100+Rb)Ω to (120+Rb)Ω. If other parameters remain unchanged, the I2Z2Lc term increases, and the error is amplified accordingly.

[0099] like Figure 13 As shown, in the negative temperature resistance compensation system 4, R1 is a negative temperature thermistor NTC resistor connected in parallel with conventional resistors such as R2, and the temperature coefficient of its equivalent resistance meets the reverse compensation requirement.

[0100] In this example, the determination of resistance is mainly based on the physical mechanism by which temperature affects resistance.

[0101] like Figure 4 , Figure 13 As shown, the formula for calculating the equivalent resistance unit is:

[0102] The equivalent resistance of Rcomplement = (R1 + R3) x R2 / (R1 + R3 + R2).

[0103] Where: R1: is an NTC negative temperature thermistor;

[0104] R2: This is a standard resistor, and its resistance value cannot be zero;

[0105] R3: This is a standard resistor with a resistance value that can be zero. It is used to fine-tune the negative temperature compensation of the negative temperature resistance compensation system 4.

[0106] Rb: Load resistance;

[0107] Rcu: Resistance of the transformer coil.

[0108] Specifically, the NTC negative temperature thermistor R1 (taking 20 ohms as an example) is very sensitive to temperature changes, and its resistance value changes at a very large rate.

[0109] In practical application, this embodiment may present two scenarios: temperature increase and temperature decrease.

[0110] When the temperature rises:

[0111] Change: Rcu (copper coil) increases due to the positive temperature coefficient (e.g., +0.0039% / ℃).

[0112] R1 (NTC) decreases due to the negative temperature coefficient, resulting in an overall decrease in Rcomplement.

[0113] Compensation effect: The decrease of Rcomplement offsets the increase of Rcu, keeping the total resistance Rtotal = Rcu + "Rcomplement" stable.

[0114] When the temperature decreases:

[0115] Changes: Rcu decreases, but R1 increases, which in turn increases the overall Rcomp.

[0116] Compensation effect: The increase of Rcomplement compensates for the decrease of RCU, maintaining the stability of Rtotal.

[0117] Practical application results:

[0118] Improved accuracy: Within the temperature range of -40℃ to 85℃, the change in ratio / phase difference caused by temperature fluctuations is reduced. Through this compensation network, the power measurement error can be reduced from ±5% to within ±0.5%.

[0119] By working in concert with the negative temperature thermistor R1 and the ordinary resistor network R2 and R3, R-compensation achieves dynamic reverse compensation for the resistance change of the transformer coil. This design cleverly utilizes material properties and circuit topology to efficiently solve the temperature drift problem without the need for complex algorithms.

[0120] like Figure 13 As shown, after the current transformer coil is connected in series with the negative temperature resistance compensation system 4R, The change is very small as the temperature varies, which is used to compensate for the impact of ambient temperature changes on the impedance of the transformer.

[0121] In the implementation of this embodiment, dynamic compensation is formed between the negative temperature characteristics of R-compensation and the positive temperature characteristics of the transformer coil.

[0122] Therefore, the temperature characteristics of the current transformer coil and the R-compensator are matched;

[0123] The positive temperature characteristic of the current transformer coil resistance (Rcu): The current transformer coil is usually wound with copper wire. The temperature coefficient of resistance of copper is positive (about +0.004% / ℃). That is, as the temperature rises, the thermal vibration of the copper wire lattice intensifies, the scattering of electrons is enhanced, and the resistance increases linearly.

[0124] The negative temperature resistance compensation system 4R compensation has negative temperature characteristics. R compensation is composed of NTC thermistor R1, conventional resistor R2 and conventional fine-tuning resistor R3. The equivalent resistance of R compensation = (R1+R3)×R2 / (R1+R3+R2).

[0125] Since R1 is an NTC thermistor, its resistance decreases exponentially with increasing temperature (as described by the B-value parameter equation), while R2 and R3 are conventional resistors (with a temperature coefficient close to 0). Therefore, the overall equivalent resistance of Rcomplement decreases with increasing temperature (see...). Figure 4), which changes inversely to the positive temperature characteristic of Rcu;

[0126] It should be noted that, Figure 1 and Figure 14 S1 / S2 are components, and P1 / P2 are circuit interfaces.

[0127] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method of temperature-compensated DC current transformer, the current transformer comprising: The shell (1) is internally fixedly installed with an iron core (2), and the outer side of the iron core (2) is wound with a mutual inductor coil (3), characterized in that it further comprises a negative temperature resistance compensation system (4) connected in series with the mutual inductor coil (3), the negative temperature resistance compensation system (4) comprising a series resistance composed of an NTC negative temperature thermistor R1 and a resistance R3 with a resistance value greater than or equal to 0, and a resistance R2 not equal to zero connected in parallel with the series resistance, the resistance values of R1, R2 and R3 being adjusted to fit the negative temperature resistance compensation system (4) curve, so as to adapt to different mutual inductor coils; The equivalent resistance value of the negative temperature resistance compensation system (4) decreases with the increase of the ambient temperature, so as to offset the influence of the increase of the coil resistance caused by the temperature rise, so that the angle difference variation caused by the temperature is reduced to ≤1-2%, and the ratio difference variation is ≤0.1%; The error calculation formula of the negative temperature resistance compensation system (4) is as follows: Ratio difference: ； Angle difference: ； Wherein, is the secondary side current: when the load or primary side current changes, changes, the secondary side current is affected by the temperature of the transformer core; is the total impedance of the compensated transformer; ; =(R1+R3)×R2 / (R1+R3+R2); is the internal resistance of the transformer coil, is the load resistance of the transformer, is the equivalent resistance of the negative temperature resistance compensation system (4); is the average magnetic path length of the transformer core, that is, the average path length of the magnetic force line when the magnetic force line is closed inside the magnetic core; The size will indirectly affect the strength of the magnetic flux in the magnetic core, and affect the error of the transformer through the electromagnetic induction relationship; is the angular frequency, reflecting the rate of change of electromagnetic field in AC circuit; is the magnetic permeability of the magnetic core; is the effective cross-sectional area of the magnetic core, that is, the cross-sectional area of the magnetic core perpendicular to the magnetic path direction, which together with the magnetic path length determines the magnetic permeability of the magnetic core; is the number of turns of the secondary winding, which is the core parameter of current transformation; n refers to the ratio of the number of turns of the primary winding to the secondary winding; is the primary rated current, that is, the rated working current of the primary side of the transformer.

2. A method of temperature-compensated DC current transformer according to claim 1, characterized in that: The transformer coil (3) is connected in series with a negative temperature resistance compensation system (4), The numerical value will change with the temperature change impedance close to constant.

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