Anti-DC current transformer and method based on temperature compensation

Abstract

The invention relates to the technical field of anti-direct-current current transformers, and discloses an anti-direct-current current transformer and method based on temperature compensation, the anti-direct-current current transformer comprises a shell, an iron core is mounted on the inner side of the shell, a transformer coil is wound on the outer side of the iron core, and the anti-direct-current current transformer further comprises a negative temperature resistance compensation system connected with the transformer coil in series, the negative temperature resistance compensation system comprises an NTC negative temperature sensitive resistor R1, a common resistor R3 and a common resistor R2 which are connected in parallel to form a parallel resistance system, a parallel loop is connected with a mutual inductor coil in series, and the equivalent resistance value of the negative temperature resistance compensation system is reduced along with the rise of the environment temperature. The problem that the phase difference / ratio error variation of a traditional single-iron-core anti-direct-current mutual inductor is large due to working environment temperature changes is solved, the phase difference variation caused by temperature is reduced to 1-2% from traditional about 15%, the ratio error variation is reduced to be within 0.1%, temperature drift errors are greatly reduced, and the precision of the mutual inductor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anti-DC current transformers, and particularly relates to an anti-DC current transformer based on temperature compensation and a method. BACKGROUND

[0002] The anti-DC transformer is mainly applied to electric energy metering equipment as a current signal acquisition element, is a key device for the precision of electric energy metering equipment, and can significantly improve the precision of electric energy metering. The precision of the transformer directly affects the precision of metering. There are two main categories of anti-DC transformers on the market: the first is a double-iron-core anti-DC transformer, and the second is a single-iron-core anti-DC transformer. Both of the two anti-DC transformers have certain shortcomings.

[0003] For example, the double-iron-core anti-DC transformer (high magnetic permeability core superimposed on low magnetic permeability core) has the advantages of high AC precision, a difference of ≤0.2%, and an angle difference of ≤10', but has poor anti-DC capability. When a half-wave DC input is used, the difference changes by about 3%, and the phase difference is 300'-600'. Compared with a sine AC and a half-wave DC, the phase difference of the two is several hundred percent (radian angle), and the anti-DC function of the transformer cannot be realized in a true sense.

[0004] The single-iron-core anti-DC transformer (single low magnetic permeability core) has good anti-DC effect. When a sine AC and a half-wave DC are tested, the phase difference of the two is close, and can be only 10-30'. Although the original phase difference is large, generally designed to be 200'-500', the full-range measurement range changes little at different current points, and can be compensated to within 10' by phase shifting once. However, since the single-iron-core anti-DC transformer must be designed and produced by a low magnetic permeability soft magnetic core, the original phase difference is relatively large. When the working temperature changes in the environment, the phase difference changes a lot in the full working temperature range, reaching about ±15% of the original phase difference at room temperature. At the same time, the difference also changes a lot. Therefore, technical means are needed to optimize the precision consistency of the transformer at different temperature environments. SUMMARY

[0005] The present application provides an anti-DC current transformer based on temperature compensation and a method. The anti-DC current transformer based on temperature compensation and the method use a series compensation negative temperature resistance system to reduce the influence of the increase in the coil resistance caused by the increase in the ambient temperature, so as to ensure the measurement precision, reduce the error, and improve the precision.

[0006] To solve the above technical problems, the technical scheme of the present application is as follows:

[0007] The first aspect is a temperature compensation based DC resistance current transformer, comprising a shell, an iron core is installed inside the shell, a transformer coil is wound outside the iron core, and further comprising: a negative temperature resistance compensation system connected in series with the transformer coil, the negative temperature resistance compensation system comprises a negative temperature thermistor (NTC thermistor), an NTC negative temperature thermistor R1, and a series resistance value of zero ordinary resistor R3, and a parallel resistance value of non-zero ordinary resistor R2, the resistance value of R1, R2 and R3 is adjusted to fit the negative temperature resistance compensation system 4 curve, so as to adapt to different transformer coils.

[0008] A method of a DC resistance current transformer, applied to the DC resistance current transformer, comprising: a negative temperature resistance compensation system and an equivalent resistance unit composed of the negative temperature resistance compensation system, the negative temperature thermistor is arranged inside the negative temperature resistance compensation system, the negative temperature resistance compensation system comprises at least one negative temperature thermistor and at least one ordinary resistor in parallel;

[0009] Further, the parallel circuit is connected in series with the transformer coil, the equivalent resistance value of the negative temperature resistance compensation system decreases with the increase of the ambient temperature, so as to offset the influence of the increase of the coil resistance caused by the increase of the temperature, so that the change of the ratio error caused by the temperature is reduced to ≤1-2%, and the change of the ratio error is ≤0.1%;

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

[0011] The ratio error is: ;

[0012] The angle error is: ;

[0013] Wherein, The total impedance of the compensated transformer is ; The coil resistance of the transformer is The load resistance of the transformer is The equivalent resistance of the negative temperature resistance compensation system is The magnetic permeability of the magnetic core is.

[0014] Further, the negative temperature thermistor in the negative temperature resistance compensation system is an NTC thermistor, and the temperature coefficient satisfies that the resistance value changes with the ambient temperature;

[0015] Further, the equivalent resistance unit calculation formula is:

[0016] The equivalent resistance value of Rcomp is (R1+R3)×R2 / (R1+R3+R2);

[0017] Wherein: R1: NTC is a negative temperature thermistor, R2: is a conventional resistance, R3: is a conventional resistance, the resistance value is zero---several ohms, used for fine tuning the negative temperature compensation curve of the negative temperature resistance compensation system, Rb: load resistance, Rcu: mutual inductor coil resistance.

[0018] Further, after the mutual inductor coil is connected in series with the negative temperature resistance compensation system, the value of Z' remains basically unchanged with temperature change.

[0019] The above scheme of the present application at least includes the following beneficial effects:

[0020] The present application solves the problem of large phase difference / ratio difference variation of single-core DC resistance mutual inductor caused by temperature change of working environment, so that the phase difference variation: the variation caused by temperature is reduced from about 15% of the traditional to 1-2%, and the ratio difference variation is reduced to within 0.1%, greatly reducing the temperature drift error of the mutual inductor and improving the precision. BRIEF DESCRIPTION OF DRAWINGS

[0021] The present application will be further described below in combination with the drawings.

[0022] Figure 1 The present application provides a schematic diagram of the overall structure of the DC resistance mutual inductor;

[0023] Figure 2 The present application provides a schematic diagram of the temperature variation curve of the coil resistance;

[0024] Figure 3 The present application provides a schematic diagram of the temperature variation curve of the mutual inductor core permeability;

[0025] Figure 4 The present application provides a schematic diagram of the temperature variation equivalent resistance curve of the negative temperature resistance compensation system;

[0026] Figure 5 The present application provides a schematic diagram of the typical temperature variation curve of the NTC negative temperature thermistor R1 (taking 20 ohms as an example);

[0027] Figure 6 The present application provides a data schematic diagram of the NTC negative temperature thermistor R1;

[0028] Figure 7 The present application provides a schematic diagram of the high and low temperature test angle difference data of the traditional single-core DC resistance mutual inductor product (German VAC sample) on the market;

[0029] Figure 8 The present application provides a schematic diagram of the high and low temperature test ratio difference data of the traditional single-core DC resistance mutual inductor product (German VAC sample) on the market;

[0030] Figure 9 A partial schematic diagram of high and low temperature ratio difference test data of a single-core DC-resistant transformer product designed using the present invention provided in an embodiment of the present invention;

[0031] Figure 10 A partial schematic diagram of high and low temperature angle difference test data of a single-core DC-resistant transformer product designed using the present invention provided in an embodiment of the present invention;

[0032] Figure 11 A schematic diagram of angular difference comparison provided by an embodiment of the present invention;

[0033] Figure 12 A schematic diagram of a ratio difference comparison provided by an embodiment of the present invention;

[0034] Figure 13 A schematic diagram of a negative temperature resistance compensation system provided by an embodiment of the present invention;

[0035] Figure 14 A schematic diagram of the internal analysis of a housing provided in an embodiment of the present invention.

[0036] In the figure: 1. Housing; 2. Iron core; 3. Transformer coil; 4. Negative temperature resistance compensation system. DETAILED DESCRIPTION

[0037] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0038] like Figures 1 to 14 As shown, a DC current transformer and method based on temperature compensation include a housing 1, an iron core 2 is installed on the inner side of the housing 1, and a transformer coil 3 is wound on the outer side of the iron core 2. It also includes: a negative temperature resistance compensation system 4, which is connected in series with the transformer coil 3. The negative temperature resistance compensation system 4 includes: an NTC negative temperature thermistor R1 is arranged inside the negative temperature resistance compensation system (4), and a parallel resistance system composed of at least one negative temperature thermistor (NTC thermistor) and at least one conventional resistor.

[0039] A method for resisting direct current current transformer, applied to the aforementioned direct current transformer, includes: the aforementioned negative temperature resistance compensation system 4 and the equivalent resistance unit generated therefrom, a negative temperature thermistor (NTC thermistor) disposed within the negative temperature resistance compensation system 4, and the negative temperature resistance compensation system 4 comprising a parallel circuit consisting of at least one negative temperature thermistor and at least one conventional resistor.

[0040] The said parallel circuit is connected in series with the transformer coil, and 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 caused by the temperature is reduced to 1-2%, and the difference is less than or equal to 0.1%.

[0041] Specifically, the phase difference of the DC resistance transformer refers to the phase difference between the AC current waveform of the primary side (measured current) and the secondary side (output signal), which is usually expressed in degrees (°), 1°=60'.

[0042] Ideally, the current waveforms of the primary side and the secondary side should be completely the same (phase difference is 0°),

[0043] But in fact, there is a phase shift due to the electromagnetic characteristics and loss of the transformer.

[0044] Mathematical expression:

[0045] If the primary side current is ;

[0046] The secondary side current is , the phase difference is (unit: degree or minute).

[0047] Specifically, is the instantaneous current expression of the primary side of the transformer; wherein i represents the current (physical quantity symbol), and the subscript "1" represents "primary side" (i.e. the input end of the transformer, usually connected to the main circuit of the measured circuit), represents that the current is a function of time (i.e. the instantaneous value of the AC current changes with time), and the entire expression describes the variation characteristics of the primary side current:

[0048] is the peak value (maximum value) of the primary side current, is the angular frequency, represents that the current changes with time according to the sine law, which is the typical change form of the current in the AC circuit;

[0049] is the instantaneous current expression of the secondary side of the transformer;

[0050] wherein the subscript "2" represents "secondary side" (i.e. the output end of the transformer, usually connected to the measuring instrument or protection device), also represents that the current is a function of time;

[0051] is the peak value of the secondary side current; The secondary side current also varies according to the sine law, but there is a phase shift with the primary side current, and the shift is (i.e. the phase difference of the two);

[0052] Phase difference The core source of the transformer angle difference is (combined with the error formula, the angle difference is essentially the phase difference of the primary side and the secondary side current).

[0053] In the actual application process of the embodiment, first, the negative temperature resistance compensation system 4 is installed in the transformer, the output ends S1 and S2 are connected with the load sampling resistance Rb, and the intelligent electric metering module is connected. 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 as to ensure the measurement accuracy, reduce the error, and improve the measurement accuracy of the intelligent electric meter.

[0054] Further, the error calculation formula of the negative temperature resistance compensation system 4 is as follows:

[0055] Ratio error: ;

[0056] Phase difference: ;

[0057] The phase difference / ratio error changes with the temperature according to the above transformer error calculation formula: mainly due to the large change of the resistance value of the transformer coil 3 RCU with the change of the temperature, such as the temperature change rate of the copper resistance rate is about 0.0039% / °C, assuming that the resistance of a single iron core DC resistance transformer coil is 60 ohms at 25°C, the phase difference is about 300' at 25°C, when the transformer is heated from 25°C to 85°C, the coil resistance will be increased to about 75Ω (see Figure 2 ), which has a great influence on the accuracy error of the transformer, and the phase difference may become about 340', which will increase by several tenths;

[0058] When the DC resistance transformer coil 3 RCU increases with the temperature, the resistance value increases, but at this time, through the series negative temperature resistance compensation system 4, the NTC negative temperature thermistor R1 adjusts the resistance value by sensing the temperature change, and cooperates with R2 and R3 to realize that the R compensation resistance becomes smaller. When the coil resistance RCU increases with the temperature, the resistance value increases, but at this time, the "R compensation" resistance connected in series becomes smaller, and the two are close to offset, so as to realize that the total impedance is basically unchanged, so as to realize that the phase difference / ratio error of the transformer changes with the temperature. Similarly, when the temperature decreases, the coil resistance RCU becomes smaller, and the "R compensation" resistance becomes larger.

[0059] Coil resistance Rcu high and low temperature test data table:

[0060] Inductance (magnetic permeability) high and low temperature test data table:

[0061] Rcompensate equivalent resistance value at different temperatures:

[0062] The difference data comparison table of the present scheme and the conventional scheme: temperature Invention solution is worse than German VAC ratio 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

[0063] As shown in Figures 2 to 4 The error calculation formula of the negative temperature resistance compensation system (4) is as follows:

[0064] Difference: ;

[0065] Angular difference: ;

[0066] Wherein, Z2 is the total impedance of the compensated transformer, ; Rcu is the coil resistance of the transformer, Rb is the load resistance of the transformer, Rcompensate is the equivalent resistance of the negative temperature resistance compensation system 4, μ is the magnetic permeability of the magnetic core.

[0067] In the process of implementing and applying the embodiment,

[0068] I. Physical meaning and core variables of error formula:

[0069] Difference: measure the amplitude ratio error of the primary side and the secondary side current (or voltage) of the transformer, the result is expressed in percentage;

[0070] Angular difference: measure the phase deviation of the primary side and the secondary side current (or voltage), the result is expressed in minutes (').

[0071] Key variables and temperature sensitive parameters in the formula:

[0072] Z2 (total impedance): Z2=Rcu (coil resistance) +Rb (load resistance), wherein Rcu changes significantly with temperature (copper conductor positive temperature coefficient);

[0073] μ (magnetic permeability of the magnetic core): the magnetic permeability of the magnetic core material changes with temperature, which affects the excitation characteristics of the magnetic core;

[0074] I2 (secondary side current): I2 changes when the load or primary side current changes, and is affected by the temperature (such as the change of Rcu causes the fluctuation of the circuit current);

[0075] Lc is the average magnetic path length of the transformer core, that is, the average path length of the magnetic force line when it is closed inside the core, which is one of the core geometric parameters of the core, directly affecting the distribution of the magnetic field strength in the core: according to the magnetic circuit ohm law, the magnetomotive force (related to winding current and number of turns) needs to overcome the magnetic resistance brought by the magnetic path length to generate effective magnetic flux in the core, therefore, the size of Lc will indirectly affect the strength of the magnetic flux in the core, and then affect the error of the transformer through the electromagnetic induction relationship:

[0076] The denominator in the formula is mainly composed of a "reference term" composed of multiple core physical parameters, the size of which directly determines the reference of error calculation, and the meanings and effects of each parameter are as follows:

[0077] 2pf: angular frequency (f is the power frequency), reflecting the rate of electromagnetic field change in an alternating current circuit. The transformer works based on electromagnetic induction, and the frequency directly affects the rate of change of magnetic flux, and then affects the transformation accuracy of induced electromotive force and current, so the angular frequency is a basic parameter for error calculation.

[0078] μ: magnetic permeability of the core, a physical quantity that measures the magnetic conductivity of the core (the larger μ is, the stronger the magnetic conductivity of the core). The magnetic permeability is significantly affected by temperature: temperature changes will cause the magnetic properties of the core material to change (such as high temperature may cause μ to decrease), and then affect the establishment of the magnetic flux in the core, which is one of the key factors of the error with temperature change.

[0079] Ac: effective cross-sectional area of the core, that is, the cross-sectional area of the core perpendicular to the magnetic path direction. It determines the "magnetic conductance" of the core together with the magnetic path length Lc (similar to the electrical conductance in an electrical circuit), the larger the Ac is, the more magnetic flux can pass through under the same magnetic field, and the stronger the "carrying capacity" of electromagnetic induction, which is a core geometric parameter affecting the size of the magnetic flux.

[0080] N2: number of turns of the secondary winding, which is a core parameter for current transformation (the transformation ratio of the transformer is directly related to the ratio of the number of turns of the primary and secondary windings). The accuracy of the number of turns of the secondary winding will directly affect the proportional relationship of the current transformation, and then affect the error.

[0081] n: usually refers to the ratio of the number of turns of the primary winding to the number of turns of the secondary winding (n=N1 / N2, N1 is the number of turns of the primary winding), which reflects the "transformation ratio coefficient" of the transformer. The accuracy of the number of turns is the basis for ensuring the accuracy of the transformation ratio of the transformer, and its deviation will directly amplify the error.

[0082] (I n)1: primary current, i.e. the rated working current of the primary side of the transformer (the reference current in the design). The error calculation is based on the rated working condition, so the primary current is the reference value for measuring the relative size of the error;

[0083] The formula contains "Z2" (Z2=Rcu+Rb, Rcu is the coil resistance, and Rb is the load resistance) in the numerator, and temperature changes will affect the error through two core paths:

[0084] Z2 changes: when the temperature rises, the coil resistance Rcu increases (the positive temperature coefficient of conductor resistance), causing Z2 to increase, making the numerator larger, and the error (percentage difference, angle difference) changes accordingly;

[0085] μ changes: temperature changes will change the magnetic permeability μ of the magnetic core (such as high temperature may cause μ to drop), causing the denominator to change, further amplifying the fluctuation of the error.

[0086] The "negative temperature resistance compensation system 4" mentioned earlier is to compensate for the change of Z2 (to reduce the fluctuation of Z2 with temperature), thereby reducing the change range of the numerator, and ultimately reducing the temperature drift of the percentage difference and angle difference.

[0087] The temperature effect on Z2 and the temperature characteristics of the error coupling mechanism Rcu directly affect Z2. The copper coil resistance Rcu increases linearly with temperature (α≈+0.004% / ℃), causing Z2=Rcu+Rb to increase with temperature.

[0088] If Rb is a fixed resistance, Z2 will increase linearly with temperature, and then affect the numerator term (I2Z2Lc) in the formula percentage difference f% and angle difference δ'. When Z2 increases, the product of I2Z2 increases, causing the calculation results of percentage difference f% and angle difference δ' to increase proportionally. For example: the temperature rises from 100Ω to 120Ω (ΔT=50℃), Z2 from (100+Rb)Ω to (120+Rb)Ω, if other parameters remain unchanged, the I2Z2Lc term increases, and the error is amplified.

[0089] As shown in Figure 13 , R1 in the negative temperature resistance compensation system 4 is a negative temperature NTC resistance in parallel with R2 and other conventional resistances, and the temperature coefficient of the equivalent resistance meets the reverse compensation requirement;

[0090] In the implementation and application process of the present example, the physical mechanism of temperature affecting resistance value is mainly used to determine:

[0091] As shown in Figure 4 , Figure 13 , the equivalent resistance unit calculation formula is:

[0092] Equivalent resistance of Rcomp=(R1+R3)xR2 / (R1+R3+R2)

[0093] Wherein: R1: is the resistance of NTC negative temperature thermistor;

[0094] R2: is a conventional resistance, and the resistance value cannot be zero;

[0095] R3: is a conventional resistance, and the resistance value can be zero, and is used for fine tuning of negative temperature compensation of the negative temperature resistance compensation system 4;

[0096] Rb: load resistance;

[0097] Rcu: mutual inductor coil resistance.

[0098] Specifically, the NTC negative temperature thermistor R1 (for example, 20 ohms) is very sensitive to temperature change, and the resistance change rate is very large;

[0099] In the implementation and application of the embodiment, there are two cases of temperature rise and temperature drop:

[0100] When the temperature rises:

[0101] Change: Rcu (copper coil) increases due to the positive temperature coefficient (for example, +0.0039% / °C);

[0102] R1: (NTC) decreases due to the negative temperature coefficient, resulting in a decrease in Rcomp as a whole.

[0103] Compensation effect: The decrease of Rcomp offsets the increase of Rcu, so that the total resistance Rtotal=Rcu+“Rcomp” remains stable.

[0104] When the temperature drops:

[0105] Change: Rcu decreases, but R1 increases, and then Rcomp as a whole increases.

[0106] Compensation effect: The increase of Rcomp compensates for the decrease of RCU, maintaining the stability of Rtotal.

[0107] Actual application effect:

[0108] Precision improvement: In the temperature range of-40°C~85°C, the change of ratio difference / phase difference caused by temperature fluctuation is reduced, and the electrical energy measurement error can be reduced from ±5% to within ±0.5% through the compensation network.

[0109] Through the cooperation of the negative temperature thermistor R1 and the ordinary resistance network R2 and R3, Rcomp realizes dynamic reverse compensation for the change of the mutual inductor coil resistance. This design cleverly utilizes the material characteristics and circuit topology, and efficiently solves the temperature drift problem without complex algorithms.

[0110] As Figure 13 As shown, the transformer coil is connected in series with the negative temperature resistance compensation system 4 Rcomp, With the change of different temperatures, the change is very small, and the influence of environmental temperature change on the impedance of the transformer is compensated.

[0111] In the process of implementing the application, the negative temperature characteristic of Rcomp and the positive temperature characteristic of the transformer coil form dynamic compensation;

[0112] Therefore, the temperature characteristics of the transformer coil and Rcomp are matched;

[0113] That is, the positive temperature characteristic of the transformer coil resistance (Rcu): the transformer coil is usually wound by copper wire, and the resistance temperature coefficient of copper is positive (about +0.004% / ℃), that is, when the temperature rises, the lattice thermal vibration of the copper wire intensifies, and the scattering of electrons increases, and the resistance value increases linearly.

[0114] The negative temperature characteristic Rcomp of the negative temperature resistance compensation system 4 Rcomp is composed of NTC thermistor R1, conventional resistance R2 and conventional trimming resistance R3, and the equivalent resistance of Rcomp=(R1+R3)×R2 / (R1+R3+R2);

[0115] Since R1 is an NTC thermistor, its resistance decreases exponentially with the increase of temperature (as described by the B value parameter equation), and R2 and R3 are conventional resistors (temperature coefficient close to 0), so the overall equivalent resistance of Rcomp decreases with the increase of temperature (see Figure 4 ), which is opposite to the positive temperature characteristic of Rcu;

[0116] It should be noted that, Figure 1 and Figure 14 S1 / S2 in and P1 / P2 are elements and circuit interfaces.

[0117] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A temperature-compensated DC current transformer, comprising a housing (1), an iron core (2) fixedly mounted on the inner side of the housing (1), and a transformer coil (3) wound on the outer side of the iron core (2), characterized in that: Also includes: A negative temperature resistance compensation system (4) is connected in series with the mutual inductor coil (3). The negative temperature resistance compensation system (4) includes: a negative temperature thermistor (NTC thermistor), an NTC negative temperature thermistor R1, and a series resistance value can be zero ordinary resistor R3, and a parallel resistance value cannot be zero ordinary resistor R2. The resistance values ​​of R1, R2, and R3 are adjusted to fit the curve of the negative temperature resistance compensation system (4) so ​​that it can adapt to different mutual inductor coils.

2. A method for a DC current transformer based on temperature compensation, applied to the DC current transformer according to claim 1, characterized in that: The negative temperature resistance compensation system (4) and the equivalent resistance unit composed thereof, wherein the negative temperature thermistor (NTC thermistor) is arranged inside the negative temperature resistance compensation system (4), and the negative temperature resistance compensation system (4) is a parallel resistance system composed of at least one negative temperature thermistor (NTC thermistor) and at least one conventional resistor.

3. The method of a temperature-compensated DC current transformer according to claim 2, characterized in that: The parallel circuit is connected in series with the mutual inductor coil (3), and the equivalent resistance value of the negative temperature resistance compensation system (4) decreases as the ambient temperature increases, so as to offset the effect of the increase in the internal resistance of the coil caused by the temperature increase, so that the angle difference change caused by the temperature is reduced to ≤1-2%, and the ratio difference change is ≤0.1%.

4. The method of a DC current transformer based on temperature compensation according to claim 3, characterized in that: The error calculation formula of the negative temperature resistance compensation system (4) is as follows: Ratio difference: ； Angular difference: ； in, is the total impedance of the compensated transformer, ; is the internal resistance of the transformer coil, is the transformer load resistance, is the equivalent resistance of the negative temperature resistance compensation system (4), It is the magnetic permeability of the core; the size of Lc will indirectly affect the strength of the magnetic flux in the core, and affect the error of the mutual inductor through the electromagnetic induction relationship.

5. The method of a DC current transformer based on temperature compensation according to claim 2, characterized in that: The negative temperature thermistor R1 (NTC thermistor) in the negative temperature resistance compensation system (4) has a temperature coefficient that satisfies the change in resistance value with the ambient temperature.

6. The method of a DC current transformer based on temperature compensation according to claim 2, characterized in that: The equivalent resistance unit calculation formula is: The equivalent resistance of R complement = (R1+R3)×R2 / (R1+R3+R2); Among them: R1: NTC is a negative temperature thermistor, R2: is a conventional resistor, the resistance value cannot be zero, R3: is a conventional resistor, the resistance value can be zero, used to fine-tune the negative temperature compensation curve of the negative temperature resistor compensation system (4), Rb: load resistance, Rcu: transformer coil resistance.

7. The method of a DC current transformer based on temperature compensation according to claim 2, characterized in that: After the mutual inductor coil (3) is connected in series with the negative temperature resistance compensation system (4), The impedance value remains nearly constant as the temperature changes.

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