A test current and voltage acquisition circuit structure for transformer direct resistance measurement

Abstract

The utility model relates to transformer direct resistance measurement technical field, concretely relates to a kind of test current and voltage acquisition circuit structure for transformer direct resistance measurement. Including: constant-current source generation loop, including differential amplifier circuit and error comparison circuit;The voltage pin of current detection resistance is connected to the noninverting input terminal of first operational amplifier U1A;The voltage pin of current detection resistance is connected to the inverting input terminal of first operational amplifier U1B, simultaneously connected to the output terminal of first operational amplifier U1B, the output terminal of first operational amplifier U1A is connected to the inverting input terminal of first operational amplifier U1B;Calibratable integration amplifier circuit, including the integration amplifier circuit connected with current detection resistance and connected with the load both ends, output terminal is connected to the input channel of the ADC acquisition chip of voltage acquisition circuit.This technical scheme can solve the problems of small test current output range, instability and inaccurate voltage acquisition in the prior art.

Description

Technical Field

[0001] This utility model relates to the field of transformer DC resistance measurement technology, specifically to a test current and voltage acquisition circuit structure for transformer DC resistance measurement. Background Technology

[0002] In power systems, transformers are critical equipment, and accurate measurement of their winding DC resistance is of great significance for evaluating transformer performance, assessing winding insulation conditions, and ensuring the safe and stable operation of the power system. Transformer winding DC resistance measurement can reveal potential faults such as broken strands in the winding conductors or poor contact at joints.

[0003] Currently, in the field of transformer winding DC resistance measurement, the widely used method is to apply a constant DC current to the winding, then measure the voltage across the winding, and finally calculate the winding resistance. While this method seems simple and direct, it faces many problems in practical applications: From the perspective of test current generation, the DC resistance values ​​of windings vary greatly among different types and specifications of transformers. This necessitates a wide range of test current to accommodate the measurement needs of varying DC resistance values. However, current common excitation current output structures have significant drawbacks. On the one hand, the output range is small, failing to meet the requirements of large-range resistance measurements; on the other hand, poor output stability severely affects the accuracy of measurement results. When a large range of constant current source DC current is required, to address the issue of severe heat generation in the sampling resistor under high current conditions, a smaller sampling resistor value is typically selected to reduce heat generation. However, a smaller sampling resistor introduces new problems: when outputting a small constant current, the input reference voltage must achieve a small and stable output. However, under the influence of various interference factors, the reference voltage chip struggles to maintain good output stability at the millivolt level, leading to low stability of the constant current source circuit at low current output. Furthermore, some wide-range circuits that use switching current sensing resistors to switch between different ranges, while extending the output range to some extent, complicate the circuit structure and control strategy, increasing system cost and failure risk.

[0004] In voltage acquisition, due to the coupling effect of the internal magnetic field of the transformer, when a stable test current is applied to the winding, it will be affected by the induced electromotive force of the other winding, resulting in noise interference on the voltage across the winding. This severely affects the accuracy of the winding voltage acquisition, causing the measurement results to deviate from the true value. Moreover, in transformer DC resistance measurement, the test current requirements vary greatly depending on the transformer specifications and operating conditions. Small currents are needed to adapt to low-resistance winding measurements, while large currents are needed to meet high-resistance winding tests. Stability control at low current output has always been a technical challenge, making it difficult to guarantee a stable and reliable test current under various operating conditions. Utility Model Content

[0005] The purpose of this invention is to propose a test current and voltage acquisition circuit structure for transformer DC resistance measurement. This technical solution can solve the problems of small and unstable test current output range and inaccurate voltage acquisition in the prior art.

[0006] To achieve the above objectives, this disclosure provides a test current and voltage acquisition circuit structure for measuring the DC resistance of a transformer, comprising: a constant current source generating circuit, a calibrable integrating amplifier circuit, and a voltage acquisition circuit; the constant current source generating circuit includes a differential amplifier circuit connected to a current sensing resistor and an error comparison circuit connected to the gate of a first MOS transistor; the voltage pin of the current sensing resistor is connected to the non-inverting input of the first operational amplifier U1A in the differential amplifier circuit; the other voltage pin of the current sensing resistor is connected to the inverting input of the first operational amplifier U1B in the error comparison circuit, and is also connected to the output of the first operational amplifier U1B; the output of the first operational amplifier U1A is connected to the inverting input of the first operational amplifier U1B; the calibrable integrating amplifier circuit includes an integrating amplifier circuit connected to the current sensing resistor and an integrating amplifier circuit connected to both ends of the load, and the output of the calibrable integrating amplifier circuit is connected to the input channel of the ADC acquisition chip of the voltage acquisition circuit.

[0007] Beneficial effects of the basic solution: Traditional solutions typically rely on a high-precision, small-output-range DAC (Digital-to-Analog Converter) to provide a reference voltage to achieve small excitation current output. However, ordinary DACs have poor accuracy and linearity in the small voltage output range, easily leading to large fluctuations and insufficient stability in small current output. This solution uses a differential amplifier circuit to accurately amplify the voltage signal of the current sensing resistor. With appropriate amplification, the larger reference voltage output from an ordinary DAC can be used to indirectly achieve a stable output of a small excitation constant current source, significantly improving current stability under low current conditions and avoiding DC resistance measurement errors caused by small current fluctuations.

[0008] In this technical solution, the differential amplifier circuit is designed to optimize the reference voltage adaptation only for low current scenarios. Under high current output conditions, the circuit can naturally adapt to the larger reference voltage of ordinary DACs without additional circuit parameter adjustments. It will not have a negative impact on the output stability and linearity of high current, thus achieving full-range current output performance assurance and meeting the testing requirements of different transformer windings.

[0009] The system design difficulty and cost have also been reduced. On the one hand, the solution does not require the use of a high-precision, high-cost dedicated small-range DAC. A stable output with low current can be achieved simply by using a common DAC in conjunction with a differential amplifier circuit, which reduces the selection cost of core components. On the other hand, the coordination logic between the differential amplifier circuit and the error comparison circuit (including the first MOS transistor and the first operational amplifier U1B) in the circuit structure is clear. There is no need for complex feedback adjustment algorithms or additional compensation circuits, which simplifies the hardware design process and the difficulty of software control. At the same time, it reduces the complexity of circuit debugging and improves the reliability and mass production of the system.

[0010] Furthermore, during testing, the connecting cables between the current sensing resistor and the constant current source, and between the load winding and the acquisition circuit, have a certain internal resistance. Traditional voltage acquisition circuits will include the voltage drop caused by the cable internal resistance in the acquired value, resulting in inflated measurements of the current sensing resistor voltage and the load winding voltage. In this solution, the calibrable integrating amplifier circuit directly acquires and integrates the current sensing resistor voltage and the load winding voltage. Combined with a calibration algorithm, it can dynamically identify and eliminate the extra voltage signal caused by the cable internal resistance, ensuring that the acquired voltage value completely corresponds to the voltage drop of the current sensing resistor or the load winding itself, thus improving the accuracy of the voltage acquisition.

[0011] Components in a circuit, such as operational amplifiers and precision resistors, can experience parameter drift due to changes in ambient temperature (e.g., input offset voltage of the operational amplifier, temperature coefficient of resistance of resistors), leading to deviations in voltage amplification. This is especially problematic during wide-range measurements, where the amplification error caused by temperature drift accumulates further with range changes. A calibrable integrating amplifier circuit can dynamically correct amplification deviations caused by component temperature drift through periodic or real-time calibration, ensuring that the amplifier gain remains stable under different temperature environments and voltage ranges, thus avoiding the impact of temperature drift on voltage acquisition accuracy.

[0012] The resistance values ​​of transformer windings vary significantly. Under a fixed test current, the voltage across the load winding fluctuates over a wide range as the resistance changes. Simultaneously, the voltage across the current sensing resistor also varies with the test current. A calibrable integrating amplifier circuit utilizes its integrating amplification characteristics to achieve precise amplification of voltage signals over a wide range. It is suitable for low-noise amplification of small voltages as well as linear amplification of large voltages. Combined with calibration functions, it ensures the accuracy of the amplification factor across the entire voltage range, thereby guaranteeing the accuracy of the input signal to the ADC acquisition chip. Ultimately, this achieves high-precision measurement of the load winding and current sensing resistor voltages over a wide range, providing reliable voltage data support for DC resistance calculations.

[0013] The stable output of the constant current source circuit across the entire range provides an accurate current reference for voltage acquisition. The high-precision voltage acquisition of the calibrable integrating amplifier circuit provides reliable voltage data for DC resistance calculation. The combined effect of these two factors significantly improves the overall accuracy, stability, and range adaptability of transformer DC resistance measurement. It can be widely used in power systems, transformer production and testing, and other scenarios, and is especially suitable for occasions with high measurement accuracy requirements and complex test conditions.

[0014] As a feasible preferred solution, in the integrating amplifier circuit connected to the current sensing resistor, the voltage pin of the current sensing resistor is connected to the non-inverting input terminal of the third operational amplifier U3A, and the other voltage pin of the current sensing resistor or the low voltage terminal of the load winding is connected to the inverting input terminal of the third operational amplifier U3A. At the same time, the output terminal and the inverting input terminal of the third operational amplifier U3A are connected. The twelfth resistor and the second capacitor are connected in parallel to the output terminal and the inverting input terminal of the third operational amplifier U3A. The output voltage of the third operational amplifier U3A is filtered by the thirteenth resistor and then output to the input channel of the ADC chip.

[0015] As a feasible preferred solution, in the integrating amplifier circuit connected to both ends of the load, the high voltage end of the load winding is connected to the non-inverting input of the third operational amplifier U3B, and the low voltage end of the load winding is connected to the inverting input of the third operational amplifier U3B. The seventeenth resistor and the third capacitor are connected in parallel and then connected to the output and inverting input of the third operational amplifier U3B. The output voltage of the third operational amplifier U3B is filtered by the eighteenth resistor and then output to the input channel of the ADC chip.

[0016] As a preferred feasible solution, the voltage acquisition circuit also includes a reference voltage chip and a main control microcontroller (DAC).

[0017] As a preferred feasible embodiment, the differential amplifier circuit further includes a first resistor, a second resistor, a third resistor, and a fourth resistor; the first resistor is disposed between the non-inverting input terminal of the first operational amplifier U1A and the voltage pin of the current sensing resistor, the second resistor is disposed between the inverting input terminal of the first operational amplifier U1A and another voltage pin of the current sensing resistor, the non-inverting input terminal of the first operational amplifier U1A is grounded through the third resistor, and the fourth resistor is disposed between the inverting input terminal of the first operational amplifier U1A and the output terminal of the first operational amplifier U1A.

[0018] As a feasible preferred embodiment, the first resistor has the same resistance value as the second resistor, and the third resistor has the same resistance value as the fourth resistor.

[0019] As a feasible preferred embodiment, the gate of the first MOS transistor is connected to the output terminal of the first operational amplifier U1B, the drain is connected to the load circuit, and the source is grounded through a current sensing resistor.

[0020] As a feasible preferred embodiment, the error comparison circuit further includes a follower circuit for outputting a reference voltage, including a second operational amplifier U2A. The reference voltage is output by the microcontroller's internal DAC and connected to the non-inverting input of the second operational amplifier U2A through a sixth resistor.

[0021] As a feasible preferred embodiment, the error comparison circuit includes a fifth resistor, a seventh resistor, an eighth resistor, and a first capacitor. The fifth resistor is disposed between the output terminal of the first operational amplifier U1A and the inverting input terminal of the first operational amplifier U1B. The seventh resistor is disposed between the output terminal of the second operational amplifier U2A and the non-inverting input terminal of the first operational amplifier U1B. The eighth resistor is disposed between the first MOS transistor Q1 and the output terminal of the first operational amplifier U1B. The first capacitor is connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier U1B. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the circuit structure of the constant current source generation loop.

[0023] Figure 2 This is a schematic diagram of the circuit structure of a calibrable integrating amplifier circuit. Detailed Implementation

[0024] To make the technical solution and advantages of this application clearer, the technical solution of this utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some embodiments of this utility model, and are only used to explain this application, not to limit it. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated; they can be combined with each other to achieve better technical effects. The same reference numerals appearing in the accompanying drawings of the following embodiments represent the same features or components, and can be applied to different embodiments.

[0025] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection (including various forms of mechanical connection, such as couplings or gear pairs), or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0026] Furthermore, unless otherwise defined, the technical or scientific terms used in this description shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings: Reference Figure 1 and Figure 2 As shown, a test current and voltage acquisition circuit structure for transformer DC resistance measurement includes a constant current source generation circuit, a calibrable integrating amplifier circuit, and a voltage acquisition circuit.

[0028] Reference Figure 1 The constant current source generation circuit includes a differential amplifier circuit connected to the current sensing resistor DR1, an error comparison circuit connected to the gate of the first MOS transistor Q1, and a follower circuit for the output reference voltage.

[0029] The differential amplifier circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a first operational amplifier U1A.

[0030] In this embodiment, the first operational amplifier U1 uses a dual operational amplifier chip, including U1A and U1B, with the chip model being OPA2188.

[0031] The voltage pin (pin 2) of the current sensing resistor DR1 is connected to the non-inverting input (pin 3) of the first operational amplifier U1A through the first resistor R1, and is grounded through the third resistor R3; the other voltage pin (pin 3) of the current sensing resistor DR1 is connected to the inverting input (pin 2) of the first operational amplifier U1A through the second resistor R2, and is connected to the output (pin 1) of the first operational amplifier U1A through the fourth resistor R4.

[0032] In this embodiment, the current sensing resistor DR1 is preferably a high thermal stability four-wire resistor, specifically an ESAB PBV resistor with a resistance of 1 milliohm and a thermal stability of 50 ppm.

[0033] The first resistor R1 and the second resistor R2 preferably have the same resistance value, and the third resistor R3 and the fourth resistor R4 preferably have the same resistance value, so as to realize the differential amplification function. The differential amplification factor is determined by the ratio of the fourth resistor R4 to the second resistor R2. The output voltage of the differential amplifier circuit is equal to the product of the voltage across the current sensing resistor DR1 and the amplification factor.

[0034] The error comparison circuit includes a fifth resistor R5, a seventh resistor R7, an eighth resistor R8, a first capacitor C1, a first operational amplifier U1B, and a follower circuit consisting of a second operational amplifier U2A connected to the non-inverting input of the first operational amplifier U1B. In this embodiment, the reference voltage can be output from the microcontroller's internal DAC and connected to the non-inverting input of the second operational amplifier U2A via a sixth resistor R6. The seventh resistor R7 is positioned between the output of the second operational amplifier U2A and the non-inverting input of the first operational amplifier U1B. The voltage follower circuit includes a second operational amplifier U2A, which provides impedance isolation and voltage following functionality. In this embodiment, the second operational amplifier U2A uses an OPA2365 chip, which features low bias and low offset. The reference voltage output from the microcontroller's internal DAC is filtered by the sixth resistor R6 and then connected to the non-inverting input (pin 3) of the second operational amplifier U2A. The inverting input (pin 2) of the second operational amplifier U2A is connected to its output pin (pin 1), forming a voltage follower. Its output voltage is filtered by the seventh resistor R7 and then input to the non-inverting input of the first operational amplifier U1B. The first MOSFET Q1 is a voltage-controlled device. In this embodiment, it is preferably a high-power N-channel MOSFET, model IRFP4368. Its gate is filtered by the sixth resistor R6 and then connected to the output terminal of the first operational amplifier U1B. Its drain is connected to the load circuit, and its source is grounded through the current-sensing resistor DR1. By adjusting the gate voltage, the magnitude of the drain current is controlled to achieve constant current output. The eighth resistor is placed between the first MOSFET Q1 and the output terminal of the first operational amplifier U1B.

[0035] The output voltage of the differential amplifier circuit is filtered by the fifth resistor R5 and then connected to the inverting input terminal (pin 6) of the first operational amplifier U1B in the error comparator circuit; the first capacitor C1 is connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier U1B to filter out high-frequency signal interference.

[0036] Positional relationship and working principle of constant current source generation circuit: The load (transformer winding), the first MOSFET Q1, and the sampling resistor DR1 are connected in series to form the main current loop, and the loop current is equal to the current flowing through the sampling resistor.

[0037] The loop current is sampled by the first sampling resistor DR1. The loop current value is amplified and converted into a feedback voltage value. After high-frequency signal interference is filtered out by the RC filter network composed of the fifth resistor R5 and the first capacitor C1, it is compared with the reference voltage output by the DAC inside the microcontroller after passing through a follower. The difference is amplified by the first operational amplifier U1B and output as a gate drive voltage. After being filtered by the sixth resistor R6, it is connected to the gate (pin 1) of the first MOS transistor Q1.

[0038] The first MOSFET Q1 is a field-effect transistor, a voltage-controlled device. It modulates the drain current by adjusting the gate voltage, thereby controlling the output value of the DAC inside the microcontroller to control the current in the circuit.

[0039] In this embodiment, resistors R1 and R2 in the differential amplifier circuit are 1KΩ, and resistors R3 and R4 are 50KΩ. The amplification factor of this differential amplifier circuit is 50 times, and the output voltage of the microcontroller's internal DAC is stable and less than 10ppm when the voltage range is 50-3000mV. According to the working principle of this constant current source generation circuit, when the amplification factor of the differential amplifier circuit is 50 times, the voltage range that can be output with high stability is (1-60)A.

[0040] In this embodiment, the DC resistance of the power transformer is inversely proportional to its capacity; the larger the capacity, the smaller the DC resistance. The minimum DC resistance on the low-voltage side of the power transformer is in the milliohm range. A large current excitation is used when the DC resistance is small, and a small current excitation is used when the DC resistance is large. This maintains the voltage across the winding within a suitable range for measurement, with the maximum voltage drop across the winding in the tens of millivolts. Furthermore, since the on-resistance Rds(on) of the first modulation transistor Q1 is also in the milliohm range when operating in the linear region, its drain-source voltage is 0.3 volts. The voltage drop across the current sensing resistor is also small during the full current range. Due to the long measurement transmission cable and its high resistance, the maximum voltage drop is 1 volt. In this constant current source generation circuit, a PTH08T250W switching power supply is used at the front end, with an output voltage set to 1.5V.

[0041] Reference Figure 2 The calibrable integrating amplifier circuit includes an integrating amplifier circuit connected to both ends of the load and an integrating amplifier circuit connected to the current sensing resistor.

[0042] The integrating amplifier circuit connected to the load consists of a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a second capacitor C2, and a third operational amplifier U3A, which realizes the integration amplification and filtering functions of the voltage across the load.

[0043] The integrating amplifier circuit connected to the current sensing resistor has a similar structure to the integrating amplifier circuit connected to both ends of the load. It consists of the fourteenth resistor R14, the fifteenth resistor R15, the sixteenth resistor R16, the seventeenth resistor R17, the third capacitor C3, and the third operational amplifier U3B, which realizes the integration amplification and filtering of the current sensing resistor voltage.

[0044] The voltage acquisition circuit includes an ADC chip, a reference voltage chip, and a main control microcontroller. In this embodiment, the third operational amplifier U3 uses a dual operational amplifier chip, model AD8629, which includes U3A and U3B.

[0045] In this embodiment, the voltage acquisition circuit uses an ADS1256 ADC chip with 24-bit resolution, and a REF5025 reference voltage chip, outputting an accurate 2.5V voltage to the external reference voltage pin of the ADS1256. The voltage acquisition range of the ADS1256 is 0-5V. The main controller uses an STM32F407 microcontroller. Data transmission and control with the ADS1256 are achieved via software SPI. In this example, the integrating amplifier circuit, after setting an appropriate amplification factor, uses a source meter to input a highly stable voltage signal. After integration, amplification, and filtering, the signal is input to the voltage acquisition channel of the ADS1256 chip. By changing the input highly stable voltage signal and the different measured voltage signal values ​​of the ADS1256 chip, the amplification linearity of the integrating amplifier circuit can be calibrated using the actual and measured values.

[0046] Positional relationship and working principle of calibrable integrating amplifier circuit: The voltage pin (pin 2) of the current sensing resistor DR1 is connected to the non-inverting input (pin 3) of the third operational amplifier U3A through the ninth resistor R9. The non-inverting input is then connected to ground through the eleventh resistor R11. The voltage pin (pin 3) of the current sensing resistor DR1 is connected to the inverting input (pin 2) of the third operational amplifier U3A through the tenth resistor R10. The twelfth resistor R12 and the second capacitor C2 are connected in parallel to the output (pin 1) and the inverting input (pin 2) of the third operational amplifier U3A. The output voltage of the third operational amplifier U3A is filtered by the thirteenth resistor R13 and then output to the input channel of the ADC chip.

[0047] The high-voltage end of the load winding is connected to the non-inverting input (pin 3) of the third operational amplifier U3B through the fourteenth resistor R14. The non-inverting input is then connected to ground through the sixteenth resistor R16. The low-voltage end of the load winding is connected to the inverting input (pin 2) of the third operational amplifier U3B through the fifteenth resistor R15. The seventeenth resistor R17 and the third capacitor C3 are connected in parallel to the output (pin 1) and the inverting input (pin 2) of the third operational amplifier U3B. The output voltage of the third operational amplifier U3B is filtered by the eighteenth resistor R18 and then output to the input channel of the ADC chip.

[0048] The voltage signals across the current sensing resistor and the load are acquired by two integrating amplifier circuits.

[0049] After setting an appropriate amplification factor, the integrating amplifier circuit uses a source meter to input a highly stable voltage signal at the input terminal. After integration, amplification, and filtering, the signal is input to the voltage acquisition channel of the ADC chip.

[0050] By changing the input high-stability voltage signal and the different measured voltage signal values ​​of the ADC chip, the amplification linearity relationship of the integrating amplifier circuit is calibrated by comparing the actual value with the measured value.

[0051] The above content is merely an embodiment of this utility model. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can improve and implement this solution based on the guidance provided in this application and their own capabilities. Typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of this utility model. These should also be considered within the scope of protection of this utility model, and will not affect the effectiveness of the implementation of this utility model or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A test current and voltage acquisition circuit structure for measuring the DC resistance of a transformer, characterized in that: include: The circuit comprises a constant current source generating circuit, a calibrable integrating amplifier circuit, and a voltage acquisition circuit. The constant current source generating circuit includes a differential amplifier circuit connected to a current sensing resistor and an error comparator circuit connected to the gate of a first MOS transistor. The voltage pin of the current sensing resistor is connected to the non-inverting input of the first operational amplifier U1A in the differential amplifier circuit. The other voltage pin of the current sensing resistor is connected to the inverting input of the first operational amplifier U1B in the error comparator circuit, and also to the output of the first operational amplifier U1B. The output of the first operational amplifier U1A is connected to the inverting input of the first operational amplifier U1B. The calibrable integrating amplifier circuit includes an integrating amplifier circuit connected to the current sensing resistor and an integrating amplifier circuit connected to both ends of the load. The output of the calibrable integrating amplifier circuit is connected to the input channel of the ADC acquisition chip in the voltage acquisition circuit.

2. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 1, characterized in that: In the integrating amplifier circuit connected to the current sensing resistor, the voltage pin of the current sensing resistor is connected to the non-inverting input of the third operational amplifier U3A, and the other voltage pin of the current sensing resistor or the low voltage end of the load winding is connected to the inverting input of the third operational amplifier U3A. At the same time, it is connected to the output and inverting input of the third operational amplifier U3A. The twelfth resistor and the second capacitor are connected in parallel to the output and inverting input of the third operational amplifier U3A. The output voltage of the third operational amplifier U3A is filtered by the thirteenth resistor and then output to the input channel of the ADC chip.

3. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 1, characterized in that: In the integrating amplifier circuit connected to both ends of the load, the high voltage end of the load winding is connected to the non-inverting input of the third operational amplifier U3B, and the low voltage end of the load winding is connected to the inverting input of the third operational amplifier U3B. The seventeenth resistor and the third capacitor are connected in parallel to the output and inverting input of the third operational amplifier U3B. The output voltage of the third operational amplifier U3B is filtered by the eighteenth resistor and then output to the input channel of the ADC chip.

4. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 1, characterized in that: The voltage acquisition circuit also includes a reference voltage chip and a main control microcontroller.

5. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 1, characterized in that: The differential amplifier circuit further includes a first resistor, a second resistor, a third resistor, and a fourth resistor; the first resistor is disposed between the non-inverting input terminal of the first operational amplifier U1A and the voltage pin of the current sensing resistor, the second resistor is disposed between the inverting input terminal of the first operational amplifier U1A and another voltage pin of the current sensing resistor, the non-inverting input terminal of the first operational amplifier U1A is grounded through the third resistor, and the fourth resistor is disposed between the inverting input terminal of the first operational amplifier U1A and the output terminal of the first operational amplifier U1A.

6. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 5, characterized in that: The first resistor has the same resistance value as the second resistor, and the third resistor has the same resistance value as the fourth resistor.

7. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 1, characterized in that: The gate of the first MOS transistor is connected to the output of the first operational amplifier U1B, the drain is connected to the load circuit, and the source is grounded through a current sensing resistor.

8. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 7, characterized in that: The error comparison circuit also includes a follower circuit for outputting a reference voltage, including a second operational amplifier U2A. The reference voltage is output by the microcontroller's internal DAC and connected to the non-inverting input of the second operational amplifier U2A through a sixth resistor.

9. The test current and voltage acquisition circuit structure for transformer DC resistance measurement according to claim 8, characterized in that: The error comparison circuit includes a fifth resistor, a seventh resistor, an eighth resistor, and a first capacitor. The fifth resistor is located between the output terminal of the first operational amplifier U1A and the inverting input terminal of the first operational amplifier U1B. The seventh resistor is located between the output terminal of the second operational amplifier U2A and the non-inverting input terminal of the first operational amplifier U1B. The eighth resistor is located between the first MOS transistor Q1 and the output terminal of the first operational amplifier U1B. The first capacitor is connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier U1B.

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