A weak error current measuring device and method based on magnetic potential balance

Abstract

This invention discloses a device and method for measuring weak error current based on magnetomotive force balance. The method includes: a feedback loop consisting of a magnetomotive force balance device, a phase shifter, a first DA sampling module, a second DA sampling module, an AD sampling module, an adder, a filter, an amplifier, and a control module; and a closed-loop feedback optimization control strategy to control and adjust the constructed quadrature and in-phase components, indirectly measuring the amplitude and phase of the weak output error current, thereby calculating the error of the weak output current transformer. This invention improves the accuracy of weak output current transformer error measurement and overcomes the shortcomings and technical limitations of existing analog and digital comparison methods in weak output current transformer error measurement.

Description

Technical Field

[0001] This invention relates to the field of precision measurement technology, and more specifically, to a device and method for measuring weak error current based on magnetomotive force balance. Background Technology

[0002] In the field of current transformer error measurement technology, there are currently two main methods: analog comparison and digital comparison. The analog comparison method measures the error by taking the secondary standard current and the difference between the secondary standard current and the secondary test current. A typical representative device is the electrical transformer calibrator. Most electronic transformer calibrators on the market also use the analog comparison method. The secondary standard current input is generally designed to be 1A or 5A. When the secondary standard current input is designed to be 1mA or 5mA, the difference between the secondary standard current and the secondary test current becomes smaller and easily drowned out by noise. The sampling technology for this difference is too demanding, thus the analog comparison method presents technical challenges for measuring the error of low-output current transformers. The digital comparison method measures the error directly by taking the secondary standard current and the secondary test current. However, the measurement accuracy is affected by power supply fluctuations, sampling accuracy, and inherent channel errors, making it technically challenging to meet the high-precision error measurement requirements of low-output current transformers. Both of these measurement devices have limitations in achieving error measurement of low-output current transformers.

[0003] Therefore, there is a need for a precision measurement device and method for the weak error current based on magnetomotive force balance. Summary of the Invention

[0004] This invention proposes a device and method for measuring weak error current based on magnetomotive force balance, in order to solve the problem of how to improve the measurement level of weak error current.

[0005] To address the aforementioned problems, according to one aspect of the present invention, a weak error current measurement device based on magnetomotive force balance is provided. The device comprises: a magnetomotive force balance device, a standard current transformer, a current transformer under test, a phase shifter, a first DA sampling module, a second DA sampling module, an AD sampling module, an adder, a filter, an amplifier, and a control module; wherein... The magnetic potential balancing device is used to balance the secondary current I of a standard current transformer. N and the secondary current I of the current transformer under test X This causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage; The standard current transformer is used to output the reference current I of the reference winding. REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively. The first DA sampling module is used to acquire the in-phase voltage component based on the reference voltage; The phase shifter is used to obtain quadrature voltage components based on the reference voltage; The adder is used to add the in-phase voltage component and the quadrature voltage component and then input them to the magnetomotive force balance device. The amplifier is used to amplify the unbalanced voltage and then input it to the filter; The filter is used to filter the input signal before it is input to the AD sampling module; The control module is used to update the output signals of the first DA sampling module and the second DA sampling module based on the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

[0006] Preferably, the filter is a two-stage low-pass filter, and the filter's transfer function is: , in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

[0007] Preferably, the control module updates the output signals of the first DA sampling module and the second DA sampling module using a half-lookup table method.

[0008] Preferably, the relationship between the in-phase voltage component and the reference voltage is as follows: , , The relationship between the quadrature voltage components and the reference voltage is as follows: , in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. τs represents the proportional adjustment coefficient of the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the main traffic lane. is the time constant; s is the complex frequency variable.

[0009] Preferably, the device further includes: A communication device, connected to the control module, is used to set the control parameters of the control module and display the current error.

[0010] According to another aspect of the present invention, a method for measuring weak error current based on magnetopotential balance is provided, the method comprising: Using a magnetomotive force balancing device, based on the secondary current I of a standard current transformer N and the secondary current I of the current transformer under test X This causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage; Using a standard current transformer, the reference current I of the output reference winding is... REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively. Using the first DA sampling module, the in-phase voltage component is obtained based on the reference voltage; Using a phase shifter, quadrature voltage components are obtained based on the reference voltage; The in-phase voltage component and the quadrature voltage component are added together using an adder and then input to the magnetomotive force balance device. An amplifier is used to amplify the unbalanced voltage before it is input to a filter. The input signal is filtered and then input to the AD sampling module. The control module updates the output signals of the first and second DA sampling modules based on the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

[0011] Preferably, the filter is a two-stage low-pass filter, and the filter's transfer function is: , in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

[0012] Preferably, the method further includes: The output signals of the first DA sampling module and the second DA sampling module are updated using the control module and the half-lookup table method.

[0013] Preferably, the relationship between the in-phase voltage component and the reference voltage is as follows: , , The relationship between the quadrature voltage components and the reference voltage is as follows: , in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. τs represents the proportional adjustment coefficient of the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the main traffic lane. is the time constant; s is the complex frequency variable.

[0014] This invention provides a device and method for measuring weak error current based on magnetomotive force balance. The method includes: a feedback loop consisting of a magnetomotive force balance device, a phase shifter, a first DA sampling module, a second DA sampling module, an AD sampling module, an adder, a filter, an amplifier, and a control module; and a closed-loop feedback optimization control strategy to control and adjust the constructed quadrature and in-phase components, indirectly measuring the amplitude and phase of the weak output error current, thereby calculating the error of the weak output current transformer. This invention improves the accuracy of weak output current transformer error measurement and overcomes the shortcomings and technical limitations of existing analog and digital comparison methods in weak output current transformer error measurement. Attached Figure Description

[0015] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 This is a schematic diagram of the structure of a weak error current measuring device 100 based on magnetopotential balance according to an embodiment of the present invention. Figure 2This is a structural diagram of a weak error current measuring device based on magnetomotive force balance according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the measurement principle according to an embodiment of the present invention; Figure 4 This is a flowchart of a method 400 for measuring weak error current based on magnetopotential balance according to an embodiment of the present invention. Detailed Implementation

[0016] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0017] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0018] Figure 1 This is a schematic diagram of the structure of a weak error current measuring device 100 based on magnetopotential balance according to an embodiment of the present invention. Figure 1As shown, the weak error current measurement device based on magnetomotive force balance provided by the embodiments of the present invention comprises a magnetomotive force balance device, a phase shifter, a first DA sampling module, a second DA sampling module, an AD sampling module, an adder, a filter, an amplifier, and a control module forming a feedback loop. Through a closed-loop feedback optimization control strategy, the orthogonal and in-phase components of the constructed structure are controlled and adjusted to indirectly measure the amplitude and phase of the weak output error current, thereby calculating the error of the weak output current transformer. The method of the present invention improves the accuracy of weak output current transformer error measurement and overcomes the shortcomings and technical limitations of existing analog comparison methods and digital comparison methods in weak output current transformer error measurement. The weak error current measurement device 100 based on magnetomotive force balance provided by the embodiments of the present invention includes: a magnetomotive force balance device 101, a standard current transformer 102, a current transformer under test 103, a phase shifter 104, a first DA sampling module 105, a second DA sampling module 106, an AD sampling module 107, an adder 108, a filter 109, an amplifier 110, and a control module 111. The primary side of the magnetomotive force balancing device has a first proportional winding connected to the secondary terminals of a standard current transformer and the current transformer under test, respectively. The primary side of the magnetomotive force balancing device has a second proportional winding connected to an adder and a ground terminal, respectively. One end of the reference winding on the secondary side of the standard current transformer is grounded, and the other end is connected to a phase shifter and a first DA sampling module, respectively. The first DA sampling module is connected to the magnetomotive force balancing device through the adder. The phase shifter is connected to the adder through a second DA sampling module. The secondary winding of the magnetomotive force balancing device is connected in sequence through an amplifier, a filter, an AD sampling module, and a control module. The control module is also connected to the first DA sampling module and the second DA sampling module. The magnetomotive force balancing device, the phase shifter, the first DA sampling module, the second DA sampling module, the AD sampling module, the adder, the filter, the amplifier, and the control module form a feedback loop.

[0019] Preferably, the magnetomotive force balancing device is used to balance the secondary current I of a standard current transformer. N and the secondary current I of the current transformer under test X This causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage.

[0020] Preferably, the standard current transformer is used to output the reference current I of the reference winding. REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively.

[0021] Preferably, the first DA sampling module is used to obtain the in-phase voltage component based on the reference voltage.

[0022] Preferably, the phase shifter is used to obtain quadrature voltage components based on the reference voltage.

[0023] Preferably, the adder is used to add the in-phase voltage component and the quadrature voltage component and then input them to the magnetomotive force balancing device.

[0024] Preferably, the amplifier is used to amplify the unbalanced voltage before inputting it to the filter.

[0025] Preferably, the filter is used to filter the input signal before it is input to the AD sampling module.

[0026] Preferably, the filter is a two-stage low-pass filter, and the filter's transfer function is: , in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

[0027] Preferably, the control module is used to update the output signals of the first DA sampling module and the second DA sampling module according to the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

[0028] Preferably, the control module updates the output signals of the first DA sampling module and the second DA sampling module using a half-lookup table method.

[0029] Preferably, the relationship between the in-phase voltage component and the reference voltage is as follows: , , The relationship between the quadrature voltage components and the reference voltage is as follows: , in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. τs represents the proportional adjustment coefficient of the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the main traffic lane. is the time constant; s is the complex frequency variable.

[0030] Preferably, the device further includes: A communication device, connected to the control module, is used to set the control parameters of the control module and display the current error.

[0031] In this invention, in order to improve the accuracy of error measurement of weak output current transformer, a closed-loop feedback control strategy is designed to continuously adjust the phase and amplitude of the constructed error current until the constructed vector and the test weak error current achieve zero magnetic flux in the magnetomotive force balancing device. At this time, the constructed current vector and the test weak error current are exactly equal in magnitude and opposite in direction, thereby indirectly measuring the error of the weak output current transformer.

[0032] Combination Figure 2 As shown, in this invention, the measuring device mainly includes: a magnetomotive force balancing device, a phase shifter, an AD sampling module, two DA sampling modules, an adder, a filter, an amplifier, a control module, and a connection cable with high shielding performance. The control module can be an STM32 controller.

[0033] like Figure 2 As shown, in this invention, a weak output standard current transformer (CT) is used. N The secondary current I of the proportional winding N and weak output current transformer CT X The secondary current I of the second proportional winding X When connected to a magnetomotive force balancing device, the zero-detection winding of the magnetomotive force balancing device will output a voltage U. d The current I in the reference winding of a standard current transformer. REF The reference current I is obtained through the sampling resistor. REF The voltage is converted into a reference voltage, which directly enters the AD sampling module to obtain an in-phase component with adjustable magnitude. The reference voltage passes through a phase shifter and then enters the AD sampling module to obtain an orthogonal component with adjustable magnitude. The in-phase and orthogonal components pass through an adder and then enter the magnetomotive force balance device.

[0034] like Figure 3As shown, in the design of a high-precision calibrator, the core to achieving stable and accurate output lies in closed-loop feedback control. The feedback loop is mainly divided into two parts: the acquisition of the zero-detection signal from the magnetomotive force balance device and the output of the zero-adjustment signal from the control module. In the actual control process, the in-phase orthogonal components are placed in the inner loop of the control feedback loop, that is, the output of the zero-adjustment signal is in the inner loop, and the zero-detection voltage signal from the magnetomotive force balance device is placed in the outer loop of the control feedback loop, that is, the acquisition of the zero-detection signal from the magnetomotive force balance device is in the outer loop.

[0035] In the feedback system, the output voltage of the outer loop zero-detection winding is used as the feedback signal, and the zero-detection voltage U d First, the signal is amplified by a factor of K by a programmable amplifier, and then input to the ADC through a filter. To ensure the accuracy of the sampled signal and enhance the filtering effect, a two-stage second-order low-pass filter is used. The transfer function of the filter is shown in equation (1). (1) in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

[0036] During measurement, the initial comparator zero-detection output signal is first passed through a process-controlled amplifier and filter to an A / D sampler to obtain the sampling data code CODE. The STM32 then updates the output signals of the two digital-to-analog converters (DACs) using a half-lookup table method based on the sampling results. The two signals are then vector-synthesized to obtain the output zero-adjustment signal ΔI. X Compare with the differential signal ΔI until ΔI = -ΔI X This means that the zero-detection signal output of the zero-detection instrument is 0.

[0037] During sampling, the ADC has a sampling voltage Ur within a certain range. Voltage Ud is used as the unbalanced voltage, and the sampling voltage Ur is related to this voltage Ud. d The ratio is used to represent the effect of the unbalanced voltage Ud on the output results of the two DACs. The in-phase voltage ΔU f and orthogonal voltage ΔU δ The reference voltage Uref is proportional to the secondary reference current of the current transformer. Therefore, the proportional adjustment coefficients of the in-phase channel and the quadrature channel are set to k1 and k2, respectively. At this time, formulas (2) and (3) are used to represent the in-phase and quadrature voltages, respectively. A1 is used to represent the relationship between the in-phase voltage and the reference voltage, and A2 is used to represent the relationship between the quadrature voltage and the reference voltage. 1 / (1+τs) in A2 represents the transfer function of the 90º phase shifter in the quadrature channel. Formula (4) represents the result of adding the in-phase and quadrature voltages, and formula (5) represents the unbalanced voltage U. d The relationships between voltage ΔU and voltage are as follows: (2) in, ; (3) in, ; (4) in, ; (5) in, .

[0038] Wherein, the angular frequency of the filter is ω n , representing the undamped oscillation frequency of the system; ξ The damping ratio represents the degree of damping of the system, affecting its stability and response speed. The parameter values ​​after actual debugging are as follows: ω n =862.58 rad / s; ξ =5.80E+05. The phase shifter is a quadrature phase shifter. τ =0.0032, the amplification factor K of the programmable amplifier ranges from 1 to 64. 3 The device uses a standard reference voltage of 100V or 57.7V, which is converted to a voltage range of 0.7V to 7.2V via a potential transformer and operational amplifier. The supply voltage can be selected as ±10V or ±5V depending on the application. The values ​​of A1 and A2, determined by k1 and k2, are in the range of 0 to 1.

[0039] In addition, in this invention, the control parameters of the control module and the current error can be set and displayed through a communication device.

[0040] This invention continuously adjusts the phase and amplitude of the constructed error current by designing a closed-loop feedback control strategy until the constructed vector and the weak error current of the test subject achieve zero magnetic flux in the magnetomotive force balancing device. This indirect measurement method improves the measurement level of the weak error current.

[0041] Figure 4 This is a flowchart of a weak error current measurement method 400 based on magnetopotential balance according to an embodiment of the present invention. Figure 4 As shown, the weak error current measurement method 400 provided by the embodiment of the present invention, based on the weak error current measurement device based on magnetic potential balance as described above, includes: Step 401: Using a magnetomotive force balancing device, based on the secondary current I of the standard current transformer... N and the secondary current I of the current transformer under test XThis causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage; Step 402: Using a standard current transformer, output the reference current I of the reference winding. REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively. Step 403: Using the first DA sampling module, obtain the in-phase voltage component based on the reference voltage; Step 404: Using a phase shifter, obtain the quadrature voltage components based on the reference voltage; Step 405: Using an adder, the in-phase voltage component and the quadrature voltage component are added together and then input to the magnetomotive force balancing device. Step 406: Using an amplifier, the unbalanced voltage is amplified and then input to the filter; Step 407: The input signal is filtered using a filter and then input to the AD sampling module; Step 408: Using the control module, update the output signals of the first DA sampling module and the second DA sampling module based on the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

[0042] Preferably, the filter is a two-stage low-pass filter, and the filter's transfer function is: , in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

[0043] Preferably, the method further includes: The output signals of the first DA sampling module and the second DA sampling module are updated using the control module and the half-lookup table method.

[0044] Preferably, the relationship between the in-phase voltage component and the reference voltage is as follows: , , The relationship between the quadrature voltage components and the reference voltage is as follows: , in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. This is the proportional adjustment coefficient for the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the positive traffic lane; is the time constant; s is the complex frequency variable.

[0045] Preferably, the method further includes: Using communication equipment, the control parameters of the control module are set and the current error is displayed.

[0046] The weak error current measurement method 400 based on magnetopotential balance in one embodiment of the present invention corresponds to the weak error current measurement device 100 based on magnetopotential balance in another embodiment of the present invention, and will not be described again here.

[0047] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0048] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated otherwise.

[0049] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0050] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0051] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0052] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A device for measuring weak error current based on magnetomotive force balance, characterized in that, The equipment includes: a magnetomotive force balancing device, a standard current transformer, a current transformer under test, a phase shifter, a first DA sampling module, a second DA sampling module, an AD sampling module, an adder, a filter, an amplifier, and a control module; wherein, The magnetic potential balancing device is used to balance the secondary current I of a standard current transformer. N and the secondary current I of the current transformer under test X This causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage; The standard current transformer is used to output the reference current I of the reference winding. REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively. The first DA sampling module is used to acquire the in-phase voltage component based on the reference voltage; The phase shifter is used to obtain quadrature voltage components based on the reference voltage; The adder is used to add the in-phase voltage component and the quadrature voltage component and then input them to the magnetomotive force balance device. The amplifier is used to amplify the unbalanced voltage and then input it to the filter; The filter is used to filter the input signal before it is input to the AD sampling module; The control module is used to update the output signals of the first DA sampling module and the second DA sampling module based on the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

2. The device according to claim 1, characterized in that, The filter is a two-stage low-pass filter, and its transfer function is: ， in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

3. The device according to claim 1, characterized in that, The control module uses a 1 / 2 lookup table method to update the output signals of the first DA sampling module and the second DA sampling module.

4. The device according to claim 1, characterized in that, The relationship between the in-phase voltage component and the reference voltage is as follows: ， ， The relationship between the quadrature voltage components and the reference voltage is as follows: ， in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. τs represents the proportional adjustment coefficient of the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the main traffic lane. is the time constant; s is the complex frequency variable.

5. The device according to claim 1, characterized in that, The device also includes: A communication device, connected to the control module, is used to set the control parameters of the control module and display the current error.

6. A method for measuring weak error current based on magnetomotive force balance, characterized in that, The method includes: Using a magnetomotive force balancing device, based on the secondary current I of a standard current transformer N and the secondary current I of the current transformer under test X This causes the zero-detection winding on the secondary side of the magnetomotive force balancing device to output an unbalanced voltage; Using a standard current transformer, the reference current I of the output reference winding is... REF And the reference current I is obtained through the sampling resistor. REF After being converted into a reference voltage, the voltage is input to the first DA sampling module and the phase shifter, respectively. Using the first DA sampling module, the in-phase voltage component is obtained based on the reference voltage; Using a phase shifter, quadrature voltage components are obtained based on the reference voltage; The in-phase voltage component and the quadrature voltage component are added together using an adder and then input to the magnetomotive force balance device. An amplifier is used to amplify the unbalanced voltage before it is input to a filter. The input signal is filtered and then input to the AD sampling module. The control module updates the output signals of the first and second DA sampling modules based on the sampling results of the AD sampling module, thereby controlling the zero-adjustment signal ΔI on the second proportional winding of the magnetomotive force balancing device. X Until the differential current signal ΔI on the first proportional winding satisfies ΔI = -ΔI X At that time, the zero-detection signal of the magnetomotive force balance device is 0, and the zero-adjustment signal ΔI is determined. X This is for current error.

7. The method according to claim 6, characterized in that, The filter is a two-stage low-pass filter, and its transfer function is: ， in, Let be the transfer function of the filter; ξ is the angular frequency of the filter; ξ is the damping ratio; It is a complex frequency variable.

8. The method according to claim 6, characterized in that, The method further includes: The output signals of the first DA sampling module and the second DA sampling module are updated using the control module and the half-lookup table method.

9. The method according to claim 6, characterized in that, The relationship between the in-phase voltage component and the reference voltage is as follows: ， ， The relationship between the quadrature voltage components and the reference voltage is as follows: ， in, A1 is the in-phase voltage component; A2 is the first relationship coefficient. Reference voltage; This is the proportional adjustment coefficient for the in-phase channel; This represents the amplifier's gain. This is an unbalanced voltage; The sampling voltage of the AD sampling module; A1 represents the orthogonal voltage components; A2 represents the second relationship coefficient. τs represents the proportional adjustment coefficient of the main traffic lane; 1 / (1+τs) represents the transfer function of the 90° phase shifter in the main traffic lane. is the time constant; s is the complex frequency variable.

10. The method according to claim 6, characterized in that, The method further includes: Using communication equipment, the control parameters of the control module are set and the current error is displayed.

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