Electric energy metering system and method with magnetic field immunity

Abstract

The application discloses a kind of electric energy metering system and method with magnetic field anti-interference ability, belong to electric energy metering technical field.The system includes current connection terminal, multi-winding current transformer, first analog-digital conversion unit, voltage connection terminal, voltage division conversion unit, second analog-digital conversion unit and electric energy metering unit, further include external magnetic field detection unit, active compensation control unit and micro power amplifier.The multi-winding current transformer of the application adopts the structure of double magnetic core+multi-winding, which can effectively detect magnetic field interference current, and also can realize accurate compensation, and has the advantages of simple structure, small size, etc.The active compensation control unit of the application accurately extracts interference signals through multi-stage feedback filter and four-stage comb filter, and combines active compensation control, which can effectively suppress the interference components in the difference current and ensure the accuracy of measurement.

Description

Technical Field

[0001] This invention belongs to the field of electrical energy metering technology, specifically relating to an electrical energy metering system and method with magnetic field anti-interference capability. Background Technology

[0002] Electricity metering equipment is the core tool for settlement between power companies and users, and its accuracy directly affects the economic interests of both parties. Accurate electricity metering is not only crucial for individual electricity bill settlement, but also a vital foundation for the efficient operation of the power system, energy transition, and social governance. The basic principle of electricity metering is to collect voltage and current signals from the power grid in real time, convert analog quantities into digital signals, and then perform electricity calculations.

[0003] Current high-precision electricity metering equipment requires signal conversion via current transformers when measuring phase current. However, when the installation spacing of three-phase current transformers is insufficient or the protection measures are inadequate, the alternating magnetic field generated by the phase current will couple to the secondary windings of the current transformers of adjacent phases, forming magnetic field interference current (mainly including power frequency (50Hz) and its third harmonic (150Hz), which together account for more than 98%), causing distortion of the secondary current signal and affecting the overall accuracy of electricity metering.

[0004] To address the aforementioned issues, a common solution is to construct a Faraday cage inside the electricity metering equipment using highly conductive materials such as copper mesh and aluminum foil, utilizing the principle of electromagnetic induction to attenuate external magnetic field interference. For example, Chinese invention patent application CN119534969A proposes a high-precision current sensing circuit and current transformer with electromagnetic interference resistance, which uses a metal shielding box to protect the sensor. The design of the metal shielding box is based on the principle of the Faraday cage, providing a closed conductive shielding layer to block external electromagnetic field interference. However, this approach has the following limitations: the shielding effect is limited by the magnetic field attenuation capability and dynamic response characteristics of the shielding material, making it difficult to meet high-level metering requirements. It also suffers from problems such as large size, high manufacturing process requirements, and low yield. Summary of the Invention

[0005] This invention proposes an electrical energy metering system and method with magnetic field anti-interference capability. Its purpose is to solve the problems of existing solutions, such as failure to meet metering accuracy requirements, large size, complex process, and low yield.

[0006] The technical solution of this invention is as follows:

[0007] An energy metering system with magnetic field anti-interference capability includes a current terminal block, a current transformer, a first analog-to-digital converter, a voltage terminal block, a voltage divider converter, a second analog-to-digital converter, and an energy metering unit.

[0008] The current terminal is connected to the primary winding of the current transformer, the secondary winding of the current transformer is connected to the input terminal of the first analog-to-digital converter, and the output terminal of the first analog-to-digital converter is connected to the current input terminal of the energy metering unit.

[0009] The input terminal of the voltage divider conversion unit is connected to the voltage terminal block, and the output terminal is connected to the input terminal of the second analog-to-digital converter unit. The output terminal of the second analog-to-digital converter unit is connected to the voltage input terminal of the energy metering unit.

[0010] The current transformer is a multi-winding current transformer, which further includes a main magnetic core, an auxiliary magnetic core, a compensation winding, and a primary and secondary differential winding. The main magnetic core and the auxiliary magnetic core are arranged side by side. The primary winding is wound on both the main magnetic core and the auxiliary magnetic core, and the secondary winding is wound on both the main magnetic core and the auxiliary magnetic core in the opposite direction to the primary winding. The compensation winding is wound on the main magnetic core, and the primary and secondary differential winding is wound on the auxiliary magnetic core.

[0011] The primary and secondary differential windings are connected to the compensation windings in sequence through an external magnetic field detection unit, an active compensation control unit, and a miniature power amplifier to form a current compensation control loop. The current compensation control loop is used to compensate the magnetic flux of the main magnetic core based on the difference between the current in the primary winding and the corresponding primary side current in the secondary winding, thereby canceling the interference of the external magnetic field on the current in the secondary winding.

[0012] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the main magnetic core is a power magnetic core, and the auxiliary magnetic core is a high-permeability magnetic core.

[0013] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the main magnetic core is a Class A silicon steel sheet magnetic core with a saturation magnetic flux greater than 1T, and the auxiliary magnetic core is a wound magnetic core made of iron-based amorphous or nanocrystalline material.

[0014] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the external magnetic field detection unit includes an operational amplifier OP1, a capacitor C2, and a resistor R3;

[0015] The inverting input terminal of the operational amplifier OP1 is the input terminal of the external magnetic field detection unit; the inverting input terminal of the operational amplifier OP1 is also connected to the output terminal of the operational amplifier OP1 through a parallel capacitor C2 and a resistor R3; the non-inverting input terminal of the operational amplifier OP1 is grounded; the output terminal of the operational amplifier OP1 is the output terminal of the external magnetic field detection unit.

[0016] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the active compensation control unit includes a 50Hz multi-stage feedback filter, a 150Hz multi-stage feedback filter, and an operational amplifier OP4.

[0017] The input terminal of the active compensation control unit is connected to the input terminals of both the 50Hz multi-stage feedback filter and the 150Hz multi-stage feedback filter. The output terminals of both the 50Hz and 150Hz multi-stage feedback filters are connected to the input terminals of the operational amplifier OP4. The output terminal of the operational amplifier OP4 is the output terminal of the active compensation control unit.

[0018] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the 50Hz multi-stage feedback filter includes operational amplifier OP2, resistor R7, resistor R10, resistor R2, capacitor C3, and capacitor C1;

[0019] The input of the 50Hz multi-stage feedback filter is grounded via resistors R7 and R10. The connection point between resistors R7 and R10 is connected to the inverting input of operational amplifier OP2 via capacitor C3, and also to the output of operational amplifier OP2 via capacitor C1. The inverting input of operational amplifier OP2 is also connected to the output of operational amplifier OP2 via resistor R2. The non-inverting input of operational amplifier OP2 is grounded. The output of operational amplifier OP2 is the output of the 50Hz multi-stage feedback filter.

[0020] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the 150Hz multi-stage feedback filter includes operational amplifier OP3, resistors R14, R15, and R12, capacitors C6 and C5.

[0021] The input of the 150Hz multi-stage feedback filter is grounded via resistors R14 and R15. The connection point between resistors R14 and R15 is connected to the inverting input of operational amplifier OP3 via capacitor C6, and also to the output of operational amplifier OP3 via capacitor C5. The inverting input of operational amplifier OP3 is also connected to the output of operational amplifier OP3 via resistor R12. The non-inverting input of operational amplifier OP3 is grounded. The output of operational amplifier OP3 is the output of the 150Hz multi-stage feedback filter.

[0022] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the output of the 50Hz multi-stage feedback filter is connected to the inverting input of the operational amplifier OP4 through resistor R6; the output of the 150Hz multi-stage feedback filter is connected to the inverting input of the operational amplifier OP4 through resistor R13; the inverting input of the operational amplifier OP4 is connected to the output of the operational amplifier OP4 through capacitor C4; and the non-inverting input of the operational amplifier OP4 is grounded.

[0023] As a further improvement to the aforementioned power metering system with magnetic field anti-interference capability: the miniature power amplifier includes operational amplifier OP5, resistors R1, R5, R9, R11, R4, R8, NPN transistor V1, and PNP transistor V2.

[0024] The non-inverting input of operational amplifier OP5 is the input of the miniature power amplifier. Resistors R1, R5, R9, and R11 are connected in series between the positive power supply VCC and the negative power supply VEE. The connection point between resistors R5 and R9 is connected to the output of operational amplifier OP5. The connection point between resistors R1 and R5 is connected to the base of NPN transistor V1, and the connection point between resistors R9 and R11 is connected to the base of PNP transistor V2. The collector of NPN transistor V1 is connected to the positive power supply VCC, and its emitter is connected to the output of the miniature power amplifier through resistor R4. The collector of PNP transistor V2 is connected to the negative power supply VEE, and its emitter is connected to the output of the miniature power amplifier through resistor R8. The output of the miniature power amplifier is also connected to the inverting input of operational amplifier OP5.

[0025] This invention also discloses an energy metering method based on the above-mentioned energy metering system with magnetic field interference resistance, wherein the energy metering system with magnetic field interference resistance performs the following steps in real time:

[0026] Step S1: Obtain the difference current between the current of the primary winding and the primary side current of the secondary winding through the primary and secondary differential windings.

[0027] Step S2: Input the differential current into an external magnetic field detection unit and convert it into a differential voltage signal;

[0028] Step S3: Input the differential voltage signal into the active compensation control unit for comb filtering to extract the 50Hz and 150Hz power frequency magnetic field interference signals;

[0029] Step S4: Integrate and amplify the extracted power frequency magnetic field interference signal to generate a reverse voltage control signal;

[0030] Step S5: Convert the reverse voltage control signal into a compensation current using a miniature power amplifier and input it into the compensation winding;

[0031] Step S6: The compensation current generates a reverse magnetic flux on the main magnetic core, which cancels the change in magnetic flux caused by external magnetic field interference, so that the output current of the secondary winding and the input current of the primary winding satisfy the ideal mutual inductance relationship.

[0032] Step S7: The current signal output from the secondary winding and the voltage signal output from the voltage divider conversion unit are converted into digital signals by the first analog-to-digital conversion unit and the second analog-to-digital conversion unit, respectively. Then, the digital signals of voltage and current are input into the power metering unit for high-precision power metering.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The current transformer of this invention adopts a dual-core + multi-winding structure. The primary winding is wound simultaneously on two cores, and the secondary winding is wound in opposite directions on the two cores. Combined with the primary and secondary differential windings and compensation windings wound on the auxiliary and main cores respectively, it can effectively detect magnetic field interference current and achieve accurate compensation. This structure ensures high-precision power metering while being simple in structure, easy to manufacture, and significantly reduces the size of the equipment, making it suitable for miniaturized design.

[0035] 2. The active compensation control unit of the present invention accurately extracts the power frequency (50Hz) and third harmonic (150Hz) magnetic field interference signals through a multi-order feedback filter and a fourth-order comb filter. Combined with active compensation control, it effectively suppresses the interference components in the differential current, realizes dynamic cancellation of magnetic field interference, and ensures that the secondary winding output current strictly follows the primary winding input current, thus ensuring the accuracy of measurement.

[0036] 3. The miniature power amplifier of the present invention uses a bias resistor network to suppress crossover distortion of the output current and avoid signal distortion; at the same time, it eliminates the DC component through a neutral point correction resistor to prevent DC bias magnetization of the compensation winding and realizes accurate output of the current control signal of the miniature power amplifier. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of the power metering system of the present invention;

[0038] Figure 2 This is a schematic diagram of the current compensation control loop in this invention;

[0039] Figure 3 This is a circuit diagram of the external magnetic field detection unit, the active compensation control unit, and the miniature power amplifier section.

[0040] The reference numerals in the figures include:

[0041] 1. Main magnetic core; 2. Primary winding; 3. Auxiliary magnetic core; 4. Primary-secondary differential winding; 5. Secondary winding; 6. Compensation winding. Detailed Implementation

[0042] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0043] like Figure 1 An energy metering system with magnetic field anti-interference capability includes a current terminal block, a current transformer, a first analog-to-digital converter, a voltage terminal block, a voltage divider converter, a second analog-to-digital converter, and an energy metering unit.

[0044] The current terminal is connected to the primary winding 2 of the current transformer, the secondary winding 5 of the current transformer is connected to the input terminal of the first analog-to-digital converter (ADC), and the output terminal of the first ADC is connected to the current input terminal of the energy metering unit. The current transformer is used to acquire analog current signals, and the first ADC is used to convert the analog current signals into digital signals.

[0045] The input terminal of the voltage divider converter is connected to the voltage terminal block, and the output terminal is connected to the input terminal of the second analog-to-digital converter. The output terminal of the second analog-to-digital converter is connected to the voltage input terminal of the energy metering unit. The voltage divider converter is used to acquire the analog voltage signal, and the second analog-to-digital converter is used to convert the analog voltage signal into a digital signal.

[0046] The power metering unit measures power based on digital signals of voltage and current.

[0047] Specifically, such as Figure 2 The current transformer is a multi-winding current transformer, which also includes a main magnetic core 1, an auxiliary magnetic core 3, a compensation winding 6, and a primary and secondary differential winding 4.

[0048] The main magnetic core 1 is a power magnetic core, selected as a Grade A silicon steel sheet core with a saturation flux greater than 1T. The auxiliary magnetic core 3 is a high-permeability magnetic core, selected as a wound magnetic core made of iron-based amorphous or nanocrystalline material. The main magnetic core 1 and the auxiliary magnetic core 3 are arranged side by side. The primary winding 2 is wound on both the main magnetic core 1 and the auxiliary magnetic core 3, and the secondary winding 5 is wound on both the main magnetic core 1 and the auxiliary magnetic core 3, with the winding direction opposite to that of the primary winding 2. The turns ratio of the primary winding 2 to the secondary winding 5 is N. The compensation winding 6 is wound on the main magnetic core 1, and the primary-secondary difference winding 4 is wound on the auxiliary magnetic core 3.

[0049] Ideally, the current output by the secondary winding 5 is 1 / N of the input current of the primary winding 2. However, the multi-winding current transformer is affected by external magnetic field interference, causing the output current of the secondary winding 5 to not satisfy the above relationship with the input current of the primary winding 2. At this time, the magnetic flux of the auxiliary magnetic core 3 changes, generating an induced electromotive force, which induces a current in the primary-secondary differential winding 4. This invention uses the primary-secondary differential winding 4 to detect the induced current, obtain the difference current between the current of the primary winding 2 and the primary side current corresponding to the secondary winding 5, and then connects it sequentially to the compensation winding 6 through an external magnetic field detection unit, an active compensation control unit, and a micro power amplifier to form a current compensation control loop, compensating for the magnetic flux of the main magnetic core 1 and canceling the interference of the external magnetic field on the output current of the secondary winding 5.

[0050] Furthermore, such as Figure 3 The external magnetic field detection unit converts the analog differential current into an analog voltage signal, filters out extremely high-frequency noise signals to ensure detection accuracy, and outputs a differential voltage signal. Specifically, the external magnetic field detection unit includes an operational amplifier OP1, a capacitor C2, and a resistor R3. The inverting input of operational amplifier OP1 is the input of the external magnetic field detection unit. The inverting input of operational amplifier OP1 is also connected to its output through a parallel connection of capacitor C2 and resistor R3. The non-inverting input of operational amplifier OP1 is grounded. The output of operational amplifier OP1 is the output of the external magnetic field detection unit. Operational amplifier OP1 is selected with extremely low bias current to prevent detection errors introduced by the device itself.

[0051] The active compensation control unit includes a 50Hz multi-stage feedback filter, a 150Hz multi-stage feedback filter, and an operational amplifier OP4, which are used to obtain a voltage control signal based on the differential voltage signal.

[0052] Specifically, the input of the active compensation control unit is connected to the input of both the 50Hz multi-stage feedback filter and the 150Hz multi-stage feedback filter. The outputs of both filters are connected to the input of operational amplifier OP4, forming a fourth-order comb filter used to extract the power frequency magnetic field interference portion (power frequency and third harmonic interference account for over 98%) caused by the 50Hz and 150Hz frequencies in the magnetic field interference current. The output of operational amplifier OP4 is the output of the active compensation control unit.

[0053] The 50Hz multi-stage feedback filter includes an operational amplifier OP2, resistors R7, R10, and R2, and capacitors C3 and C1. The input of the 50Hz multi-stage feedback filter is grounded sequentially through resistors R7 and R10. The connection point between resistors R7 and R10 is connected to the inverting input of operational amplifier OP2 through capacitor C3, and also to the output of operational amplifier OP2 through capacitor C1. The inverting input of operational amplifier OP2 is also connected to its output through resistor R2. The non-inverting input of operational amplifier OP2 is grounded. The output of operational amplifier OP2 is the output of the 50Hz multi-stage feedback filter.

[0054] The 150Hz multi-stage feedback filter includes an operational amplifier OP3, resistors R14, R15, and R12, and capacitors C6 and C5. The input of the 150Hz multi-stage feedback filter is grounded sequentially through resistors R14 and R15. The connection point between resistors R14 and R15 is connected to the inverting input of operational amplifier OP3 via capacitor C6, and also to the output of operational amplifier OP3 via capacitor C5. The inverting input of operational amplifier OP3 is also connected to its output via resistor R12. The non-inverting input of operational amplifier OP3 is grounded. The output of operational amplifier OP3 is the output of the 150Hz multi-stage feedback filter.

[0055] Furthermore, the output of the 50Hz multi-stage feedback filter is connected to the inverting input of operational amplifier OP4 via resistor R6, and the output of the 150Hz multi-stage feedback filter is connected to the inverting input of operational amplifier OP4 via resistor R13. The inverting input of operational amplifier OP4 is connected to its output via capacitor C4. The non-inverting input of operational amplifier OP4 is grounded. Capacitor C4 is an integrating capacitor, which integrates the output signal of the fourth-order comb filter to generate an inverted voltage control signal, which serves as the control input signal for the miniature power amplifier.

[0056] The miniature power amplifier is used to convert voltage control signals into current signals and provide load-driving capability. It includes an operational amplifier OP5, resistors R1, R5, R9, R11, R4, R8, an NPN transistor V1, and a PNP transistor V2. The non-inverting input of operational amplifier OP5 is the input terminal of the miniature power amplifier. Resistors R1, R5, R9, and R11 are connected in series between the positive power supply terminal VCC and the negative power supply terminal VEE. The connection point between resistors R5 and R9 is connected to the output terminal of operational amplifier OP5. The connection point between resistors R1 and R5 is connected to the base of NPN transistor V1, and the connection point between resistors R9 and R11 is connected to the base of PNP transistor V2. The collector of NPN transistor V1 is connected to the positive power supply terminal VCC, and the emitter is connected to the output terminal of the miniature power amplifier through resistor R4. The collector of PNP transistor V2 is connected to the negative terminal of the power supply, VEE, and its emitter is connected to the output of the miniature power amplifier via resistor R8. The output of the miniature power amplifier is also connected to the inverting input of operational amplifier OP5. When the output signal of operational amplifier OP5 changes positively, the base voltage of NPN transistor V1 increases, further turning it on. Current flows from VCC through NPN transistor V1 and resistor R4 to the load, amplifying the positive half-cycle signal. When the output signal of operational amplifier OP5 changes negatively, the base voltage of PNP transistor V2 decreases, further turning it on. Current flows from the load through resistor R8 and PNP transistor V2 to VEE, amplifying the negative half-cycle signal.

[0057] Operational amplifier OP5 is selected as a high-bandwidth, high-slew-rate high-speed operational amplifier to ensure a flat passband for the miniature power amplifier and achieve accurate output of the compensation current. Resistors R1, R5, R9, and R11 are connected in series to form a voltage divider network to reduce crossover distortion of the miniature power amplifier's output current signal and avoid signal distortion. Resistors R4 and R8 are used for neutral point correction to reduce the DC component of the miniature power amplifier's output current signal and prevent DC bias in the compensation winding 6. Transistors V1 and V2 are selected as high-gain, high-collector-current transistors to ensure the miniature power amplifier's load-driving capability.

[0058] In this embodiment, the operational amplifier is preferably a high-precision, low-offset voltage operational amplifier, such as OPA192 or ADA4077. The resistors are preferably low-temperature drift, non-inductive resistors, such as RJ711 metal foil resistors and MMA glass enamel resistors. The capacitors are preferably NP0, COG, or polypropylene film capacitors.

[0059] The power metering system with magnetic field interference resistance capability performs the following steps in real time during operation:

[0060] Step S1: Obtain the difference current between the current of the primary winding 2 and the primary side current corresponding to the secondary winding 5 through the primary and secondary differential winding 4.

[0061] Step S2: Input the differential current into the external magnetic field detection unit and convert it into a differential voltage signal.

[0062] Step S3: Input the differential voltage signal into the active compensation control unit for comb filtering to extract the 50Hz and 150Hz power frequency magnetic field interference signals.

[0063] Step S4: Integrate and amplify the extracted power frequency magnetic field interference signal to generate a reverse voltage control signal.

[0064] Step S5: Convert the reverse voltage control signal into a compensation current using a miniature power amplifier and input it into the compensation winding 6.

[0065] Step S6: The compensation current generates a magnetic flux on the main magnetic core 1 that is opposite to the interference magnetic field, which cancels the change in magnetic flux caused by the external magnetic field interference, so that the output current of the secondary winding 5 and the input current of the primary winding 2 satisfy the ideal mutual inductance relationship.

[0066] Step S7: The current signal output from the secondary winding 5 and the voltage signal output from the voltage divider conversion unit are converted into digital signals by the first analog-to-digital conversion unit and the second analog-to-digital conversion unit, respectively. Then, the digital signals of voltage and current are input into the power metering unit for high-precision power metering.

[0067] It should be noted that, as will be apparent to those skilled in the art, the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics thereof. The scope of the present invention is defined by the claims rather than the foregoing description.

Claims

1. An energy metering system with magnetic field anti-interference capability, comprising current terminals, a current transformer, a first analog-to-digital converter, a voltage terminals, a voltage divider converter, a second analog-to-digital converter, and an energy metering unit; The current terminal is connected to the primary winding (2) of the current transformer, the secondary winding (5) of the current transformer is connected to the input terminal of the first analog-to-digital converter, and the output terminal of the first analog-to-digital converter is connected to the current input terminal of the energy metering unit. The input terminal of the voltage divider conversion unit is connected to the voltage terminal block, and the output terminal is connected to the input terminal of the second analog-to-digital converter unit. The output terminal of the second analog-to-digital converter unit is connected to the voltage input terminal of the energy metering unit. Its features are: The current transformer is a multi-winding current transformer, which also includes a main magnetic core (1), an auxiliary magnetic core (3), a compensation winding (6), and a primary and secondary differential winding (4); the main magnetic core (1) and the auxiliary magnetic core (3) are arranged side by side, the primary winding (2) is wound on both the main magnetic core (1) and the auxiliary magnetic core (3), and the secondary winding (5) is wound on both the main magnetic core (1) and the auxiliary magnetic core (3) with the winding direction opposite to that of the primary winding (2); the compensation winding (6) is wound on the main magnetic core (1), and the primary and secondary differential winding (4) is wound on the auxiliary magnetic core (3); The main magnetic core (1) is a power magnetic core, and the auxiliary magnetic core (3) is a high-permeability magnetic core; the main magnetic core (1) is a Grade A silicon steel sheet magnetic core with a saturation magnetic flux greater than 1T, and the auxiliary magnetic core (3) is a wound magnetic core made of iron-based amorphous or nanocrystalline material. The primary and secondary differential windings (4) are connected to the compensation windings (6) in sequence through an external magnetic field detection unit, an active compensation control unit, and a micro power amplifier to form a current compensation control loop. The current compensation control loop is used to compensate the magnetic flux of the main core (1) based on the difference between the current of the primary winding (2) and the primary side current of the secondary winding (5), thereby canceling the interference of the external magnetic field on the current of the secondary winding (5). The external magnetic field detection unit includes an operational amplifier OP1, a capacitor C2, and a resistor R3; The inverting input terminal of the operational amplifier OP1 is the input terminal of the external magnetic field detection unit; the inverting input terminal of the operational amplifier OP1 is also connected to the output terminal of the operational amplifier OP1 through a parallel capacitor C2 and a resistor R3; the non-inverting input terminal of the operational amplifier OP1 is grounded; the output terminal of the operational amplifier OP1 is the output terminal of the external magnetic field detection unit. The active compensation control unit includes a 50Hz multi-stage feedback filter, a 150Hz multi-stage feedback filter, and an operational amplifier OP4. The input terminal of the active compensation control unit is connected to the input terminal of both the 50Hz multi-order feedback filter and the 150Hz multi-order feedback filter. The output terminals of both the 50Hz and 150Hz multi-order feedback filters are connected to the input terminal of the operational amplifier OP4, forming a fourth-order comb filter. The output terminal of the operational amplifier OP4 is the output terminal of the active compensation control unit. The output of the 50Hz multi-stage feedback filter is connected to the inverting input of the operational amplifier OP4 through resistor R6; the output of the 150Hz multi-stage feedback filter is connected to the inverting input of the operational amplifier OP4 through resistor R13; the inverting input of the operational amplifier OP4 is connected to the output of the operational amplifier OP4 through capacitor C4; the non-inverting input of the operational amplifier OP4 is grounded. The miniature power amplifier includes operational amplifier OP5, resistors R1, R5, R9, R11, R4, R8, NPN transistor V1, and PNP transistor V2. The non-inverting input of operational amplifier OP5 is the input of the miniature power amplifier. Resistors R1, R5, R9, and R11 are connected in series between the positive power supply VCC and the negative power supply VEE. The connection point between resistors R5 and R9 is connected to the output of operational amplifier OP5. The connection point between resistors R1 and R5 is connected to the base of NPN transistor V1, and the connection point between resistors R9 and R11 is connected to the base of PNP transistor V2. The collector of NPN transistor V1 is connected to the positive power supply VCC, and its emitter is connected to the output of the miniature power amplifier through resistor R4. The collector of PNP transistor V2 is connected to the negative power supply VEE, and its emitter is connected to the output of the miniature power amplifier through resistor R8. The output of the miniature power amplifier is also connected to the inverting input of operational amplifier OP5.

2. The power metering system with magnetic field anti-interference capability as described in claim 1, characterized in that: The 50Hz multi-stage feedback filter includes operational amplifier OP2, resistors R7, R10, and R2, capacitors C3 and C1; The input of the 50Hz multi-stage feedback filter is grounded via resistors R7 and R10. The connection point between resistors R7 and R10 is connected to the inverting input of operational amplifier OP2 via capacitor C3, and also to the output of operational amplifier OP2 via capacitor C1. The inverting input of operational amplifier OP2 is also connected to the output of operational amplifier OP2 via resistor R2. The non-inverting input of operational amplifier OP2 is grounded. The output of operational amplifier OP2 is the output of the 50Hz multi-stage feedback filter.

3. The power metering system with magnetic field anti-interference capability as described in claim 1, characterized in that: The 150Hz multi-stage feedback filter includes operational amplifier OP3, resistor R14, resistor R15, resistor R12, capacitor C6, and capacitor C5. The input of the 150Hz multi-stage feedback filter is grounded via resistors R14 and R15. The connection point between resistors R14 and R15 is connected to the inverting input of operational amplifier OP3 via capacitor C6, and also to the output of operational amplifier OP3 via capacitor C5. The inverting input of operational amplifier OP3 is also connected to the output of operational amplifier OP3 via resistor R12. The non-inverting input of operational amplifier OP3 is grounded. The output of operational amplifier OP3 is the output of the 150Hz multi-stage feedback filter.

4. A method for measuring electricity based on an electricity metering system with magnetic field anti-interference capability as described in claim 1, characterized in that, The power metering system with magnetic field anti-interference capability performs the following steps in real time: Step S1: Obtain the difference current between the current of the primary winding (2) and the primary side current of the secondary winding (5) through the primary and secondary differential winding (4); Step S2: Input the differential current into an external magnetic field detection unit and convert it into a differential voltage signal; Step S3: Input the differential voltage signal into the active compensation control unit for comb filtering to extract the 50Hz and 150Hz power frequency magnetic field interference signals; Step S4: Integrate and amplify the extracted power frequency magnetic field interference signal to generate a reverse voltage control signal; Step S5: Convert the reverse voltage control signal into a compensation current through a miniature power amplifier and input it into the compensation winding (6). Step S6: The compensation current generates a reverse magnetic flux on the main magnetic core (1) to counteract the change in magnetic flux caused by external magnetic field interference, so that the output current of the secondary winding (5) and the input current of the primary winding (2) satisfy the ideal mutual inductance relationship. Step S7: The current signal output from the secondary winding (5) and the voltage signal output from the voltage divider conversion unit are converted into digital signals by the first analog-to-digital conversion unit and the second analog-to-digital conversion unit, respectively. Then, the digital signals of voltage and current are input into the power metering unit for high-precision power metering.

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