A non-intrusive residual current sensor based on magneto-impedance effect

Abstract

The application provides a non-invasive residual current sensor based on a magnetic impedance effect, which comprises a magnetic sensitive unit, the magnetic sensitive unit comprises two amorphous wires and a coil, the two amorphous wires are arranged in parallel and connected in series, the coil is wound on the two amorphous wires, the two ends of the coil are connected in series, and a circular through hole is arranged between the two amorphous wires; the two ends of the series-connected amorphous wires are connected to the same excitation circuit, one of the two ends of the coil is grounded, the other end is connected to a signal conditioning circuit, a differential signal of the coil is sequentially returned to a starting connection point through an instrument amplifier, a rectifier circuit, an integration circuit, a sampling resistor, a feedback loop and a feedback resistor, and a feedback magnetic field generated by the signal conditioning circuit only offsets a magnetic field generated by a current; a residual current value in a measured conductor is calculated according to a calibration relationship based on a voltage between the sampling resistor and the feedback current. The structure does not reflect a background magnetic field and isolates environmental interference. Meanwhile, common-mode noise caused by the excitation circuit is removed, and the measurement is more accurate.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology and relates to a non-invasive residual current sensor based on the magnetoresistance effect. Background Technology

[0002] In electric vehicle conductive charging systems, residual current sensors typically have a range of 0-300mA. This range is designed to cover the detection needs of both AC and DC residual current, meeting the sensitivity requirements for electric shock protection while also considering electrical fire prevention and standard compliance. It needs to have a resolution of 6mA DC to 30mA AC, while maintaining measurement accuracy within ±1% over a wide temperature range. To meet these application requirements, high-precision residual current sensors are crucial. Current measurement methods are mainly divided into invasive current sensors, which primarily use sampling resistors, and non-invasive current sensors, which utilize various magnetic measurement methods. For non-invasive current sensors, achieving the aforementioned accuracy within the 0-300mA measurement range requires extremely high magnetic sensitivity and low noise. GMI (Grammoresistivity) magnetic sensors perfectly meet this requirement, offering high sensitivity and low noise. However, applying GMI magnetic sensors to residual current measurement in vehicle systems requires solving a key problem: the magnetic environment in vehicles is complex, and the magnetic field generated by a 0-300mA current is much smaller than the ambient magnetic field in the vehicle. Even with a shielding shell, the external magnetic field may not be completely blocked. If the complex magnetic field environment is adapted by reducing sensitivity and expanding the sensor range, some sensor accuracy will be sacrificed. Therefore, a method to isolate the ambient magnetic field urgently needs to be proposed.

[0003] Against this backdrop, this patent proposes a non-invasive GMI residual current sensor suitable for electric vehicle conductive charging systems. With a special signal demodulation method, it perfectly solves the problem of limited current measurement accuracy caused by excessive background magnetic field. Summary of the Invention

[0004] To address the problem that GMI magnetic sensors are greatly affected by environmental magnetic fields in current sensing applications, this invention proposes a non-invasive residual current sensor based on magnetoresistance effect, which balances range and accuracy and is suitable for residual current detection in complex magnetic environments of electric vehicle conductive charging systems.

[0005] The technical solution of this invention is as follows: A non-invasive residual current sensor based on magnetoresistive effect, comprising a magnetically sensitive unit, wherein the magnetically sensitive unit contains two amorphous wires and two sets of coils. The amorphous wires and coils are fixed on a PCB frame. The two amorphous wires are arranged in parallel and connected in series. The two sets of coils are wound on the two amorphous wires respectively, with the same winding specifications and consistent winding direction. The two ends on the same side of the two coils are connected in series. A circular through hole is opened at the geometric center between the two amorphous wires for the current-carrying conductor to be measured to pass through. The two ends of the series-connected amorphous wires are connected to the same excitation circuit. The excitation current direction in the two amorphous wires is consistent. One of the two ends of the non-series-connected ends of the two sets of coils is grounded, and the other is connected to a signal conditioning circuit. The signal conditioning circuit is a closed-loop negative feedback loop. The differential signal of the coil passes through an instrumentation amplifier, a rectifier circuit, an integrator circuit, a sampling resistor, a feedback loop, and a feedback resistor in sequence and returns to the starting connection point. The feedback magnetic field generated by the signal conditioning circuit only cancels the magnetic field generated by the current. The voltage across the sampling resistor is measured to obtain the feedback current, and the residual current value in the conductor being measured is calculated according to the calibration relationship.

[0006] The excitation circuit uses a square wave excitation signal with a frequency of 300kHz and a peak-to-peak voltage of 5V. The square wave excitation signal is generated by a microcontroller and applied to both ends of the series amorphous wire after passing through the driving circuit.

[0007] The amorphous wire is a Co-based amorphous wire, CoFeSiB.

[0008] The center distance between the two amorphous wires is 20mm, the diameter of the circular through hole is 10mm, and the length of the amorphous wire is 30mm and the diameter is 100μm.

[0009] The coil has 1000 turns, a wire diameter of 0.03 mm, and an axial length of 15 mm on the amorphous wire.

[0010] The integrating circuit uses an OPA2277 operational amplifier, with an integrating capacitor C=100nF, an integrating resistor R=10kΩ, a sampling resistor Rs=10Ω, and a feedback resistor Rf=3000Ω.

[0011] Principle: The magnetic sensing unit with dual amorphous wire differential configuration uses the differential signal of the coils on the two amorphous wires for signal conditioning, and then feeds the conditioned signal back to the coil series circuit, so that the feedback magnetic field is only used to balance the magnetic field generated by the current, thereby achieving isolation from the ambient magnetic field.

[0012] The beneficial effects of this invention are: the differential signal of the coil only reflects the magnitude of the conductor current placed between the two amorphous wires, and does not reflect the background magnetic field, thus isolating environmental interference. The differential method eliminates common-mode noise caused by the excitation circuit, making the measurement data more accurate. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the magnetic sensing unit structure; Figure 2 This is a schematic diagram of the operation of a residual current sensor; Figure 3 This is the circuit schematic of the residual current sensor; Figure 4 This invention relates the relationship between the output voltage and the measured current value of the product under normal temperature conditions, and the results of its linear fitting. Figure reference numerals: 1-amorphous wire, 2-coil, 3-circular through hole, 4-PCB skeleton. Detailed Implementation

[0014] like Figure 1 As shown, a magnetic sensing unit is composed of two parallel Co-based amorphous wires 1 (composed of CoFeSiB), with the same magnetic sensitivity direction. The two amorphous wires 1 are placed parallel to each other in the same direction, with a center-to-center distance of 20 mm. A circular through-hole 3 (10 mm in diameter) is opened at the geometric center between the two amorphous wires 1 for the current-carrying conductor to be measured to pass through. The coil is wound on the two amorphous wires with the same winding specifications and consistent winding direction.

[0015] Figure 2 This is a schematic diagram of the magnetic sensing unit in operation. Two amorphous wires 1 are connected in series, and two coils 2 are connected in series through terminals BD, with point A grounded. When an excitation is applied to amorphous wire 1, the excitation current in both amorphous wires maintains the same direction. The coil on the left in the diagram will generate a signal. V AB The right coil generates a signal. V CD When only an external magnetic field exists B At time 0, due to the short circuit of BD, the differential signal of the two coils... V CA for: V CA = V CD - V AB = S * B 0- S * B 0=0, in the formula S denoted as the magnetoelectric conversion coefficient of the sensor.

[0016] When current flows through the central circular aperture, it generates magnetic fields of equal magnitude and opposite direction at the two amorphous wires. B l+ and B l- At this time, the differential signal between the two coils is: VCA = S *( B 0+ B l+ )- S *( B 0+ B l- )= S * B l+ - S * B l- ,because B l+ and B l- Equal in size but opposite in direction, that is B l+ =- B l- ,so S * B l+ - S * B l- =2 S * B l+ Therefore, the differential signal between the two coils V CA It is only related to electric current.

[0017] Due to the GMI effect, under analog signal excitation, the signal in coil 2 is an alternating current quantity, so it is necessary to process this differential signal. V CA Demodulation is performed, and to improve the linearity of the residual current sensor, it needs to be set to negative feedback mode. Figure 3 This is the overall circuit diagram of the residual current sensor. The differential voltage signal between the two coils is first amplified by an instrumentation operational amplifier, then rectified to DC, and then passed through an integrator circuit to obtain a near-infinite gain. Finally, it returns to the coil series circuit via a feedback loop. When the feedback current... I fb When current flows through coil 2, coil 2 will generate a magnetic field that interacts with the current due to the electromagnetism effect. B l Magnetic fields of equal magnitude but opposite direction B fb Because the integrator circuit has infinite gain, the two magnetic fields become infinitely close. Finally, by measuring the current in the feedback loop using the sampling resistor, the current flowing through the measured current-carrying conductor can be calculated. I P .

[0018] Implementation Cases Sensor probe fabrication: Two CoFeSiB amorphous wires, 100μm in diameter and 30mm in length, were selected. After annealing, the two amorphous wires were arranged parallel to each other along the sensing axis on the PCB skeleton 4, with a spacing of 20mm. A coil 2 was wound on each amorphous wire using enameled wire, with 1000 turns and a wire diameter of 0.03mm. The two amorphous wires were connected in series via PCB wiring, and the two coils were also connected in series via PCB wiring to form a differential detection structure. A 10mm diameter circular through-hole was machined at the geometric center of the two amorphous wires.

[0019] Excitation circuit: The amorphous wire uses a square wave excitation signal with a frequency of 300kHz and a peak-to-peak voltage of 5V. The excitation signal is generated by a microcontroller and applied to both ends of the series-connected amorphous wire after passing through the driver circuit.

[0020] Signal conditioning circuit: The differential signal from the coil is first pre-amplified by an instrumentation operational amplifier (such as AD8421, gain G=100), and then converted into a DC signal by a precision rectifier circuit. The rectified signal is input to an integrating circuit (using an OPA2277 operational amplifier, integrating capacitor C=100nF, integrating resistor R=10kΩ) to achieve high-gain negative feedback control. The output of the integrating circuit is connected to the coil series circuit via a feedback resistor Rf=3000Ω to form a closed-loop negative feedback. A sampling resistor Rs=10Ω is connected in series in the feedback circuit. The feedback current can be obtained by measuring the voltage across the sampling resistor, and then determined according to the calibration relationship. I p = I fb The residual current value in the current-carrying conductor under test is calculated by using 1.91*1000.

[0021] The accuracy testing method for the product of this invention: (1) Install the sensor on the copper conductor of the analog charging cable. The diameter of the copper conductor is 8mm. (2) Use a precision current source (such as Keithley 6221) to generate a DC and AC (50Hz / 60Hz) test current of 0-300mA, and perform point-by-point scanning in 10mA increments; (3) Use Helmholtz coils to generate a variable background magnetic field of 0-10G to simulate the complex magnetic environment of the vehicle; (4) Measure the output characteristics of the sensor under normal temperature (25℃), high temperature (+85℃) and low temperature (-40℃) conditions respectively. After holding the temperature at each point for 1 hour, start the test. (5) Each test point was measured 10 times, and the average value was recorded. The sensor voltage output value and the corresponding test current value were linearly fitted. The experimental results under normal temperature conditions are as follows: Figure 4 As shown. From Figure 4It can be seen that the residual current sensor prepared according to this application has a high degree of agreement between the measured data and the fitted straight line, and excellent accuracy.

Claims

1. A non-invasive residual current sensor based on magnetoresistive effect, comprising a magnetically sensitive unit, characterized in that: The magnetically sensitive unit contains two amorphous wires and two sets of coils. The amorphous wires and coils are fixed on the PCB frame. The two amorphous wires are arranged in parallel and connected in series. The two sets of coils are wound on the two amorphous wires respectively, with the same winding specifications and consistent winding direction. The two ends on the same side of the two coils are connected in series. A circular through hole is opened at the geometric center between the two amorphous wires for the current-carrying conductor under test to pass through. The two ends of the series-connected amorphous wires are connected to the same excitation circuit. The excitation current in the two amorphous wires is in the same direction. One of the two ends of the non-series-connected ends of the two sets of coils is grounded, and the other is connected to a signal conditioning circuit. The signal conditioning circuit is a closed-loop negative feedback loop. The differential signal of the coil passes through the instrumentation amplifier, rectifier circuit, integrator circuit, sampling resistor, feedback loop, and feedback resistor in sequence and returns to the starting connection point. The feedback magnetic field generated by the signal conditioning circuit only cancels the magnetic field generated by the current. The voltage across the sampling resistor is measured to obtain the feedback current, and the residual current value in the conductor under test is calculated according to the calibration relationship.

2. The non-invasive residual current sensor based on magnetoresistance effect according to claim 1, characterized in that: The excitation circuit uses a square wave excitation signal with a frequency of 300kHz and a peak-to-peak voltage of 5V. The square wave excitation signal is generated by a microcontroller and applied to both ends of the series amorphous wire after passing through the driving circuit.

3. A non-invasive residual current sensor based on magnetoresistance effect according to claim 1, characterized in that: The amorphous wire is a Co-based amorphous wire, CoFeSiB.

4. A non-invasive residual current sensor based on magnetoresistance effect according to claim 1, characterized in that: The center distance between the two amorphous wires is 20mm, the diameter of the circular through hole is 10mm, and the length of the amorphous wire is 30mm and the diameter is 100μm.

5. A non-invasive residual current sensor based on magnetoresistance effect according to claim 1, characterized in that: The coil has 1000 turns, a wire diameter of 0.03 mm, and an axial length of 15 mm on the amorphous wire.

6. A non-invasive residual current sensor based on magnetoresistance effect according to claim 1, characterized in that: The integrating circuit uses an OPA2277 operational amplifier, with an integrating capacitor C=100nF, an integrating resistor R=10kΩ, a sampling resistor Rs=10Ω, and a feedback resistor Rf=3000Ω.

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