Leakage current sensor

Abstract

The invention discloses a leakage current sensor, and relates to the technical field of current detection. According to the leakage current sensor, the TMR elements with opposite magnetization directions are adopted to form a bridge, magnetic field changes corresponding to current are converted into differential voltage signals, a reference magnetic field is established through a reference circuit, online calibration of the sensitivity of the sensor is achieved, the sensitivity of the sensor is dynamically calibrated, the problem of temperature excursion of the TMR elements is solved, and the sensor has the ultrahigh sensitivity. Long-term stability; the signal modulation module injects a specific frequency signal through an alternating current power supply and modulates a to-be-detected leakage current of an electrode to a high frequency band, the demodulation module adopts a phase sensitive detector (PSD) to lock a reference frequency and suppress power frequency interference and white noise, the influence of low-frequency noise on the TMR current sensor is reduced, and the detection precision of the sensor is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of current detection, and particularly to a leakage current sensor. Background Art

[0002] In the process of the power system developing towards intelligence and high reliability, current measurement technology, as a core basic link, is facing unprecedented accuracy challenges. Traditional electromagnetic current transformers are limited by the core saturation effect and frequency band limitation, and it is difficult to meet the requirements of new power electronic equipment for current detection in a wide frequency domain and high dynamic range. In this context, new current sensors based on the magnetosensitive principle have gradually emerged. Among them, the tunneling magnetoresistance (TMR) sensor shows unique advantages due to its nanoscale quantum tunneling effect. Compared with the sensitivity of 0.1 - 1 mV / V / Oe of Hall elements, modern TMR elements can achieve a sensitivity span of 20 - 200 mV / V / Oe, while maintaining excellent temperature stability of 0.01% / °C, which makes it irreplaceable in the field of μA-level leakage detection. However, the non-linear error caused by the hysteresis effect has always been the key bottleneck restricting the performance improvement of TMR sensors. Even using closed-loop compensation technology, the error can only be controlled at the 0.1% level, and it comes at the cost of increased power consumption and decreased response speed.

[0003] Especially for the detection of human body's minute leakage current, the magnitude of the leakage current is extremely small, possibly as low as μA level, which is easily submerged by noise, and the dynamic range requirement is high, and it is necessary to detect both μA-level leakage and mA-level normal current simultaneously, resulting in the difficulty of current sensors in detecting the minute leakage current of the human body. Summary of the Invention

[0004] The object of the present invention is to solve the problems in the above background art, and to propose a leakage current sensor.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] An embodiment of the present invention provides a leakage current sensor, which includes: a reference circuit, a signal modulation module, a signal demodulation module, and a signal compensation module;

[0007] Wherein, the signal modulation module includes a Wheatstone bridge circuit, a DC power supply interface, and an AC power supply interface; the Wheatstone bridge circuit is composed of 4 tunneling magnetoresistance (TMR) elements, and the magnetization direction sensitive axes of adjacent TMR elements are opposite; the magnetic field direction generated by the reference circuit is parallel to the magnetization direction sensitive axes of each TMR element; the Wheatstone bridge circuit is powered by the DC power supply interface and the AC power supply interface;

[0008] The signal demodulation module successively includes a first amplifier, a phase-sensitive detector, a low-pass filter, and a signal separator; the input signal of the AC power interface serves as the reference signal of the phase-sensitive detector, and the differential output signal of the Wheatstone bridge circuit serves as the input signal of the first amplifier; the signal separator is used to divide the input signal into a reference electrical signal and a to-be-detected electrical signal; the frequencies of the reference electrical signal and the to-be-detected electrical signal are different;

[0009] The signal compensation module is used to calculate the sensor sensitivity according to the reference electrical signal and generate the original signal corresponding to the to-be-detected electrical signal according to the sensor sensitivity.

[0010] Optionally, the signal compensation module includes a sensor sensitivity calculation unit, a second amplifier, and a current back-calculation module; the amplification factor of the second amplifier is where α is the peak value output by the AC power supply;

[0011] The second amplifier is used to process the to-be-detected electrical signal to obtain the original voltage signal;

[0012] The sensor sensitivity calculation unit is used to calculate the sensor sensitivity according to the reference electrical signal;

[0013] The current back-calculation module back-calculates the original current signal corresponding to the to-be-detected electrical signal according to the original voltage signal and the sensor sensitivity.

[0014] Optionally, the specific method for calculating the sensor sensitivity is:

[0015]

[0016] where S is the sensor sensitivity, V c is the voltage of the reference electrical signal, G1 is the amplification factor of the first amplifier, B c is the magnetic induction intensity generated by the reference circuit at the Wheatstone bridge circuit.

[0017] Optionally, if the reference circuit is a DC wire, then where μ is the magnetic permeability of vacuum, I c is the current of the reference circuit, D c is the distance from the reference circuit to the to-be-detected line.

[0018] Optionally, the current back-calculation module is specifically used to substitute the sensor sensitivity into V d = G1SB d where V d is the voltage of the original voltage signal, B d is the magnetic induction intensity generated by the to-be-detected line at the Wheatstone bridge circuit;

[0019] The reverse inference restores the original current signal as: where D d is the distance from the Wheatstone bridge circuit to the line to be detected.

[0020] Optionally, the reference circuit is an AC coil; then where μ is the magnetic permeability of vacuum, I c is the current of the reference circuit, and N is the number of turns of the AC coil.

[0021] Optionally, the current reverse inference module is specifically configured to substitute the sensor sensitivity into V d = G1SB d where V d is the voltage of the original voltage signal, and B d is the magnetic induction intensity generated by the line to be detected at the Wheatstone bridge circuit;

[0022] The reverse inference restores the original current signal as: where D d is the distance from the Wheatstone bridge circuit to the line to be detected.

[0023] Advantages of the present invention:

[0024] The embodiment of the present invention provides a leakage current sensor, which includes: a reference circuit, a signal modulation module, a signal demodulation module, and a signal compensation module; wherein, the signal modulation module includes a Wheatstone bridge circuit, a DC power supply interface, and an AC power supply interface; the Wheatstone bridge circuit is composed of 4 tunnel magnetoresistance (TMR) elements, and the magnetization direction sensitive axes of adjacent TMR elements are opposite; the magnetic field direction generated by the reference circuit is parallel to the magnetization direction sensitive axes of each TMR element; the Wheatstone bridge circuit is powered through the DC power supply interface and the AC power supply interface; the signal demodulation module successively includes a first amplifier, a phase-sensitive detector, a low-pass filter, and a signal separator; the input signal of the AC power supply interface is used as the reference signal of the phase-sensitive detector, and the differential output signal of the Wheatstone bridge circuit is used as the input signal of the first amplifier; the signal separator is used to divide the input signal into a reference electrical signal and a signal to be measured; the frequencies of the reference electrical signal and the signal to be measured are different; the signal compensation module is used to calculate the sensor sensitivity according to the reference electrical signal and generate the original signal corresponding to the signal to be measured according to the sensor sensitivity.

[0025] A bridge is formed by TMR elements with opposite magnetization directions, which converts the magnetic field change corresponding to the current into a differential voltage signal. A reference magnetic field is established through a reference circuit to realize on-line calibration of the sensor sensitivity and dynamically calibrate the sensor sensitivity, solving the problem of temperature drift of TMR elements, making the sensor have ultra-high sensitivity and long-term stability. The signal modulation module injects a signal with a specific frequency through an AC power supply, modulates the leakage current to be measured to a high-frequency band, and the demodulation module uses a phase-sensitive detector (PSD) to lock the reference frequency, suppressing power frequency interference and white noise, reducing the influence of low-frequency noise on the TMR current sensor, and improving the detection accuracy of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] Figure 1 FIG. is a schematic structural diagram of a leakage current sensor provided by an embodiment of the present invention;

[0028] Figure 2 FIG. is a schematic diagram of a Wheatstone bridge circuit of a TMR element provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] An embodiment of the present invention provides a leakage current sensor, see Figure 1 , Figure 1 FIG. is a schematic structural diagram of a leakage current sensor provided by an embodiment of the present invention. Among them, an electrode generates a leakage current to be measured, and the sensor includes: a reference circuit, a signal modulation module, a signal demodulation module, and a signal compensation module;

[0031] Among them, the signal modulation module includes a Wheatstone bridge circuit, a DC power supply interface, and an AC power supply interface; the Wheatstone bridge circuit is composed of 4 tunnel magnetoresistance (TMR) elements, and the magnetization direction sensitive axes of adjacent TMR elements are opposite; the magnetic field direction generated by the reference circuit is parallel to the magnetization direction sensitive axes of each TMR element; the Wheatstone bridge circuit is powered through the DC power supply interface and the AC power supply interface;

[0032] The signal demodulation module sequentially includes a first amplifier, a phase-sensitive detector, a low-pass filter, and a signal separator; the input signal of the AC power supply interface serves as the reference signal of the phase-sensitive detector, and the differential output signal of the Wheatstone bridge circuit serves as the input signal of the first amplifier; the signal separator is used to divide the input signal into a reference electrical signal and a to-be-measured electrical signal; the frequencies of the reference electrical signal and the to-be-measured electrical signal are different;

[0033] The signal compensation module is used to calculate the sensor sensitivity according to the reference electrical signal and generate the original signal corresponding to the to-be-measured electrical signal according to the sensor sensitivity.

[0034] An embodiment of the present invention provides a leakage current sensor, which uses TMR elements with opposite magnetization directions to form a bridge, converts the magnetic field change corresponding to the current into a differential voltage signal, establishes a reference magnetic field through a reference circuit, realizes on-line calibration of the sensor sensitivity, dynamically calibrates the sensor sensitivity, solves the temperature drift problem of the TMR element, and enables the sensor to have ultra-high sensitivity and long-term stability; the signal modulation module injects a specific frequency signal through an AC power supply, modulates the to-be-measured leakage current to a high frequency band, and the demodulation module uses a phase-sensitive detector (PSD) to lock the reference frequency, suppress power frequency interference and white noise, reduce the influence of low-frequency noise on the TMR current sensor, and improve the detection accuracy of the sensor.

[0035] In one implementation, refer to Figure 2 , Figure 2 is a schematic diagram of the Wheatstone bridge circuit of the TMR element provided by the embodiment of the present invention. There are four TMR elements, R1, R2, R3, and R4, and the adjacent sensitive axes of the TMR elements are arranged in opposite directions to form a Wheatstone bridge, which doubles the magnetic field response sensitivity (differential outputs V1 and V2), and at the same time suppresses common-mode interference, such as the resistance drift caused by temperature. The differential output signals V1 and V2 are superimposed and used as the input signal of the first amplifier; the input signals of the DC power supply interface and the AC power supply interface are jointly used as V0.

[0036] In one implementation, the DC power supply interface of the signal modulation module is used to externally connect a DC power supply to establish a stable bias operating point for the TMR elements of the Wheatstone bridge circuit and realize the self-calibration function of the sensor. The AC power supply interface is used to externally connect a high-frequency AC power supply to modulate the to-be-measured leakage current to a high frequency band and simultaneously move the low-frequency noise to the high frequency band for subsequent effective filtering. In one implementation, the combination of phase-sensitive detection + low-pass filtering can achieve a signal-to-noise ratio of >80 dB, and the detection resolution can reach the μA level.

[0037] In one implementation, the reference signal and the to-be-measured signal use different frequencies, usually the leakage current (such as the reference signal is 1 kHz and the leakage current is 50 Hz), and real-time on-line calibration is realized through frequency division multiplexing, avoiding measurement interruption caused by traditional periodic calibration.

[0038] In one embodiment, the signal compensation module includes a sensor sensitivity calculation unit, a second amplifier, and a current back-calculation module; the amplification factor of the second amplifier is where α is the peak value output by the AC power supply;

[0039] The second amplifier is used to process the electrical signal to be measured to obtain the original voltage signal;

[0040] The sensor sensitivity calculation unit is used to calculate the sensor sensitivity according to the reference electrical signal;

[0041] The current back-calculation module back-calculates the original current signal corresponding to the electrical signal to be measured based on the original voltage signal and the sensor sensitivity.

[0042] In one implementation, the leakage current to be measured will be amplified after modulation and demodulation times, and the signal needs to be restored by the second amplifier.

[0043] In one embodiment, the method for calculating the sensor sensitivity is specifically as follows:

[0044]

[0045] where S is the sensor sensitivity, V c is the voltage of the reference electrical signal, G1 is the amplification factor of the first amplifier, B c is the magnetic induction intensity generated by the reference circuit at the Wheatstone bridge circuit.

[0046] In one implementation, since the leakage current is much smaller than the current signal of the reference circuit, the magnetic field intensity generated by the leakage current can be regarded as a small perturbation of the mixed magnetic field intensity, and the value of the sensor sensitivity is only affected by the current signal of the reference circuit. Therefore, the sensor sensitivity can be calculated by the above formula (1).

[0047] In one embodiment, if the reference circuit is a DC wire, then

[0048]

[0049] where μ is the vacuum permeability, I c is the current of the reference circuit, D c is the distance from the reference circuit to the line to be detected.

[0050] The current back-calculation module is specifically used to substitute the sensor sensitivity into

[0051] V d = G1SB d (3)

[0052] where V d is the voltage of the original voltage signal, B dThe magnetic induction intensity generated by the circuit to be detected at the Wheatstone bridge circuit;

[0053]

[0054] The reverse inference restores the original current signal to:

[0055]

[0056] where D d The distance from the Wheatstone bridge circuit to the circuit to be detected.

[0057] In one implementation, a DC wire reference source is used, which is suitable for millimeter-level short-distance detection (such as PCB leakage detection), and the spatial resolution reaches 0.1 mm.

[0058] In one embodiment, the reference circuit is an AC coil; then

[0059]

[0060] where μ is the magnetic permeability of vacuum, I c The current of the reference circuit, and N is the number of turns of the AC coil.

[0061] The current reverse inference module is specifically used to substitute the sensor sensitivity into formula (3);

[0062] The reverse inference restores the original current signal to:

[0063]

[0064] where D d The distance from the Wheatstone bridge circuit to the circuit to be detected.

[0065] In one implementation, an AC coil is used as the reference source, and a remote large-current-adapted AC coil scheme is adopted. The magnetic field intensity is increased by the number of turns N. It is suitable for meter-level distance detection of power equipment (such as transformer bushings), and the measurement range can be extended to 10 kA. The anti-interference design reverse inference formula introduces the number of turns N as an adjustment factor, and different voltage levels can be adapted by adjusting the coil parameters.

[0066] In one implementation, in order to measure the tiny leakage current of the human body more accurately, the AC coil can adopt a micro Rogowski coil (the number of turns N = 100 - 200), the reference current is set to 1 mA level, a high-sensitivity TMR element (such as TMR5001 of TDK, sensitivity 20 mV / V / Oe) is selected, and with the second amplifier, a weak magnetic field less than 0.1 μT can be detected. The Wheatstone bridge circuit can be encapsulated in a permalloy shielding case to suppress environmental magnetic field interference, and the reference signal frequency is set to 1 kHz (far from 50 Hz power frequency and high-frequency noise of medical equipment).

[0067] The above has described an embodiment of the present invention in detail, but the above content is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A leakage current sensor, characterized in that, The sensor includes: a reference circuit, a signal modulation module, a signal demodulation module, and a signal compensation module; Among them, the signal modulation module includes a Wheatstone bridge circuit, a DC power supply interface, and an AC power supply interface; the Wheatstone bridge circuit is composed of 4 tunnel magnetoresistance (TMR) elements, and the magnetization direction sensitive axes of adjacent TMR elements are opposite; the magnetic field direction generated by the reference circuit is parallel to the magnetization direction sensitive axes of each TMR element; the Wheatstone bridge circuit is powered by the DC power supply interface and the AC power supply interface; The signal demodulation module sequentially includes a first amplifier, a phase-sensitive detector, a low-pass filter, and a signal separator; the input signal of the AC power supply interface serves as the reference signal of the phase-sensitive detector, and the differential output signal of the Wheatstone bridge circuit serves as the input signal of the first amplifier; the signal separator is used to divide the input signal into a reference electrical signal and a to-be-detected electrical signal; the frequencies of the reference electrical signal and the to-be-detected electrical signal are different; The signal compensation module is used to calculate the sensor sensitivity according to the reference electrical signal and generate an original signal corresponding to the to-be-detected electrical signal according to the sensor sensitivity.

2. A leakage current sensor according to claim 1, characterized in that, The signal compensation module includes a sensor sensitivity calculation unit, a second amplifier, and a current backstepping module; the amplification factor of the second amplifier is where α is the peak value output by the AC power supply; The second amplifier is used to process the to-be-detected electrical signal to obtain an original voltage signal; The sensor sensitivity calculation unit is used to calculate the sensor sensitivity according to the reference electrical signal; The current back-calculation module back-calculates an original current signal corresponding to the to-be-detected electrical signal according to the original voltage signal and the sensor sensitivity.

3. A leakage current sensor according to claim 2, characterized in that, The specific method for calculating the sensor sensitivity is as follows: where S is the sensor sensitivity, V c is the voltage of the reference electrical signal, G1 is the amplification factor of the first amplifier, B c is the magnetic induction intensity generated by the reference circuit at the Wheatstone bridge circuit.

4. A leakage current sensor according to claim 3, characterized in that, The reference circuit is a DC wire, then where μ is the permeability of free space, I c is the current of the reference circuit, D c is the distance from the reference circuit to the line to be detected.

5. A leakage current sensor according to claim 4, characterized in that The current backstepping module is specifically configured to substitute the sensor sensitivity into V d = G1SB d , where V d is the voltage of the original voltage signal, and B d is the magnetic induction intensity generated by the line to be detected at the Wheatstone bridge circuit; The reverse deduction restores the original current signal as: where D d is the distance from the Wheatstone bridge circuit to the line to be detected.

6. A leakage current sensor according to claim 3, characterized in that, The reference circuit is an AC coil; then where μ is the permeability of free space, I c is the current of the reference circuit, and N is the number of turns of the AC coil.

7. A leakage current sensor according to claim 6, characterized in that, The current backstepping module is specifically configured to substitute the sensor sensitivity into V d = G1SB d , where V d is the voltage of the original voltage signal, and B d is the magnetic induction intensity generated by the line to be detected at the Wheatstone bridge circuit; The reverse deduction restores the original current signal to be: where D d is the distance from the Wheatstone bridge circuit to the line to be detected.

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