Zero-flux current sensor and zero-flux insulation leakage current detection method

Abstract

The invention discloses a zero-flux current sensor and a zero-flux insulation leakage current detection method, and belongs to the technical field of electric leakage detection. According to the zero-flux current sensor, the iron core, the coil and the circuit of the sensor are designed, and a zero-flux closed-loop feedback structure is formed by arranging the induction iron core unit, the measuring coil unit and the detection circuit module and is used for detecting insulation leakage current, so that measurement of weak alternating-current and direct-current leakage current can be realized; the structure is simple, practical and convenient to produce and manufacture. Furthermore, a first excitation coil, a second excitation coil and a compensation coil are arranged to form a magnetic field modulation current feedback compensation structure, magnetic field balance can be achieved, noise elimination detection is further achieved, and therefore the sensor has the advantages of being high in measurement precision, high in anti-interference capacity and stable in performance. Therefore, detection of tiny current of hundreds of microamperes to several mA levels can be realized.

Description

Technical Field

[0001] The invention relates to a zero-flux current sensor and a zero-flux insulation leakage current detection method, belonging to the technical field of leakage detection. Background Art

[0002] During normal operation, power supply lines or power equipment are not completely insulated from the ground. There is a certain impedance to the ground, which causes leakage current to the ground. This is distributed leakage, and the harm is far less than the leakage concentrated in a certain part of the same power equipment. Therefore, normal leakage of power supply lines or power equipment will not cause safety problems.

[0003] In the event of a power supply system or electrical equipment failure, the leakage current increases, affecting safe electricity use and even causing electrical fires and electric shocks. The distributed impedance to ground and the leakage current under different line lengths are also different. The distributed impedance to ground is proportional to the length of the power supply line, and is also affected by environmental factors such as temperature and humidity. When the power supply line is operating normally, its leakage current is mainly capacitive leakage, while the resistive leakage current accounts for a very small proportion, usually less than 0.5mA. With the increase in power electronic electrical equipment, the capacitive leakage current component continues to increase, even reaching hundreds of milliamperes. Conducting leakage detection and adopting different protection strategies based on the characteristics of the leakage current are effective measures to ensure the reliable operation of the power supply system and electrical equipment.

[0004] Therefore, leakage current is a key parameter to characterize the insulation state of power equipment. Leakage current is usually a mixture of AC and DC components. The electromagnetic environment of high-voltage power equipment is complex and the leakage current is weak, which brings great challenges to leakage current monitoring. There is an urgent need for current sensing technology with high resolution and strong anti-interference ability.

[0005] The non-contact current sensors mainly include Hall current sensors, magnetoresistive current sensors and magnetic modulation current sensors. Among them, Hall and magnetoresistive sensors measure the magnetic field generated by weak current. When the measured magnetic field is very weak, the resolution of the sensor is greatly affected by its own noise, temperature drift and other factors, and it is difficult to measure currents below 100uA.

[0006] Electromagnetic current sensors usually use a through-core toroidal core structure, and the primary winding of the toroidal structure is the current winding to be measured. According to the number of turns, it can be divided into two types: multi-turn series and single-turn through-core. The multi-turn series primary winding is wound on the core. Because it has more turns, it can increase the induced current on the secondary side. However, this structure will change the inherent wiring form of the device under test, increase potential fault points, and is not conducive to the safe operation of power equipment. The single-turn through-core primary winding only passes through the core. Since the current to be measured is weak, its output signal is also weak, and it is still impossible to measure weak AC and DC leakage currents.

[0007] The information disclosed in this Background Art is only for understanding the background of the inventive concept and therefore it may include information that does not constitute the prior art. Summary of the invention

[0008] In response to the above problem or one of the above problems, an object of the present invention is to provide a zero-flux current sensor and a zero-flux insulation leakage current detection method, which utilizes an inductive core unit, a measuring coil unit and a detection circuit module to form a zero-flux closed-loop feedback structure for detecting insulation leakage current, thereby realizing the measurement of weak AC and DC leakage currents. The structure is simple, practical and easy to produce.

[0009] In response to the above problem or one of the above problems, the second object of the present invention is to provide a zero flux current sensor and a zero flux insulation leakage current detection method, which utilizes a first excitation coil, a second excitation coil and a compensation coil to form a magnetic field modulation current feedback compensation structure, and can achieve magnetic field balance, thereby realizing noise elimination detection, so that the sensor has the advantages of high measurement accuracy, strong anti-interference ability and stable performance, and thus can realize the detection of tiny currents of several hundred μA to several mA.

[0010] To achieve one of the above purposes, the first technical solution of the present invention is:

[0011] A magnetic modulation zero flux current sensor, comprising an induction core unit, a measuring coil unit and a detection circuit module;

[0012] The induction core unit is provided with a toroidal magnetic core, which can generate a magnetic field that fully reflects the magnitude of the conductor current;

[0013] The measuring coil unit comprises a first excitation coil, a second excitation coil and a compensation coil which are wound on a ring-shaped magnetic core;

[0014] The first excitation coil and the second excitation coil have the same number of coils and are wound in opposite directions, so as to generate magnetic fluxes of equal magnitude and opposite directions in the annular magnetic core;

[0015] A compensation coil is used to generate opposite magnetic flux to maintain the zero magnetic flux state of the annular magnetic core;

[0016] The detection circuit module is provided with an excitation circuit, a preamplifier circuit, a phase shifter and a demodulator;

[0017] An excitation circuit, used for outputting an excitation current;

[0018] A preamplifier circuit is used to preamplify the bridge signal to obtain an amplified signal;

[0019] A phase shifter, used to shift the phase of the excitation signal to obtain a reference signal;

[0020] The demodulator is used to demodulate the amplified signal and the reference signal to obtain a voltage output signal that can represent the magnitude of the current signal.

[0021] After continuous exploration and experiments, the present invention forms a zero-flux closed-loop feedback structure by setting an induction core unit, a measuring coil unit and a detection circuit module, which is used to detect insulation leakage current, thereby realizing the measurement of weak AC and DC leakage currents. The structure is simple, practical and easy to produce.

[0022] Furthermore, the present invention forms a magnetic field modulation current feedback compensation structure by setting a first excitation coil, a second excitation coil and a compensation coil, and can achieve magnetic field balance, thereby realizing noise elimination detection, so that the sensor of the present invention has the advantages of high measurement accuracy, strong anti-interference ability and stable performance, and thus can realize the detection of tiny currents of several hundred μA to several mA.

[0023] Furthermore, the present invention designs the sensor core, coil and circuit. Compared with the traditional open-loop current sensor, the sensor of the present invention has a more compact structure, and its anti-interference ability and sensitivity are improved.

[0024] As the preferred technical measures:

[0025] According to the error being proportional to the average magnetic path length d, the magnetic path length d of the annular core is related to the inner diameter a and outer diameter b of the annular core. The inner diameter a, outer diameter b and height h of the annular core are set, and the relationship is as follows:

[0026] 1.5(ba)≤h≤2(ba);

[0027] Or / and, the inner diameter a of the annular magnetic core is 5 mm, the outer diameter b is 11 mm, and the height h is 12 mm.

[0028] As the preferred technical measures:

[0029] The coil in the measuring coil unit is wound with 0.19 mm enameled wire. The number of turns of the first excitation coil and the second excitation coil is 50, and the number of turns of the compensation coil is 2.

[0030] When the frequency is less than 1.3KHz, the inductance of the excitation coil is 294mH.

[0031] As the preferred technical measures:

[0032] The excitation circuit uses a single-chip microcomputer to control the DDS module to generate a sine wave, and then provides an excitation current through a power amplifier circuit; the DDS module is a closed AD9833, which is programmed by a single-chip microcomputer to output sine waves of different frequencies, and includes capacitors C1 and C3, as well as capacitors C4, C16, C17 and C18 arranged in parallel;

[0033] The power amplifier circuit is provided with an OPA691 amplifier, which can output an excitation current of up to 190 mA, and includes a capacitor C20, a capacitor C21, a resistor R6, a resistor R7, a resistor R8 and a resistor R9.

[0034] As the preferred technical measures:

[0035] The preamplifier circuit is equipped with an instrumentation amplifier AD8421 with large bandwidth and low noise and a resistor Rg, which changes the amplification factor A of the circuit through the resistor Rg. The calculation formula of the amplification factor A is as follows:

[0036] A=1+9.9k / Rg;

[0037] Or / and, the preamplifier circuit includes a capacitor C7, a resistor R5, a resistor R6 and a resistor R7.

[0038] As the preferred technical measures:

[0039] The phase shifter includes amplifier U3A, amplifier U3B, capacitor C4, resistor R7, resistor R8, resistor R9 and resistor RP1, which are used to make the amplified signal of the preamplifier circuit have the same phase as the excitation signal to detect the amplitude of the amplified signal, so as to shift the phase of the excitation signal. The signal after phase shift is the reference signal, which is sent to the multiplier with the amplified signal for demodulation.

[0040] As the preferred technical measures:

[0041] The demodulator includes a multiplier AD835, an amplifier U4B, a capacitor C43, a capacitor C46, ​​a resistor R43, a resistor R44, a resistor R45, a resistor R46, a resistor Sig and a resistor Vref. The multiplier AD835 is used to implement signal multiplication demodulation. The demodulated signal is low-pass filtered and amplified to obtain a voltage output signal representing the magnitude of the current signal.

[0042] The AD835 multiplier has a high bandwidth and its input signal amplitude is controlled within the range of ±1V.

[0043] To achieve one of the above purposes, the second technical solution of the present invention is:

[0044] A zero-flux closed-loop feedback insulation leakage current detection method, using the above-mentioned magnetic modulation zero-flux current sensor, includes the following contents:

[0045] Obtaining the measured current I of the primary side to be detected;

[0046] Place the primary side measured current I at the middle position of the magnetic modulation zero flux current sensor;

[0047] The magnetic flux deviation signal of the annular magnetic core is used to generate a magnetic flux in the secondary circuit that is opposite in direction to the measured current and has the same magnitude, so that the magnetic flux of the annular magnetic core approaches zero.

[0048] The first excitation coil C1 and the first excitation coil C2 are supplied with excitation modulation currents of equal magnitude, and generate a first magnetic flux Φ1 and a second magnetic flux Φ2 of equal magnitude and opposite direction in the annular magnetic core according to the winding direction of the coils;

[0049] When the measured current I flows through the primary side conductor, a magnetic flux Φ is generated in the annular magnetic core. The superposition of the magnetic fluxes causes the magnetic fluxes of the annular magnetic cores at the first excitation coil C1 and the first excitation coil C2 to change in different directions, resulting in a difference in the local magnetic permeability of the annular magnetic cores.

[0050] This difference is detected by the first excitation coil C1 and the second excitation coil C2, and converted into a current and added to the compensation coil C3 to generate a compensation magnetic flux Φ opposite to the magnetic flux Φ, thereby maintaining the zero magnetic flux state of the annular magnetic core;

[0051] The magnitude of the current of the compensation coil C3 is measured by the sampling resistor to obtain the magnitude of the measured current.

[0052] The present invention utilizes a first excitation coil, a second excitation coil and a compensation coil to form a magnetic field modulation current feedback compensation structure, and can achieve magnetic field balance, thereby realizing noise elimination detection, so that the sensor of the present invention has the advantages of high measurement accuracy, strong anti-interference ability and stable performance, and thus can realize the detection of tiny currents of several hundred μA to several mA.

[0053] As the preferred technical measures:

[0054] The first excitation coil C1 outputs the inductance L1;

[0055] The first excitation coil C2 outputs the inductance L2;

[0056] Compensation coil C3 outputs inductance L3;

[0057] The excitation current with a frequency of f is loaded on the inductor L1 and the inductor L2 through the bridge circuit. When the measured current I on the primary side is zero, the bridge is in a balanced state, so that the output of the amplifier A1 and the amplifier A2 is zero, and the current loaded on the compensation coil L3 is zero;

[0058] When the measured current I on the primary side is not zero, the bridge loses balance due to the different magnetization states of the annular cores at the inductors L1 and L2. The amplifier A1 outputs an AC carrier signal proportional to the current. The carrier signal and the excitation signal are demodulated by the demodulator and low-pass filtered and amplified by the amplifier A2. The output current is applied to the inductor L3, and the voltage drop of the sampling resistor R3 is proportional to the measured current.

[0059] Since the inductance of the inductor L3 is small, when the frequency of the measured current is low, the voltage drop on the inductor L3 can be ignored.

[0060] As the preferred technical measures:

[0061] When the measured current I flows through a wire of length L, a magnetic field will be generated around it. The magnetic field at point P is the magnetic field of each current element. The vector of the magnetic field generated at point P is superposition;

[0062] The magnetic induction intensity at point P is:

[0063]

[0064] Where μ0 is the vacuum magnetic permeability;

[0065]

[0066] When the magnetic field of the conductor acts on the annular core, it should be ensured that the conductor has enough straight sections. At this time, the magnetic field in the annular core can fully reflect the magnitude of the conductor current. The annular core is maintained in the middle of the straight conductor, and the conductor passes vertically through the center of the annular core. The measurement error will decrease as the ratio of the straight section length L of the conductor to the radius r0 of the annular core increases.

[0067] The error of the annular core is proportional to the average magnetic path length d, which is related to the inner diameter a and outer diameter b of the annular core. At the same time, when the cross-section of the annular core increases, the volume of the annular core increases, which increases the excitation impedance and reduces the excitation current, that is, the error decreases.

[0068] For the annular core, the inner diameter a, outer diameter b and height h of the annular core are set, and the relationship is as follows:

[0069] 1.5(ba)≤h≤2(ba);

[0070] The inner diameter of the magnetic modulation zero flux current sensor is a=5 mm, the outer diameter is b=11 mm, and the height is h=12 mm.

[0071] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0072] After continuous exploration and experiments, the present invention forms a zero-flux closed-loop feedback structure by setting an induction core unit, a measuring coil unit and a detection circuit module, which is used to detect insulation leakage current, thereby realizing the measurement of weak AC and DC leakage currents. The structure is simple, practical and easy to produce.

[0073] Furthermore, the present invention forms a magnetic field modulation current feedback compensation structure by setting a first excitation coil, a second excitation coil and a compensation coil, and can achieve magnetic field balance, thereby realizing noise elimination detection, so that the sensor of the present invention has the advantages of high measurement accuracy, strong anti-interference ability and stable performance, and thus can realize the detection of tiny currents of several hundred μA to several mA.

[0074] Furthermore, the present invention designs the sensor core, coil and circuit. Compared with the traditional open-loop current sensor, the sensor of the present invention has a more compact structure, and its anti-interference ability and sensitivity are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 A schematic diagram of a zero-flux feedback current sensor of the present invention;

[0076] Figure 2 A measurement principle diagram of the zero flux current sensor of the present invention;

[0077] Figure 3 A schematic diagram of the magnetic field generated by the current-carrying conductor of the present invention;

[0078] Figure 4 A structural schematic diagram of a ring-shaped magnetic core of the present invention;

[0079] Figure 5 A schematic diagram of the excitation circuit of the present invention;

[0080] Figure 6 A schematic diagram of a preamplifier circuit of the present invention;

[0081] Figure 7 A schematic diagram of the phase shift circuit of the present invention;

[0082] Figure 8 A schematic diagram of a demodulation circuit of the present invention. DETAILED DESCRIPTION

[0083] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0084] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the following detailed description of the present invention. Those skilled in the art can fully understand the present invention without the description of these details.

[0085] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention pertains. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0086] The first specific embodiment of the magnetic modulation zero flux current sensor of the present invention:

[0087] A magnetic modulation zero flux current sensor, comprising an induction core unit, a measuring coil unit and a detection circuit module;

[0088] The induction core unit is provided with a toroidal magnetic core, which can generate a magnetic field that fully reflects the magnitude of the conductor current;

[0089] The measuring coil unit comprises a first excitation coil, a second excitation coil and a compensation coil which are wound on a ring-shaped magnetic core;

[0090] The first excitation coil and the second excitation coil have the same number of coils and are wound in opposite directions, so as to generate magnetic fluxes of equal magnitude and opposite directions in the annular magnetic core;

[0091] A compensation coil is used to generate opposite magnetic flux to maintain the zero magnetic flux state of the annular magnetic core;

[0092] The detection circuit module is provided with an excitation circuit, a preamplifier circuit, a phase shifter and a demodulator;

[0093] An excitation circuit, used for outputting an excitation current;

[0094] A preamplifier circuit is used to preamplify the bridge signal to obtain an amplified signal;

[0095] A phase shifter, used to shift the phase of the excitation signal to obtain a reference signal;

[0096] The demodulator is used to demodulate the amplified signal and the reference signal to obtain a voltage output signal that can represent the magnitude of the current signal.

[0097] In this embodiment: according to the error being proportional to the average magnetic path length d, the magnetic path length d of the annular magnetic core is related to the inner diameter a and the outer diameter b of the annular magnetic core, and the inner diameter a, the outer diameter b and the height h of the annular magnetic core are set, and the relationship is as follows:

[0098] 1.5(ba)≤h≤2(ba);

[0099] Or / and, the inner diameter a of the annular magnetic core is 5 mm, the outer diameter b is 11 mm, and the height h is 12 mm.

[0100] In this embodiment: the coil in the measuring coil unit is wound with 0.19 mm enameled wire, the number of turns of the first excitation coil and the second excitation coil are both 50, and the number of turns of the compensation coil is 2;

[0101] When the frequency is less than 1.3KHz, the inductance of the excitation coil is 294mH.

[0102] In this embodiment: the excitation circuit uses a single-chip microcomputer to control the DDS module to generate a sine wave, and then provides an excitation current through a power amplifier circuit; the DDS module is a closed AD9833, which is programmed by the single-chip microcomputer to output sine waves of different frequencies, and includes capacitors C1 and C3, as well as capacitors C4, C16, C17 and C18 arranged in parallel;

[0103] The power amplifier circuit is provided with an OPA691 amplifier, which can output an excitation current of up to 190 mA, and includes a capacitor C20, a capacitor C21, a resistor R6, a resistor R7, a resistor R8 and a resistor R9.

[0104] In this embodiment: the preamplifier circuit includes a capacitor C7, a resistor R5, a resistor R6, a resistor R7, an instrument amplifier AD8421 with large bandwidth and low noise, and a resistor Rg, which changes the amplification factor A of the circuit through the resistor Rg.

[0105] The calculation formula of magnification A is as follows:

[0106] A=1+9.9k / Rg.

[0107] In this embodiment: the phase shifter includes an amplifier U3A, an amplifier U3B, a capacitor C4, a resistor R7, a resistor R8, a resistor R9 and a resistor RP1, which are used to make the amplified signal of the preamplifier circuit have the same phase as the excitation signal. In order to detect the amplitude of the amplified signal, the excitation signal needs to be phase shifted, and the signal after phase shift is the reference signal, which is sent to the multiplier together with the amplified signal for demodulation.

[0108] In this embodiment: the demodulator includes a multiplier AD835, an amplifier U4B, a capacitor C43, a capacitor C46, ​​a resistor R43, a resistor R44, a resistor R45, a resistor R46, a resistor Sig and a resistor Vref, and the multiplier AD835 is used to implement signal multiplication demodulation, and the demodulated signal is low-pass filtered and amplified to obtain a voltage output signal representing the magnitude of the current signal;

[0109] The AD835 multiplier has a high bandwidth and its input signal amplitude is controlled within the range of ±1V.

[0110] A specific embodiment of the zero-flux closed-loop feedback insulation leakage current detection method of the present invention:

[0111] A zero-flux closed-loop feedback insulation leakage current detection method, using the above-mentioned magnetic modulation zero-flux current sensor, includes the following contents:

[0112] Obtaining the measured current I of the primary side to be detected;

[0113] Place the primary side measured current I at the middle position of the magnetic modulation zero flux current sensor;

[0114] The magnetic flux deviation signal of the annular magnetic core is used to generate a magnetic flux in the secondary circuit that is opposite in direction to the measured current and has the same magnitude, so that the magnetic flux of the annular magnetic core approaches zero.

[0115] The first excitation coil C1 and the first excitation coil C2 are supplied with excitation modulation currents of equal magnitude, and generate a first magnetic flux Φ1 and a second magnetic flux Φ2 of equal magnitude and opposite direction in the annular magnetic core according to the winding direction of the coils;

[0116] When the measured current I flows through the primary side conductor, a magnetic flux Φ is generated in the annular magnetic core. The superposition of the magnetic fluxes causes the magnetic fluxes of the annular magnetic cores at the first excitation coil C1 and the first excitation coil C2 to change in different directions, resulting in a difference in the local magnetic permeability of the annular magnetic cores.

[0117] This difference is detected by the first excitation coil C1 and the second excitation coil C2, and converted into a current and added to the compensation coil C3 to generate a compensation magnetic flux Φ opposite to the magnetic flux Φ, thereby maintaining the zero magnetic flux state of the annular magnetic core;

[0118] The magnitude of the current of the compensation coil C3 is measured by the sampling resistor to obtain the magnitude of the measured current.

[0119] In this embodiment: the first excitation coil C1 outputs the inductance L1;

[0120] The first excitation coil C2 outputs the inductance L2;

[0121] Compensation coil C3 outputs inductance L3;

[0122] The excitation current with a frequency of f is loaded on the inductor L1 and the inductor L2 through the bridge circuit. When the measured current I on the primary side is zero, the bridge is in a balanced state, so that the output of the amplifier A1 and the amplifier A2 is zero, and the current loaded on the compensation coil L3 is zero;

[0123] When the measured current I on the primary side is not zero, the bridge loses balance due to the different magnetization states of the annular cores at the inductors L1 and L2. The amplifier A1 outputs an AC carrier signal proportional to the current. The carrier signal and the excitation signal are demodulated by the demodulator and low-pass filtered and amplified by the amplifier A2. The output current is applied to the inductor L3, and the voltage drop of the sampling resistor R3 is proportional to the measured current.

[0124] Since the inductance of the inductor L3 is small, when the frequency of the measured current is low, the voltage drop on the inductor L3 can be ignored.

[0125] In this embodiment, when the measured current I flows through the wire with a length of L, a magnetic field will be generated around it. The magnetic field at point P is the magnetic field of each current element. The vector of the magnetic field generated at this location Superposition; the magnetic induction intensity at point P is:

[0126]

[0127] Where μ0 is the vacuum magnetic permeability;

[0128]

[0129] When the magnetic field of the conductor acts on the annular core, it should be ensured that the conductor has enough straight sections. At this time, the magnetic field in the annular core can fully reflect the magnitude of the conductor current. The annular core is maintained in the middle of the straight conductor, and the conductor passes vertically through the center of the annular core. The measurement error will decrease as the ratio of the straight section length L of the conductor to the radius r0 of the annular core increases.

[0130] The error of the annular core is proportional to the average magnetic path length d, which is related to the inner diameter a and outer diameter b of the annular core. At the same time, when the cross-section of the annular core increases, the volume of the annular core increases, which increases the excitation impedance and reduces the excitation current, that is, the error decreases.

[0131] For the annular core, the inner diameter a, outer diameter b and height h of the annular core are set, and the relationship is as follows:

[0132] 1.5(ba)≤h≤2(ba);

[0133] The inner diameter of the magnetic modulation zero flux current sensor is a=5 mm, the outer diameter is b=11 mm, and the height is h=12 mm.

[0134] like Figure 1 , Figure 2 As shown, the second specific embodiment of the magnetic modulation zero flux current sensor of the present invention is:

[0135] A magnetic modulation zero flux current sensor comprises a high permeability annular magnetic core, excitation coils C1 and C2, a compensation coil C3, and a sensor detection circuit, which can accurately measure the primary side measured current I. The magnetic modulation zero flux current sensor uses the magnetic flux deviation signal of the magnetic core to generate a magnetic flux with the same magnitude and opposite direction to the measured current (primary) in the secondary circuit, so that the magnetic flux of the magnetic core approaches zero.

[0136] The magnetic modulation coils C1 and C2 are supplied with excitation modulation currents of equal magnitude, and generate magnetic fluxes Φ1 and Φ2 of equal magnitude and opposite direction in the magnetic core according to the winding direction of the coils.

[0137] The sensor detection circuit mainly includes key circuit modules such as excitation circuit, preamplifier module, phase shifter, and demodulator.

[0138] When the measured current I flows through the primary side conductor, a magnetic flux Φ is generated in the magnetic core. The superposition of the magnetic flux causes the magnetic flux of the magnetic core at coils C1 and C2 to change in opposite directions, resulting in a difference in the local magnetic permeability of the magnetic core. This difference is detected by coils C1 and C2, and converted into a current and added to the compensation coil C3 to generate a magnetic flux Φ opposite to the magnetic flux Φ, maintaining the "zero flux" state of the magnetic core. The magnitude of the measured current can be obtained by measuring the magnitude of the C3 current through the sampling resistor.

[0139] The measurement principle of zero flux current sensor is as follows Figure 2 As shown, L1, L2 and L3 are the inductances corresponding to coils C1, C2 and C3 respectively. The excitation current with a frequency of f is loaded on L1 and L2 through the bridge circuit. When the current I to be measured on the primary side is zero, the bridge is in a balanced state, the outputs of A1 and A2 are zero, and the current loaded on coil L3 is also zero. When the current I on the primary side is not zero, the bridge loses balance due to the different magnetization states of the magnetic cores at L1 and L2. A1 outputs an AC carrier signal proportional to the current. This carrier signal and the excitation signal are demodulated by the demodulator and low-pass filtered and amplified by A2. The output current is added to L3, and the voltage drop of the sampling resistor R3 is proportional to the current to be measured. Because the inductance of L3 is small, when the frequency of the current to be measured is low, the voltage drop on L3 can be ignored.

[0140] As a key component for tiny current detection, the current sensor should have high precision, high stability, anti-interference, and resistance to harsh environments, and its measurement range is usually in the range of several hundred μA to several mA. The present invention designs a tiny current sensor based on zero flux closed-loop feedback, and adopts modulation and demodulation technology to effectively improve the anti-interference performance of the sensor.

[0141] In this embodiment: the method for setting the core material and structure is as follows:

[0142] The micro current sensor is composed of a magnetic core, an excitation coil, a compensation coil and a measurement circuit. Its basic principle is Ampere's loop law. Figure 3 As shown in the figure, when a current I flows through a wire of length L, a magnetic field will be generated around it. The magnetic field at point P is the sum of the current elements. The vector of the magnetic field generated at this location Overlay.

[0143] The magnetic induction intensity at point P is:

[0144]

[0145] Where μ0 is the magnetic permeability of vacuum.

[0146] Further we can get:

[0147]

[0148] When the magnetic field of the conductor acts on the annular core, it should be ensured that the conductor has enough straight sections, so that the magnetic field in the core can fully reflect the magnitude of the conductor current. Maintaining the core in the middle of the straight conductor and the conductor vertically passing through the center of the core, the measurement error will decrease as the ratio of the straight length L of the conductor to the core radius r0 increases. The calculation results are shown in Table 1. When the ratio is greater than 14, the measurement error will be less than 1%.

[0149] Table 1 Relationship between magnetic field error and ratio ra

[0150] <![CDATA[L / r0]]> 3 4 5 6 7 8 error% 16.8 10.5 7.1 5.1 3.8 3.0 <![CDATA[L / r0]]> 9 10 11 12 13 14 error% 2.4 1.9 1.6 1.33 1.13 0.97 <![CDATA[L / r0]]> 15 16 17 18 19 20 error% 0.85 0.74 0.65 0.58 0.52 0.47

[0151] When a 1mA current flows through a long straight wire, the magnetic field generated at a distance of 16mm is about 12.5nT, which is much smaller than the tens of thousands of nT of the geomagnetic field. It can be seen that to achieve the measurement of milliampere current, not only shielding, differential and other measures must be taken to reduce the interference of the geomagnetic field, but also the current sensor and its circuit must have good anti-interference and low noise performance.

[0152] The structure of the ring core is as follows Figure 4 As shown. The error is proportional to the average magnetic path length d. The magnetic path length d of the magnetic core is related to the inner diameter a and the outer diameter b of the magnetic core. At the same time, when the cross-section of the magnetic core increases, the volume of the magnetic core will increase, making the excitation impedance larger and thus reducing the excitation current, even if the error is reduced at this time. In actual production, not only the influence of the core parameters on the measurement error should be considered, but also the feasibility of production. For annular magnetic cores, it is generally more appropriate to choose 1.5 (ba) ≤ h ≤ 2 (ba). The inner diameter of the sensor of the present invention is a = 5mm, the outer diameter is b = 11mm, and the height is h = 12mm.

[0153] On the other hand, the performance of the sensor is directly related to the core material. The better the magnetic properties of the material, the smaller the size of the core can be. Therefore, the main measure to reduce the error is to improve the magnetic properties of the core. The core material is usually required to have high magnetic permeability, low coercive force and low saturation magnetization. By comparison, nano-amorphous alloys have better performance and are suitable as the core of high-precision micro-current sensors.

[0154] In this embodiment: the method for designing coil parameters is as follows:

[0155] The excitation coil is usually wound with enameled wire, and the coil must consider the inductance and its coverage area. Therefore, the present invention connects the excitation coil to the bridge circuit and obtains the measurement signal from the bridge circuit output. According to the principle of this sensor, the coverage area of ​​the excitation coil should be controlled and the inductance should not be too large, otherwise it will affect the matching relationship between the excitation voltage and the excitation current. In addition, the oscillation frequency of the excitation voltage cannot be too low. Too low a frequency will cause the sensor response speed to slow down, causing signal frequency aliasing, and it is difficult to apply to the measurement of AC current. It is usually required that the modulation frequency is at least 10 times greater than the useful signal frequency. The excitation frequency in the present invention is 1.3kHz. The compensation coil is mainly used to generate a compensation magnetic field opposite to the measured current. In the present invention, the measured current is a small current, and the primary side coil is a direct-through single-turn coil, so the compensation coil can also use a coil with a smaller number of turns.

[0156] The coil is wound with 0.19mm enameled wire, both excitation coils have 50 turns, and the compensation coil is wound with 2 turns. After experimental testing, the inductance of the excitation coil is 294mH at a frequency of 1.3KHz.

[0157] In this embodiment: Figure 5 As shown, the setting method of the excitation circuit is as follows:

[0158] The sensor uses sinusoidal excitation. In order to make the excitation frequency easy to adjust, the design uses a single-chip microcomputer to control the DDS module to generate a sine wave, and then provides a strong excitation current through the power amplifier circuit. The DDS uses the small-volume enclosed AD9833, which is programmed by the single-chip microcomputer to output sine waves of different frequencies. The power amplifier uses the OPA691 amplifier, which can output an excitation current of up to 190mA.

[0159] In this embodiment: Figure 6 As shown, the preamplifier module includes the following:

[0160] The bridge signal is preamplified by using the AD8421 instrumentation amplifier with large bandwidth and low noise. The amplification factor A of the circuit can be changed by the resistor Rg. The calculation formula is as follows:

[0161] A=1+9.9k / Rg.

[0162] In this embodiment: Figure 7 As shown, the phase shifter includes the following:

[0163] In order to make the preamplified signal and the excitation signal have the same phase and accurately detect the amplitude of the preamplified signal, the excitation signal needs to be phase-shifted. The phase-shifted signal is the reference signal, which is sent to the multiplier with the preamplified signal for demodulation.

[0164] In this embodiment: Figure 8 As shown, the demodulator includes the following:

[0165] The signal multiplication demodulation is realized by the multiplier AD835. The multiplication demodulation is sensitive to the frequency and phase of the signal and has strong anti-interference ability. AD835 has a very high bandwidth. It should be noted that the input signal amplitude of AD835 is required to be controlled within the range of ±1V. The demodulated signal is low-pass filtered and amplified to obtain a voltage output signal representing the current signal size.

[0166] Micro current detection is an important means of insulation leakage current monitoring, fault leakage current protection and identification, and can provide important characteristic status information for smart grids and smart appliances. The present invention adopts a zero-flux closed-loop feedback structure to design a sensor that can be used to measure milliampere current. At present, there is no zero-flux closed-loop feedback structure design for insulation leakage current detection in China.

[0167] The present invention designs the sensor core, coil and circuit based on the analysis of the working principle of the sensor. Compared with the traditional open-loop current sensor, this type of sensor has a more compact structure, and its anti-interference ability and sensitivity are improved.

[0168] An embodiment of a device applying the method of the present invention:

[0169] An electronic device comprising:

[0170] one or more processors;

[0171] A storage device for storing one or more programs;

[0172] When the one or more programs are executed by the one or more processors, the one or more processors implement the above-mentioned zero-flux closed-loop feedback insulation leakage current detection method.

[0173] A computer medium embodiment using the method of the present invention:

[0174] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the above-mentioned zero-flux closed-loop feedback insulation leakage current detection method.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field can still modify or replace the specific implementation methods of the present invention with equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A magnetic modulation zero flux current sensor, characterized in that: It includes an inductive core unit, a measuring coil unit and a detection circuit module; The induction core unit is provided with a toroidal magnetic core, which can generate a magnetic field that fully reflects the magnitude of the conductor current; The measuring coil unit comprises a first excitation coil, a second excitation coil and a compensation coil which are wound on a ring-shaped magnetic core; The first excitation coil and the second excitation coil have the same number of coils and are wound in opposite directions, so as to generate magnetic fluxes of equal magnitude and opposite directions in the annular magnetic core; A compensation coil is used to generate opposite magnetic flux to maintain the zero magnetic flux state of the annular magnetic core; The detection circuit module is provided with an excitation circuit, a preamplifier circuit, a phase shifter and a demodulator; An excitation circuit, used for outputting an excitation current; A preamplifier circuit is used to preamplify the bridge signal to obtain an amplified signal; A phase shifter, used to shift the phase of the excitation signal to obtain a reference signal; The demodulator is used to demodulate the amplified signal and the reference signal to obtain a voltage output signal that can represent the magnitude of the current signal.

2. A magnetic modulation zero flux current sensor as claimed in claim 1, characterized in that: According to the error being proportional to the average magnetic path length d, the magnetic path length d of the annular core is related to the inner diameter a and outer diameter b of the annular core. The inner diameter a, outer diameter b and height h of the annular core are set, and the relationship is as follows: 1.5(ba)≤h≤2(ba); Or / and, the inner diameter a of the annular magnetic core is 5 mm, the outer diameter b is 11 mm, and the height h is 12 mm.

3. The magnetic modulation zero flux current sensor according to claim 1, characterized in that: The coil in the measuring coil unit is wound with 0.19 mm enameled wire. The number of turns of the first excitation coil and the second excitation coil is 50, and the number of turns of the compensation coil is 2. When the frequency is less than 1.3KHz, the inductance of the excitation coil is 294mH.

4. The magnetic modulation zero flux current sensor according to claim 1, characterized in that: The excitation circuit uses a single-chip microcomputer to control the DDS module to generate a sine wave, and then provides an excitation current through a power amplifier circuit; the DDS module is a closed AD9833, which is programmed by a single-chip microcomputer to output sine waves of different frequencies, and includes capacitors C1 and C3, as well as capacitors C4, C16, C17 and C18 arranged in parallel; The power amplifier circuit is provided with an OPA691 amplifier, which can output an excitation current of up to 190 mA, and includes a capacitor C20, a capacitor C21, a resistor R6, a resistor R7, a resistor R8 and a resistor R9.

5. The magnetic modulation zero flux current sensor according to claim 1, characterized in that: The preamplifier circuit is equipped with an instrumentation amplifier AD8421 with large bandwidth and low noise and a resistor Rg, which changes the amplification factor A of the circuit through the resistor Rg. The calculation formula of the amplification factor A is as follows: A=1+9.9k / Rg; Or / and, the preamplifier circuit includes a capacitor C7, a resistor R5, a resistor R6 and a resistor R7.

6. The magnetic modulation zero flux current sensor according to claim 1, characterized in that: The phase shifter includes amplifier U3A, amplifier U3B, capacitor C4, resistor R7, resistor R8, resistor R9 and resistor RP1, which are used to make the amplified signal of the preamplifier circuit have the same phase as the excitation signal to detect the amplitude of the amplified signal, so as to shift the phase of the excitation signal. The signal after phase shift is the reference signal, which is sent to the multiplier with the amplified signal for demodulation.

7. The magnetic modulation zero flux current sensor according to claim 1, characterized in that: The demodulator includes a multiplier AD835, an amplifier U4B, a capacitor C43, a capacitor C46, ​​a resistor R43, a resistor R44, a resistor R45, a resistor R46, a resistor Sig and a resistor Vref. The multiplier AD835 is used to implement signal multiplication demodulation. The demodulated signal is low-pass filtered and amplified to obtain a voltage output signal representing the magnitude of the current signal. The AD835 multiplier has a high bandwidth and its input signal amplitude is controlled within the range of ±1V.

8. A zero-flux closed-loop feedback insulation leakage current detection method, characterized in that: A magnetic modulation zero flux current sensor as claimed in any one of claims 1 to 7, wherein Includes the following: Obtaining the measured current I of the primary side to be detected; Place the primary side measured current I at the middle position of the magnetic modulation zero flux current sensor; The magnetic flux deviation signal of the annular magnetic core is used to generate a magnetic flux in the secondary circuit that is opposite in direction to the measured current and has the same magnitude, so that the magnetic flux of the annular magnetic core approaches zero. The first excitation coil C1 and the first excitation coil C2 are supplied with excitation modulation currents of equal magnitude, and generate a first magnetic flux Φ1 and a second magnetic flux Φ2 of equal magnitude and opposite direction in the annular magnetic core according to the winding direction of the coils; When the measured current I flows through the primary side conductor, a magnetic flux Φ is generated in the annular magnetic core. The superposition of the magnetic fluxes causes the magnetic fluxes of the annular magnetic cores at the first excitation coil C1 and the first excitation coil C2 to change in different directions, resulting in a difference in the local magnetic permeability of the annular magnetic cores. This difference is detected by the first excitation coil C1 and the second excitation coil C2, and converted into a current and added to the compensation coil C3 to generate a compensation magnetic flux Φ opposite to the magnetic flux Φ, thereby maintaining the zero magnetic flux state of the annular magnetic core; The magnitude of the current of the compensation coil C3 is measured by the sampling resistor to obtain the magnitude of the measured current.

9. A zero-flux closed-loop feedback insulation leakage current detection method as claimed in claim 8, characterized in that: The first excitation coil C1 outputs the inductance L1; The first excitation coil C2 outputs the inductance L2; Compensation coil C3 outputs inductance L3; The excitation current with a frequency of f is loaded on the inductor L1 and the inductor L2 through the bridge circuit. When the measured current I on the primary side is zero, the bridge is in a balanced state, so that the output of the amplifier A1 and the amplifier A2 is zero, and the current loaded on the compensation coil L3 is zero; When the measured current I on the primary side is not zero, the bridge loses balance due to the different magnetization states of the annular cores at the inductors L1 and L2. The amplifier A1 outputs an AC carrier signal proportional to the current. The carrier signal and the excitation signal are demodulated by the demodulator and low-pass filtered and amplified by the amplifier A2. The output current is applied to the inductor L3, and the voltage drop of the sampling resistor R3 is proportional to the measured current. Since the inductance of the inductor L3 is small, when the frequency of the measured current is low, the voltage drop on the inductor L3 can be ignored.

10. A zero-flux closed-loop feedback insulation leakage current detection method as claimed in claim 9, characterized in that: When the measured current I flows through a wire of length L, a magnetic field will be generated around it. The magnetic field at point P is the magnetic field of each current element. The vector of the magnetic field generated at point P is superposition; The magnetic induction intensity at point P is: Where μ0 is the vacuum magnetic permeability; When the magnetic field of the conductor acts on the annular core, it should be ensured that the conductor has enough straight sections. At this time, the magnetic field in the annular core can fully reflect the magnitude of the conductor current. The annular core is maintained in the middle of the straight conductor, and the conductor passes vertically through the center of the annular core. The measurement error will decrease as the ratio of the straight section length L of the conductor to the radius r0 of the annular core increases. The error of the annular core is proportional to the average magnetic path length d, which is related to the inner diameter a and outer diameter b of the annular core. At the same time, when the cross-section of the annular core increases, the volume of the annular core increases, which increases the excitation impedance and reduces the excitation current, that is, the error decreases. For the annular core, the inner diameter a, outer diameter b and height h of the annular core are set, and the relationship is as follows: 1.5(ba)≤h≤2(ba); The inner diameter of the magnetic modulation zero flux current sensor is a=5 mm, the outer diameter is b=11 mm, and the height is h=12 mm.

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