Leakage current measurement fluxgate excitation circuit

Abstract

This utility model discloses a fluxgate excitation circuit for leakage current measurement. An excitation coil and a self-test coil are wound onto a magnetic ring, along with an excitation self-excitation circuit and a magnetic demodulation circuit. The excitation self-excitation circuit generates an excitation signal of a certain frequency and direction, which is then output to the magnetic ring via the excitation coil. Under the combined action of the excitation magnetic field and the magnetic field of the measured current, the magnetic ring generates an induced electrical signal. The induced electrical signal collected by the excitation self-excitation circuit is output to the magnetic demodulation circuit, thereby realizing the measurement of DC, AC, and pulse current signals. Furthermore, because this solution generates the excitation signal through self-excitation, the measurement accuracy does not excessively rely on the manufacturing precision and consistency of the magnetic core, improving product quality and reducing product costs. Moreover, the self-test circuit ensures that the device does not erroneously trigger signal output, thus preventing accidental power outages on high-voltage input lines.

Description

Technical Field

[0001] This utility model relates to the technical field of leakage current detection devices, and in particular to a fluxgate excitation circuit for leakage current measurement. Background Technology

[0002] Currently, there are two main types of leakage current detection technologies: single-phase, two-phase, and three-phase.

[0003] The first method is instrument transformer detection technology, which collects leakage current through the electromagnetic induction principle of the instrument transformer. This technology is direct and low-cost, but it has significant drawbacks: the instrument transformer device is relatively large, and because it relies on the electromagnetic induction principle, strong external electromagnetic signals or instantaneous large currents can easily cause sudden changes in the magnetic flux of the iron core, resulting in weak anti-interference capabilities and susceptibility to false triggering; furthermore, it can only measure pure AC current and cannot effectively measure DC current or pulse current containing DC components (when such currents are superimposed in the circuit, the iron core is prone to magnetic bias, further reducing measurement reliability). Therefore, instrument transformers are no longer sufficient to meet the measurement needs of today's complex electrical equipment (such as inverters, frequency converters, DC charging equipment, and photovoltaic equipment), because the circuits of these devices not only contain AC current but also often have pulse or DC components superimposed.

[0004] The second type is the externally excited magnetic induction technology. Its detection circuit uses a fixed-frequency PWM wave output by an MCU to excite the coil, thereby reversing the positive and negative magnetic field of the coil. Although this solves the problem that current transformers cannot measure DC and pulse currents, it still has many drawbacks: the magnetic core is prone to entering the saturation region under the excitation of a fixed-frequency excitation current, which not only limits the measurement range but also causes the output signal to be distorted, leading to problems such as large measurement errors, low sensitivity, and large current distortion. It is also prone to falsely triggering leakage alarms. In addition, this technology has strict requirements on parameters such as the magnetic permeability and saturation flux density of the magnetic core, and the corresponding manufacturing process is difficult. It is difficult to ensure the consistency of magnetic core parameters during mass production, which is not conducive to product quality control and large-scale application. Utility Model Content

[0005] To address the aforementioned problems, this invention proposes a fluxgate excitation circuit for measuring leakage current, which mainly solves the problems in the background technology.

[0006] To solve the above-mentioned technical problems, the technical solution of this utility model is as follows:

[0007] A fluxgate excitation circuit for measuring leakage current, comprising:

[0008] A magnetic ring, which is magnetically coupled to both the excitation coil and the self-test coil.

[0009] An excitation self-excited circuit, wherein the excitation output terminal is connected to the excitation coil;

[0010] A magnetic demodulation circuit, the signal input terminal of which is connected to the signal output terminal of the excitation self-excitation circuit;

[0011] The output terminal of the reference voltage circuit is connected to the reference voltage input terminal of the excitation self-excitation circuit and the excitation self-excitation circuit, respectively.

[0012] The output terminal of the self-test circuit is connected to the self-test coil.

[0013] The ESD protection circuit has its signal input terminal connected to the signal output terminal of the magnetic demodulation circuit, and its control terminal connected to the controlled terminal of the self-test circuit.

[0014] The power supply circuit is used to supply power to the excitation self-excitation circuit, the magnetic demodulation circuit, the reference voltage circuit and the ESD protection circuit respectively.

[0015] In some embodiments, the excitation self-excited circuit includes a first operational amplifier, a first bias resistor, and a second bias resistor. The non-inverting input of the first operational amplifier is connected to a standard reference voltage source through the first bias resistor. Simultaneously, one end of the first bias resistor and one end of the second bias resistor are connected to one end of the excitation coil. The other end of the second bias resistor is connected to the output of the first operational amplifier, together forming a positive feedback unit. An input resistor is provided at the inverting input of the first operational amplifier, and a negative feedback resistor is provided between the inverting input and output of the first operational amplifier. The ground terminal of the first operational amplifier is connected to analog ground. The circuit also includes a current sampling resistor, one end of which is connected to the standard reference voltage source, and the other end of which is connected to one end of the excitation coil and the input resistor, together forming a self-excited oscillation unit.

[0016] In some embodiments, a low-pass filter circuit is also included at the inverting input of the first operational amplifier, the low-pass filter circuit consisting of resistors and capacitors.

[0017] In some embodiments, the device further includes a TVS diode, a first clamping diode, and a second clamping diode, wherein the two ends of the TVS diode are respectively connected to the two ends of the excitation coil, and the first clamping diode and the second clamping diode are connected in parallel and disposed after the TVS diode.

[0018] In some implementations, the first operational amplifier is a TLV9062IDDFR dual-channel low-voltage operational amplifier.

[0019] The beneficial effects of this invention are as follows: An excitation coil and a self-test coil are wound onto a magnetic ring, and an excitation self-excitation circuit and a magnetic demodulation circuit are provided. The excitation self-excitation circuit generates an excitation signal of a certain frequency and direction, which is then output to the magnetic ring via the excitation coil. Under the combined action of the excitation magnetic field and the magnetic field of the measured current, the magnetic ring generates an induced electrical signal. The induced electrical signal collected by the excitation self-excitation circuit is output to the magnetic demodulation circuit, thereby realizing the measurement of DC, AC, and pulse current signals. Furthermore, since this solution generates the excitation signal through self-excitation, the measurement accuracy does not excessively rely on the manufacturing precision and consistency of the magnetic core, improving product quality and reducing product costs. Moreover, by setting up a self-test circuit, the problem of erroneous trigger signal output is ensured, thereby ensuring that the high-voltage input line will not be accidentally tripped and disconnected. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the leakage current measurement fluxgate excitation circuit disclosed in an embodiment of the present utility model;

[0021] Figure 2a This is a waveform diagram of an excitation self-excited circuit in a free self-excited oscillation state.

[0022] Figure 2b A schematic diagram of the waveform after a positive DC current is input to the primary side;

[0023] Figure 2c A schematic diagram of the waveform after a negative DC current is input to the primary side;

[0024] Figure 2d A schematic diagram of the waveform after inputting AC current to the primary side;

[0025] Figure 3 This is a circuit diagram of the excitation self-excitation circuit disclosed in an embodiment of the present utility model;

[0026] Figure 4 This is a circuit diagram of the reference voltage circuit disclosed in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this utility model clearer and more explicit, the content of this utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining this utility model and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts related to this utility model are shown in the accompanying drawings, not all of them.

[0028] This embodiment proposes a fluxgate excitation circuit for leakage current measurement, belonging to a self-excited fluxgate circuit. An excitation coil and a self-test coil are wound on a magnetic ring, along with an excitation self-excitation circuit 1 and a magnetic demodulation circuit 2. The excitation self-excitation circuit 1 generates an excitation signal of a certain frequency, which is output to the magnetic ring via the excitation coil. Under the combined action of the excitation magnetic field and the magnetic field of the measured current, the magnetic ring generates an induced electrical signal. The induced electrical signal Is collected by the excitation self-excitation circuit 1 is output to the magnetic demodulation circuit 2, thereby realizing the measurement of DC, AC, and pulse current signals. Furthermore, since this scheme actively generates the excitation signal, the measurement accuracy does not excessively rely on the manufacturing precision and consistency of the magnetic core, improving product quality and reducing product cost. Moreover, by incorporating the self-test circuit 4, this device avoids the problem of erroneous triggering.

[0029] like Figure 1 As shown, it includes:

[0030] The magnetic ring is magnetically coupled to the excitation coil SENCE COIL and the self-test coil CHECK COIL, respectively.

[0031] The excitation self-excitation circuit 1 has its excitation output terminal connected to the excitation coil SENCE COIL. After generating an excitation signal of a certain frequency, the excitation self-excitation circuit 1 outputs it to the magnetic ring L1 through the excitation coil SENCE COIL, and at the same time outputs the induced and acquired induced electrical signal Is to the magnetic demodulation circuit 2.

[0032] The magnetic demodulation circuit 2 has its signal input terminal connected to the signal output terminal of the excitation self-excitation circuit 1, and receives the current sampling signal Is from the excitation self-excitation circuit 1.

[0033] Reference voltage circuit 3 has its output connected to the reference voltage input of excitation self-excited circuit 1 and excitation self-excited circuit 1, respectively. In one example, reference voltage circuit 3 steps down a 5V DC voltage to a 2.5V reference voltage and transmits it to excitation self-excited circuit 1 and excitation self-excited circuit 1 to keep their reference operating voltages consistent.

[0034] Self-test circuit 4, whose output is connected to the self-test coil CHECK COIL, outputs a constant DC current to the CHECK COIL on the magnetic ring L1 under the control of the CHECK signal input. Considering the voltage drift, temperature drift, and errors in the operational amplifier, resistors, and capacitors in the excitation circuit 1, and the errors in the magnetic ring due to material and manufacturing process, and considering that the self-test coil and excitation coil are wound on the same magnetic ring, when a known DC current is input to the primary side of self-test circuit 4, the excitation coil CHECK COIL will measure the current flowing through the CHECK COIL. The difference between the measured current value and the actual current flowing through the CHECK COIL is the error of the entire circuit. Users can correct the measured current value based on this error, reducing the error and improving the accuracy of the measured current value, thus greatly reducing the output of false trigger signals.

[0035] ESD protection circuit 5 has its signal input terminal connected to the signal output terminal of magnetic demodulation circuit 2, and its control terminal connected to the controlled terminal of self-test circuit 4.

[0036] Power supply circuit 6 is used to supply power to the excitation self-excitation circuit 1, the magnetic demodulation circuit 2, the reference voltage circuit 3, and the ESD protection circuit 5 respectively. In this scheme, in addition to the 2.5V reference voltage, the excitation self-excitation circuit 1 and the magnetic demodulation circuit 2 also require a 5V TTL level for their chips or circuits as power supply. The reference voltage circuit 3 and the ESD protection circuit 5 also require a 5V TTL level for power supply. The transmission speed is fast and it is convenient to expand and connect to the microcontroller.

[0037] Specifically, when no current flows through the primary side, the magnetic ring and the excitation self-excited circuit 1 are in a state of free self-excited oscillation. Under the influence of the positive and negative excitation currents of the excitation coil, the magnetic ring continuously undergoes positive and negative saturation, generating an oscillation waveform as shown below. Figure 2a As shown.

[0038] When a DC, AC, or pulse current flows through the primary side, the excitation coil will induce a current in the primary side, disrupting the oscillation balance and causing premature saturation of the magnetic core. The DC, AC, or pulse current flowing through the primary side will be magnetically modulated into the excitation coil. This modulated current is then restored to the primary side current via the magnetic demodulation circuit 2. After a positive DC current is input to the primary side, the waveform is as follows: Figure 2b As shown, after a negative DC current is input to the primary side, as... Figure 2c As shown, after an AC current is input to the primary side, the waveform is as follows: Figure 2d As shown.

[0039] The excitation self-excitation circuit 1 described in this scheme can be any gate circuit capable of generating an excitation signal and correspondingly producing an induced electrical signal. In one example, the first operational amplifier U5A is illustrated using the TLV9062IDDFR dual-channel low-voltage operational amplifier. As shown in Figure 2, the excitation self-excitation circuit 1 includes a first operational amplifier U5A (pin 1 is the output terminal, pin 2 is the inverting input terminal, pin 3 is the non-inverting input terminal, and pin 4 is the ground terminal), a first bias resistor R37 (10kΩ), and a second bias resistor R41 (10kΩ) to provide bias voltage. The first operational amplifier U5A serves as the core oscillation device of the excitation self-excitation circuit 1. In this configuration, the non-inverting input of the first operational amplifier U5A is connected to a standard reference voltage source via a first bias resistor R37. Simultaneously, the first bias resistor R37 (10kΩ) is connected to one end of a second bias resistor R41 and one end of the excitation coil. The other end of the second bias resistor R41 is connected to the output of the first operational amplifier U5A, together forming a positive feedback unit. The inverting input of the first operational amplifier U5A is equipped with an input resistor R36 (1kΩ). The inverting input of the first operational amplifier U5A is connected to the output... A negative feedback resistor R50 (4.7kΩ) is set between them to form a negative feedback unit to limit the amplification factor and stabilize the oscillation. Its resistance value can be adjusted to adjust the circuit response speed. The ground terminal of the first operational amplifier U5A is connected to analog ground. It also includes a current sampling resistor R42 (6.2R). One end of the current sampling resistor R42 is connected to a standard reference voltage source, and the other end of the current sampling resistor R42 is connected to one end of the excitation coil and the input resistor. Together, they form a self-excited oscillation unit, which makes the current direction of the excitation coil periodically reverse.

[0040] It also includes a low-pass filter circuit located at the inverting input of the first operational amplifier U5A. The low-pass filter circuit consists of a resistor R45 (15kΩ) and a capacitor C26 (1000pF). The cutoff frequency is attenuated by -3dB (0.707). R45=15kΩ, C26=1000pF, then the cutoff frequency Fc is calculated according to the following formula.

[0041] Fc=1 / 2ΠRC

[0042] Fc = 1 / 2 * 3.14 * 15000 x 1000 x 10^-12

[0043] Fc = 1 / 94.2 * 10^-6

[0044] Fc = 10.615 kHz.

[0045] If the input signal from terminal R45 exceeds 10.615kHz, the signal will attenuate by -3dB (0.707). This is because, due to an inherent characteristic of op-amp U5A, when a 5V power supply is applied to pin 8 of the second operational amplifier U5B, pins 2 and 3 of U5A exhibit an input offset voltage. This offset voltage varies depending on the op-amp model and its quality, typically ranging from a few tenths of a millisecond to several milliseconds.

[0046] It also includes a TVS diode D12 (SMAJ6.0CA), a first clamping diode D15, and a second clamping diode D16. The two ends of the TVS diode are connected to the two ends of the excitation coil, respectively. The TVS diode is used to absorb the surge voltage induced by the excitation coil to avoid damaging the first operational amplifier U5A. The first clamping diode D15 and the second clamping diode D16 are connected in parallel and set after the TVS diode to clamp the two ends of the excitation coil to prevent overvoltage damage to the first operational amplifier U5A.

[0047] like Figure 3 As shown, the reference voltage circuit 3 described above may include a second operational amplifier U5B, whose pins 6 and 7 are connected to form a 1:1 follower circuit; a REF2V5 power supply network, providing a high-precision standard constant 2.5V voltage, connected to pin 5 of the second operational amplifier U5B; and a filter energy storage capacitor C24 (1μF), connected to the output terminal of pin 7 of the second operational amplifier U5B, used to smooth load current fluctuations to stabilize the voltage; wherein, the second operational amplifier U5B converts the 2.5V voltage of the REF2V5 power supply network into a high-precision, highly stable standard reference voltage source DIRVER_REF2V5 with strong current driving capability through the 1:1 follower circuit, and outputs it to one end of the current sampling resistor R42 of the excitation self-excitation circuit to provide a reference voltage for the excitation self-excitation circuit.

[0048] Due to the inherent offset voltage of operational amplifiers (op-amps), this design assumes that op-amp U5A has an offset voltage of +0.3mV. Considering the negative feedback resistor R50 (4.7kΩ) and the input resistor R36 (1kΩ), the amplification factor is approximately 4.7kΩ / 1kΩ = 4.7 times. At this point, due to the +0.3mV offset voltage, pin 1 of op-amp U5A will output VOUT = 2.5V - 4.7 * 0.003 = 2.4859V. This voltage is fed back to pin 3 (the non-inverting input) of U5A through R41. Since the reference voltage source DIRVER_REF2V5 is fixed, and resistors R41 and R37 (both 10kΩ) form a 0.5 times voltage divider, the voltage at pin 3 is approximately 0.5 * (2.5V - 2.4859V) = 0.00705V. Meanwhile, the two ends of the excitation coil L1 are connected to the reference voltage source DIRVER_REF2V5 through the current sampling resistor R42. At this moment, the voltage at end 2 of the excitation coil L1 is 2.5V, which is higher than the voltage at end 1 is 2.4859V. The current flows from end 2 to end 1, then from pin 1 of U5A to pin 4, and finally to ground.

[0049] According to the principle of self-induction, the excitation coil L1 generates a self-induced voltage with terminals 2 positive and terminal 1 negative. The voltage at terminal 2 is input to pin 2 of U5A through resistor R36. After amplification by U5A, a lower voltage is output from pin 1 than before, forcing the current flowing from terminal 2 to terminal 1 of excitation coil L1 to continuously increase. At this time, the self-induced electromotive force also increases. This voltage is then input to pin 2 of U5A again through resistor R36. This time, the voltage output from pin 1 is even lower, and this cycle continues, with the self-induced electromotive force of excitation coil L1 increasing linearly. When the current in the excitation coil reaches the maximum magnetic induction intensity, the current flowing from terminal 2 to terminal 1 will no longer increase linearly. Instead, the coil acts like a wire, effectively short-circuiting terminals 2 and 1, causing the current to increase rapidly. Finally, the voltages at terminals 2 and 1 of excitation coil L1 and pin 1 of U5A are equal and approximately 0V. At this moment, the input voltage at pin 2 of U5A instantaneously changes from a positive peak value to 0V.

[0050] Because pin 3 of U5A is connected to a 2.5V constant voltage source DIRVER_REF2V5 through a resistor, the voltage at pin 3 is equal to 0.5*(2.5V-0V)=1.25V. At this moment, the voltage at pin 3 is higher than that at pin 2 (inverting input terminal). The voltage at pin 1 of U5A starts to reverse, starting from 0V and outputting positive. When the voltage at pin 1 is greater than the voltage at the two ends of the excitation coil, the current flowing through the excitation coil flows from pin 1 to pin 2 of U5A. The self-induced electromotive force begins to reverse, and the self-induction direction of the excitation coil L1 is negative at terminal 2 and positive at terminal 1. The current begins to increase linearly in the reverse direction (relative to the previous cycle). When the current increases to the maximum magnetic induction intensity of the excitation coil, the excitation coil is equivalent to a wire, which is equivalent to a short circuit between terminals 1 and 2 of the excitation coil L1. At this moment, the output current from pin 1 of U5A increases instantaneously. The voltage at pin 1 of U5A, the voltage at terminals 1 and 2 of the excitation coil are equal, approximately 5V, because the current sampling resistor R42 is connected to the constant reference voltage source DIRVER_REF2V5. The voltage at pin 2 of U5A is equal to 5V - 2.5V = 2.5V, and the voltage at pin 3 of U5A is equal to 0.5 * (5 - 2.5V) = 1.25V. Since pin 2 is higher than pin 3, pin 1 of U5A begins to reverse again.

[0051] At this point, the voltage at pin 1 starts to shift from 5V to 0V. When the output voltage drops below 2.5V, the current flowing through the excitation coil L1 reverses again, flowing from terminal 2 to terminal 1. The self-induced electromotive force also reverses, returning to the state where terminal 2 of the excitation coil L1 is positive and terminal 1 is negative. The entire excitation self-excited circuit continues to operate in this cyclical manner, causing the direction of the current in the excitation coil to change continuously.

[0052] The above embodiments are merely illustrative of the technical concept and features of this utility model, and are intended to enable those skilled in the art to understand the content of this utility model and implement it accordingly. They should not be construed as limiting the scope of protection of this utility model. All equivalent changes or modifications made based on the substance of the content of this utility model should be covered within the scope of protection of this utility model.

Claims

1. A fluxgate excitation circuit for measuring leakage current, characterized in that, include: A magnetic ring, which is magnetically coupled to both the excitation coil and the self-test coil. An excitation self-excited circuit, wherein the excitation output terminal is connected to the excitation coil; A magnetic demodulation circuit, the signal input terminal of which is connected to the signal output terminal of the excitation self-excitation circuit; The output terminal of the reference voltage circuit is connected to the reference voltage input terminal of the excitation self-excitation circuit and the excitation self-excitation circuit, respectively. The output terminal of the self-test circuit is connected to the self-test coil. The ESD protection circuit has its signal input terminal connected to the signal output terminal of the magnetic demodulation circuit, and its control terminal connected to the controlled terminal of the self-test circuit. The power supply circuit is used to supply power to the excitation self-excitation circuit, the magnetic demodulation circuit, the reference voltage circuit and the ESD protection circuit respectively.

2. The leakage current measurement fluxgate excitation circuit as described in claim 1, characterized in that, The excitation self-excited circuit includes a first operational amplifier, a first bias resistor, and a second bias resistor. The non-inverting input of the first operational amplifier is connected to a standard reference voltage source through the first bias resistor. Simultaneously, one end of the first bias resistor and one end of the second bias resistor are connected to one end of the excitation coil. The other end of the second bias resistor is connected to the output of the first operational amplifier, together forming a positive feedback unit. An input resistor is provided at the inverting input of the first operational amplifier, and a negative feedback resistor is provided between the inverting input and output of the first operational amplifier. The ground terminal of the first operational amplifier is connected to analog ground. The circuit also includes a current sampling resistor, one end of which is connected to the standard reference voltage source, and the other end of which is connected to one end of the excitation coil and the input resistor, together forming a self-excited oscillation unit.

3. The leakage current measurement fluxgate excitation circuit as described in claim 2, characterized in that, It also includes a low-pass filter circuit disposed at the inverting input terminal of the first operational amplifier, the low-pass filter circuit being composed of resistors and capacitors.

4. The leakage current measurement fluxgate excitation circuit as described in claim 2, characterized in that, It also includes a TVS diode, a first clamping diode, and a second clamping diode, wherein the two ends of the TVS diode are respectively connected to the two ends of the excitation coil, and the first clamping diode and the second clamping diode are connected in parallel and disposed after the TVS diode.

5. The leakage current measurement fluxgate excitation circuit as described in claim 2, characterized in that, The first operational amplifier is a TLV9062IDDFR dual-channel low-voltage operational amplifier.

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