A flexible ring current sensor based on amorphous wire and its bandwidth compensation method

Abstract

A flexible annular current sensor based on an amorphous wire and a bandwidth compensation method thereof include a magnetic core, an induction coil, a low-pass filter, and a bandwidth compensation circuit; the induction coil is wound around the magnetic core and connected to the low-pass filter; the output end of the low-pass filter is connected to the bandwidth compensation circuit; the low-pass filter is used to integrate the induced electromotive force generated by the induction coil, and the bandwidth compensation circuit is used to perform bandwidth compensation and signal amplification on the filtered signal before outputting a voltage signal. By using ultrafine amorphous alloy wire as the magnetic core, the present invention overcomes the shortcomings of conventional current transformers with iron cores and Rogowski coils, such as large size, fixed shape, and low sensitivity, thereby significantly improving the flexibility and performance of the current transformer. The bandwidth compensation circuit based on parallel resonance greatly broadens the bandwidth of the current transformer, and the bandwidth compensation circuit has the advantages of simple structure, low cost, and stable performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of current sensors, and in particular relates to a flexible annular current sensor based on an amorphous wire and a bandwidth compensation method thereof. Background Art

[0002] High-performance current sensors are widely used in fields such as smart grids, rail transit, power electronics, and aerospace. Currently, a wide variety of current sensors exist, including resistor shunts, current transformers, Rogowski coils, Hall effect current sensors, magnetoresistive current sensors, and fluxgate current sensors, each with its own advantages and disadvantages. Current transformers, among others, have found widespread application in power grids and other fields due to their simple structure, low cost, electrical isolation, and wide bandwidth.

[0003] A current transformer primarily consists of a closed iron core, a primary coil winding, and a secondary coil winding. According to Faraday's law of electromagnetic induction, when an alternating current flows through the conductor under test (the primary winding), an alternating magnetic field is generated. This induces an electromotive force in the secondary winding, allowing the magnitude of the measured current to be calculated. Traditional electromagnetic current transformers, due to their large size, high insulation costs, and stringent secondary-side requirements, are becoming increasingly unsuitable for the demands of modern power system development. New electronic current transformers are increasingly offering advantages in terms of cost-effectiveness, accuracy, and safety. Electronic current transformers based on Rogowski coils, which lack a magnetic core, avoid saturation and offer a wide frequency bandwidth, but their sensitivity is limited. Furthermore, existing current transformers, due to the presence of a magnetic core or rigid non-magnetic frame, have fixed probe shapes and sizes, making them difficult to adapt to current measurements on conductors of varying shapes in a variety of situations. Furthermore, the sensors are bulky, making them difficult to carry and use in confined spaces. Furthermore, the bandwidth of current transformers with iron or magnetic cores is limited. This is primarily because the core experiences increased magnetic field loss and decreased magnetic permeability in high-frequency magnetic fields, causing the transformer output to decrease with increasing frequency, making it difficult to increase bandwidth. Consequently, high-bandwidth Rogowski coil sensors suffer from insufficient sensitivity, while highly sensitive current transformers with magnetic cores have limited bandwidth. This creates a difficult balance between high sensitivity and high bandwidth, hindering the expansion of transformer applications. Therefore, developing a flexible current transformer with both high sensitivity and high bandwidth is of paramount importance. Summary of the Invention

[0004] The object of the present invention is to provide a flexible ring current sensor based on amorphous wire and a bandwidth compensation method thereof to solve the above problems.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A flexible annular current sensor based on amorphous wire includes a magnetic core, an induction coil, a low-pass filter and a bandwidth compensation circuit; the induction coil is wound on the magnetic core, and the induction coil is connected to the low-pass filter; the output end of the low-pass filter is connected to the bandwidth compensation circuit; the low-pass filter is used to integrate the induced electromotive force generated by the induction coil, and the bandwidth compensation circuit is used to perform bandwidth compensation and signal amplification on the filtered signal and output a voltage signal.

[0007] Furthermore, the magnetic core is a soft magnetic amorphous wire; the amorphous wire is an iron-nickel-cobalt amorphous alloy wire, the diameter of the amorphous wire is 0.5 mm, and the length is 10-50 cm.

[0008] Furthermore, the induction coil is a 0.2 mm enameled copper wire, which is wound evenly and without overlap on the magnetic core for 100-500 turns using a single-wire unidirectional dense winding method; the coil is adhered to the magnetic core by epoxy resin.

[0009] Furthermore, the low-pass filter is a passive RC low-pass filter composed of a chip resistor R1 and a chip capacitor C1, which are soldered on the printed circuit board.

[0010] Furthermore, one end of the magnetic core and the coil wound with the coil are welded to the printed circuit board, and the other end is welded to the SMA interface and grounded; the magnetic core and the coil are electrically isolated; one end of the coil welded on the circuit board is connected to the resistor R1 of the low-pass filter, and one end of the coil welded on the SMA interface is connected to the capacitor C1 of the low-pass filter.

[0011] Furthermore, the bandwidth compensation circuit includes a resistor R2, a capacitor C2, an inductor L1, a resistor R3, and a first operational amplifier and a second operational amplifier; the two output ends of the capacitor C1 are respectively connected to the first operational amplifier and the second operational amplifier; the inductor L1 and the resistor R3 are connected in series and in parallel with the capacitor C2 to form a parallel resonant circuit; the parallel resonant circuit and the resistor R2 are connected in series to form a bandwidth compensation circuit.

[0012] Furthermore, the inductor L1 is a LQW18ANR20G00D high-frequency chip inductor, and the capacitor C2 is a GRM188R61E106KA73D multilayer ceramic capacitor.

[0013] Furthermore, the first operational amplifier is a THS3091 current-mode operational amplifier, and the second operational amplifier is an OPA847 voltage-mode operational amplifier.

[0014] A bandwidth compensation method for a flexible ring current sensor based on an amorphous wire comprises the following steps:

[0015] The wire through which the current to be measured passes passes through the induction coil, which generates an induced electromotive force Vd;

[0016] The induced electromotive force output by the induction coil is input to the low-pass filter as the input signal, and after integration, the waveform of the current to be measured is restored;

[0017] The voltage signal across capacitor C1 in the low-pass filter serves as the input of the first operational amplifier, and the amplified output signal serves as the input of the bandwidth compensation circuit; the voltage signal across capacitor C2 in the bandwidth compensation circuit serves as the input of the second operational amplifier, and the amplified output serves as the final output of the current transformer.

[0018] Compared with the prior art, the present invention has the following technical effects:

[0019] The present invention overcomes the shortcomings of conventional current transformers with iron cores and Rogowski coils, such as large size, fixed shape, and low sensitivity, by using ultrafine amorphous alloy wire as the magnetic core, thereby greatly improving the flexibility and performance of the current transformer. The bandwidth of the current transformer is greatly broadened by a bandwidth compensation loop based on parallel resonance, and the bandwidth compensation loop has the advantages of simple structure, low cost, and stable performance.

[0020] The present invention improves the problems of previous current transformers, such as large size, fixed shape, and inconvenience in flexible use on conductors of various shapes and in narrow spaces. It also has good performance in terms of high sensitivity and high bandwidth. The prepared flexible sensor is also easy to connect to the back-end signal processing circuit and analog-to-digital conversion module, making it easy to process and digitize the output signal.

[0021] Compared with flexible Rogowski coil sensors and existing current transformers with iron cores, the present invention uses ultra-fine nickel-iron-cobalt amorphous wire as the magnetic core, which has the advantages of flexibility and higher sensitivity while greatly reducing the size of the sensor; the introduction of the bandwidth compensation circuit also broadens the transformer bandwidth. Amorphous alloys have a unique structure and excellent soft magnetic properties, namely high saturation magnetic induction intensity, high initial magnetic permeability, low coercive force, low loss over a wide frequency range, and high mechanical strength and good toughness. Therefore, using ultra-fine amorphous alloy wire as a magnetic core will greatly improve the performance of the current transformer, overcoming the shortcomings of previous iron core and Rogowski coil current transformers, such as large size, fixed shape, and low sensitivity. The bandwidth compensation circuit has a simple structure, low cost, stable performance, and can greatly broaden the transformer bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flexible induction coil with magnetic core

[0023] Figure 2 Circuit structure of RC passive low-pass filter

[0024] Figure 3 The output signal of the transformer with a magnetic core changes with frequency

[0025] Figure 4 Circuit structure of bandwidth compensation loop

[0026] Figure 5 Simulation curve of the amplitude-frequency characteristic of the bandwidth compensation loop

[0027] Figure 6 Bandwidth of flexible current transformer before and after compensation

[0028] Figure 7 Input-output curve and relative error curve of flexible current transformer. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings:

[0030] The present invention provides a flexible annular current sensor based on an amorphous wire, comprising a magnetic core, an induction coil, a low-pass filter and a bandwidth compensation circuit; the induction coil is wound on the magnetic core, and the induction coil is connected to the low-pass filter; the output end of the low-pass filter is connected to the bandwidth compensation circuit; the low-pass filter is used to integrate the induced electromotive force generated by the induction coil, and the bandwidth compensation circuit is used to perform bandwidth compensation and signal amplification on the filtered signal, and then output a voltage signal.

[0031] Specific examples Figure 1 As shown, the probe portion of the flexible ring current sensor based on the amorphous wire core consists of a magnetic core 1 and an induction coil 2 wound around the magnetic core.

[0032] The magnetic core is made of soft magnetic amorphous wire, which is an iron-nickel-cobalt amorphous (nanocrystalline, microcrystalline) alloy wire with a diameter of 0.5 mm and a length of 10-50 cm.

[0033] The induction coil is formed by winding 100-500 turns of 0.2mm enameled copper wire uniformly and without overlap around a magnetic core using a single-wire, unidirectional, close-wound method. Because the amorphous wire used is relatively thin, a layer of epoxy resin is evenly coated on the surface of the amorphous wire before winding the coil to enhance adhesion. After the coil is wound, epoxy resin is applied again to seal and secure it.

[0034] like Figure 2 As shown in the figure, the low-pass filter part of a flexible ring current sensor based on an amorphous wire core is a passive RC low-pass filter composed of a chip resistor R1 and a chip capacitor C1, which is soldered on a printed circuit board with a thickness of 1.0 mm.

[0035] Resistor R1 and capacitor C1 are connected in series to form a low-pass filter with a cutoff frequency of f = 1 / 2πRC. When the signal frequency is much higher than the cutoff frequency, the low-pass filter exhibits an integrating characteristic and is used as an integrator. According to Faraday's law of electromagnetic induction, the induced electromotive force generated by the induction coil is proportional to the time differential of the measured current. Therefore, the induced electromotive force increases with the frequency of the measured current, with a rate of increase of 20dB per decade. After the induced electromotive force is integrated by the integrator, the output signal is proportional to the measured current, and the waveform of the measured current is restored.

[0036] One end of the coil and the core are soldered to a printed circuit board and grounded, while the other end is soldered to SMA connector 1. The core and coil are electrically isolated. One end of the coil soldered to the circuit board is connected to resistor C1 of the low-pass filter, while the other end of the coil soldered to SMA connector 1 is connected to capacitor R1 of the low-pass filter.

[0037] The magnetic permeability of amorphous wire made of soft magnetic material decreases with the increase of magnetic field frequency, which causes the induced electromotive force generated by the induction coil of the mutual inductor to increase at a slower rate as the frequency increases. Figure 3 As shown in the figure, the higher the magnetic field frequency, the faster the permeability decreases, and thus the slower the coil output increases. To compensate for the reduced coil output caused by the decreased permeability of the amorphous wire, the present invention proposes a bandwidth compensation circuit based on a parallel resonant circuit. The gain of this bandwidth compensation circuit increases with increasing frequency, and the higher the frequency, the faster the gain increases, which coincides with the decreasing permeability of the amorphous wire, thus achieving compensation.

[0038] like Figure 4 As shown, the bandwidth compensation circuit includes a resistor R2, a capacitor C2, an inductor L1, a resistor R3, and a first operational amplifier and a second operational amplifier; the two output ends of the capacitor C1 are connected to the operational amplifier; the inductor L1 and the resistor R3 are connected in series and in parallel with the capacitor C2 to form a parallel resonant circuit; the parallel resonant circuit and the resistor R2 are connected in series to form a bandwidth compensation circuit.

[0039] The induced electromotive force output by the induction coil is fed into a low-pass filter as an input signal. After integration, the waveform of the current to be measured is restored. The voltage signal across capacitor C1 in the low-pass filter serves as the input to the first operational amplifier, and the amplified output signal serves as the input to the bandwidth compensation circuit. The voltage signal across capacitor C2 in the bandwidth compensation circuit serves as the input to the second operational amplifier, and the amplified output serves as the final output of the current transformer.

[0040] Inductor L1 is a LQW18ANR20G00D high-frequency chip inductor, and capacitor C2 is a GRM188R61E106KA73D multilayer ceramic capacitor. The first operational amplifier is a THS3091 current-mode operational amplifier, used to amplify the signal attenuated by the low-pass filter; the second operational amplifier is an OPA847 voltage-mode operational amplifier, used to amplify the signal attenuated by the bandwidth compensation loop. The input impedance of the first operational amplifier is effectively connected in parallel with capacitor C1 of the low-pass filter. To prevent this parallel connection from affecting the low-pass filter's characteristics, the first operational amplifier's input impedance is set to high impedance. The input impedance of the second operational amplifier is effectively connected in parallel with capacitor C2 of the bandwidth compensation loop. To prevent this parallel connection from affecting the bandwidth compensation loop's characteristics, the second operational amplifier's input impedance is also set to high impedance.

[0041] The impedance of a parallel resonant circuit increases first and then decreases as the signal frequency increases. At resonance, the circuit's impedance reaches its maximum value. When the signal frequency is below the resonant frequency, the circuit's impedance is inductive and increases with frequency. When the signal frequency is above the resonant frequency, the circuit's impedance is capacitive and decreases with frequency. When a parallel resonant circuit is connected in series with resistor R2, if R2 is comparable to the parallel circuit's impedance, the voltage drop across the circuit is determined by the ratio of the circuit impedance to R2. Furthermore, the larger the value of R2, the faster the voltage drop in the parallel circuit changes with frequency, resulting in a sharper circuit resonance curve. Conversely, the curve becomes flatter.

[0042] The resonant frequency of the parallel resonant circuit is: Adjust the capacitance of capacitor C2 and the inductance of inductor L1 so that the resonant frequency is greater than the maximum operating frequency of the transformer. At this time, the impedance of the resonant circuit increases as the frequency increases; the resonant circuit is connected in series with resistor R2 to divide the voltage, and the voltage across capacitor C2 serves as the output of the bandwidth compensation circuit, thereby increasing the gain as the frequency increases. Adjust the resistance of resistor R2 to adjust the speed at which the gain of the bandwidth compensation circuit changes with frequency, thereby compensating for the decrease in the magnetic permeability of the amorphous wire. The magnetic permeability decrease trend of magnetic cores made of different materials is different, so the gain curve of the required bandwidth compensation circuit is also different. By adjusting the capacitance of capacitor C2, the inductance of inductor L1, and the resistance of resistor R2, the resonant frequency and gain curve of the bandwidth compensation circuit can be adjusted, thereby compensating for different types of magnetic cores.

[0043] The relationship between the gain Gain of the bandwidth compensation loop and the signal frequency is: Gain=R2 / (Z+R2), where Z is the impedance of the parallel resonant circuit.

[0044] like Figure 5As shown in the figure, the amplitude-frequency characteristics of the bandwidth compensation loop are simulated using Multisim software. In the frequency range of 1MHz-20MHz, the gain curve of the bandwidth compensation loop fits the required gain curve well. As the frequency increases, the loop gain continues to increase. Figure 6 As shown in the figure, the actual effect of the bandwidth compensation loop was measured using a standard current generated by a signal generator. Before compensation, the amplitude-frequency characteristic of the transformer decreased by 9.8dB at a frequency of 20MHz, indicating that the transformer bandwidth was far below 20MHz. After compensation, the amplitude-frequency characteristic of the transformer only decreased by 2.4dB at a frequency of 20MHz, indicating that the transformer bandwidth has exceeded 20MHz. Based on the analysis of the test results, the following clear conclusions can be drawn: the bandwidth compensation loop proposed in the present invention is completely feasible in expanding the bandwidth of current transformers with magnetic cores, both in theory and in practice; and the test results prove its excellent performance.

[0045] like Figure 7 As shown in the figure, a signal generator and a load resistor are used to generate a standard current to test the sensitivity and current detection limit (LoD) of the present invention. The test results show that the current detection limit of the present invention is 2mA and has high sensitivity. At the same time, when the current is greater than the detection limit, the transformer has a low error. Based on the above analysis, the following conclusions can be drawn: the present invention uses amorphous wire to achieve the flexibility of the current transformer, and the invention of a bandwidth compensation circuit greatly broadens the transformer bandwidth, so that the current transformer in the present invention has the advantages of high sensitivity and high bandwidth, and excellent overall performance.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A flexible ring current sensor based on amorphous wire, characterized in that: The invention comprises a magnetic core, an induction coil, a low-pass filter and a bandwidth compensation circuit; the induction coil is wound on the magnetic core, and the induction coil is connected to the low-pass filter; the output end of the low-pass filter is connected to the bandwidth compensation circuit; the low-pass filter is used to integrate the induced electromotive force generated by the induction coil, and the bandwidth compensation circuit is used to perform bandwidth compensation and signal amplification on the filtered signal and output a voltage signal; The low-pass filter includes a chip resistor R1, a chip capacitor C1 and a first operational amplifier. The chip resistor R1 and the chip capacitor C1 form a passive RC low-pass filter, which is soldered on a printed circuit board; the output end of the capacitor C1 is connected to the first operational amplifier; The bandwidth compensation circuit includes a resistor R2, a capacitor C2, an inductor L1, a resistor R3, and a second operational amplifier; the output end of the capacitor C2 is connected to the second operational amplifier; the inductor L1 and the resistor R3 are connected in series and in parallel with the capacitor C2 to form a parallel resonant circuit; the parallel resonant circuit and the resistor R2 are connected in series to form a bandwidth compensation circuit; and a low-pass filter and the bandwidth compensation circuit are connected in series.

2. The flexible annular current sensor based on amorphous wire according to claim 1, characterized in that: The magnetic core is a soft magnetic amorphous wire; the amorphous wire is an iron-nickel-cobalt amorphous alloy wire, the diameter of the amorphous wire is 0.5 mm, and the length is 10-50 cm.

3. The flexible annular current sensor based on amorphous wire according to claim 1, characterized in that: The induction coil is a 0.2mm enameled copper wire, which is wound evenly and without overlap on the magnetic core for 100-500 turns using a single-wire unidirectional dense winding method; the coil is adhered to the magnetic core by epoxy resin.

4. The flexible annular current sensor based on amorphous wire according to claim 1, characterized in that: One end of the magnetic core and the coil wound with the coil are welded to the printed circuit board, and the other end is welded to the SMA interface and grounded; the magnetic core and the coil are electrically isolated; one end of the coil welded to the circuit board is connected to the resistor R1 of the low-pass filter, and one end of the coil welded to the SMA interface is connected to the capacitor C1 of the low-pass filter.

5. The flexible annular current sensor based on amorphous wire according to claim 1, characterized in that: The inductor L1 is a LQW18ANR20G00D high-frequency chip inductor, and the capacitor C2 is a GRM188R61E106KA73D multilayer ceramic capacitor.

6. The flexible annular current sensor based on amorphous wire according to claim 1, characterized in that: The first operational amplifier is a THS3091 current-mode operational amplifier, and the second operational amplifier is an OPA847 voltage-mode operational amplifier.

7. A bandwidth compensation method for a flexible ring current sensor based on amorphous wire, characterized in that: The flexible annular current sensor based on amorphous wire according to any one of claims 1 to 6 comprises the following steps: The wire through which the current to be measured passes passes through the induction coil, which generates an induced electromotive force Vd; The induced electromotive force output by the induction coil is input to the low-pass filter as the input signal, and after integration, the waveform of the current to be measured is restored; The voltage signal across capacitor C1 in the low-pass filter serves as the input of the first operational amplifier, and the amplified output signal serves as the input of the bandwidth compensation circuit; the voltage signal across capacitor C2 in the bandwidth compensation circuit serves as the input of the second operational amplifier, and the amplified output serves as the final output of the current transformer.

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