WO2022037099A1

WO2022037099A1 - Low-cost current sensor

Info

Publication number: WO2022037099A1
Application number: PCT/CN2021/089269
Authority: WO
Inventors: 李菊萍; 郑良广; 关克; 吴明明
Original assignee: 宁波中车时代传感技术有限公司
Priority date: 2020-08-18
Filing date: 2021-04-23
Publication date: 2022-02-24
Also published as: CN111948438A; CN111948438B

Abstract

A low-cost current sensor, comprising a single-iron-core assembly (2) and a control circuit. The control circuit is realized by means of a microprocessor and comprises an excitation loop, a mutual inductor loop, a compensation module (4) and a feedback loop. The excitation loop, the mutual inductor loop and the feedback loop are all connected to the single-iron-core assembly (2), and the mutual inductor loop is connected to the feedback loop by means of the compensation module (4). The current sensor utilizes a mutual inductor principle to extract a fluxgate secondary harmonic signal, and uses a single-ring iron core; therefore, cost is low.

Description

A low-cost current sensor

technical field

The present invention relates to the technical field of magnetic field detection sensors, in particular to a low-cost current sensor.

Background technique

The fluxgate principle is often used for current measurement due to its high accuracy.

For the double-ring iron-core fluxgate, since the excitation magnetic field is mutually canceled by the two iron cores, the excitation magnetic field noise is reduced, and higher accuracy can be achieved. For the three-ring iron core fluxgate, two iron cores can also be used to offset the excitation magnetic field to achieve higher accuracy.

However, the more cores the greater the cost. Using a single-ring iron core fluxgate, the cost is small, but the excitation signal is much larger than the measured signal. If the second harmonic method is used to extract the measured signal like the double-ring or three-ring fluxgate, the extraction process is complicated and the noise is large. . For a single-ring iron core, the time difference method or the average value method can usually be used to extract the measured signal, but it is difficult to use for high frequency measurement, and the resolution of the average value method is not as good as that of the second harmonic method, and the time difference method has a limited range.

When the single-core fluxgate current sensor works, under the action of sinusoidal voltage, the excitation coil generates a periodic magnetic field in the iron core, and the iron core is periodically magnetized. When the measured current is zero, the forward and reverse magnetization of the iron core is symmetrical, and when the measured current is not zero, the iron core is asymmetrical in the forward and reverse directions. The measured signal can be obtained by extracting the asymmetric signal, that is, the second harmonic signal. Compared with the excitation signal, the second harmonic signal is small, and it is difficult to directly extract the second harmonic from the excitation circuit.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention proposes a current sensor based on the combination of the closed-loop fluxgate principle and the transformer principle.

In order to achieve the above purpose, the present invention provides a low-cost current sensor for measuring the current flowing through the primary conductor (1), which mainly includes a single-core component and a control circuit, and the control circuit is realized by a microprocessor; the control circuit Including excitation loop, transformer loop, compensation module and feedback loop;

The single core component is a single annular core;

the excitation circuit includes an excitation coil;

the transformer loop includes a transformer coil;

the feedback loop includes a feedback coil;

The excitation coil of the excitation circuit is wound on the single-iron core assembly, the transformer coil of the transformer circuit is wound on the single-iron core assembly, and the feedback coil of the feedback loop is wound on the single-iron core assembly;

The transformer loop and the feedback loop are connected.

Further, the excitation loop also includes a sinusoidal excitation module and a resistor R1;

The excitation coil is wound on a single iron core assembly, one end of the excitation coil is connected to one end of the resistor R1, the other end of the resistor R1 is grounded; the other end of the excitation coil is connected to the sinusoidal excitation module.

Further, the transformer loop includes a current extraction circuit and a compensation module, and the current extraction circuit includes an operational amplifier unit and a resistor R2;

One end of the transformer coil is connected to the compensation module, the other end of the transformer coil is connected to the operational amplifier unit, the operational amplifier is also connected to one end of the resistor R2 and one end of the feedback loop, the operational amplifier is connected to the compensation module connected, the other end of the resistor R2 is grounded.

Further, the feedback loop further includes a second harmonic extraction module, a compensation module, a filter integration module and a resistor R3;

One end of the feedback coil is connected to one end of the compensation module and the filter integration module, the other end of the filter integration module is connected to one end of the second harmonic extraction module, and the other end of the second harmonic extraction module is connected to the transformer Loop connection, the other end of the feedback coil is connected to one end of the resistor R3, and the other end of the resistor R3 is grounded.

Further, the excitation loop is used to generate a second harmonic signal in the single-core assembly through the excitation coil when the primary conductor (1) has current passing through it.

Further, the transformer loop is used to obtain the current of the transformer coil through the transformer coil.

Further, the feedback loop is used to extract the second harmonic signal at the end of the resistor R2 through the second harmonic extraction module, and transmit the extracted second harmonic signal to the feedback coil through the filter integration module.

Further, the compensation module is used to cancel the induced voltage generated by the transformer coil and the feedback coil.

The present invention has at least the following beneficial effects:

(1) The low-cost current sensor adopts a single annular iron core, and the cost is low.

(2) The low-cost current sensor utilizes the transformer principle, and the excitation coil (7), the transformer coil (8), and the feedback coil (10) interact with each other. When there is a measured current, compared with the excitation loop and the feedback loop, the The transformer loop resistance is only the coil internal resistance. If the coil internal resistance of the transformer loop is much smaller than the excitation loop resistance R1 and the feedback loop resistance R3, most of the measured signals pass through the transformer loop. Through the current extraction circuit, the voltage of the resistor R2 connected to the operational amplifier unit can be measured to obtain the current signal of the transformer coil, and the current of the transformer can be processed to obtain the measured current. It solves the problem that the fluxgate excitation magnetic field is noisy and the second harmonic is difficult to extract.

Description of drawings

Figure 1 is a structural block diagram of a low-cost current sensor;

Figure 2 shows the sensor broadband;

Figure 3 is the current signal of the excitation coil, in which the dotted line shows the coil current when the measured current is zero, and the solid line shows the coil current when the measured current is 5mA.

Figure 4 is the excitation coil current when the measured signal is extracted through the transformer;

Figure 5 is the measured signal received by the transformer coil when the measured signal is extracted through the transformer;

Figure 6 shows the sum of the currents of each turn of the transformer coil and the measured current when the measured current is a mixed AC and DC current. The dotted line is the measured current;

Figure 7 shows the sum of the currents of each turn of the feedback coil and the measured current when the measured current is a mixed current of AC and DC, wherein the solid line is the sum of the currents of each turn of the feedback coil when the mixed current of AC and DC is present, and the dotted line is the measured current;

Figure 8 shows the sum of the transformer signal and the feedback signal when the measured current is a mixed AC and DC current.

(1), primary conductor; (2), single core assembly; (3) sinusoidal excitation module; (4) compensation module; (5) second harmonic extraction module; (6) filter integration module; (7) Excitation coil; (8) Transformer coil; (9) Operational amplifier unit; (10) Feedback coil.

detailed description

The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

Example

This embodiment provides a low-cost current sensor. As shown in FIGS. 1 to 8 , the low-cost current sensor includes: a single core component and a control circuit, the control circuit is realized by a microprocessor; the control circuit includes an excitation loop , transformer loop, compensation module and feedback loop;

The single core component is a single annular core;

the excitation circuit includes an excitation coil;

the transformer loop includes a transformer coil;

the feedback loop includes a feedback coil;

The transformer loop and the feedback loop are connected.

The excitation loop mainly includes a sinusoidal excitation module (3), an excitation coil (7), and a series resistance R1. Under the action of the sinusoidal voltage, the excitation coil generates a periodic magnetic field in the iron core, and the iron core is periodically magnetized. When the measured current is zero, the forward and reverse magnetization of the iron core is symmetrical, and when the measured current is not zero, the forward and reverse magnetization of the iron core is asymmetrical. The measured signal can be obtained by extracting the asymmetric signal, that is, the second harmonic signal. Compared with the excitation signal, the second harmonic signal is smaller, and it is difficult to directly extract the second harmonic from the excitation circuit. This application extracts the second harmonic through the following transformer loop.

The transformer loop is composed of a transformer coil (8), a compensation module (4) and a current extraction circuit. The current extraction circuit is composed of an operational amplifying unit (9) connected with the coil and an output resistor R2. Due to the principle of the transformer, the excitation coil (7), the transformer coil (8), and the feedback coil (10) interact with each other. When there is a measured current, compared with the excitation loop and the feedback loop, the transformer loop resistance is only the internal resistance of the coil. , if the coil internal resistance of the transformer loop is much smaller than the excitation loop resistance R1 and the feedback loop resistance R3, most of the measured signal passes through the transformer loop. Through the current extraction circuit, the voltage of the resistor R2 connected to the operational amplifier unit can be measured to obtain the current signal of the transformer coil, and the current of the transformer can be processed to obtain the measured current.

Further, the excitation circuit is used to generate the second harmonic signal in the single-core assembly through the excitation coil when the primary conductor 1 has current flowing therethrough.

The compensation module stores the induced voltage when the transformer coil (8) and the feedback coil (10) are open-circuited, that is, the compensation voltage, to the microprocessor under the action of the excitation voltage when the measured signal is not applied, and the compensation voltage constitutes the compensation module. data. Under the action of the magnetic field generated by the excitation coil (7), the transformer coil (8) and the feedback coil (10) will generate an induced voltage, which in turn affects the excitation signal, so a compensation module is required to offset the induced voltage. When the sensor is working, a compensation voltage is respectively applied to both ends of the transformer coil (8) and the feedback coil (10) through the compensation module to offset the induced voltage.

The feedback loop mainly includes a second harmonic extraction module (5), a filter integration module (6), a feedback coil (10), a resistor R3, and a compensation module (4). The second harmonic signal at the end of the resistor R2 is extracted through the second harmonic module (5), and then the integrated signal is connected to the feedback coil (10) through the filtering integration module (6) to cancel the measured low frequency signal.

The low-frequency signal uses the principle of fluxgate, adopts the second harmonic extraction method, and cancels the measured signal through the feedback coil. The high-frequency signal cancels the measured signal through the transformer coil through the transformer principle, as shown in Figure 2. Reasonable design of the parameters of each part, so that the cut-off frequency of the fluxgate and the feedback loop is greater than the cut-off frequency of the transformer, the AC-DC mixed signal can be measured.

Among them, when the current sensor disconnects the transformer coil and the feedback coil, and only the excitation loop has a signal, the analysis is as follows.

As shown in FIG. 3, FIG. 3 is the current signal of the excitation coil. The dotted line shows the excitation coil current when the measured primary conductor (1) is zero. The solid line shows the coil current when the measured current is 5mA. The fundamental wave, that is, the excitation signal, is much larger than the second harmonic signal to be extracted.

The signal when only the feedback coil is disconnected is analyzed as follows.

Since the transformer coil (8) and the feedback coil (10) are offset by the compensation module to generate an induced voltage, when the measured current is zero, the current of the transformer coil is zero. When the measured signal is 5mA, the measured current is modulated by the excitation coil, and then through the action of the transformer, the transformer coil current has an obvious second harmonic signal, as shown in Figure 4. Since the internal resistance of the transformer loop is much smaller than the internal resistance of the other two loops, the second harmonic signal of the excitation coil shown by the solid line in Figure 3 is reflected to the transformer coil through the action of the transformer, as shown in Figure 5, while the excitation coil only has the excitation signal, as shown in Figure 4. Compared with when the transformer loop in Fig. 3 is disconnected, the second harmonic signal in Fig. 5 increases significantly.

The signals when all three loops are disconnected are analyzed as follows.

Through the second harmonic extraction module (5) and the filter integration module (6), the second harmonic signal of the voltage of the resistor R2 is extracted, and the measured signal is fed back to the feedback coil (10).

The sum of the currents of each turn of the transformer coil and the feedback coil is opposite to the measured current;

N ₂ ×i ₂ +N ₃ ×i ₃ =I,

N ₂ , N ₃ where N2 is the number of turns of the transformer coil, and N3 is the number of turns of the feedback coil;

Among them, i ₂ is the current of the transformer coil, and i ₃ is the current of the feedback coil.

The voltage signal of the resistor R2 is u ₁ , where u ₁ =R ₂ *i ₂ ; the integral signal is u ₂ , where u ₁ =R ₃ *i ₃ adds the voltage signal of the resistor R2 to the integral signal after processing, that is The measured signal can be obtained.

The DC component of the measured signal is 20mA, and the AC component is a sinusoidal signal with an amplitude of 20mA and a frequency of 1kHz.

Figure 6 shows the current N ₂ ×i ₂ of all coil turns of the transformer.

Figure 7 shows the current N ₃ ×i ₃ for all turns of the feedback coil.

Fig. 8 is the sum of the currents of all turns of the transformer coil and the feedback coil, N ₂ ×i ₂ +N ₃ ×i ₃ .

The current sensor has low cost, and uses the transformer principle to extract the second harmonic signal of the fluxgate, which solves the problem that the excitation magnetic field of the fluxgate is noisy and the second harmonic is difficult to extract.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention pertains can make various modifications or additions to the described specific embodiments or substitute in similar manners, but will not deviate from the spirit of the present invention or go beyond the definitions of the appended claims range.

Claims

A low-cost current sensor for measuring the current flowing through a primary conductor (1), characterized in that it comprises a single iron core assembly and a control circuit; the control circuit comprises an excitation loop, a transformer loop and a feedback loop;

The single core component is a single annular core;

the excitation circuit includes an excitation coil;

the transformer loop includes a transformer coil;

the feedback loop includes a feedback coil;

The excitation coil of the excitation circuit is wound on the single-iron core assembly, the transformer coil of the transformer circuit is wound on the single-iron core assembly, and the feedback coil of the feedback loop is wound on the single-iron core assembly;

the transformer loop and the feedback loop are connected;

The transformer loop includes a current extraction circuit and a compensation module, and the current extraction circuit includes an operational amplifier unit and a resistor R2;

One end of the transformer coil is connected to the compensation module, the other end of the transformer coil is connected to the operational amplifier unit, the operational amplifier is also connected to one end of the resistor R2 and one end of the feedback loop, the operational amplifier is connected to the compensation module connected, the other end of the resistor R2 is grounded.
The low-cost current sensor according to claim 1, wherein the excitation loop further comprises a sinusoidal excitation module and a resistor R1;

The excitation coil is wound on a single iron core assembly, one end of the excitation coil is connected to one end of the resistor R1, the other end of the resistor R1 is grounded; the other end of the excitation coil is connected to the sinusoidal excitation module.
The low-cost current sensor according to claim 1, wherein the feedback loop further comprises a second harmonic extraction module, a compensation module, a filter integration module and a resistor R3;

One end of the feedback coil is connected to one end of the compensation module and the filter integration module, the other end of the filter integration module is connected to one end of the second harmonic extraction module, and the other end of the second harmonic extraction module is connected to the transformer Loop connection, the other end of the feedback coil is connected to one end of the resistor R3, and the other end of the resistor R3 is grounded.
A low-cost current sensor according to claim 2, characterized in that, the excitation circuit is used to generate a second harmonic signal in the single-core assembly through the excitation coil when the primary conductor (1) has current flowing therethrough.
The low-cost current sensor according to claim 1, wherein the transformer loop is used to obtain the current of the transformer coil through the transformer coil.
The low-cost current sensor according to claim 3, wherein the feedback loop is used to extract the second harmonic signal at the end of the resistor R2 through the second harmonic extraction module, and pass the extracted second harmonic signal through the The filter-integral block is transmitted to the feedback coil.
The low-cost current sensor according to claim 1, wherein the compensation module is used to cancel the induced voltage generated by the transformer coil and the feedback coil.