JP2002022774A - Magnetic-field-controlled balancing current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic-field-controlled balancing current sensor having high precision and high resolution by using cores having abruptly saturated conditions in hysteresis characteristics. SOLUTION: A driving coil wound on a measurement core 5 and a reference core 6 is connected in parallel to a high frequency driving power source, a detecting coil wound on both cores is connected in parallel to a zero-magnetic- field control circuit, and a reversely exciting coil wound on the measurement core in which a conductor 7 is inserted is connected to a reversely exciting circuit. The reversely exciting circuit is actuated with the output of the zero- magnetic-field control circuit for the flow of a current in the reversely exciting coil so that a difference in magnetic field between both cores is zero. The current output is measured to find a current flowing in the conductor. The use of two cores improves stability and dispersion, enhances resolution as a result of the cores having abrupt saturation characteristics and provides the highly precise current sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type magnetic field control balanced type current sensor using a core.

[0002]

2. Description of the Related Art A magnetic field control balanced current sensor using a core is roughly classified into an open loop type and a closed loop type in terms of a control method. Although the open loop type simplifies the circuit configuration, there is room for improvement in detection accuracy, linearity, and detection range.
On the other hand, many closed-loop types generally have high accuracy. For example, there is a circuit in which a Hall element is inserted into a part of a core, and which is used for both AC and DC which controls and detects a magnetic flux level to be zero. However, none of them can obtain sufficient detection characteristics due to the influence of leakage inductance, the temperature dependency of the Hall element, the hysteresis characteristics of the core, and the like.

[0003] In order to eliminate such effects,
A current sensor using a zero magnetic field type circuit has been proposed. The zero magnetic field indicates that when the externally applied magnetic field is zero, the magnetization characteristic is symmetric with respect to the origin, and the zero magnetic field type circuit detects the current by controlling the magnetic field level of the core to be equivalently zero. In the zero-magnetic-field type circuit, for example, an excitation coil 2 and a detection coil 3 are wound around a core 1 shown in FIG. 5, a conductor 4 is arranged on the core 1, and an excitation frequency from a sine-wave current source is placed on the excitation coil 2. To excite the core 1 in advance. The current is output from the detection coil 3 when a current to be detected flows through the conductor 4. The core 1 is an amorphous material based on nickel and iron, and the hysteresis characteristics are as shown in FIG. Here, ΔH is the magnetic field applied by the exciting current, and Hc is the midpoint.

When the current to be detected in the core 1 is zero, FIG.
As shown in (a), the magnetization level shown in the lower part of the figure (see the hysteresis characteristic in FIG. 7) is detected from the detection coil 3 with respect to the excitation frequency shown in the upper part of the figure. When the core 1 detects the current to be detected, the excitation frequency shown in the upper part of the figure is biased as shown in FIG. 6B, and a bias magnetic field is applied to the core 1 so that the magnetization level shown in the lower part of the figure is obtained. Varies in the direction of the arrow in this case. This variation is reversely excited so as to be in the original state (zero magnetic field state), and the magnitude and polarity of the current to be detected can be obtained from the current.

[0005]

However, there are many instability factors in the magnetization characteristics of the amorphous core, so that it is difficult to obtain one having high measurement accuracy.
When measuring a large capacity, the outer shape such as the coil shape also becomes large. By the way, in an apparatus using the above-mentioned circuit, there is a charge / discharge inspection machine for a lithium ion battery. The batteries to be inspected range from small batteries used for mobile phones to large batteries for hybrid cars. Also, the range of the measured current extends over a wide range from milliamps to hundreds of amps. The measurement accuracy is also required to be high. At present, a device having a resolution of 1 / 100,000 and a response time of about 10 μs is required. However, in the above-described circuit configuration, a device having many instability elements and high measurement accuracy cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-precision, high-resolution magnetic field control balanced current sensor which eliminates the influence of leakage inductance and hysteresis of a core.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, according to the present invention, the gradient of the magnetic flux level of hysteresis is almost 90 degrees, and the magnetic flux density in the saturation region is about 20 degrees. It is characterized by using a core of １０００1000 gauss. For example, in a general amorphous core, for a characteristic of approximately 7,000 gauss, 1 / (14 to
25) Produce and use a core (about 260-500 gauss) with low characteristics. Also, by setting the magnetic flux density to be low, the thickness of the core can be reduced. In addition, 2
At about 0 Gauss, the characteristics are maintained and the manufacturing limit is approached. On the other hand, when it is about 1000 Gauss, the measurement accuracy is low, but the product management of the core is easy.

According to a second aspect of the present invention, a pair of the cores according to the first aspect is arranged, each of which is divided into a measurement core and a reference core. And a pair of excitation coils are connected in parallel to a high frequency excitation power supply, a pair of detection coils are connected in parallel to a zero magnetic field control circuit, and a measurement conductor is inserted through the measurement core. A reverse excitation coil is wound, the reverse excitation coil is connected to a reverse excitation circuit, the reverse excitation circuit is operated by an output signal of the zero magnetic field control circuit, and an output current of the reverse excitation circuit is detected. It is characterized by.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the pair of cores is divided into a measurement core 5 and a reference core 6, and an excitation coil, a detection coil (shift magnetic field detection), and a reverse excitation coil are wound around the measurement core 5. The measuring conductor 7 is inserted. An excitation coil and a detection coil (zero magnetic field detection) are wound around the reference core 6.

The two exciting coils are connected in parallel to the output side of the high frequency excitation power supply, the two detection coils are connected in parallel to the input side of the zero magnetic field control circuit, and the reverse excitation coil is connected to the output side of the reverse excitation circuit. And are connected in series. The output side of the zero magnetic field control circuit is connected to the input side of the reverse excitation circuit to control the current flowing to the reverse excitation coil of the reverse excitation circuit. The output signal to be detected is calculated by detecting the voltage applied to the resistor to obtain the current.

The cores 5 and 6 used here have a gradient of the magnetic flux level of the hysteresis of approximately 90 degrees and a saturation region of approximately 7,000 gauss, which is a typical example of the core (see A1 in FIG. 2). On the other hand, it has characteristics as low as about 1 / (20 to 25) (see A2 in FIG. 2). That is, the saturation region is about 260 to 370 Gauss, and actually, about 300 Gauss is manufactured and used. Also, the lower the magnetic flux density, the more easily the gradient of the magnetic flux level can be increased, and the thickness of the core can be reduced.

Next, a magnetic field control balanced current sensor according to the present invention will be described with reference to FIGS. By transmitting a high frequency (for example, several tens KHz) (FIG. 3A) from a high frequency excitation power supply to a coil of the same type, the two cores 5 and 6 are excited. When the current to be measured is zero, the waveforms detected by the two detection coils are the same, and FIG.
As shown in Fig. 7, when the saturation region is reached, the waveform suddenly becomes zero. Therefore, even if these two waveforms are calculated, the phase difference is zero, and no current flows through the reverse excitation coil. FIG. 3B shows a waveform obtained by shaping the detection signal of the detection coil when the current is zero and the plus side of the magnetization level in the zero magnetic field control circuit.

As shown in FIG. 4A, the output waveform of the detection coil is one cycle between triggers on both sides in a zero magnetic field, and a negative trigger is a half cycle in a zero magnetic field. The position of the negative trigger shown in FIG. 4B changes by an amount corresponding to the deviation of the magnetic field level when the current flows (phase difference). Size.

When the current to be measured flows to the positive side through the conducting wire 7, the magnetization level of the measuring core 5 shifts to the upper side, and the output signal of the detecting coil of the measuring core 5 (FIG. 4B) and the reference The output signal (FIG. 4A) of the detection coil of the application core 6 is input to the zero magnetic field control circuit. Outputs from these two detection coils are input to a zero magnetic field control circuit, and waveforms cut out at the magnetization levels are shown in FIGS. 3B and 3C. By subtracting the two signals in the zero magnetic field control circuit, the waveform shown in FIG. 3D is obtained. By operating the reverse excitation circuit with this waveform, a reverse magnetic field having the same magnitude as the magnetic field depending on the current to be measured is generated, and control is performed so that the magnetic field becomes zero. Since this value is equivalent to the current to be measured, this is output as the measurement current. At this time, the measurement level can be changed according to the number of turns of the reverse excitation coil. When the current to be measured flows through the conducting wire 7 on the negative side, the magnetization level of the measuring core 5 shifts to the lower side, and a waveform cut and shaped at the magnetization level in the zero magnetic field control circuit is shown in FIG. ). Then, the reverse excitation circuit is activated by a waveform (see FIG. 3 (f)) obtained by subtracting this waveform in the zero magnetic field control circuit in the same manner, and a reverse magnetic field having the same magnitude as the magnetic field depending on the current to be measured is generated. Control so that it becomes a magnetic field.

As described above, when the zero magnetic field of the two cores is subtracted in the zero magnetic field control circuit, the output waveform becomes symmetric and the current value becomes zero. In addition, one of the advantages is that measurement can be performed irrespective of the magnitude of the current to be measured since the two detection coils are always balanced and actuated so as to be equivalent to the zero magnetic field when the conducting wire 7 is energized. is there. Also, that the operating point of the core does not move like this,
It is possible to remove the influence of the peripheral circuit and the influence of the characteristics of the core material.

In the zero-magnetic-field control circuit, the difference between the zero magnetic field and the magnetic field on the measurement side is measured in the two cores. Therefore, the core characteristics should be such that when the magnetic force level changes, the magnetic field level also changes rapidly. As a result, the period of the excitation frequency can be measured stably, and since the saturation region is remarkable, the trigger waveform becomes sharp, the position of the measurement point becomes clear, and the deviation decreases. In the past, even if the frequency was finely divided, an error appeared, so that it was meaningless to divide the frequency very finely. However, in the present invention, one cycle can be finely divided and current measurement with high accuracy can be performed. Further, even if the current to be measured is not constant and changes at a high speed, if the change is lower than the excitation frequency, the change follows the change, so that high-accuracy measurement of the AC current is possible.

[0017]

The present invention is as described above. According to the first aspect of the present invention, a measured value having a high resolution can be obtained by using a core in which the rising level of the magnetic force changes rapidly and the saturation region is small. Can be obtained, and the measurement accuracy can be improved. According to the second aspect of the present invention, two cores are used to balance in a zero magnetic field and the measurement is performed in this state. , The resolution can be increased, and a current sensor with high measurement accuracy can be obtained in current measurement with zero magnetic field.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magnetic field control balanced current sensor according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a hysteresis characteristic of a core used in the embodiment according to the present invention.

FIG. 3 is a diagram illustrating signal waveforms at various points of a current sensor circuit at an excitation frequency used in the embodiment according to the present invention.

FIG. 4 is a diagram showing a waveform of (a) a zero current and a waveform of a measured current in the embodiment.

FIG. 5 is a schematic view of a conventional general magnetic field sensor.

6A and 6B are diagrams illustrating output waveforms with respect to an excitation frequency, (a) a waveform of a zero current, and (b) a waveform of a measurement current.

7 is a diagram of a conventional hysteresis characteristic for explaining the output waveform shown in FIG.

[Explanation of symbols]

 5 Measurement core 6 Reference core

Continuation of the front page (72) Inventor Kenji Miura 2-13-10 Katanoshinmachi, Kokurakita-ku, Kitakyushu Japan System Engineering Co., Ltd. F term (reference) 2G017 AA04 AB03 AC09 AD04 AD05 BA08 CA03 CB02 CC03 2G025 AA14 AB15 2G035 AA00 AB04 AC05 AC08 AD18 AD20

Claims (2)

[Claims] The gradient of the magnetic flux level of the hysteresis is almost 90 degrees, and the magnetic flux density in the saturation region is about 20 to 1
A magnetic field control balanced current sensor using a 000 gauss core. 2. A pair of cores according to claim 1 are arranged, each of which is divided into a measurement core and a reference core, and a pair of excitation coils and a pair of detection coils are wound around both cores, respectively. A pair of excitation coils are connected in parallel to the high frequency excitation power supply, a pair of detection coils are connected in parallel to the zero magnetic field control circuit, a measurement conductor is inserted through the measurement core, and a reverse excitation coil is wound. A magnetic field, wherein the reverse excitation coil is connected to a reverse excitation circuit, the reverse excitation circuit is operated by an output signal of the zero magnetic field control circuit, and an output current of the reverse excitation circuit is detected. Control balance type current sensor.