JPH10332744A - Direct current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a direct current sensor which is effective in detecting leakage of micro direct current of an inverter and can obtain stable output with substantially zero influence of alternating current mixed in the direct current. SOLUTION: A pair of electrically connected detection coils 3a and 3b are wound and arranged in the toroidal state at a short side part opposing a detection core 2 made of soft magnetic material in the shape of a rectangular frame, a pair of exciting cores 4a and 4b made of soft magnetic material constituting a squire cylinder state at a long side part opposing the detection cores 2, an exciting coil 5 is wound and arranged in the circumferential direction of the outer circumference of the detection core 2, and a conductor to be detected 1 through which direct current flows is pierced and arranged inside the detection cores 2. And an alternating current cancel coil 10 is wound and arranged over an alternating current transducer coil 9 made of the ring-shaped soft magnetic material constituting an alternating current transducer so as to cancel influence of the alternating current mixed in the direct current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a DC current sensor arranged in various devices using DC current, and particularly to a small DC current of an inverter in a technical field of an electric vehicle, a photovoltaic power generation system and the like. The present invention relates to a DC current sensor that is effective for detecting leakage of DC current and that can obtain a stable output by substantially eliminating the effect of AC current mixed into DC current.

[0002]

2. Description of the Related Art Conventionally, as a DC current sensor,
A configuration employing a shunt resistance method, a mag amplifier method, a magnetic multivibrator method, a Hall element method, or the like is known. However, these DC current sensors are not only complicated in configuration, but also difficult to employ in earth leakage breakers, etc., which inherently require the detected conductor to pass through one turn. It was impossible to measure. The applicant of the present invention has a relatively simple structure as a DC current sensor that solves the above-described problems, and in particular, has a high sensitivity DC current having excellent detection capability even for minute current changes. A sensor was proposed earlier (Japanese Patent Laid-Open No. 6-74978).

For example, as shown in FIG. 3, a pair of detection coils 3a and 3b which are electrically connected to each other are formed in a toroidal shape on a short side of a detection core 2 which is made of a soft magnetic material in a rectangular frame shape and is opposed to the detection core. And the detection core 2
The configuration is such that the detected conducting wire 1 through which a direct current flows is arranged to penetrate inside. Further, as means for switching the magnetic flux Φ ₀ in the detection core 2 generated based on the DC current I flowing through the detection target wire 1, a soft magnetic material having a quadrangular cylindrical shape on a long side portion at a position facing the detection core 2 is used. A pair of exciting cores 4a and 4b made of a material are arranged, and an exciting coil 5 is wound around the detecting core 2 in a circumferential direction.

In such a configuration, when a DC current I flows through the conductor 1 to be detected, a magnetic flux Φ ₀ is generated in the detection core 2. At this time, a predetermined AC current (frequency f ₀ ) is applied to the exciting coil 5. When flowing, an alternating magnetic flux is generated in the exciting cores 4a and 4b in the α direction in the figure, and the alternating magnetic flux saturates the orthogonal portion 6 between the detecting core 2 and the exciting cores 4a and 4b, and flux [Phi ₀ becomes to be switched, the frequency is modulated alternating magnetic flux twice the excitation frequency (2f _0). Electromotive force of the magnetic flux Φ frequency 2f ₀ in proportion to the DC current I flowing through the lead wire being detected 1 with changes in ₀ (V
_DET ) is detected by the detection coils 3a and 3b, and as a result, the absolute value of the DC current I flowing through the detected conductor 1 can be known.

In addition, a DC current sensor having the above configuration is covered with a shield case made of permalloy, non-oriented silicon steel plate, or the like, and a configuration capable of preventing induction noise from being mixed has been proposed. That is, as shown in FIG.
This is a configuration in which the DC current sensor 20 having the above configuration is surrounded by a shield case including a case body 21a and case lids 21b and 21c.

The DC current sensor shown in FIG. 5 has been proposed for the purpose of simplifying the structure of the core and having a high S / N ratio, and has an annular configuration in which the detection coil 3 is wound in a toroidal shape. The detection core 2 made of a soft magnetic material is formed into a tubular shape, and the exciting coil 5 is wound around a hollow portion communicating with the detection core 2 in the circumferential direction (Japanese Patent Laid-Open No. 7-198754).

In such a configuration, when a DC current I flows through the detected conductor 1, a magnetic flux Φ ₀ is generated in the detection core 2. At this time, a predetermined exciting current (AC current) flows through the exciting coil 5. And an alternating magnetic flux in the direction α in the drawing is generated in the detecting core 2, and the alternating magnetic flux periodically magnetically saturates substantially the entire area of the detecting core 2, and the magnetic flux Φ ₀ in the detecting core 2 is switched. Becomes In this configuration, the detection core 2 also plays the role of the excitation core, but it is necessary to know the absolute value of the DC current I flowing through the detected wire 1 basically in the same manner as the operation principle of the DC current sensor of FIG. Can be.

In the DC current sensor having the configuration shown in FIGS. 3 and 5 described above, the means for switching the magnetic flux Φ ₀ in the detection core generated based on the DC current I flowing through the detected wire 1 includes the detection core 2. Has a configuration in which a magnetically saturated region is formed by an alternating magnetic flux in part or all of the circumferential direction to periodically block the magnetic flux Φ _0. However, a DC current having the configuration shown in FIGS. The sensors differ in the means for switching the magnetic flux Φ ₀ .

[0009] DC current sensor shown in FIG. 6, the direction of the magnetic flux [Phi ₀ in the detecting core 2 to generate on the basis of the DC current I flowing through the lead wire being detected 1, a direction perpendicular to the magnetic flux [Phi ₀ (figure The magnetic flux Φ ₀ is periodically interrupted by being changed by the repulsive action with the alternating magnetic flux in the α direction), and as a result, the magnetic flux Φ ₀ is switched. Although the switching means is different, it is substantially the same as the DC current sensor of FIG. 3 (Japanese Patent Laid-Open No. 7-55846).

In the drawing, reference numerals 3a and 3b denote detection coils which are wound around the detection core 2 in a toroidal shape, and 5a and 5b are excitation coils which are wound and disposed through a plurality of through holes 7 formed in the detection core 2. Coil. By applying a predetermined exciting current (alternating current) to the exciting coils 5a and 5b, an alternating magnetic flux in the α direction in the drawing is generated, and as described above, the absolute value of the DC current I flowing through the target conductive wire 1 to be detected. You can know the value.

In the DC current sensor shown in FIG. 7, a circumferential magnetic field in the detection core 2 generated based on a DC current I flowing through the detected wire 1 changes periodically in a direction orthogonal to the circumferential magnetic field. The magnetic field generated in the detection core 2 is rotated by rotating the magnetization direction in the detection core 2 based on the combined magnetic field, and the magnetic flux Φ ₀ generated in the detection core 2 substantially based on the DC current I flowing through the detected wire 1. And performs magnetic switching. Also in this configuration, the mechanism of generating an electromotive force to the detection coil 3 is substantially the same as that of the DC current sensor of FIG. 3 except for the switching means (Japanese Patent Laid-Open No. 9-5361).

More specifically, in the detection core 2, the direction of the current in the same through hole and the direction of the current in the adjacent through hole are the same in a plurality of through holes 8 formed on the side surface of the detection core 2. Are arranged in the opposite direction, and the detection coil 3 is wound in a toroidal shape on the outer periphery. By applying a predetermined exciting current (AC current) to the exciting coils 5a and 5b,
By rotating the magnetization direction in the detection core 2, the absolute value of the DC current I flowing through the target wire 1 to be detected can be known as described above.

As described with reference to FIG. 4, the DC current sensor having the configuration shown in FIGS. 5, 6, and 7 is also covered with a shield case corresponding to the shape of each detection core to thereby reduce induced noise. It is possible to prevent contamination.

Each of the DC current sensors described above has a relatively simple structure, and is a high-sensitivity DC current sensor having an excellent detection capability even for a minute current change.

[0015]

As described above, the direct current sensors having various structures proposed by the applicant of the present invention have relatively simple structures, and in particular, have a small current. The structure has excellent detection ability against changes, so that the use of the DC current sensor can be greatly expanded.

However, when detecting the leakage of the minute DC current of the inverter in the technical fields of electric vehicles, solar power generation systems, etc., since the minute AC current is mixed in the inverter output, the AC current is superimposed on the DC current. There was a problem that the sensor output was not stable.

The present invention is proposed in view of the above-mentioned situation, and does not impair the inherent advantages of the DC current sensor having various configurations proposed by the applicant of the present invention. It is a DC current sensor that is effective for detecting minute DC current leakage, and aims to propose a DC current sensor that can obtain a stable output with substantially zero effect of AC current mixed in DC current. is there.

[0018]

As a result of studying various configurations to achieve the above object, the inventor has proposed a configuration for canceling the effect of AC current mixed with DC current.
The DC current sensor proposed by the applicant of the present application, further, an AC current transformer made of a ring-shaped soft magnetic material is arranged, and an AC current canceling coil is provided between a detection core and an AC current transformer core constituting the DC current sensor. It was confirmed that the advantages of each DC current sensor could be effectively utilized by wrapping and arranging the coils, and that an unexpected effect could be obtained.

That is, according to the present invention, a detection target wire through which a direct current flows is disposed inside a detection core made of a soft magnetic material having a coil wound in a toroidal shape, and a direct current flowing through the detection target wire is disposed. In a DC current sensor having means for switching a magnetic flux in a detection core generated based on an electric current, the detected current is detected so as to cancel a magnetic flux in the detection core generated based on an AC current mixed into a DC current flowing through the detected conductor. A DC current sensor comprising an AC current transformer core made of an annular soft magnetic material through which a lead wire is arranged, and having a detection core and an AC current canceling coil wound around the AC current transformer core. It is. Further, in the above configuration, a DC current sensor characterized in that a detection core is disposed in a shield case is also proposed.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the DC current sensor of the present invention, the annular soft magnetic material forming the detection core and the AC current transformer core is not limited to a so-called ring shape, but is formed inside the ring. The soft magnetic material may be connected so as to electromagnetically form a closed circuit, and the annular soft magnetic material forming the detection core will be described later. Rectangular frame shape as shown in the figure due to the relationship with the switching means,
Various configurations such as a tubular shape and a tubular shape can be adopted.

The annular soft magnetic material constituting the AC current transformer core may have any shape as long as it can pass an alternating magnetic flux generated by the AC current flowing through the conductor to be detected. It is not necessary to always have the same shape as the soft magnetic material. However, it is desirable to select the shape and dimensions according to the amount of magnetic flux generated in the transformer core.

The soft magnetic material constituting the detection core needs to be selected in consideration of magnetic properties according to the detection sensitivity required for the DC current sensor, workability, and the like. Known soft magnetic materials such as amorphous, soft magnetic iron, and soft ferrite can be used.

The annular soft magnetic material constituting the AC current transformer core is preferably made of a material having a high magnetic permeability in order to obtain an output with high sensitivity to the magnetic flux generated in the transformer core as described above. Is most desirable. Further, it is desirable to select a material corresponding to the frequency of the alternating current to be canceled for the transformer core, and it is particularly desirable to use soft ferrite for high frequency alternating current exceeding several tens kHz to 100 kHz.

In the present invention, the configuration in which the AC current canceling coil is wound and arranged over the detection core and the AC current transformer core means that the same magnetomotive force (ampere turn) is applied to each of the detection core and the AC current transformer core. Any configuration is possible, and the configuration is not limited to the illustrated one. For example, a configuration in which the detection core and the AC current transformer core are independently wound and arranged and then connected in series with each other can be adopted. Further, as the cancel coil, a copper foil, for example, having a thickness of 0.0
A thing of about 5 mm may be wound.

In the present invention, the means for switching the magnetic flux (Φ ₀ ) in the detection core generated based on the DC current flowing through the conductor to be detected includes, as described above, a part or the whole in the circumferential direction of the detection core. configuration to form a magnetic saturation region by the alternating magnetic flux blocking the magnetic flux ([Phi ₀₎ periodically, magnetic flux direction of the magnetic flux in the detecting core which occurs on the basis of the DC current flowing through the lead wire being detected ([Phi ₀₎ ([Phi ₀₎ orthogonal substantially flux ([Phi ₀₎ periodically interrupting constituting by changing the repulsion action of the direction of the alternating magnetic flux with respect to the detection generated based on the DC current flowing through the lead wire being detected Various means such as a configuration for modulating the magnetic flux (Φ ₀ ) in the core with a composite magnetic field of a circumferential magnetic field in the detection core and a magnetic field orthogonal to the circumferential magnetic field and periodically changing its direction are provided. Including, as a specific configuration, It can be realized by the arrangement configuration of the output core and the exciting core and the excitation coil.

The operation principle of the DC current sensor according to the present invention will be described with reference to FIG. The DC current sensor of the present invention shown in FIG. 1 is an AC current that is wound and disposed over an AC current transformer core 9 made of an annular soft magnetic material and a detection core constituting an AC current transformer, which is a main feature of the present invention. Except for the arrangement of the cancel coil 10,
The detection core, excitation core, detection coil, and excitation coil are all the same as the conventional configuration shown in FIG. That is, a pair of electrically connected detection coils 3a and 3b are wound and arranged in a toroidal shape on a short side portion of the detection core 2 made of a soft magnetic material having a rectangular frame shape at a position facing the detection core. The configuration is such that the detected conducting wire 1 through which a DC current flows is disposed inside the inside 2.

Further, the DC current I flowing through the conductive wire 1 to be detected is
As a means for switching the magnetic flux Φ ₀ in the detection core 2 generated based on the above, a pair of excitation cores 4 a and 4 b made of a soft magnetic material forming a quadrangular cylindrical shape on a long side portion at a position facing the detection core 2 are used. In addition to the arrangement, the exciting coil 5 is wound around the detection core 2 in the circumferential direction.

The AC current transformer core 9 is made of a soft magnetic material in the shape of a rectangular plate, and is arranged below the detection core 2 with a predetermined distance (gap) in the figure. It may be arranged with a predetermined distance (gap) above, or a pair may be arranged above and below the detection core 2 as necessary. In any case, it is necessary to select an arrangement configuration within a range that does not hinder miniaturization of the sensor. Although a single plate is shown in the drawing, a configuration in which a plurality of plates are stacked via an insulator can also be employed.

In the figure, the alternating current canceling coil 10 is shown to be wound in a toroidal shape on the outer periphery of one side 4b of a pair of exciting cores 4a, 4b, but it is necessary to take electromagnetic balance into consideration. Excitation cores 4a, 4b on both sides
It is also a preferable configuration to arrange them in each of.

In such a configuration, when a DC current I flows through the detected conductor 1, a magnetic flux Φ ₀ is generated in the detection core 2. At this time, a predetermined AC current (frequency f ₀ ) is applied to the exciting coil 5. When flowing, an alternating magnetic flux is generated in the exciting cores 4a and 4b in the α direction in the figure, and the alternating magnetic flux saturates the orthogonal portion 6 between the detecting core 2 and the exciting cores 4a and 4b, and flux [Phi ₀ becomes to be switched, the frequency is modulated alternating magnetic flux twice the excitation frequency (2f _0). Electromotive force of the magnetic flux Φ frequency 2f ₀ in proportion to the DC current I flowing through the lead wire being detected 1 with changes in ₀ (V
_DET ) is detected by the detection coils 3a and 3b.

In the state where the DC current I flowing through the conductor 1 to be detected is measured as described above, if a minute AC current is mixed and superimposed on the DC current I, the detection coils 3a, 3
As b, a value in which not only the DC current I but also a minute AC current is superimposed is output, and the value becomes extremely unstable.

However, in the configuration of the present invention, the DC current I
The effect of the minute alternating current superimposed on the current can be made substantially zero. That is, when an alternating current is mixed and superimposed on the detected conductor 1, a (alternating) magnetic field based on the alternating current is applied to the detecting core 2 and the alternating current transformer core 9, and the magnetic field causes the inside of the detecting core 2 and the alternating current to change. Each (alternating) magnetic flux Φ _AC is generated in the current transformer core 9. A predetermined AC current flows through the AC current canceling coil 10 due to the magnetic flux Φ _AC generated in the AC current transformer core 9.

Further, since the AC current canceling coil 10 is wound around the detection core 2 and the AC current transformer core 9, the AC current generated based on the magnetic flux Φ _AC generated in the AC current transformer core 9. As a result, a magnetic field is applied to the detection core 2. Since the magnetic field based on the alternating current of the alternating current canceling coil 10 and the magnetic field based on the alternating current mixed and superimposed on the detection target wire 1 act in directions to cancel each other, their combined magnetic field in the detection core 2 becomes zero, As a result, the magnetic flux Φ _AC generated in the detection core 2 based on the alternating current mixed and superimposed on the detected conductor 1 is canceled.

Accordingly, even when a minute AC current is mixed and superimposed on the DC current I in a state where the DC current I flowing through the detection target wire 1 is measured as described above, the influence of the AC current is substantially reduced. Thus, high-sensitivity measurement inherent in the DC current sensor can be realized in an extremely stable state.

FIG. 3 shows the configuration of the DC current sensor of the present invention.
1 having the configuration in which the AC current transformer core 9 and the AC current canceling coil 10 are arranged in the configuration shown in FIG. 1, any one of FIGS. 5, 6, and 7 other than FIG. By arranging the AC current transformer core 9 and the AC current canceling coil 10 also in the configuration of, the same effect as the configuration of FIG. 1 can be obtained.

In any of the above-described DC current sensors, the detection core 2 is covered with a shield case to cancel the magnetic field generated by the current flowing through the detection target wire 1 and the AC current flowing through the AC current canceling coil 10. Can be reduced.

In the drawing, the AC current canceling coil 10 in the detection core 2 and the AC current transformer core 9 is shown.
However, the number of turns on the detection core 2 may be slightly larger than the number of turns on the AC current transformer core 9 in consideration of the electrical resistance of the coil 10 and the like.

[0038]

EXAMPLE In order to confirm the effect of the present invention, a DC current sensor shown in FIG. 1 was prepared. The detection core 2 has a thickness of 0.
35 mm permalloy C (78% Ni-5% Mo-4%
(Cu-balFe). Excitation core part 4
a, the overall dimension including 4b width W ₁ = 27 mm (exciting core members 4a, the width W ₂ = 3.5 mm of 4b), the length L = 35
mm and height H = 7 mm. These were subjected to a predetermined heat treatment to complete the detection core 2.

Further, the detection coils 2a and 3b and the excitation coil 5 are wound around the detection core 2 while ensuring electrical insulation. Each of the detection coils 3a and 3b winds an enamel wire having an outer diameter of 0.18 mm for 60 turns (120 turns as a whole), and the excitation coil 5 has an outer diameter of 0.1 turn.
It has a configuration in which an 8 mm formal wire is wound 30 turns.

The main body of the DC current sensor having the above configuration is covered with a shield case made of a silicon steel plate having a thickness of 0.35 mm. .5mm, length 46mm,
0.35mm thick (window: width 14mm, length 24mm)
Permalloy C (78% Ni-5% Mo-4% Cu-b
alFe), and an AC current transformer core 9 made of
An AC current canceling coil 10 is wound and arranged so as to straddle the shield case and the AC current transformer core 9. The AC current canceling coil 10 has an outer diameter of 0.18 m.
The m formal wires were wound one turn each at a symmetric position of the shield case so as to correspond to the locations where the excitation cores 4a and 4b were arranged, and were connected in series.

Inside the detection core 2 and the AC current transformer core 9
A detection conductor 1 made of vinyl coating having an outer diameter of 16 mm is penetrated therein, and the detection coils 3a, 3b and the excitation coil previously wound independently of the detection core 2 are pulled out from predetermined positions of the shield case. The detection coil and the excitation coil were electrically connected by a predetermined method, and a predetermined electronic circuit was connected thereto, thereby completing the DC current sensor of the present invention. The exciting current applied to the exciting coils 5a and 5b was an alternating current of f = 256 Hz and 30 mArms.

Here, the AC current transformer core 9 and the AC current canceling coil 10 which are the main features of the present invention.
In the case of the DC current sensor having the configuration in which the DC current sensor is disposed (the present invention), and in the case of the DC current sensor having the configuration in which the AC current transformer core 9 and the AC current canceling coil 10 are not disposed (the comparative example), the detected conductors are respectively provided. ± 2 for 1
500 mA, 15 Hz with DC current in the range of
Input / output characteristics were measured when an AC current equivalent to mA was superimposed and passed, and the results are shown in FIG. In FIG. 2, the present invention is indicated by white triangles, and the comparative example is indicated by black triangles.

As shown in FIG. 2, when the ratio of the output voltage when the direct current is 100 mA to the output voltage when the direct current is 0 mA is defined as the S / N ratio, the S / N ratio before the countermeasure is almost 1, and the S / N ratio after the countermeasure. N
It was clear that the ratio was approximately 9, confirming that highly accurate measurement could be stably realized. Further, in the configuration of the comparative example, an output current is generated even when the DC current is originally 0 mA, and the DC current is apparently flowing, and the operation required as a sensor becomes difficult.

[0044]

According to the DC current sensor of the present invention, each of the AC current transformer core and the AC current canceling coil is effectively combined with the DC current sensors having various configurations proposed by the present applicant. The advantages of the DC current sensor have been effectively utilized, and it has become possible to measure minute DC current with high accuracy.

In particular, by making it possible to obtain a stable output by substantially eliminating the influence of the alternating current mixed in the direct current, it is possible to obtain a very small direct current of the inverter in the technical fields such as electric vehicles and solar power generation systems. It has become possible to provide a DC current sensor having a configuration effective for detecting leaks of air.

[Brief description of the drawings]

FIG. 1 is an explanatory perspective view showing a configuration of a DC current sensor of the present invention.

FIG. 2 is a graph showing a relationship between a measured current and an output current.

FIG. 3 is a perspective explanatory view showing a configuration of a conventional DC current sensor.

FIG. 4 is a perspective explanatory view showing a configuration of a conventional DC current sensor.

FIG. 5 is an explanatory perspective view showing a configuration of a conventional DC current sensor.

FIG. 6 is a perspective explanatory view showing a configuration of a conventional DC current sensor.

FIG. 7 is an explanatory perspective view showing a configuration of a conventional DC current sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 detected conductor 2 detection core 3, 3 a, 3 b detection coil 4 a, 4 b excitation core 5, 5 a, 5 b excitation coil 6 orthogonal part 7, 8 through hole 9 AC current transformer core 10 AC current cancel coil 20 DC current sensor 21 a Case Body 21b, 21c Case lid

Claims (2)

[Claims] 1. A detection wire through which a direct current flows through a detection core made of a soft magnetic material having an annular shape in which a detection coil is wound and arranged in a toroidal shape, and is generated based on the DC current flowing through the detection wire. A DC current sensor having means for switching the magnetic flux in the detecting core,
In order to cancel the magnetic flux in the detection core generated based on the AC current mixed with the DC current flowing through the detected wire, an AC current transformer core made of a ring-shaped soft magnetic material penetrating the detected wire is arranged, A DC current sensor comprising a detection core and an AC current canceling coil wound and wound over an AC current transformer core. 2. The direct current sensor according to claim 1, wherein the detection core is disposed in a shield case.