JP6008756B2 - Current sensor and three-phase AC current sensor device - Google Patents

Description

  The present invention relates to a configuration of a magnetic shield in a current sensor using a magnetoelectric conversion element, particularly a magnetoresistive element.

  Since the Hall element has low sensitivity, a magnetic flux collecting core is essential for use as a current sensor. For this reason, it is common to use a ring-shaped or C-shaped core, but there is a problem that the size is large and it is difficult to attach.

  Further, although a method using a highly sensitive magnetoresistive element and not using a core has been proposed, the magnetic field generated by the current has a high strength and the magnetoresistive element is saturated. Therefore, in order to detect a current of several amperes or more, it is necessary to place an element at a location away from the current line.

  Therefore, for example, Patent Document 1 proposes a current sensor in which a current line is divided into three parts to weaken the current intensity, and a magnetic field generated by one of the current lines is detected by a magnetoresistive element.

JP 2011-38874 A

  In the current sensor of Patent Document 1, there is a problem that a structure such as dedicated processing of a current line becomes complicated, and the size of the current sensor eventually increases.

  This is a problem assumed also in a current sensor using another magnetoelectric conversion element such as a magnetic impedance element.

  An object of the present invention is to provide a small-sized current sensor that is easy to install and uses an existing current line in a current sensor using a magnetoelectric conversion element.

  In order to achieve the above object, a current sensor according to the present invention is a current sensor for detecting a current flowing in a current line arranged along a first direction, and has a through hole extending along the first direction. A magnetic shield including a magnetic member; and a magnetoelectric conversion element that is disposed inside the through hole and senses a magnetic field generated by a current flowing through the current line. A gap portion extending along the first direction is formed on the side surface of the magnetic member. The current sensor is arranged such that the current line is located on the gap side with respect to the magnetoelectric conversion element and on the inner side of the outer peripheral surface of the magnetic member.

  According to the present invention, it is possible to provide a small and easy-to-install current sensor using an existing current line by arranging the magnetic shield so that the current line is positioned on the gap side with respect to the magnetoelectric transducer. it can.

  Furthermore, according to the present invention, by arranging the magnetic shield so that the current line is located on the inner side of the outer peripheral surface of the magnetic member, even when a current line other than the current line to be detected exists adjacently, the detection target The current flowing through the current line can be accurately detected.

It is a perspective view which shows the current sensor by Embodiment 1 of this invention. It is sectional drawing which shows the current sensor by Embodiment 1 of this invention. It is a side view which shows the current sensor by Embodiment 1 of this invention. It is a block diagram which shows the signal processing of the current sensor by this invention. It is a figure showing the relationship between the distance from an electric current line, and the strength of a magnetic field. It is a figure which shows the characteristic of a typical anisotropic magnetoresistive element. It is a perspective view which shows the current sensor by Embodiment 2 of this invention. It is sectional drawing which shows the current sensor by Embodiment 2 of this invention. It is a side view which shows the current sensor by Embodiment 2 of this invention. It is sectional drawing which shows the current sensor apparatus by Embodiment 3 of this invention. It is a side view which shows the current sensor apparatus by Embodiment 3 of this invention. It is sectional drawing which shows the alternative current sensor apparatus by Embodiment 3 of this invention. It is sectional drawing which shows the current sensor by Embodiment 4 of this invention. It is a side view which shows the current sensor by Embodiment 4 of this invention. It is sectional drawing corresponding to FIG. 10 which shows the current sensor apparatus which has a current sensor by Embodiment 4 of this invention.

Embodiment 1 FIG.
1, 2 and 3 are a perspective view, a sectional view and a side view, respectively, showing the current sensor according to the first embodiment of the present invention. The cross-sectional views referred to in this specification are all cross-sectional views (xy cross-sectional views) showing a cross section along the xy plane, and are cross-sectional views at positions where the magnetoresistive element 2 exists.
A current sensor 10 according to the present embodiment includes a magnetic shield 1 and a magnetoresistive element 2 that senses a magnetic field generated by a current to be measured flowing in an existing current line 3. The current line 3 extends in the z direction in the figure, and the current flows in the z direction. The current sensor 10 can be used for any current line 3 having, for example, a general cylindrical shape, a plate shape, or a rectangular parallelepiped shape.

  The magnetic shield 1 has a cylindrical shape, for example, a cylindrical shape or a hollow quadrangular prism shape, and the through hole or the hollow portion extends along the z direction. The magnetic shield 1 has no gap on the circumferential surface around the z direction.

  The magnetic shield 1 can be composed of, for example, an electromagnetic steel plate such as a silicon steel plate, or a magnetic member such as ferrite or permalloy. The magnetic member to be used is selected in consideration of characteristics such as processability, cost, and physical property values. In general, physical properties such as magnetic characteristics, relative permeability, frequency characteristics, and Curie temperature are determined by conditions such as the relationship between the magnetic field strength created by the current line and the sensitivity range of the magnetoresistive element, the sensor operating temperature, and the operating frequency.

  The magnetic shield 1 can also be manufactured by, for example, a method of punching a thin plate into a zy cross-sectional shape and laminating it in the z direction, or a method of sintering powder such as ferrite. Alternatively, a plate material extending in the z direction can be bent in the xy direction.

  As shown in FIGS. 1 and 2, the magnetoresistive element 2 is arranged at a predetermined distance r from the current line 3 in the −y direction. The magnetoresistive element 2 is disposed in the through hole or the hollow portion of the magnetic shield 1.

  As the magnetoresistive element 2, for example, an anisotropic magnetoresistive (AMR) element can be used. Alternatively, as the magnetoresistive element, a giant magnetoresistive (GMR) element or a tunnel effect magnetoresistive (TMR) element may be used.

  In general, a magnetoelectric conversion element, for example, a magnetoresistive element, has a characteristic that the magnetic field strength to be sensed differs depending on the direction in which it is arranged. Therefore, in the present invention, the distance r and the arrangement direction of the magnetoresistive element 2 are determined so that the magnetic field intensity sensed by the magnetoresistive element 2 is within the sensitivity range of the magnetoelectric conversion element, that is, the magnetoresistive element 2 is not saturated. To do.

  That is, in order to cause the magnetoresistive element 2 to sense a magnetic field having a high strength, the magnetic sensing direction can be arranged so as to coincide with the magnetic field direction created by the current line. The magnetic field generated by the current line 4 is curved, and the magnetosensitive area of the magnetoresistive element 2 is sufficiently wide. Therefore, it can arrange | position in the direction where a magnetic field becomes the strongest when it decomposes | disassembles into a vector component in a three-dimensional orthogonal coordinate system. Alternatively, by disposing the magnetoresistive element 2 from this direction, it is possible to cause the magnetoresistive element 2 to sense a magnetic field having a low intensity.

  FIG. 4 is a block diagram showing signal processing of the current sensor according to the present invention. The magnetoresistive element 2 outputs a voltage signal that changes according to the sensed magnetic field to the signal processing unit 4. The signal processing unit 4 includes, for example, an A / D converter, a microcomputer, a memory, and the like, and outputs the detected current direction and magnitude.

  Next, the operation of the current sensor 10 according to the present embodiment will be described. When a current flows through the current line 3, a magnetic field is generated around the current line 3. The strength and direction of the magnetic field can be described by Biosavart's law.

  If the thickness of the current line is ignored and the wire is sufficiently long, the intensity H of the generated magnetic field is expressed by the following formula (1).

  Here, H is the magnetic field strength [A / m], I is the current value [A] flowing through the current line, and r is the distance [m] from the current line. FIG. 5 is a diagram illustrating the relationship between the distance from the current line and the strength of the magnetic field. FIG. 5 shows a case where a current of 120 [A] flows through a wire-like current line. The magnetic field strength H decreases as the distance r from the current line increases.

  FIG. 6 is a diagram showing characteristics of a typical anisotropic magnetoresistive element. An anisotropic magnetoresistive element (AMR) is generally saturated at 5 to 20 [Oe]. The region where the output of the magnetoresistive element is highly linear with respect to the magnetic field intensity is further narrowed. For example, an anisotropic magnetoresistive element that is saturated at 15 [Oe] and has a linearity maintaining range of 0 to 5 [Oe] is assumed. In the case of FIG. 5, it can be seen that, in order to measure in a region where the magnetoresistive element is not saturated and the linearity is high, it is necessary to be at least 5 cm away from the current line. Therefore, in order to perform measurement in a region where the magnetoresistive element 2 is not saturated and has high linearity, the space required by the entire current sensor is increased.

  On the other hand, the current sensor 10 according to the present embodiment includes the magnetic shield 1, and the magnetic field concentrates on the magnetic shield 1, so the inner magnetic field strength becomes small. Since there is no air gap in the magnetic shield 1, the magnetic field from the outside does not enter the inside of the magnetic shield 1 where the magnetoresistive element 2 is installed without passing through the magnetic shield 1, thus enhancing the attenuation effect of the magnetic field strength. be able to. The magnetic field strength inside the magnetic shield 1 is optimized by conditions such as the relative magnetic permeability of the magnetic shield 1, the opening area of the through hole or the hollow portion, the distance r from the current line, and the like.

  The resistance value of the magnetoresistive element 2 changes corresponding to the optimized magnetic field. When a voltage is applied from the power source to the magnetoresistive element 2, the magnetoresistive element 2 outputs a voltage signal that changes according to the sensed magnetic field to the signal processing unit 4. The signal processing unit 4 outputs the direction and magnitude of the current detected by the voltage signal output from the magnetoresistive element 2.

  As described above, in the present embodiment, by providing the magnetic shield 1, the magnetoresistive element 2 can be arranged at a large distance from the current line 3, and the space required for the entire current sensor can be increased without increasing the size of the magnetoresistive element. There is an advantage that the magnetic field intensity sensed by the element 2 can be attenuated. As a result, there is an advantage that the magnetoresistive element 2 can be used in a range where the linearity is maintained without being saturated.

  Therefore, the current sensor 10 can be used not only for detecting a minute current but also for detecting a large current. Further, the current sensor 10 can be reduced in size, and only one yz plane or xz plane can be installed in one direction with respect to the current line 3. Furthermore, since it is not necessary to process the current line 3 such as shunting or bending, the current sensor 10 can be easily installed on the existing current line 3.

Embodiment 2. FIG.
7, 8, and 9 are a perspective view, a cross-sectional view, and a side view, respectively, showing a current sensor according to Embodiment 2 of the present invention. The magnetic shield 1 of the current sensor 10 according to the present embodiment has a magnetic barrier portion 11 on the peripheral surface. In this embodiment, in addition to the current line 3 through which the current to be measured flows, it is assumed that there is an adjacent current line 5 that is arranged adjacent to the current line 3 and through which a current that is not a measurement target flows. The adjacent current line 5 extends along the z direction in the figure, and the current also flows along the z direction. Other configurations are the same as those of the first embodiment.

  As shown in FIG. 8, it is assumed that the adjacent current line 5 is arranged at a predetermined distance from the current line 3 in the + x direction. In this case, as shown in FIGS. 7 to 9, the magnetic barrier portion 11 of the magnetic shield 1 is provided on the + x side of the peripheral surface of the magnetic shield 1.

  The magnetic barrier unit 11 is disposed between the current line 3 and the adjacent current line 5 and has a configuration for absorbing a magnetic field generated by a current flowing through the adjacent current line 5. For example, as shown in FIG. 7, the magnetic barrier portion 11 may have a shape that extends in a plane along the yz plane. In addition, the magnetic barrier portion 11 preferably has a shape extending in the + y direction to a position indicated by a dotted line in FIG. 8, that is, a position longer than the end of the adjacent current line 5.

  Moreover, the magnetic barrier part 11 can be integrally formed with the magnetic shield 1 or can be attached to the magnetic shield 1 as a separate member.

  Next, the operation will be described. When a current flows through the current line 3, a magnetic field is generated around the current line 3. As in the first embodiment, the magnetic field concentrates on the magnetic shield 1, and the magnetic field strength is reduced inside the magnetic shield 1.

In the present embodiment, a current flows through the adjacent current line 5 to generate a magnetic field, but it is sufficiently absorbed by the magnetic barrier portion 11. The magnetoresistive element 2 senses the sum of the magnetic field component H _m that the current line 3 creates at the position of the magnetoresistive element 2 and the magnetic field component H _n that the adjacent current line 5 creates at the position of the magnetoresistive element 2. The value of | H _m | / | H _n | can be reduced to 1/1000 or less by adjusting the shape and size of the magnetic barrier portion 11.

  As described above, in this embodiment, similarly to the first embodiment, the magnetic field intensity sensed by the magnetoresistive element 2 can be suppressed to a desired level. In addition, since the magnetic shield 1 includes the magnetic barrier portion 11, the magnetic field strength created by the adjacent current line 5 at the position of the magnetoresistive element 2 can be made sufficiently smaller than the magnetic field strength created by the current line 3. The current sensor 10 can accurately detect the current to be measured. Furthermore, since the above two functions are performed by an integrated current sensor, positioning is easier than in the case where the magnetic shield and the magnetic barrier portion are provided separately.

Embodiment 3 FIG.
10 and 11 are a sectional view and a side view, respectively, showing a current sensor device according to Embodiment 3 of the present invention. The current sensor device 20 according to the present embodiment is provided with two current sensors according to the second embodiment. In the present embodiment, there are three current lines, which are adjacently arranged between the current lines 3a and 3b through which the current to be measured flows and the current lines 3a and 3b and through which the current not to be measured flows through. explain. The three current lines extend along the z direction, but need not be parallel to each other.

  Current sensors 10a and 10b are installed at predetermined distances from current lines 3a and 3b, respectively. The magnetic barrier portions 11a and 11b of the magnetic shields 1a and 1b included in the current sensors 10a and 10b are provided on the adjacent current line 5 side. That is, as shown in FIG. 10, the magnetic barrier portion 11a is provided on the + x side, and the magnetic barrier portion 11b is provided on the −x side.

  In general, in a three-phase alternating current, current flows not only through the current lines 3a and 3b at both ends, but also through the central current line 5. The current sensor device 20 according to the present embodiment can be used even when a large current flows through the current lines 3a and 3b. Moreover, the measurement error of the current to be measured caused by the magnetic field generated by the adjacent current line 5 can be minimized. Therefore, the current sensor device 20 can be used as a current sensor device for three-phase alternating current.

  In the present embodiment, the case where the current line 5 through which the current not to be measured flows is arranged between the current lines 3a and 3b at both ends through which the current to be measured flows is described. As an alternative, as shown in FIG. 12, the current lines 3a and 3b through which the current to be measured flows are arranged adjacent to each other, and the current line 3b is arranged between the current line 3a and the current line 5 through which a current not to be measured flows. You may have. In this case, similarly to the above configuration, magnetic barrier portions are provided between adjacent current lines, that is, between the current line 3a and the current line 3b, and between the current line 3b and the current line 5, respectively. . That is, as shown in FIG. 12, the magnetic barrier portions 11a and 11b are both provided on the + x side.

Embodiment 4 FIG.
13 and 14 are a sectional view and a side view, respectively, showing a current sensor according to Embodiment 4 of the present invention. Only the configuration different from that of the first embodiment will be described below. The magnetic shield 1 of the current sensor 10 according to the present embodiment has a shape in which a gap portion 12 is formed along the z direction on the circumferential surface around the z direction of the cylindrical body portion.

  As shown in the xy sectional view in FIG. 13, the magnetic shield 1 is formed by cutting out a part of a quadrangle when viewed from the z direction. For example, a U shape (recessed shape) or a U shape is formed. It may be formed in an arbitrary shape such as a C shape or an arc shape.

  The magnetic shield 1 is arranged so that the current line 3 is located on the gap 12 side with respect to the magnetoresistive element 2 and on the inner side of the outer peripheral surface of the magnetic shield 1. Thus, the current line 3 is sandwiched or surrounded by the magnetic shield 1. However, the current line 3 does not necessarily have to be located inside the inner peripheral surface of the magnetic shield 1.

  According to the configuration of the present embodiment, since the magnetic field concentrates on the magnetic shield 1 as in the first embodiment, the magnetic field strength is reduced inside the magnetic shield 1 on which the magnetoresistive element 2 is installed. As shown in FIG. 15, when there is an adjacent current line 5 that is not a detection target, the magnetic field generated by the adjacent current line 5 is concentrated on the closest magnetic shield 1a (1b) made of a magnetic member. . Therefore, the influence of the adjacent current line 5 on the magnetoresistive element 2 can be reduced. FIG. 15 corresponds to FIG. 10, and detailed description thereof is omitted.

  Here, for example, in the case of a current sensor using a Hall element, the Hall element may be disposed in the gap of the magnetic core. At this time, a magnetic flux is generated from the magnetic core into the air and returned to the magnetic core. By reducing the area of the end face of the gap, the magnetic flux density can be further increased. For example, by installing a current line inside a C-shaped magnetic core and installing a Hall sensor in the C-shaped gap, the magnetic field strength created by the current line is increased compared to the case without a magnetic core, Magnetic field strength that can be detected by the sensor.

  In the present embodiment, on the contrary, there is a purpose to moderately attenuate the magnetic field strength. Therefore, it is necessary to prevent the magnetic shield 1 from functioning as a magnetic flux collecting core, contrary to the arrangement of the Hall sensor. Therefore, the magnetic shield 1 is arranged so that the current line 3 is located on the gap 12 side with respect to the magnetoresistive element 2 so that the magnetoresistive element 2 is not installed in the gap 12 having a small end surface area. Thereby, the same effect as Embodiment 1 can be acquired.

  Further, by arranging the magnetic shield 1 so that the current line 3 is positioned on the inner side of the outer peripheral surface of the magnetic shield 1, the effect obtained by providing the magnetic barrier unit 11 in the second embodiment can be obtained.

  In the above embodiment, a current sensor using a magnetoresistive element has been described. However, a current sensor using a flux gate type magnetoelectric conversion element utilizing saturation of a magnetic substance as well as a magnetoelectric conversion element such as a magnetic impedance type is described. In addition, the present invention can be applied in that it is not suitable for use in a strong magnetic field.

  DESCRIPTION OF SYMBOLS 1 Magnetic shield, 2 Magnetoresistive element, 3 Current line, 4 Signal processing part, 5 Adjacent current line, 11 Magnetic barrier part, 12 Air gap part

Claims (6)

A current sensor for detecting a current flowing in a current line arranged along a first direction,
A magnetic shield including a magnetic member having a through hole extending along the first direction;
A magnetoelectric conversion element that is disposed inside the through hole and senses a magnetic field generated by a current flowing through the current line;
A gap portion extending along the first direction is formed on the side surface of the magnetic member,
Magnetic shield, current sensor and at least a part of the current line are arranged so as to be positioned in the gap portion. A current sensor for detecting a current flowing in a current line arranged along a first direction,
A magnetic shield including a cylindrical magnetic member having a through hole extending along the first direction;
A magnetoelectric conversion element that is disposed inside the through hole and senses a magnetic field generated by a current flowing through the current line;
The current sensor is characterized in that the magnetic shield is arranged such that the current line is located outside the magnetic shield.   3. The current sensor according to claim 2, wherein the magnetic shield includes a magnetic barrier portion provided between the current line and another current line disposed adjacent to the current line. Two current sensors according to claim 3 are provided,
The two current sensors each detect a current flowing through one different current line among three current lines through which a three-phase alternating current flows.   The current sensor according to claim 1, wherein the magnetoelectric conversion element is an anisotropic magnetoresistive element. A current sensor for detecting a current flowing in a current line arranged along a first direction,
A magnetic shield including a magnetic member having a through hole extending along the first direction;
An anisotropic magnetoresistive element that senses the magnetic field generated by the current flowing in the current line,
A gap portion extending along the first direction is formed on the side surface of the magnetic member,
The anisotropic magnetoresistive element is disposed on a plane portion included in the inner peripheral surface of the magnetic member that defines the through hole,
The side surface of the magnetic member in which the gap is formed is opposed to the flat portion,
The current sensor , wherein the magnetic shield is arranged so that the current line is located in the gap.

Images