JP2015132499A - current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology of measuring a current of one of a plurality of bus bars extended in parallel, while improving SN ratio of a magnetoelectric transducer.SOLUTION: A current sensor 100 includes a first bus bar 3a to be measured, a second bus bar 2a not to be measured, which is extended in parallel with the first bus bar and has a thin and long cross section, and a magnetoelectric transducer 5. A magnetic sensitive surface 5a of the magnetoelectric transducer 5 faces a wide side face of the second bus bar 2a. A plane including the magnetic sensitive surface 5a is arranged to cross a side face of the first bus bar 3a. The second bus bar 2a is larger in lateral width at both ends than in the longitudinal center.

Description

  The present invention relates to a current sensor.

  A system that performs current feedback control of a three-phase AC motor includes a current sensor that monitors a three-phase output current. When the output of the motor is large, an elongated metal bar or metal plate called a bus bar is used to transmit the three-phase AC output. Three-phase alternating current is transmitted by bus bars extending in parallel. The current sensor is provided in at least one bus bar. The current sensor is typically a magnetoelectric conversion element and detects a magnetic field caused by a current flowing through the bus bar. The magnitude of the current flowing through the bus bar can be understood from the magnitude of the detected magnetic field.

  In the past, the bus bar was surrounded by a C-shaped magnetic collecting core and the magnetoelectric conversion element was placed at the C-shaped break. However, the sensitivity of the magnetoelectric conversion element was improved, and the current was passed only by the magnetoelectric conversion element without the magnetic collecting core. Current sensor to measure has appeared. Since a magnetic core is not required, it is small and low cost. However, since the magnetic collecting core is not provided, the magnetoelectric conversion element detects a magnetic field caused by the current flowing through the bus bar other than the measurement target. That is, the SN ratio is not high.

  Hereinafter, for convenience of explanation, a current measurement target bus bar is referred to as a “measurement target bus bar”, and a bus bar other than the measurement target bus bar is referred to as a “noise source bus bar”. Strictly speaking, the magnetoelectric conversion element measures (detects) the magnetic field generated due to the current flowing through the bus bar, but this is expressed simply as measuring (detecting) the magnetic field of the bus bar. . Lowering the ratio of the magnetic field of the noise source bus bar to the magnetic field measured by the magnetoelectric conversion element leads to an improvement in the SN ratio.

  Techniques for increasing the S / N ratio are disclosed in Patent Documents 1 and 2, for example. The current sensor disclosed in Patent Document 1 is as follows. Magnetoelectric conversion elements are arranged on a straight line (common center line) passing through the cross-sectional centers of the plurality of noise source bus bars. The magnetoelectric conversion element is arranged in a direction in which the magnetosensitive surface is orthogonal to the common center line. Further, the measurement target bus bar is disposed at a position offset from the common center line so that the wide surface thereof is orthogonal to the magnetosensitive surface of the magnetoelectric transducer. The magnetic flux of the bus bar to be measured penetrates the magnetic sensitive surface at right angles. On the other hand, since the magnetic flux of the noise source bus bar is orthogonal to the common center line, it is parallel to the magnetic sensitive surface and does not penetrate the magnetic sensitive surface. Therefore, a high S / N ratio can be obtained. In addition, the “cross section” in this specification means a cross section orthogonal to the extending direction of the bus bar. Such a cross section may be referred to as a “cross section”.

  Furthermore, in Patent Document 2, a noise source bus bar having a rectangular cross section is prepared, and the magnetoelectric conversion element is disposed so as to face the wide surface. In the cross section orthogonal to the bus bar, the magnetic field of the noise source bus bar is parallel to the wide surface. Therefore, the variation of the SN ratio with respect to the variation in the position of the magnetoelectric conversion element in the longitudinal direction of the cross section of the noise source bus bar is reduced.

JP 2001-074783 A International Patent Publication WO2013 / 005545

  The technique disclosed in this specification also relates to a technique for measuring one current of a plurality of bus bars extending in parallel, and aims to improve the SN ratio of the magnetoelectric conversion element. In particular, a technique is provided for reducing fluctuations in the SN ratio with respect to variations in the position of the magnetoelectric transducer. Note that the technology disclosed in this specification achieves a reduction in sensitivity change of the SN ratio by devising the shape of the bus bar and the layout of the magnetoelectric transducer. Therefore, it should be noted that the current sensor disclosed in the present specification does not exist independently from the bus bar, and a part of the bus bar having a specific shape is also an element constituting the current sensor.

  As described in Patent Document 2, when a metal plate having a long cross-sectional shape is employed as the noise source bus bar, the magnetic flux in the cross section becomes parallel along the wide surface. However, it is not completely parallel and is strictly an ellipse. Therefore, there is a slight magnetic flux penetrating the magnetosensitive surface of the magnetoelectric transducer. Further, in the cross section of the noise source bus bar, the curvature of the ellipse increases as it approaches the end in the longitudinal direction of the cross section, and the magnetic flux penetrating the magnetic sensitive surface increases. That is, the SN ratio variation with respect to the change in position of the magnetoelectric transducer in the longitudinal direction of the cross section of the noise source bus bar becomes large.

  The technology disclosed in the present specification devise the cross-sectional shape of the noise source bus bar to reduce the magnetic flux penetrating the magnetoelectric transducer. The current sensor disclosed in this specification includes the following structure. The current sensor includes a first bus bar that is a current measurement target (measurement target bus bar), a second bus bar that is a current non-measurement target (noise source bus bar) extending in parallel with the first bus bar, and a magnetoelectric transducer. Consists of. The magnetoelectric conversion element is arranged such that its magnetic sensitive surface faces the wide side surface of the second bus bar and the magnetic sensitive surface is orthogonal to the side surface of the first bus bar (measurement target bus bar). The magnetoelectric conversion element itself also faces the side surface of the first bus bar. In other words, the magnetoelectric conversion element is disposed so that its magnetosensitive surface is orthogonal to the magnetic field generated due to the current flowing through the first bus bar.

  On the other hand, in the above-described current sensor, the second bus bar (noise source bus bar) has a width in the cross-sectional short direction that is larger at both ends than the center in the cross-sectional longitudinal direction. More specifically, the cross-sectional shape of the second bus bar (noise source bus bar) is narrow at the center in the longitudinal direction, and its width (width in the short direction) increases toward both ends in the longitudinal direction.

  The above shape of the noise source bus bar brings the shape of the magnetic flux closer to the straight line from the ellipse in a region facing the wide surface of the noise source bus bar in the cross section. Therefore, the magnetic flux of the noise source bus bar penetrating the magnetosensitive surface of the magnetoelectric transducer is reduced near the center of the noise source bus bar in the longitudinal direction of the cross section. As a result, the SN ratio is improved. In addition, the curvature of the magnetic flux decreases near the end of the noise source bus bar in the longitudinal direction of the cross section. That is, the curve of the magnetic flux line becomes gentle. Therefore, the variation of the SN ratio with respect to the variation in the position of the magnetoelectric transducer along the longitudinal direction of the cross section of the noise source bus bar is reduced. The shape of the magnetic flux with respect to the above shape of the noise source bus bar will be specifically described in the column of the embodiment of the invention.

  The technology disclosed in this specification relates to a technology for measuring one current of a plurality of bus bars extending in parallel, and improves the SN ratio of the magnetoelectric transducer. Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a typical perspective view which shows two bus bars and a magnetoelectric conversion element which are extended in parallel in the current sensor of an Example. It is the figure which represented typically the magnetic flux which generate | occur | produces the cross section of the bus bar and magnetoelectric conversion element in the II-II line of FIG. FIG. 3 is a cross-sectional view of a conventional bus bar and a magnetoelectric conversion element compared with FIG. 2 and a diagram schematically showing magnetic flux generated around the bus bar to be measured. It is the figure which represented typically the magnetic flux which generate | occur | produces the cross-sectional view of the bus bar and magnetoelectric conversion element of a modification, and the bus bar of non-measurement object.

  A current sensor according to an embodiment will be described with reference to the drawings. FIG. 1 shows a bus bar that transmits three-phase AC power to a three-phase AC motor. In order to transmit the three-phase AC power, three bus bars are required, but two of them are shown as representatives in FIG. As shown in FIG. 1, the two bus bars 2 and 3 are arranged in parallel to each other, and the bus bars 2 and 3 are provided with current sensors 100 and 200 for measuring current. Actually, the bus bars 2 and 3 extend long in the Z-axis direction, but only the portion where the current sensors 100 and 200 are provided is shown in FIG. Each of the current sensors 100 and 200 includes magnetoelectric conversion elements 4 and 5 that detect a magnetic field caused by a current flowing through the bus bars 2 and 3. The current sensors 100 and 200 monitor the magnitude of the current flowing through the bus bars 2 and 3 with the magnitude of the detected magnetic field. Note that the shapes of the magnetoelectric conversion elements 4 and 5 are schematically drawn in a rectangular parallelepiped for convenience of explanation.

  In addition, the technology disclosed in the present specification realizes a reduction in the sensitivity change of the S / N ratio by devising the shape of the non-measurement target bus bar and the layout of the magnetoelectric transducer. For this reason, a part of the non-measurement target bus bar having a specific shape is also an element constituting the current sensor. The current sensor 100 in the embodiment includes a part of the bus bar 2 to be measured (measurement bus bar 2a) and a part of the bus bar 3 to be non-measured. A magnetic field generated from a part of the bus bar 3 that is not to be measured becomes a noise source of the magnetoelectric transducer 4. For the sake of explanation, a part of the bus bar 3 to be non-measured is referred to as a noise source bus bar 3a. Similarly, the current sensor 200 includes a part of the bus bar 3 to be measured (measurement bus bar 3b) and a part of the bus bar 2 to be non-measured (noise source bus bar 2b).

  As well represented in FIG. 1, the magnetoelectric conversion element 4 provided in the vicinity of the bus bar 2 and the magnetoelectric conversion element 5 provided in the vicinity of the bus bar 3 are inclined in the extending direction (Z-axis direction) of the bus bars 2 and 3. It is arranged opposite. In other words, when viewed from the direction in which the bus bars 2 and 3 are arranged (X-axis direction), the magnetoelectric conversion element 4 provided in the bus bar 2 and the magnetoelectric conversion element 5 provided in the bus bar 3 are arranged so as not to overlap each other. ing. The magnetic field caused by the current flowing through the bus bar is substantially parallel to a plane (XY plane in the figure) orthogonal to the extending direction of the bus bar. Therefore, the magnetic field generated in the range where the current sensor 100 is located has little effect on the range where the current sensor 200 is located. Therefore, the current sensors 100 and 200 can monitor the currents of the bus bars 2 and 3 independently of each other. The current sensors 100 and 200 have the same configuration except that the measurement target and the non-measurement target are interchanged. Hereinafter, the current sensor 100 will be described.

  The current sensor 100 will be described with reference to FIG. First, the shape of the measurement bus bar 2a will be described. As shown in FIG. 2, the shape of the cross section of the measurement bus bar 2a (the cross section perpendicular to the extending direction of the bus bar 2) is rectangular. The thickness (width in the X-axis direction) is the same as the thickness of the lower end (upper end) in the height direction (Y-axis direction) of the noise source bus bar 3a described later, and the height (length in the Y-axis direction) is The height of the noise source bus bar 3a is lower.

  The shape of the noise source bus bar 3a will be described. As shown in FIG. 2, the noise source bus bar 3a has an elongated cross-sectional shape in the height direction (Y-axis direction), and is different from the cross-sectional shape of the measurement bus bar 2a. As for the cross-sectional shape of the noise source bus bar 3a, the width in the short side direction (X-axis direction) is larger at both ends than the center in the cross-sectional longitudinal direction. In other words, the thickness W1 of the noise source bus bar 3a at the center in the cross-sectional longitudinal direction (Y-axis direction) is smaller than the thickness W2 of the noise source bus bar 3a at both ends in the cross-sectional longitudinal direction. That is, both surfaces of the noise source bus bar 3a in the thickness direction (X-axis direction) are curved and recessed at the center in the height direction (Y-axis direction). The noise source bus bar 3a maintains the above-described cross-sectional shape along the extending direction at least in a range facing the magnetoelectric conversion element 4.

  As a material for the bus bars 2 and 3, a highly conductive metal, typically copper, is used. The use of a highly conductive material can suppress the internal resistance of the bus bar and reduce the loss of power transmitted to the three-phase motor.

  With reference to FIG. 2, the positional relationship among the measurement bus bar 2a, the noise source bus bar 3a, and the magnetoelectric transducer 4 will be described. The magnetoelectric conversion element 4 is located on the upper surface of the measurement bus bar 2a. And the magnetoelectric conversion element 4 is located in the center of the thickness direction (X-axis direction) of the measurement bus bar 2a. Further, the magnetoelectric conversion element 4 is located on the center line CL in the longitudinal direction (Y-axis direction) of the cross section of the noise source bus bar 3a.

  In the magnetoelectric conversion element, the direction in which the magnetic flux is detected is generally determined. Specifically, the magnetoelectric conversion element detects a magnetic flux component orthogonal to a side surface called a magnetosensitive surface among magnetic fluxes penetrating the element. This means that the magnetoelectric conversion element does not detect a magnetic flux component parallel to the magnetic sensitive surface in the magnetic flux penetrating the element. In FIG. 2, reference numeral 4 a indicates a magnetosensitive surface. The sensitivity for detecting the magnetic flux is highest when the magnetic sensitive surface 4a is orthogonal to the magnetic flux. The direction perpendicular to the magnetic sensitive surface 4a is referred to as a magnetic sensitive direction. The magnetoelectric conversion element 4 is arranged such that the magnetosensitive surface 4a faces the wide side surface 31 of the noise source bus bar 3a. In other words, the magnetosensitive surface 4a is disposed so as to face the side surface (wide side surface 31) facing the thickness direction (X-axis direction) of the noise source bus bar 3a. The magnetoelectric transducer 4 is arranged such that the magnetic sensitive surface 4a is orthogonal to the upper surface 21 of the measurement bus bar 2a and the magnetic sensitive surface 4a is parallel to the extending direction (Z-axis direction) of the measurement bus bar 2a. . Therefore, the magnetic sensing direction of the magnetoelectric conversion element 4 coincides with the direction (X-axis direction) parallel to the side surface (upper surface 21) of the measurement bus bar 2a and orthogonal to the extending direction of the measurement bus bar 2a.

  The current flowing through the measurement bus bar 2a flows along the extending direction (Z-axis direction) of the measurement bus bar 2a. Accordingly, the magnetic flux generated by the current flowing through the measurement bus bar 2a has an elliptical shape centered on the cross-sectional center of the measurement bus bar 2a on a plane (XY plane) orthogonal to the extending direction of the measurement bus bar 2a. Therefore, by arranging the magnetoelectric conversion element 4 as described above, the direction of the magnetic flux coincides with the magnetic sensitive direction at the position where the magnetoelectric conversion element 4 is arranged. That is, the magnetic flux generated from the measurement bus bar 2a is orthogonal to the magnetosensitive surface 4a. Therefore, the magnetic flux generated from the measurement bus bar 2a can be detected with high sensitivity. In other words, the magnetoelectric transducer 4 is arranged so that the direction of the magnetic field generated due to the current flowing through the measurement bus bar 2a coincides with the direction of magnetic sensing.

  The influence which the magnetoelectric conversion element 4 receives with the magnetic flux which generate | occur | produces from the noise source bus bar 3a is demonstrated. First, as a comparative example, a case where the cross-sectional shape of the noise source bus bar is rectangular will be described with reference to FIG. As shown in FIG. 3, the cross-sectional shape of the noise source bus bar 13a of the comparative example is a rectangle elongated in the height direction (Y-axis direction). The height and width of the cross section of the noise source bus bar 13a are the same as the cross section of the noise source bus bar 3a of the embodiment. The comparative example is the same as the embodiment except that the noise source bus bar 3a is changed to the noise source bus bar 13a. As shown in FIG. 3, the magnetic flux M2 generated from the noise source bus bar 13a has an elliptical shape centered on the cross-sectional center of the noise source bus bar 13a. When the magnetoelectric conversion element 4 is positioned on the center line CL in the longitudinal direction of the cross section of the noise source bus bar 13a, the magnetic flux M2 passes through the magnetoelectric conversion element 4 in a direction parallel to the magnetosensitive surface 4a. Therefore, since the magnetic flux M2 is not orthogonal to the magnetic sensitive surface 4a, it does not affect the detection of the magnetic flux of the measurement bus bar 2a. However, when the position of the magnetoelectric transducer 4 is slightly shifted in the longitudinal direction of the cross section, the direction of the magnetic flux M2 is inclined due to the curvature of the ellipse. Furthermore, the curvature of the ellipse increases as it approaches the end in the longitudinal direction of the cross section. For example, when the position of the magnetoelectric conversion element 4 is shifted to the position indicated by the broken line in FIG. 3 in the longitudinal direction of the cross section, the direction of the magnetic flux M2 is not parallel to the magnetosensitive surface 4a as shown in FIG. That is, the magnetic flux M2 has a component in the magnetosensitive direction (X-axis direction). Therefore, when the magnetoelectric conversion element 4 is displaced from the center line CL, the magnetic flux in the direction penetrating the magnetosensitive surface 4a increases. The increased magnetic flux becomes noise with respect to the magnetic flux generated by the measurement bus bar 2a to be measured. That is, the SN ratio variation with respect to the change in position of the magnetoelectric transducer 4 in the longitudinal direction of the cross section of the noise source bus bar becomes large.

  On the other hand, the shape of the magnetic flux M1 generated from the noise source bus bar 3a of the embodiment has a longer range parallel to the major axis of the ellipse as shown in FIG. Become. The range parallel to the long axis is in a region facing the wide side surface of the noise source bus bar 3a, and extends in parallel with the cross-sectional longitudinal direction (Y-axis direction). That is, as compared with the comparative example of FIG. 3, the shape of the magnetic flux is brought closer to a straight line extending in the longitudinal direction of the cross section in the region facing the wide side surface of the noise source bus bar 3 a. In other words, in the region facing the wide side surface of the noise source bus bar 3a, the curvature of the magnetic flux M1 becomes smaller than an ellipse (the radius of curvature becomes larger) and approaches a straight line. The straight line is parallel to the magnetosensitive surface 4a. For comparison, when the magnetoelectric conversion element 4 is shifted to the same position as in the comparative example of FIG. 3 (position indicated by the broken line in FIG. 2), the direction of the magnetic flux M1 is parallel to the magnetic sensitive surface 4a as shown in FIG. Become. Therefore, even if the position of the magnetoelectric conversion element 4 moves in the longitudinal direction of the cross section, the component in the magnetic sensing direction (X-axis direction) of the magnetic flux M1 at the moved position is compared with the comparative example in which the magnetic flux is elliptical. Get smaller. Therefore, the SN ratio variation with respect to the position change of the magnetoelectric transducer 4 in the longitudinal direction of the cross section of the noise source bus bar is reduced.

  In the current sensor 100, the measurement bus bar 2 a detected by the magnetoelectric conversion element 4 with respect to an error in the Y-axis direction of the mounting position of the magnetoelectric conversion element 4 by making the cross section of the noise source bus bar 3 a as described above. The fluctuation of the magnetic flux error can be kept low. Therefore, the fluctuation of the SN ratio with respect to the mounting position of the magnetoelectric conversion element 4 of the current sensor 100 can be suppressed small. This makes it possible to measure the current value transmitted to the three-phase AC motor with high accuracy.

  Again, the configuration of the current sensor 200 is the same as that of the current sensor 100 except that the measurement target and the non-measurement target are interchanged. As shown in FIG. 1, the current sensor 200 includes a measurement bus bar 3b, a noise source bus bar 2b, and a magnetoelectric conversion element 5. The noise source bus bar 2b of the current sensor 200 has the same shape as the noise source bus bar 3a of the current sensor 100. The positional relationship between the magnetoelectric conversion element 5, the measurement bus bar 3b, and the noise source bus bar 2b is the same as that of the current sensor 100. Therefore, the current sensor 200 can obtain the same effect as the current sensor 100. Detailed description of the current sensor 200 is omitted.

  A modification shown in FIG. 4 will be described. In the modification shown in FIG. 4, the cross-sectional shape of the noise source bus bar 23a is different from the above-described embodiment. About another structure, it is the same as that of said Example. The cross-sectional shape of the noise source bus bar 23a is a shape that extends from the center of the cross-sectional longitudinal direction (Y-axis direction) to the both ends with the same width and widens at both ends. The shape of both ends in the longitudinal direction of the cross section is a substantially square shape. If the cross-sectional shape of the noise source bus bar 23a is intuitively expressed, the shape is similar to the capital letter “I”. That is, similarly to the above-described embodiment, the width in the cross-sectional short direction (X-axis direction) is larger at both ends than the center in the cross-sectional longitudinal direction. Even in such a cross-sectional shape, as in the embodiment, the shape of the magnetic flux M3 generated from the noise source bus bar 23a has a small curvature in a region facing the wide side surface 31 of the noise source bus bar. That is, the cross-sectional shape of the modified example also brings the shape of the magnetic flux M3 close to a straight line in a region facing the wide side surface 31 of the noise source bus bar 23a. Therefore, it is possible to reduce the SN ratio variation with respect to the position change of the magnetoelectric transducer 5 in the longitudinal direction of the cross section of the noise source bus bar 23a.

  Hereinafter, points to be noted regarding the technology shown in the embodiments will be described. In FIG. 1, current sensors are provided for two of the three-phase AC bus bars, but the current sensors of the embodiment may be provided for three of the three-phase AC bus bars. For example, in FIG. 1, when another bus bar exists in the positive direction of the X axis of the bus bar 2, the magnetoelectric conversion element that monitors the current of the bus bar is disposed at a position facing the wide surface of the noise source bus bar 2b. . That is, when the three bus bars are viewed from above (from the Y-axis direction) in plan view, the magnetoelectric conversion element provided in each bus bar is positioned at each apex of the triangle shape. The magnetic flux of the noise source bus bar 2b is straightened in a region facing the wide surface of the noise source bus bar 2b due to its cross-sectional shape, as in the embodiment. Therefore, the SN ratio variation with respect to the position change in the longitudinal direction (Y-axis direction) of the magnetoelectric conversion element can be suppressed to a small value.

  Moreover, the cross-sectional shape of the noise source bus bar shown in FIGS. 2 and 3 is only an example. The cross-sectional shape of the wide side surface of the noise source bus bar in FIG. 2 may be V-shaped instead of the curved shape as shown in FIG. Further, the shape of both ends of the noise source bus bar in the longitudinal direction of the cross section in FIG. 4 may be a circular shape or a polygonal shape instead of a substantially rectangular shape.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2, 3: Bus bar 2a, 3b: Noise source bus bar 2b, 3a: Measurement bus bar 4, 5: Magnetoelectric transducer 4a, 5a: Magnetosensitive surface 100, 200: Current sensor

Claims (1)

A first bus bar for current measurement;
A second bus bar that is parallel to the first bus bar and has a long and narrow cross section and is not to be measured for current;
A magnetoelectric conversion element arranged such that the magnetic sensitive surface faces the wide side surface of the second bus bar and the magnetic sensitive surface is orthogonal to the side surface of the first bus bar;
With
The second bus bar is a current sensor characterized in that the width in the short direction is larger at both ends than the center in the long direction.

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