JP2015141100A - current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor which measures a current flowing in a bus bar by means of a magnetoelectric transducer, configured to improve current density and current measurement accuracy, while preventing reduction in strength and increase in temperature due to heat generation.SOLUTION: A current sensor 100 includes a bus bar 2 having a small cross-sectional area part 2a smaller in cross-sectional area than other parts, and a magnetoelectric transducer 4 arranged adjacent to the small cross-sectional area part 2a. The small cross-sectional area part 2a includes a projection 6. A current hardly flows into the projection 6, thereby preventing reduction in current density. The projection 6 contributes to improvement in strength of the bus bar and heat dissipation.

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 power. 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.

  Conventionally, the bus bar is surrounded by a C-shaped magnetic collecting core, and the magnetoelectric conversion element is arranged at the C-shaped break. However, the sensitivity of the magnetoelectric conversion element is improved, and the current can be generated 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 no magnetic collecting core is provided, it is difficult to say that the performance of magnetic field detection is still sufficient, and a technique for improving current measurement accuracy is desired.

  An example of a technique for improving current measurement accuracy of a magnetoelectric conversion element is disclosed in Patent Document 1. In this technique, a portion (small cross-sectional area) having a smaller cross-sectional area than other portions is provided in the bus bar, and a magnetoelectric conversion element is disposed in the small cross-sectional area portion. The small cross-sectional area has a higher current density than other parts, and the generated magnetic field also becomes stronger. Since the magnetic field measured by the magnetoelectric transducer increases, the current measurement accuracy increases. In addition, the “cross section” in this specification means a cross section orthogonal to the longitudinal direction of the bus bar. In addition, this cross section may be referred to as a “cross section”.

JP 2006-244831 A

  The smaller the cross-sectional area of the part (the small cross-sectional area part) where the magnetoelectric conversion element is arranged, the higher the current density, and the larger the magnetic flux measured by the magnetoelectric conversion element. However, the smaller the cross-sectional area of the small cross-sectional area portion, the lower the strength of the bus bar. In addition, the amount of heat generated in the small cross-sectional area increases as the current density increases. The invention disclosed in this specification has been created in view of the above problems. The present specification provides a current sensor in which a part of a bus bar is thinned to increase current density to improve current measurement accuracy and to suppress a decrease in strength of the thinned portion and a temperature increase due to heat generation.

  Note that the technology disclosed in this specification increases current measurement accuracy 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.

  The technology disclosed in the present specification copes with a decrease in strength and heat generation of the small cross-sectional area by providing a protrusion on the small cross-sectional area of the bus bar in which the magnetoelectric conversion element is disposed. The small cross-sectional area is typically realized by a notch provided in the bus bar. Providing the protrusion on the small cross-sectional area increases the strength of the small cross-sectional area. Further, since the protrusion also functions as a heat spreader, the heat dissipation performance of the small cross-sectional area portion is enhanced, and the temperature rise due to heat generation can be suppressed. In addition, a protrusion expands the cross-sectional area of a small cross-sectional area part. However, the length of the protrusion in the bus bar longitudinal direction is shorter than the length of the small cross-sectional area in the longitudinal direction, and the section where the cross-sectional area expands is only the bus bar longitudinal direction, that is, the section short in the current flowing direction. . Therefore, the current does not spread over the entire interior of the protrusion, and a decrease in current density can be suppressed as compared with an increase in the cross section of the protrusion. In order to suppress the spread of current into the protrusion, it is preferable to suppress the length of the protrusion in the longitudinal direction of the bus bar. As a guideline, the length of the protrusion in the longitudinal direction of the bus bar is shorter than the length in the longitudinal direction of the small cross-sectional area, and is preferably less than or equal to half the length in the longitudinal direction of the small cross-sectional area. More preferably, the length of the protrusion in the longitudinal direction of the bus bar is shorter than the width of the small cross-sectional area portion in the lateral direction of the bus bar. By providing a plurality of protrusions instead of suppressing the protrusion length in the bus bar longitudinal direction, a decrease in current density can be suppressed, and further improvement in strength and heat dissipation can be expected. The bus bar longitudinal direction means the longitudinal direction of the bus bar, that is, the direction in which the bus bar extends. Moreover, the bus bar lateral direction means a direction orthogonal to the longitudinal direction of the bus bar.

  As described above, the small cross-sectional area is typically realized by a notch provided in the bus bar. As a layout of the magnetoelectric conversion element and the protrusion, the protrusion is preferably provided on the side of the small cross-sectional area portion opposite to the side facing the magnetoelectric conversion element. This is because the magnetoelectric transducer can be disposed in the immediate vicinity of the small cross-sectional area regardless of the position, size, and number of protrusions. Further, the above layout is also a place where the magnetoelectric conversion element is most difficult to receive a change in magnetic flux density due to the protrusion.

  When the above structure is applied to one of a plurality of bus bars extending in parallel, that is, when a non-current measurement target adjacent bus bar extends in parallel to the current measurement target bus bar, it is orthogonal to the longitudinal direction of the bus bar. It is desirable that the cross-sectional area of the small cross-sectional area portion is smaller than the cross-sectional area of the adjacent bus bar in the cross section. This is because the magnetic flux density by the adjacent bus bar measured by the magnetoelectric transducer is relatively small. That is, the above structure can increase the SN ratio.

  The present specification relates to a current sensor for measuring a current flowing through a bus bar by a magnetoelectric conversion element, and a current density is increased by thinning a part of the bus bar to improve current measurement accuracy, and due to a decrease in strength of the thinned portion and heat generation. Provide technology to suppress temperature rise.

It is a perspective view which shows the current sensor of an Example. It is a top view of the bus bar of the measuring object with which the current sensor of an example is equipped. It is sectional drawing of the current sensor in the III-III line of FIG. It is a graph which shows an example of the relationship between the length of the notch part of the measurement object bus bar with which the current sensor of an Example is provided, and magnetic flux density. It is a modification of the bus bar with which the current sensor of an Example is equipped. It is the further modification of the bus bar with which the current sensor of an Example is equipped.

  A current sensor according to an embodiment will be described with reference to the drawings. FIG. 1 shows a part of 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, two bus bars 2 and 3 are arranged in parallel. Although the bus bars 2 and 3 extend in the Z-axis direction, only the portion where the current sensor 100 is located is shown in FIG. The current sensor 100 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. The current sensor 100 according to the embodiment includes a bus bar 2 that is a current measurement target, an adjacent bus bar 3 adjacent to the bus bar 2, and a magnetoelectric conversion element 4. The bus bar 2 is provided with a notch 5 in a part thereof. And the protrusion 6 is provided in the lower surface of the bus bar 2 in the range in which the notch part 5 exists along the bus bar longitudinal direction. A magnetoelectric conversion element 4 is provided inside the notch 5. The magnetoelectric conversion element 4 detects a magnetic field caused by the current flowing through the bus bar 2. The adjacent bus bar 3 is not a measurement target, and a magnetic field caused by a current flowing through the adjacent bus bar 3 becomes a noise source of the magnetoelectric transducer 4. The current sensor 100 monitors the magnitude of the current flowing through the bus bar 2 based on the magnitude of the magnetic field detected by the magnetoelectric conversion element 4. It should be noted that the shape of the magnetoelectric conversion element 4 is schematically drawn in a rectangular parallelepiped for convenience of explanation.

  The shape of the cross section orthogonal to the longitudinal direction (Z-axis direction) of the bus bar 2 and the bus bar 3 is a rectangular shape elongated in the height direction (Y-axis direction). Hereinafter, the “cross section” in this specification means a cross section orthogonal to the longitudinal direction of the bus bar. The cross section of the bus bar 2 other than the notch 5 is the same as the adjacent bus bar 3 in height and width. The bus bar 2 and the adjacent bus bar 3 are arranged in parallel so that the wide side surfaces face each other.

  The shape of the notch 5 provided in the bus bar 2 is a rectangle as shown in FIG. The place where the notch 5 is provided is a small cross-sectional area 2a whose cross section is smaller than that of other parts, and its cross-sectional shape is rectangular. As shown in FIG. 3, the cross-sectional area of the small cross-sectional area portion 2 a of the bus bar 2 is smaller than the cross-sectional area of the bus bar 3.

  As shown in FIG. 2, a plurality of protrusions 6 are provided on the lower surface of the small cross-sectional area 2a at equal intervals in the longitudinal direction (Z-axis direction). Each protrusion 6 extends below the small cross-sectional area 2a with the same length. In other words, the protrusion 6 is provided on the lower surface opposite to the upper surface of the small cross-sectional area 2a facing the magnetoelectric conversion element 4 described later. The shape of the protrusion 6 is a rectangular parallelepiped, and the protrusion 6 extends from one end to the other end in the transverse direction (X-axis direction) of the lower surface of the small cross-sectional area 2a. The length B of the protrusion 6 in the longitudinal direction of the bus bar 2 (hereinafter referred to as the bus bar longitudinal direction) coinciding with the Z-axis direction in FIG. 1 is larger than the length A of the small cross-sectional area 2a (notch 5) in the bus bar longitudinal direction. short. Further, the length B of the protrusion 6 in the bus bar longitudinal direction is shorter than half of the length A of the small cross-sectional area 2a (notch 5) in the bus bar longitudinal direction. Furthermore, in the embodiment, the length B of the protrusion 6 in the longitudinal direction of the bus bar is shorter than the length W of the bus bar 2 in the transverse direction (X-axis direction). In other words, the length B of the protrusion 6 in the bus bar longitudinal direction is shorter than the width of the small cross-sectional area 2a in the lateral direction.

  The magnetoelectric conversion element 4 is an element that converts the magnetic flux density of a magnetic field penetrating through the inside into an electric signal. As shown in FIG. 3, the magnetoelectric transducer 4 is adjacent to the upper surface of the small cross-sectional area 2a. In other words, the magnetoelectric conversion element 4 is disposed so as to face the surface opposite to the surface of the small cross-sectional area portion 2a on which the protrusion 6 is provided. And the magnetoelectric conversion element 4 is located in the center of the transverse direction (X-axis direction) of the small cross-sectional area part 2a. As shown in FIG. 4, the shape of the magnetic flux M2 generated by the current flowing in the bus bar longitudinal direction (Z-axis direction) of the bus bar 2 is a cross section of the bus bar 2 on a plane (XY plane) orthogonal to the bus bar longitudinal direction. It becomes an ellipse centered on the center. Therefore, the magnetic flux M2 generated from the bus bar 2 can be measured by arranging the magnetoelectric conversion element 4 at the above position. It should be noted that in FIG. 3, the shape of the protrusion 6 that is visible from the direction of the arrow III is omitted.

  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.

  The effect of providing the notch 5 and the protrusion 6 on the bus bar 2 will be described. The current passing through the bus bar 2 is the same in every part. However, since the cross-section of the small cross-sectional area 2a is smaller than the cross-section of other parts, the density of current passing through the small cross-sectional area 2a is increased. Therefore, the magnetic flux density generated around the small cross-sectional area portion 2a is also higher than other portions of the bus bar 2. Therefore, a large magnetic flux can be measured by arranging the magnetoelectric conversion element 4 in the small cross-sectional area 2a. Since the amount of magnetic flux to be measured increases, the current measurement accuracy corresponding to the amount of magnetic flux is improved.

  On the other hand, since the density of the current passing through the small cross-sectional area 2a is increased, the small cross-sectional area 2a is likely to generate heat as compared with other parts. However, a plurality of protrusions 6 are provided on the small cross-sectional area 2a. The plurality of protrusions 6 increase the surface area of the lower surface of the small cross-sectional area 2a, and the plurality of protrusions 6 function as a heat spreader. The protrusion 6 can improve the heat dissipation performance of the small cross-sectional area 2a and suppress the temperature rise due to heat generation.

  The protrusion 6 widens the cross-sectional area of the small cross-sectional area 2a in a part of the section. However, the section in which the cross-sectional area expands is a section that is short with respect to the bus bar longitudinal direction (current flow direction). In the longitudinal direction of the bus bar, the protrusion 6 enlarges the cross-sectional area of the bus bar in a step shape, but the flowing current does not change in a step shape. Therefore, the current flowing into the protrusion 6 is smaller than the enlarged cross-sectional area of the protrusion 6, and the current density of the small cross-sectional area portion 2a can be suppressed from decreasing. Specifically, the current density in the small cross-sectional area 2a including the protrusion 6 is higher than the current density of the bus bar having the cross-sectional area of the small cross-sectional area 2a as the protrusion 6 uniformly in the bus bar longitudinal direction. In the embodiment, the length B of the protrusion 6 in the longitudinal direction of the bus bar is shorter than the length W of the small cross-sectional area 2a in the lateral direction of the bus bar. It is hard to spread. Therefore, a decrease in current density can be suppressed.

  Further, since the bus bar 2 is provided with the notch 5, the strength of the bus bar 2 is reduced by the notch 5. However, as described above, the strength of the small cross-sectional area portion 2a can be increased by providing the plurality of protrusions 6 while minimizing the decrease in current density.

  In general, when the bus bar 2 is manufactured, the notch 5 is manufactured by press working. As the length in the height direction (Y-axis direction) of the cutout portion 5 is increased, the cross-sectional area of the small cross-sectional area portion 2a can be reduced, and the current density can be increased. When only the notch portion 5 is provided in the bus bar 2, if the length in the height direction of the small cross-sectional area portion 2a of the bus bar 2 is shortened, the area that can be pressed by the press working die is limited, and manufacturing becomes difficult. However, the provision of the protrusions 6 increases the area that can be held by the press working mold, and enables manufacturing by press working.

  Further, the protrusion 6 is provided on the surface of the small cross-sectional area 2a opposite to the side facing the magnetoelectric transducer 4. Thereby, regardless of the position, size, and number of the protrusions 6, the magnetoelectric conversion element 4 can be disposed in the immediate vicinity of the small cross-sectional area portion 2 a. Further, the above position is a place where the magnetoelectric transducer 4 is most difficult to receive a change in magnetic flux density due to the protrusion 6.

  The inventor examined the relationship between the length A of the small cross-sectional area 2a in the bus bar longitudinal direction (the length A of the notch 5 in the bus bar longitudinal direction) and the magnetic flux density generated around the small cross-sectional area 2a. . An example of the result is shown in FIG. As shown in FIG. 4, the magnetic flux density of the small cross-sectional area portion 2a increases as the length A of the small cross-sectional area portion 2a increases. As the length A increases, the magnetic flux density converges to a certain value. I understood. That is, in order to obtain a sufficient effect of improving the magnetic flux density by providing the small cross-sectional area portion 2a, the length A of the small cross-sectional area portion 2a of a certain level or more is required. The length A is determined based on the graph shown in FIG. 4 so as to be a magnetic flux density required for design (value indicated by a broken line in FIG. 4).

  Next, the influence which the magnetoelectric conversion element 4 receives with the magnetic flux from the adjacent bus bar 3 extended in parallel with the bus bar 2 is demonstrated. As shown in FIG. 1, the adjacent bus bar 3 extends in parallel adjacent to the bus bar 2 to be measured. Here, as shown in FIG. 3, the cross-sectional area of the small cross-sectional area portion 2 a is smaller than the cross-sectional area of the adjacent bus bar 3. Thereby, the density of the current flowing through the small cross-sectional area 2a becomes relatively larger than the density of the current flowing through the adjacent bus bar 3. Therefore, the magnetic flux density of the magnetic flux M3 of the adjacent bus bar 3 is smaller than the magnetic flux density of the magnetic flux M2 of the bus bar 2. As a result, the magnetic flux density of the adjacent bus bar 3 that is the non-measurement target is relatively smaller than the magnetic flux density of the bus bar 2 that is the measurement target, and the magnetic flux density detected by the magnetoelectric conversion element 4 greatly depends on the magnetic flux density of the bus bar 2. Will do. That is, with this configuration, the SN ratio of the current sensor 100 can be increased.

  A modification of the protrusion 6 of the embodiment will be described. FIG. 5 is a plan view showing a bus bar 12 which is a modification of the bus bar 2 of the embodiment. In the bus bar 12, the shape of the protrusion 6 of the bus bar 2 is changed to the shape of the protrusion 16. As shown in FIG. 5, the protrusion 16 is composed of one protrusion. According to such a structure, although the effect which raises a magnetic flux density is inferior to an Example, the intensity | strength of the small cross-sectional area part 12a can be made higher than an Example. FIG. 6 shows another modification of the shape of the protrusion 6. The shape of the protrusion 6 viewed from the lateral direction (X-axis direction) of the bus bar 2 may be semicircular as shown in FIG. Moreover, although illustration is abbreviate | omitted, a triangle and a polygon may be sufficient.

  Hereinafter, points to be noted regarding the technology shown in the embodiments will be described. In the embodiment, the plurality of protrusions 6 are provided at equal intervals, but may not be provided at equal intervals. Moreover, in the Example, although the shape of the notch part 5 was a rectangle, the corner | angular part of the notch part may be chamfered.

  Further, the position of the protrusion may not be the lower surface of the small cross-sectional area 2a (the surface opposite to the side facing the magnetoelectric conversion element) as in the embodiment. You may provide in the side surface of the transverse direction (X-axis direction) of the small cross-sectional area part 2a. Further, the length of the protrusion in the lateral direction may be shorter than the length of the bus bar 2 (small cross-sectional area 2a) in the lateral direction. Furthermore, the shape of the protrusion viewed from the bus bar longitudinal direction (Z-axis direction) may not be rectangular. A semi-circle or a polygon may be sufficient.

  In the embodiment, the current sensor is provided in one of the three bus bars used for transmitting the three-phase AC power. However, the current sensor is provided in two or all three of the three bus bars. May be. In this case, it is preferable that the magnetoelectric conversion elements provided in each current sensor are arranged so as not to overlap when viewed from the direction in which the three bus bars are arranged (the X-axis direction shown in FIG. 1). Furthermore, it is better to arrange the small cross-sectional areas (notches) provided in each current sensor so that they do not overlap when viewed from the direction in which the three bus bars are arranged. Since the magnetic field caused by the current flowing through the bus bar is generated on a plane (XY plane shown in FIG. 1) orthogonal to the longitudinal direction of the bus bar, the magnetic field generated at the small cross-sectional area of each bus bar is arranged as described above. Each current sensor does not affect each other. When the current sensors are arranged as described above, the magnetoelectric conversion elements and the small cross-sectional area portions are arranged so as to face each other diagonally. Further, when providing current sensors to three bus bars, in order to accommodate them in a compact manner, each magnetoelectric conversion element has a triangular shape when viewed from the height direction of the bus bar (the Y-axis direction shown in FIG. 1). It is good to arrange so that.

  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, 12, 22: Bus bars 2a, 12a, 22a: Small cross-sectional area 3: Adjacent bus bar 4: Magnetoelectric transducers 5, 15, 25: Notches 6, 16, 26: Protrusion 100: Current sensor

Claims (6)

A bus bar having a small cross-sectional area with a smaller cross-sectional area than other parts;
A magnetoelectric transducer disposed adjacent to the small cross-sectional area, and
With
A current sensor, wherein a projection is provided on the small cross-sectional area.   The current sensor according to claim 1, wherein a length of the protrusion in the longitudinal direction of the bus bar is shorter than a length of the small cross-sectional area portion in the longitudinal direction of the bus bar.   3. The current sensor according to claim 1, wherein a length of the protrusion in the longitudinal direction of the bus bar is shorter than a width of the small cross-sectional area portion in the lateral direction of the bus bar.   The said protrusion is provided in the bus bar longitudinal direction on the opposite side to the side facing the said magnetoelectric conversion element of the said bus bar, The any one of Claim 1 to 3 characterized by the above-mentioned. Current sensor.   5. The current sensor according to claim 1, wherein the small cross-sectional area portion is a notch provided in the bus bar. An adjacent bus bar subject to non-current measurement extends in parallel with the bus bar, and a cross-sectional area of the small cross-sectional area portion is smaller than a cross-sectional area of the adjacent bus bar in a cross section orthogonal to the longitudinal direction of the bus bar. The current sensor according to claim 1.

Images