Current Sensor

Abstract

A first magnetic detecting element (121), a second magnetic detecting element (122) and a third magnetic detecting element (123) are each disposed such that a first magnetic field (B1) generated around a first bus bar (111) when a current flows through the first bus bar (111) is perpendicular to sensitivity axes (121a, 122a, 123a) of each of the first magnetic detecting element (121), the second magnetic detecting element (122) and the third magnetic detecting element (123). If the value of the current flowing through the first bus bar is I1, the value of a current flowing through a second bus bar is I2, the value of a current flowing through a third bus bar is I3, an output value of the first magnetic detecting element is V1, an output value of the second magnetic detecting element is V2, an output value of the third magnetic detecting element is V3, and an output component due to a uniform external magnetic field is Bex, then a processing circuit can calculate at least one of I1, I2, and I3 that respectively satisfy the relationships I2∝(d-f)V1+(f-b)V2+(b-d)V3, I3∝(c-e)V1+(e-a)V2+(a-c)V3, and I1=-(I2+I3) from the ternary linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex.

Description

[Technical Field]

[0001] The present invention relates to a current sensor. [Background technology]

[0002] A prior art document disclosing the configuration of a current detection device is JP 2013-113631 A (Patent Document 1). The current detection device disclosed in Patent Document 1 includes a conductor, a magnetic detection element, and a magnetic shield. The magnetic detection element is installed near the conductor, facing the center of the conductor in the width direction. A pair of magnetic shields, each having the same dimensions, are arranged symmetrically opposite the conductor, sandwiching both side edges of the conductor in the width direction from the outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-113631 Summary of the Invention [Problem to be solved by the invention]

[0004] In the current detector described in Patent Document 1, the influence of the magnetic field from the adjacent bus bars is reduced by a magnetic shield, and the configuration is complicated.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a current sensor that can measure the current value flowing through each of three bus bars through which three-phase AC current flows, while suppressing the influence of external magnetic fields with a simple configuration that does not use a magnetic shield. [Means for solving the problem]

[0006] A current sensor according to the present invention includes three bus bars, a first magnetic detection element, a second magnetic detection element, and a third magnetic detection element, and a processing circuit. The three bus bars are the first bus bar, the second bus bar, and the third bus bar, through which a three-phase AC current flows. The first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are arranged at intervals relative to the three bus bars. The processing circuit is electrically connected to each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element, and processes detection signals from each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element. The sensitivity axes of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are parallel to each other. The first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are each arranged so that a first magnetic field generated around the first bus bar when a current flows through the first bus bar is perpendicular to the sensitivity axis of each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element. If the value of the current flowing through the first busbar is I1, the value of the current flowing through the second busbar is I2, the value of the current flowing through the third busbar is I3, the output value of the first magnetic detection element is V1, the output value of the second magnetic detection element is V2, the output value of the third magnetic detection element is V3, and the output component due to a uniform external magnetic field is Bex, the processing circuit can calculate at least one of I1, I2, and I3 that satisfy the relationships I2 ∝ (df)V1 + (fb)V2 + (bd)V3, I3 ∝ (ce)V1 + (ea)V2 + (ac)V3, and I1 = -(I2 + I3), respectively, from the three linear equations V1 = aI2 + bI3 + Bex, V2 = cI2 + dI3 + Bex, and V3 = eI2 + fI3 + Bex. [Effects of the Invention]

[0007] According to the present invention, the current values ​​flowing through three bus bars through which three-phase AC current flows can be measured with a simple configuration that does not use a magnetic shield while suppressing the influence of external magnetic fields. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a configuration of a current sensor according to a first embodiment of the present invention. [Figure 2] 1 is a perspective view showing a mounting structure of a current sensor according to a first embodiment of the present invention. [Figure 3] 1 is a circuit diagram showing a circuit configuration of a first magnetic detection element, a second magnetic detection element, a third magnetic detection element, and a processing circuit in a current sensor according to a first embodiment of the present invention. [Figure 4] 10 is a flowchart showing a method for determining coefficients a to f when calibrating the current sensor. [Figure 5] FIG. 5 is a cross-sectional view showing the configuration of a current sensor according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a cross-sectional view showing the configuration of a current sensor according to a modified example of the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, current sensors according to embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and description thereof will not be repeated.

[0010] (Embodiment 1) Fig. 1 is a cross-sectional view showing the configuration of a current sensor according to embodiment 1 of the present invention. Fig. 2 is a perspective view showing a mounting structure of the current sensor according to embodiment 1 of the present invention. As shown in Figs. 1 and 2, a current sensor 100 according to embodiment 1 of the present invention includes three bus bars, a first magnetic detection element 121, a second magnetic detection element 122, and a third magnetic detection element 123, and a processing circuit 130.

[0011] In this embodiment, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are mounted on one chip 140. However, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may each be mounted on a separate chip. The processing circuit 130 is mounted on the chip 140. The chip 140 is mounted on a substrate 150. The substrate 150 is arranged on three bus bars.

[0012] The three busbars are first busbar 111, second busbar 112, and third busbar 113, through which three-phase AC current flows. First busbar 111, second busbar 112, and third busbar 113 are three-phase, three-wire busbars. In principle, AC currents of equal amplitude and phase shifted by 120° are applied to the three busbars. For example, a U-phase AC current I1 flows through first busbar 111, a V-phase AC current I2 flows through second busbar 112, and a W-phase AC current I3 flows through third busbar 113. As a result, a first magnetic field B1 is generated around first busbar 111, a second magnetic field B2 is generated around second busbar 112, and a third magnetic field B3 is generated around third busbar 113.

[0013] In this embodiment, first bus bar 111, second bus bar 112, and third bus bar 113 are arranged parallel to each other at intervals in a first direction (X-axis direction). First bus bar 111, second bus bar 112, and third bus bar 113 are arranged side by side in this order in the first direction (X-axis direction). However, the arrangement of first bus bar 111, second bus bar 112, and third bus bar 113 is not limited to this.

[0014] The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are arranged at intervals with respect to the three bus bars. The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are arranged along a virtual plane (XZ plane) that extends in a first direction (X-axis direction) and a second direction (Z-axis direction) perpendicular to the first direction (X-axis direction) and is perpendicular to the three bus bars. Furthermore, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are arranged side by side in a direction that intersects both the first direction (X-axis direction) and the second direction (Z-axis direction).

[0015] The first magnetic detection element 121 has a sensitivity axis 121a. The second magnetic detection element 122 has a sensitivity axis 122a. The third magnetic detection element 123 has a sensitivity axis 123a. The sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123 are parallel to one another. The sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123 are oriented in the same direction.

[0016] Each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 has an odd function input / output characteristic, in which a positive value is output when a magnetic field component oriented in one direction of the sensitivity axis is detected, and a negative value is output when a magnetic field component oriented in the other direction of the sensitivity axis is detected.

[0017] Each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 is arranged so that a first magnetic field B1 generated around the first bus bar 111 when an alternating current I1 flows through the first bus bar 111 is perpendicular to each of the sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123.

[0018] With this arrangement, the output of each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 with respect to the first magnetic field B1 is 0. That is, the influence of the first magnetic field B1 generated by the current I1 flowing through the first bus bar 111 on the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 is canceled out.

[0019] 3 is a circuit diagram showing the circuit configuration of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element and the processing circuit in the current sensor according to the first embodiment of the present invention. As shown in FIG. 3, each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 has a Wheatstone bridge circuit composed of four TMR (Tunnel Magneto Resistance) elements. Each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may have a bridge circuit composed of magnetoresistive elements such as GMR (Giant Magneto Resistance) elements or AMR (Anisotropic Magneto Resistance) elements instead of the TMR elements. Each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may have a half-bridge circuit composed of two magnetoresistive elements.

[0020] The processing circuit 130 is electrically connected to each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123, and processes the detection signals from each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123.

[0021] In this embodiment, the processing circuit 130 includes three differential amplifier circuits 131 connected to the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123, respectively, three summing and inverting amplifier circuits 132, and four inverting amplifier circuits 133. The circuit configuration of the processing circuit 130 is set appropriately depending on the relative positions of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123.

[0022] If the current value flowing through the first bus bar 111 is I1, the current value flowing through the second bus bar 112 is I2, the current value flowing through the third bus bar 113 is I3, the output value of the first magnetic detection element 121 is V1, the output value of the second magnetic detection element 122 is V2, the output value of the third magnetic detection element 123 is V3, and the output component due to a uniform external magnetic field is Bex, the processing circuit 130 can calculate at least one of I1, I2, and I3 that satisfy the relationships I2 ∝ (df)V1 + (fb)V2 + (bd)V3, I3 ∝ (ce)V1 + (ea)V2 + (ac)V3, and I1 = -(I2 + I3), respectively, from the three linear equations V1 = aI2 + bI3 + Bex, V2 = cI2 + dI3 + Bex, and V3 = eI2 + fI3 + Bex.

[0023] Specifically, the processing circuit 130 pre-stores the three linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex, and by determining the coefficients a to f when calibrating the current sensor 100, it is possible to calculate the current value I1 flowing through the first bus bar 111, the current value I2 flowing through the second bus bar 112, and the current value I3 flowing through the third bus bar 113.

[0024] 4 is a flowchart showing a method for determining coefficients a to f during calibration of the current sensor. Calibration of the current sensor 100 is performed in a state where no uniform external magnetic field is applied to each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123. First, calibration of the current sensor 100 is performed based on the outputs of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 when I3=0 while a three-phase AC current is flowing through the three bus bars. That is, the first half of the calibration of the current sensor 100 is performed in a state where I3=0 and Bex=0.

[0025] As a result, as shown in FIG. 4, the processing circuit 130 calculates and stores a=V1 / I2, c=V2 / I2, and e=V3 / I2 from the relational equations V1=aI2, V2=cI2, and V3=eI2 by substituting 0 for each of I3 and Bex in the linear equations with three unknowns V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex (step S1).

[0026] Next, the current sensor 100 is calibrated based on the outputs of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 when I2=0 while the three-phase AC current is flowing through the three bus bars. That is, the second half of the calibration of the current sensor 100 is performed in the state where I2=0 and Bex=0.

[0027] As a result, as shown in FIG. 4, the processing circuit 130 calculates and stores b=V1 / I3, d=V2 / I3, and f=V3 / I3 from the relational equations V1=bI3, V2=dI3, and V3=fI3 by substituting 0 for each of I2 and Bex in the linear equations with three unknowns V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex (step S2).

[0028] By calculating the coefficients a to f as described above, the processing circuit 130 can calculate the current value I2 flowing through the second bus bar 112, which satisfies the relationship I2 ∝ (df)V1 + (fb)V2 + (bd)V3, based on the output value V1 of the first magnetic detection element 121, the output value V2 of the second magnetic detection element 122, and the output value V3 of the third magnetic detection element 123 when three-phase AC current flows through the three bus bars. In this way, the influence of the current value I1 is suppressed by the arrangement relationship between the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 and the three bus bars, while the influence of the current value I3 and the output component Bex due to the uniform external magnetic field is arithmetically removed, thereby enabling the current value I2 to be calculated with high accuracy.

[0029] Similarly, the processing circuit 130 calculates the output value V1 of the first magnetic detection element 121, the output value V2 of the second magnetic detection element 122, and the output value V3 of the third magnetic detection element 123 when three-phase AC current flows through the three bus bars. Output value V3 Based on this, it is possible to calculate the current value I3 flowing through the third bus bar 113, which satisfies the relationship I3 ∝ (ce)V1 + (ea)V2 + (ac)V3. In this way, the influence of the current value I1 is suppressed by the arrangement relationship between the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 and the three bus bars, while the influence of the current value I2 and the output component Bex due to the uniform external magnetic field is arithmetically removed, and the current value I 3 can be calculated with high accuracy.

[0030] In principle, the relationship I1+I2+I3=0 is satisfied for three-phase AC current, so the processing circuit 130 can calculate the current value I1 flowing through the first busbar 111 from the relational equation I1=-(I2+I3).

[0031] As described above, the current sensor 100 according to this embodiment can measure the current values ​​flowing through each of the three bus bars through which three-phase AC current flows, based on the output value V1 of the first magnetic detection element 121, the output value V2 of the second magnetic detection element 122, and the output value V3 of the third magnetic detection element 123, with a simple configuration that does not use a magnetic shield, while suppressing the influence of external magnetic fields. The current sensor 100 does not necessarily need to calculate all of the current values ​​I1 to I3; it is sufficient if it can calculate at least one of the current values ​​I1 to I3. The current sensor 100 retains the coefficients a to f determined during calibration and calculates the current values ​​I1 to I3 using the coefficients a to f, thereby maintaining quick response.

[0032] The current sensor 100 according to this embodiment is a coreless current sensor that does not use a current transformer, a contactless current sensor that does not use a busbar-embedded current sensor, and a shieldless current sensor that does not have a magnetic shield disposed between the busbars. Therefore, the configuration of the current sensor 100 is simplified, making it easy to assemble while also being small and lightweight.

[0033] In the current sensor 100 according to the first embodiment of the present invention, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are mounted on one chip 140. This simplifies the configuration of the current sensor 100, making it smaller, lighter, and easier to assemble.

[0034] In the current sensor 100 according to the first embodiment of the present invention, the processing circuit 130 is mounted on a chip 140. This simplifies the configuration of the current sensor 100, making it possible to reduce the size and weight and to assemble it easily.

[0035] In current sensor 100 according to the first embodiment of the present invention, first bus bar 111, second bus bar 112, and third bus bar 113 are arranged in parallel and spaced apart from one another in a first direction (X-axis direction). As a result, by placing substrate 150 on which chip 140 is mounted on the three bus bars, first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123 can be easily arranged with respect to the three bus bars.

[0036] In the current sensor 100 according to the first embodiment of the present invention, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are arranged along a virtual plane (XZ plane) that extends in a first direction (X-axis direction) and a second direction (Z-axis direction) that is perpendicular to the first direction (X-axis direction) and is perpendicular to the three bus bars. This allows a measurement magnetic field to be applied in the in-plane direction of the magnetoresistive elements, such as the TMR element, the GMR element, and the AMR element, that constitute the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123, thereby improving the measurement accuracy of the current sensor 100.

[0037] In addition, the processing circuit 130 may have a redundant function that, when one of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 fails, can switch to a circuit that can calculate at least one of the current values ​​I1 to I3 by solving a two-dimensional linear equation with two variables, the two current values ​​that can generate magnetic field components to which the two non-failed magnetic detection elements are sensitive.

[0038] (Embodiment 2) A current sensor according to a second embodiment of the present invention will be described below with reference to the drawings. The current sensor according to the second embodiment of the present invention differs from the current sensor according to the first embodiment of the present invention in the arrangement of the first, second, and third magnetic detection elements and the order of the three bus bars, and therefore, description of the same configuration as the current sensor according to the first embodiment of the present invention will not be repeated.

[0039] Fig. 5 is a cross-sectional view showing the configuration of a current sensor according to embodiment 2 of the present invention. As shown in Fig. 5, in current sensor 200 according to embodiment 2 of the present invention, second bus bar 112, first bus bar 111, and third bus bar 113 are arranged side by side in this order in the first direction (X-axis direction).

[0040] The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are positioned directly above the first bus bar 111 and are aligned in the second direction (Z-axis direction). The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are arranged so that a first magnetic field B1 generated around the first bus bar 111 when an AC current I1 flows through the first bus bar 111 is perpendicular to the sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123. Specifically, the sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123 are oriented in the second direction (Z-axis direction).

[0041] In the current sensor 200 according to the second embodiment of the present invention, the current values ​​flowing through each of the three bus bars through which three-phase AC current flows can also be measured based on the output value V1 of the first magnetic detection element 121, the output value V2 of the second magnetic detection element 122, and the output value V3 of the third magnetic detection element 123, with a simple configuration that does not use a magnetic shield, while suppressing the influence of external magnetic fields.

[0042] 6 is a cross-sectional view showing the configuration of a current sensor according to a modification of the second embodiment of the present invention. As shown in FIG. 6, in a current sensor 200a according to the modification of the second embodiment of the present invention, a first magnetic detection element 121, a second magnetic detection element 122, and a third magnetic detection element 123 are positioned directly above a first bus bar 111 and are aligned in a first direction (X-axis direction). Each of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 is arranged so that a first magnetic field B1 generated around the first bus bar 111 when an AC current I1 flows through the first bus bar 111 is perpendicular to a sensitivity axis 121a of the first magnetic detection element 121, a sensitivity axis 122a of the second magnetic detection element 122, and a sensitivity axis 123a of the third magnetic detection element 123. Specifically, the sensitivity axis 121a of the first magnetic detection element 121, the sensitivity axis 122a of the second magnetic detection element 122, and the sensitivity axis 123a of the third magnetic detection element 123 are each oriented in the second direction (Z-axis direction).

[0043] In the current sensor 200a according to the modified example of the second embodiment of the present invention, the current values ​​flowing through each of the three bus bars through which three-phase AC current flows can also be measured based on the output value V1 of the first magnetic detection element 121, the output value V2 of the second magnetic detection element 122, and the output value V3 of the third magnetic detection element 123, with a simple configuration that does not use a magnetic shield, while suppressing the influence of external magnetic fields.

[0044] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0045] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0046] 100, 200, 200a current sensor, 111 first bus bar, 112 second bus bar, 113 third bus bar, 121 first magnetic detection element, 121a, 122a, 123a sensitivity axis, 122 second magnetic detection element, 123 third magnetic detection element, 130 processing circuit, 131 differential amplifier circuit, 132 summing inverting amplifier circuit, 133 inverting amplifier circuit, 140 chip, 150 substrate.

Claims

1. three bus bars, including a first bus bar, a second bus bar, and a third bus bar, through which a three-phase AC current flows; a first magnetic detection element, a second magnetic detection element, and a third magnetic detection element that are arranged at intervals with respect to the three bus bars; a processing circuit electrically connected to each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element, and configured to process detection signals from each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element; the sensitivity axes of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are parallel to each other; the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are arranged so that a first magnetic field generated around the first bus bar when a current flows through the first bus bar is perpendicular to a sensitivity axis of each of the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element, where I1 is the value of the current flowing through the first bus bar, I2 is the value of the current flowing through the second bus bar, I3 is the value of the current flowing through the third bus bar, V1 is the output value of the first magnetic detection element, V2 is the output value of the second magnetic detection element, V3 is the output value of the third magnetic detection element, and Bex is the output component due to a uniform external magnetic field. The processing circuit is capable of calculating at least one of I1, I2, and I3, which satisfy the relationships I2 ∝ (d-f)V1 + (f-b)V2 + (b-d)V3, I3 ∝ (c-e)V1 + (e-a)V2 + (a-c)V3, and I1 = -(I2 + I3), respectively, from the linear equations with three unknowns V1 = aI2 + bI3 + Bex, V2 = cI2 + dI3 + Bex, and V3 = eI2 + fI3 + Bex. Current sensor.

2. The current sensor according to claim 1 , wherein the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are mounted on a single chip.

3. The current sensor of claim 2 , wherein the processing circuitry is on-board the chip.

4. The current sensor according to claim 1 , wherein the first bus bar, the second bus bar, and the third bus bar are arranged in parallel and spaced apart from each other in the first direction.

5. 5. The current sensor according to claim 4, wherein the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element extend in the first direction and a second direction perpendicular to the first direction, and are arranged along an imaginary plane perpendicular to the three bus bars.

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