Current sensor

Abstract

The first magnetic detection element (121), the second magnetic detection element (122), and the third magnetic detection element (123) are each disposed such that a first magnetic field (B1) generated around the first bus bar (111) when a current flows through the first bus bar (111) is orthogonal to sensitivity axes (121a, 122a, 123a) of the first magnetic detection element (121), the second magnetic detection element (122), and the third magnetic detection element (123). If the value of current flowing through the first bus bar is set as I1, the value of current flowing through the second bus bar is set as I2, the value of current flowing through the third bus bar is set as I3, the output value of the first magnetic detection element is set as V1, the output value of the second magnetic detection element is set as V2, the output value of the third magnetic detection element is set as V3, and the output component caused by the uniform external magnetic field is set as Bex. The processing circuit is capable of calculating at least one of I1, I2, and I3 satisfying 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, according to a ternary linear equation of 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 Art

[0002] Japanese Patent Application Publication No. 2013-113631 (Patent Document 1) discloses a current detection device. 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 positioned near the conductor, facing the conductor's center in its width direction. The magnetic shields are arranged symmetrically with a pair of identically sized magnetic shields, sandwiching the conductor's widthwise edges from the outside.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-113631 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In the current detection device described in Patent Document 1, the influence of the magnetic field from the adjacent bus bar is reduced by a magnetic shield, and the structure is complicated.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a current sensor capable of suppressing the influence of an external magnetic field with a simple structure without using a magnetic shield and measuring the current value flowing through each of three bus bars through which a three-phase AC current flows.

[0009] Technical solutions to solve problems

[0010] The current sensor based on the present invention comprises 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 include a first bus bar, a second bus bar and a third bus bar through which a three-phase alternating 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 the first magnetic detection element, the second magnetic detection element and the third magnetic detection element, respectively, and processes the 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 the first magnetic field generated around the first bus bar when a current flows through the first bus bar is orthogonal to the sensitivity axes of the first magnetic detection element, the second magnetic detection element and the third magnetic detection element. If the current value flowing through the first bus bar is set to I1, the current value flowing through the second bus bar is set to I2, the current value flowing through the third bus bar is set to I3, the output value of the first magnetic detection element is set to V1, the output value of the second magnetic detection element is set to V2, the output value of the third magnetic detection element is set to V3, and the output component caused by the uniform external magnetic field is set to Bex, then the processing circuit can calculate at least one of I1, I2 and I3 that respectively satisfies the relationships I2∝(df)V1+(fb)V2+(bd)V3, I3∝(ce)V1+(ea)V2+(ac)V3, and I1=-(I2+I3) based on the three linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to measure the current value flowing through each of the three bus bars through which the three-phase AC current flows while suppressing the influence of the external magnetic field with a simple structure that does not use a magnetic shield. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a cross-sectional view showing the structure of the current sensor according to the first embodiment of the present invention.

[0014] Figure 2 It is a perspective view showing a mounting structure of a current sensor according to Embodiment 1 of the present invention.

[0015] Figure 3 This 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 the current sensor according to the first embodiment of the present invention.

[0016] Figure 4 This is a flowchart showing a method for obtaining coefficients a to f when calibrating the current sensor.

[0017] Figure 5 It is a cross-sectional view showing the structure of a current sensor according to Embodiment 2 of the present invention.

[0018] Figure 6 This is a cross-sectional view showing the structure of a current sensor according to a modified example of the second embodiment of the present invention. DETAILED DESCRIPTION

[0019] Hereinafter, current sensors according to various embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, identical or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated.

[0020] (Implementation Method 1)

[0021] Figure 1 This is a cross-sectional view showing the structure of the current sensor according to the first embodiment of the present invention. Figure 2 1 is a perspective view showing the mounting structure of the current sensor according to the first embodiment of the present invention. Figure 1 as well as Figure 2 As shown, the current sensor 100 according to the first embodiment 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 .

[0022] 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 a single chip 140. However, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may be mounted on separate chips. 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.

[0023] The three busbars include a first busbar 111, a second busbar 112, and a third busbar 113, through which three-phase AC current flows. Busbars 111, 112, and 113 are three-phase, three-wire buses. In principle, AC currents of equal amplitude and 120° phase shift are applied to the three busbars. For example, U-phase AC current I1 flows through busbar 111, V-phase AC current I2 flows through busbar 112, and W-phase AC current I3 flows through busbar 113. As a result, a first magnetic field B1 is generated around busbar 111, a second magnetic field B2 is generated around busbar 112, and a third magnetic field B3 is generated around busbar 113.

[0024] In this embodiment, the first bus bar 111, the second bus bar 112, and the third bus bar 113 are arranged in parallel with each other in the first direction (X-axis direction) with a gap therebetween. The first bus bar 111, the second bus bar 112, and the third bus bar 113 are arranged in sequence in the first direction (X-axis direction). However, the arrangement of the first bus bar 111, the second bus bar 112, and the third bus bar 113 is not limited to this.

[0025] The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are spaced apart from each other relative 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 an imaginary 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 in a direction that intersects both the first direction (X-axis direction) and the second direction (Z-axis direction).

[0026] 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 axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123a are parallel to each other. The sensitivity axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123a of the third magnetic detection element 123 are oriented in the same direction.

[0027] The first magnetic detection element 121, the second magnetic detection element 122 and the third magnetic detection element 123 each have the following odd function input-output characteristics, that is, when a magnetic field component is detected in one direction of the sensitivity axis, a positive value is output, and when a magnetic field component is detected in the other direction of the sensitivity axis, a negative value is output.

[0028] The first magnetic detection element 121, the second magnetic detection element 122 and the third magnetic detection element 123 are each configured so that the first magnetic field B1 generated around the first bus bar 111 when the alternating current I1 flows through the first bus bar 111 is orthogonal 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.

[0029] 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 becomes zero. In other words, 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 eliminated.

[0030] Figure 3 1 is a circuit diagram showing the circuit configuration of the first magnetic detection element, the second magnetic detection element, the third magnetic detection element, and the processing circuit in the current sensor according to the first embodiment of the present invention. Figure 3 As shown, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 each have a Wheatstone bridge circuit including four Tunnel Magneto Resistance (TMR) elements. Alternatively, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may each have a bridge circuit including magnetoresistive elements such as GMR (Giant Magneto Resistance) elements or AMR (Anisotropic Magneto Resistance) elements instead of TMR elements. Furthermore, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 may each have a half-bridge circuit including two magnetoresistive elements.

[0031] The processing circuit 130 is electrically connected to the first magnetic detection element 121 , the second magnetic detection element 122 , and the third magnetic detection element 123 , and processes detection signals from each of the first magnetic detection element 121 , the second magnetic detection element 122 , and the third magnetic detection element 123 .

[0032] In this embodiment, the processing circuit 130 includes three differential amplifier circuits 131, three inverting summing amplifier circuits 132, and four inverting amplifier circuits 133, each connected to the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123. The circuit configuration of the processing circuit 130 can be appropriately set based on the respective arrangements of the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123.

[0033] If the current value flowing through the first bus bar 111 is set to I1, the current value flowing through the second bus bar 112 is set to I2, the current value flowing through the third bus bar 113 is set to I3, the output value of the first magnetic detection element 121 is set to V1, the output value of the second magnetic detection element 122 is set to V2, the output value of the third magnetic detection element 123 is set to V3, and the output component caused by the uniform external magnetic field is set to Bex, then the processing circuit 130 can calculate at least one of I1, I2 and I3 that respectively satisfy the relationships I2∝(df)V1+(fb)V2+(bd)V3, I3∝(ce)V1+(ea)V2+(ac)V3, and I1=-(I2+I3) based on the three-variable linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex.

[0034] Specifically, the processing circuit 130 pre-stores the three-variable linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex. The coefficients a to f are obtained during calibration of the current sensor 100, thereby being able 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, respectively.

[0035] Figure 4 This flowchart illustrates a method for calculating coefficients a through f during current sensor calibration. Current sensor 100 is calibrated without applying a uniform external magnetic field to each of first, second, and third magnetic detection elements 121, 122, and 123. First, current sensor 100 is calibrated based on the outputs of each of first, second, and third magnetic detection elements 121, 122, and 123 at the time I3 = 0, while three-phase AC current is flowing through the three busbars. Specifically, the first half of the calibration of current sensor 100 is performed with I3 = 0 and Bex = 0.

[0036] As a result, if Figure 4 As shown, the processing circuit 130 substitutes 0 for I3 and Bex in the three-variable linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex, respectively, thereby calculating a=V1 / I2, c=V2 / I2, and e=V3 / I2 based on the relationships V1=aI2, V2=cI2, and V3=eI2 and storing them (step S1).

[0037] Next, current sensor 100 is calibrated based on the outputs of first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123 at the time I2 = 0 while three-phase AC current is flowing through the three bus bars. Specifically, the second half of the calibration of current sensor 100 is performed with I2 = 0 and Bex = 0.

[0038] As a result, if Figure 4 As shown, the processing circuit 130 substitutes 0 for I2 and Bex in the three-variable linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex, respectively, thereby calculating b=V1 / I3, d=V2 / I3, and f=V3 / I3 based on the relationships V1=bI3, V2=dI3, and V3=fI3 and storing them (step S2).

[0039] By calculating coefficients a through f as described above, processing circuit 130 can calculate current value I2 flowing through second bus bar 112, satisfying the relationship I2∝(df)V1+(fb)V2+(bd)V3, based on output value V1 of first magnetic detection element 121, output value V2 of second magnetic detection element 122, and output value V3 of third magnetic detection element 123 when three-phase AC current is flowing through the three bus bars. In this way, the influence of current value I1 is suppressed by the arrangement of first, second, and third magnetic detection elements 121, 122, and 123 relative to the three bus bars. The influence of current value I3 and the output component Bex caused by the uniform external magnetic field are mathematically eliminated, allowing for highly accurate calculation of current value I2.

[0040] Similarly, processing circuit 130 can calculate current value I3 flowing through third bus bar 113, satisfying the relationship I3∝(ce)V1+(ea)V2+(ac)V3, based on output value V1 of first magnetic detection element 121, output value V2 of second magnetic detection element 122, and output value V3 of third magnetic detection element 123 when three-phase AC current is flowing through the three bus bars. In this way, the influence of current value I1 is suppressed by the arrangement of first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123 relative to the three bus bars. The influence of current value I2 and the output component Bex caused by the uniform external magnetic field are mathematically eliminated, allowing for highly accurate calculation of current value I2.

[0041] In principle, the three-phase AC current satisfies the relationship I1+I2+I3=0. Therefore, the processing circuit 130 can calculate the current value I1 flowing through the first bus bar 111 based on the relationship I1=−(I2+I3).

[0042] As described above, the current sensor 100 according to this embodiment can suppress the influence of external magnetic fields 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, using a simple structure that does not use magnetic shields, and can measure the current value flowing through each of the three busbars through which three-phase AC current flows. Furthermore, the current sensor 100 does not necessarily need to calculate all of the current values ​​I1 to I3; it only needs to be able to calculate at least one of the current values ​​I1 to I3. The current sensor 100 retains the coefficients a to f obtained during calibration and uses these coefficients a to f to calculate the current values ​​I1 to I3, thereby maintaining short-term responsiveness.

[0043] The current sensor 100 of this embodiment is a coreless current sensor that is not a current transformer, a contactless current sensor that is not a busbar-embedded current sensor, and a shieldless current sensor that does not employ magnetic shields between busbars. Therefore, the structure of the current sensor 100 is simplified, enabling miniaturization, weight reduction, and ease of assembly.

[0044] In current sensor 100 according to Embodiment 1 of the present invention, first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123 are mounted on a single chip 140. This simplifies the structure of current sensor 100, enabling miniaturization, weight reduction, and easy assembly.

[0045] In the current sensor 100 according to the first embodiment of the present invention, the processing circuit 130 is mounted on the chip 140. This simplifies the structure of the current sensor 100, enabling miniaturization, weight reduction, and easy assembly.

[0046] In current sensor 100 according to Embodiment 1 of the present invention, first bus bar 111, second bus bar 112, and third bus bar 113 are arranged in parallel with each other in the first direction (X-axis direction) with a gap therebetween. Thus, by placing substrate 150 with chip 140 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 relative to the three bus bars.

[0047] In current sensor 100 according to Embodiment 1 of the present invention, first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123 are arranged along a virtual plane (XZ plane) extending in a first direction (X-axis direction) and a second direction (Z-axis direction) perpendicular to the first direction (X-axis direction) and perpendicular to the three bus bars. This allows a measurement magnetic field to be applied in the plane of the magnetoresistive elements (TMR elements, GMR elements, and AMR elements) that constitute first magnetic detection element 121, second magnetic detection element 122, and third magnetic detection element 123, thereby improving the measurement accuracy of current sensor 100.

[0048] In addition, the processing circuit 130 may also have the following redundant function, that is, when one of the first magnetic detection element 121, the second magnetic detection element 122 and the third magnetic detection element 123 fails, it can switch to the following circuit: by solving a two-variable linear equation with two current values ​​that can produce the magnetic field components with sensitivity of the two magnetic detection elements that have not failed as two variables, at least one of the current values ​​I1~I3 can be calculated.

[0049] (Implementation Method 2)

[0050] A current sensor according to a second embodiment of the present invention is 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 in which the three bus bars are arranged. Therefore, the same structures as those of the current sensor according to the first embodiment of the present invention will not be described again.

[0051] Figure 5 1 is a cross-sectional view showing the structure of a current sensor according to Embodiment 2 of the present invention. Figure 5 As shown, in the current sensor 200 according to the second embodiment of the present invention, the second bus bar 112 , the first bus bar 111 , and the third bus bar 113 are arranged in sequence in the first direction (X-axis direction).

[0052] The first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are located directly above the first bus bar 111 and arranged in the second direction (Z-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 the first magnetic field B1 generated around the first bus bar 111 when an AC current I1 flows through the first bus bar 111 is orthogonal to the sensitivity axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123, respectively. Specifically, the sensitivity axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123a of the third magnetic detection element 123 are oriented in the second direction (Z-axis direction).

[0053] In the current sensor 200 involved in embodiment 2 of the present invention, it is also possible to suppress the influence of the external magnetic field 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, by using a simple structure that does not use a magnetic shielding part, and measure the current value flowing through each of the three bus bars through which the three-phase AC current flows.

[0054] Figure 6 1 is a cross-sectional view showing the structure of a current sensor according to a modified example of embodiment 2 of the present invention. Figure 6 As shown, in a current sensor 200a according to a modified example of Embodiment 2 of the present invention, the first magnetic detection element 121, the second magnetic detection element 122, and the third magnetic detection element 123 are located directly above the first bus bar 111 and arranged in the first direction (X-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 the first magnetic field B1 generated around the first bus bar 111 when an AC current I1 flows through the first bus bar 111 is orthogonal to the sensitivity axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123, respectively. Specifically, the sensitivity axes 121a, 122a, and 123a of the first, second, and third magnetic detection elements 121, 122, and 123a of the third magnetic detection element 123 are each oriented in the second direction (Z-axis direction).

[0055] In the current sensor 200a involved in a modified example of embodiment 2 of the present invention, it is also possible to suppress the influence of the external magnetic field 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, by using a simple structure that does not use a magnetic shielding part, and measure the current value flowing through each of the three bus bars through which the three-phase AC current flows.

[0056] In the description of the above-mentioned embodiments, combinable structures may be combined with each other.

[0057] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims and equivalents thereof.

[0058] Description of Reference Numerals

[0059] 100, 200, 200a: current sensor;

[0060] 111: Bus bar 1;

[0061] 112: Bus bar 2;

[0062] 113: Bus 3;

[0063] 121: first magnetic detection element;

[0064] 121a, 122a, 123a: sensitivity axis;

[0065] 122: second magnetic detection element;

[0066] 123: 3rd magnetic detection element;

[0067] 130: processing circuit;

[0068] 131: Differential amplifier circuit;

[0069] 132: Inverting summing amplifier circuit;

[0070] 133: Inverting amplifier circuit;

[0071] 140: chip;

[0072] 150: Substrate.

Claims

1. A current sensor comprising: three bus bars, including a first bus bar, a second bus bar, and a third bus bar through which three-phase alternating current flows; The first magnetic detection element, the second magnetic detection element, and the third magnetic detection element are arranged with intervals with respect to the three bus bars; and a processing circuit electrically connected to the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element, and processing detection signals from the first magnetic detection element, the second magnetic detection element, and the third magnetic detection element, respectively; 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 orthogonal 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 current value flowing through the first bus bar is set to I1, the current value flowing through the second bus bar is set to I2, the current value flowing through the third bus bar is set to I3, the output value of the first magnetic detection element is set to V1, the output value of the second magnetic detection element is set to V2, the output value of the third magnetic detection element is set to V3, and the output component caused by the uniform external magnetic field is set to Bex, then the processing circuit can calculate at least one of I1, I2 and I3 that respectively satisfies the relationships I2∝(df)V1+(fb)V2+(bd)V3, I3∝(ce)V1+(ea)V2+(ac)V3, and I1=-(I2+I3) based on the three-variable linear equations V1=aI2+bI3+Bex, V2=cI2+dI3+Bex, and V3=eI2+fI3+Bex.

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 one chip.

3. The current sensor according to claim 2, wherein: The processing circuit is mounted on the chip.

4. The current sensor according to any one of claims 1 to 3, wherein: The first bus bar, the second bus bar, and the third bus bar are arranged in parallel with a gap therebetween in a first direction.

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 are arranged along a virtual plane extending in the first direction and a second direction perpendicular to the first direction and perpendicular to the three bus bars.

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