JP2019158631A - Current sensor correction method and current sensor - Google Patents

Abstract

To provide a current sensor correction method and a current sensor capable of accurately performing linear correction and interference correction.SOLUTION: The system includes a first shield board 41 and a second shield board 42 consisting of magnetic materials arranged so that three busbars 2 into which a current of each phase in a three-phase alternating current flows, and three busbars 2 may be collectively put in the thickness direction; three magnetic detection elements 3 which detect an intensity of a magnetic field occurring according to a current which flows through the busbar 2 arranged respectively and corresponding between each of the busbars 2 and the first shield board 41, and an output voltage of the three magnetic detection elements 3 is measured, and alignment correction of the output voltage and interference correction are carried out using an alignment correction factor and interference correction factor which derives the alignment correction factor and the interference correction factor based on the measurement result concerned in a state in which a current is sent on condition of the current ratio that is the correction method of the preparation having a current sensor 1 and is not included in the three busbars 2 at the time of flowing the current ratio and the three-phase alternating current.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a current sensor correction method using a magnetic detection element and a current sensor.

  2. Description of the Related Art Conventionally, a current sensor is known that includes a magnetic detection element that detects the intensity of a magnetic field generated by a current to be measured (see, for example, Patent Document 1). By detecting the strength of the magnetic field by the magnetic detection element, the current can be obtained by calculation based on the strength of the magnetic field.

  In a magnetic detection element such as a GMR (Giant Magneto Resistive effect) element, the relationship of the output voltage of the magnetic detection element to the current flowing through the bus bar (referred to as the bus bar current) is not linear, and this tendency is particularly pronounced in a region where the bus bar current is large. Become prominent. Therefore, linear correction for correcting the output voltage of the magnetic detection element is performed so as to be linear with respect to the bus bar current.

JP2015-78872A

  The above-described linear correction is normally performed based on the measurement result at the time of single-phase energization. However, in a current sensor in which a shield plate is provided so that three bus bars through which current of each phase in three-phase alternating current flows are collectively sandwiched in the thickness direction, the three sensors that are actually used are At the time of phase energization, the state of the magnetic field on the shield plate is greatly different, so that correction may not be made properly.

  Patent Document 1 describes interference correction that corrects a current detection value in consideration of the influence of ambient current, but does not describe that both interference correction and linear correction are performed. Therefore, a current sensor correction method capable of accurately performing both interference correction and linear correction is desired.

  Therefore, an object of the present invention is to provide a current sensor correction method and a current sensor capable of accurately performing linear correction and interference correction.

  In order to solve the above-mentioned problems, the present invention is formed in a plate shape and is arranged in a spaced manner in the width direction of the plate so that three bus bars through which a current of each phase in a three-phase alternating current flows. A first shield plate and a second shield plate made of a magnetic material arranged so as to sandwich the three bus bars in a thickness direction perpendicular to the plate width direction, the bus bars, A current sensor correction method comprising: three magnetic detection elements, each of which is arranged between each of the first shield plates and detects the intensity of a magnetic field generated by a current flowing through the corresponding bus bar, Measure the output voltage of the three magnetic sensing elements in a state where current flows to the bus bar under the conditions of the current ratio during three-phase alternating current and the current ratio not included during three-phase alternating current, and based on the measurement results Linear correction coefficient and interference correction unit Derives, using the derived linear correction coefficient and interference correction coefficient, performs linear correction and interference correction of the output voltage, to provide a method of correcting the current sensor.

  Further, in order to solve the above-mentioned problems, the present invention is formed in a plate shape and is arranged in a spaced manner in the width direction of the plate so that three phase currents flow in a three-phase alternating current. A first shield plate and a second shield plate made of a magnetic material arranged so as to sandwich the three bus bars in a thickness direction perpendicular to the plate width direction, and each bus bar. And the first shield plate, respectively, and three magnetic detection elements for detecting the strength of the magnetic field generated by the current flowing through the corresponding bus bar, and the correction for correcting the output voltage of the three magnetic detection elements The correction unit is configured to detect the three magnetic sensors in a state where a current is passed through the three bus bars under a condition of a current ratio during three-phase alternating current and a current ratio not included during three-phase alternating current. The result of measuring the output voltage of the device Using the linear correction coefficient and interference correction coefficient derived on the basis of, performs linear correction and interference correction of the output voltage, to provide a current sensor.

  According to the present invention, it is possible to provide a current sensor correction method and a current sensor capable of accurately performing linear correction and interference correction.

It is a figure which shows the current sensor which concerns on one embodiment of this invention, (a) is a perspective view, (b) is the sectional view on the AA line. (A) is a graph showing the time change of the current of each phase of the three-phase AC, (b) is a diagram schematically showing the magnetic flux density in the shield plate when only the V-phase current is passed, (c). FIG. 5 is a diagram schematically showing the magnetic flux density in the shield plate when all three phases of current are passed. FIG. 3 is a flowchart showing a procedure for deriving a correction coefficient in the current sensor correction method according to the present embodiment. It is a graph which shows an example of the relationship between the electric current of V phase, and the GMR output voltage of V phase. FIG. 5A is a graph showing an example of the relationship between the V-phase current and the output voltage after linear correction of the V-phase in the current sensor of FIG. 4, and FIG. It is a graph which shows an example of the relationship with the output voltage after phase correction.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Overall configuration of current sensor)
1A and 1B are diagrams showing a current sensor according to the present embodiment, in which FIG. 1A is a perspective view, and FIG.

  As shown in FIGS. 1 (a) and 1 (b), the current sensor 1 is formed in a plate shape and is arranged in a spaced manner in the plate width direction so that the current of each phase in the three-phase alternating current is A first shield plate 41 and a second shield plate 42 made of a magnetic material are arranged so as to sandwich the three bus bars 2 flowing and the three bus bars 2 in a thickness direction perpendicular to the plate width direction. And three magnetic detection elements 3 that are arranged between each bus bar 2 and the first shield plate 41 and detect the intensity of the magnetic field generated by the current flowing through the corresponding bus bar 2.

  The bus bar 2 is a plate-like conductor made of a good electrical conductor such as copper or aluminum, and serves as a current path through which a current flows. The bus bar 2 is used as a power line between a motor and an inverter in an electric vehicle or a hybrid vehicle, for example. In the present embodiment, a case will be described in which three bus bars 2a to 2c corresponding to the U-phase, V-phase, and W-phase of three-phase alternating current are used. A U-phase current flows through the bus bar 2a, a V-phase current flows through the bus bar 2b, and a W-phase current flows through the bus bar 2c.

  A through-hole 5 that penetrates each bus bar 2a to 2c in the thickness direction is formed at the center in the width direction of each bus bar 2a to 2c. Here, although the case where the rectangular through-hole 5 is formed is shown, the shape of the through-hole 5 is not particularly limited. By forming the through hole 5, current paths 6 are formed on both sides of the through hole 5. In the through hole 5, the magnetic fields generated in both current paths 6 cancel each other, so that the strength of the magnetic field in the through hole 5 and in the vicinity of the through hole 5 can be reduced. As a result, even in applications that detect large currents, it is possible to reduce the strength of the magnetic field detected by the magnetic detection element 3 and use the highly sensitive magnetic detection element 3, which contributes to improved current detection accuracy. To do. The through-hole 5 is not essential and can be omitted.

  Hereinafter, the vertical direction in FIG. 1A is referred to as the thickness direction, the left rear to the right front direction is referred to as the length direction, and the left front to the right rear direction is referred to as the width direction. The bus bars 2a to 2c are arranged at equal intervals so as to be arranged in the width direction, and are arranged in parallel to each other.

  The magnetic detection element 3 is configured to output an output signal having a voltage corresponding to the intensity (magnetic flux density) of the magnetic field in the direction along the detection axis D. As the magnetic detection element 3, for example, a Hall element, a GMR (Giant Magneto Resistive effect) element, an AMR (Anisotropic Magneto Resistive) element, a TMR (Tunneling Magneto Resistive) element, or the like can be used. In the present embodiment, a GMR element having high sensitivity is used as the magnetic detection element 3.

  In the current sensor 1, a total of three magnetic detection elements 3a to 3c are provided so as to correspond to the respective bus bars 2a to 2c. Each magnetic detection element 3a-3c is arrange | positioned in the position which overlaps with the through-hole 5 by planar view seen from the thickness direction. Each of the magnetic detection elements 3 a to 3 c is mounted on a substrate (not shown), and is disposed at a predetermined position by inserting the substrate between the first shield plate 41 and the bus bar 2. Here, some of the magnetic detection elements 3 a to 3 c are disposed in the through hole 5, but the magnetic detection elements 3 a to 3 c may be entirely disposed outside the through hole 5. The magnetic detection elements 3a to 3c have the maximum magnetic field intensity that can be detected by the magnetic detection elements 3a to 3c when the maximum current flows through the bus bars 2a to 2c. It is good to arrange | position in the position which becomes substantially equal.

  In the present embodiment, each of the magnetic detection elements 3 a to 3 c has a magnetic sensing position (a detection position of the magnetic field strength) shifted from the center position O in the thickness direction of the bus bar 2 toward the first shield plate 41. Has been placed. That is, the magnetic detection elements 3 a to 3 c are arranged so as to be closer to the first shield plate 41 than the second shield plate 42.

  The first shield plate 41 and the second shield plate 42 are for shielding an external magnetic field so that the external magnetic field does not affect the detection result of the magnetic detection element 3. The first shield plate 41 and the second shield plate 42 are formed in a rectangular plate shape having two sides facing each other in the width direction and two sides facing each other in the length direction.

  The first shield plate 41 and the second shield plate 42 are spaced apart from the bus bar 2 so as to sandwich the bus bar 2 from the thickness direction. Further, the first shield plate 41 and the second shield plate 42 are parallel to the surface of the bus bar 2 (the thickness direction of the first shield plate 41 and the second shield plate 42 and the bus bar 2 It is arranged so that the thickness direction matches.

  In this current sensor 1, the distances (distances along the thickness direction) a and b of the first shield plate 41 and the second shield plate 42 from the bus bar 2 are equal. That is, in the current sensor 1, the intermediate position between the first shield plate 41 and the second shield plate 42 (position where the distance between the first shield plate 41 and the second shield plate 42 is equal) and the thickness direction of the bus bar 2. The center position O in FIG.

  Although not shown in the drawing, a mold resin is filled between the shield plates 41, 42, and the shield plates 41, 42, the magnetic detection element 3, and the bus bar 2 are integrally formed of the mold resin. The mold resin serves to keep the positional relationship among the magnetic detection element 3, the bus bar 2, and both the shield plates 41 and 42 constant and suppress detection errors due to vibration and the like, and because foreign matter enters between the shield plates 41 and 42. It also serves to suppress detection errors.

  In addition, the current sensor 1 includes a correction unit 7 that corrects the output voltages of the three magnetic detection elements, and a bus bar current calculation unit 8 that calculates the current flowing in the bus bar 2 based on the output voltage corrected by the correction unit. And. The correction unit 7 and the bus bar current calculation unit 8 are realized by appropriately combining a calculation element such as a CPU, a memory, software, an interface, and the like. The correction unit 7 and the bus bar current calculation unit 8 may be mounted on, for example, a substrate on which the magnetic detection element 3 is mounted, or may be mounted on a dedicated calculation unit or a calculation device such as a personal computer. . Details of the correction unit 7 and the bus bar current calculation unit 8 will be described later.

(Influence of current of other phases)
Here, the influence of the current of the other phase will be described. The time change of the current of each phase of the three-phase alternating current is as shown in FIG. Here, the magnetic field of the shield plates 41 and 42 under the condition of U-phase current: V-phase current: W-phase current = 1: -2: 1 (conditions indicated by white arrows in FIG. 2A). Examine the condition.

  As shown in FIG. 2 (b), in the above conditions (conditions indicated by white arrows in FIG. 2 (a)) in which current flows in all three-phase bus bars 2, the U phase and the W phase have the V phase. A reverse current flows. In FIG. 2B, a current flows from the back to the front in the paper direction in the U phase and the W phase, and a current flows from the front to the back in the paper direction in the V phase. Therefore, the direction of the magnetic field generated by the current flowing through the U phase and the W phase is opposite to the direction of the magnetic field generated by the current flowing through the V phase. Therefore, the magnetic field generated by the current flowing through the U phase and the W phase in the shield plates 41 and 42 and the magnetic field generated by the current flowing through the V phase cancel each other, and the magnetic flux density in the shield plates 41 and 42 is reduced. The permeability of the plates 41 and 42 is also difficult to decrease. Therefore, even when a large current is applied to the bus bar, the proportional relationship between the current flowing through the V-phase bus bar 2b and the output voltage output from the magnetic detection element 3 by detecting the magnetic field generated by this current is maintained. .

  On the other hand, as shown in FIG. 2C, a case is considered in which no current flows in the U phase and the W phase, and a current flows in the V phase from the front side to the back side. When a current is supplied only to the V-phase bus bar 2b arranged at the center in the width direction, the shield plates 41 and 42 are only affected by the magnetic field generated by the current flowing through the V-phase bus bar 2b. When the effect of the generated magnetic field is large, the magnetic flux density in both shield plates 41 and 42 approaches saturation, and the magnetic permeability of both shield plates 41 and 42 decreases. If it does so, the effect that both the shield plates 41 and 42 will collect the magnetic field produced from the bus bar 2b will also fall, and a magnetic field will not collect on the shield plates 41 and 42. FIG. Therefore, a magnetic field flows in the region surrounded by the first shield plate 41 and the second shield plate 42, that is, in the vicinity of the magnetic detection element 3 by adding the reduced magnetic flux collection effect. As a result, the proportional relationship between the current flowing through the bus bar 2b and the output voltage output from the magnetic detection element 3 by detecting the magnetic field generated by this current is disrupted in the large current region (the slope (proportional coefficient) changes). . 2B and 2C, the direction of the magnetic field in the shield plates 41 and 42 is represented by the direction of the white arrow, and the magnitude of the magnetic field is schematically represented by the size of the white arrow. Represents.

  That is, in the case where only one of the U-phase, V-phase, and W-phase currents flows, and in the actual use in which current flows in all three-phase bus bars 2 (three-phase energization), the bus bar 2 Even when the same current is applied, the magnetic field intensity around the magnetic detection element 3 corresponding to the bus bar 2 is different, and the detection accuracy decreases particularly as the maximum measurement current is approached. Therefore, in the present embodiment, measurement is performed in a state where current flows through all three-phase bus bars 2, and a correction coefficient is derived based on the measurement result. Hereinafter, the correction method of the current sensor according to the present embodiment will be described in detail.

(Current sensor correction method)
FIG. 3 is a flowchart showing a procedure for deriving a correction coefficient in the current sensor correction method according to the present embodiment. In the present embodiment, finally, the following formula (1)
V _out = M × I + N (1)
The output voltage of each magnetic detection element 3 is corrected so that the relationship In Equation (1), M is a gain setting value and N is an offset output voltage setting value. These values of M and N are set appropriately in advance.

As shown in FIG. 3, first, in step S1, a current is passed through each of the bus bars 2a to 2c (three-phase energization), and output voltages (referred to as GMR output voltages) of the respective magnetic detection elements 3a to 3c are measured. The U-phase current is I _u , the V-phase current is I _v , and the W-phase current is I _w . Also, the GMR output voltage of the U-phase magnetic detection element 3a is V _{m_u} , the GMR output voltage of the V-phase magnetic detection element 3b is V _{m_v} , and the GMR output voltage of the W-phase magnetic detection element 3c is V _{m_w} .

In the present embodiment, the measurement in step S1 is performed under the following four conditions.
First condition I _u : I _v : I _w = 2: −1: −1
Second condition I _u : I _v : I _w = −1: 1: −1
Third condition I _u : I _v : I _w = −1: −1: 2
Fourth condition I _u : I _v : I _w = −1: 2: −1
Of these four conditions, the first, third and fourth conditions are current ratios during three-phase alternating current. The first condition is the current ratio at the three-phase AC that maximizes I _u , the third condition is the current ratio at the three-phase AC that maximizes I _w , and the fourth condition is the three currents that maximize I _v It is a current ratio at the time of phase alternating current. The second condition is a current ratio condition that is not included during three-phase alternating current. As described above, in the present embodiment, the three bus bars 2a to 2c are subjected to three magnetic detections in a state where a current is passed under the conditions of the current ratio during three-phase alternating current and the current ratio not included during three-phase alternating current. The output voltage of elements 3a-3b is measured.

  The current ratio condition that is not included in the three-phase AC is included in the calculation of only the three current ratio conditions (first, third, and fourth conditions) in the three-phase AC when deriving the interference correction coefficient described later. This is because the conditions are not independent of each other and the interference correction coefficient cannot be derived. The procedure for deriving the interference correction coefficient will be described later.

Thereafter, linear correction coefficients are derived in steps S2 to S5. In step S2, the measurement result of step S1 is applied to an arbitrary fitting equation, and various coefficients (referred to as fitting factors) set in the fitting equation are obtained. Here, since a GMR element is used as the magnetic detection element 3, the fitting formulas (2) and (3) shown in [Equation 1] are used for the U phase. In these formulas (2) and (3), V _off , V _sat , B _bias / k, φ, θ, b _u1 , and b _u2 are fitting coefficients, and these fitting coefficients are expressed by least square method or the like. Use to calculate.

For the V phase, the fitting equations of equations (4) and (5) shown in [Equation 2] were used. Note that b _v1 and b _v2 are fitting coefficients.

Similarly, for the W phase, the fitting equations (6) and (7) shown in [Equation 3] were used. Note that b _w1 and b _w2 are fitting coefficients.

Thereafter, in step S3, each fitting equation is substituted into the fitting equation of equation (2), and the GMR output voltage V _{m_u} measured in step S1 is substituted to obtain I _{det_u} . The obtained I _{det_u} is _set as a virtual output voltage V _{L_u} (a variable is replaced). Similarly, the fitting equations are substituted into the fitting equations of equations (4) and (6), and the GMR output voltages V _{m_v} and V _{m_w} measured in step S1 are substituted to _obtain I _{det_v} and I _{det_w} , respectively. Output _{VL_v} and _{VL_w} .

Thereafter, in step S4, I _{det_u} is _obtained from equation (3), and the relationship between this I _{det_u} and the virtual output V _{L_u} obtained in step S3 is obtained by linear approximation. That is, based on the virtual output V _{L — u} obtained from the equation (2) and I _{det — u} obtained from the equation (3), the following equation (8)
V _L — _u = m ′ _u × I _det — _u + n ′ _u (8)
The coefficients m ′ _u and n ′ _{u at} are obtained.

Further, based on the virtual output V _{L_v} obtained from the equation (4) and I _{det_v} obtained from the equation (5), the following equation (9) is obtained by the least square method or the like.
V _L — _v = m ′ _v × I _det — _v + n ′ _v (9)
The coefficients m ′ _v and n ′ _{v at} are obtained.

Similarly, the following equation (10) is obtained by the least square method or the like based on the virtual output V _{L_w} obtained from equation (6) and I _{det_w} obtained from equation (7).
V _L — _w = m ′ _w × I _det — _w + n ′ _w (10)
The coefficients m ′ _w and n ′ _{w at} are obtained.

Thereafter, in step S5, derivation of the linear correction coefficient and calculation of the output voltage after the linear correction are performed based on the relations of the equations (8) to (10). Specifically, for the U phase, the following equations (11), (12)
m _u = M / m ′ _u (11)
n _u = M × n ′ _u / m ′ _u (12)
Thus, the linear correction coefficients m _u and n _u are derived. Here, M is the gain setting value of the above equation (1). Using these linear correction coefficients m _u and n _u , the following equation (13)
V _LC — _u = m _u × V _L — _u + n _u (13)
Thus, the output voltage V _{LC_u} after linear correction is calculated. If the above equations (8), (11), and (12) are substituted into this equation (13), the following equation: V _{LC_u} = M × I _{det_u}
It will be represented by

For the V phase, the following equations (14), (15)
m _v = M / m ′ _v (14)
n _v = M × n ′ _v / m ′ _v (15)
Thus, linear correction coefficients m _v and n _v are derived. Also, the following formula (16)
V _LC — _v = m _v × V _L — _v + n _v (16)
Thus, the output voltage V _{LC_v} after linear correction is calculated.

Similarly, for the W phase, the following equations (17), (18)
m _w = M / m ′ _w (17)
n _w = M × n ′ _w / m ′ _w (18)
Thus, the linear correction coefficients m _w and n _w are derived. Also, the following formula (19)
_{V LC_w = m w × V L_w} + n w ··· (19)
Thus, the output voltage V _{LC_w} after linear correction is calculated.

Thereafter, in step S6 to S9, the linear corrected output voltage _V LC_u obtained in step _S5, V _{LC_V,} using _{V LC_w,} the derivation of the interference correction coefficient. In step S6, based on the above equations (3), (5), and (7), a temporary interference correction coefficient A ′ (a ′ _uu ,..., A by the equation (20) shown in [3]. ' _ww ) is _calculated .

  Since this temporary interference correction coefficient A ′ includes a condition (second condition) other than the three-phase AC, it includes an error. Therefore, in this embodiment, the interference correction coefficient is adjusted in the following steps S7 to S9. Note that only the conditions (first, third, and fourth conditions) for the current ratio during three-phase alternating current are used without using the current ratio (second condition) that is not included during three-phase alternating current during linear correction. It is also conceivable to use the measurement results. However, in this case, since the fourth condition is automatically obtained from the first condition and the third condition, the three conditions are not mutually independent. For this reason, when only the conditions for the current ratio at the time of three-phase alternating current are used, there is no inverse matrix in the temporary interference correction coefficient A ′, making it difficult to calculate the interference correction coefficient. As in the present embodiment, at the time of linear correction, two conditions (first and third conditions) that are current ratios during three-phase AC and one condition (second condition) that is not included during three-phase AC By calculating the linear correction coefficient using the measurement result in (), the interference correction coefficient can be calculated.

After obtaining the temporary interference correction coefficient A ′, in step S7, the output voltage after the temporary interference correction when the interference correction is performed with the temporary interference correction coefficient A ′ is obtained. Specifically, output voltages V ′ _{IC_u1} , V ′ _{IC_v4} , and V ′ _{IC_w3} after provisional interference correction are obtained by Expression (21) shown in [Formula 5]. In equation (21), at the end of the variable of each voltage (the output voltage after provisional interference correction and the output voltage after linear correction), the number of the condition is indicated by one digit. For example, V _{LC_u1} represents an output voltage after linear correction of the U-phase in the first condition, and V ′ _{IC_u1} represents an operation result (V _{LC_u1} , V _{LC_v1} , and V _{LC_w1} ) in the first condition. Represents the output voltage after the temporary interference correction of the U phase calculated by using.

As described above, in the present embodiment, the output voltage V ′ _{IC_u} after the U-phase temporary interference correction is calculated under the first condition (V _{LC_u1} , V _{LC_v1} , V 1) at which the U-phase current becomes maximum. _{LC_w1} ). The V-phase provisional interference-corrected output voltage V ′ _{IC_v} is calculated using calculation results (V _{LC_u4} , V _{LC_v4} , V _{LC_w4} ) under the fourth condition that maximizes the V-phase current. Similarly, the output voltage V ′ _{IC_w} after W-phase temporary interference correction is calculated using the calculation results (V _{LC_u3} , V _{LC_v3} , V _{LC_w3} ) under the third condition that maximizes the W-phase current. .

  In other words, in the present embodiment, the current ratio during three-phase alternating current and the U-phase, V-phase, or W-phase current are maximized under three conditions (first, third, and fourth conditions). The interference correction coefficient is derived based on the output voltage after the linear correction. As a result, the gain error is minimized under the maximum current of the U-phase, V-phase, or W-phase, so that the output error can be reduced.

Thereafter, at step S8, the temporary interference corrected output voltage V _{'IC_u1,} V' obtained at step S7 _{IC_v4,} and V _{'IC_w3,} the U-phase of a current _{I u1} (first condition flowing through each bus bar 2 The relationship between the currents I _u ), I _v4 (V-phase current I _{v under} the fourth condition), I _w3 (W-phase current I _{w under} the third condition) is obtained by linear approximation. That is, the coefficients m ″ _u , m ″ _v and m ″ _w in (22) shown in [Equation 6] are obtained by the least square method or the like.

Based on the coefficients m ″ _u , m ″ _v , and m ″ _w obtained in step S7, the interference correction coefficient A (a _uu ,..., A _ww ). As described above, the interference correction coefficient A adjusted to the temporary interference correction coefficient A ′ is derived.

Using this interference correction coefficients A, by using the relational expression of Formula (24) shown in [Expression 8], the output voltage _V LC_u after linear _correction, V _{LC_V,} from _{V LC_w,} the corrected output voltage _{V OUT_U,} V _{out_v} and V _{out_w} can be obtained. Note that N in Equation (24) is the offset output voltage setting value in Equation (1) above.

Further, the currents I _u , I _v , I _w flowing through the bus bar 2 are obtained from the corrected output voltages V out — _u , V out — _v , V out — _w obtained by the equation (24) using the above equation (1). be able to. In addition, said Formula (1) can be represented by the following Formula (25)-(27), if it applies to each phase of a three-phase alternating current.
V _out — _u = M × I _u + N (25)
V _out — _v = M × I _v + N (26)
V _out — _w = M × I _w + N (27)

Here, the effect of each correction will be described. An example of the relationship between the V-phase current I _v and the V-phase GMR output voltage V _{m_v} is shown in FIG. As shown in FIG. 4, the influence of interference from properties and other phases of the GMR element, the relationship between the current I _v and the GMR output voltage V _{m_v} is not a linear relationship.

Relationship between the output voltage _{V LC_V} after current _{I v} and linear correction in the current sensor 1 is as shown in FIG. 5 (a). As shown in FIG. 5 (a), the relationship between the output voltage V _{LC_V} after current I _v and linear correction is close to linear relationship. However, depending on the current ratio of the three-phase alternating current, an error occurs due to the influence of interference from other phases.

Further, the relationship between the current I _v and the corrected output voltage V _{out_v} in the current sensor 1 is as shown in FIG. As shown in FIG. 5 (b), by performing both linear correction and interference correction, the relationship between the output voltage V _{Out_v} after correction current I _v, a linear relationship regardless of the current ratio of the three-phase AC Thus, the error due to the correction is suppressed and high-precision detection is possible.

(Correction unit 7 and bus bar current calculation unit 8)
Based on the linear correction coefficients m and n derived in FIG. 3 and the interference correction coefficient A, the correction unit 7 corrects the output from the output voltages (GMR output voltages V _{m_u} , V _{m_v} , V _{m_w} ) of each magnetic detection element 3. Output voltages V out — _u , V out — _v , and V out — _w are calculated.

Specifically, the correction unit 7 uses the equation (28) shown in [Equation 9] based on the GMR output voltage V _{m_u} input from each magnetic detection element 3 to output the linear corrected output voltage V _{LC_u.} Ask for. Similarly, GMR output voltage _{V m_v,} based on _{V m_w,} the output voltage _{V LC_V,} seek _{V LC_w.}

Then, the correction unit 7 obtains linear corrected output voltage _{V LC_u, V LC_v,} from _{V LC_w,} by using equation (24), the corrected output voltage _{V out_u, V out_v,} seek _{V out_w.} The correction unit 7 outputs the obtained corrected output voltages V _{out_u} , V _{out_v} , and V _{out_w} to the bus bar current calculation unit 8.

Busbar current computing section 8, it is input from the correction unit 7 the corrected output voltage _{V out_u, V out_v,} based on _{V out_w,} the equation (25) the following formula was modified to (27) (29) - ( 31)
I _u = (V _out — _u −N) / M (29)
I _v = (V _out — _v −N) / M (30)
I _w = (V _out — _w −N) / M (31)
The currents I _u , I _v and I _w flowing through the bus bar 2 are obtained.

(Operation and effect of the embodiment)
As described above, in the current sensor correction method according to the present embodiment, a current is passed through the three bus bars 2 under the conditions of the current ratio during three-phase alternating current and the current ratio not included during three-phase alternating current. In this state, the output voltages of the three magnetic detection elements 3 are measured, the linear correction coefficient and the interference correction coefficient are derived based on the measurement results, and the linearity of the output voltage is calculated using the derived linear correction coefficient and the interference correction coefficient. Correction and interference correction are performed.

  In the current sensor 1 provided with the shield plates 41 and 42 so that the three bus bars 2 through which the current of each phase in the three-phase alternating current flows are collectively sandwiched in the thickness direction, the single-phase energization and the three-phase energization However, in this embodiment, the correction is performed using the measurement result of the output voltage in the state where current is passed through the three bus bars 2, although the distribution of the magnetic flux density in the shield plates 41 and 42 is greatly different. As a result, the correction accuracy is increased, and highly accurate current measurement is possible.

  In addition, when measuring the output voltage, not only the current ratio condition during three-phase alternating current but also the current ratio condition not included during three-phase alternating current can be used to accurately perform both linear correction and interference correction. As a result, current measurement can be performed with higher accuracy.

(Modification)
In the above embodiment, the influence of the temperature was not mentioned. However, when the temperature of the magnetic detection element 3 changes greatly due to Joule heat and the GMR output voltages V _{m_u} , V _{m_v} , V _{m_w} change greatly, fitting is performed. You may use what considered the influence by temperature as a type | formula. For example, V _off and V _sat in the above formulas (2), (4), and (6) are set as, for example, the following formulas (32) and (33):
_{V off (T) = l o} × T 2 + m o × T + n o ··· (32)
V _sat (T) = l _s × T ² + m _s × T + n _s (33)
As shown in the equation, temperature correction can be performed at the same time by defining it as a function of temperature. In the equations (32) and (33), l _o , m _o , n _o , l _s , m _s , and n _s are fitting coefficients.

Further, when using a magnetic detection element 3 that does not require linear correction, such as a Hall IC, the following equation (34) is used as the fitting equation:
V _m = V _gain × I _det + V _off (34)
It is also possible to use a simple linear equation represented by Note that V _gain and V _off in equation (34) are fitting coefficients.

(Summary of embodiment)
Next, the technical idea grasped from the embodiment described above will be described with reference to the reference numerals in the embodiment. However, the reference numerals and the like in the following description are not intended to limit the constituent elements in the claims to the members and the like specifically shown in the embodiments.

[1] Three bus bars (2) that are formed in a plate shape and are arranged apart from each other in the width direction of the plate and through which current of each phase in three-phase alternating current flows, and the three bus bars ( 2), a first shield plate (41) and a second shield plate (42) made of a magnetic material arranged so as to be sandwiched in a thickness direction perpendicular to the plate width direction, and each bus bar ( 2) and the first shield plate (41), and three magnetic detection elements (3) for detecting the strength of the magnetic field generated by the current flowing through the corresponding bus bar (2). In the current sensor (1) correction method, a current is passed through the three bus bars (2) under conditions of a current ratio during three-phase alternating current and a current ratio not included during three-phase alternating current. The output voltage of the three magnetic detection elements (3) is measured, and the measurement result It derives a linear correction coefficient and interference correction coefficient group using the derived linear correction coefficient and interference correction coefficient, performs linear correction and interference correction of the output voltage, the correction method of the current sensor.

[2] The linear correction coefficient is derived using measurement results under two conditions that are current ratios during three-phase AC and one condition that is not included during three-phase AC. The method for correcting a current sensor according to [1], wherein an output after correction is obtained by performing interference correction on the output voltage.

[3] An interference correction coefficient is derived based on the output voltage after linear correction, which is obtained under three conditions in which the current ratio during three-phase alternating current is obtained and the U-phase, V-phase, or W-phase current is maximum. The correction method of the current sensor according to [2].

[4] Three bus bars (2) that are formed in a plate shape and are arranged apart from each other in the width direction of the plate and through which current of each phase in three-phase AC flows, and the three bus bars ( 2), a first shield plate (41) and a second shield plate (42) made of a magnetic material arranged so as to be sandwiched in a thickness direction perpendicular to the plate width direction, and each bus bar ( 2) and the first shield plate (41), respectively, and three magnetic detection elements (3) for detecting the strength of the magnetic field generated by the current flowing through the corresponding bus bar (2), A correction unit (7) that corrects the output voltages of the two magnetic detection elements, and the correction unit (7) has a current ratio during three-phase alternating current and a three-phase alternating current in the three bus bars (2). The above three magnetic detections with current flowing under the condition of current ratio not included Using the linear correction coefficient and interference correction coefficient output voltage derived based on the results of measurement of the child (3), performs linear correction and interference correction of the output voltage, the current sensor (1).

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential for the means for solving the problems of the invention. Further, the present invention can be appropriately modified and implemented without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Current sensor 2 ... Bus bar 3 ... Magnetic detection element 41 ... 1st shield board 42 ... 2nd shield board 7 ... Correction | amendment part

Claims (4)

Three bus bars that are formed in a plate shape and are arranged apart from each other in the width direction of the plate, and each phase current in three-phase alternating current flows;
A first shield plate and a second shield plate made of a magnetic material arranged so as to sandwich the three bus bars in a thickness direction perpendicular to the plate width direction;
A current sensor correction method comprising: three magnetic detection elements that are arranged between each bus bar and the first shield plate and detect the intensity of a magnetic field generated by a current flowing through the corresponding bus bar. And
The output voltage of the three magnetic detection elements was measured in a state where current was passed through the three bus bars under the conditions of the current ratio during three-phase alternating current and the current ratio not included during three-phase alternating current. Deriving linear correction coefficient and interference correction coefficient based on
Using the derived linear correction coefficient and interference correction coefficient, linear correction and interference correction of the output voltage,
Current sensor correction method. Deriving the linear correction coefficient using the measurement results under two conditions that are current ratios during three-phase AC and one condition that is not included during three-phase AC,
By performing interference correction on the output voltage after linear correction, the corrected output is obtained.
The current sensor correction method according to claim 1. An interference correction coefficient is derived based on the output voltage after linear correction obtained under the three conditions where the current ratio is three-phase AC and the current of the U-phase, V-phase, or W-phase is maximized.
The current sensor correction method according to claim 2. Three bus bars that are formed in a plate shape and are arranged apart from each other in the width direction of the plate, and each phase current in three-phase alternating current flows;
A first shield plate and a second shield plate made of a magnetic material arranged so as to sandwich the three bus bars in a thickness direction perpendicular to the plate width direction;
Three magnetic detection elements that are respectively arranged between the bus bars and the first shield plate and detect the intensity of a magnetic field generated by a current flowing through the corresponding bus bars;
A correction unit for correcting the output voltage of the three magnetic detection elements,
The correction unit measures the output voltage of the three magnetic detection elements in a state where a current is passed through the three bus bars under conditions of a current ratio during three-phase alternating current and a current ratio not included during three-phase alternating current. Using the linear correction coefficient and the interference correction coefficient derived based on the result, linear correction and interference correction of the output voltage,
Current sensor.

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