JP3092746B2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the value of a current flowing in a conducting wire, and more particularly, to measuring the current value by measuring the rotation angle of a magneto-optical element and the plane of deflection of linearly polarized light incident thereon. The present invention relates to a current detection device to be obtained.

[0002]

2. Description of the Related Art The technique of detecting the value of a current flowing in a conductive wire has been used in various fields in electronic technology, and has been the oldest practical technique in electrical engineering.
Therefore, the detection method is also diverse, and for example, the following methods are known. A method of arranging a resistor pair having a constant resistance value in a conducting wire and detecting a current from a potential difference generated at both ends of the resistor,
A method based on Ohm's law. A method of detecting the magnetic field generated by current and detecting the current value based on Ampere's law. In this method, magnetic field detection is fundamental, and a method using electromagnetic induction, a method using a current magnetic effect such as a Hall effect or a magnetoresistance effect, and the like have been put into practical use (for example, Japanese Utility Model Laid-Open No. 1-121869).

[0003]

However, for example, in an electric vehicle or the like, the above-described conventional method of detecting a current value is not always effective. The reason is as follows. For example, in a conventional electric vehicle, electric power stored in a battery or the like is taken out as direct current, and a motor is driven by voltage control. In order to control the direct current, a method using a resistor is generally used, and the current is detected from a potential difference generated between both ends of the resistor. That is, the above method is adopted. Since this method is simple in terms of mechanism, it has been used for a long time in a device such as an electric railway that can supply power at any time. However, since this method basically controls a DC current value by consuming a predetermined power by a resistor and converting it into Joule heat, the energy loss is large. Therefore, this method can be adopted in electric railways and the like that can supply power as needed.
In an electric vehicle or the like that uses a power source having a limited capacity such as a storage battery, performing the current control by such a method results in an extremely short travelable distance, causing a fatal problem. That is, the above-described current value detection method is not suitable for electric vehicles and the like.

As one method of solving such a problem of energy loss, a technique of controlling a chopper is introduced into an electric vehicle. This method switches a DC current in a short time and drives a DC motor with a pulse current. In this method, the effective voltage can be changed by controlling the switching time, and the energy loss can be reduced as compared with the resistance control. However, since a DC motor can control a stator and a rotor separately, it has good controllability, but a commutator is indispensable and it is difficult to draw out characteristics of a high rotation type.

[0005] Therefore, recently, a method of applying a three-phase induction motor to a motor has been established. The three-phase induction motor drives a rotor that is not electrically connected by power supplied to a stator, and is controlled by a frequency of supplied power and a voltage or a current. This method has a high rotation characteristic because there is no mechanical connection such as a commutator, and is effective in a device having a wide power band such as an automobile. In order to apply this three-phase induction motor to an electric vehicle having only a DC power supply, it is necessary to use an inverter device. Inverter equipment is changed from DC to three-phase AC,
In addition, it is a device that can convert from three-phase AC to DC. By appropriately controlling the frequency, powering and regeneration can be performed without a load circuit, and control with higher energy efficiency than chopper control can be performed. Such a situation is not limited to electric vehicles, but is common to electric railways, factory power, and power control using electric power.

As described above, in the motor control, the chopper control or the inverter method has a decisive advantage as compared with the resistance control, but it is used when a wide power characteristic is to be realized. The frequency of the power spreads over a wide band. As a result, electromagnetic waves caused by the high-frequency current cause inconveniences such as causing induction trouble in a control device for power control. This induction disorder
The above-described current detection method using electromagnetic induction and the current detection method using a current-magnetism effect such as the Hall effect or the magnetoresistance effect also pose a problem, and cause a reduction in current value detection accuracy.

In summary, in an electric vehicle or the like, the method of measuring a voltage generated at both ends of a resistor and obtaining a current value as described above has a large energy loss and is not practical. To reduce
In the case where the chopper control or the inverter method is introduced, the detection accuracy of the current detection method based on the magnetic field detection shown by the above becomes lower due to the induction failure due to the high frequency induction.

On the other hand, besides such a problem of current detection, as described above, there is a problem that an induction fault caused by a high-frequency current causes an induction fault in a control device for power control, and this problem is solved. To this end, it has been proposed to use a technique of optical communication to construct a control signal system.
In the current system, detection signals from various sensors are converted from electrical signals to optical signals and transmitted.
Although there is an effect, since the detection signal is an electric signal,
It is indispensable to implement electromagnetic shielding etc. for electromagnetic interference entering various sensors. Therefore, in order to further promote the use of optical technology and abolish electromagnetic shielding, etc., use sensors that detect various state quantities as changes in the state quantity of light (that is, sensors whose detection signals themselves are optical signals). ), And the detection information is left as an optical signal,
A transmission method using an optical fiber or the like is also being studied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object the purpose of not only detecting current by optical technology but also transmitting a detected value as an optical signal. An object of the present invention is to provide a current detection device capable of solving the problems of energy loss and radio interference.

[0010]

In order to solve the above-mentioned problems and achieve the object, a current detecting device according to the present invention includes a main current path, a branch from the main current path, and a main current path. A current path having a branch current path orthogonally disposed with a predetermined gap therebetween, and a current path provided in the gap and having an axis of easy magnetization parallel to the main current path or the branch current path. A magneto-optical element provided with a magneto-optical effect, a light source for inputting linearly polarized light having a predetermined deflection surface to the magneto-optical element in parallel with its easy axis of magnetization, and light emitted from the magneto-optical element And a calculating means for calculating a value of a current flowing through the current path based on a detection result of the detecting means.

Further, in the current detecting device according to the present invention, a current value flowing in a current path parallel to the easy axis of the magneto-optical element is set to be larger than a current value flowing in a current path orthogonal to the easy axis. It is characterized by having.

[0012]

As described above, since the current detecting device according to the present invention is constructed, a magnetic field generated by a current is applied to the magneto-optical element, and the deflection surface of the linearly polarized light incident on the magneto-optical element is deflected. By detecting the rotation angle, it is possible to detect the current value, and the problem of energy loss,
The problem of radio interference can be solved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described. Before describing the configuration of the embodiment, the principle of detecting a current value by the current detecting device of the embodiment will be described. (Magneto-optical element and rotation of deflection surface) The magneto-optical element is a single crystal or polycrystal in which GdIG (gadolinium iron garnet) or YIG (yttrium iron garnet) is used as a base material and a part of Gd or Y is replaced by Bi or Pb. It is composed of a body, can transmit light, and exhibits ferromagnetic properties.

When linearly polarized light is incident on the magneto-optical element, the light transmitted through the magneto-optical element rotates its deflection surface in accordance with the magnetization state of the magneto-optical element. This is called the Faraday effect among the magneto-optical effects. From the principle of the Faraday effect, the magnetization state of the magneto-optical element can be known by detecting the rotation angle of the deflection surface of the light transmitted through the magneto-optical element. On the other hand, the magnetization state of the magneto-optical element changes due to a magnetic field applied from the outside,
It is possible to detect the external magnetic field strength from the magnetization state.

In one embodiment, utilizing this principle, the rotation angle of the plane of deflection of the linearly polarized light transmitted through the magneto-optical element is detected.
As a result, the magnetic field intensity applied to the magneto-optical element, that is, the magnetic field intensity formed by the current flowing through the conductor is detected, and the current value generating the magnetic field is calculated back from the magnetic field intensity. In the current detection method using the magneto-optical effect, the magneto-optical effect is generated by the interaction between light and the magneto-optical element. There is an advantage that it does not occur. (Relationship between magnitude of magnetic field applied from outside and Faraday rotation angle) As described above, in the current detection device of one embodiment, the intensity of the magnetic field applied to the magneto-optical element is detected from the magnitude of the Faraday rotation angle. (First step), and a current value is calculated from the magnetic field strength (second step). Here, the principle of detecting the magnetic field intensity from the magnitude of the Faraday rotation angle, which is the first step, will be described.

FIG. 1 is a diagram for explaining a principle of detecting a magnetic field intensity in one embodiment. In FIG. 1, the magneto-optical element 12 is arranged such that its easy axis of magnetization is oriented in the direction of arrow A, and the magneto-optical element 12 is provided with a magnetic field of intensity H from the outside in a direction parallel to the easy axis of magnetization. Is applied, and a magnetic field of intensity λH (λ is a predetermined constant) is applied in a direction orthogonal to the easy axis of magnetization. At this time, the direction of the saturation magnetization (magnitude Ms) generated in the magneto-optical element is in the direction indicated by arrow B, that is, the direction at an angle of φ with the easy axis.

In order to detect the magnetization state of the magneto-optical element 12, linearly polarized light is incident on the magneto-optical element 12 in a direction parallel to the axis of easy magnetization, as indicated by an arrow C in FIG. The rotation angle (Faraday rotation angle) θF of the deflecting surface of the linearly polarized light transmitted through the magneto-optical element 12 has a maximum value θFs when the incident direction of light coincides with the direction of the saturation magnetization Ms, and becomes 0 when the light is orthogonal. As shown in FIG. 1, when the incident direction of light and the direction of the saturation magnetization Ms form an angle φ,
The Faraday rotation angle θF is expressed by the following equation.

ΘF = θFs · cosφ (1) Here, assuming that the value obtained by normalizing the Faraday rotation angle θF of the deflecting surface with θFs is represented by Θ, the equation (1) is modified as follows. Θ = θF / θFs = cosφ (2) That is, the relationship between the Faraday rotation angle θF (or the standardized Faraday rotation angle Θ) and the inclination angle φ of the saturation magnetization Ms with respect to the incident direction of light is expressed by equation (2). Will be represented.

In addition to the equation (2), the saturation magnetization Ms
Is derived, the relational expression between the Faraday rotation angle θF and the magnetic field strength H can be obtained by solving these two simultaneous equations. The magnetic field intensity H can be calculated from the measured value of the Faraday rotation angle θF. Hereinafter, the relationship between the magnetic field strength H and the inclination angle φ of the saturation magnetization Ms will be described.

The inclination angle φ between the magnetic field strength H and the saturation magnetization Ms
In order to derive the relationship, "the magnetization state of the magneto-optical element is
The magnetic energy is determined to be minimal. " Here, this magnetic energy is represented by (a)
The magnetization state is determined so as to be divided into static magnetic energy and (b) magnetic anisotropic energy.

The magnetostatic energy and the magnetic anisotropic energy will be described with reference to FIG. (A) Magnetostatic energy Magnetostatic energy is energy generated between the saturation magnetization of a magneto-optical element as a ferromagnetic material and an externally applied magnetic field, and is expressed by the following equation.

Es = −Ms · H · cosφ (3) where Es, Ms and H are magnitudes of magnetostatic energy,
Φ represents the angle between the saturation magnetization (magnitude Ms) and the external magnetic field (magnitude H). (In the above description,
Although the angle between the light incident direction (arrow C) and the saturation magnetization (arrow B) has been described as φ, in this embodiment, FIG.
Since the direction of the magnetic field applied from the outside is parallel to the incident direction of light as shown in Fig. 4, the angle between the saturation magnetization and the magnetic field is represented by the same symbol φ for easy understanding. . (B) Magnetic Anisotropy Energy Ferromagnetic materials have magnetic anisotropy. The magnetic anisotropy refers to a property that the saturation magnetization of the ferromagnetic material is easily oriented in a specific direction (or hardly oriented in some cases). Magnetic anisotropy arises from the main axis and strain of the crystal and other structural directions formed on the magnetic material. The magnetic anisotropy energy is determined by the angle between the easy axis (the direction in which the saturation magnetization of the ferromagnetic material is easily oriented) and the saturation magnetization, and is expressed by the following equation.

Ea = Ku · sin ² φ (4) where Ea and Ku represent the magnitude of the magnetic anisotropy energy and the magnetic anisotropy constant, respectively, and φ is the relationship between the saturation magnetization and the easy axis of magnetization. Represents a corner. (In the above description, the angle between the incident direction of light (arrow C) and the saturation magnetization (arrow B) is φ
However, in this embodiment, as shown in FIG. 1, the direction of the axis of easy magnetization is parallel to the direction of incidence of light. Is represented by the same symbol φ. )
In the bulk of the magneto-optical element in which YIG, GdIG, and Y or Gd are replaced by Bi or Pb, the direction of the easy axis is the direction of the cubic (111) axis, and the direction of the thin film is the direction perpendicular to the film surface. Or, it is the direction in the film plane. (C) Total magnetic energy The total magnetic energy Et is the sum of the above-mentioned magnetostatic energy and magnetic anisotropic energy, and is expressed by the following equation.

Et = −Ms · H · cos φ−Ms · (λH) · sin φ + Ku · sin ² φ (5) In this way, the total magnetic energy E expressed by the equation (5) is obtained.
Although the equation of t has been derived, in order to determine the magnetization state from this equation, it is sufficient to find a condition that minimizes the total magnetic energy Et. That is, d / dφ (Et) =
0 and d such that d ² / dφ ² (Et)> 0 may be obtained. Then, the first-order differentiation and the second-order differentiation of Expression (5) with φ are as follows.

Ms · Hk (h · sinφ−λ · h · cosφ + 0.5 · sin2φ) = 0 (6) Ms · Hk (h · cosφ + λ · h · sinφ + cos2φ)> 0 (7) However, Hk is different. This is a parameter called an isotropic magnetic field, and is represented by Hk = 2 Ku / Ms. H is H to H
It is a quantity normalized by k.

Equations (6) and (7) can be further summarized as follows: h · sinφ−λ · h · cosφ + 0.5 · sin2φ = 0 (8) h · cosφ + λ · h · sinφ + cos2φ> 0 (9) Become. This is a relational expression between the inclination angle φ of the saturation magnetization Ms and the intensity H of the magnetic field applied from the outside, and these equations (8), (9) and (2) are used as simultaneous equations. By solving, the relational expression between the Faraday rotation angle θF and the magnetic field strength H is obtained, and the magnetic field strength H can be calculated from the measured value of the Faraday rotation angle θF.

From Equations (8) and (2), when φ is eliminated, the relationship between the standardized Faraday rotation angle Θ and the standardized magnetic field strength h is obtained. Looks like As shown in this figure, the relationship between the two values Θ and h has a hysteresis characteristic, and Θ and h do not always correspond one-to-one, but the strength h of the magnetic field is equal to or greater than the limit magnetic field indicated by the broken line. Then, a one-to-one relationship holds. Moreover,
The region where the one-to-one relationship does not hold can be reduced as much as possible by setting λ to a large value as shown in the figure. In accordance with the range of the magnitude of the magnetic field intensity to be actually measured, By setting the value, there is no practical problem and the polarity of the magnetic field can be detected.

FIG. 3 shows the graph shown in FIG. 2 in a semi-logarithmic representation. (Relationship between magnetic field strength and current value)
The calculation of the magnetic field strength from the Faraday rotation angle, which is the step, has been realized. Here, the calculation of the current value from the obtained magnetic field strength, which is the second step, will be described.

The current flowing in the wire generates a magnetic field around the wire according to the so-called Ampere's law. The strength H of the magnetic field formed by the current having the current value I at a distance of r from the center of the current is represented by the following equation. H = f (r) · I (10) where f (r) is a function that varies depending on the boundary conditions of the flowing current. This function has already been determined for various boundary conditions.

In the first step, by substituting the magnetic field strength obtained from the Faraday rotation angle into the equation (10) and solving for I, the finally required current value I can be obtained. What has been described above is the principle of obtaining the current value from the Faraday rotation angle of the light transmitted through the magneto-optical element in this embodiment.

Next, the configuration of the current detecting device of one embodiment will be described. FIG. 4 is a plan view showing the configuration of the current detecting device according to one embodiment, and FIG. 5 is a perspective view of a main part of the current detecting device. As shown in FIG. 4, a main current path 20 through which a current to be measured flows is branched into a branch current path 22 at a branch point A. The branch current path 22 is arranged so as to be orthogonal to the main current path 20 at an intermediate portion (point B), and is arranged so as to intersect with the main current path 20 and to merge with the main current path 20 again at a point C. Have been.

At the intersection (point B) between the main current path 20 and the branch current path 22, a magneto-optical element 24 is arranged between them, as shown in FIG. This magneto-optical element 24
In addition to performing the insulating function of the main current path 20 and the branch current path 22, the magnetic field generated from both current paths is detected. The magneto-optical element 24 is arranged so that its easy axis of magnetization matches the direction of the current in the branch current path 22.
4, linearly polarized light emitted from the light source 26 is incident in a direction parallel to the axis of easy magnetization. A detector 28 for detecting the rotation angle (Faraday rotation angle) of the deflection surface of the light emitted from the magneto-optical element 24 is disposed on the opposite side of the light source 26 with the magneto-optical element 24 interposed therebetween. An arithmetic unit 30 for calculating a current value from the value of the Faraday rotation angle detected by the detector 28 is further connected to the detector 28. The resistance values of the main current path 20 and the branch current furnace 22 are determined in advance so that the current value flowing in the branch current path 22 becomes λ times (λ> 1) the current value flowing in the main current path 20. I have.

In the current detecting device thus constructed, the main current path 2 extends in the direction of the easy axis of the magneto-optical element 24.
A magnetic field having a strength H is generated by the current having the current value I flowing through zero. In addition, a magnetic field having the intensity λH is formed in the direction perpendicular to the easy axis of magnetization by the current having the current value λI flowing through the branch current furnace. FIG. 6 shows this state, and FIG.
And the magnetization state shown in FIG. Accordingly, the relationship between the standardized Faraday rotation angle Θ and the standardized magnetic field strength h at this time is the same as that shown in FIG. h is I
Therefore, I can be obtained as a function of Θ according to the principle described above, and the current value I can be calculated from the value of Θ.

FIG. 7 shows a modification of the embodiment, in which the axis of easy magnetization of the magneto-optical element 24 is set in the current direction of the main current path 20, linearly polarized light is made incident in this direction, and 22 is 1 / (the current value flowing in the main current path)
λ (λ> 1). Again in this case,
The detection result is exactly the same as in the embodiment. Next, the current detection accuracy in this embodiment will be described.

In this embodiment, the magnetic field strength h is detected based on the Faraday rotation angle Θ, and the current value I is calculated from the magnetic field strength h. However, it depends on the detection accuracy of the Faraday rotation angle Θ. Therefore, assuming that the detection accuracy of Θ is ε and the detection accuracy of h is δ, the following expression holds.

Δ / ε = (Δh / h) / (ΔΘ / Θ) (11) where ΔΘ and Δh are the detection error of Θ and the detection error of h, respectively. FIG. 8 shows the relationship of δ / ε with Θ. As shown in this figure, when λ = 1, δ / ε
Is close to Θ = 8.4, δ (ie, the detection accuracy of the magnetic field strength h) is larger than ε (ie, the detection accuracy of the Faraday rotation angle Θ), and the detection accuracy of the magnetic field strength is One digit lower than the angle detection accuracy. On the other hand, when λ> 2, the minimum value decreases, and it is possible to suppress the decrease in the detection accuracy of the magnetic field strength h to within one digit. Further, if λ> 5, the value of δ / ε becomes 2 or less, and h can be detected with a detection accuracy of approximately Θ.

That is, considering FIGS. 2 and 8, λ
Taking the value of larger than a certain value leads to an increase in the magnetic field detection range and an improvement in the magnetic field detection accuracy. The present invention can be applied to a modification or modification of the above embodiment without departing from the scope of the invention.

[0038]

As described above, according to the current detecting device of the present invention, the magnetic field generated by the current is applied to the magneto-optical element, and the rotation angle of the deflecting surface of the linearly polarized light incident on the magneto-optical element. , The current value can be detected, and the problem of energy loss and the problem of radio interference can be solved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a principle of detecting a magnetic field intensity in one embodiment.

FIG. 2 is a diagram showing a relationship between a standardized Faraday rotation angle Θ and a standardized magnetic field strength h.

FIG. 3 is a diagram showing FIG. 2 in a semi-logarithmic display.

FIG. 4 is a plan view showing a configuration of a current detection device according to one embodiment.

FIG. 5 is a perspective view of a main part of the current detection device.

FIG. 6 is a diagram showing a magnetization state of the magneto-optical element.

FIG. 7 is a diagram showing a modification of the embodiment.

FIG. 8 is a diagram showing the relationship of δ / ε to ε.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Magneto-optical element 20 Main current path 22 Branch current path 24 Magneto-optical element 26 Light source 28 Detector 30 Arithmetic unit

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kazushi Fukuba 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 15/24 G01R 19/00

Claims (2)

(57) [Claims] A current path having a main current path, a branch current path branched from the main current path, and orthogonally disposed with a predetermined gap to the main current path; A magneto-optical element having a magneto-optical effect disposed so that its easy axis of magnetization is parallel to the main current path or the branch current path; and A light source for inputting linearly polarized light having a predetermined deflecting surface; detecting means for detecting a rotation state of the deflecting surface of the light emitted from the magneto-optical element; and a current path based on a detection result of the detecting means. And a calculating means for calculating a value of a current flowing through the current detecting device. 2. A current value flowing in a current path parallel to the easy axis of the magneto-optical element is set to be larger than a current value flowing in a current path orthogonal to the easy axis of the magneto-optical element. 2. The current detection device according to 1.