JP2019002768A - Current sensor - Google Patents

Abstract

To provide a current sensor with which it is possible to detect over a wider range than possible before with high accuracy.SOLUTION: The current sensor comprises: two core members 10; excitation coils 20 connected to a signal source 100 of an excitation signal Iac; an excitation path 30 for supplying the excitation signal Iac to each of the excitation coils 20; detection coils 40 in which a detection signal Ic flows that corresponds to a magnetic flux generated in the core members 10; a differential detection path 50 that connects two detection coils 40 to each other; a component separation unit 60 for separating a signal obtained by going through the differential detection path 50 into a DC signal component and an AC signal component; a current feedback control unit 70 for controlling the signal level of the DC signal component so that the signal level of the AC signal component becomes less than a threshold; and a signal output unit 80 for outputting the signal level of the DC signal component as a signal level that corresponds to a current Im to be detected.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current sensor for detecting a detected current.

  Conventionally, in a current sensor in which an excitation coil and a detection coil are wound around a ring-shaped core member, the signal level detected on the detection coil side changes depending on the signal level of the detected signal that penetrates the ring-shaped region of the core member. For this reason, it is common to specify (detect) the detected current based on the change (see Patent Document 1).

Japanese Patent Laid-Open No. 10-010161

  However, the current sensor configured as described above is configured to distort the sinusoidal magnetic flux generated in the core member by the excitation signal with the detected current and specify the signal level corresponding to the change as the signal level of the detected current. However, since the area where the linearity as a sensor is maintained is near the magnetic saturation area of the core member, the signal level can be detected only in a narrow level range corresponding to that area, and the influence of hysteresis is also present. Therefore, it cannot always be detected accurately.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a current sensor that can detect a level range wider than the conventional one with higher accuracy.

  In order to solve the above problems, as a first aspect (Claim 1), there are two core members that are each formed in a ring shape and arranged so as to flow a current to be detected along a direction penetrating the ring. An excitation coil wound around each of the core members and connected to a signal source of an excitation signal composed of a fundamental component, and a path for supplying the excitation signal supplied from the signal source to each excitation coil, The magnetic flux generated in the core member by the excitation signal is wound around each of the core members and an excitation path connecting the signal source and the excitation coil so that the core members have the same phase or opposite phases. The detection coil in which the detection signal corresponding to the magnetic flux generated in the core member flows, and the detection signal flowing in each of the detection coils cancel the fundamental wave component included in the detection signal. A differential detection path that connects the two detection coils so as to merge in a polarity relationship, and a component separation unit that separates a signal obtained by passing through the differential detection path into a DC signal component and an AC signal component And the signal level of the AC signal component separated by the component separation unit (the combined amount of the excitation signal residual component and the excitation signal harmonic component in the differential detection component of the excitation signal) becomes less than a predetermined threshold value. As described above, the feedback control unit that controls the signal level of the DC signal component separated by the component separation unit, and the signal level of the DC signal component separated by the component separation unit is a signal level corresponding to the detected current. And a signal output unit that outputs as

  The core member has a magnetic permeability that decreases with the external magnetic field “0” as a vertex in accordance with the external magnetic field, and the change of the magnetic permeability μ is shown in the coordinate system of “external magnetic field H−magnetic permeability μ”. When the detected current flows in a state where an excitation signal is flowing in the excitation coil, the curvature of the curve is increased by the absolute value of the external magnetic field. The magnetic permeability is μ corresponding to the external magnetic field generated according to the magnitude, and the harmonic magnetic flux corresponding to the magnetic permeability μ is superposed on the magnetic flux of the fundamental wave component generated by the excitation signal. And the feedback control unit generates a magnetic flux in one of the detection coils by controlling the signal level of the DC signal component separated by the component separation unit, and the magnetic flux is used according to the magnitude of the detected current. Occur outside By offsetting the magnetic field, the signal level of the AC signal component separated by the component separating unit less than the predetermined threshold.

  Further, in order to solve the above-mentioned problem, as a second aspect (Claim 2), two cores that are formed in a ring shape and are arranged so that a current to be detected flows along a direction penetrating the ring are provided. A member, an excitation coil wound around each of the core members and connected to a signal source of an excitation signal composed of a fundamental component, and a path for supplying the excitation signal supplied from the signal source to each excitation coil Yes, the magnetic flux generated in the core member by the excitation signal spans the two core members and the excitation path connecting the signal source and the excitation coil so that the core members are in opposite phases. And a component coil for separating a signal flowing through the detection coil into a DC signal component and an AC signal component. A feedback control unit that controls the signal level of the DC signal component separated by the component separation unit so that the signal level of the AC signal component separated by the component separation unit is less than a predetermined threshold value; A signal output unit that outputs a signal level of the DC signal component separated by the component separation unit as a signal level corresponding to the detected current.

  The core member has a magnetic permeability that decreases with the external magnetic field “0” as a vertex in accordance with the external magnetic field, and the change of the magnetic permeability μ is shown in the coordinate system of “external magnetic field H−magnetic permeability μ”. When the detected current flows in a state where an excitation signal is flowing in the excitation coil, the curvature of the curve is increased by the absolute value of the external magnetic field. The magnetic permeability μ corresponding to the external magnetic field generated according to the signal level is obtained, and the harmonic magnetic flux corresponding to the magnetic permeability μ is superposed on the magnetic flux of the fundamental wave component generated by the excitation signal. And the feedback control unit generates a magnetic flux in one of the detection coils by controlling the signal level of the DC signal component separated by the component separation unit, and the magnetic flux is used according to the magnitude of the detected current. Occur By canceling the external magnetic field, the signal level of the AC signal component separated by the component separating unit less than the predetermined threshold.

  According to the current sensor in the first and second aspects described above, a magnetic flux corresponding to the magnitude of the detected current is superimposed on the core member. However, depending on the characteristics of the core member itself, the external magnetic field H = The magnetic permeability μ decreases with 0 as the apex, and the curvature of the μ-H curve defined by the external magnetic field H and the magnetic permeability μ increases according to the magnitude of the absolute value in the external magnetic field H. This shows the tendency.

  When this tendency is seen in the μ-H coordinate where the magnetic field H is taken on the x-axis and the magnetic permeability μ as the differential value of the magnetization M is taken on the y-axis, along the x-axis at an arbitrary position on the quadratic curve. A harmonic component corresponding to the “bending” of the quadratic curve is superimposed on the output signal from the detection coil whose amplitude changes along the y-axis with respect to the excitation signal whose amplitude changes. Since the amplitude center of the excitation signal is on the quadratic curve, a unique harmonic component corresponding to the magnetic field H is superimposed on the output signal over a wide range from the vicinity of the magnetic field H = 0 to the vicinity of the magnetic field Hs corresponding to the saturation magnetization. The Rukoto.

  That is, in the above aspect, the signal level of the detected signal can be specified (detected) over a wide range from the vicinity of the magnetic field H = 0 to the vicinity of the magnetic field Hs as well as the extremely narrow range near the magnetic field Hs corresponding to the saturation magnetization. it can.

  Furthermore, in the above aspect, the DC signal that cancels out the magnetic flux generated by the detected current is controlled by current feedback of the DC signal component so that the signal level of the AC signal component flowing to the detection coil side is less than the threshold value. The component is specified as corresponding to the magnitude of the detected current.

  Since the AC signal component flowing to the detection coil side is a signal component mainly composed of harmonics generated according to the signal level of the detected signal, setting this below the threshold value means that the detected signal is virtually This means that the DC signal component necessary for the creation of this situation is made to correspond to the signal level of the original signal to be detected while creating a situation where only a small amount is flowing.

  Since the magnetic material used for the core member etc., when the relationship between the magnetic field and the magnetic flux is magnetically saturated according to the magnitude of the magnetic field, it is gradually distorted from a linear proportional relationship and becomes non-linear. Usually, a current sensor having a core member needs to be operated so as not to generate a magnetic field exceeding a region with little distortion in a linear proportional relationship.

  However, if a situation where only a small amount of the signal to be detected flows can be created as in the above aspect, only a small magnetic field corresponding to the signal component corresponding to the difference between the signal to be detected and the DC signal component is generated. Regardless of the signal level of the signal to be detected, it is possible to operate in a region with little distortion with a linear proportional relationship, and thereby the detection accuracy as a current sensor can be made higher than in the past.

Moreover, in the said aspect, it is good to carry out like the following 3rd aspects (Claim 3).
In the second aspect, a filter circuit for removing the fundamental wave component of the excitation signal from the AC signal component separated by the component separation unit, and a level specifying circuit for specifying the signal level in the output signal from the filter circuit, The feedback control unit includes a DC signal separated by the component separation unit so that the signal level specified by the level specifying circuit of the filter unit is less than a predetermined threshold value. Control the signal level of the component.

  According to the current sensor in this aspect, after removing the fundamental wave component of the excitation signal from the AC signal component on the detection coil side, the DC signal component can be feedback-controlled based on the AC signal component.

  Although the fundamental wave component of the signal from the detection coil has been canceled by the previous signal path, if the variation in the characteristics of the core members around which the respective detection coils are wound increases, the fundamental wave component will be sufficient. This is not canceled out, and this may affect the detection accuracy of the current sensor.

  For this, there is no problem if the characteristics of each of the two core members are aligned, but aligning the characteristics of the core members in the individual current sensors can lead to an unintentional cost increase. It is desirable to have a structure that assumes the influence of the above, and from that point of view, the configuration including the filter unit as in the above aspect suppresses an unintended increase in cost, while the fundamental wave component serves as a current sensor. This is suitable for suppressing the influence on the detection accuracy.

  Moreover, the filter part in this 2nd aspect should just be able to remove the fundamental wave component of an excitation signal, and its specific structure is not specifically limited. For example, it is conceivable that the filter unit is configured by a high-pass filter that removes the excitation signal and signal components less than the second harmonic component. Also, the following may be considered.

  For example, the filter unit is a circuit in which the filter circuit synchronously detects the AC signal component separated by the component separation unit with a period twice that of the fundamental wave component in the excitation signal, and the level specifying circuit includes: The output signal of the filter circuit is rectified into a DC signal.

  Further, as in the fourth aspect, the filter unit is a circuit in which the filter circuit synchronously detects the AC signal component separated by the component separation unit at a frequency twice the fundamental frequency of the excitation signal. It is also possible to think.

According to the current sensor in these aspects, the influence of the fundamental wave component on the detection accuracy as the current sensor can be effectively suppressed by synchronous detection rectification.
For the signal output unit described above, the signal level of the DC signal component separated by the component separation unit is output. Specifically, the filter unit and the current feedback control are performed from the AC signal component separated by the component separation unit. The DC voltage generated via the unit is not particularly limited as long as the DC voltage generated can be set to an output proportional to the detected current.

The block diagram which shows the whole structure of the current sensor in 1st Embodiment. The graph which shows the characteristic which a core member has (MH curve prescribed | regulated by the change of the magnetization M with respect to the external magnetic field H) The graph which shows the characteristic which a core member has (MH curve prescribed | regulated by the change of the magnetization M with respect to the external magnetic field H; what expanded the low magnetic field area in FIG. 2A) Graph showing characteristics of core member (μ-H curve defined by external magnetic field H and permeability μ) Graph showing characteristics of core member (μ-H curve defined by external magnetic field H and magnetic permeability μ; expanded low magnetic field region in FIG. 2C) The figure which shows the state by which each coil was wound around the core member (1) The figure which shows the state by which each coil was wound around the core member (2) The figure which shows the state by which each coil was wound around the core member (3) The block diagram which shows the whole structure of the current sensor in 2nd Embodiment. Graph showing the relationship between detected current and detected value (without magnetic balance) Graph showing correspondence between detected current and detected value (Contrast with no magnetic balance and with magnetic balance) Graph showing the relationship between detected current and detected output (when feedback rate is low) Graph showing the relationship between detected current and detected output (when feedback rate is high)

Embodiments of the present invention will be described below with reference to the drawings.
(1) First Embodiment As shown in FIG. 1, a current sensor 1 according to this embodiment includes a sensor element 2 and a detection device 3 that detects the signal level of the detected current Im based on the output from the sensor element 2. And.

  Each of the sensor elements 2 is formed in a ring shape, and is wound around each of the core members 10 and two core members 10 arranged so as to flow the detected current Im along a direction penetrating the ring, The excitation coil 20 connected to the signal source 100 of the excitation signal Iac consisting of the fundamental wave component, the excitation path 30 for supplying the excitation signal Iac supplied from the signal source 100 to each excitation coil 20, and the core member 10 respectively. And a detection coil 40 through which a detection signal Ic corresponding to the magnetic flux generated in the core member 10 flows, and a differential detection path 50 that connects the two detection coils 40 to each other.

  The detection device 3 converts a signal obtained by passing through the differential detection path 50 (a signal flowing through a path not connected to the differential detection path 50 in one detection coil 40) into a DC signal component and an AC signal component. And the signal level of the DC signal component separated by the component separator 60 so that the signal level of the AC signal component separated by the component separator 60 is less than a predetermined threshold. A current feedback control unit 70 to be controlled and a signal output unit 80 that outputs the signal level of the DC signal component separated by the component separation unit 60 as a signal level corresponding to the detected current Im.

  In this detection device 3, first, an AC signal component in a signal flowing through a path not connected to the differential detection path 50 in one detection coil 40 among the detection coils 40 connected in the differential detection path 50. Therefore, the signal level of the DC signal component in the signal flowing through the same path is controlled so that the signal level of the signal component is less than a predetermined threshold value. The magnetic field generated by the detection coil 40 in accordance with the signal level cancels out the external magnetic field generated in accordance with the signal level of the detected current, and the signal level of the DC signal component in the canceled state is set. The signal level corresponding to the detected current is detected.

  As shown in FIGS. 2A and 2B, the core member 10 has a magnetic permeability (expressed as a differential value χi by the magnetic field H of the magnetization M in FIGS. 2A and 2B) with the external magnetic field “0” as a vertex in accordance with the external magnetic field. In addition, the change of the magnetic permeability μ is shown in the coordinate system of “external magnetic field H−magnetic permeability μ”, and the curvature of the curve in the case becomes larger according to the absolute value of the external magnetic field H. Has been. When the detected current Im flows in the state where the excitation signal Iac flows in the excitation coil 20, the core member 10 has a permeability μ corresponding to the external magnetic field generated according to the signal level of the detected current Im. A harmonic magnetic flux corresponding to the magnetic permeability μ is superposed on the magnetic flux of the fundamental wave component generated by the excitation signal Iac.

  As a member constituting the core member 10, for example, as described in Japanese Patent Application No. 2010-215871 by the applicant of the present application, a magnetic member containing superparamagnetic particles having a particle diameter corresponding to a magnetic field environment at the time of use is used. It is possible to adopt. Since this magnetic member does not cause magnetic hysteresis (energy loss defined by the area of the BH curve), it is suitable for maintaining accuracy as a sensor, and of course, the magnetic permeability μ is steep and linear. By using a region near the changing magnetic field H = 0, the change in the permeability μ is relatively gentle, and a wider detection range as a sensor can be obtained with higher accuracy than using a non-linear region. Can be realized.

  The magnetic permeability μ described above depends on the slope of the MH curve (see FIGS. 2C and 2D) defined by the change of the magnetization M with respect to the external magnetic field H (that is, the magnetic field H of the magnetization M, as shown in the following equation 1). This is a value expressed based on the differential value. In the present embodiment, a magnetic member having a relatively small magnetic permeability μ (specifically, one having a magnetic permeability μ = 5) is used as the magnetic member constituting the core member 10.

  The excitation path 30 is a path for supplying the excitation signal Iac supplied from the signal source 100 to each of the excitation coils 20, and the magnetic flux generated in the core member 10 by the excitation signal Iac is in phase between the core members 10. Each of the signal source 100 and the exciting coil 20 is connected so as to be in reverse phase.

  The differential detection path 50 connects the two detection coils 40 so that the detection signals Ic flowing through the detection coils 40 merge with a polarity relationship that cancels out the fundamental wave component included in the detection signals Ic. . The “polarity relationship that cancels the fundamental wave component” here means that when the magnetic flux generated by the excitation signal Iac is in phase between the core members 10 (the signal source 100 and the excitation coil 20 are connected to be in phase). The detection signals Ic flowing in the detection coils 40 are joined in opposite phases, and the magnetic flux generated by the excitation signal Iac is in opposite phases between the core members 10 (reverse). If the signal source 100 and the excitation coil 20 are connected so as to be in phase), the connection state is such that the detection signals Ic flowing through the detection coils 40 merge in the same phase.

  In the present embodiment, the component separation unit 60 includes a capacitor 61 connected in series in a path from the side not connected to the differential detection path 50 to the current feedback control unit 70 in one detection coil 40. Has been. The component separation unit 60 has a path in which the capacitor 61 is connected in series and a path branched upstream of the capacitor 61 (on the detection coil 40 side), and an AC signal component is supplied to the former path. On the other hand, a DC signal component that generates a feedback current proportional to the detected current flows from the latter path.

  Here, the connection relationship of the coils by the excitation path 30 and the differential detection path 50 described above is such that the detection signal Ic flowing in each of the detection coils 40 joins in a polarity relationship that cancels out the fundamental wave component included in the detection signal Ic. It only has to be a relationship that As a specific example, for example, as shown in FIG. 3A, two excitation coils 20 are connected to each other through an excitation path 30 so that the excitation signal Iac flows in opposite phase, and two detection coils 40 are detected respectively. It can be considered that the signal ICs are connected by the differential detection path 50 so that they flow in the same phase. Further, as shown in FIG. 3B, the two excitation coils 20 are connected to each other through the excitation path 30 so that the excitation signal Iac flows in the same phase, and the detection signals IC flow in the opposite phases to the two detection coils 40, respectively. A configuration in which the differential detection path 50 is used for connection is also conceivable.

  In addition, as shown in FIG. 3C, the connection relationship between the coils is that the two excitation coils 20 are connected to each other through the excitation path 30 so that the excitation signal Iac flows in opposite phase, and one detection coil 40 has two cores. The configuration may be such that the member 10 is wound around the member 10. In this case, the detection coil 40 functions as the differential detection path 50. This configuration is highly economical and practical in that it can be configured by a single detection coil 40.

  The current feedback control unit 70 is a DC signal component separated by the component separation unit 60 (a component generated corresponding to the detected current Im, and a component corresponding to a DC voltage among the components input to the component separation unit 60. ) Is controlled, and the external magnetic field generated according to the signal level of the detected current Im is canceled by the magnetic flux generated at the detection coil 40 according to the signal level. In this way, the magnetic permeability μ of the core member 10 is set to the magnetic permeability μ in a state in which the external magnetic field is canceled as described above, and the generation of harmonic magnetic flux according to the magnetic permeability μ is suppressed, so that the separation is performed by the component separation unit 60. The signal level of the AC signal component is set to be lower than a predetermined threshold value. In the present embodiment, the AC signal component is configured such that the signal level of the DC signal component is subjected to current feedback control at a feedback rate described later.

  Here, the current feedback control unit 70 performs control so that the signal level of the DC signal component separated by the component separation unit 60 increases in order to cancel the external magnetic field having a polarity corresponding to the polarity of the detected current Im. In some cases, it may be controlled in the direction of decreasing. Therefore, the polarity of the detected current Im can be indirectly specified by checking the direction of this control on the output terminal 71 side.

  In this configuration, current feedback control is performed from the DC signal component in the output signal from the detection coil 40, and a dedicated coil for feedback control is not required. This is because the magnetic permeability μ of the member forming the core member 10 is extremely small, so that the signal level of the harmonic component superimposed on the output signal from the detection coil 40 does not affect the operation of the entire sensor. Because it is made small.

  The signal output unit 80 may be configured to output a signal level corresponding to the detected current Im. For example, an element is provided in a path separated from the component separation unit 60, and a signal flowing through the element is detected. It may be configured to output as a signal level corresponding to the current Im, or to be configured to include a current sensor that detects a current value itself flowing through a path separated from the component separation unit 60. In the present embodiment, a resistor 81 connected in series is provided in the path through which the DC signal component separated by the component separation unit 60 flows, and the voltage value Vc generated at both ends of the resistor 81 corresponds to the detected current Iac. The signal is output as a signal level.

The DC signal component flowing through the path separated from the component separation unit 60 is a signal component having a polarity corresponding to the polarity of the detected current Im by the feedback control of the current feedback control unit 70. By checking the polarity of the component on the output terminal 83 side, the signal level corresponding to the detected current Im can be specified together with the polarity.
(2) Second Embodiment As shown in FIG. 4, the current sensor 1 according to the present embodiment has a predetermined value from the AC signal component separated by the component separation unit 60 in addition to the current sensor 1 according to the first embodiment. A filter unit 90 for removing signal components is provided.

  The filter unit 90 removes the fundamental wave component (excitation frequency component) of the excitation signal Iac from the AC signal component separated by the component separation unit 60, and specifies the signal level in the output signal of the filter circuit 91. A level specifying circuit 93.

  The current feedback control unit 70 performs feedback based on the signal level from the DC signal component separated by the component separation unit 60 so that the signal level specified by the level specifying circuit 93 of the filter unit 90 is less than a predetermined threshold value. Will be controlled.

  The filter unit 90 is a circuit in which the filter circuit 91 synchronously detects the AC signal component separated by the component separation unit 60 at a frequency twice the fundamental frequency of the excitation signal Iac, and the level specifying circuit 93 is a filter circuit. The output signal 91 is rectified into a DC signal.

  The filter circuit 91 only needs to remove the fundamental wave component of the excitation signal Iac, and the specific configuration thereof is not particularly limited, and the AC signal component separated by the component separation unit 60 is converted to the fundamental frequency of the excitation signal Iac. Alternatively, it may be configured by a high-pass filter that can remove components less than twice the frequency, or a circuit that performs synchronous detection at a period twice the fundamental frequency.

The level specifying circuit 93 only needs to rectify the output signal of the filter circuit 91 into a DC signal, and may be configured as a known rectifier circuit. Since the level specifying circuit 93 outputs a DC signal with a polarity corresponding to the polarity of the output signal from the filter circuit 91, the level detection circuit 93 checks the polarity of the DC signal on the output terminal 95 side, thereby detecting the detected signal. It is also possible to specify the signal level corresponding to the current Im as well as the polarity.
(3) Experiment and result (3-1) Presence / absence of magnetic equilibrium In the above embodiment, the current feedback control unit 70 has the signal level of the AC signal component separated by the component separation unit 60 less than a predetermined threshold value. Thus, feedback control is performed based on the signal level from the DC signal component separated by the component separation unit 60.

  In the configuration of the second embodiment, the applicant of the present application is to confirm how much the detected current Im and the detected value Ic by the signal output unit 80 are improved by the presence or absence of magnetic balance by such control. The detection performance was measured when current feedback control was not performed (without magnetic balance) and when feedback control was performed (with magnetic balance).

  In actual performance measurement, the core member 10 has a magnetic material containing superparamagnetic particles having a particle size corresponding to the excitation signal (a particle size determined so that the Neel relaxation time τn is shorter than the period T of the excitation signal). Using a material formed in a ring shape, the number of turns of the excitation coil 20 is 250, the number of turns of the detection coil 40 is 1000, the time constant C of the level specifying circuit 93 in the filter unit 90 is 1 μF, the drive power is ± 12 V, the excitation The parameters of the signal Iac = 100 mA (pp), the resistance value Rs = 200Ω of the resistor 81 in the signal output unit 80, and the gain of the amplifier provided in the current feedback control unit 70 = 4.3 are set. By measuring the detected value Ic (converting the output from the signal output unit into a current value) for each current value while changing Im from -100A to + 100A in increments of 10A. Carried out.

  As a result of this performance measurement, when feedback control is not carried out, as shown in FIG. 5A, linearity deteriorates in a region smaller than −40 A and larger than +40 A, and accurate current detection cannot be performed. When the feedback control is performed, as shown in FIG. 5B, high linearity is maintained over the entire range of ± 100 A, and it can be seen that the detection accuracy is improved.

In the above-described embodiment, a configuration is employed in which feedback control by the current feedback control unit 70 is performed based on such experimental results.
(3-2) High and Low Feedback Rate The applicant of the present application determines how much the signal level of the DC signal component controlled by the current feedback control unit 70 of the above embodiment is relative to the signal level of the detected current Im. In order to confirm whether it should be a size (feedback rate), in the configuration of the second embodiment, the detection performance was measured when the feedback rate was different.

  This feedback rate is obtained when the voltage value when the feedback control is not performed is Vc ′ and the voltage value when the feedback control is performed is Vc for the signal level of the DC signal component output from the current feedback control unit 70. Is defined by the formula “1-Vc / Vc ′”.

  In actual performance measurement, as a condition different from the above (3-1), the resistance value Rs of the resistor 81 in the signal output unit 80 is either 68Ω to 100Ω, or the gain of the amplifier provided in the current feedback control unit 70 = 25, and the detected current Im was changed from −100 A to +100 A in increments of 10 A. Specific feedback rates include 63.0% (Rs = 68Ω), 63.5% (Rs = 100Ω), 63.6% (Rs = 82Ω), 68.7% (Rs = 68Ω), 74. 6% (Rs = 100Ω), 82.6% (Rs = 100Ω), 85.0% (Rs = 68Ω), and 85.8% (Rs = 100Ω) are set and detected for each. It was checked as detection performance whether the linearity between the signal Im and the detection output Vc was deteriorated.

63.0%: Low linearity over the entire area ... Evaluation ×
・ 63.5%: Linearity deteriorates in high current region (60A or more)… Evaluation △
・ 63.6%: Linearity deteriorates in high current region (60A or more)… Evaluation △
・ 68.7%: Low linearity over the entire area… Evaluation ×
・ 74.6%: Linearity deteriorates in high current region (90A or more)… Evaluation ◎
82.6%: Linearity deteriorates in high current region (80 A or more) ... Evaluation
85.0%: Linearity deteriorates in high current region (100A) ... Evaluation
・ 85.8%: Linearity deteriorates in high current region (90A or more)… Evaluation ◎
As a result of this performance measurement, the linearity between the detected signal Im and the detection output Vc is particularly large when the feedback rate is as low as less than 70% under the above conditions as compared with the case where the feedback rate is as high as more than 70%. It can be seen that deterioration tends to occur in a large area. A case where the feedback rate is 63.0% is shown in FIG. 6A as a case of a low feedback rate, and a case where the feedback rate is 85.0% is shown in FIG. 6B as a case of a high feedback rate.

In the above-described embodiment, a configuration in which each parameter is adjusted based on such experimental results so that the feedback rate by the current feedback control unit 70 is as high as 70% or more (the AC signal component is less than 70%). Is adopted.
(4) Action and Effect According to the current sensors 1 and 2 described above, the core member 10 generates a magnetic flux corresponding to the signal level of the detected signal Im in a superimposed manner, but depending on the characteristics of the core member 10 itself, The magnetic permeability μ decreases with the external magnetic field H = 0 as the apex, and the curvature of the μ-H curve defined by the external magnetic field H and the magnetic permeability μ increases according to the absolute value of the external magnetic field H. It shows a tendency to become.

  When this tendency is seen in the μ-H coordinate where the magnetic field H is taken on the x-axis and the magnetic permeability μ as the differential value of the magnetization M is taken on the y-axis, along the x-axis at an arbitrary position on the quadratic curve. A harmonic component corresponding to the “curvature” of the quadratic curve is superimposed on the output signal from the detection coil 40 whose amplitude changes along the y-axis with respect to the excitation signal whose amplitude changes. Since the amplitude center of the excitation signal is on the quadratic curve, a unique harmonic component corresponding to the magnetic field H is superimposed on the output signal over a wide range from the vicinity of the magnetic field H = 0 to the vicinity of the magnetic field Hs corresponding to the saturation magnetization. Will be.

  That is, in the above configuration, the signal level of the detected signal Im is specified (detected) not only in the extremely narrow range near the magnetic field Hs corresponding to the saturation magnetization but also in the wide range from the magnetic field H = 0 to the magnetic field Hs. Can do.

  Further, in the above configuration, the current signal is controlled by the DC signal component so that the signal level of the AC signal component flowing on the detection coil 40 side is less than the threshold value, whereby this AC signal component (differential detection of the excitation signal) is performed. The DC signal component that cancels out the harmonic component of the component or the magnetic flux generated by the detected current) is specified as corresponding to the signal level of the detected signal.

  The AC signal component flowing to the detection coil 40 side is a signal component mainly composed of harmonics generated according to the signal level of the detected signal. It means that while creating a situation where only a small amount of the current flows virtually, the DC signal component necessary for the creation of this situation corresponds to the signal level of the original detected signal.

  The magnetic material used for the core member 10 and the like is gradually distorted from a linear proportional relationship and becomes non-linear when the relationship between the magnetic field and the magnetic flux is magnetically saturated according to the magnitude of the magnetic field. Usually, the current sensor having the core member 10 needs to be operated so as not to generate a magnetic field exceeding a region with little distortion in a linear proportional relationship.

  However, if a situation in which the signal to be detected flows only slightly as in the above configuration can be created, only a small magnetic field corresponding to the signal component corresponding to the difference between the signal to be detected Im and the DC signal component is generated. Therefore, regardless of the signal level of the signal to be detected, it is possible to operate in a region with little distortion with a linear proportional relationship, and thereby, the detection accuracy as a current sensor can be made higher than in the past.

  In the current sensor 2 according to the second embodiment, the fundamental wave component of the excitation signal is removed from the AC signal component on the detection coil 40 side, and the DC signal component is fed back based on the AC signal component. Can be controlled.

  Although the fundamental wave component of the signal from the detection coil 40 is canceled by the signal path 50 until then, when the variation in the characteristics of the core members 10 around which the detection coils 40 are wound increases, The components are not sufficiently canceled out, and this may affect the detection accuracy of the current sensors 1 and 2.

  For this, although there is no problem if the characteristics of the two core members 10 are aligned, it is possible to unintentionally increase the cost of aligning the characteristics of the core members 10 in individual current sensors. In view of this, it is desirable that the structure including the filter unit 90 as in the above configuration suppresses an unintended increase in cost, while the fundamental component is a current. It is suitable for suppressing the influence on the detection accuracy as a sensor.

  Further, according to the current sensor 2 according to the second embodiment, the filter circuit 91 synchronously detects the AC signal component separated by the component separation unit 60 at a frequency twice that of the fundamental wave component in the excitation signal Iac. The level specifying circuit 93 rectifies the output signal of the filter circuit 91 into a DC signal. Thereby, the influence of the fundamental wave component on the detection accuracy as the current sensor 2 can be effectively suppressed.

Further, according to the above embodiment, the voltage value generated at both ends of the resistor 81 by the DC signal component can be specified as the signal level corresponding to the detected current Im.
(5) Modification The current sensor 1 includes a sensor element 2 that outputs a signal including a harmonic component corresponding to the signal level of the current to be detected, and a harmonic component included in the signal output from the sensor element 2. Accordingly, the detection device 3 detects the signal level of the current to be detected, and in the above embodiment, the sensor element 2 that extracts and outputs the harmonic component, and the detection from the harmonic component. The case where it consists of the detection apparatus 3 which can detect the signal level of an electric current is illustrated.

  However, a case where the current sensor 1 includes a sensor element 2 that outputs a signal itself including a harmonic component and a detection device 3 that can detect the signal level of the detected current from the output signal is considered. You can also. In this case, the sensor element 2 outputs the detection signal flowing through each of the detection coils 40 without canceling the fundamental wave component, and the detection device 3 analyzes or extracts the component of the signal output in this way and generates a higher harmonic. A configuration in which the wave level is specified and the signal level of the detected current is detected can be considered.

  Here, “to output without canceling the fundamental wave component” of the sensor element 2 means that the detection signals Ic flowing through the detection coils 40 are output without being merged, or the detection flows through the detection coils 40, respectively. The signal Ic is combined and output so as not to have a “polarity relationship that cancels the fundamental wave component”. Also, “detecting or extracting the component of the output signal and identifying the harmonic component” of the detection device 3 means, for example, that the detection signal from each of the detection coils 40 of the sensor element 2 is a differential detection path. The harmonic component is specified by a method of analyzing the frequency distribution in the output signal from the sensor element 2 through a circuit to be merged as in the case of 50.

  DESCRIPTION OF SYMBOLS 1 ... Current sensor, 2 ... Sensor element, 3 ... Detection apparatus, 10 ... Core member, 20 ... Excitation coil, 30 ... Excitation path, 40 ... Detection coil, 50 ... Differential detection path, 60 ... Component separation part, 61 ... Capacitor 70 ... Current feedback control unit 80 ... Signal output unit 81 ... Resistor 90 ... Filter unit 91 ... Filter circuit 93 ... Level specifying circuit 100 ... Signal source

Claims (4)

Two core members which are each formed in a ring shape and are arranged so as to flow a current to be detected along a direction penetrating the ring;
An excitation coil wound around each of the core members and connected to a signal source of an excitation signal composed of a fundamental wave component;
A path for supplying an excitation signal supplied from the signal source to each of the excitation coils, and the magnetic flux generated in the core member by the excitation signal is in phase or in phase between the core members. An excitation path connecting the signal source and each of the excitation coils;
A detection coil wound around each of the core members and through which a detection signal corresponding to the magnetic flux generated in the core member flows;
A differential detection path for connecting the two detection coils, and the differential detection path so that detection signals flowing through the detection coils merge with a polarity relationship that cancels out the fundamental wave component included in the detection signal; A component separation unit that separates a signal obtained by going through a DC signal component and an AC signal component;
A feedback control unit that controls the signal level of the DC signal component separated by the component separation unit so that the signal level of the AC signal component separated by the component separation unit is less than a predetermined threshold;
A signal output unit that outputs a signal level of the DC signal component separated by the component separation unit as a signal level corresponding to the detected current;
The core member has a magnetic permeability that decreases with the external magnetic field “0” at the apex in accordance with the external magnetic field, and a curve when the change of the magnetic permeability μ is shown in the coordinate system of “external magnetic field H−magnetic permeability μ”. When the detected current flows in a state where the excitation signal is flowing through the excitation coil, the signal level of the detected current is formed by a member having a characteristic that the curvature of the current increases in accordance with the absolute value of the external magnetic field. And a magnetic flux μ corresponding to an external magnetic field generated in response to the magnetic field, and a harmonic magnetic flux corresponding to the magnetic permeability μ is superimposed on the magnetic flux of the fundamental wave component generated by the excitation signal.
The feedback control unit generates a magnetic flux in one of the detection coils by controlling the signal level of the DC signal component separated by the component separation unit, and the magnetic flux is generated according to the magnitude of the detected current. A current sensor, wherein the signal level of the AC signal component separated by the component separation unit is made less than a predetermined threshold value by canceling out the external magnetic field. Two core members which are each formed in a ring shape and are arranged so as to flow a current to be detected along a direction penetrating the ring;
An excitation coil wound around each of the core members and connected to a signal source of an excitation signal composed of a fundamental wave component;
A path for supplying an excitation signal supplied from the signal source to each of the excitation coils, and the signal source so that a magnetic flux generated in the core member by the excitation signal is in reverse phase between the core members; And an excitation path for connecting each of the excitation coils,
A detection coil wound so as to straddle the two core members, and a detection signal corresponding to the magnetic flux generated in the core member flows;
A component separator that separates a signal flowing through the detection coil into a DC signal component and an AC signal component;
A feedback control unit that controls the signal level of the DC signal component separated by the component separation unit so that the signal level of the AC signal component separated by the component separation unit is less than a predetermined threshold;
A signal output unit that outputs a signal level of the DC signal component separated by the component separation unit as a signal level corresponding to the detected current;
The core member has a magnetic permeability that decreases with the external magnetic field “0” at the apex in accordance with the external magnetic field, and a curve when the change of the magnetic permeability μ is shown in the coordinate system of “external magnetic field H−magnetic permeability μ”. When the detected current flows in a state where the excitation signal is flowing through the excitation coil, the signal level of the detected current is formed by a member having a characteristic that the curvature of the current increases in accordance with the absolute value of the external magnetic field. And a magnetic flux μ corresponding to an external magnetic field generated in response to the magnetic field, and a harmonic magnetic flux corresponding to the magnetic permeability μ is superimposed on the magnetic flux of the fundamental wave component generated by the excitation signal.
The feedback control unit generates a magnetic flux in one of the detection coils by controlling the signal level of the DC signal component separated by the component separation unit, and the magnetic flux is generated according to the magnitude of the detected current. A current sensor, wherein the signal level of the AC signal component separated by the component separation unit is made less than a predetermined threshold value by canceling out the external magnetic field. A filter circuit comprising: a filter circuit for removing the fundamental wave component of the excitation signal from the AC signal component separated by the component separation unit; and a level specifying circuit for specifying a signal level in an output signal from the filter circuit. And
The feedback control unit controls the signal level of the DC signal component separated by the component separation unit so that the signal level specified by the level specifying circuit of the filter unit is less than a predetermined threshold value. The current sensor according to claim 1, wherein the current sensor is a current sensor. The filter unit is a circuit in which the filter circuit synchronously detects the AC signal component separated by the component separation unit at a frequency twice the fundamental frequency of the excitation signal, and the level specifying circuit includes the filter The current sensor according to claim 3, wherein the output signal of the circuit is rectified into a DC signal.