CN111183362A

CN111183362A - Current detector

Info

Publication number: CN111183362A
Application number: CN201880065486.3A
Authority: CN
Inventors: 冈山祐辅
Original assignee: Tamura Corp
Current assignee: Tamura Corp
Priority date: 2017-10-12
Filing date: 2018-10-11
Publication date: 2020-05-19
Anticipated expiration: 2038-10-11
Also published as: JP2019074341A; WO2019074062A1; JP6605007B2; CN111183362B

Abstract

The magnetic flux density passing through the magnetic core is increased, and the arrangement of the detection coil is optimized according to the structure of the magnetic core. A current sensor (10) is provided with: a plurality of magnetic core members (22, 23) in which plate-like long legs (22b, 23b) overlap each other in the thickness direction at positions along one long side, and plate-like upper short legs (22c, 23c) and lower short legs (22d, 23d) are stacked so as to face each other at positions along the other long side with a gap therebetween; a detection coil unit (50) arranged at a position along the other long side on the magnetic path; a secondary winding (60a, 70a) that causes the magnetic circuit to generate a magnetic field in a direction opposite to a magnetic field generated by the current to be detected; a detection circuit for outputting a detection signal corresponding to the detected current based on a secondary current required to cancel the output current of the detection coil; and a primary conductor (30) that forms a flow path that extends through the inside of the magnetic circuit and surrounds the outside of the search coil.

Description

Current detector

Technical Field

The present invention relates to a fluxgate-type current detector.

Background

As for such a current detector, conventionally, there is known a current sensor of the related art: a magnetic core constituting a magnetic circuit is formed of two plate-like members obtained by bending, and two bent portions are arranged to face each other from both sides with a gap (air gap) therebetween (see, for example, patent document 1). The two plate-like members are a pair of substantially 3-shaped members formed by integrally connecting two plate-like members each bent in a substantially コ -shape, and the bent portions are formed at portions where the portions bent in a substantially コ -shape are connected.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5926911

Disclosure of Invention

Problems to be solved by the invention

The above-described conventional technique is useful in that the structure is simple and the manufacturing cost can be reduced because the magnetic core can be formed by only two plate-like members.

However, since the current sensor of the related art is formed by bending the magnetic core in the thickness direction, the cross-sectional area viewed in the direction of passage of the magnetic flux is small, and the magnetic flux density cannot be made too large.

Further, although the current sensor of the related art is configured such that the search coil is disposed on the opposite side of the mounting surface (the upper side when the lower surface is the mounting surface), it is unknown whether the arrangement is optimal or not when the structure of the magnetic core is changed.

Accordingly, the present invention provides a technique for improving the magnetic flux density passing through the magnetic core and optimizing the arrangement of the search coil according to the structure of the magnetic core.

Means for solving the problems

In order to solve the above problems, the present invention adopts the following solving means.

The invention provides a current detector. A current detector of the present invention has a structure in which a plurality of plate-like magnetic core members are stacked in a direction in which a detected current flows. The current detector of the present invention employs a primary conductor extending through the inside of the magnetic circuit and surrounding the outside of the search coil.

The magnetic core member constitutes a rectangular magnetic circuit that converges a magnetic field generated by the flow of a current to be detected. In this case, in the magnetic core member, the plate-like long legs extending to face each other are overlapped with each other in the thickness direction at a position along one long side of the magnetic circuit, and the plate-like short legs extending to face each other are laminated in the flowing direction of the detected current (transverse direction of the magnetic circuit) with gaps at the ends thereof at a position along the other long side. In this way, in a state where a plurality of magnetic core members are stacked, the cross-sectional area when viewed in the transverse direction of the magnetic path can be increased by the number of stacked pieces, and therefore the magnetic flux density passing therethrough can be increased. The primary conductor is disposed so as to surround the outside of the search coil, and can be disposed optimally with respect to a configuration in which a plurality of magnetic core members are stacked.

Preferably, the magnetic core member is arranged around the detection coil except for the inside of the magnetic circuit so as to open the detection coil without shielding the space between the primary conductor and the detection coil. This can further improve optimization of the arrangement of the structure in which the plurality of magnetic core members are stacked.

Effects of the invention

According to the present invention, the magnetic flux density passing through the magnetic core can be increased, and the arrangement of the search coil can be optimized according to the structure of the magnetic core.

Drawings

Fig. 1 is a perspective view schematically showing the structure of a current sensor according to an embodiment.

Fig. 2 is a front view schematically showing the structure of a current sensor according to one embodiment.

Fig. 3 is an exploded perspective view showing the structure of the magnetic core.

Fig. 4 is a longitudinal sectional view (a sectional view taken along line IV-IV in fig. 2) of the current sensor.

Fig. 5 is a perspective view of the magnetic core shown in fig. 4.

Fig. 6 is a block diagram schematically showing a circuit configuration of the current sensor.

Fig. 7 is a perspective view schematically showing the structure of a current sensor as a comparative example.

Fig. 8 is a waveform diagram showing the response characteristic of the output voltage obtained when the detected current changes stepwise by the current sensor according to the present embodiment.

Fig. 9 is a waveform diagram showing response characteristics of an output voltage obtained when a detected current changes stepwise in a current sensor of a comparative example.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, a fluxgate current sensor is given as an example of the current detector, but the present invention is not limited thereto.

Fig. 1 is a perspective view schematically showing the structure of a current sensor 10 according to an embodiment. Fig. 2 is a front view schematically showing the structure of the current sensor 10 according to one embodiment.

[ magnetic Circuit ]

The current sensor 10 includes a magnetic core 20, and the magnetic core 20 forms a rectangular magnetic path extending in a direction perpendicular to a penetration direction (horizontal direction in fig. 1) of a current to be detected. The magnetic core 20 is formed by stacking (laminating in the penetrating direction of the detected current) a plurality of plate-shaped

magnetic core members

22 and 23, and the

magnetic core members

22 and 23 have a shape symmetrical with each other in pairs. The

magnetic core members

22 and 23 will be described later with reference to other drawings.

[ Secondary winding ]

The current sensor 10 includes two

bobbin units

60, 70, and each

bobbin unit

60, 70 houses a magnetic core 20 (magnetic core members 22, 23) inside and holds a

secondary winding

60a, 70a outside. In the state shown in fig. 1 and 2, one bobbin unit 60 is positioned above, and the other bobbin unit 70 is positioned below. Although not shown, each

bobbin unit

60, 70 may have a plurality of lead terminals in addition to the secondary windings 30a, 40a described above. The current sensor 10 can be mounted on a circuit board or connected to other electronic devices via these lead terminals. In addition to the

bobbin units

60 and 70, a bobbin unit not shown may be disposed.

[ search coil (field Probe) ]

As shown in fig. 2 (omitted in fig. 1), the current sensor 10 includes a search coil unit 50, and the search coil unit 50 is housed inside a lower bobbin unit 70. More specifically, the two

magnetic core members

22 and 23 form a housing portion (no reference numeral) inside the bobbin unit 70, and the detection coil unit 50 is housed inside the bobbin unit 70 in a state of being disposed inside the housing portion. The search coil unit 50 includes a search coil (field probe), not shown, and the search coil is disposed on the magnetic circuit (in the air gap of the magnetic core 20) in the assembled state of the current sensor 10. The search coil unit 50 may further include a plurality of lead terminals, not shown, and may be connected to the search coil through the lead terminals.

The current sensor 10 includes a housing 40 made of, for example, resin, and the magnetic core 20, the

bobbin units

60 and 70, the detection coil unit 50, and the like are housed inside the housing 40. The housing 40 has a through path (or a through hole), not shown, on the inner side of the magnetic circuit (the inner periphery of the magnetic core 20), through which a current to be detected can pass.

[ Primary conductor ]

The current sensor 10 includes, for example, two primary conductors 30. These primary conductors 30 are disposed so as to penetrate the inside of the magnetic circuit, and when the current sensor 10 is used, the detected current passes through both primary conductors 30. In the state shown in fig. 1 and 2, the magnetic circuit is in an upright posture, and therefore the two primary conductors 30 penetrate the inside of the magnetic circuit in the horizontal direction. The primary conductors 30 are bent in one direction (downward in fig. 1 and 2) on both sides of the through magnetic path, and have both ends extending in the same direction, and are formed in an inverted U shape as a whole. When a current is detected, the primary conductor 30 forms a flow path extending through the inside of the magnetic circuit and surrounding the outside of the search coil unit 50. The two primary conductors 30 are arranged inside the magnetic circuit in a state of being supported by the frame 40, a holding groove communicating with the through path is formed in the frame 40, and both bent end portions of the primary conductor 30 are held in the holding groove. The number of primary conductors 30 is not limited to two, and may be one or three or more.

[ detection Circuit ]

A circuit board (not shown) is connected to the search coil unit 50, and a signal output IC (also not shown) is mounted on the circuit board. When the current sensor 10 is used, the following control is performed: when a magnetic field is generated around the primary conductor 30 (magnetic circuit) by the flow of the current to be detected, the signal output IC outputs a secondary current (feedback current) to the

secondary coils

60a and 70a to generate a magnetic field in the opposite direction, and the output current of the detection coil is eliminated. At this time, the signal output IC converts the secondary current into a voltage signal by the shunt resistor, and outputs the voltage signal as a detection signal corresponding to the detected current.

Fig. 3 is an exploded perspective view showing the structure of the magnetic core 20. As described above, the magnetic core 20 is formed by stacking a plurality of plate-like

magnetic core members

22 and 23. In this example, the

magnetic core members

22 and 23 are alternately stacked with a predetermined number of pieces (for example, 6 pieces).

The

magnetic core members

22 and 23 are made of a high-permeability material such as permalloy. The

magnetic core members

22 and 23 are symmetrical with respect to a center line when viewed in the longitudinal direction of the rectangular magnetic path, and the

magnetic core members

22 and 23 have

short side portions

22a and 23a, respectively, at positions along short sides on both sides of the magnetic path. The

magnetic core members

22 and 23 have

long leg portions

22b and 23b at positions along one (upper) long side of the magnetic circuit, and the

long leg portions

22b and 23b extend from the upper ends of the

short side portions

22a and 23a in the longitudinal direction so as to face each other, and are alternately arranged so as to overlap substantially the entire region in the longitudinal direction. The magnetic core member 22 has upper

short leg portions

22c, 23c and lower

short leg portions

22d, 23d, respectively, at positions along the other (here, lower) long side of the magnetic circuit, wherein the lower

short leg portions

22d, 23d extend from the lower ends of the

short side portions

22a, 23a, respectively, so as to be opposed to each other in the longitudinal direction. The upper

short leg portions

22c, 23c extend from the

short side portions

22a, 23a at positions spaced upward from the lower

short leg portions

22d, 23, respectively, so as to face each other in the longitudinal direction.

Here, the upper

short leg portions

22c and 23c and the lower

short leg portions

22d and 23d are not alternately overlapped but are oppositely disposed in the longitudinal direction. Therefore, in the assembled state of the magnetic core 20, the upper

short legs

22c, 23c and the lower

short legs

22d, 23d are connected to each other in a magnetic path in an opposed manner. At this time,

upper contact portions

22e and 23e are formed in the upper

short leg portions

22c and 23c, respectively, and

lower contact portions

22f and 23f are formed in the lower

short leg portions

22d and 23d, respectively (see fig. 4). These

upper contact portions

22e and 23e and

lower contact portions

22f and 23f are in contact with each other in a combined state or are close to each other with a slight gap (for example, about 0.1 mm). This can provide gaps (air gaps) between the upper

short leg portions

22c and 23c and between the lower

short leg portions

22d and 23d, and can increase the magnetic flux density at the

upper contact portions

22e and 23e and the

lower contact portions

22f and 23 f.

Fig. 4 is a longitudinal sectional view (a sectional view taken along line IV-IV in fig. 2) of the current sensor 10. Fig. 5 is a perspective view of the magnetic core 22 shown in fig. 4. As described above, in the assembled state of the magnetic core 20, the

long legs

22b and 23b of the

magnetic core members

22 and 23 overlap each other at the position along the long side above the magnetic path to be dense, and therefore the magnetic path has a relatively large cross-sectional area. At the position along the long side below the magnetic path, the upper

short leg portions

22c and 23c and the lower

short leg portions

22d and 23d are opposed to each other, but are not in contact except for the

upper contact portions

22e and 23e and the

lower contact portions

22f and 23f, and a gap (air gap) is formed. By disposing the search coil unit 50 between the

upper contact portions

22e and 23e and the

lower contact portions

22f and 23f, the magnetic flux leaking out to the gap passes through the search coil unit 50.

As is apparent from fig. 4, the primary conductor 30 penetrates the inside of the magnetic circuit, and forms a flow path extending so as to surround the outside of the search coil unit 50 as described above.

The

magnetic core members

22 and 23 do not surround the search coil unit 50 except for the upper

short leg portions

22c and 23c and the lower

short leg portions

22d and 23d, and the space between the search coil unit 50 and the primary conductor 30 is not shielded, and the space between the search coil unit 50 and the primary conductor 30 is opened to the surroundings. This can optimize the arrangement of the search coil unit 50 with respect to the

magnetic core members

22 and 23.

[ Circuit Structure of Current sensor ]

Fig. 6 is a block diagram schematically showing the circuit configuration of the current sensor 10. The detection coil 50a is connected to a signal output IC80, and a pulse power supply circuit, not shown, is incorporated in the signal output IC 80. The detection coil 50a is wound around the fluxgate core 50c, and when a high-frequency rectangular wave current is supplied from the pulse power supply circuit to the detection coil 50a, the magnetic flux density in the fluxgate core 50c is periodically saturated. Therefore, when a magnetic field is generated in the magnetic circuit (magnetic core 20) by the detected current Ip flowing through the primary conductor 30, the waveform of the voltage applied to the search coil 50a is deformed by the magnetic field generated in the magnetic circuit.

The signal output IC80 incorporates an interface circuit 84, and the interface circuit 84 converts the voltage between the detection coils 50a into a PWM signal. The PWM signal output from the interface circuit 84 is a pulse signal having a predetermined duty ratio (for example, 50%) in a state where no magnetic field is generated in the fluxgate core 50c (a non-flowing state of the detected current Ip). The duty ratio of the PWM signal varies according to the intensity of the magnetic field applied to the fluxgate core 50 c.

The signal output IC80 incorporates a filter 86 and a drive circuit 88, and the filter 86 performs analog conversion of the PWM signal from the interface circuit 84 and outputs the converted output voltage to the drive circuit 88. The

secondary windings

60a, 70a are connected to the drive circuit 88 via two terminals Ic1, Ic 2. The drive circuit 88 detects a difference between the output voltage from the filter circuit 86 and a predetermined reference voltage Vref, and outputs a secondary current having a magnitude based on the difference to the

secondary coils

60a and 70 a. The following control is performed: by generating a feedback magnetic field by the secondary current, the magnetic field in the magnetic circuit induced by the detected current Ip flowing through the primary conductor 30 is cancelled, and the output current of the detection coil 50a is eliminated.

The current sensor 10 extracts an output voltage Vout obtained by detecting the secondary current by the shunt resistor Rs, and outputs a detection signal corresponding to the detected current Ip. Although the secondary currents flowing through the

secondary coils

60a and 70a periodically change due to the negative feedback, the waveform of the output voltage Vout substantially matches the waveform of the detected current Ip by signal processing using the differential amplifier circuit 89 in the signal output IC80, and therefore, the output voltage Vout substantially has a value correlated with the magnitude of the detected current Ip.

[ Excellent Property verification ]

The superiority of the current sensor 10 of the present embodiment as described above was verified by comparison with a comparative example.

[ comparative example ]

Fig. 7 is a perspective view schematically showing the structure of a current sensor 200 as a comparative example. The current sensor 200 in the comparative example is different from the present embodiment in that the primary conductor 30 is bent in the direction opposite to the detection coil unit 50, in other words, the primary conductor 30 is in the following positional relationship with respect to the current sensor 10 shown in fig. 1: the magnetic core 20 and its attachments are rotated by half a turn in the circumferential direction of the magnetic circuit as a whole. Other configurations are common to the present embodiment, and the same reference numerals are given to such common configurations, including the drawings, and redundant description is omitted.

[ step response characteristics ]

Fig. 8 is a waveform diagram showing response characteristics of the output voltage Vout obtained when the detected current Ip changes stepwise in the current sensor 10 according to the present embodiment. In contrast, fig. 9 is a waveform diagram showing the response characteristic of the output voltage Vout obtained when the detected current Ip changes stepwise in the current sensor 200 of the comparative example. The advantages of the present embodiment will be described below in detail in comparison with comparative examples.

[ present embodiment ]

Fig. 8 (a): at a certain time t1, the waveform of the detected current Ip changes (rises) stepwise. Such a stepped waveform change may occur, for example, when the target device to which the current sensor 10 is applied is started (or outputs a PWM current) by turning on the power supply, and the detected current Ip abruptly rises.

[ comparative example ]

Fig. 9 (a): in the comparative example, the waveform of the detected current Ip also changes stepwise under the same conditions as in the present embodiment.

[ present embodiment ]

In fig. 8 (B): in the case of the present embodiment, the waveform of the output voltage Vout of the current sensor 10 also responds in a step from time t 1. In addition, it can be confirmed that immediately after time t1, although a temporary fluctuation is seen in the response waveform, a stable step response waveform appears as a whole.

[ comparative example ]

Fig. 9 (B): in contrast, in the comparative example, even if the waveform of the output voltage Vout changes from time t1, the step response characteristic as in the present embodiment is not shown, but the waveform of the quick praying becomes disturbed.

[ Observation of voltages between terminals Ic1-Ic2 ]

The inventors of the present invention conducted the following verification with attention paid to the fact that the change in the voltage between the terminals Ic1-Ic2 is related to the change in the output voltage Vout in the circuit configuration shown in fig. 6.

[ present embodiment ]

(C) in fig. 8: that is, in the present embodiment, when the detected current Ip changes stepwise at time t1, the waveform of the voltage between the terminals Ic1-Ic2 rises in a short time following this, and thereafter, the voltage between the terminals Ic1-Ic2 is maintained for a long period Tf until time t 2. Further, after time t2, the change in the voltage between the terminals of Ic1-Ic2 also becomes gentle.

[ comparative example ]

(C) in fig. 9: in the comparative example, the voltage between the terminals Ic1-Ic2 temporarily changes to fall, contrary to the rise of the detected current Ip at the time t1, and rises after a lapse of time from the time, but it is understood that the period Tf during which the voltage between the terminals Ic1-Ic2 can be maintained at the high level is extremely short as compared with the present embodiment. Further, even after time t2, the change in the voltage between the terminals Ic1-Ic2 is more rapid than in the present embodiment.

[ present embodiment ]

In fig. 8, (a), (B): as a result, in the present embodiment, it is found that the output voltage Vout exhibits substantially good step response characteristics throughout the period in which the detected current Ip changes in a step-like manner.

[ comparative example ]

In fig. 9, (a), (B): in contrast, in the comparative example, it is found that immediately after the detected current Ip changes into a step shape, the waveform of the output voltage Vout is greatly disturbed, and the entire voltage Vout exhibits an undesirable step response characteristic.

As described above, according to the present embodiment, the following advantages are provided.

(1) Since the magnetic core 20 is configured by stacking a plurality of plate-like

magnetic core members

22 and 23, the cross-sectional area can be increased compared to the form of a bent plate material, and the magnetic flux density can be increased.

(2) Further, since the primary conductor 30 is disposed so as to wind the search coil unit 50, the arrangement of the search coil unit 50 with respect to the structure in which the plurality of plate-shaped

magnetic core members

22 and 23 are laminated can be optimized, and the response characteristic of the output voltage Vout can be improved.

(3) In addition, in the region other than the inner side of the magnetic circuit, the

magnetic core members

22 and 23 are opened without shielding the gap between the search coil unit 50 and the primary conductor 30, so that the arrangement of the search coil 50a with respect to the

magnetic core members

22 and 23 can be further optimized, and the response characteristic of the output voltage Vout can be further improved.

(4) In particular, even when the detected current Ip changes stepwise, good and stable response characteristics of the output voltage Vout can be obtained.

The present invention is not limited to the above embodiments, and can be implemented in various modifications. For example, the

magnetic core members

22 and 23 are shaped to form a rectangular magnetic circuit, but may be shaped to form a magnetic circuit in other shapes.

Further, the current sensor 10 is applicable not only as a fluxgate type current detector but also as a magnetic balance type current detector using a hall element.

It should be noted that the configurations shown in the drawings in the embodiments are merely preferred examples, and it is obvious that the present invention can be appropriately implemented even if various elements are added to the basic configuration or a part thereof is replaced.

Industrial applicability

The magnetic flux density passing through the magnetic core can be increased, and the arrangement of the search coil can be optimized according to the structure of the magnetic core.

Description of the reference symbols

10: a current sensor;

20: a magnetic iron core;

22. 23: a magnetic core member;

22b, 23 b: a long leg portion;

22c, 23 c: an upper short leg;

22d, 23 d: a lower short leg;

30: a primary conductor;

40: a frame body;

50: a detection coil unit;

50 a: a detection coil;

60. 70: a bobbin unit;

60a, 70 a: a secondary winding.

Claims

1. A current detector is provided with:

a plurality of plate-like magnetic core members that constitute a rectangular magnetic circuit that converges a magnetic field generated by the flow of a current to be detected, wherein plate-like long legs extending opposite to each other are overlapped with each other in a thickness direction at a position along one long side of the magnetic circuit, and plate-like short legs extending opposite to each other are stacked in a state where the plate-like short legs face each other with a gap at a distal end in a flowing direction of the current to be detected at a position along the other long side;

a detection coil disposed at a position along the other long side on the magnetic path;

a secondary winding that generates a magnetic field in the magnetic circuit, the magnetic field being in a reverse direction with respect to a magnetic field generated by the flow of a current to be detected;

a detection circuit for outputting a detection signal corresponding to a detected current based on a secondary current of the secondary winding required for eliminating an output current of the detection coil; and

and a primary conductor that forms a flow path that passes through the inside of the magnetic circuit and extends so as to surround the outside of the search coil when a current to be detected flows.

2. The current detector of claim 1,

the magnetic core member opens the search coil without shielding a space between the primary conductor and the search coil in a periphery of the search coil except for an inner side of the magnetic circuit.