WO2019056095A1

WO2019056095A1 - Helical electro magnetic field concentrator using soft magnetic materials

Info

Publication number: WO2019056095A1
Application number: PCT/CA2018/051163
Authority: WO
Inventors: Yiqiang Jake ZHANG
Original assignee: Zhang Yiqiang Jake
Priority date: 2017-09-19
Filing date: 2018-09-18
Publication date: 2019-03-28

Abstract

An electromagnetic device including an elongated electrical current conductor and a soft magnetic wire made of a soft magnetic material and having a helical section wound around the electrical current conductor for two or more turns, where the turns are free from physical contact with adjacent turns. The soft magnetic wire-farther includes a straight section joined to two ends of the helical section, and the straight section, can either, have a gap in it or be continuous without gaps. The electromagnetic device can be used as a current detector with a Hall-effect sensor placed in, the gap of the straight section, or as an inductor when the straight section is continuous, or as a transformer when a secondary electrical conductor winding is wound around the straight section that is continuous.

Description

HELICAL ELECTRO MAGNETIC FIELD CONCENTRATOR USING SOFT MAGNETIC

MATERIALS

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to electromagnetic devices, and in particular, it relates to an electromagnetic field concentrator.

Description of Related Art

Electro-magnetic devices are widely used. Lenz's law has guided the design rules of transformers, motors, and many other electromagnetic devices, etc. A conductor wound around a soft magnetic material (like silicon steel lamination, ferrite powder magnetic ring etc.) is the classic method of fabrication for electro-magnetic, for converting electrical current to magnetic flux. In a transformer, when a current goes through the primary conductor, the transformer iron core forms a circuit for the magnetic flux lines produced by the current. By the right hand rule, the magnetic flux circles around the conductor at 90 degree of the current direction. Typically, the magnetic circuit inside of an iron core is considered a two-dimensional circuit, in a view of single magnetic flux lines.

In one application, for example, as described in U.S. Pat. No. 9,966,873, a current detection device can be constructed using a C shaped iron core with a gap, a current carrying conductor that is wound around the iron core for one or more turns, and a Hall-Effect switch place inside of the gap. The current carrying conductor of the current detection device is connected in series in a circuit for current detection. In some applications, the device is capable of carrying and detecting 100 Amps or more current passing through the conductor. Commonly available Hall effect switches require at least 100-150 Gauss for its Bop (ON) and Brp (OFF) to safeguard against the magnetic interferences from the operation environment.

SUMMARY

Accordingly, the present invention is directed to an electromagnetic device, such as a current detector, an inductor, a current transformer, etc., that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. An object of the present invention is to provide an electromagnetic device, such as a current detector, an inductor, a current transformer, etc., that can concentrate magnetic field and is easy to manufacture.

Additional features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.

To achieve the above objects, the present invention provides an electromagnetic device, which includes: an elongated electrical current conductor; and a soft magnetic wire made of a soft magnetic material and having a helical section wound around the electrical current conductor for more than one turn, wherein no parts of the soft magnetic wire have direct physical contact with other parts at their side surfaces.

Preferably, the elongated electrical current conductor has a straight shape.

Preferably, the electromagnetic device further includes an insulating material disposed between the electrical current conductor and the soft magnetic wire.

Preferably, the soft magnetic material includes one or more materials selected from a group consisting of: silicon steel, nickel iron, cobalt iron, supermalloy, orthonol, magnetic powders, amorphous alloys containing iron, and nanocrystalline alloys containing iron.

Preferably, the soft magnetic wire further includes a straight section joined to two ends of the helical section, the straight section including two subsections defining a gap between them, the soft magnetic wire being continuous except for the gap.

Preferably, the gap is filled with air or a non magnetic material.

Preferably, two ends of the two subsections of the straight section that define the gap between them have substantially flat end surfaces facing each other to define the gap.

Preferably, the electromagnetic device further includes a Hall-effect switch or Hall-effect sensor device disposed inside of the gap to sense a magnetic field in the gap.

Preferably, the soft magnetic wire further includes a straight section joined to two ends of the helical section, wherein the soft magnetic wire including the helical section and the straight section form a continuous loop without any gaps. Preferably, the electromagnetic device further includes a metal wire wound around the straight section of the soft magnetic wire, wherein the metal wire include two ends configure to output a signal.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically illustrates a current detector employing a helical electro magnetic field concentrator according to a first embodiment of the present invention.

Figures 2A and 2B schematically illustrate an inductor employing a helical electro magnetic field concentrator according to a second embodiment of the present invention.

Figures 3A and 3B schematically illustrate a transformer employing a helical electro magnetic field concentrator according to a third embodiment of the present invention.

Figure 4 schematically illustrates magnetic flux line directions in a front view and a cross section view in the helical portion of the soft magnetic wire of the first to third embodiments.

Figure 5 shows three tables listing some soft magnetic materials useful for making the soft magnetic wire in embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the current detection device described in the Background section above, to detect a small real time current in a large current application (for example, when the current than passes through the current conductor has large peak values, but the threshold current to be detected is a small value), the conductor requires a substantial AWG (American wire gauge) size in order to carry a current on the order of 100 Amps. It is a technical challenge to wind a single turn over a small C shaped iron core's window using such a heavy gauge wire. The iron core's design can be relatively small in size. This will make the whole current detection device's size bulky and involve substantial manual labour to fabricate it.

Another suggestion is to allow the thick conductor to pass straight through the C shaped iron core. This technique has drawbacks as well. A typical Hall-Effect switch IC packaging size is about 3x3 mm². The Hall plate inside of the IC which actually detects the magnetic flux is smaller than 1x1 mm² . The straight through conductor and its surrounding iron core often cannot produce magnetic flux density strong enough in the gap at a given current. The output of voltage signal from the Hall plate is very weak at a given small current as a result. Then, a very sensitive integrate amplifier is required to boost the signal from the Hall plate inside the chip. This type of Hall-Effect switch becomes very sensitive and subject to the magnetic interferences of the environment. As a result, the current detection device as a whole is not reliable in many applications, for example when it is placed nearby a heavy-duty electrical motor or transformer.

Embodiments of the present invention provide a helical electro magnetic field concentrator using soft magnetic materials, which is useful in, for example, detecting small to large current in current detection applications, as an inductor, choke useful in low frequency, or a current transformer with better performance, etc.

Fig. 1 shows a current detector according to a first embodiment of the present invention, which uses a straight through electrical current conductor 11 and a helical electro magnetic field concentrator. The current conductor 11 is preferably covered with an electrical insulating material 12. Preferably, the current conductor 1 1 is made of a material that has good electrical conducting properties but is non magnetic or has poor magnetic properties, to avoid large magnetic field being generated inside of the conductor. For example, preferable materials for the current conductor 11 include copper and aluminum, and iron is not preferred because of its magnetic properties. The current conductor 11 may have, but is not limited to, a round cross- sectional shape. A wire 13 (which may be, but is not limited to, a round shape in the cross- section) made of a soft magnetic material is wound around the straight conductor in a helical path, preferably close to the surface of the conductor and outside of the insulating material 12, for more than one turn to form a helical portion 13 A (the number of turns may be custom designed). There is a small gap between adjacent turns of the soft magnetic wire in the helical portion 13A. The gap may be filled with air, or another non-magnetic material. For example, the soft magnetic wire 13 may be covered with a non- magnetic material (not shown in the drawings) and the wire 13 covered with the non-magnetic material may be wound closely to each other so that the non-magnetic cover material of different turns contact each other. No parts of the soft magnetic wire have direct physical contact with other parts at their side surfaces, and the helical portion 13A of the wire does not have any cross over of the wire. In the embodiment shown in Fig. 1, the soft magnetic wire 13 is wound in one layer around the straight current conductor 1 1. While it is possible to wound the soft magnetic wire 13 for additional layers outside of and overlaying the first layer, this is not preferred.

A substantially straight portion 13B of the wire 13, including two subsections 13B 1 and 13B2, connects the two ends of the helix 13A, with a gap 14 between the two subsections of the straight portion. This gap 14 may be, for example but without limitation, a few mm (e.g. 1-10 mm) wide (the gap size is dependent on specific applications), and can be filled with air or a material that is non magnetic. In other words, the soft magnetic wire 13 is continuous except for the gap 14 in the straight portion 13B . The two ends of the soft magnetic wire 13 preferably have substantially flat end surfaces facing each other, forming the gap 14. The magnetic flux density in the gap 14 will increase or decrease as the current inside of the current conductor increases or decreases. A Hall-effect switch or Hall-effect sensor 15 can be placed inside of the gap 14 to sense the magnetic field.

In one example, the current conductor 11 is about 4 mm in diameter, and the soft magnetic wire 1 3 is about 2 mm in diameter. More generally, the size of the current conductor 11 can range from 2 to 6 mm in diameter, and the size of the soft magnetic wire 13 can range from 1 to 3 mm in diameter. The size of the current conductor 11 is typically determined by the amount of current to be detected and how much heat is allowable. For example, 100 A current requires at least AWG 6 (4.1 mm diameter) for a single core conductor for safety. Slightly smaller conductors can be used, but not by much. The size of the magnetic wire 13 is also related to heat generation. For example, a 4 A current can generate 150 Gauss using a 5-turn magnetic wire, where the magnetic wire size is 1 mm in diameter. But the current may go up to 140 A peak value in some applications. The magnetic wire 13 may be saturated, and magnetic resistance of the wire will produce heat. It may be important to provide heat dissipation mechanisms to cool the magnetic wire 13. Different magnetic materials have different resistance at a given frequency. Generally speaking, materials having relatively low magnetic resistance and remanence and relatively high permeability are preferred for the wire 13.

Because the soft magnetic wire material has better permeability and lower magnetic resistance than the air or non magnetic materials, the magnetic flux line generated by the current conductor 1 1 will travel through and follow the soft magnetic wire 13 to form a magnetic circuit. Generally speaking, the magnetic flux density in the gap 14 will increase with the number of helical turns of the magnetic wire 13, and/or the turn density (number of turns per unit length of the straight current conductor), and/or the length of the straight current conductor 11 that the helical portion covers. Of course, the magnetic field also depends on the material of the soft magnetic wire 13 and the current in the current conductor 11.

In the current detector shown in Fig. 1, the helical portion 13A preferably has uniform cross-sectional size and shape, but the straight portion 13B (or a segment thereof) may have different cross-sectional size and shape than the helical portion. For example, the two end portions that face each other to form the gap 14 may have cross- sectional size and shape that are designed to generate a desired size and shape of the gap to suit the Hall-effect switch or Hall- effect sensor 15.

To summarize, the current detection device described above is based on Lenz' law, but the structure is the "reverse" of conventional current detectors that use a C shaped iron core with a current conductor wound around it.

To operate the device of the first embodiment, a variable current is passed through the electrical current conductor 1 1 , and a signal is output from the Hall-effect switch or Hall-effect sensor 15. The output signal may be used to control an electrical circuit (not shown) as desired, such as a rectifier circuit.

Figs. 2A and 2B show a helical shape of soft magnetic wire 23 wound around a straight conductor 21 according to a second embodiment of the present invention. It is similar to the device shown in Fig. 1 except that the two ends of the soft magnetic wire 23 in the straight portion 23B are physically jointed together instead of forming a gap. In other words, the entire soft magnetic wire 23 is a continuous loop without any gaps. The magnetic flux generated inside of the soft magnetic wire 23 will be a short circuit. This type of devices can be used as an inductor, a choke, etc. It also can be used as an induction heater when a high frequency AC current passes through the current conductor 21.

In an alternative embodiment, the soft magnetic wire 23 can be formed with one or more gaps each extending across the cross-section of the wire and having a predefined width (here the width is defined in the direction along the wire), where the gaps may be filled with a material that is not a soft magnetic material. For example, the soft magnetic wire 23 can be made in multiple segments jointed together with gaps having predefined widths between some of the adjacent segments (more detailed descriptions of the manufacturing method are provided later). The gaps of predefined widths can be used to control the magnetic properties (e.g. magnetic resistance) of the soft magnetic wire. Thus, for example, the device may be used as an inductor and its inductance may be controlled by forming one or more gaps of desired widths. In further alternatives, the soft magnetic wire 23 can be formed with interior cavities which can also be used to control the magnetic properties. The soft magnetic wire of the first and third embodiments may also be made to have such gaps and/or cavities as desired.

To operate the device of the second embodiment, in one example, a variable current is passed through the electrical current conductor 21, and the device acts as an inductor providing an inductance to the circuit that includes the electrical current conductor 21. In another embodiment, a current is passed through the electrical current conductor 21 , and the heat generated by the soft magnetic wire 23 is collected for heating or other purposes.

Figs. 3A and 3B illustrate a current transformer according to a third embodiment of the present invention. This device is similar to the second embodiment shown in Figs. 2A and 2B, but has a secondary electrical conductor 36. More specifically, the current transformer includes a soft magnetic wire 33 wound around a straight current conductor 31 in a helical direction along the conductor. The conductor 31 acts as the primary winding. The two ends of the soft magnetic wire 33 are joint together, similar to the second embodiment. The soft magnetic wire 33 acts as iron core to create a magnetic flux circuit. A metal (e.g. copper) wire 36 is wound around and along the straight section 33B of the soft magnetic wire 33 and acts as the secondary winding. The two ends of the copper wire 36 provide the signal output. The metal wire 35 is preferably thinner than the soft magnetic wire 33.

To operate the device of the third embodiment, an AC current is passed through the electrical current conductor 31, and an electrical signal is generated at the two free ends of the secondary electrical conductor 36. The secondary electrical conductor 36 may be connected to another electrical circuit (not shown).

Compared to conventional current transformer in which primary windings and secondary windings are wound around two sections of a closed (e.g., ring shaped or rectangular shaped) iron core, the device of the third embodiment provide a much longer magnetic flux path, and higher magnetic flux density in the cross section of the magnetic circuit 33. This device is capable to detect small, low frequency input current signal in the current conductor 31. In the above embodiments, the electrical current conductor 11/21/31 is described as being straight through. Note that the conductor is not strictly required to be a straight shape; it is only required to have an elongated segment, which can be straight or bent, that can be wound around by the wire 13/23/33. As described earlier, one practical problem solved by embodiments of the present invention is the difficulty of winding a thick electrical current conductor into turns around a conventional iron core; nothing in the operating principle of the above embodiments requires the electrical current conductor 11/21/31 to be strictly straight through, although it is often convenient to keep it straight.

Fig. 4 shows the magnetic flux line directions in a front view (i.e. with a viewing direction perpendicular to the current conductor) and a cross section view (i.e. with a viewing direction parallel to the current conductor) in the helical portion of the soft magnetic wire 13/23/33 of the embodiments shown in Figs. 1, 2A-2B and 3A-3B.

In the above embodiments, a variety of materials may be used to form the soft magnetic material, including iron alloys such as silicon steel, nickel iron (permalloy), cobalt iron, supermalloy, orthonol, etc.; magnetic powders such as iron powder, ferrite (nickel zinc), and commercially available powder core materials known under the trade names of MPP, High Flux, Kool Mu (all from Magnetics), etc.; and amorphous alloys and nanocrystalline alloys containing iron. Some of the useful materials are listed in three tables in Fig. 5. Each type of soft magnetic material has its own magnetic properties which can be suited to meet the specific design specifications. As the term is used in the relevant technology field, soft magnetic materials are materials that are easily magnetized and demagnetized. More generally speaking, soft magnetic materials have relatively low magnetic coercivity and relatively high permeability. For embodiments of the present invention, the soft magnetic wire 13/23/33 may be made of a material having permeability (ui) between 1 u and 100 Ku, and more preferably, between 10 u and 20 Ku; having a maximum flux density (B) between 0.1 T and 2.5 T, and more preferably, between 0.1 T and 2.0 T; and having a DC coercive force (he) between 0.01 oersted 9 oersted, and more preferably, between 0.01 oersted and 0.6 oersted.

The soft magnetic wire 13/23/33 may be manufactured by bending a wire of a soft magnetic material into the desired shape. It may also be manufactured from a powder of a soft magnetic material and formed into the desired shape by molding, such as injection molding.

Further, the helical shaped soft magnetic wire can be made in multiple segments jointed together without gaps, or with gaps as described earlier. When they are joined together without gaps, the magnetic flux lines can travel through the joint with the minimum loss (Br).

When an electrical current flows through a conductor, the magnetic flux lines form around the conductor. Using the right hand rule, the flux lines will he circles in planes perpendicular to the current direction in the air. In a view of each magnetic flux line, it always maintains a two dimensional shape (i.e. each flux line lies in a two dimensional surface). When the current conductor is wound around an iron core for transformers, inductors or motors, the iron core creates its own magnetic flux circuit. The magnetic flux lines travel in a loop inside of the iron core, also considered a two dimensional form. In embodiments of the present invention, on the other hand, each magnetic flux line follows the shape of the soft magnetic wire, forming a three dimensional helical shape in the helical portion of the soft magnetic wire, and is then guided by the soft magnetic wire to the straight portion of the wire to complete the loop. Thus, the electromagnetic device forms a three dimensional magnetic flux circuit within a helical shape soft magnetic wire, where the electromagnetic flux lines is able to travel more than 360 degrees and more than one plane.

It will be apparent to those skilled in the art that various modification and variations can be made in the helical electro magnetic field concentrator of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An electromagnetic device comprising:

an elongated electrical current conductor; and

a soft magnetic wire made of a soft magnetic material and having a helical section wound around the electrical, current conductor for more than one turn, wherein no parts of the soft, magnetic wire have direct physical contact with other parts at their side surfaces.

2. The electromagnetic device of claim 1 , wherein the elongated electrical current cond.iict.or has a straight shape.

3. The electromagnetic device of claim 1, further comprising an insulating material disposed between, the electrical current conductor and the soft magnetic wire.

4. The electromagnetic device of claim 1 wherein the soft, magnetic material includes one or more materials selected from, a group consisting of: silicon steel, nickel iron, cobalt iron, supermalloy, orthonol, magnetic powders, amorphous alloys containing iron and nanocrystalline alloys containing iron.

5. The electromagnetic device of claim. 1 » wherein the soft magnetic wire further includes a, straight section joined to two ends of the helical section, the straight section including two subsections defining a, gap between them, the soft magnetic wire being continuous except for the gap.

6. The electromagnetic device of claim.5, wherein the gap is filled with, air or a non magnetic material.,

7. The electromagnetic device of claim 5, wherein two ends of the two subsections of the straight, section that define the gap between, them have substantially flat, end surfaces facing each other to define the gap.

8. The electromagnetic device of claim. 5, further comprising a Hall -effect switch or Hall- effect sensor device disposed inside of the gap to sense a magnetic field in. the gap.

9, The electromagnetic device of claim, 1, wherein the soft magnetic wire further includes a straight; section, joined to two ends of the helical section, wherein the soft magnetic wire including the helical section and. the straight section form, a continuous loop without any gaps.

10,. The electromagnetic device of claim 9, further comprising a metal wire wound around the straight section of the soft: magnetic wire, wherein the metal wire include two ends configure to output a signal.