GB2534842A

GB2534842A - Arrangement of foil windings and method of arranging foil windings

Info

Publication number: GB2534842A
Application number: GB1500974.9A
Authority: GB
Inventors: Joseph Bryan Frank; john forsyth Andrew
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2015-01-21
Filing date: 2015-01-21
Publication date: 2016-08-10
Also published as: GB201500974D0

Abstract

Foil windings C1, C2 or a method of forming foil windings, comprises: a continuous length of foil strip 30 forming first and second winding sections 31, 32 interconnected by a further folded section 33. The first and second winding sections 31, 32 are formed around an axis parallel with the respective width direction of the foil strip forming them. The axes of the first and second foil windings C1, C2 may be coaxial, parallel or non-parallel. The folded intersection 33 may include overlapping regions of foil strip 33a, 33b, 33c. The foil strip may include a slit which may allow folding to provide interconnection strips or the strip may be formed to include different foil strip widths providing H-shaped bridging formation. Two interconnections may be formed by folding strip portions in opposite directions relative to the foil strip width direction. The foil strip 30 may be made from aluminium or copper material. The foil windings C1, C2 may be simple to produce and only require connections at either end of the foil strip 30. The foil windings C1, C2 may be used to provide compact, efficient electromagnetic device arrangements suitable for vehicle power converters or other applications.

Description

ARRANGEMENT OF FOIL WINDINGS AND METHOD OF ARRANGING FOIL

WINDINGS

The present disclosure relates to an arrangement of foil windings and a method of arranging foil windings. More particularly, the foil windings may be for an electromagnetic device such as, by way of example and not by way of limitation, a transformer, an inductor and similar devices.

Engines are being developed in which mechanically driven engine accessories such as oil pumps, fuel pumps, hydraulic pumps and generators, are being replaced with electrically driven machines and generators. The electrically driven machines and generators may be attached directly to the engine shafts. Such engines may bring gains in engine efficiency and operational flexibility. Electrical power converters may be used in such engines. An electrical power converter converts electrical energy from one form to another.

Furthermore, electrical power converters may be used in the field of integrated power generation and distribution systems. Such integrated power generation and distribution systems may be used on an airborne platform or a marine platform, for example.

Electrical power converters may comprise semiconductor devices, capacitors and magnetic components such as inductors and high-frequency transformers. The magnetic components may be expected to account for about 30 to 40% of the overall mass of the electrical power converter. Semiconductor technologies such as silicon carbide and gallium nitride may be used to increase operating frequencies of an electrical power converter. This can potentially reduce the size of the electrical power converter. However, to fully realise the potential size reductions, new magnetic component structures and manufacturing techniques are desired.

One approach is to use a thin metal foil; such as a copper foil or an aluminium foil, for the windings of an electromagnetic device, instead of using wire. However, use of foil can make it more difficult to form the interconnections between windings.

Accordingly, it is desirable to make it easier to form interconnections between windings and to simplify the method of arranging two foil windings of an electromagnetic device such as a magnetic component.

According to an aspect, there is provided a method of arranging foil windings for an electromagnetic device that has two or more windings. The method comprises providing a continuous length of foil having a width direction and a length direction. The continuous length of foil comprises a first winding section, a second winding section and an interconnection section that connects the first winding section and the second winding section. The method comprises forming a first foil winding from the first winding section around a first winding axis such that the first winding axis is substantially parallel to the width direction of the first winding section. The method comprises forming a second foil winding from the second winding section around a second winding axis such that the second winding axis is substantially parallel to the width direction of the second winding section. The method comprises folding the interconnection section to form a foil interconnection that connects the first foil winding to the second foil winding such that the first foil winding, the second foil winding and the foil interconnection are formed from the continuous length of foil.

Accordingly, it is not necessary to bond the foil interconnection to the first foil winding or to the second foil winding. This reduces the complexity of the fabrication process for manufacturing the electromagnetic device. This also reduces the possibility of a bonding method damaging the electromagnetic device, for example by causing tears in the windings. This also helps to reduce the volume of the electromagnetic device. In particular, it is not necessary to prepare the foil windings to have lead out sections that extend beyond the core so as to allow the lead out sections to be bonded to a piece of conducting material. This is because it is not necessary for the foil windings to be manufactured separately and joined externally.

Furthermore, the number of connections within the electromagnetic device may be reduced. This makes it easier for all of the connections within the electromagnetic device to be inspected, thus making it easier to perform quality control. Additionally, variations in electrical resistance within the electromagnetic device can be reduced because joints that otherwise have increased electrical resistance can be reduced.

The step of folding the interconnection section to completely form the foil interconnection may be performed after the step of forming the first foil winding and the step of forming the second foil winding, such that by the step of folding the interconnection section the first foil winding and the second foil winding are arranged to be around different parallel axes.

The first winding axis may be coaxial with the second winding axis.

The first winding axis may be non-parallel to the second winding axis.

The interconnection section may be folded so as to form the foil interconnection by overlapping the interconnection section with itself such that: the foil interconnection is narrower than the first foil winding in the width direction and narrower than the second foil winding in the width direction; and/or the foil interconnection is at least two times, or at least three times deeper than the continuous length of foil from which the first foil winding, the second foil winding and the foil interconnection are formed.

The method may comprise: forming at least one slit in the length direction within the interconnection section so as to separate a plurality of interconnection strips within the interconnection section from each other by the at least one slit; wherein the interconnection section is folded such that the interconnection strips substantially overlap each other.

The interconnection section may be folded such that it connects the first foil winding to the second foil winding at a position beyond the first foil winding and the second foil winding in the width direction.

The length of foil may be provided such that the interconnection section comprises a first bridge section for connecting the first foil winding to the second foil winding and a second bridge section connected to the first bridge section; the interconnection section is folded by folding the second bridge section onto the first bridge section such that the first bridge section and the second bridge section substantially overlap each other; and each of the first bridge section and the second bridge section has a U-shape comprising sides that connect to the first winding section and the second winding section respectively and a bottom for connecting the sides at a position beyond the first foil winding and the second foil winding in the width direction.

The method may comprise bonding the first bridge section and the second bridge section together.

Each of the first foil winding and the second foil winding may have a first end and a second end opposite the first end in the width direction, wherein the foil interconnection is formed to have: a first interconnection part that connects the first foil winding to the second foil winding at the respective first ends; and a second interconnection part that connects the first foil winding to the second foil winding at the respective second ends.

The method may comprise: forming one slit in the length direction within the interconnection section so as to separate two interconnection strips within the interconnection section from each other by the one slit; wherein the interconnection section is folded by folding the two interconnection strips to form the first interconnection part and the second interconnection part respectively at positions beyond the first ends and the second ends respectively in the width direction.

According to an aspect, there is provided a method of manufacturing an electromagnetic device, the method comprising: providing a core having a first limb and a second limb; and arranging foil windings using the method described above or as claimed such that the first foil winding is around the first limb and the second foil winding is around the second limb.

According to an aspect, there is provided an arrangement of foil windings for an electromagnetic device that has two or more windings. The arrangement comprises a continuous length of foil having a width direction and a length direction. The continuous length of foil comprises a first winding section, a second winding section and an interconnection section that connects the first winding section and the second winding section. The arrangement comprises a first foil winding formed from the first winding section around a first winding axis such that the first winding axis is substantially parallel to the width direction of the first winding section. The arrangement comprises a second foil winding formed from the second winding section around a second winding axis such that the second winding axis is substantially parallel to the width direction of the second winding section. The arrangement comprises a foil interconnection folded from the interconnection section that connects the first foil winding to the second foil winding, such that the first foil winding, the second foil winding and the foil interconnection are formed from the continuous length of foil.

Accordingly, the volume of the electromagnetic device is reduced. In particular, it is not necessary to prepare the foil windings to have lead out sections that extend beyond the core so as to allow the lead out sections to be bonded to a piece of conducting material. This is because it is not necessary for the foil windings to be manufactured separately and joined externally.

Furthermore, the number of connections within the electromagnetic device may be reduced. Additionally, variations in electrical resistance within the electromagnetic device can be reduced because joints that otherwise have increased electrical resistance can be reduced.

The foil interconnection may be narrower than the first foil winding in the width direction and narrower than the second foil winding in the width direction; and/or the foil interconnection may be at least three times deeper than the continuous length of foil from which the arrangement is formed.

The foil interconnection may connect the first foil winding to the second foil winding at a position beyond the first foil winding and the second foil winding in the width direction.

The interconnection section may comprise a first bridge section for connecting the first foil winding to the second foil winding and a second bridge section connected to the first bridge section; wherein the first bridge section and the second bridge section substantially overlap each other; and each of the first bridge section and the second bridge section has a U-shape comprising sides that connect to the first winding section and the second winding section respectively and a bottom for connecting the sides at a position beyond the first foil winding and the second foil winding in the width direction.

Each of the first foil winding and the second foil winding may have a first end and a second end opposite the first end in the width direction; and the foil interconnection may comprise: a first interconnection part that connects the first foil winding to the second foil winding at the first ends; and a second interconnection part that connects the first foil winding to the second foil winding at the second ends.

According to an aspect, there is provided an electromagnetic device comprising: a core having a first limb and a second limb; and the arrangement of foil windings as described above or as claimed, wherein the electromagnetic device is arranged such that the first foil winding is around the first limb and the second foil winding is around the second limb.

According to an aspect, there is provided a method of arranging foil windings for an electromagnetic device that has two or more windings, the method being substantially as described herein and/or with reference to the accompanying drawings.

According to an aspect, there is provided an arrangement of foil windings for an electromagnetic device that has two or more windings, the arrangement being substantially as described herein and/or with reference to the accompanying drawings.

Embodiments of the invention will now be described by way of non-limitative examples with reference to the accompanying drawings in which: Figure 1 shows an electromagnetic device with two coil windings; Figure 2 shows possible interconnections between the coil windings shown in Figure 1; Figure 3 shows a method of arranging foil windings for an electromagnetic device; Figure 4 shows an alternative method of arranging foil windings for an electromagnetic device; Figure 5 depicts a further alternative method of arranging foil windings for an electromagnetic device; and Figure 6 depicts yet a further alternative method of arranging foil windings for an electromagnetic device.

With reference to Figure 1, an electromagnetic device generally indicated at 10 comprises a core 11, a first foil winding Ci and a second foil winding C2. The electromagnetic device 10 may be a magnetic component such as a transformer, an inductor or a similar device. The core 11 may be called a magnetic core. The core 11 may be formed from a magnetic material such as iron. The core 11 may be a U-core (sometimes referred to as a C-core), an E-core or an 0-core, for example. A U-core or an E-core are particularly suitable because they have straight sides or limbs for the windings. The core 11 comprises at least a first limb 12 and a second limb 13. The core 11 may comprise more than two limbs. The arrangement of foil windings and the method of arranging foil windings described herein may be extended to more than two windings. The windings may be called coils or coil windings.

In the top half of Figure 1, the direction of the magnetic field is indicated by symbols in the first limb 12 and the second limb 13 of the core 11. In the bottom half of Figure 1, the direction of the magnetic field is indicated by arrows in the core 11. In Figure 1, the direction of current flow through the first foil winding C1 and the second foil winding C2 is indicated by arrows in the first foil winding C1 and the second foil winding C2.

The electromagnetic device 10 may be used in various types of circuit. An example of such a circuit is a dual interleaved boost converter with an interphase transformer. Such a circuit may contain both an inductor and a transformer such as a centre tapped transformer. The electromagnetic device 10 may be an inductor or a centre tapped transformer, for example. The electromagnetic device 10 may be used in a circuit of an electrical power converter. Such electromagnetic devices 10 may be used as the basic building blocks of electrical power converters and may be used in a variety of topologies and applications.

In Figure 1, the first foil winding C1 has a first outer end C11 and a first inner end C12. The second foil winding C2 has a second outer end C21 and a second inner end C22. As depicted in Figure 1, the first inner end C12 is adjacent to the core 11 and forms the innermost winding around the first limb 12 of the core 11. The first outer end Cii is outward of the first inner end C12 relative to the core 11. Similarly, the second inner end C22 is adjacent to the second limb 13 of the core 11 and forms the innermost winding of the second foil winding C2 around the second limb 13 of the core 11. The second outer end C21 of the second foil winding C2 is outward of the second inner end C22 of the second foil winding C2.

A centre tapped transformer may have a first foil winding C1 on a first limb 12 and a second foil winding C2 on a second limb 13 of the core 11, with the first foil winding C1 interconnected with the second foil winding C2. Similarly, an inductor may have a first foil winding C1 on a first limb 12 and a second foil winding C2 on a second limb 13 of a core 11, with the first foil winding C1 interconnected with the second foil winding C2. In other words, the inductor winding may be split across the first limb 12 and the second limb 13 of the core 11. This may reduce the volume of the inductor by making the construction lower profile and more symmetrical compared to a construction in which the inductor winding is on only one limb. This may also reduce the thermal path from the innermost winding to the outermost winding.

Although not depicted in Figure 1, the first foil winding C1 may be connected to the second foil winding C2 by connecting the first inner end C12 with the second inner end C22 of the second foil winding C2.

Foil may be used for the windings instead of wire. This can reduce eddy current losses. However, use of foil can make it more difficult to form the winding interconnections such as the interconnection between the first inner end C12 of the first foil winding C1 with the second inner end C22 of the second foil winding C2. As depicted in Figure 1, the outer windings obstruct the first inner end C12 of the first foil winding C1 and the second inner end C22 of the second inner winding C2. Insulation layers (not shown) may be positioned between winding layers to prevent short-circuiting.

Figure 2 depicts possible ways to interconnect the first foil winding Ci to the second foil winding C2. As shown in the left-hand side of Figure 2, conducting material pieces X, Y and Z may be used to connect the first foil winding C1 to the second foil winding C2. This requires electrical connections to be made between the first inner end C12 of the first foil winding Ci and the material piece X, between the material piece X and the material piece Z, between the material piece Z and the material piece Y and between the material piece Y and the second inner end C22 of the second foil winding C2. Mechanical and electrical joints are formed at these connections.

The right-hand side of Figure 2 shows that the number of connections can be reduced by replacing the conducting material pieces X, Y and Z with a single conducting material piece W. Connections are formed between the first inner end C12 of the first foil winding C1 and the single material piece W and between the single material piece W and the second inner end C22 of the second foil winding C2. Mechanical and electrical joints are formed at these connection points.

Figures 3 to 6 show alternative methods of arranging foil windings C1, C2. The foil windings C1, C2 may be for an electromagnetic device 10. The electromagnetic device 10 may have a core 11 and two windings Ci, C2. The core may have a first limb 12 and a second limb 13.

More particularly, the methods may be for the construction of two foil windings C1, C2 fabricated from a single piece of conducting foil. The two foil windings C1, C2 may be wound around two parallel axes, for example for being positioned around the first limb 12 and the second limb 13 of the core 11. The arrangement of foil windings C2 may be produced before combining it with a core 11 to form an electromagnetic device 10. The arrangement of foil windings C1, C2 may be manufactured and sold separately from the core 11. Alternatively, the foil windings C1. C2 may be formed around the limbs 12, 13 of the core 11 of an electromagnetic device 10.

The methods may reduce manufacturing complexity and reduce the number of components of the electromagnetic device 10. The methods may simplify manufacturing of the electromagnetic device 10 as well as reducing the number of mechanical and electrical connections in the electromagnetic device 10. This in turn may improve robustness of the electromagnetic device 10 and the efficiency of the electromagnetic device 10 when compared with constructions in which two foil windings C1, C2 are bonded together as shown in Figure 2.

Each method may comprise a series of folds which form the interconnection that connects the first foil winding C1 and the second foil winding C2. The methods vary in complexity and performance.

The present disclosure provides a method of arranging foil windings for an electromagnetic device 10 that has two windings. The method may comprise providing a continuous length of foil 30. In this context, the term continuous means that the length of foil 30 is a single, unitary piece of foil. The length of foil 30 is not formed from a plurality of sections that are mechanically or electrically joined together. There are no such joints in the length of foil 30 that would otherwise make the length of foil 30 discontinuous.

The continuous length of foil 30 has a width direction and a length direction. The continuous length of foil 30 is longer in the length direction than it is wide in the width direction. As depicted in Figures 3, 5 and 6, the continuous length of foil 30 may be substantially rectangular. However, this is not necessarily the case. For example, as shown in Figure 4, the continuous length of foil 30 may have a more complex shape that is not rectangular.

The continuous length of foil 30 may comprise a first winding section 31, a second winding section 32 and an interconnection section 33. The interconnection section 33 connects the first winding section 31 and the second winding section 32. This is depicted at the top of Figure 3, for example. At the top of Figure 3, the dashed lines represent where the first winding section 31 ends and the interconnection section 33 begins and where the interconnection section 33 ends and the second winding section 32 begins. The dashed lines do not represent features of the physical construction of the continuous length of foil 30. There is no additional section of foil between the first winding section 31 and the interconnection section 33 or between the interconnection section 33 and the second winding section 32.

The method may comprise forming a first foil winding C1 from the first winding section 31 around a first winding axis. The first foil winding C1 may be for fitting around a first limb 12 of a core 11 of the electromagnetic device 10.

The first foil winding C1 may be arranged such that the first winding axis of the first foil winding C1 is substantially parallel to the width direction of the first winding section 31. This arrangement is depicted in Figure 1 and Figure 2. The foil is wound axially as opposed to edgeways, so as to form the first foil winding Ci. In an edgeways arrangement, the edges of the foil would be adjacent the limbs that the winding is fitted around. In an edgeways arrangement, the axis of the limb is perpendicular to the major surfaces of the foil. In contrast, in an axial arrangement as used in the arrangements formed by the methods depicted in Figures 3 to 6, the winding axis (which may correspond to the longitudinal axis of the limb that the winding is for fitting around) is parallel to the surfaces of the foil.

The method may comprise forming a second foil winding C2 from the second winding section 32 around a second winding axis such that the second winding axis is substantially parallel to the width direction of the second winding section 32. In Figure 3, the winding axes are shown in part (e). The winding axes are shown by broken lines in Figures 4 to 6.

The second foil winding C2 may be for fitting around the second limb 13 in a similar manner to which the first foil winding C1 is to be wound around the first limb 12. This is depicted in Figure 1, for example.

The first foil winding Ci and the second foil winding C2 may be formed (e.g. wound) without requiring the core 11 of the electromagnetic device 10 to be present. The arrangement of foil winding C1, C2 may be prepared in advance of being combined with the core 11 to form the electromagnetic device 10. Alternatively, the foil may be wound around the limbs 12, 13 of the core 11 such that when the foil windings C1, C2 are formed, they are formed around the limbs 12, 13.

The method may comprise folding the interconnection section 33 to form a foil interconnection 23. The foil interconnection 23 may connect the first foil winding C1 to the second foil winding C2 such that the first foil winding C1, the second foil winding C2 and the foil interconnection 23 are formed from the continuous length of foil 30.

It is not necessary to fold the interconnection section 33 in order that the connection between the two foil windings C1, C2 is made. This is because the connection between the two foil windings C1, C2 is always there because of the continuous length of foil 30. In particular, the interconnection section 33 connects the first winding section 31 (that forms the first foil winding Cl) and the second winding section (that forms the second foil winding C2). However, the connection is given a new form, relative to the state of the art, by the folding the interconnection section 33 instead of adhering an extra piece of foil to the two foil windings C1, C2. In particular, the folding of the interconnection section 33 allows both foil windings C1, C2 and their connection to be formed from a single, unbroken, continuous length of foil 30.

Accordingly, it is not necessary to bond the foil interconnection 23 to the first foil winding Ci or to the second foil winding C2. This may reduce the complexity of the fabrication process for manufacturing the electromagnetic device 10. This may also reduce the possibility of a bonding method damaging the electromagnetic device 10, for example by causing tears in the windings. This may also help to reduce the volume of the electromagnetic device. In particular, it is not necessary to prepare the foil windings C1, C2 to have lead out sections that extend beyond the core 11 so as to allow the lead out sections to be bonded to a piece of conducting material. This is because it is not necessary for the foil windings C1, C2 to be manufactured separately and joined externally.

Furthermore, the number of connections within the electromagnetic device 10 may be reduced. This makes it easier for all of the connections within the electromagnetic device 10 to be inspected, thus making it easier to perform quality control. Additionally, variations in electrical resistance within the electromagnetic device 10 can be reduced because joints that otherwise have increased electrical resistance can be reduced.

The method may comprise arranging the foil windings C1, C2 such that a cross sectional area of the first foil winding C1, the foil interconnection 23 and the second foil winding Ci Is substantially constant. The foil windings C1, C2 may be arranged such that the electrical resistance may be substantially constant along the first foil winding C1, the foil interconnection 23 and the second foil winding C1.

For example, as depicted in Figures 3, 5 and 6, the cross section of the continuous length of foil 30 from which the foil winding arrangement is formed may be substantially constant along its length. This allows the electrical resistance of the foil winding arrangement that is formed to be consistent along its length simply by folding the continuous length of foil 30 appropriately to form the desired arrangement.

Alternatively, as depicted in Figure 4, the cross section of the continuous length of foil 30 may vary, with some parts (e.g. the central part shown at part (d) of Figure 4) having a narrower width but a thicker depth. In the case of Figure 4, this is achieved by folding a second bridge section 42 onto a first bridge section 41 and bonding them together so that the second bridge section 42 together with the first bridge section 41 act as a deeper section of foil having the same cross section as the shallower but wider winding sections 31, 32.

Providing that the cross sectional area of the continuous length of foil is substantially constant it can provide the further improvement of further reducing variation of electrical resistance along the first foil winding Ci, the foil interconnection 23 and the second foil winding C2. This reduces localised heating deep within the electromagnetic device 10, which could otherwise limit the size and mass reduction possible.

The continuous length of foil 30 may have a substantially constant width w throughout its length I. For example, the continuous length of foil 30 may have a rectangular shape, as shown at the top of Figures 3, 5 and 6. This can reduce material waste because the continuous length of foil 30 has a simple shape that allows more lengths of foil 30 to be cut from a given area of foil. Multiple lengths of foil 30 can be cut from a single wider sheet of foil reducing material wastage.

Alternatively, as shown at the top of Figure 4, the continuous length of foil 30 may have a varying width throughout its length. As shown at the top of Figure 4, multiple lengths of coil 30 may be tessellated so that multiple lengths of foil 30 can be cut from a single wider sheet reducing material wastage.

The step of folding the interconnection section 33 to form the foil interconnection 23 may be performed after the step of forming the first foil winding C1 and the step of forming the second foil winding C2. In other words, the foil windings C1, C2 may be formed before the foil windings C1, C2 are arranged in their final position relative to each other. Accordingly, the step of folding the interconnection section 33 may result in the first foil winding C1 and the second foil winding C2 being arranged to be around different parallel axes, which may correspond to different parallel limbs 12, 13 of a core 11.

For example, Figure 3 shows that the foil windings C1. C2 are formed in steps (d) and (e) before the foil interconnection 23 is completely formed by folding the interconnection section 33 so that the first foil winding C1 and second foil winding C2 are correctly positioned with respect to each other. This is also shown in Figure 4, which shows that the first foil winding C1 and the second foil winding C2 are formed in steps (f) and (g) before the interconnection section 33 is folded in step (h) such that the first foil winding C1 and the second foil winding C2 are arranged to be around different parallel axes.

Similarly, Figure 5 shows that the first foil winding C1 and the second foil winding C2 are formed in steps (d) and (e) before the interconnection section 33 is completely formed such that the first foil winding Ci and the second foil winding C2 are arranged to be around different parallel axes.

Alternatively, the foil interconnection 23 may be formed by folding the interconnection section 33 before the foil windings C1, C2 are formed. This is shown in Figure 6, which shows that the foil interconnection 23 is formed in step (d) and the first foil winding Gland the second foil winding C2 are subsequently formed in steps (e) and (f). This is also shown in the second alternative shown in Figure 5.

Figure 5 shows two alternatives. Steps (a) to (c) are common to both alternatives shown in Figure 5. Steps (d) to (f) correspond to the first alternative, whereas steps (g) to (i) correspond to the second alternative. The second alternative of Figure 5 shows that the foil interconnection 23 is formed in step (g) before the foil windings C1, C2 are formed in steps (h) and (i).

By forming the foil winding Ci, C2 before they are correctly positioned relative to each other (by folding the interconnection section 33), it can be easier to form the foil windings C1, C2 by providing more clearance. It may be easier to form the foil winding C1, C2 when there is more clearance. For example, in step (d) and step (e) of Figure 3, there is a lot of clearance surrounding the foil windings C1, C2, thereby making it easier for them to be formed. In contrast, in step (e) and step (f) of Figure 6, there is less clearance for the foil windings C1, C2 to be formed. Where there is little clearance, the foil may need to be threaded through a smaller gap in order to form each loop of the winding.

The interconnection section 33 may be folded to form the foil interconnection 23 such that the foil interconnection 23 is narrower than the first foil winding Ci and narrower than the second foil winding C2. In this context, the term "narrower" refers to the width direction indicated by the reference w in Figure 3, for example.

This is shown in Figure 3, where the foil interconnection 23 is narrower than the first foil winding C1 and the second foil winding C2. The first foil winding C1 and the second foil winding C2 have substantially the same width as the continuous length of foil 30 from which the first foil winding Ci, the foil interconnection 23 and the second foil winding C2 are formed.

By forming the foil interconnection 23 such that it is narrower than the foil windings C1, C2, the foil interconnection 23 can be reduced in width to suit a wide range of core geometries. For example, as depicted in Figure 1, the width of the crossbars of the core 11 that connect the limbs 12, 13 together may be less than the width w of the continuous length of foil 30. If the foil interconnection 23 is not narrowed relative to the foil windings C1, C2, then the foil interconnection 23 could extend beyond the crossbars of the core 11. The foil interconnection 23 would then contribute to the overall size of the electromagnetic device 10 in the width direction of the continuous length of foil 30. However, by narrowing the foil interconnection 23, the foil interconnection 23 can be designed such that it has a width w that is no more than the width of the crossbar of the core 11. This helps to reduce the overall size of the electromagnetic device 10.

There are various ways of folding the interconnection section 33 to form the foil interconnection 23 such that the foil interconnection 23 is narrower than the foil winding C1, C2. For example, as shown in Figure 3, the method comprises forming at least one slit 34 within the interconnection section 33. In the method depicted in Figure 3, there are two slits 34 formed. However, the number of slits 34 is not particularly limited. The slits 34 extend in the length direction of the length of foil 30.

This results in separating a plurality of interconnection strips 33a, 33b, 33c within the interconnection section 33 from each other by the at least one slit 34. The interconnection section 33 can then be folded such that the interconnection strips 33a, 33b, 33c substantially overlap each other. For example, each of the interconnection strips 33a, 33b, 33c can be folded or doubled at right angles upon itself. Each interconnection strip 33a, 33b, 33c is bent over and against itself on a diagonal line at a fold.

An exemplary sequence of folds for folding the interconnection section 33 according to what is shown in Figure 3 is set out as follows. Firstly, the interconnection strip 33a may be folded or doubled at right angles upon itself at the end of the interconnection strip 33a closest to the first winding section 31. Second, the interconnection strip 33b may be bent over and against itself on a diagonal line of a fold at the corresponding end such that the interconnection strip 33b lies on top of the interconnection strip 33a. Third, the interconnection strip 33c can be folded in corresponding fashion such that it lies on top of the interconnection strip 33b and the interconnection strip 33a. Fourth, the opposite end of the interconnection strip 33c may be folded or doubled at right angles upon itself. Fifth and sixth, corresponding folds are made to the interconnection strip 33b and the interconnection strip 33a so that the interconnection strips 33a, 33b and 33c lie flat on top of each other as shown in the picture at step (c) of Figure 3.

The folds may be formed in a different sequence. Once the interconnection strips 33a, 33b, 33c are laid on top of each other, the interconnection strips 33a, 33b, 33c may be bonded together, but this is not necessary.

There are alternative ways of forming the foil interconnection 23 to be narrower than the foil winding C1, C2. For example, as shown in Figure 4, the continuous length of foil 30 may be provided such that the interconnection section 33 comprises a first bridge section 41 and a second bridge section 42. The first bridge section 41 may be for connecting the first foil winding Ci to the second foil winding C2. The second bridge section 42 is connected to the first bridge section 41.

As depicted in step (b) and step (c) of Figure 4, the interconnection section 33 may be folded by folding the second bridge section 42 onto the first bridge section 41 such that the first bridge section 41 and the second bridge section 42 substantially overlap each other. The first bridge section 41 may be bonded to the second bridge section 42.

Each of the first bridge section 41 and the second bridge section 42 has a U-shape. The U-shape comprises sides 43 that connect the first winding section 31 and the second winding section 32 respectively. The U-shape comprises a bottom 44 for connecting the sides 43 at a position beyond a longitudinal extent of the first foil winding C1 and the second foil winding C2. As shown in step (d) of Figure 4, the bottom 44 is beyond the longitudinal extent of the first foil winding Ci and the second foil winding C2. The longitudinal direction of the foil winding C1, C2 corresponds to the width direction of the continuous length of foil 30. The longitudinal direction of the foil winding C1, C2 corresponds to the axial direction of the winding axes that the foil windings C1, C2 are wound around. Accordingly, the width of the bottom 44 of the U-shape of the first bridge section 41 and the second bridge section 42 can be selected so as to fit a range of core geometries. The bottom 44 can be designed to fit against the crossbar of the core 11 of the electromagnetic device 10.

The first winding axis and the second winding axis may be coaxial, as shown in Figure 3. This is shown in steps (d) and (e) of Figure 3. This can make it even easier to form the foil windings Ci, C2 with good clearance. The foil windings C1, C2 may be formed manually or may be formed automatically by a machine. By providing that the first winding axis is coaxial with the second winding axis, it may be easier for the winding process to be automated.

Alternatively, the foil windings C1, C2 may be formed by winding the first winding section 31 and the second winding section 32 around different axes. For example, the first foil winding Ci may be formed by winding the first winding section 31 around a first winding axis and the second foil winding C2 may be formed by winding the second winding section 32 around a second winding axis that is non-parallel to the first winding axis 49.

For example, as shown in Figure 4, the first winding axis may be substantially perpendicular to the second winding axis. Similarly, as shown in steps (d) and (e) of the first alternative of Figure 5, the first winding axis may be perpendicular to the second winding axis. By providing that the first winding axis is perpendicular to the second winding axis, good clearance may be provided for forming the foil windings Ci, C2.

The angle between the first winding axis 48 and the second winding axis 49 can be varied to be angles other than 90°. The angle may be selected so as to provide good clearance for forming the foil windings C1, C2. The desired angle may depend on the geometry of the environment in which the arrangement of foil windings Ci, C2 is formed.

Alternatively, the first foil winding C1 may be formed around an axis that is different but parallel to the axis around which the second foil winding C2 is formed. For example, this is shown in step (i) of Figure 5 and in steps (e) and (f) of Figure 6.

The interconnection section 33 may be folded so as to overlap the interconnection section 33 with itself. As a result, the foil interconnection 23 may be at least three times deeper than the continuous length of foil 30 from which the first foil winding C1, the second foil winding C2 and the foil interconnection 23 are formed. Three times deeper occurs in the case of there being two slits in the foil. This is shown in Figure 3, for example, where the foil interconnection 23 is primarily three times deeper than the initial continuous length of foil 30. However, the foil interconnection 23 could be formed by making only one slit in the foil, in which case the foil interconnection 23 would be double the original foil thickness. Hence, the foil interconnection 23 may be at least two times deeper than the continuous length of foil 30 from which the first foil winding C1, the second foil winding C2 and the foil interconnection 23 are formed.

At sections where the foil interconnection 23 is folded or doubled at right angles upon itself, the foil interconnection 23 is even deeper, namely six times deeper than the initial continuous length of foil 30, for the case of there being two slits in the foil. However, primarily the foil interconnection 23 is three times deeper than the initial continuous length of foil 30.

Depending on the number of longitudinal slits 34 and the number of interconnection strips, the foil interconnection 23 can be made to have various depths. By providing that the depth of the foil interconnection 23 can be increased relative to the initial continuous length of foil 30, the width of the foil interconnection 23 can be reduced without changing the cross sectional area of the foil interconnection 23 relative to the foil windings C1, C2. This helps to keep the electrical resistance consistent throughout the arrangement of windings.

The foil interconnection 23 may be formed to have different depths, for example more than three times deeper than the initial continuous length of foil 30 or only two times deeper than the initial continuous length of foil 30. For example, Figure 4 shows that the foil interconnection 23 may have a depth that is twice the depth of the initial continuous length of foil 30.

The interconnection section 33 may be continuous in the width direction. This means that the interconnection section 33 may not have any holes or any slits. For example, Figure 5 shows that no slits or cuts or holes are formed in the interconnection section 33 before it is formed into the foil interconnection 23. This can simplify the method of arranging the foil windings C1, C2. This can speed up the manufacturing process and can reduce the cost of the manufacturing process for manufacturing the electromagnetic device 10.

Alternatively, the interconnection section 33 may be discontinuous in the width direction. For example, Figure 3 and Figure 6 show that slits 34, 64 may be formed in the interconnection section 33.

Each of the first foil winding Ci and the second foil winding C2 may have a first end 61 and a second end 62 opposite the first end 61 in the width direction. The windings may be longitudinal, though this is not necessarily the case. The foil interconnection 23 may be formed to have a first interconnection part 23a that connects the first foil winding Ci to the second foil winding C2 at the first ends 61. The foil interconnection 23 may be formed to have a second interconnection part 23b that connects the first foil winding Ci to the second foil winding C2 at the second ends 62. This is shown in Figure 6, for example.

This makes it possible to interconnect the foil windings C1, C2 on both sides of the coils. This can provide a better path for current to flow between the first foil winding Ci and the second foil winding C2 Alternatively, the first foil winding C1 may be interconnected with the second foil winding C2 only at one of the longitudinal ends of the foil winding C1, C2. This is shown in each of Figures 3 to 5, for example.

The interconnection section 33 may be folded such that it connects the first foil winding C1 to the second foil winding C2 at a position beyond a longitudinal extent of the first foil winding Ci and the second foil winding C2. This is shown in each of Figures 3 to 6. This allows the foil windings C1, C2 to be interconnected with each other without causing any interference for the electromagnetic device 10. In particular, the foil interconnection 23 can avoid the core gap between the limbs 12, 13 of the core 11.

The method may comprise forming one slit 64 within the interconnection section 33. The one slit 64 extends in the length direction and separates two interconnection strips 63a, 63b within the interconnection section 33. This is depicted in Figure 6.

The interconnection section 33 may be folded by folding the two interconnection strips 63a, 63b to form the first interconnection part 23a and the second interconnection part 23b respectively at positions beyond the first end 61 and the second end 62 respectively.

An electromagnetic device 10 may be manufactured by providing a core 11 having a first limb 12 and a second limb 13 and arranging foil windings C1, C2 using the method described above or as claimed. The foil windings C1, C2 may be arranged such that the first foil winding C1 is around the first limb 12 and the second foil winding C2 is around the second limb 13.

The continuous length of foil may be made of a material such as copper or aluminium. Other conducting materials may be used to form the foil.

The electromagnetic device 10 may be a centre tapped transformer or an inductor. Other electromagnetic devices may be manufactured according to the present disclosure.

The methods shown in Figures 3 to 5 are exemplary and non-limiting examples. The methods may provide different advantages relative to each other. For example, the method shown in Figure 3 may provide a particularly flexible solution which does not require any additional bonding, but provides an increase in depth at the foil interconnection 23 and allows the foil windings C1, C2 to be wound with good clearance. The method shown in Figure 4 is simpler than the methods depicted in Figures 3, 5 and 6. The methods shown in Figures 4 and 5 do not require slicing of the material to achieve the interconnection that connects the foil windings C1, C2.

As described above, the foil winding C1, C2 and the foil interconnection 23 may be formed by folding the initial continuous length of foil 30. Folds may be made at right angles by bending part of the foil over and against itself on a diagonal line of a fold. It is not necessary for the folds to be performed at exact right angles. The angles of the folds may be varied depending on the desired design.

The size of the length of foil 30 and the electromagnetic device is not particularly limited. Merely as an example, the width w of the length of foil 30 may be in the range from about 20mm to about 100mm, and may be about 45mm.

Below is a detailed step-by-step folding method for the method depicted in Figure 3. The original template is the length of foil 30. The shape of the length of foil 30 is a rectangle. The width W of the length of foil may be in the range from about 20 mm to about 100 mm. The length of foil 30 is longer in the length direction than in the width direction. The length of the length of foil 30 depends on the desired number of loops in the foil windings C1, C2.

The method comprises forming two slits 34 in the length of foil. The slits 34 are formed in the length direction of a length of foil 30. The slits 34 are formed to be parallel to the long sides of the length of foil 30. The slits 34 are formed so as to form three equally wide interconnection strips 33a, 33b, 33c separated by the select 34. This is shown in picture (b) of Figure 3.

The slits 34 are formed in the interconnection section 33 of the length of foil 30. The slits 34 begin and end at the same points as each other in the length direction of the length of foil 30. The length of the slits 34 depends on the dimensions of the core 11 that the foil windings C1, C2 are intended to fit around. In particular, the length of the slits 34 may depend on the width and length of the crossbar that connected the two limbs 12, 13 of the core 11. The length of the crossbar corresponds to the distance between the two limbs 12, 13 of the core 11. The width of the crossbar is perpendicular to the length of the crossbar. The length of the slits may be equal to the sum of the length of the crossbar and six times the width of the crossbar of the core 11.

The next step is shown in part (c) of Figure 3. The foil is folded such that the interconnection strips 33a, 33b, 33c overlap each other forming a narrower middle section of the foil. To form the bottom (as viewed in part (c) of Figure 3) folds, each interconnection strip 33a, 33b, 33c is folded at right angles under itself in turn. For example, first the top (from the view point of part (b) of Figure 3) interconnection strip 33a is folded at right angles under itself in the direction shown by the lower arrow in part (c) of Figure 3. Second, the middle interconnection strip 33b is folded at right angles under itself so that interconnection strip 33b lies underneath interconnection strip 33a. Third, the bottom interconnection strip 33c is folded at right angles under itself so that interconnection strip 33c lies under interconnection strip 33b.

To form the upper set of folds shown in part (c) of Figure 3, the interconnection strips 33a, 33b, 33c are folded at right angles at their other ends. For example, first the interconnection strip 33c may be folded at right angles at its upper end so that the second winding section 32 extends at right angles to the interconnection strip 33c. Second, the middle interconnection strip 33b is folded at right angles to itself so that interconnection strip 33b lies neatly on top of interconnection strip 33c along the full length of the interconnection strips 33b, 33c. Third, the interconnection strip 33a is folded at right angles so that it lies neatly on top of interconnection strips 33b, 33c.

Step (d) of Figure 3 shows how the first foil winding C1 is formed. The first winding section 31 is looped multiple times in the direction indicated by the arrow in step (d) of Figure 3 to form the first foil winding Ci. An object having a similar shape to the first limb 12 may be used to help in forming the first foil winding Ci. An insulation layer may be laid on top of the first winding section 31 before forming the loops so that a thin layer of insulation insulates each loop from each other when the first foil winding C1 is formed. In the view shown in step (c) of Figure 3, the limb-shaped object would be positioned behind the bottom part of the interconnection strips 33a, 33b, 33c.

Step (e) of Figure 3 shows the second foil winding C2 being formed. The second winding section 32 is wound around in loops to form the second foil winding C2. A limb-shaped object may be used to help form the second foil winding C2 to have the appropriate size and shape. A layer of insulation may be laid adjacent to the second winding section 32 so that a thin insulation layer is provided between each loop of the second foil winding C2 when it is formed. It is possible to use a single limb-shaped object around which both the first foil winding C1 and the second foil winding C2 are formed. This is because as shown in step (e) of Figure 3, both foil windings C1, C2 can be formed around the same axis.

Step (f) of Figure 3 shows the first stage of moving the foil windings C1, C2 into their final position. In step (f), the three interconnection strips 33a, 33b, 33c are folded at right angles on top of themselves according to the arrow shown in step (f) of Figure 3.

In step (g) of Figure 3, the other end of the three interconnection strips 33a, 33b, 33c are folded at right angles on top of each other so that the second foil winding C2 is parallel to the first foil winding C1 as shown in the Figure. The foil interconnection 23 is formed by the three overlapping interconnection strips 33a, 33b, 33c extending between the foil windings C1, C2. The arrangement is then ready for the limbs 12, 13 of a core 11 to be inserted in the foil winding C1, C2.

Below is a detailed step-by-step folding method for the method depicted in Figure 4. The original template is the length of foil 30. The length of foil 30 has a shape of two rectangles connected to the lower legs of a H-shape, as shown in steps (a) and (b) of Figure 4. The length of the rectangles on each side depends on how many loops each foil winding C1, C2 it intended to have. The width W of each of the rectangles may be in the region of from about 20 mm to about 100 mm. The width W may correspond to the length of the limbs 12, 13 of the core 11. The width of the crossbar of the H-shape may correspond to twice the width of the crossbar of the core 11.

As shown in step (a) of Figure 4, multiple templates may be tessellated so as to save on the amount of foil used to form multiple arrangements of foil windings C1, C2. Step (b) of Figure 4 shows a single template for forming the arrangement of foil windings C1, C2. The H-shape part of the length of foil 30 corresponds to the interconnection section 33. The rectangles on either side of the H-shape correspond to the first winding section 31 and the second winding section 32. The lower half of the H-shape corresponds to the first bridge section 41 that is for connecting the first winding section 31 to the second winding section 32. The upper half of the H-shape corresponds to the second bridge section 42 that is connected to the first bridge section 41. The lower limbs of the H-shape corresponds to the sides 43 of the U-shape (i.e. half of the H-shape) of the first bridge section 41.

In step (c) of Figure 4, the H-shape is folded in half so that the top half of the H-shape overlaps the bottom half of the H-shape. Accordingly, a U-shape is formed. Step (d) of Figure 4 shows the result of the fold. The two halves of the H-shape may be adhered together.

In step (e) of Figure 4, the lower right limb of what was the H-shape is folded upwards 90° as shown in the Figure. The second winding section 32 is therefore in a different plane from the first winding section 31. This gives clearance for the second foil winding C2 to be formed.

In step (f) of Figure 4, the second foil winding C2 is formed. The second foil winding C2 is formed by looping the second winding section 32 around itself. An electrically insulating material may be laid on top or under the second winding section 32 so that when the second winding section 32 is wound around itself, an insulating layer is provided between each loop. A limb-shaped object may be placed above the left-hand end of the second winding section 32 so as to aid the formation of the second foil winding C2 in the desired shape.

In step (g) of Figure 4, the first foil winding C1 is formed by looping the first winding section 31 around itself. An insulating layer may be provided between each loop of the first foil winding In step (h) of Figure 4, the lower right limb of what was the H-shape is folded back down so that the second foil winding C2 is parallel to the first foil winding C1. The two limbs 12, 13 of a core 11 may then be inserted into the first and second foil windings Ci, C2.

Below is a detailed step-by-step folding method of the method depicted in Figure 5. The original template is the length of foil 30. The shape of the length of foil 30 may be the same as the length of foil 30 used for the method depicted in Figure 3 and described above. Step (a) of Figure 5 shows the original template.

In step (b) of Figure 5, the length of foil 30 is folded at right angles against itself. The fold is formed near the part of the length of foil 30 where the first winding section 31 transitions into the interconnection section 33.

In step (c) of Figure 5, the interconnection section 33 is folded at right angles over itself so that the length direction of the first winding section 31 is parallel with the length direction of the second winding section 32. The distance between the two folds can be as small as possible.

After step (c) of Figure 5, there are two alternative sets of steps for forming the arrangement of foil windings Ci, C2. The first alternative is shown in steps (d) to (f) of Figure 5. The second alternative is shown in steps (g) to (i) of Figure 5.

In step (d), the other end (the end nearest the second winding section 32) of the interconnection section 33 is folded at right angles under itself. As a result, the length direction of the second winding section 32 is perpendicular to the length direction of the first winding section 31. This provides space (i.e. clearance) for the foil windings C1, C2 to be formed without interfering with each other. As shown in step (d) of Figure 5, the first foil winding C1 is formed by looping the first winding section around itself in the direction shown in the diagram. A limb-shaped object may be positioned behind the end of the first winding section 31 nearest the interconnection section 33. The limb-shaped object may help to form the first foil winding C1 to have the right size and shape.

In step (e) of Figure 5, the second foil winding C2 is formed by looping the second winding section 32 around itself in the direction shown in the diagram. Insulating layers may be provided between the loops of the foil winding Ci, C2.

In step (f) of Figure 5, after the foil windings C1, C2 have been formed, the second foil winding C2 is folded back down so that it is parallel to the first foil winding C1. The foil interconnection 23 is formed between the first and second foil winding C1, C2. The limbs 12, 13 of a core 11 may then be inserted into the first and second foil windings CI, C2.

Alternatively, as shown in step (g) of Figure 5, after step (c) of Figure 5, the foil may be folded such that the length direction of the second winding section 32 is the same as the length direction of the first winding section 31. In particular, the end of the interconnection section 33 near the second winding section 32 may be folded at right angles under itself. Subsequently, the second winding section 32 may be folded at right angles on top of itself so that the second winding section 32 overlaps the first winding section 31.

As shown in step (h) of Figure 5, the first and second foil windings C1, C2 may then be formed. There is limited space or clearance for the foil windings C1, C2 to be formed. When each loop is formed, the winding section 31, 32 is threaded through the space between the foil windings C1, C2.

As shown in step (i) of Figure 5, once the foil windings Ci, C2 have been formed, the foil interconnection 23 connects the first foil winding Ci to the second foil winding C2. The limbs 12, 13 of a core 11 may then be inserted into the foil windings C1, C2. Insulating layers may be positioned between each loop of each foil winding C1, C2.

Below is a detailed step-by-step folding method corresponding to the method depicted in Figure 6. The original template is the length of foil 30. The shape of the length of foil 30 may be the same as that used for the original template used in the method depicted in Figure 3 or Figure 5. Step (a) of Figure 6 shows the original template from which the arrangement of foil windings C1, C2 is formed.

In step (b) of Figure 6, one slit 64 is formed within the interconnection section 33 of the length of foil 30. The slit 64 extends in the length direction of the length of foil 30. The slit 64 splits the interconnection section 33 into two interconnection strips 63a, 63b. The slit 64 is formed such that the interconnection strips 63a, 63b have an equal width. The length of the slit 64 depends on the dimensions of the core 11 that the arrangement of foil windings C1, C2 is designed for. For example, the length of the slit 64 may correspond to the distance from the outer edge of the first limb 12 to the outer edge of the second limb 13 of the core. This is equivalent to the sum of the distance between the limbs 12, 13 of the core and the width of each of the limbs 12, 13 of the core 11.

In step (c) of Figure 6, the ends of the interconnection strips 63a, 63b are folded at right angles over themselves so that the interconnection strips 63a, 63b extend away from each other. As depicted in step (c) of Figure 6, it can help if the interconnection strips 63a, 63b are folded in half, with the fold extending in the width direction.

In step (d) of Figure 6, the interconnection strips 63a, 63b are again folded at either end adjacent to the previous folds such that the unfolded portions of the interconnection strips 63a, 63b lie parallel to the first winding section 31 and the second winding section 32. This leaves a gap in the middle of the piece of foil. The gap is bounded by the interconnection strips 63a, 63b in the width direction and is bounded by the first winding section 31 and the second winding section 32 in the length direction. The gap is shown in step (d) of Figure 6. The central unfolded portions of the interconnection strips 63a, 63b correspond to the first interconnection part 23a and the second interconnection part 23b, respectively.

In step (e) of Figure 6, the first foil winding C1 is formed by wrapping the first winding section 31 around itself. A limb-shaped object may be used to control the size and shape of the first foil winding C1. When forming the first foil winding C1, the first winding section 31 is threaded through the gap in the piece of foil each time a new loop is formed. A layer of insulating material may be used to insulate between loops of the first foil winding C1.

In step (f) of Figure 6, the second foil winding C2 may be similarly formed by wrapping the second winding section 32 around itself, possibly using a limb-shaped object to control the size and shape of the second foil winding C2. The second winding section 32 is threaded through the gap in the piece of foil so as to form each loop. A layer of insulating material may be provided between each loop of the second foil winding C2. Limbs 12, 13 of a core 11 may then be inserted into the first and second foil windings C1, C2.

Whilst aspects of the disclosure relate to provide foil windings Ci, C2 at different parallel axes, it will be appreciated that the axis could be non-parallel to fit different core geometries. Where the disclosure relates to the exemplary arrangements/methods described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary arrangements/methods set forth above are considered to be illustrative and not limiting. Various changes to the described arrangements/methods may be made without departing from the scope of the invention.

Where reference is made herein to an electromagnetic device, it will be appreciated that this term may be any type of electromagnetic device, including, but not limited to, a centre tapped transformer and an inductor. Aspects of the disclosure may be applicable, for example, to any electromagnetic devices comprising connected foil windings. Any feature described and/or claimed herein may be combined with any other compatible feature described in relation to the same or another embodiment.

Claims

CLAIMS1. A method of arranging foil windings (Cl. C2) for an electromagnetic device (10) that has two or more windings, the method comprising: providing a continuous length of foil (30) having a width direction and a length direction and comprising a first winding section (31), a second winding section (32) and an interconnection section (33) that connects the first winding section (31) and the second winding section (32); forming a first foil winding (C1) from the first winding section (31) around a first winding axis such that the first winding axis is substantially parallel to the width direction of the first winding section (31); forming a second foil winding (C2) from the second winding section (32) around a second winding axis such that the second winding axis is substantially parallel to the width direction of the second winding section (32); and folding the interconnection section (33) to form a foil interconnection (23) that connects the first foil winding (C1) to the second foil winding (C2) such that the first foil winding (C1), the second foil winding (C2) and the foil interconnection (23) are formed from the continuous length of foil (30).
2. The method of claim 1, wherein the step of folding the interconnection section (33) to completely form the foil interconnection (23) is performed after the step of forming the first foil winding (Ci) and the step of forming the second foil winding (C2), such that by the step of folding the interconnection section (33) the first foil winding (C1) and the second foil winding (C2) are arranged to be around different parallel axes.
3. The method of claim 2, wherein the first winding axis is coaxial with the second winding axis.
4. The method of claim 2, wherein the first winding axis is non-parallel to the second winding axis.
5. The method of any preceding claim, wherein the interconnection section (33) is folded so as to form the foil interconnection (23) by overlapping the interconnection section (33) with itself such that: the foil interconnection (23) is narrower than the first foil winding (Ci) in the width direction and narrower than the second foil winding (C2) in the width direction; and/or the foil interconnection (23) is at least two times deeper than the continuous length of foil (30) from which the first foil winding (C1), the second foil winding (C2) and the foil interconnection (23) are formed.
6. The method of claim 5, comprising: forming at least one slit (34) in the length direction within the interconnection section (33) so as to separate a plurality of interconnection strips (33a, 33b, 33c) within the interconnection section from each other by the at least one slit (34); wherein the interconnection section (33) is folded such that the interconnection strips (33a, 33b, 33c) substantially overlap each other.
7. The method of any preceding claim, wherein the interconnection section (33) is folded such that it connects the first foil winding (C1) to the second foil winding (C2) at a position beyond the first foil winding (C1) and the second foil winding (C2) in the width direction.
8. The method of any of claims 1, 2 and 4, wherein: the length of foil (30) is provided such that the interconnection section (33) comprises a first bridge section (41) for connecting the first foil winding (C1) to the second foil winding (C2) and a second bridge section (42) connected to the first bridge section (41); the interconnection section (33) is folded by folding the second bridge (42) section onto the first bridge section (41) such that the first bridge section (41) and the second bridge section (42) substantially overlap each other; and each of the first bridge section (41) and the second bridge section (42) has a U-shape comprising sides (43) that connect to the first winding section (31) and the second winding section (32) respectively and a bottom (44) for connecting the sides (43) at a position beyond the first foil winding (Ci) and the second foil winding (C2) in the width direction.
9. The method of claim 8, comprising bonding the first bridge section (41) and the second bridge section (42) together.
10. The method of any of claims 1 and 2, wherein each of the first foil winding (C1) and the second foil winding (C2) has a first end (61) and a second end (62) opposite the first end (61) in the width direction, wherein the foil interconnection (23) is formed to have: a first interconnection part (23a) that connects the first foil winding (C1) to the second foil winding (C2) at the respective first ends (61); and a second interconnection part (23b) that connects the first foil winding (C1) to the second foil winding (C2) at the respective second ends (62).
11 The method of claim 10, comprising: forming one slit (64) in the length direction within the interconnection section (33) so as to separate two interconnection strips (63a, 63b) within the interconnection section (33) from each other by the one slit (64); wherein the interconnection section (33) is folded by folding the two interconnection strips (63a, 63b) to form the first interconnection pad (23a) and the second interconnection part (23b) respectively at positions beyond the first ends (61) and the second ends (62) respectively in the width direction.
12.A method of manufacturing an electromagnetic device (10), the method comprising: providing a core (11) having a first limb (12) and a second limb (13); and arranging foil windings (C1,C2) using the method of any preceding claim such that the first foil winding (Ci) is around the first limb (12) and the second foil winding (C2) is around the second limb (13).
13 An arrangement of foil windings (Ci, C2) for an electromagnetic device (10) that has two or more windings, the arrangement comprising: a continuous length of foil (30) having a width direction and a length direction and comprising a first winding section (31), a second winding section (32) and an interconnection section (33) that connects the first winding section (31) and the second winding section (32); a first foil winding (Ci) formed from the first winding section (31) around a first winding axis such that the first winding axis is substantially parallel to the width direction of the first winding section (31); a second foil winding (C2) formed from the second winding section (32) around a second winding axis such that the second winding axis is substantially parallel to the width direction of the second winding section (32); and a foil interconnection (23) folded from the interconnection section (33) that connects the first foil winding (C1) to the second foil winding (C2), such that the first foil winding (Ci), the second foil winding (C2) and the foil interconnection (23) are formed from the continuous length of foil (30).
14.The arrangement of claim 13, wherein: the foil interconnection (23) is narrower than the first foil winding (C1) in the width direction and narrower than the second foil winding (C2) in the width direction; and/or the foil interconnection (23) is at least three times deeper than the continuous length of foil (30) from which the arrangement is formed.
15. The arrangement of any of claims 13 and 14, wherein the foil interconnection (23) connects the first foil winding (C1) to the second foil winding (C2) at a position beyond the first foil winding (C1) and the second foil winding (C2) in the width direction.
16. The arrangement of any of claims 13 to 15, wherein: the interconnection section (33) comprises a first bridge section (41) for connecting the first foil winding (Ci) to the second foil winding (C2) and a second bridge section (42) connected to the first bridge section (41); the first bridge section (41) and the second bridge section (42) substantially overlap each other; and each of the first bridge section (41) and the second bridge section (42) has a U-shape comprising sides (43) that connect to the first winding section (31) and the second winding section (32) respectively and a bottom (44) for connecting the sides (43) at a position beyond the first foil winding (C1) and the second foil winding (C2) in the width direction.
17. The arrangement of any of claims 13 to 15, wherein: each of the first foil winding (Ci) and the second foil winding (C2) has a first end (61) and a second end (62) opposite the first end (61) in the width direction; and the foil interconnection (23) comprises: a first interconnection part (23a) that connects the first foil winding (Ci) to the second foil winding (C2) at the first ends (61); and a second interconnection part (23b) that connects the first foil winding (Ci) to the second foil winding (C1) at the second ends (62).
18.An electromagnetic device (10) comprising: a core (11) having a first limb (12) and a second limb (13); and the arrangement of foil windings of any of claims 13 to 17, wherein the electromagnetic device (10) is arranged such that the first foil winding (C1) is around the first limb (12) and the second foil winding (C2) is around the second limb (13).
19.A method of arranging foil windings (C1 C2) for an electromagnetic device (10) that has two or more windings, the method being substantially as described herein and/or with reference to the accompanying drawings.
20.An arrangement of foil windings (Ci. C2) for an electromagnetic device (10) that has two or more windings, the arrangement being substantially as described herein and/or with reference to the accompanying drawings.