Technical Field

This application relates to a winding arrangement for use in magnetic devices, in particular, a coil of electrically conductive material for use in a magnetic device.

Background

One of the major difficulties in constructing single module high frequency power magnetics is the difficulty associated with handling high frequency currents in a compact structure. The nature of the magnetic component construction requires the conductors carrying the electrical currents to be placed in close proximity to each other. This makes it impossible to avoid one current carrying conductor getting immersed in the magnetic field of neighbouring conductors. This gives the rise to the phenomena known as the‘proximity effect’.

The design of modem high power high frequency converters requires handling currents such as 250A at 20kHz. At high frequencies and high currents, there are physical limitations to the size and geometry of conductors. For example, conductors must be sufficiently thin to mitigate the skin effect, yet wide enough to accommodate the flow of such high currents.

This imposes machining challenges when manufacturing windings of conductors with such unusual aspect ratios.

Known devices have used interleaved foil windings when high frequency, high current windings are required. This has a number of machining difficulties and limits the power that can be achieved in a single unit. Larger overlapping area in this construction increases the interwinding capacitance and the amount of insulation material required. This also obstructs the flow of heat making it difficult to achieve high power densities.

We have appreciated that it would be desirable to provide a winding arrangement that addresses these issues.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a coil of electrically conductive material for use in a magnetic device is provided. The coil has a winding axis and comprises a first section having a first plurality of turns arranged around the winding axis of the coil, and a second section having a second plurality of turns arranged around the winding axis of the coil. The second plurality of turns being integral with the first plurality of turns. The outer periphery of the first plurality of turns fit within the inner periphery of the second plurality of turns when viewed along the winding axis of the coil, and the first and second sections being adjacent when viewed perpendicular to the winding axis of the coil. Optionally, the first plurality of turns and the second plurality of turns have a width in a direction perpendicular to the axis, defining the inner and outer periphery with respect to the axis of the coil.

Optionally, the electrically conductive material may be a flat wire.

Optionally, the thickness of the flat wire in the direction of the axis is less than l.5mm and the width of the flat wire in the direction perpendicular to the axis of the coil is less than 20mm.

Optionally, the first plurality of turns enclose a first area, and the second plurality of turns enclose a second area, the second area overlapping the first area and being larger than the first area. Optionally, each turn in the first plurality of turns is identical to each of the other first turns, and wherein each turn in the second plurality of turns is identical to each of the other second turns.

Optionally, the shape formed by the inner periphery of the first plurality of turns is the same as the shape formed by the inner periphery of the second plurality of turns. Optionally, the first plurality of turns is arranged helically around the winding axis of the coil, and the second plurality of turns is also arranged helically around the winding axis of the coil.

Optionally, the first plurality of turns and the second plurality of turns are concentric about the winding axis of the coil. Optionally, the number of turns in the first plurality of turns is equal to the number of turns in the second plurality of turns.

Optionally, wherein the shape of an area enclosed by the first plurality of turns and/or the shape of an area enclosed by the second plurality of turns is rectangular, square, or circular. According to a second aspect of the present invention, a winding arrangement for use in magnetic devices is provided. The winding arrangement comprises a first coil according to the first aspect of the invention or any of its embodiments, and a second coil according to the first aspect of the invention or any of its embodiments. The first coil and second coil are arranged coaxially such that the first section of the first coil is disposed within the second section of the second coil, and the first section of the second coil is disposed within the second section of the first coil.

Optionally, the number of turns in the first plurality of turns of the first coil is equal to the number of turns in the second plurality of turns in the second coil, and the number of turns in the first plurality of turns of the second coil is equal to the number of turns in the second plurality of turns of the first coil.

Optionally, the shape formed by the outer periphery of the first plurality of turns of the first coil is the same as the shape formed by the inner periphery of the second plurality of turns of the second coil, and the shape formed by the outer periphery of the first plurality of turns of the second coil is the same as the shape formed by the inner periphery of the second plurality of turns of the first coil.

Optionally, the first plurality of turns of the first coil fit snugly within the second plurality of turns of the second coil, and the first plurality of turns of the second coil fit snugly within the second plurality of turns of the first coil.

Optionally, the outer periphery of the first plurality of turns of the first coil is substantially the same distance from the winding axis of the coil as the inner periphery of the second plurality of turns of the second coil, and the outer periphery of the first plurality of turns of the second coil is substantially the same distance from the winding axis of the coil as the inner periphery of the second plurality of turns of the first axis.

According to a third aspect of the present invention, electrical transformer is provided. The electrical transformer comprises the winding arrangement of any of the twelfth to the sixteenth embodiments. The windings are arranged around a transformer core.

The proposed coils and winding arrangement allow the conductors carrying current in opposite directions to be placed in close proximity to each other. This mitigates the proximity effect and therefore lowers the high frequency losses significantly. Further, this arrangement eliminates the requirement of having to form the windings of conductors with extreme aspect ratios, substantially overcoming the manufacturing limitations previously associated with the manufacture of the high frequency, high currents components.

As such, the claimed invention makes it possible to achieve high power levels at high frequencies and eliminate the manufacturing difficulties of previous constructions that mitigate high frequency losses. It further makes it possible to construct high power transformers operating at much higher frequencies than it was possible with conventional constructions, and improves the heat flow between windings allowing compact designs with high power densities. It eliminates the frequency dependence of the power level that can be achieved in a single module construction and makes magnetic designs more prepared for future developments in the industry.

BRIEF DESCRIPTION OF THE DRAWINGS Examples of the invention will now be described, with reference to the figures, in which: Figure 1 illustrates a plan view of a coil from either end of the winding axis; Figure 2 illustrates two isometric views of a coil;

Figure 3 illustrates a winding arrangement comprising two coils;

Figure 4 illustrates the cross-over of the coils according to embodiments of the invention; Figure 5 illustrates an electrical transformer according to embodiments of the invention.

DET AIDED DESCRIPTION

Figures la and lb show an example of a coil 101 according to an embodiment of the present invention. In Figure la, a plan view of the coil 101 from one side is shown, and in Figure lb, a plan view of the coil 101 from the opposite side is shown. That is, the views are looking from opposite ends of the coil along its winding axis, which runs longitudinally through all of the turns of the coil.

In Figures la and lb, an electrically conductive material is configured into the shape of a coil 101. The coil consists of two main sections: a first section having a first plurality of turns 103 and a second section having a second plurality of turns 105. These two sections are integral to each other, in this case being joined by a cross-over portion 107, and the coil 101 terminates at either end by connection portions 109.

The first 103 and second plurality of turns 105 are each arranged around the winding axis of the coil. In the example coil 101 of Figures la and lb, the first 103 and second plurality of turns 105 are concentric about the winding axis of the coil. The centre of the first plurality of turns 103 aligns with the centre of the second plurality of turns 105 along the axis, that is, the first and second sections are coaxial. The axis of the first 103 and second plurality of turns 105 is the same as the winding axis of the coil in the present example, though this may not always be the case. In a further example, the first 103 and second plurality of turns 105 could be arranged helically around the winding axis of the coil.

Returning to the example of Figures la and lb, the first plurality of turns 103 has an outer periphery, the outer periphery being the periphery along the edge of the electrically conductive material furthest from the axis. In other words, along the edge of the electrically conductive material opposite to the edge facing the axis.

The second plurality of turns 105 has an inner periphery, the inner periphery being the periphery along the edge of the electrically conductive material closest to the axis. In other words, along the edge of the electrically conductive material opposite to the edge facing away from the axis.

The size of the first plurality of turns 103 is smaller than the size of the second plurality of turns 105. The size difference is such that the inner periphery of the second plurality of turns 105 is larger than the outer periphery of the first plurality of turns 103, such that when viewed along the axis of the coil, as in Figures la and lb, the first plurality of turns 103 fits within the second plurality of turns 105 without the material of the first plurality of turns 103 overlapping with the material of the second plurality of turns 105. That is, the outer periphery of the first plurality of turns 103 fits within the inner periphery of the second plurality of turns 105.

A first area is enclosed by the first plurality of turns 103 and a second area is enclosed by the second plurality of turns 105. The second area is larger than the first area due to the size of the second plurality of turns 105 being larger than the size of the first plurality of turns 103. The second enclosed area overlaps the first enclosed area when viewed down the axis. The shape of the first area may be the same as the shape of the second area, though a different size. In the present example, the shape of the areas enclosed by the turns of both the first 103 and second plurality of turns 105 can be seen to be a square, with rounded comers. That is, the shape formed by the inner peripheries of the first 103 and second plurality of turns 105, when viewed along the axis of the coil, is a square, with rounded comers. However, other shapes could be used. For example, the shape of the turns may be rectangular, or circular, and may or may not have rounded comers.

Figures 2a and 2b show the coil 101 in two isometric views: with the second plurality of turns 105 on top in Figure 2a, and with the first plurality of turns 103 on top in Figure 2b.

As can be seen in these figures, the first plurality of turns 103 are grouped together, as are the second plurality of turns 105. That is, the first section has a first plurality of turns 103 and the second section has a second plurality of turns 103, and the first section is adjacent to the second section, in particular when viewed perpendicular to the winding axis of the coil.

It can also be seen that there are an equal number of turns in the first plurality of turns 103 and the second plurality of turns 105. In the present example, the first plurality of turns 103 comprises two complete turns, and the second plurality of turns 105 also comprises two complete turns, though this is not limiting and more or fewer windings could be used.

Alternatively, an unequal number of turns may be used. For example, there may be more turns in the first plurality of turns 103 than in the second plurality of turns 105, or vice versa.

In the present example, each turn in the first plurality of turns 103 is identical to each of the other turns in the first plurality of turns 103, and each turn in the second plurality of turns 105 is identical to each of the other turns in the second plurality of turns 105.

The electrically conductive material in the present example is a flat wire, though other electrically conductive materials could be used. It can be seen that the flat wire has a small thickness relative to its width, where the thickness of the wire is measured in the direction parallel to the axis of the coil, and the width is measured in a direction perpendicular to the axis of the coil. The electrically conductive material is flat enamelled copper wire, and has a thickness of less than 1.5mm and a width of less than 20mm. Alternatively, other electrically conductive materials, such as aluminium, may be used, along with conductive materials with other cross sections and dimensions. A winding arrangement 111 consisting of two coils lOla, lOlb, as described above, will now be discussed with reference to Figure 3. It is appreciated that while the winding arrangement 111 is primarily discussed with respect to the specific embodiment of the coils lOla, lOlb, any two coils consistent with the discussion relating to Figures la and lb, and 2a and 2b, may be used, provided that they may be arranged as follows.

The winding arrangement comprises a first coil lOla and a second coil lOlb. The first coil lOla comprises a first plurality of turns l03a and a second plurality of turns l05a. These are connected by a cross-over portion l07a, and the ends of the coil terminate with connection portions l09a. The second coil lOlb comprises a first plurality of turns l03b and a second plurality of turns l05b. These are connected by a cross-over portion l07b, not shown, and the ends of the coil terminate with connection portions l09b. The first coil 10 la and the second coil lOlb may be electrically isolated from one another. That is to say, an electric current cannot flow from one coil to the other coil. The first coil lOla and the second coil lOlb may be magnetically coupled to each other, even if they are electrically isolated.

In the present embodiment, both the first coil 10 la and the second coil 10 lb have an equal number of turns in the first plurality of turns 103 a, l03b and in the second plurality of turns l05a, l05b, namely two complete turns. However, more or fewer turns could be used.

Additionally, the number of turns in the first plurality of turns 103 a, l03b and in the second plurality of turns l05a, l05b does not have to be equal. For example, the first coil lOla could have three turns in the first plurality of turns 103 a and five turns in the second plurality of turns l05a, while the second coil lOlb could have five turns in the first plurality of turns l03b and three turns in the second plurality of turns l05b. Advantageously, the first coil lOla has the same number of turns in the first plurality of turns l03a as the second coil lOlb has in the second plurality of turns l05b, and the first coil lOla has the same number of turns in the second plurality of turns 105a as the second coil 10 lb has in the first plurality of turns l03b.

The first coil lOla and the second coil lOlb are both arranged coaxially, with the axis of each coil lOla, lOlb aligning along the axis of the winding arrangement 111. However, the first coil lOla is arranged the other way around relative to the second coil lOlb. That is, the first plurality of turns of the first coil l03a is located at the same end of the winding arrangement 111 as the second plurality of turns of the second coil l05b, while the second plurality of turns of the first coil l05a is located at the same end of the winding arrangement 111 as the first plurality of turns of the second coil l03b. In such a way, the coils lOla, lOlb are arranged such that the first plurality of turns of the first coil l03a is disposed within the second plurality of turns of the second coil l05b, and the first plurality of turns of the second coil l03a is disposed within the second plurality of turns of the first coil 103 a.

In embodiments of the present invention, the first plurality of turns of the first coil 103 a fit snugly within the second plurality of turns of the second coil l05b, and the first plurality of turns of the second coil l03b fit snugly in the second plurality of turns of the first coil l05a. That is, there is little space between the turns of the two coils lOla, lOlb. In other words, the outer periphery of the first plurality of turns of the first coil l03a is substantially the same distance from the winding axis of the coil as the inner periphery of the second plurality of turns of the second coil l05b, and the outer periphery of the first plurality of turns of the second coil l03b is substantially the same distance from the winding axis of the coil as the inner periphery of the second plurality of turns of the first axis l05a.

In order for the coils lOla, lOlb to be arranged in the manner described above to provide the winding arrangement 111, the first coil lOla and the second coil lOlb must cross over.

Figures 4a, 4b and 4c show details of the two coils crossing over. Figures 4a and 4b show two examples by which the coils can cross for square or rectangular coils.

As shown in Figure 4a, the coils cross over via the cross-over portions l07a, l07b. The end of the first section of the first coil l03a, having a plurality of first turns, is shown inside the second portion of the second coil l05b in the lower of the diagram. These sections are connected to the cross-over sections of their respective coils l07a, l07b. The coils cross in the lower right of the figure, and the cross-over portion of the second coil l07b is shown as going over the cross-over portion of the first coil l07a. The cross-over sections l07a, l07b are then connected to the other sections of the respective coils. That is, the cross-over section of the first coil 107a is connected to the second section of the first coil l05a, whereas the cross-over section of the second coil l07b is connected to the first section of the second coil l03b.

Figure 4a shows an example with little cross over, that is the cross-over portions over the coils l07a, l07b are short, and the coils do not have much overlap. However, Figure 4b shows an example with greater cross over, where the coils overlap for approximately a quarter of a turn. Figure 4c shows an example where the turns of the coils are circular. The principles of the cross-over portions l07a, l07b in Figures 4b and 4c are substantially the same as described in relation to Figure 4a.

In another embodiment of the invention, the winding arrangement, for example that discussed in relation to Figure 3, may be used in an electrical transformer 115. An example of such an electrical transformer 115 is shown in Figure 5. In this transformer, the first coil lOla and the second coil lOlb are electrically isolated from each other, but are magnetically coupled to each other. By connecting the connection portions of the first coil l09a, acting as the inputs 123, to an alternating current (AC) voltage source 117 via input terminals, an AC voltage will be produced across the connection portions of the second coil l09b. A load 119 may then be connected across output terminals via the outputs 121 which comprise the connection portions of the second coil l09b. By varying the number of turns in each coil, a step-up or step-down in voltage can be achieved.

The transformer 115 has a transformer core 113. In the case of the present example, the core 113 is a cylindrical iron core. However, other core materials or designs may be used. In one example, the core may be an air core. Alternatively, in another example the core could be a laminated E-I type ferrous core. Such cores may improve the performance of the transformer 115. A specific core may be chosen depending upon the requirements that the transformer 115 must fulfil.

Additionally, the transformer 115 may be used individually or as a bank of connected or unconnected transformers.

In one embodiment, the transformer 115 of Figure 5 may be used in a vehicle, for example in a regenerative braking system. In this situation, the transformer may operate with the voltage source 117 being connected to an electrical generator powered by the wheels of a vehicle, and the load 119 may be a rechargeable battery pack.

Alternatively, such a transformer 115 could be used in power generation equipment, particularly in renewable energy systems. For example, it could be used to convert an output voltage from a wind turbine. In this example, the voltage source 117 may be an electrical generator powered by the rotation of the wind turbine rotors, and the load 119 may be an electrical power distribution grid. In other embodiments, instead of a wind turbine, the voltage source 117 may be a wave energy converter, or a hydropower turbine. Further applications of the present winding arrangement and transformer 115 are also contemplated. For example, the transformer 115 of Figure 5 could be used, alone or in a transformer bank of connected or unconnected transformers, in DC-DC converters, power inverters, radio frequency electronic equipment, or in miniature scale transformers. It is noted that this list is not intended to be exhaustive, and that other applications are also

contemplated.

Yet further applications of the present flat wire coil design are also contemplated. For example in a preferred example, a transformer or bank of connected or unconnected transformers may incorporate multiple flat wire coils. As a further example, the flat wire coils of two or more transformers may be inter-connected so that a resultant phase of the output or outputs of each transformer is different to the input phase.