HYBRID CONSTRUCTION TRANSFORMER

TECHNICAL FIELD

This application relates to an electrical transformer, and in particular to a hybrid construction transformer with a semi-potted and semi-open construction.

BACKGROUND ART

Murata’s pdqb winding technology makes it possible to achieve the theoretically minimum level of high frequency conductor losses in high power high frequency transformers (which typically have operating parameters above 10kW and 10kHz). Murata’s pdqb technology is described in UK patent application publication GB2574481A and international patent application publication WO 2019/234453 A1 , which are hereby incorporated by reference in their entirety.

Further Murata’s thermal management technology makes it possible to extract heat generated in compact transformer structures effectively. Murata’s thermal management technology is described in UK patent application publications GB2597670A and GB2597470A, and international patent application publications WO 2022/023744 A1 and WO 2022/018436 A1 , which are hereby incorporated by reference in their entirety.

Figure 1 shows an example of an existing Murata pdqb transformer 100. The transformer 100 includes a transformer core and set of windings contained within a closed housing. In other words, the transformer 100 has a closed construction. Known transformers, such as the transformer 100 of Figure 1 , use either completely potted constructions or completely unpotted open constructions. Both of these options have associated disadvantages.

Moreover, there are a number of parameters, approximately 40, that affect the design of a high power high frequency transformer. These include the primary voltage, secondary voltage, rated power (continuous), operating frequency, primary inductance, secondary inductance, leakage inductance, primary DC resistance, secondary DC resistance, primary AC resistance, secondary AC resistance, and the interwinding capacitance. Different parameters have a different degree of significance for different applications of the transformer, making it difficult provide a single construction or even a small group of different constructions that will be suitable for all these applications.

Previous attempts to provide a universal transformer have included using different core sizes and/or core assemblies to make the transformer suitable for different voltage and frequency levels. A power level in the range of 30kW to 70kW, preferably 50kW, is desirable for many applications. A 50kW power level is a reasonable power level that would cover over 90% of the common applications.

We have appreciated that it would be desirable to provide an improved, cost-effective single transformer construction applicable to many applications. In particular, a construction where only minor adjustments are needed to make the transformer universal for the above- mentioned power level for a range of voltages and frequencies of operation.

SUMMARY OF THE INVENTION

The invention is defined by the independent claims, to which reference should now be made. Advantageous features are set out in the dependent claims.

According to a first aspect of the present invention, an electrical transformer is provided. The electrical transformer comprises: a transformer core; a winding unit arranged around the transformer core, the winding unit comprising a primary coil and a secondary coil encased in a potting material; and a housing surrounding the transformer core and the winding unit, said housing comprising a plurality of thermally conductive sections in thermal contact with the winding unit and/or the transformer core, and said housing having one or more open sides such that the winding unit is exposed.

Optionally, the housing comprises two open sides located on opposing sides of the housing, to expose the winding unit at both of said opposing sides of the housing.

Optionally, the two open sides expose a portion of each of the plurality of thermally conductive sections.

Optionally, wherein the transformer is substantially cuboid in shape, and each open side extends across an entire face of the cuboid transformer.

Optionally, the housing comprises an upper panel and a lower panel disposed on opposing sides of the transformer.

Optionally, the upper panel and lower panel extend in planes normal to a winding axis of the winding unit.

Optionally, the upper panel and lower panel are in contact with the transformer core.

Optionally, the plurality of thermally conductive sections includes a first set of thermally conductive sections that extend between the upper panel and the lower panel and are in thermal contact with the upper panel and lower panel.

Optionally, each of the first set of thermally conductive sections is releasably secured to the upper panel at a first end, and releasably secured to the lower panel at a second end.

Optionally, the plurality of thermally conductive sections includes a second set of thermally conductive sections disposed between the upper panel and the winding unit, and in thermal contact with the upper panel and the winding unit; and/or the plurality of thermally conductive sections includes a third set of thermally conductive sections disposed between the lower panel and the winding unit, and in thermal contact with the lower panel and the winding unit.

Optionally, each of the second set of thermally conductive sections is releasably secured to the upper panel; and/or each of the third set of thermally conductive sections is releasably secured to the lower panel.

Optionally, the electrical transformer further comprises one or more additional thermally conductive sections disposed against a central portion of the transformer core, wherein each additional thermally conductive section extends between the upper panel and the lower panel and is in thermal contact with the upper panel and lower panel; wherein the winding unit is arranged around the transformer core and the additional thermally conductive sections.

Optionally, the one or more additional thermally conductive sections are integral with the winding unit.

Optionally, the housing comprises gaps between the first set of thermally conductive sections and the third set of thermally conductive sections; and/or the housing comprises gaps between the second set of thermally conductive sections and the one or more additional thermally conductive sections.

Optionally, the transformer core comprises: one or more core layers, wherein each core layer comprises two closed cores, and each closed core is constructed from either two U-shaped cores or from a U-shaped core and an l-shaped core; a thermally conductive plate that is disposed between the closed cores and extends along a winding axis of the winding unit so as to bisect the one or more core layers; and optionally, when the transformer core comprises a plurality of core layers, one or more secondary thermally conductive plates disposed between the core layers.

Optionally, the transformer core comprises: one or more core layers, wherein each core layer comprises one closed core constructed from either two U-shaped cores or from a U-shaped core and an l-shaped core; a thermally conductive plate that is disposed one side of the transformer core and extends along a winding axis of the winding unit; and optionally, when the transformer core comprises a plurality of core layers, one or more secondary thermally conductive plates disposed between the core layers.

Optionally, the winding unit comprises a pair of protrusions configured to engage with the transformer core, with a portion of the transformer core located between the protrusions when the winding unit is arranged around the transformer core.

Optionally, the pair of protrusions extend between the winding unit and the lower panel.

Optionally, the pair of protrusions are formed from the potting material. Optionally, the plurality of thermally conductive sections prevent movement of the winding unit within the housing.

Optionally, the winding unit comprises a primary coil and a secondary coil, and: the primary coil and the secondary coil each comprise a first section and a second section, and each of the first and second sections include a first set of turns having a first diameter and a second set of turns having a second diameter; the first diameter is larger than the second diameter; the first section and second section of the primary coil are electrically connected in parallel and are wound around a common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; the first section and second section of the secondary coil are electrically connected in parallel and are also wound around the common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; and the turns of the primary coil are interleaved with the turns of the secondary coil.

Optionally, the winding unit further comprises a plurality of secondary coils, preferably up to ten secondary coils.

Optionally, the winding unit comprises connection points for the primary coil and secondary coil that extend through the upper panel.

Optionally, the lower panel is a cold plate, or is disposed in thermal contact with a cold plate.

Optionally, one or more of the plurality of thermally conductive sections includes radiating fins.

Optionally, one or more of the plurality of conductive sections are formed from aluminium; and/or one or more of the plurality of conductive sections includes at least one outer surface that is coloured black.

Optionally, the electrical transformer further comprises one or more winding cooling plates; wherein each winding cooling plate is in thermal contact with an upper or lower surface of the winding unit; and wherein each winding cooling plate is in thermal contact with at least one of the plurality of thermally conductive sections.

Optionally, the plurality of thermally conductive sections includes a first pair of thermally conductive sections disposed in thermal contact with an upper surface of the winding unit; and/or the plurality of thermally conductive sections includes a second pair of thermally conductive sections disposed in thermal contact with a lower surface of the winding unit.

Optionally, the electrical transformer further comprises: one or more winding cooling plates disposed between an upper surface of the winding unit and the first pair of thermally conductive sections; and/or one or more winding cooling plates disposed between a lower surface of the winding unit and the second pair of thermally conductive sections.

Optionally, each winding cooling plate extends in a direction parallel to the plane of the winding unit and extends through the transformer core in a direction perpendicular to the plane of the transformer core.

Optionally, each winding cooling plate extends between a pair of thermally conductive sections positioned on opposing sides of the transformer core.

The electrical transformer of the first aspect provides a number of advantages. The semi-open construction enhances the cooling of the transformer core and winding, whilst also reducing the weight and cost of the device. Moreover, the electrical transformer is modifiable after installation, thus providing an adaptable transformer that is applicable to many applications, and universal over power ratings in the range of 50kW to 100kW.

In particular, a simple change of the plurality of thermally conductive sections (between those with and without radiating fins) and/or a simple change of the lower panel (such as introducing a cooling plate) mean that the transformer can be made suitable for various different forced air cooled, natural convention cooled or water cooled plate mounted constructions. The winding arrangement can also be changed after initial installation. These modifications are easily performed by, for example, using releasable connections, helping to provide a universal transformer construction.

According to a second aspect of the present invention, a winding arrangement for an electrical transformer is provided. The winding arrangement of the second aspect is described in the following clauses:

(1) A winding arrangement for an electrical transformer, the winding arrangement comprising a primary coil and a secondary coil, wherein: the primary coil and the secondary coil each comprise a first section and a second section, and each of the first and second sections include a first set of turns having a first diameter and a second set of turns having a second diameter; the first diameter is larger than the second diameter; the first section and second section of the primary coil are electrically connected in parallel and are wound around a common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; the first section and second section of the secondary coil are electrically connected in parallel and are also wound around the common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; and the turns of the primary coil are interleaved with the turns of the secondary coil. (2) The winding arrangement of clause 1 , wherein the primary coil is interleaved with the secondary coil such that each turn of the secondary coil is disposed between two turns of the primary coil when viewed along a direction perpendicular to the common winding axis.

(3) The winding arrangement of clauses 1 or 2, wherein the primary coil is interleaved with the secondary coil such that the turns of the first sets of turns of the primary coil and the turns of the first sets of turns of the secondary coil alternate as you move along the common winding axis, and the turns of the second sets of turns of the primary coil and the turns of the second sets of turns of the secondary coil alternate as you move along the common winding axis.

(4) The winding arrangement of any preceding clause, wherein the primary coil is identical to the secondary coil.

(5) The winding arrangement of clause 4, wherein the secondary coil is rotated by 180° about the common winding axis relative to the primary coil.

(6) The winding arrangement of clause 1 , further comprising one or more additional secondary coils, wherein: the one or more additional secondary coils each comprise a first section and a second section, and each of the first and second sections include a first set of turns having the first diameter and a second set of turns having the second diameter; the first section and second section of each additional secondary coil are electrically connected in parallel and are wound around the common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; and the turns of the primary coil are interleaved with the turns of the one or more additional secondary coils.

(7) The winding arrangement of clause 6, wherein the primary coil is interleaved with the secondary coil and the one or more additional secondary coils such that: each turn of the secondary coil is disposed between two turns of the primary coil when viewed along a direction perpendicular to the common winding axis; and each turn of the one or more additional secondary coils is disposed between two turns of the primary coil when viewed along the plane containing the common winding axis.

(8) The winding arrangement of clauses 6 or 7, wherein the primary coil is interleaved with the secondary coil and the one or more additional secondary coils such that: the turns of the first sets of turns of the primary coil and the turns of the first sets of turns of the secondary coil alternate as you move along a first portion of the common winding axis, and the turns of the second sets of turns of the primary coil and the turns of the second sets of turns of the secondary coil alternate as you move along the first portion of the common winding axis; and the turns of the first sets of turns of the primary coil and the turns of the first sets of turns of the one or more additional secondary coils alternate as you move along a second portion of the common winding axis, and the turns of the second sets of turns of the primary coil and the turns of the second sets of turns of the one or more additional secondary coils alternate as you move along the second portion of the common winding axis.

(9) The winding arrangement of any of clauses 6 to 8, wherein the number of turns in the primary coil is greater than or equal to the combined total number of turns in the secondary coil and the one or more additional secondary coils.

(10) The winding arrangement of any of clauses 6 to 9, wherein the winding arrangement comprises up to nine additional secondary coils.

(11) The winding arrangement of any of clauses 6 to 10, wherein the secondary coil and the one or more additional secondary coils are stacked such that the secondary coil and the one or more additional secondary coils fully overlap when viewed along the common winding axis.

(12) The winding arrangement of any preceding clause, wherein the primary coil and the secondary coil fully overlap when viewed along the common winding axis.

(13) The winding arrangement of any preceding clause, wherein for each coil the number of turns in the first set of turns of each of the first and second sections of that coil is equal, and the number of turns in the second sets of turns of each of the first and second sections of that coil is equal.

(14) The winding arrangement of any preceding clause, wherein for each section of each coil the number of turns in the first set of turns is equal to the number of turns in the second set of turns of that section.

(15) The winding arrangement of any preceding clause, wherein the first sets of turns and the second sets of turns of each coil are concentric about the common winding axis.

(16) The winding arrangement of any preceding clause, wherein: the turns of each of the coils has a rectangular, square, or circular shape about the winding axis; and/or each set of turns is arranged helically around the common winding axis.

(17) The winding arrangement of any preceding clause, wherein each of the coils are formed from aluminium wire.

(18) The winding arrangement of any preceding clause, wherein each of the coils is formed from flat wire.

(19) The winding arrangement of clause 18, wherein the flat wire has a width of between 10mm and 15mm, and a thickness of between 0.8mm and 1.2mm, preferably a thickness of 1mm.

(20) The winding arrangement of any preceding clause, wherein each of the coils are encased in a potting material.

(21) The winding arrangement of any preceding clause, wherein each coil includes connection terminals extending substantially parallel to the direction of the common winding axis, for allowing an electrical connection to be made with that coil. (22) The winding arrangement of clause 21 , wherein the connection terminals of the primary coil and the connection terminals of the secondary coil or coils are located on opposing sides of the winding arrangement.

According to a third aspect of the present invention, a winding arrangement for an electrical transformer is provided. The winding arrangement of the third aspect is described in the following clauses:

(23) A winding arrangement for an electrical transformer, the winding arrangement comprising a primary coil and plurality of secondary coils, wherein: the primary coil comprises a first section and a second section, and each of the first and second sections include a first set of turns having a first diameter and a second set of turns having a second diameter; the first diameter is larger than the second diameter; the first section and second section of the primary coil are electrically connected in parallel and are wound around a common winding axis, with the second set of turns of the second section positioned within the first set of turns of the first section, and the second set of turns of the first section positioned within the first set of turns of the second section, when viewed along the common winding axis; each of the plurality of secondary coils includes a first set of turns having the first diameter and a second set of turns having the second diameter, both wound around the common winding axis; the turns of the primary coil are interleaved with the turns of the plurality of secondary coils.

(24) The winding arrangement of clause 23, wherein the primary coil is interleaved with the secondary coils such that each turn of the plurality of secondary coils is disposed between two turns of the primary coil when viewed along a direction perpendicular to the common winding axis.

According to a fourth aspect of the present invention, an electrical transformer is provided. The electrical transformer of the fourth aspect is described in the following clause:

(25) An electrical transformer comprising: a transformer core; and the winding arrangement of any of clauses 1 to 24 arranged around the transformer core.

The winding arrangements of the second and third aspects reduce losses caused by the proximity effect, due to the interleaving of the primary and secondary coils. Moreover, the winding arrangements allow for multiple secondary coils to be used whilst retaining a compact structure and small footprint, allowing a transformer including the winding arrangement to power multiple circuits and/or provide redundancy in both high and low current situations. Lastly, when multiple secondary coils are used, series and parallel connections between the secondary coils can be tailored to allow the transformer to operate with the desired power over and large voltage and frequency range. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in relation to the accompanying drawings, in which:

Figure 1 shows an example of a known transformer;

Figure 2a shows a transformer according to an embodiment of the present invention;

Figure 2b shows the transformer core and winding unit of the transformer of Figure 2a in isolation;

Figure 3a shows the transformer of Figure 2a with the upper panel removed.

Figure 3b shows a plan view of Figure 3a;

Figure 3c shows a side view of the transformer of Figure 2a;

Figure 3d shows a second side view of the transformer of Figure 2a;

Figure 3e shows a bottom view of the transformer of Figure 2a;

Figure 3f shows a bottom view of the transformer of Figure 2a with the lower panel removed.

Figure 4 shows a winding unit in another embodiment of the present invention;

Figure 5 shows a transformer according to an embodiment of the present invention;

Figure 6 shows a transformer core according to another embodiment of the present invention in isolation;

Figure 7a shows a winding arrangement in an embodiment of the present invention;

Figure 7b shows a first section of a coil of an embodiment of the present invention;

Figure 7c shows a second section of a coil of an embodiment of the present invention;

Figure 7d shows an alternative view of the second section of Figure 7c;

Figure 7e shows a coil of an embodiment of the present invention;

Figure 7f shows a cross sectional view of the winding arrangement of Figure 7a;

Figure 8a shows a winding arrangement in an embodiment of the present invention;

Figure 8b shows an alternative view of the winding arrangement of Figure 8a;

Figure 9a shows a first section of a secondary coil of an embodiment of the present invention;

Figure 9b shows an alternative view of the first section of Figure 9a;

Figure 9c shows a second section of a secondary coil of an embodiment of the present invention;

Figure 9d shows an alternative view of the second section of Figure 9c;

Figure 9e shows two secondary coils of an embodiment of the present invention;

Figure 10a shows four secondary coils of an embodiment of the present invention;

Figure 10b shows nine secondary coils of an embodiment of the present invention;

Figure 10c shows ten secondary coils of an embodiment of the present invention;

Figure 11a shows two secondary coils of an embodiment of the present invention; Figure 11b shows two secondary coils of an embodiment of the present invention;

Figure 11c shows two secondary coils of an embodiment of the present invention;

Figure 12a shows four secondary coils of an embodiment of the present invention;

Figure 12b shows nine secondary coils of an embodiment of the present invention;

Figure 12c shows ten secondary coils of an embodiment of the present invention;

Figure 12d shows an alternative view of the ten secondary coils of Figure 12c;

Figure 13 shows a cross sectional view of a winding material in an embodiment of the present invention;

Figure 14 is a graph showing the maximum operating power of an electrical transformer according to embodiments of the present invention;

Figure 15a shows a transformer according to a second embodiment of the present invention;

Figure 15a shows a cutaway view of a transformer according to a second embodiment of the present invention;

Figure 15a shows a cutaway view of a transformer according to a second embodiment of the present invention;

Figure 16a shows a transformer according to a third embodiment of the present invention;

Figure 16b shows a cutaway view of a transformer according to a third embodiment of the present invention.

DETAILED DESCRIPTION

Transformer Construction

Figure 2a shows a transformer 200 according to a first embodiment of the present invention. The transformer 200 includes a transformer core 202 and a winding unit 204 arranged around the transformer core (both shown lightly shaded in Figure 2a). The transformer 200 further includes a mounting arrangement, referred to herein as a housing 208 surrounding the transformer core 202 and the winding unit 204. The housing 208 includes an upper panel 210 and a lower panel 212, and includes a plurality of thermally conductive sections 214,216,218 in thermal contact with the winding unit 204 and the transformer core 202, as will be explained in more detail below.

The transformer 200 can be a high frequency transformer, a high voltage transformer, a high power transformer, a high power high frequency transformer, a high voltage high frequency high power transformer, or the like. A single phase shell type transformer is considered in Figure 2 and throughout this specification, however the present invention could also be applied in multiphase shell type transformers and multiphase core type transformers. Figure 2b shows the transformer core 202 and a winding unit 204 in isolation. The transformer core 202 includes a ULI type core constructed from four U-shaped cores. Although UU type cores will be used as the main example throughout this description, Ul type cores could also be used as an alternative, or in combination with UU type cores. The UU core construction can alternatively be achieved with El arrangements as well as Ul arrangements. Two U-shaped cores are combined to create a closed core. Two closed cores are then combined side by side to construct a core layer. When only U-shaped cores are used, each core layer will include four U-shaped cores, as shown in Fig. 2b. However, more than two core layers could be used in some embodiments, with multiple core layers stacked together, as shown in Figure 6 later. Therefore in general, the number of U-shaped cores used varies in multiples of four, depending on the application. Multiple core layers are typically used at higher power levels. The U-shaped cores are made from a magnetic material such as a ferrite material. An optional thermally conductive plate 228 may also be included in the transformer core 202, as will be explained in more detail later.

The winding unit 204 includes at least one primary coil and one or more secondary coils encased in a potting material. The coils in the winding unit 204 share a common winding axis. The winding unit 204 is arranged around the transformer core 202. Specifically, the winding unit 204 surrounds the central portion (the middle strut) of the transformer core as shown in Figure 2b. Each coil within the winding unit is therefore wound around the central portion of the transformer core 202. Connection terminals 206 extend out of the potting material, for allowing an electrical connection to be made with the coils within the winding unit 204. The connection terminals 206 may extend in a direction substantially parallel to the winding axis of the winding unit 204 (perpendicular to the plane of the winding unit).

A number of different winding arrangements could be used for in the winding unit 204. For example, round wire windings, flat wire windings or even litz wire may be used. The windings may be formed from substantially square turns. The winding unit 204 as a whole including the potting material may therefore a be a square toroidal (donut) shape, as shown in Figure 2b. The windings may be Murata’s pdqb type windings, as detailed in UK patent application GB2574481A and international patent application publication WO 2019/234453 A1 , which are hereby incorporated by reference in their entirety.

Alternatively other winding arrangements could be used. More than one set of windings may be used in the winding unit 204, and each set of windings may contain a number of different coils, for example a primary and one or more secondary coils. The windings in the winding unit 204 may be insulted and protected due to the potting material. The potting material may be cast resin or epoxy or the like. Other transformer grade potting materials can be used, including silicon. Preferably the potting material has a temperature class of class H or higher. However, for certain applications Class B or Class F potting materials may also be used. In general, any winding configuration may be used with the transformer core 202 and housing 208. Specific configurations of possible winding arrangements in some embodiments of the present invention will be discussed in more detail later in Figures 7a onwards.

Returning to Figure 2a, the housing has one or more open sides such that the winding unit 204 is exposed. In other words, the winding unit 204 is not contained within a fully enclosed housing, unlike the transformer 100 of Figure 1 . Instead the housing 208 is not fully enclosed in the present invention, but instead acts as a mounting arrangement for the transformer core 202 and the winding unit 204.

In the present embodiment, the housing comprises two open sides, marked by arrows A,B in Figure 2, that expose the winding unit 204. The two open sides A,B are located on opposing sides of the housing. The transformer 200 of Figure 2a is substantially cuboid in shape, with the two open sides A,B on opposing faces of the cuboid. Each open side may extend across an entire face of the cuboid shaped transformer. A typical size of the transformer 200 in a specific embodiment is about 200mm by 140mm by 110mm, however various other dimensions are possible. In the specific example given, each of the open sides A,B therefore has an area of about 200mm by 140mm. However, in some embodiments the open sides may extend over only a portion of a given face of the transformer 200. Moreover, in some embodiments only one of the sides marked A and B in Figure 2a may be open so as to expose the winding unit 204 at that side only.

This semi-open construction has a number of benefits. Rather than the entire transformer being encased in a potting material, the hybrid construction where only the winding unit 204 is encased in a potting material results in a reduced weight and manufacturing cost. Moreover cooling for the winding unit 204 is improved by allowing portions of the winding unit to be exposed to the surrounding air, without having a completely exposed coils (i.e. an unpotted winding unit) and the associated challenges that such a configuration would present (for example movement of the coils, insulation and vulnerability to damage). The semi-open construction of the present invention is a specifically configured to optimise the trade-off between enhanced cooling and reduced weight versus retaining the necessary structural integrity of the transformer.

In more detail, the housing 208 includes an upper panel 210 and a lower panel 212 disposed on opposing sides of the transformer. The upper and lower panels 210,212 both extend in planes normal to a winding axis of the winding unit 204. In other words, the upper panel 210 is located on the top surface of the transformer 200 in Figure 2a, and the lower panel 210 is located on the bottom surface of the transformer 200 in Figure 2a. The open sides A,B of the transformer that expose the winding unit 204 may be adjacent to the upper panel 210 and lower panel 212, and may extend between the upper and lower panel 210,212. For example, in the embodiment shown in Figure 2a, the two open sides A,B of the housing extend between upper panel 210 and the lower panel 212 along faces on opposing sides of the device that are perpendicular to the upper and lower panels 210,212.

The upper panel and lower panel are in contact with the transformer core 202 on the top and bottom sides of the transformer 200. The remaining four sides of the transformer 200 do not include panels in the embodiment shown in Figure 2a. Therefore in the present embodiment there are in fact four open sides (four sides not covered by any panels). The winding unit 204 is exposed at the two opposing open sides A,B as mentioned above. The transformer core 202 is exposed at the other two opposing open sides, marked C and D in Figure 2, that do not include panels. In other words, in the embodiment shown in Figure 2a in which the transformer is substantially a cuboid shape, the two opposing sides A,B that expose the winding unit 204, the two opposing sides C,D that expose the transformer core 202, and the upper and lower panels 210,212 are mutually orthogonal.

In general, of the four open sides A,B,C,D shown in Figure 2a (the four sides other than those covered by the upper and lower panels 210,212), one or both of the sides marked A and B in Figure 2a may be open so as to expose the winding unit 204, and one or both or neither of the sides marked C and D in Figure 2a may be open so as the expose the transformer core 202. The preferred embodiment of Figure 2a has all four of these sides open, which provides maximal cooling for the transformer 200, as will be discussed below.

The upper and lower panels 210,212 may be formed from sheets of material with a high thermal conductivity that will not disrupt the magnetic properties of the transformer, for example a non-magnetic metal could be used, such as aluminium or copper. In some embodiments, alternative materials may be used for the upper panel 210, such as a non- metallic material. The connection terminals 206 for the primary coil and secondary coil may extend through the upper panel, to allow ease of access.

Figures 3a to 3f show the housing 208 of the embodiment of Figure 2a in more detail. Figure 3a shows the transformer 200 of Figure 2a with the upper panel 210 removed. Figure 3b shows a plan view of Figure 3a. Figure 3c shows a side view of the transformer 200 of Figure 2a. Figure 3d shows a second side view of the transformer 200 of Figure 2a. Figure 3e shows a bottom view of the transformer 200 of Figure 2a. Figure 3f shows a bottom view of the transformer 200 of Figure 2a with the lower panel 212 removed.

As can be seen from Figures 2a and 3a to 3f, the transformer 200 includes a plurality of thermally conductive sections 214,216,218 in thermal contact with the winding unit 204 and the transformer core 202. The thermally conductive sections 214,216,218 may be blocks of thermally conductive material. The plurality of thermally conductive sections 214,216,218 include a first set of thermally conductive sections 214, a second set of thermally conductive sections 216, and a third set of thermally conductive sections 218.

The first set of thermally conductive sections 214 extend between the upper panel 210 and the lower panel 212 and are in thermal contact with the upper panel and lower panel. Each of the first set of thermally conductive sections 214 is also positioned in thermal contact with the transformer core 202 and the winding unit 204. The first set of thermally conductive sections 214 includes four thermally conductive sections located towards the four corners of the lower panel 212. In other words, two of the first set of thermally conductive sections 214 are located on one side of the winding unit 204, with the transformer core 202 positioned between those two thermally conductive sections 214, and the other two of the thermally conductive sections 214 are located on the opposing side of the winding unit 204, also on either side of the transformer core 202. Each of first set of thermally conductive sections 214 extend in a lengthwise direction parallel to the winding axis of the winding unit 2014.

The second set of thermally conductive sections 216 are disposed between the upper panel 210 and the winding unit 204, and are in thermal contact with both the upper panel and the winding unit. The second set of thermally conductive sections 216, as best seen in Figure 3b, are located between the upper surface of the winding unit 204 and the lower surface of the upper panel 210. The second set of thermally conductive sections 216 includes four thermally conductive sections in the present embodiment, with each being in thermal contact with a respective one of the first set of thermally conductive sections 214.

The third set of thermally conductive sections 218 are disposed between the lower panel 212 and the winding unit 204, and in thermal contact with the lower panel and the winding unit. The third set of thermally conductive sections 218 are located between the lower surface of the winding unit 204 and the upper surface of the lower panel 212. The third set of thermally conductive sections 218 includes two thermally conductive sections in the present embodiment. Each of the third set of thermally conductive sections 218 extends in a lengthwise direction parallel to the plane of the core layer in the transformer core 202, and perpendicular to the winding axis of the winding unit 204. The third set of thermally conductive sections 218 are best seen in Figure 3f.

Each of the plurality of thermally conductive sections 214,216,218 performs a number of functions.

Firstly, the plurality of thermally conductive sections 214,216,218 retain the winding unit 204 within the housing 208, and prevent any movement of movement of the winding unit 204 within the housing 208. All degrees of freedom of the winding (movement in any direction) is prevented by the plurality of thermally conductive sections 214,216,218.

Secondly, the plurality of thermally conductive sections 214,216,218 extract heat from the transformer core 202 and the winding unit 204. Each of the plurality of thermally conductive sections 214,216,218 is positioned in thermal contact with the transformer core 202 and/or the winding unit 204, depending on the specific embodiment. In the embodiment of Figures 2a and Figures 3a to 3f, each of the first and second sets of thermally conductive sections 214,216 is in thermal contact with both the transformer core 202 and the winding unit 204, and each of the third set of thermally conductive sections 218 is in thermal contact with the winding unit 204.

Heat from the transformer core 202 and the winding unit 204 is transferred to the plurality of thermally conductive sections 214,216,218 through conduction. This heat extracted by the plurality of thermally conductive sections 214,216,218 can be removed via various different cooling means, which will be discussed later. The plurality of thermally conductive sections 214,216,218 therefore act as cooling channels within the housing 208.

The plurality of thermally conductive sections 214,216,218 provide effective removal of heat from the interior of the transformer device. This allows the correct temperature levels to be maintained inside the transformer device, which prevents damage or failure of the device occurring.

Some or all of thermally conductive sections may be exposed as well as the winding unit, due to the one or more open sides. In the present embodiment, the two open sides A,B that expose the winding unit also expose a portion of each of the plurality of thermally conductive sections 214,216,218. This allows and airflow to reach the plurality of thermally conductive sections 214,216,218 to aid cooling, as will be discussed in more detail below. The two open sides C,D that expose the transformer core 202 also expose a portion of the first set of thermally conductive sections 214.

The plurality of thermally conductive sections 214,216,218 are preferably made from a material with a high thermal conductivity that will not disrupt the magnetic properties of the transformer, for example a non-magnetic metal could be used, such as aluminium or copper. Each of the plurality of thermally conductive sections 214,216,218 may be made out of the same material, or out of various different materials. Blocks of aluminium are preferred as the plurality of thermally conductive sections 214,216,218, due to the lightweight properties of aluminium.

The housing 208 may be releasably secured together. In particular, some or all of the plurality of thermally conductive sections 214,216,218 may be releasably secured to the upper and/or lower panels 210,212.

In the present embodiment, each of the first set of thermally conductive sections 214 is releasably secured to the upper panel at a first end of the thermally conductive section, and releasably secured to the lower panel at a second end of the thermally conductive section. Each of the second set of thermally conductive sections 216 is releasably secured to the upper panel. Each of the third set of thermally conductive sections 218 is releasably secured to the lower panel.

In the present embodiment, the plurality of thermally conductive sections 214,216,218 are releasably secured using screw attachments. This is shown in Figures 3a, 3b and 3e for the first and second sets of thermally conductive sections. The screws are not shown for the third set of thermally conductive sections in the Figures, however may be included in some embodiments. Other releasably securing means may also be used, such as clips, nails, bolts or the like.

The releasable connections between the upper and lower panels 210,212 and the plurality of thermally conductive sections 214,216,218 mean that the transformer housing 208 can be easily dismantled and reassembled. This means that the configuration of the transformer housing 208 can be modified after installation, creating a more versatile transformer which may be applied to various different applications.

Optionally, the transformer can include one or more additional thermally conductive sections 220, best seen in Figure 3a. In the present embodiment, two additional thermally conductive sections 220 are included. The additional thermally conductive sections 220 are disposed against the central portion of the transformer core, on either side of the core layer. Each of the additional thermally conductive section 220 extends between the upper panel 210 and the lower panel 212 and is in thermal contact with the upper panel and lower panel. The additional thermally conductive sections 220 may also be in thermal contact with the third set of thermally conductive sections 218 in some embodiments, as shown in Figure 3f. When the additional thermally conductive sections 220 are included, the winding unit 204 is arranged around both the central portion of the transformer core 202 and the additional thermally conductive sections 220.

The additional thermally conductive sections 220 perform a similar heat extraction function as the plurality of thermally conductive sections 214,216,218, and the description above for the plurality of thermally conductive sections 214,216,218 applies analogously. Namely, the additional thermally conductive sections 220 are preferably made from a material with a high thermal conductivity that will not disrupt the magnetic properties of the transformer. The additional thermally conductive sections 220 provide further improvements in the cooling of the transformer 202, as the additional thermally conductive sections 220 can extract heat from the most central part of the transformer 200.

The additional thermally conductive sections 220 may also be attached to the upper panel and/or lower panel 210,212 by a releasably securing means, such as a screw. Alternatively, the additional thermally conductive sections 220 may be held in position by a gluing or a tight fit arrangement. Moreover, the additional thermally conductive sections 220 may be incorporated into the potting material of the winding unit 204 in some embodiments, as discussed in more detail later.

The housing 208 may include gaps 222 between the one or more additional thermally conductive sections 220 and the second set of thermally conductive sections 216, as best seen in Figure 3b. The gaps 222 prevent any eddy current paths being formed due to stray leakage magnetic fields. In other words, the introduction of the gaps 222 in the heat conduction circuit formed by the plurality of thermally conductive sections 214,216,218 and the additional thermally conductive sections 220 avoids the formation of conductive paths through the heat conduction circuit. Such conductive paths can result in eddy currents which can cause high temperature rises and energy losses, and could lead to shorting due to voltages induced by leakage magnetic fields.

The housing 208 may further include gaps 224 between the ends of each of the third set of thermally conductive sections 218 and the first set of thermally conductive sections 214. The gaps 224 also prevent eddy currents and shorting, similarly to the gaps 222. Due to the gaps 222 and gaps 224 an electrically conductive path round the perimeter of the transformer 200 through the plurality of thermally conductive sections 214,216,218 and the additional thermally conductive sections 220 is advantageously prevented.

In the embodiment shown in Figures 2a to 3f, a winding unit 204 with a square toroidal shape is used (as shown in figure 2b) is used. When such a winding unit is used, cavities 226 are present between the third set of thermally conductive sections 218 and the transformer core 202, best seen in Figure 3f. If the additional thermally conductive sections 220 are included, the additional thermally conductive sections 220 extend into these cavities.

Figure 4 shows an alternative winding unit 254, for use in another embodiment of the present invention. The winding unit 254 is the same as the winding unit 204 in Figure 2b, except that the winding unit 254 includes a pair of protrusions 260 which fill the cavities 226 shown in Figure 3f. The pair of protrusions 260 engage with the transformer core 202 when the winding unit 254 is arranged around the transformer core, with a portion of the transformer core 220 located between the protrusions 260. In other words, a grove is formed between the protrusions 260, into which the transformer core 202 is seated. The interlocking between the protrusions 260 and the transformer core 202 means that the winding unit 204 is held securely in place arranged around the transformer core 202, preventing any movement of the winding unit 204 within the housing 208.

When the winding unit 254 is fitted into the housing 208, the pair of protrusions 260 extend between the winding unit 254 and the lower panel 212. The pair of protrusions 260 may be formed from the potting material. In other words, the potting material surrounding the coils within the winding unit 254 and the potting material forming the protrusions 260 may be formed as one integral piece (formed as a single unit).

In some embodiments, the protrusions 260 may themselves be releasably secured to the lower panel 212, in a similar fashion to the plurality of thermally conductive sections 214,216,218, for example by screw fixings. The protrusions 260 may include aluminium blocks moulded into the potting material, into which a screw or the like can engage to couple the protrusions to the lower panel 212. This can provide a strong mechanical fixing, with all the possible degrees of freedom of movement of the winding unit 254 restricted.

In both embodiments of the winding unit 204 and 254, the winding unit may be formed by injection moulding, specifically insert moulding or overmoulding. The coils in the winding unit are positioned into a mould, such as a Teflon or silicone mould, and then the potting material is cast into the mould to encase the coils, and optionally form the protrusions 260. The mould is then removed to leave the integrally formed winding unit. The mould may be formed of two halves which can be disconnected from each other after the moulding process, to release the finished winding unit. Other methods of forming the winding unit are also possible.

In further embodiments, when the one or more additional thermally conductive sections 220 are included, the one or more additional thermally conductive sections may be formed integrally with the winding unit. In other words, the one or more additional thermally conductive sections 220 may also be positioned within the mould prior to the introduction of the potting material, such that portions of the one or more additional thermally conductive sections 220 may be incorporated into (encased in) the potting material in the completed winding unit. The additional thermally conductive sections 220 will then be integral with the winding unit.

In the case of the winding unit 204 of Figure 2b, when the additional thermally conductive sections 220 are integral with the winding unit 204, the central portion of each additional thermally conductive section 220 will be included within the potting material. In the case of the winding unit 254 of Figure 4, the central portion of each additional thermally conductive section 220 will be included within the potting material, and the bottom portion of each additional thermally conductive section 220 (towards the lower panel 212) will be included in potting material of the protrusions 260.

Moulding the winding unit together with the additional thermally conductive section 220 to form a single integral unit means that when the winding unit 204 is arranged around the transformer core 202, the additional thermally conductive sections 220 will be held securely against the central portion of the transformer core 202 by the potting material.

The above described embodiments provide a number of advantages. Firstly, the hybrid semi-potted and open construction, where just the winding unit is potted and sides of the housing remain open, means that cooling air can reach the winding unit with ease. However, due to the potting material around the windings, the challenges associated with fully exposed windings, such as movement of the coils, insulation and vulnerability to damage, are negated.

Moreover, the reduction in the amount of potting material needed leads to a reduction in manufacturing costs, as well as a reduction in the weight of the device. For example, a typical dimension of the transformer 200 of the above embodiments is 200mm by 140mm by 110mm. In transformers of this size, approximately 6kg to 7kg of potting material can be removed due to the hybrid construction, compared to a comparably sized fully potted or enclosed transformer of the type shown in Figure 1.

In addition, the above described construction, particularly the plurality of thermally conductive sections 214,216,218 mean that the winding unit 204,254 is securely held in a fixed position with respect to the transformer core 202 and housing 208, with all degrees of freedom of movement restricted. This ensures optimal performance of the device, as well as increasing durability.

Furthermore, the releasable securing of the various components of the housing 208 mean that the transformer can be readily dismantled and reassembled, leading to a transformer that is modifiable after construction. For example, the winding unit used in the transformer may be removed and replaced with a different winding unit configuration. Moreover, the transformer can easily be modified between different cooling arrangements, as outlined in more detail below. Therefore the transformer of the embodiments described above provides a adaptable yet compact construction.

As well as holding the housing 208, and fixing the winding unit 204 in place, the plurality of thermally conductive sections 214,216,218 act as cooling channels, along with additional thermally conductive sections 220, to create a thermal conduction circuit. The thermal conduction circuit allows heat to be removed from the windings and the transformer core 202. The positions of the thermally conductive sections 214,216,218 are selected such that they provide the most efficient heat conduction paths from the hottest areas of the transformer 200 during operation.

The transformer 200 can be optimised for water cooling arrangement. For example, the transformer 200 can be cold plate mounted to remove the heat extracted by the plurality of thermally conductive sections 214,216,218 and the additional thermally conductive sections 220.

In one embodiment the lower panel 212 may be mounted onto a cold plate, so as to be in thermal contact with the cold plate. In another embodiment, the lower panel 212 may itself be a cold plate. A cold plate may also be referred to as a cooling plate, and is typically water cooled. Heat is able to flow through the plurality of thermally conductive sections 214,216,218 and the additional thermally conductive sections 220, into the lower panel 212, to be removed from the transformer 200.

Other cooling methods are possible. For example, alternatively to the cooling plate arrangement described above, or in addition to the cooling plate arrangement, in some embodiments one or more of the plurality of thermally conductive sections 214,216,218 may include radiating fins. The radiating fins increase the surface area of the plurality of thermally conductive sections 214,216,218. These radiating fins may be cooled by forced air cooling or natural air cooling, to remove heat from the plurality of thermally conductive sections 214,216,218 that has been extracted from the winding unit 204,254 and/or transformer core 202. The open sides of the housing allow the airflow to reach the plurality of thermally conductive sections 214,216,218 in order to cool the radiating fins.

Radiating fins may be included on the outer surfaces of any or all of the plurality of thermally conductive sections 214,216,218. Figure 5 shows one example of such a transformer 300, that includes radiating fins 350 on the first set of thermally conductive sections 214 and the third set of thermally conductive sections 218. The transformer 300 of Figure 5 is identical to the transformer 200 of Figure 2a, except for the addition of the radiating fins 350. In other embodiments, the second set of thermally conductive sections 216 may also include radiating fins. The radiating fins may be located on any outer surface (any surface exposed to the air) of any of the plurality of thermally conductive sections 214,216,218.

The releasably secured connection between the components of the housing 208, particularly the plurality of thermally conductive sections 214,216,218 and the upper and lower panels 210,212, means that the transformer can be easily swapped between different cooling configurations, for example attaching to different cooling plates, or swapping out thermally conductive sections without radiating fins for thermally conductive sections with radiating fins as necessary. In other words, a simple change of the plurality of thermally conductive sections 214,216,218 and/or lower panel 212 mean that the transformer can be made suitable for various different forced air cooled, natural convention cooled or water cooled plate mounted constructions. This modification is easily performed, for example, using the screw fastenings described in Figures 2 and 3.

Typically a cold plate will be used for transformers with a higher power, to provide active cooling of the transformer. Water cooled cold plates can therefore provide a considerable boost in the level of the power that can be derived from the transformer without overheating.

The transformer 200,300 according to the present invention is therefore compatible with almost all cooling techniques used in the industry for applications over various different power levels. The above described transformer construction therefore provides a universal high frequency transformer design that can be adapted to be used in almost all applications with a power rating in the range of 50kW to 100kW. Of course, the features of the embodiments described above may also be applied to transformers with different power ratings.

Optionally, some or all of the plurality of thermally conductive sections 214,216,218 include at least one outer surface that is coloured black. In some embodiments the entire surface of one or more of the thermally conductive sections 214,216,218 may be coloured black. This colouring can lead to better heat radiation, and therefore improved cooling, due to the increase in black body radiation. In some embodiments, the outer surfaces of the upper and lower panels 210,212 may also be coloured black.

In initial tests it was found that colouring the thermally conductive sections 214,216,218 in a black colour allowed the transformer to be used at approximately 5kW higher power for the same temperature increase. Returning to Figures 2a to 3f, the transformer core may optionally include a thermally conductive plate 228 within the transformer core 202. Such thermally conductive plates are described in UK patent application publication GB2597670A and international patent application publication WO 2022/023744, which are hereby incorporated by reference in their entirety.

The thermally conductive plate 228 is best seen in Figure 2b. The thermally conductive plate 228 is disposed between the closed cores in the single core layer of the transformer core 202 of Figure 2b, and extends along the winding axis of the winding unit 204,254 so as to bisect the core layer. The thermally conductive plate 228 is in contact with the upper and lower panels 210 and 212 at either end of the thermally conductive plate 228, and is also in thermal contact with the additional thermally conductive sections 220 if these are present. The thermally conductive plate 228 transfers heat away from the interior of the transformer core 202 via conduction, which can then be removed via the cooling means discussed above. The thermal conductive plate 228 further improves the cooling of the transformer 200,300.

Figure 15a shows a transformer 1500 according to a second embodiment of the present invention. The transformer 1500 includes a transformer core 1502 and a winding unit 1504 arranged around the transformer core (both shown lightly shaded in Figure 15a). The transformer 1500 further includes a housing 1508 surrounding the transformer core 1502 and the winding unit 1504. The housing 1508 includes a plurality of thermally conductive sections 1516,1518 in thermal contact with the winding unit 1504 and the transformer core 1502. Further, the housing may optionally include an upper panel 1510 (not shown in Figure 15a) and a lower panel 1512, which are the same as the upper and lower panels described above for the first embodiment.

The transformer core 1502 may be the same to that of the first embodiment, and again may optionally include a thermally conductive plate 1528, analogous to thermally conductive plate 228 of the first embodiment. The winding unit 1504 is also the same as the winding unit described above for the first embodiment. Further, if upper and lower panels 1510.1512 are present, they may be releasably secured to the thermally conductive sections 1516,1518 using any of the releasably securing means described in the first embodiment

The second embodiment differs due to the configuration of the plurality of thermally conductive sections 1516,1518. The plurality of thermally conductive sections 1516,1518, together with the upper and lower plates, if present, form the housing 1508 with one or more open sides such that the winding unit 204 is exposed, analogous to the housing of the first embodiment. In the second embodiment shown in Figure 15a, the transformer 1500 has four open sides with two of these open sides exposing the winding unit 1504, and the other two exposing the transformer core 1502. However in the second embodiment, the plurality of thermally conductive sections 1516,1518 do not extend between the upper and lower panel, unlike the first set of thermally conductive sections of the first embodiment. Instead, the thermally conductive sections 1516,1518 of the second embodiment extend along the width of the transformer core 1502, parallel to the plane of the winding unit 1504, as shown in Figure 15a.

In the second embodiment a first pair of thermally conductive sections 1516 are disposed in thermal contact with the upper surface of the winding unit 1504, and the lower surface of the upper panel 1510 (if present), similar to the second set of thermally conductive sections of the first embodiment. A second pair of thermally conductive sections 1518 are disposed in thermal contact with the lower surface of the winding unit 1504, and the upper surface of the lower panel 1512 (if present) ), similar to the third set of thermally conductive sections of the first embodiment. The thermally conductive sections 1516,1518 perform the same functions as described in the first embodiment, namely transferring heat away from the winding unit 1504 and transformer core 1502 by acting as cooling channels. The heat transferred by the thermally conductive sections 1516,1518 may be removed by each of the cooling methods described for the first embodiment. For example, the thermally conductive sections 1516,1518 may include radiating fins as described previously (and as shown in Figure 15a), and/or the lower panel 1512 may be a cold plate to transfer heat out of the thermally conductive sections 1516,1518.

As well as each of the benefits outlined for the first embodiment, namely the improved cooling, reduced weight, increased durability and an adaptable construction, the configuration of the thermally conductive sections 1516,1518 in the second embodiment results in a transformer 1500 with a reduced height compared to the first embodiment. This reduced height is beneficial when seeking to miniaturise the transformer device.

The second embodiment may also include one or more winding cooling plates 1550. The winding cooling plates 1550 are best seen in the cutaway views of Figures 15b and 15c. Figure 15b is the same as Figure 15a except that one of the nearside thermally conductive sections 1516 has been omitted. Figure 15c is the same as Figure 15b except that the II- shaped cores of the transformer core 1502 have also been omitted.

The winding cooling plates 1550 are disposed in thermal contact with the winding unit 1504, and extend in a direction parallel to the plane of the winding unit 1504 (i.e. a plane normal to the winding axis) and perpendicular to the plane of the transformer core 1502 (i.e. the plane of the core layers). The winding cooling plates 1550 extend through the transformer core 1502. In the second embodiment, two winding cooling plates 1550 are shown disposed against the upper surface of the winding unit 1504. Further two winding cooling plates 1550 may be disposed against the lower surface of the winding unit 1504 in some embodiments (not shown in Figures 15b or 15c). The winding cooling plates 1550 are located between the thermally conductive sections 1516,1518 and the winding unit 1504, in thermal contact with both the winding unit 1504 and the thermally conductive sections 1516,1518. In this way, the winding cooling plates 1550 facilitate heat transfer from the winding unit 1504, particularly the centre of the winding unit, and into the thermally conductive sections 1516,1518 where the heat can be removed, for example via the radiating fins. In other words, the winding cooling plates 1550 extend between two opposing open sides of the transformer 1500, between the pairs of thermally conductive sections 1516,1518 positioned on opposing sides of the transformer core, to allow transfer of heat away from the centre of the transformer 1500. In general any number of winding unit cooling plates 1550 may be used, with any combination of winding cooling plates disposed above or below the winding unit 1504.

The winding cooling plates 1550 improve the thermal management and cooling of the transformer 1550, particularly in the reduced height transformer 1500 of the second embodiment. However the winding cooling plates 1550 may also be used in combination with any of the other embodiments herein, such as the first embodiment of Figures 2 to 5. Further, the additional thermally conductive sections 220 and winding unit with protrusions 260 as described in the first embodiment, may both also be used in the second embodiment.

Figure 6 shows another example of a transformer core 602, that may be used in any of the previous embodiments. The transformer core 602 includes a three core layers stacked together, and therefore includes twelve u-shaped cores 650 in total. The upper six u-shaped cores 650 have been omitted in Figure 6, to allow the thermally conductive plates to be seen more clearly. The transformer core 602 includes a thermally conductive plate 228 between the closed cores, bisecting the core layers, similar to the thermally conductive plate 228 described above.

The transformer core 602 including multiple core layers may optionally include one or more secondary thermally conductive plates 628 disposed between the core layers, as shown in Figure 6. The one or more secondary thermally conductive plates 628 are disposed between adjacent U-shaped cores, between the core layers, in a plane orthogonal to the plane of the (primary) thermally conductive plate 228, and parallel to the axial direction of the windings. The secondary thermally conductive plates 628 are in contact with the upper and lower panels 210 and 212 at either end of the secondary thermally conductive plates 628. The secondary thermally conductive plates 628 further increase the amount of heat extracted from the transformer core 602, due to the increased contact area with the U-shaped cores 650.

The thermally conductive plates 228,628 are positioned in planes which are parallel to the magnetic field inside the core, so as to have no effect on the magnetic circuit. The thermally conductive plates 228,628 are preferably made from a material with a high thermal conductivity that will not disrupt the magnetic properties of the transformer, such as aluminium. For example, a non-magnetic metal could be used, such as aluminium or copper. Of course, in general various transformer core constructions may be used, with any number of core layers being included, and different combinations of the thermally conductive plates 228,628.

Figure 16a shows an alternative configuration of a transformer 1600 according to a third embodiment of the present invention. The transformer 1600 of Figure 16a is similar to the transformer 200 of the first embodiment, and includes a transformer core 1602, a winding unit 1604, connection terminals 1606, and a housing 1608 that includes an upper panel 1610, a lower panel 1612, and a plurality of thermally conductive sections 1614,1616,1618. Each of these components is analogous to the corresponding components in the first embodiment, and therefore a repeat description will be omitted. The transformer core 1602 of the third embodiment also includes a thermally conductive plate 1628 within the core, analogous to thermally conductive plate 228 of the first embodiment, and also secondary thermally conductive plates 1630 analogous to the secondary thermally conductive plates 628 described in relation to Figure 6 above. Figure 16b shows a cutaway view of the transformer 1600, with the upper panel 1610 and thermally conductive sections 1616 removed to enable to interior of the transformer to be seen.

The transformer 1600 of the third embodiment differs in that each core layer of the transformer core 1602 includes only one closed core (e.g. two combined U-shaped cores). The embodiment of Figures 16a and 16b includes two core layers, however any number of core layers may be used, as discussed previously. In this way, the third embodiment can be thought of as a bisected version of the transformer core 202 of the first embodiment, with one half of each core layer and one half of the plurality of thermally conductive sections 1614,1616,1618 removed compared to the first embodiment. The winding unit is arranged around the remaining half of the transformer core 1602 and the thermally conductive plate 1628 as previously described.

In more detail, the transformer 1600 of the third embodiment includes a first set of thermally conductive sections 1614 on one side of the transformer 1600, extending between the upper panel 1610 and the lower panel 1612. The transformer 1600 further includes a second set of thermally conductive sections 1616 and a third set of thermally conductive sections 1618 disposed between the winding unit 1604 and the upper panel 1610 or lower panel 1612 respectively. These sets of thermally conductive sections 1614,1616,1618 are analogous to those of the first embodiment. However in the third embodiment of Figures 16a and 16b, the third set of thermally conductive sections 1618 further includes an extra thermally conductive section 1618’ that extends along the side of the transformer 1600 opposing the first set of thermally conductive sections 1614. This extra thermally conductive section 1618’ extends normal to the plane of the core layers of the transformer core 1602, perpendicular to both of the other thermally conductive sections 1618 in the third set of thermally conductive sections 1618. In some embodiments, the second set of thermally conductive section 1616 may also include an analogous extra thermally conductive section 1616’ (hidden from view in Figure 16a).

The transformer 1600 of the third embodiment may also include an optional side plate 1660 disposed on the side of the transformer 1600 opposing the first set of thermally conductive sections 1614 (and perpendicular to both the upper panel 1610 and lower panel 1612). Despite the side plate 1660 shown in Figures 16a and 16b, the transformer 1600 still has three open sides, two exposing the winding unit 1604, and one exposing the transformer core 1602 and first set of thermally conductive sections 1614, result in improved cooling.

The connection terminals 1606 for the winding unit 1604 may all be arranged towards the same side of the transformer 1600 in the third embodiment, specifically the side with the side plate 1660 in the present embodiment.

As well as the advantages outlined for the first embodiment if Figures 2 to 5 above, the transformer 1600 of the third embodiment has the advantage of a more compact footprint compared to the transformer 200 of the first embodiment. Further, the transformer 1600 of the third embodiment has an increased leakage inductance, which can be beneficial in some applications.

The third embodiment may be combined with the additional thermally conductive sections 220 and winding unit with protrusions 260 described in the first embodiment, as well as the winding cooling plates 1550 of the second embodiment.

Winding Arrangement

A number of different windings arrangements according to embodiments of the present invention will now be described. Each of the winding arrangements described below could be used in the winding units 204,254 of any of the embodiments of the transformers 200,300,1500,1600 described above. Alternatively, the winding arrangements described below could also be used in any other type of electrical transformer.

Figure 7a shows a winding arrangement 700 according to an embodiment of the present invention. The winding arrangement is a pdqb type winding, however differs from the pdqb type winding arrangements disclosed in UK patent application GB2574481A and international patent application publication WO 2019/234453 A1 in a number of ways. In particular, each coil in the winding arrangement 700 includes first and second sections connected in parallel, as described below.

The winding arrangement 700 includes a primary coil 702 and a secondary coil 704. The primary coil 702 includes a first section 710 and a second section 720. The first section 710 is shown in isolation in Figure 7b, and the second section 720 is shown in isolation in Figure 7c. The first section 710 of the primary coil 702 includes a first set of turns 712 having a first diameter and a second set 714 of turns having a second diameter. The first set of turns 712 and second set of turns 714 are wound around a common winding axis, and each set of turns may include one or more individual turns. The first diameter is larger than the second diameter, such that when viewed along the common winding axis, the first and second set of turns are concentric with the second set of turns 714 located inside the diameter of the first set of turns 712.

The first section 710 is formed from a single integral piece of wire, to form a continuous electrically conductive path. In other words, a final turn of the first set of turns 712 is connected to a first turn of the second set of turns 714, as shown in Figure 7b. The connection between the first set of turns 712 and the second set of turns 714 may be referred to as a cross-over portion. Connection terminals 716 may be included at each end of the wire of the first section 710, for allowing an electrical connection to be made with the first section 710 of the coil.

Similarly, the second section 720 of the primary coil 702 includes a first set of turns 722 having a first diameter and a second set 724 of turns having a second diameter smaller than the first diameter, with each set of turns including one or more individual turns and being arranged concentrically around a common winding axis. The first and second diameters of the second section 720 are the same as those for the first section 710. The first set of turns 722 and the second set of turns 724 of the second section 720 are also formed from a continuous piece of wire. Figure 7d shows an alternative view of the underside of the second section 720 shown in Figure 7c, to allow the connection (cross-over portion) between the first set of turns 722 and the second set of turns 724 to be seen more clearly. Connection terminals 726 may be included at each end of the wire of the second section 720, for allowing an electrical connection to be made with the second section 720 of the coil.

The first section 710 and second section 720 of the primary coil are electrically connected in parallel to form the primary coil 702. This electrical connection may be made via connecting or joining the connection terminals 716,726 of each of the first and second sections 710,720. In particular, the connection terminal 716 at a first end of the first section 710 and the connection terminal 726 at a first end of the second section 720 can be connected together, and the connection terminal 716 at a second end of the first section 710 and the connection terminal 726 at a second end of the second section 720 can be connected together.

Figure 7e shows the full primary coil 702 constructed from the combined first and second sections 710,720. The first and second sections 710,720 are wound around the same common winding axis. Therefore the first sets of turns 712 of the first section 710, the second set of turns 714 of the first section 710, the first sets of turns 722 of the second section 720, and the second set of turns 724 of the second section 720 are all arranged around the same common winding axis. Although formed from two coil sections, the combination of the first section 710 and the second section 720 forms a single primary coil 702, as shown in Figure 7e.

In the primary coil 702, the second set of turns 724 of the second section 720 are positioned within the first set of turns 712 of the first section 710, and the second set of turns 714 of the first section 710 are positioned within the first set of turns 722 of the second section 720, when viewed along the common winding axis. By “positioned within” it is meant that the second set of turns 724 of the second section 720 are inside the first set of turns 712 of the first section 710, with both the second set of turns 724 and the first set of turns 712 located within the same plane extending perpendicularly to the common winding axis. Similarly, the second set of turns 714 of the first section 710 are positioned within the first set of turns 722 of the second section 720 such that the second set of turns 714 are located inside the first set of turns 722 and both are located within the same plane extending perpendicularly to the common winding axis.

The first set of turns 712 of the first section 710 and the first set of turns 722 of the second section 720 fully overlap when viewed along the common winding axis, and the second set of turns 714 of the first section 710 and the second set of turns 724 of the second section 720 fully overlap when viewed along the common winding axis. In other words, the first and second sections 710,720 have the same footprint.

As well as the primary coil 702 described above, the winding arrangement 700 of Figure 7a includes a single secondary coil 704. In the present embodiment, the construction of the secondary coil 704 is the same as the primary coil 702. In other words, the secondary coil 704 also includes a first section 710 and a second section 720 connected in parallel and wound together, as described in relation to Figures 7b to 7e for the primary coil 702. The winding arrangement 700 shown in Figure 7a is therefore constructed from two of the coils shown in Figure 7e, with one acting as the primary coil 702 and one acting as the secondary coil 704. The primary coil 702 and secondary coil 704 are both wound around the same common winding axis. The primary coil 702 and the secondary coil 704 fully overlap when viewed along the common winding axis. In other words, the primary and secondary coils

701 .704 have the same footprint.

The winding arrangement 700 including both the primary and secondary coils

702.704 is formed by interleaving the turns of the primary coil 702 with the turns of the secondary coil 704. The primary and secondary coils 702,704 are interleaved such that each turn of the primary coil 702 (each turn of the first and second sets of turns 712,714,722,724 of both the first and second sections 710,720 of the primary coil 702) is positioned between two turns of the secondary coil 704 when viewed along a direction perpendicular to the common winding axis. Similarly, each turn of the secondary coil 704 is positioned between two turns of the primary coil when viewed along a direction perpendicular to the common winding axis. Put another way, each turn of the secondary coil 704 has turns of the primary coil 702 located above and below said secondary coil turn.

In other words, as you move along the direction of the common winding axis, the turns in the winding arrangement 700 alternate between the primary coil 702 and the secondary coil 704. Specifically, the turns of the first sets of turns 712,722 of the primary coil 702 and the turns of the first sets of turns of the secondary coil 704 alternate as you move along the common winding axis, and the turns of the second sets of turns 714,724 of the primary coil 702 and the turns of the second sets of turns of the secondary coil 704 alternate as you move along the common winding axis.

The interleaving of the primary and secondary coils 702,704 is shown in Figure 7f, which is a cross sectional view through the winding arrangement 700 of Figure 7a. Different hatching patterns are used to distinguish the primary coil 702 and secondary coil 704 in the plane of the cross section.

Due to the above described interleaving of the primary and secondary coils, sections of the coils carrying currents in the same direction are not disposed directly adjacent to each other. This has the advantageous effect of reducing the losses caused by the proximity effect.

Moreover, the winding arrangement 700 is able to handle high currents due to the primary and secondary coils being formed from the two sections 710,720 connected in parallel. This is because each section of each coil will only receive half the input current due to the parallel connection of the two sections. In some embodiments the current level may be as high as 1200A. A winding arrangement suitable for low current applications will be discussed in relation to Figures 11a to 12d.

For each of the primary coil 702 and the secondary coil 704 in the winding arrangement 700, the number of turns in the first set of turns 712,722 of each of the first and second sections 710,720 of that coil are equal, and the number of turns in the second sets of turns 714,724 of each of the first and second sections 710,720 of that coil are equal. In other words, for a given coil 702,704, the first section 710 and second section 720 both have the same number of turns in their respective first set of turns 712,722, and the first section 710 and second section 720 both have the same number of turns in their respective second set of turns 714,724.

Therefore, the first section 710 of each coil 702,704 is identical to the second section 720 of that coil, other than the folding direction of the connection terminals 716,726 (best seen from a comparison of Figures 7b and 7d). This means that the first section 710 and second section 720 advantageously have the same impedance, due to having the same length conductive path and same shape. This also necessarily means that the total number of turns in the first section 710 of each coil is equal to the total number of turns in the second section 720 of that coil. In some embodiments, within each coil section 710,720 there may be more turns in the first set of turns 712,722 than in the second set of turns 714,274. For example, in the present embodiment, as shown in figures 7b and 7c, the first sets of turns 712,722 each include six turns, and the second sets of turns 714,274 each include four turns. Alternatively, in each coil section 710,720 the second set of turns 714,274 could include more turns that the first set of turns 712,722 in some embodiments. In a specific embodiment, the number of turns in the first and second sets of turns may be equal. For example, in one embodiment within each coil section 710,720, the first set of turns 712,722 may include five turns, and the second set of turns 714,274 may include five turns. The number of turns may be tailored for the specific application.

Returning to Figure 7a, in the winding arrangement 700 of the present embodiment, the primary coil 702 and secondary coil 704 are identical, with same total number of turns in each coil (the total number of turns here being the combined number of turns in the first set of turns 712 of the first section 710, the second set of turns 714 of the first section 710, the first set of turns 722 of the second section 720, and the second set of turns 724 of the second section 720). In other embodiments, the primary coil 702 and second coil 704 could have a different number of turns. Typically, the total number of turns in primary coil 702 would be greater than or equal to the total number of turns in the secondary coil 704.

In addition, in the embodiment of the winding arrangement 700 shown in Figure 7a, the connection terminals 716,726 of the primary and secondary coils 702,704 are also identical. The connection terminals 716,726 for each section of each coil are folded so as to extend in a direction parallel to the direction of the common winding axis. The connection terminals 716,726 at each end of each coil 702,704 are folded so that they all extend in the same direction away from the sets of turns of the coils. For example, in the view of Figure 7a, each of the connection terminals 716,726 extend parallel to the common winding axis in the upward direction in the drawing.

The above described folding configuration of the connection terminals 716,726 has the advantage that each point of connection to the primary and secondary coils 702,704 can be located on the same side of a transformer including the winding arrangement. This is shown in the transformer 200 of Figure 2a, in which the connection terminals 716,726 of the winding arrangement 700 may be used as the connection terminals 206 of the transformer 200.

In alternative embodiments, other folding configurations are possible for the connection terminals 716,726. For example, the connection terminals 716,726 could be folded in different directions to each other. For example, in one embodiment, one or more of the connection terminals 716,726 may be folded so as to extend along the common winding axis in one direction, and the remaining connection terminals 716,726 may be folded so as to extend along the common winding axis in the opposing direction. In some embodiments, the connection terminals 716,726 could differ for each of primary and secondary coils 702,704. For example, the direction of extension of the connection terminals 716,726 for the primary coil 702 may be in a different direction, preferably an opposing direction, to the extension of the connection terminals 716,726 for the secondary coil 704. In some embodiments, the connection terminals 716,726 may extend along a direction other than the direction of the common winding axis. The folding configuration and direction of the connection terminals 716,726 is chosen to locate the connection points to the coils at the required position when the winding arrangement is used in a transformer device.

In the winding arrangement 700 of Figure 7a, the connection terminals 716,726 of the primary coil 702 and the connection terminals 716,726 of the secondary coil 704 are located on opposing sides of the winding arrangement. In other words, the connection terminals 716,726 of the primary coil 702 and the connection terminals 716,726 of the secondary coil 704 are located on the opposite sides of a plane containing the common winding axis that bisects the winding arrangement. In the view of Figure 7a, the connection terminals 716,726 of the primary coil 702 are located on the right hand side of the drawing, and the connection terminals 716,726 of the secondary coil 704 are located on the left hand side of the drawing. This configuration is advantageous as, when used in a transformer, the connection points of the primary and secondary coils may be more easily identified by the side that they are located at.

Put another way, the winding arrangement 700 of Figure 7a is formed using two of the coils shown in Figure 7e, with one acting as the primary coil 702, and one acting as the secondary coil 704. The secondary coil is rotated by 180° about the common winding axis relative to the primary coil 702, before the coils are interleaved, such that the connection terminals 716,726 of the primary and secondary coils 702,704 are located on opposing sides of the winding arrangement.

In an alternative embodiment, the connection terminals 716,726 of the primary and secondary coils 702,704 may be located on the same side of the winding arrangement. In other words, the winding arrangement may be formed using two of the coils shown in Figure 7e, without any rotation about the common winding axis between the two coils. Other rotation angles may also be used, for example 90° and 270°.

In general, the turns of each of the coils 702,704 in the winding arrangement 700 have a square shape about the winding axis. However a rectangular square, or circular shape, or various other shapes may also be used.

Each set of turns of each coil 702,704 is arranged (wound) helically around the common winding axis. In other words, each coil 702,704 is formed from a first helically wound first section 710 connected in parallel with a second helically wound second section 720. When the winding arrangement 700 of Figure 7a is used in winding units, such as winding units 204,254 mentioned above in Figures 2 to 6, each of the primary coil 702 and secondary coil 704 may be encased in potting material.

Multiple Secondary Coils

The winding arrangement of the present invention may also be used in applications with multiple secondary coils.

Figures 8a and 8b show front and rear perspective views of a winding arrangement 800 in an embodiment of the present invention including two secondary coils. The winding arrangement 800 includes a primary coil 702 which is the same as the primary coil 702 described in relation to Figures 7a to 7f above, and shown in Figure 7e. The winding arrangement further includes a first secondary coil 802 and an additional secondary coil 804, shown with different shading patterns in Figure 8a and 8b.

Each of the secondary coils 802,804 include a first section 810 and a second section 820 connected in parallel and wound together around a common winding axis, in a similar manner to the primary coil 702. Figure 9a shows a first section 810 of either of the secondary coils, and Figure 9b shows an alternative (bottom) view of the first section 810 of Figure 9a. Figure 9c shows a second section 820 of either of the secondary coils, and Figure 9d shows an alternative (bottom) view of the second section 820 of Figure 9c.

The first section 810 of the secondary coils 802,804 includes a first of turns 812 having a first diameter and a second set 814 of turns having a second diameter smaller than the first diameter, and the second section 820 of the secondary coils 802,804 includes a first of turns 822 having a first diameter and a second set 824 of turns having a second diameter smaller than the first diameter.

A first section 810 as shown in Figures 9a and 9b, and a second section 820 as shown in Figures 9c and 9d combine to form each secondary coil 802,804 (the secondary coil 802 and the additional secondary coil 804). Figure 9e shows the secondary coil 802 and the additional secondary coil 804 formed from the first and second sections 810,820 in isolation. Different shading patterns are used for each secondary coil in Figure 9e. To form each secondary coil 802,804, the first section 810 and second section 820 of each secondary coil 802,804 are electrically connected in parallel and are wound around the common winding axis, with the second set of turns 824 of the second section 820 positioned within the first set of turns 812 of the first section 810, and the second set of turns 814 of the first section 810 positioned within the first set of turns 822 of the second section 820, when viewed along the common winding axis.

In other words, the first section 810 and a second section 820 of the secondary coils 802,804 are analogous to the first and second sections 710,720 described above. The other features described above for the primary coil 702 apply analogously to the secondary coil 802 and additional secondary coil 804, and will therefore not be repeated here.

As shown in Figure 9e, the secondary coils 802,804 neatly stack together, with both being arranged around the same common winding axis. The secondary coils 802,804 are stacked such that the secondary coil 802 and the additional secondary coil 804 fully overlap when viewed along the common winding axis (i.e. have the same footprint). The stacking of the secondary coils in beneficial for reducing the overall size of the winding arrangement 800.

The connection terminals 816,826 of the secondary coils are folded so as to extend in a direction parallel to the direction of the common winding axis, in this case in the same direction as the connection terminals 716,726 of the primary coil 702 when the secondary coils 802,804 are combined with the primary coil 702 (as shown in Figures 8a and 8b). When the winding arrangement 800 is fully constructed, the connection terminals 816,826 of the secondary coils 802,804 are located on opposing sides of the winding arrangement to the connection terminals 716,726 of the primary coil 702, similarly to the embodiment shown in Figure 7a. Moreover, the connection terminals 816,826 of the secondary coil 802 are arranged adjacent to each other, and the connection terminals 816,826 of the additional secondary coil 804 are also arranged adjacent to each other. This positioning of the connection terminals makes it easier to identify which connection terminals 816,826 belong to which secondary coil.

To form the complete winding arrangement 800 shown in Figures 8a and 8b, the turns of the primary coil 702 (shown in Figure 7e) are interleaved with the turns of the secondary coil 802 and additional secondary coil 804 (shown in Figure 9e).

In the present embodiment, the primary coil 702 is interleaved with the secondary coils 802,804 such that each turn of the secondary coil 802 is disposed between two turns of the primary coil 702 and each turn of the additional secondary coil 804 is disposed between two turns of the primary coil 702, when viewed along a direction perpendicular to the common winding axis. Therefore each turn of each secondary coil 802,804 has turns of the primary coil 702 located above and below said secondary coil turn. Once interleaved, each of the primary coil, secondary coil 802, and additional secondary coil 804 fully overlap when viewed along the common winding axis.

In the present embodiment, the secondary coils 802 and 804 are stacked one on top of the other. This means that the secondary coil 802 interleaves with the primary coil 702 in a first portion of the primary coil 702 (the upper portion of the primary coil 702 in Figures 8a and 8b), and the additional secondary coil 804 interleaves with the primary coil 702 in a second portion of the primary coil 702 (the lower portion of the primary coil 702 in Figures 8a and 8b). Therefore, the turns of the primary coil 702 and the turns of the secondary coil 802 alternate as you move along a first portion of the common winding axis, and the turns of the primary coil 702 and the turns of the additional secondary coil 804 alternate as you move along a second portion of the common winding axis.

In an alternative embodiment, the secondary coil 802 and additional secondary coil 804 could interleave with each other as well as the primary coil 702. This will be described in more detail in relation to Figure 10a.

The interleaving of the primary coil 702 with the secondary coils 802,804 again reduces the proximity effect by ensuring conductors carrying like currents are not positioned against each other.

Moreover, similarly to the primary coil, each secondary coil is formed by two coil sections in parallel. In other words, Figure 9e shows two secondary coils 802,804 formed from four coil sections. The use of the parallel coil sections in the primary and secondary coils results in a winding arrangement 800 that is able to handle higher currents.

In further embodiments, more than two secondary coils may be used. In other words, the winding arrangement may include more than one additional secondary coil. Figure 10a shows an embodiment including four secondary coils: secondary coil 1002, and additional secondary coils 1004,1006,1008. Different shading patterns are used for each secondary coil in Figure 10a.

The secondary coils 1002,1004,1006,1008 of Figure 10a each have the same structure as the secondary coils 802,804 described above, and a description will therefore not be repeated here. Again, due to the shape and configurations of the secondary coils, the coils neatly stack together, resulting in a more compact winding arrangement.

However, the embodiment of Figure 10a differs in that the secondary windings 1002,1004,1006,1008 are interleaved with each other. Specifically, the secondary coils 1002 and first additional secondary coil 1004 interleave with each other, and the second additional secondary coil 1006 and third additional secondary coil 1008 interleave with each other. In general, some or all of the secondary windings may be interleaved with each other. Each pair of secondary windings may be fully interleaved with each other, or only partially interleaved with each other, such that only some of the turns of each secondary coil interleave.

The secondary coil arrangement 1000 of Figure 10a is then interleaved with the primary coil 702 of Figure 7e, to form the full winding arrangement. The interleaving is such that each turn of each secondary coil 1002,1004,1006,1008 is positioned between two turns of the primary coil 702, when viewed along a direction perpendicular to the common winding axis, to reduce the proximity effect.

Of course, other numbers of secondary coils may be used. In general, up to twenty secondary coils, more preferably up to ten secondary coils may be used. Figure 10b shows a secondary coil arrangement 1050 including nine secondary coils (one secondary coil and eight additional secondary coils). Similarly, Figure 10c shows a secondary coil arrangement 1060 including ten secondary coils (one secondary coil and nine additional secondary coils). In other specific embodiments, three, five, six, seven, or eight secondary coils may be used.

The shape of the primary and secondary coils in the above mentioned embodiments provides flexibility to accommodate multiple secondary coils within the same footprint and volume. The coils of the winding arrangement stack around the common winding axis to provide a very compact arrangement, whilst also preventing proximity effect losses.

Including multiple secondary coils in the winding arrangement provides a number of benefits, including the ability to power multiple circuits, as well as providing redundancy.

In general, when multiple secondary coils are used, the number of turns in the primary coil 702 is greater than or equal to the combined total number of turns in the secondary coils (the secondary coil and the one or more additional secondary coils). For example, when using a primary coil 702 with ten turns in each coil section (for example, five turns in the first set of turns of each coil section, and five turns in the second set of turns in each coil section), a single secondary coil with up to ten turns in each coil section may be used, or two secondary coils with up to five turns in each coil section each may be used, or five secondary coils with two turns in each coil section each may be used. It is also possible, however, for the primary coil to have fewer turns than the combined total number of turns in the secondary coils in some embodiments.

Each of the above-described embodiments uses secondary coils with two sections connected in parallel, for higher current applications. Figures 11a to 12d show examples of secondary coil arrangements including a plurality of secondary coils suitable for low current applications, which do not include two sections connected in parallel in the secondary coils.

Figure 11a shows a secondary coil arrangement for use in an embodiment of the invention that includes two secondary coils 1102, 1104. Different shading patterns are used for each secondary coil in Figure 11a. Each of the secondary coils 1102,1004 includes a first set of turns 1112,1122 having a first diameter and a second set of turns 1114,1124 having a second diameter concentric with the first set of turns 1112,1122. The first and second diameter are the same as the first and second diameters for the primary coil 702 described above. Each secondary coil also includes a pair of connection terminals 1116,1126 at either end of the coil.

Put another way, each secondary coil 1102,1104 in Figure 11a can be formed from one of the coil sections 810,820 shown in Figures 9a to 9d, but without a connection in parallel to a second coil section. The description relating to the coil sections 810,820 therefore applies analogously here.

In Figures 11a to 12d only one turn is shown in each set of turns, however in general each set of turns of each secondary coil 1102,1004 may include more than one turn. The two secondary coils 1102,1004 are both wound around a common winding axis. The secondary coils 1102 and 1104 are stacked such that the secondary coils fully overlap when viewed along the common winding axis.

The secondary coils 1102,1104 of Figure 11a (and Figures 11b to 12d discussed below) are combined with the primary coil 702 shown in Figure 7e including two parallel primary coil sections 710,720, to form a complete winding arrangement. Again, the primary coil 702 and secondary coils 1102,1104 are both wound around the same common winding axis and are combined by interleaving, with the turns of the primary coil 702 interleaved with the turns of the plurality of secondary coils 1102,1104. The primary coil 702 is interleaved with the secondary coils 1102,1104 such that each turn of the secondary coils is disposed between two turns of the primary coil when viewed along a direction perpendicular to the common winding axis. The above described interleaving prevents losses due to the proximity effect.

Figures 11b and 11c show two different possible arrangements for stacking the secondary coils 1102,1104. In Figures 11b and 11c the secondary coils 1102,1104 are crossed over each other at different locations, rather than being stacked one on top of the other as shown in Figure 11a without any crossing. In Figure 11c, the secondary coils are arranged with the second set of turns 1124 of second secondary coil 1104 positioned within the first set of turns 1112 of the first secondary coil 1102, and the second set of turns 1114 of the first secondary coil 1102 are positioned within the first set of turns 1122 of the second secondary coil 1104, when viewed along the common winding axis. In other words, the secondary coils may also be partially or fully interleaved with each other, analogously to as described for Figure 10a. Figure 11c shows the secondary coils 1102, 1104 interleaved in the case where only one turn is included in each set of turns.

As before, more than two secondary coils may be used. Preferably up to twenty secondary coils, more preferably up to ten secondary coils may be used. Figure 12a shows a secondary coil arrangement including four secondary coils 1202,1204,1206,1208. Different shading patterns are used for each secondary coil in Figure 12a. Figure 12b shows a secondary coil arrangement 1250 including nine secondary coils. Figure 12c shows a secondary coil arrangement 1260 including ten secondary coils. In other specific embodiments, three, five, six, seven, or eight secondary coils may be used.

Regardless of the number of secondary coils, due to the construction of the secondary coils they can be neatly stacked together, to form a more compact winding arrangement. The stacking arrangement in one embodiment of the present invention including ten secondary coils (the embodiment of Figure 12c) is shown in Figure 12d. Half of the secondary coils are shaded in Figure 12d, to help show the stacking arrangement. The secondary coils in Figure 12d are stacked one on top of the other. The secondary coils are then interleaved with the primary coil 702 as described above, with each part of each secondary coil being positioned between two turns of the primary coil 702, when viewed along a direction perpendicular to the common winding axis, to reduce the proximity effect.

As in the previous embodiments, the number of turns in the primary coil may be greater than or equal to the combined total number of turns in the plurality of secondary coils.

In general, various numbers of turns and various numbers of secondary coils may be used. In a specific embodiment, the secondary coil arrangement 1260 shown in Figure 12c and 12d, with ten secondary coils each having a single turn in each of the first and second sets of turns, may be combined with the primary coil 702 of Figure 7e including ten turns in each coil section 710,720.

The number or turns shown in the drawings and given as examples in the description above are for exemplary purposes only. In general, in each embodiment various different numbers of turns may be used in each coil.

In some embodiments, the high current secondary coils of Figures 8a to 10b including two coil sections connected in parallel could be used within the same winding arrangement as the low current secondary coils of Figures 11a to 12d.

Any of the above described winding arrangements may be used with the hybrid construction transformer described in relation to Figures 2 to 6.

Moreover, the above described winding arrangements may be used in combination with the cooling plate arrangement described in UK patent application publication GB2597470A and international patent application publication WO 2022/018436 A1 , which are hereby incorporated by reference in their entirety.

Winding Materials

The winding arrangements of each of the embodiments described above are formed from flat wire. However, in some embodiments other types of wire may also be used, such as round wire windings or the like.

The wire used in the winding arrangements of each of the embodiments may be formed from various electrically conductive materials, such as copper or the like. However, in a preferred embodiment of the present invention, the wire used in the winding arrangement is formed from aluminium, as outlined below.

Traditionally, copper litz wires and copper foils are used in high frequency transformers. Murata’s pdqb type windings (UK patent application publication GB2574481A and international patent application publication WO 2019/234453 A1) made it possible to use flat copper conductors in high power high frequency transformers. In the preferred embodiment of the present invention aluminium wires, more preferably aluminium flat wires, are used. Aluminium has not previously been used as a conductor in the windings of high frequency high power transformers. The use of aluminium as the conductive material in the windings has a number of benefits, particularly in larger high frequency transformers, which are becoming more prevalent due to new applications such as use in electric vehicles. Firstly, aluminium has a lower density than traditional conductors such as cooper, and therefore leads to weight savings. Moreover, aluminium is cheaper than traditional conductors such as copper, leading to a lower manufacturing cost.

Secondly, carefully selected design parameters can be used with the aluminium windings to provide further benefits. The size of the thickness of the wire conductor is selected to be thicker than twice the skin depth of aluminium. This slight oversizing of the aluminium conductor means that there is an unused area within the centre of the aluminium conductor (unused in the sense that it contains a very low or zero current density). Figure 13 shows a cross section through an aluminium flat wire conductor 1300, with such a central area 1302 with a low or zero current density shown in Figure 13. The majority of the current carried by the aluminium flat wire conductor 1300 is located within the outer area 1304.

Therefore, a central volume with a very low or zero current density runs along the entire length of the aluminium conductor. This central volume acts as a cooling channel running through the aluminium conductor itself, to allow heat generated within the aluminium conductor to travel along and eventually out of the aluminium conductor. In other words, the size of the aluminium conductor is chosen to make a positive use of the skin depth and proximity effect in the aluminium conductor.

In a particular embodiment, the flat wire has a width of between 10mm and 15mm, and a thickness of between 0.8mm and 1 ,2mm. More preferably, for the thickness of the flat wire is about 1 mm. The width and thickness directions are the directions perpendicular to the direction of the extension of the wire, i.e. perpendicular to the direction the current flows in. The width direction is the larger dimension of the wire perpendicular to the extension of the wire, and the thickness direction is the smaller dimension of the wire perpendicular to the extension of the wire.

In a first preferred embodiment, the flat wire has a width of 15±2mm, and a thickness of 1.0±0.2mm. In a second preferred embodiment, the flat wire has a width of 10±2mm, and a thickness of 1.0±0.2mm.

The dimensions of the flat wire above may be used with any conductive material, such as copper. However, the dimensions above are specifically tailored to achieve the maximal beneficial effects, such as the cooling benefit, when aluminium is used as the conductive material.

In some embodiments a mix of conductive materials may be used, for example different conductive materials may be used in each of the primary and secondary coils. Universal Transformer

Figure 14 is a graph showing the maximum operating power as the operating voltage and the frequency are varied for an electrical transformer using both the hybrid construction and the winging arrangements described herein. In Figure 14 the winding arrangement shown in Figure 7a was used. As can be seen from Figure 14, the electrical transformer can handle a power of between 50kW to 100kW across the majority of the voltage range of 100V to 1100V and the frequency range of 10kHz to 100kHz. As can be seen in the graph, in some regions the electrical transformer can handle up to double the rated power of 50kW.

The hybrid transformer construction of Figures 2a to 6 and the winding arrangements of Figures 7a to 13 both contribute to providing a more adaptable transformer device capable of handling at least 50kW over the above mentioned voltage and frequency ranges. Specifically, the hybrid construction of Figures 2a to 6 allows for both the winding unit and the cooling arrangement to be easily changed. The semi-open hybrid construction also improves the cooling when dealing with higher power levels. Moreover, the winding arrangement allows for multiple secondary coils to be used whilst retaining a compact structure and small footprint, allowing a transformer including the winding arrangement to power multiple circuits and/or provide redundancy in both high and low current situations.

Moreover, in each of the embodiments described above, where multiple secondary coils are used, when the winding arrangement is used in a transformer two or more of the secondary coils may be connected together in series, or may be connected together in parallel, or may be connected together using a combination of series and parallel connections. For example, the two secondary coils 802,804 shown in Figures 8a, 8b and 9e may be connected in series or parallel in some embodiments, or in another embodiment some or all of the secondary coils shown in each of Figures 10a to 12c may be connected together in series or parallel or a combination thereof. Many permutations of series and parallel connections are of course possible, and may be selected based on the specific application of the transformer.

By modifying the series and parallel connections between the secondary coils (when multiple secondary coils are present in the winding arrangement) the transformer can be adjusted to be used over a larger voltage and frequency range. For example, in some embodiments, a transformer using the winding arrangements with multiple secondary coils as described above can be used in the voltage range of 100V to 1100V, and the frequency range of 5kHz to 120kHz. In other words, modifying the series and parallel connections of the secondary coils allows the winding arrangement to be swapped between a high current low voltage situation or a low current high voltage situation, depending on the series and/or parallel connections made between the secondary coils. Therefore only minor adjustments are needed to these series and parallel connections to make the transformer universal over the desired power level, for example 50kW to 100kW.

Previous attempts to provide a universal transformer have included using different core sizes and/or core assemblies to make the transformer suitable for different voltage and frequency levels. This is not necessary with the above described hybrid transformer construction and winding arrangements.

In general, the above described concepts and embodiments may be applied to all high power high frequency transformers including those with higher or lower power ratings than 50kW. Moreover, the concepts described herein could also be used in high power inductors or the like.

In use in a transformer, the connection terminals of the primary coil of the winding arrangements described above act as input terminals for an alternating current (AC) voltage source. This will result in an AC voltage being produced at the connection terminals of the one or more secondary coil(s). In other words, the connection terminals of the one or more secondary coil(s) act as output terminals. A load may be connected across said output terminals. In some embodiments, by varying the number of turns in each coil, a step-up or step-down in voltage can be achieved.

A transformer according to the present invention may be used individually or as a bank of connected or unconnected transformers. Transformers according to the present invention may be used in various applications, such as use in a vehicle, for example in a regenerative braking system, or in power generation equipment, particularly in renewable energy systems, or 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.

Although described separately, the features of the embodiments outlined above may be combined in different ways where appropriate. Various modifications to the embodiments described above are possible and will occur to those skilled in the art without departing from the scope of the invention which is defined by the following claims.