SHIELDING ARRANGEMENTS FOR TRANSFORMER STRUCTURES

Shielding arrangements for transformer structures capable for operation in high frequency and high power density applications are disclosed. Electric shields may be incorporated within transformers to shield and/or redirect high strength electric fields away from areas of insulation material that may be prone to failure mechanisms. Such electric shields may be positioned between primary and secondary windings in order to be coupled with electric potentials of the windings. The electric shield may comprise a laminate structure that includes one or more metal layers and one or more dielectric layers, for example a printed circuit board. By positioning the electric shields in this manner, high electric fields associated with solid state transformer applications may be concentrated within planes of the electric shields and diverted away from potential problem areas, for example areas that are close to the windings where voids in the insulation material may otherwise promote failure mechanisms.

FIELD OF THE DISCLOSURE

The present disclosure relates to shielding arrangements for transformer structures, and more particularly to shielding arrangements in transformer structures for high frequency and high power density applications.

BACKGROUND

Semiconductor devices such as transistors and diodes are ubiquitous in modern electronic devices and systems. In particular, wide bandgap semiconductor material systems such as gallium arsenide (GaAs), gallium nitride (GaN), and silicon carbide (SiC) are being increasingly utilized in electronic devices and systems to push the boundaries of device performance in areas such as switching speed, power handling capability, efficiency, and thermal conductivity. Examples include individual devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), Schottky barrier diodes, GaN high electron mobility transistors (HEMTs), and integrated circuits such as monolithic microwave integrated circuits (MMICs) that include one or more individual devices.

Power devices made with SiC provide significant advantages for use in high speed, high power and/or high temperature applications due to the high critical field and wide band gap of SiC. Power conversion and transfer systems, such as those that include medium-voltage transformers for use in electric power distribution systems, are increasingly incorporating SiC power switching devices to realize increased switching frequencies, higher power densities and efficiencies with reduced device complexity. In transformer applications, increased switching frequencies and higher power handling can stress other system components, leading to challenges associated with electric field stress and distribution.

The art continues to seek improved power transfer devices having desirable characteristics such as improved switching frequencies and power densities while overcoming challenges associated with conventional power transfer devices.

SUMMARY

The present disclosure relates to shielding arrangements for transformer structures, and more particularly to shielding arrangements in transformer structures for high frequency and high power density applications. Electric shields may be incorporated within transformers of solid state transformer devices to shield and/or redirect high strength electric fields away from areas of insulation material that may be prone to failure mechanisms. Such electric shields may be positioned between primary and secondary windings in order to be coupled with electric potentials of the primary and/or secondary windings. The electric shield may comprise a laminate structure that includes one or more metal layers and one or more dielectric layers, for example a printed circuit board. By positioning the electric shields in this manner, high electric fields associated with solid state transformer applications may be concentrated within planes of the electric shields and diverted away from potential problem areas of the insulation material, for example areas close to the windings where voids that cause failure mechanisms in the insulation material may be more common.

In one aspect, a transformer comprises: a primary winding; a secondary winding; an insulation material arranged between the primary winding and the secondary winding; and at least one electric shield positioned at least partially within the insulation material and between the primary winding and the secondary winding. In certain embodiments, the at least one electric shield comprises at least one metal layer and at least one dielectric material, the at least one metal layer residing on the at least one dielectric material or within the at least one dielectric material. The at least one metal layer may comprise a plurality of metal layers, a first metal layer of the plurality of metal layers is on the at least one dielectric material, and a second metal layer of the plurality of metal layers is within the at least one dielectric material. In certain embodiments, the first metal layer is arranged closer to one of the primary winding or the secondary winding than the second metal layer, the first metal layer being arranged to extend a distance that corresponds to at least a longest dimension of the primary winding or the secondary winding, and the second metal layer is arranged to extend a distance that is greater than the first metal layer. In certain embodiments, the at least one electric shield comprises a printed circuit board. The at least one electric shield may comprise a first electric shield that is coupled with an electric potential of the primary winding and a second electric shield that is coupled with an electric potential of the secondary winding. In certain embodiments, the at least one electric shield is completely encapsulated within the insulation material.

The transformer may further comprise a coil former that at least partially defines a shape of at least one of the primary winding and the secondary winding. In certain embodiments, the coil former and the at least one electric shield define the shape of at least one of the primary winding and the secondary winding. In certain embodiments, the coil former forms at least one opening that supports at least a portion of the at least one electric shield. The transformer may further comprise a magnetic core, wherein the insulation material, the primary winding, the secondary winding, and the at least one electric shield form a winding package, the winding package forming a central opening, and a portion of the magnetic core resides within the central opening. In certain embodiments, the primary winding forms a winding turn along a corner of the winding package and the at least one electric shield extends past the winding turn. The transformer may further comprise at least one thermal plate arranged between the winding package and the magnetic core. In certain embodiments, the primary winding is configured as a medium voltage winding and the secondary winding is configured as a low voltage winding. At least one of the primary winding and the secondary winding may comprise multiple-strand wiring or a foil structure. In certain embodiments, the insulation material may comprise a viscosity in a range from 2500 centipoise (cP) to 5000 cP.

In another aspect, a solid state transformer comprises: a first voltage stage; a second voltage state; and an isolation stage arranged between the first voltage stage and the second voltage stage, the isolation stage comprising: a transformer comprising a primary winding, a secondary winding, an insulation material arranged between the primary winding and the secondary winding, and at least one electric shield positioned between the primary winding and the secondary winding. In certain embodiments, the at least one electric shield is encapsulated within the insulation material. In certain embodiments, the at least one electric shield comprises a printed circuit board. At least one of the first voltage stage and the second voltage stage may comprise a wide band gap switching device. In certain embodiments, the wide band gap switching device comprises a silicon carbide switching device. In certain embodiments, the isolation stage comprises a wide band gap switching device, such as a silicon carbide switching device. In certain embodiments, the first voltage stage comprises a medium voltage stage electrically connected to the primary winding, and the second voltage stage comprises a low voltage stage electrically coupled to the secondary winding. In certain embodiments, the solid state transformer is rated for operation up to 485 kilovolt-amperes. In certain embodiments, the insulation material may comprise a viscosity in a range from 2500 cP to 5000 cP.

DETAILED DESCRIPTION

Advances in power semiconductor switching devices, for example wide band gap semiconductor switching devices based on silicon carbide (SiC) and gallium nitride (GaN), are enabling improvements in electric power distribution systems. Solid state transformers that incorporate wide band gap semiconductor switching devices may provide improved efficiency with reduced size compared with conventional transformer systems. As used herein, a solid state transformer may include circuitry configured for operation according to various power transfer applications including alternating current (AC) and direct current (DC) configurations, for example AC-to-AC conversions or AC-to-DC-to-DC-to-AC conversions, among others. The solid state transformer additionally includes a transformer having primary and secondary windings positioned between an input and an output to transfer power and provide electrical isolation. For example, in an AC-to-DC-to-DC-to-AC solid state transformer, the transformer having primary and secondary windings may reside in the DC-to-DC converter portion. For an AC-to-AC solid state transformer without a DC-to-DC converter portion, the transformer having primary and secondary windings may reside within the AC-AC converter.

Embodiments of the present disclosure may refer to different operating voltage ranges by the terms low voltage (LV), medium voltage (MV), or high voltage (HV). As used herein LV may refer to voltages of up to 1000 volts (V), MV may refer to voltages in a range from 1000 V to 35 kilovolts (kV), and HV may refer to voltages above 35 kV.

In applications for MV or HV power, corresponding MV and HV transformers typically require an insulation material that is capable of handling high voltages, for example a potting material, to be arranged between the primary and secondary windings and provide encapsulation. Increased switching frequencies and higher power handling associated with solid state transformers can provide high strength electric fields that stress the insulation material, thereby leading to increased dielectric losses, partial discharges and corona events, and even catastrophic device failure. Additionally, it can be difficult to provide the insulation material between the primary and secondary windings without having small material voids that only exacerbate these mechanisms.

The present disclosure relates to shielding arrangements for transformer structures, and more particularly to shielding arrangements in transformer structures for high frequency and high power density applications. According to aspects disclosed herein, electric shields are incorporated within transformers of solid state transformer devices to shield and/or redirect high strength electric fields away from areas of the insulation material that may be prone to failure mechanisms. Such electric shields may be positioned between primary and secondary windings along one or more planes that are connected with electric potentials of the primary and/or secondary windings. For example, the electric shield may comprise a laminate structure that includes one or more metal layers and one or more dielectric layers. In certain aspects, the laminate structure may embody a printed circuit board or a dielectric material that supports a metal layer. Notably, a printed circuit board structure for the electric shield may allow multiple metal layers of the printed circuit board laminate to collectively form a particular shield in a confined space. By positioning the electric shields in this manner, high electric fields associated with solid state transformer applications may be concentrated within planes of the electric shields and diverted away from potential problem areas of the insulation material, for example areas close to the windings where voids in the insulation material may be more common. Additionally, electric shields may also provide planar surfaces between the primary and secondary windings that facilitate reduced voiding in areas of the insulation material that experience the high electric fields. In certain applications, this allows use of higher viscosity insulation materials within the transformer.

FIG. 1is a functional schematic diagram of a solid state transformer10according to aspects disclosed herein. InFIG. 1, the solid state transformer10is illustrated as a three stage transformer device that includes a first voltage stage12, a second voltage stage14, and an isolation stage16therebetween. By way of example, the solid state transformer10may be configured to receive an MV input from a power grid and provide an LV output to a load. In this regard, the first voltage stage12may embody an MV stage that provides AC-to-DC conversion and the second voltage stage14may embody an LV stage that provides DC-to-AC conversion. The isolation stage16includes a transformer18that comprises a primary winding configured as an MV or primary winding and a secondary winding configured as a LV or secondary winding. In such a configuration, the transformer18may be referred to as an MV transformer. It is understood that solid state transformers as disclosed herein may embody other configurations, including single stage transformers where the transformer18may reside within an AC-to-AC stage, and dual stage transformers where the transformer18may reside within an AC-to-DC or DC-to-AC stage without deviating from the principles disclosed herein. Additionally, the MV and LV designations for the primary and secondary windings may be different or reversed depending on the particular step-up or step-down voltage application. In certain aspects, one or more wide band gap switching devices, for example SiC metal-oxide-semiconductor field-effect transistors (MOSFETs), SiC insulated gate bipolar transistors (IGBTs), or GaN-based switching devices may be utilized as part of circuitry that forms one or more of the first voltage stage12, the second voltage stage14, and the isolation stage16to provide increased switching frequencies, higher power handling and efficiencies with reduced device complexity compared with conventional switching devices. According to aspects disclosed herein, the solid state transformer10may be configured for high power operation, for example a 485 kilovolt-ampere (kVa) rated solid state transformer. While wide band gap switching devices may provide improved operating characteristics, the principles of the present disclosure may also be applicable to other devices, for example silicon-based field-effect transistors (FETs), silicon-based IGBTs, and silicon controlled rectifiers (SCRs).

FIG. 2Ais a side cross-sectional view illustrating a winding arrangement for the transformer18according to aspects of the present disclosure. The transformer18includes a primary winding20arranged concentrically about a secondary winding22. For examples where the transformer18is an MV transformer as described forFIG. 1, the primary winding20may embody an MV winding that is electrically connected to an MV stage, and the secondary winding22may embody an LV winding that is electrically connected to an LV stage. Depending on the application, one or more of the primary winding20and the secondary winding22may include a single winding or coil or a plurality of layered windings or coils. The primary winding20and secondary winding22are arranged to form a gap24or spacing therebetween for isolation. In certain embodiments, the transformer18includes one or more coil formers26, or bobbins, that support and form the arrangement of the windings20,22, provide termination and electrical connections for the windings20,22, and form an opening28that is centrally located for receiving a magnetic core (not shown) of the transformer18.

FIG. 2Bis a side cross-sectional view of the winding arrangement for the transformer18ofFIG. 2Bwith an insulation material30added to encapsulate the primary and secondary windings20,22. As previously described, MV transformers for solid state transformer applications typically require insulation material30that is capable of handling high voltages to be arranged between the primary and secondary windings20,22, or within the gap24. The insulation material30may comprise a potting material, for example epoxy resin or certain silicones. The insulation material30may be provided by a potting process where the insulation material30is allowed to flow into the gap24and to surround or encapsulate the windings20,22before hardening. In certain embodiments, the potting process may comprise a molding process (e.g., epoxy molding) at atmospheric pressure or vacuum pressure potting. The resulting structure of the windings20,22, the coil former26, and the insulation material30may be referred to as a winding package32. An exterior wall32′ of the winding package32may be formed by molded insulation material30or by another pre-formed structure similar to the coil former26that encloses the windings20,22and contains flow of the insulation material30. An interior wall32″ of the winding package32that may also define the opening28may be formed by the innermost portion of the coil former26. In other embodiments, the interior wall32″ may be formed by molded insulation material30or by another pre-formed structure similar to the coil former26.

FIG. 3Ais a side view of the transformer18illustrating an arrangement of the winding package32relative to a core34. For illustrative purposes, the winding package32is shown in cross-section to illustrate the windings20,22, the coil former26, and the insulation material30. The core34, or magnetic core, may comprise any number of materials, including metals, powdered metals, and ceramics. For high frequency and high power density applications for example solid state transformers, the core34may comprise ferrite or ferrite ceramic materials with high magnetic permeability and low electrical conductivity that provide low losses at such frequencies. Depending on the application, the core34may form any number of shapes, for example a U-shaped, C-shaped, or E-shaped cores, among others.FIG. 3Bis an end view of the transformer18ofFIG. 3Aillustrating an embodiment where core portions34-1,34-2are provided with a U-shape, a portion of which is arranged within the opening (28ofFIG. 3A) of the winding package32. InFIG. 3B, the winding package32is not illustrated in cross-section as inFIG. 3Aand the orientation of the view provided inFIG. 3Bis taken from a right side of the image ofFIG. 3A.

FIG. 4Ais a cross-sectional view of the transformer18ofFIG. 3Ataken along the sectional line4A-4A ofFIG. 3A. As illustrated, a portion of the winding package32resides within the cores34-1,34-2and another portion of the winding package resides outside the cores34-1,34-2.FIG. 4Aillustrates additional details of the coil former26and the primary and secondary windings20,22. In certain embodiments, the coil former26may form one or more cup shapes or recesses to serve as a platform for separately retaining the windings20,22in a spaced apart manner. The coil former26may be formed as a single piece or a multiple piece structure. For high frequency applications, the windings20,22may comprise multiple-strand wires of copper or the like, for example litz wires, that are wound about the coil former26. By way of example, the primary winding20is illustrated as a smaller diameter litz wire wrapped in a two layer coil structure, and the secondary winding22is illustrated as a larger diameter litz wire wrapped in a single layer structure. Depending on the voltage application, the number layers and/or the wire diameters may vary. In certain applications the windings20,22may comprise single wires. For multiple-strand and single strand wires, the windings20,22may also comprise wire insulation.

FIG. 4Bis an expanded view of a portion of the winding package32ofFIG. 4Awith superimposed arrows indicating distribution of an electric field36within the winding package32during operation. As illustrated, the electric field36is formed between the primary winding20and the secondary winding22such that the electric field36traverses the insulation material30and portions of the coil former26within the winding package32. During formation of the insulation material30, it can be difficult to ensure complete filling and encapsulation around the windings20,22, particularly in areas between the one of the windings20,22and corresponding portions of the coil former26. Small voids38may form within the insulation material30that can disrupt the electric field36and result in higher dielectric losses, electrical discharge including partial discharge or corona, and even catastrophic device failure. While a single small void38is illustrated between a portion of the primary winding20and the coil former26, multiple voids38of various sizes and shapes may be distributed in any location of the insulation material30.

The problems associated with formation of voids38in the insulation material30is not just limited to transformers with multiple-strand wire arrangements.FIG. 5Ais a cross-sectional view of a transformer40that is similar to the transformer18ofFIG. 4A, but where the primary winding20comprises a foil structure. The foil structure of the primary winding20may include a laminated structure of alternating metal thin films and insulating thin films. In various configurations, the secondary winding22may comprise a foil structure and the primary winding20may comprise a multiple-strand wire (e.g., litz wire) or both the primary and secondary windings20,22may comprise a foil structure.FIG. 5Bis an expanded view of a portion of the winding package32ofFIG. 5Awith superimposed dashed arrows indicating distribution of the electric field36within the winding package32during operation. InFIG. 5B, the laminated structure of alternating metal thin films20A (or foil layers) and insulating thin films20B is more visible within the foil structure of the primary winding20. As illustrated, the electric field36may form between the primary winding20and the secondary winding22, traversing through portions of the insulation material30and the coil former26. As with the example ofFIG. 4B, one or more voids38can form within the insulation material30, particularly in areas between the coil former26and a corresponding one of the windings20,22that can disrupt the electric field36and result in one or more of higher dielectric losses, electrical discharge including partial discharge or corona, and catastrophic device failure as previously described. By way of example,FIG. 5Billustrates voids38that may form between the primary winding20and a lengthwise portion of the coil former26or along portions of the foil structure of the primary winding20.

According to aspects disclosed herein, transformers may include one or more electric shields provided within portions of a winding package that shield and/or redirect high strength electric fields away from areas of the insulation material that may be prone to formation of voids, thereby reducing failure mechanisms associated with electrical field distribution in such areas. The electric shields may be positioned between primary and secondary windings along one or more planes that are coupled with electric potentials of the primary and secondary windings. In certain embodiments, one or more portions of the electric shields form planar structures that at least partially or fully reside within insulation material between the primary and secondary windings.

FIG. 6Ais a cross-sectional view of a transformer42that is similar to the transformer40ofFIG. 4A, and further includes one or more electric shields44-1to44-3arranged within the winding package32to alter electric field distribution during operation. Each electric shield44-1to44-3may comprise one or more metal layers46-1,46-2on or within a dielectric material48. For example, the electric shields44-1to44-3may embody printed circuit boards and the metal layers46-1,46-2may comprise metal planes such as copper or the like that are laminated with the dielectric material48. One or more electrical vias may electrically interconnect the metal layers46-1,46-2within the dielectric material48. In certain embodiments, the metal layer46-1may comprise a plane of metal positioned at a surface of the electric shield44-3, and the metal layer46-2may comprise a plane of metal positioned within an interior of the electric shield44-3. In other embodiments, the electric shields44-1to44-3may comprise a single metal layer (46-1or46-2) on an exterior surface of the dielectric material48or embedded within an interior of the dielectric material48. The dielectric material48may embody a rigid board or support structure that is configured to support the one or more metal layers46-1,46-2

Each electric shield44-1to44-3is positioned proximate to a respective one of the primary winding20or the secondary winding22so that at least one of the one or more metal layers46-1,46-2is coupled with the electric potential of the particular winding20,22. For example, the electric shield44-1is coupled with the electric potential of the secondary winding22and the electric shields44-2,44-3are coupled with the electric potential of the primary winding20. In this regard, the electric field distribution between the primary and secondary windings20,22may be tailored to avoid areas of the insulation material30where voids are likely to form. In each of the primary and secondary windings20,22, each winding turn (represented as the circles inFIG. 6A) may have a different electric potential. In this manner, the electric shields44-1to44-3may be coupled with average electric potentials of corresponding windings20,22. In certain embodiments, a single winding turn of the windings20,22may be arranged to directly contact the metal layer46-1of a corresponding shield while the other winding turns of each winding20,22may be spaced from the metal layer46-1by portions of the insulation material30. In certain embodiments, the metal layers46-1,46-2may form full or continuous planes of metal that entirely extend within the insulation material30and between the windings20,22. In other embodiments, the metal layers46-1,46-2may form other patterns that are tailored to distribute the electric field away from certain areas of the insulation material30. In one example, the metal layers46-1,46-2may be arranged to cover different areas within the electric shields44-1to44-3. InFIG. 6A, the metal layer46-1is arranged closest to particular ones of the windings20,22. In this manner, the metal layer46-1is positioned to extend lengthwise a distance that is at least the same as a length or longest dimension of the corresponding winding20,22. InFIG. 6A, this distance may correspond with a distance between end portions of the coil former26that are on opposing ends (e.g., top and bottom in the view ofFIG. 6A) of each of the windings20,22. The metal layer46-2may extend in a same lengthwise direction a greater distance such that the metal layer46-2extends past boundaries defined by the coil former26. In this manner, the metal layers46-1,46-2may alter different areas the electric field during operation.

In certain embodiments, the primary and secondary windings20,22may be wrapped around the electric shields44-1to44-3before potting with the insulation material30. In this manner, the electric shields44-1to44-3may be configured to replace portions of the coil former26that would otherwise extend lengthwise across the windings20,22. In certain embodiments, the coil former26includes one or more slots50or openings formed in opposing end portions of the coil former26for positioning of the electric shields44-1to44-3. In the orientation of the view ofFIG. 6A, the end portions of the coil former26correspond with top and bottom portions on opposing top and bottom ends of the windings20,22. The primary and secondary windings20,22may then be coiled around the electric shields44-1to44-3and the other portions of the coil former26before potting. In this regard, the combination of the electric shields44-1to44-3and the coil former26may form a hybrid coil former. In other embodiments, the coil former26may be configured in a similar manner as inFIG. 4Aand the electric shields44-1to44-3may be positioned between the coil former26and respective ones of the windings20,22. The coil former26may include additional openings or channels to allow flow of the insulation material30during encapsulation.

FIG. 6Bis an expanded view of a portion of the winding package32ofFIG. 6Awith superimposed dashed arrows indicating distribution of the electric field36within the winding package32during operation. During operation, the electric filed36is strongest in areas that are directly between the primary and secondary windings20,22. By connecting the metal layers46-1,46-2of a particular electric shield44-1to44-3to the electric potential of a corresponding winding20,22, the electric field36may be confined or concentrated in the electric shields44-1to44-3and away from areas of the insulation material30that are prone to void formation, for example areas that are proximate the primary winding20. As illustrated inFIG. 6B, one or more of the voids38may be formed in such an area in a similar manner asFIG. 4B, however the presence of the electric shield44-2reduces interaction between the void38and the electric field36, thereby limiting failure mechanisms such as increased dielectric losses, partial discharges and corona events, and catastrophic device failure. Instead, the electric field36between the windings20,22may accordingly be distributed between the electric shields44-2and44-3. Additionally, the presence of the electric shields44-2,44-3may reduce void formation in portions of the insulation material30between the windings20,22where the electric field36is present. For example, the electric shields44-2and44-3may provide smoother and more even surfaces for flow of the insulation material30during encapsulation so that the insulation material30may more evenly fill the space between the electric shields44-2and44-3where the electric field36is present during operation. This may also allow the insulation material30to comprise a higher viscosity material, depending on the application. For example, conventional devices may utilize an insulation material having a viscosity of about1900centipoise (cP) while the present disclosure allows the insulation material30to comprise viscosity values greater than 1900 cP while still providing adequate fill during encapsulation. In one example, the insulation material30comprises a viscosity in a range from 2500 cP to 5000 cP, or in a range from 2700 cP to 4000 cP, or in a range from 3000 cP to 4000 cP, or in any range formed by endpoints of any of the foregoing values. In particular applications, the ability to select higher viscosity values for the insulation material30may also allow selection of materials with other desirable characteristics for the insulation material30. For example, some higher viscosity materials may also have higher thermal conductivities. In one example, a material having a viscosity of about 3100 cP for the insulation material30may also provide a thermal conductivity value that is from two to three times higher than a conventional material with a viscosity value of about 1900 cP. While the embodiments illustrated inFIGS. 6A and 6Bprovide arrangements of electric shields44-1to44-3with wire-based winding structures (e.g., litz wiring or the like), one or more of the primary and secondary windings20,22may comprise a foil structure as previously described forFIGS. 5A and 5Bwithout deviating from the principles described herein.

FIG. 7is a perspective view of a model of a transformer52according to aspects of the present disclosure. The transformer52may be configured in a similar manner as described for the transformer42ofFIGS. 6A and 6B. For illustrative purposes, the winding package32is shown without the insulation material30and the windings20,22to illustrate the arrangement of electric shields44and the coil former26. Multiple cores34are arranged along lengthwise portions of the winding package32, and one or more housing plates54may be arranged to secure the cores34relative to the winding package32. The housing plates54may comprise a material of high thermal conductivity, for example aluminum or alloys thereof, for heat dissipation within the transformer52. Additionally, one or more fluid conduits56may also be arranged along or within certain ones of the housing plates54for added heat dissipation. An end of the winding package32is illustrated as protruding from the cores34and the housing plates54. Thermal layers or plates58,60may be positioned between the winding package32and the cores34and the housing plates54to provide additional heat dissipation. In certain embodiments, the thermal layers or plates58,60comprise one or more combinations of high thermally conductive materials, for example metal plates and ceramic layers or plates. By way of example, the thermal layer58may embody an aluminum plate and the thermal layer60may embody a ceramic layer or plate. One or more electrical connections62for the windings (20,22ofFIG. 6A) may be provided at one or more ends of the winding package32.

As illustrated by the end of the winding package32that is visible inFIG. 7, the coil former26may form end caps that support the electric shields44. The electric shields44may extend through slots or openings of the coil former26and the positions of the windings (20,22ofFIG. 6A) may formed by a combination of the coil former26and the electric shields44in a similar manner as illustrated inFIG. 6A. The transformer52ofFIG. 7is arranged for a winding configuration that includes a primary winding and two halves of a secondary winding on opposing sides of the primary winding. InFIG. 7, a location of the primary winding is designated20′ and locations of the two halves of the secondary windings are designated22′-1,22′-2relative to portions of the end caps of the coil former26. When present, the primary and secondary windings will traverse between these respective locations20′,22′-1,22′-2above and below respective ones of the electric shields44. As constructed, the transformer52may be suited for sufficiently handling high frequency and high temperature operating conditions that may be present in solid state transformer devices.

FIG. 8is an expanded cross-sectional view of a corner of the winding package32ofFIG. 7illustrating an arrangement of the primary winding20and a plurality of secondary windings22-1,22-2relative to the electric shields44. While the electric shields44are illustrated with a single metal layer46within a dielectric material48, the electric shields44may include a plurality of metal layers46formed in a laminate structure as previously described. In certain embodiments, the primary winding20is centrally located within the winding package32in between and in a spaced apart manner from the two halves of the secondary winding22-1,22-2. The electric shields44at least partially define channels where the windings20,22-1,22-2reside. As illustrated, one or more of the electric shields44may be configured to extend in a linear manner past corner winding turns of different ones of the windings20,22-1,22-2to provide extended electric field shielding at corners or turns of the windings20,22-1,22-2. For example, the corresponding electric shields44that are arranged between the primary winding20and the secondary winding22-1extend past a corner turn20″ or winding turn of the primary winding20. In this manner, the electric field in operation may be sufficiently spaced from the corner turn20″ of the primary winding20without the electric shields44having to completely contact each other at the corner turn20″. While the plurality of secondary windings22-1,22-2are illustrated inFIG. 8, the aspects disclosed are also applicable to other winding arrangements, for example those with a single primary winding and a single secondary winding. In various configurations, one or more of the primary and secondary windings20,22may comprise a foil structure as previously described forFIGS. 5A and 5Bwithout deviating from the principles described herein.

FIG. 9Ais a cross-sectional view of a transformer64that is similar to the transformer42ofFIG. 6A, except the secondary winding22-1,22-2is configured with two halves on opposing sides of the primary winding20. Additionally, the primary and secondary windings20,22-1,22-2embody foil structures as previously described forFIGS. 5A and 5B. As with other embodiments, one or more of primary and secondary windings20,22-1,22-2may also embody wire structures or multiple-strand wire structures including litz wiring. As illustrated, the two halves of the secondary winding22-1,22-2are positioned in a spaced apart manner on opposing sides of the primary winding20within the winding package32. Additionally, cores34-1to34-4are respectively positioned along opposing ends of the winding package32in a manner similar to the transformer52ofFIG. 7.

FIG. 9Bis an expanded view of a portion of the winding package32ofFIG. 9A. As illustrated, the insulation material30may fill and encapsulate portions of the winding package32on opposing sides of the primary winding20where the electric field is expected to be highest in operation. As previously described, the electric shields44may define the spaces between the primary winding20and the secondary winding22-1,22-2with surfaces that promote encapsulation with reduced voiding. Additionally, the electric shields44may further distribute the electric field away from areas of the insulation that are between individual electric shields44and corresponding windings20,22-1,22-2where voiding may be more likely to occur.