POWER MAGNETIC COMPONENT

Abstract

A magnetic component having a core of a high-permittivity material with one or more apertures extending between two opposite faces of the core and filled with a thermal conductors of a non-magnetic insulator material. Preferably, the apertures extending between a flat side of the core in contact with a metallic housing and the space where the windings are laid, providing a short and direct path for heat transfer. The thermal conductors may be alumina or any suitable material.

Claims

1. A magnetic component having a core of a high-permittivity material forming a magnetic circuit, wherein the core has at least one aperture extending between two opposite faces of the core and filled with a thermal conductor of a non-magnetic insulator material.

2. The magnetic component of claim 1, comprising at least one winding concatenated with the magnetic circuit.

3. The magnetic component of claim 2, wherein the core is a pot core with a flat side and a concavity for lodging the winding therein, the at least one apertures extending between the flat side and a bottom side of the concavity, the core and the winding being potted in a metallic housing, the flat side abutting a flat bottom of the housing.

4. The magnetic component of claim 3, wherein the thermal conductors extends above the bottom side of the concavity and is partly surrounded by potting compound.

5. The magnetic component of claim 4, wherein the thermal conductors is in thermal contact with the winding and support mechanically the windings.

6. The magnetic component of claim 1, wherein the core is a ferrite core or powdered metal core, and the thermal conductors are one of: Alumina, a Al2O3 composite, ceramic, Boron Nitride, a BN composite, Silicon Carbide.

7. The magnetic component of claim 1, wherein a thermal conductivity of the thermal conductor is higher than a thermal conductivity of the high-permittivity material and a potting compound, preferably above 5 W/m.Math.K, more preferably above 10 W/m.Math.K, even more preferably above 20 W/m.Math.K.

8. The magnetic component of claim 1 configured as a transformer with two magnetically coupled windings.

9. Use of the magnetic component of claim 1 in a power converter or in a battery charger.

10. The magnetic component of claim 4, comprising a plurality of apertures and thermal conductors, wherein the said apertures and thermal conductors are arranged along a contour of the winding lodged in the concavity.

11. The magnetic component of claim 5, comprising a plurality of apertures and thermal conductors, wherein the said apertures and thermal conductors are arranged along a contour of the winding lodged in the concavity.

12. The magnetic component of claim 6, wherein the said apertures and thermal conductors are distributed along the entire contour of the winding.

13. The magnetic component of claim 7, wherein the said apertures and thermal conductors are distributed along the entire contour of the winding.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0021] Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

[0022] FIGS. 1a-1c illustrates schematically a magnetic component of known type with a ceramic plate providing a heat path around the magnetic core.

[0023] FIGS. 2a-2d show a possible realization of the inventive magnetic component.

[0024] FIG. 3 shows a variant of the inventive component with thermal conductors extending above the core into the potting compound.

[0025] FIG. 4 shows a variant of the invention involving a core of a different shape

EXAMPLES OF EMBODIMENTS OF THE PRESENT INVENTION

[0026] FIG. 1a represents a magnetic transformer with a gapped core, suitable for use in certain classes of DC-DC converters and battery chargers. The transformer is represented with the components exploded, omitting the potting compound that is poured in the housing in a final assembly step.

[0027] The transformer represented in the figures can be used, for example in a power converter or in a battery charger. On-board battery chargers for electric and hybrid vehicles are an important use case of the present invention, but not the only one. The invention can be applied also to filters, power factor converters, and any application of magnetic components where high power density is desired.

[0028] The transformer is mounted in a metallic housing 25, for example a cast aluminium element. The housing has a receptacle that is configured to contain the transformer and a flat base designed to be fastened to a flat plate. The plate may be cooled by water, forced air or natural air convection.

[0029] The winding or windings 61, 62 are inserted in the magnetic core 32 around the central leg and the magnetic circuit is completed by the lid 33. A heat-conducting ceramic plate 50 adds a thermal path that improves the transmission of heat from the windings to the bottom of the housing and thence to the cooled plate. FIGS. 1b and 1c show the same assembly from above and in section, the windings 61, 62 and the potting having been omitted for simplicity. The core 32 can comprise any suitable magnetic material such as a ferrite or powdered iron. Ferrites are the material of choice in high-performance power converters operating at carrier frequencies of hundreds of kHz or more. Ferrites suitable to use in the present invention can be obtained commercially by the company “Ferroxcube” under the denomination “3C92” among others, but many other producers and grades are available.

[0030] FIG. 2a shows a magnetic component according to the invention. The core 32 has openings 35 that traverse a thickness of the core and connect one flat face 37 of the core with an inner face, adjacent to the windings 61, 62. The openings 35 are filled by plugs 55 of a thermally conducting non-magnetic material. Preferably, the thermal conductivity of the material chosen for the plugs 55 is sensibly more than the thermal conductivity of the magnetic material composing the main part of the core 32, for example heat conducting ceramic with a thermal conductivity higher than 5 W/m.Math.K, preferably 10 W/m.Math.K or higher. Al.sub.2O.sub.3 with thermal conductivities better than 20 W/m.Math.K is available and suitable for the present invention. Al.sub.2O.sub.3 also provides the advantage that it is inexpensive, available on the market and is electrically insulating. Other technical materials that could be used for this purpose include Silicon Carbide, Boron Nitride and diamond.

[0031] Ceramic materials are attractive choices for the thermal plugs 55 because they resist to very high temperatures and their coefficient of thermal expansion is quite small; nevertheless, they are not the only choice possible. The thermal plugs 55 could be made out of any suitable insulator with a thermal conductivity higher than that of the surrounding ferrite. This includes, among others, composite materials with a thermally conductive phase in a matrix. The matrix could be a silicone polymer, or an organic polymer or any other suitable binder. Thermally conductive composites and thermally conductive plastics are inexpensive and easy to manufacture in complex shapes.

[0032] Preferably, the openings 35 and the thermal plugs 55 inserted into the openings 35 are not arranged randomly in the core 32, but run along the contour, or outline, of the overlying windings 61, 62. This means that the heat generated by the windings 61, 62 can be dissipated very efficiently, as the thermal path is relatively short due to this arrangement. This solution is simple and a complex structure for thermally connecting the windings 61, 62 to its environment can be omitted. More preferably, the openings 35 and the thermal plugs 35 run along the entire contour of the windings 61, 62 to optimise the heat transfer and avoid hot spots.

[0033] FIG. 2b shows the magnetic device of the invention from the top. FIG. 2c is a cross section that shows the core 32 alone with the openings 35 in the bottom of the receptacle that is designed to receive the windings 61, 62. In the finished product, the lower flat side 37 of the core 32 will sit directly on the bottom of the aluminium casing 25 that is fastened on a cooled plate, as in FIGS. 1a-1c. The plugs 55 provide a direct and short path to dissipate the heat generated by the losses, particularly the losses in the windings.

[0034] The aluminium casing 25 can be filled with the potting compound (not illustrated) in a final assembly step. The potting compound can have, when solidified, a thermal conductivity of 0.7 W/m.Math.K, 1.0 W/m.Math.K or 1.6 W/m.Math.K but in any case lower than 2.0 W/m.Math.K. The potting compound may be constituted of an semi-elastic material, such as silicone or urethane; or a resin material, such as acrylonitrile-butadiene-styrene, polybutylene-terephthalate, or polyphenylene sulfide.

[0035] As one can notice, the potting compound's thermal conductivity is typically far lower than the thermal conductivity of the thermal plugs 55. In return, the thermal conductivity of the thermal plugs 55 are at least two times higher than the thermal conductivity of potting compound.

[0036] In a non-illustrated example, the plugs 55 may protrude from the openings 35, so that protruding ends form a spacer between the lower flat side 37 of the core 32 and the bottom of the aluminium casing 25 when potted. The resulting distance between the lower flat side 37 of the core 32 and the bottom of the aluminium casing can reduce eddy currents in the material of the casing 25. The protruding ends, however, can still be in contact with the bottom of the aluminium casing 25 for thermal exchange.

[0037] FIG. 2d shows the core 32 from above, with a recess configured to accept the windings, which are not drawn in this figure, around a central column. The openings 35 lie on the bottom of the recess and provide a direct path to the flat underlying face. This disposition is advantageous because, on one side, the length of the heat path is limited and, on the other side, the effects of the apertures on the reluctance and the maximum flux density of the magnetic circuit are moderate.

[0038] FIG. 3 illustrates a variant of the magnetic component illustrated in FIGS. 2a-2d, in which the heat conductors 55 are not entirely contained in the thickness of the core 32 but directly extend in the space above, providing both a thermal contact and a mechanical support to the windings 61, 62. The thermal path between the windings 61, 62 and the aluminium casing 25 is improved by providing a path with higher thermal conductivity. As a result, heat generated by the windings 61, 62 is better evacuated. Furthermore the core 32 remains in connection with the heat conductors 55 and thereby also providing a thermal path for the heat generated by the core 32. In addition, the manufacturability of the magnetic component can be improved by the heat conductors 55 directly extending into the space above, as they can function as guiding means for optimally placing the windings 61, 62 in the concavity of the core 32.

[0039] Also in the present variant, the openings and the heat conductors 55 run along the contour of the windings 61, 62 providing a short thermal path.

[0040] The previous example shows a transformer with two coupled windings and an air gap in the magnetic circuit; nevertheless, the invention is not so limited, and may include plain inductors with a single winding, common-mode chokes with two coupled windings, conventional transformers without air gaps, power-factor correction impedances, multiphase devices with multiple windings and more.

[0041] While the examples represent a pot core of a special shape, magnetic cores come in a large variety of shapes, and the present invention applies to all shapes. The invention includes variants in which the core is made by two symmetrical halves, rather than a deep pot closed by a flat lid, and other shapes like “C” cores, “E” cores and many others. FIG. 4 represents a possible implementation of the invention in a ferrite core 31 with an “E” shape. In contrast with the example of FIGS. 2a-2d that had cylindrical conductors 55, the thermal inserts 56 of FIG. 3 are prismatic. According to the need, the thermal inserts could assume any suitable shape.

REFERENCE SYMBOLS IN THE FIGURES

[0042] 25 housing [0043] 31 “E” core [0044] 32 pot core, core [0045] 33 core lid [0046] 35 opening [0047] 37 flat face [0048] 50 thermal plate [0049] 55 thermal conductor, cylindrical, plug [0050] 56 thermal conductor, prismatic [0051] 61 winding [0052] 62 winding