A COMPACT MAGNETIC POWER UNIT

Abstract

 It comprises a magnetic core (10) including at least one coil (70a, 70b, 70c) wound around the magnetic core (10) and at least one cooling structure (50) including a non-metallic thermally conductive element built as a heat pipe (51) arranged inside a hole or inner cavity (30) of said magnetic core (10) and comprising at one of its ends a heat dissipation member (52). The heat pipe (51) can be made in a thermoplastic or ceramic material having magnetic, or non-magnetic, paramagnetic or diamagnetic properties and is a hollow pipe filled with a fluid having a low boiling point. The heat dissipation member (52) ends in a dissipation plate.

Description

Technical field

[0001] The present invention refers to a significantly reduced size integrated magnetic power unit comprising a magnetic core generally including a first, a second and a third winding channels respectively arranged around a first, a second and a third intersecting axis, orthogonal to each other, each of said winding channels intended for receiving at least one coil wound around the magnetic core each coil having at least one turn, and the magnetic power unit further having associated one cooling structure of the core including a non-metallic thermally conductive element.

[0002] This magnetic power unit is particularly adapted to be used for example as a transformer or inductor in the electrical power field, suitable for operating a high power electrical device, especially usable in the field of hybrid and electrical vehicles (HEVs) that nowadays is growing quite fast. The new models of electrical vehicles require more and more power electronics inside, not only for the electrical motor supply with speed and torque control, but also for high-voltage (HV) battery chargers and stable in-car continuous low-voltage (LV) power supplies.

[0003] The magnetic power unit of this invention responds to a new volumetric efficiency concept on magnetic units (better volumetric performance, mainly when a 3D magnetic flux is involved) with a magnetic core including around it orthogonal windings for producing two or three substantially orthogonal magnetic fields at all point within the core

[0004] It will be understood along this description that references to geometric position, such as parallel, perpendicular, tangent, etc. allow deviations up to ± 5° from the theoretical position defined by this nomenclature. It will also be understood that any range of values given may not be optimal in extreme values and may require adaptations of the invention to these extreme values are applicable, such adaptations being within reach of a skilled person.

Background of the invention

[0005] Different approaches have been attempted to try and remove heat (produced by the Foucault currents generated) from the core of magnetic power unit particularly in the case of power transformers. Some of these are the increasing of wire size to reduce resistive losses; immersion of the transformer in circulating coolant oil; air cooling of the transformer windings; increasing the operating frequency of the transformer to reduce windings; and increasing the thermal conductivity of the insulating potting compound around the transformer windings. All of these, however, impact on the mechanical size and weight of the transformer designs limiting the use of these applications. Without proper cooling the efficiency and reliability of these transformers and inductors are considerably reduced.

[0006] DE19814896 discloses a power transformer for high current having a closed cylindrical core of soft magnetic high permeability material high saturation induction and low magnetic losses. This is wound with a primary coil and a secondary coil. The core is within a casing that is then filled with a suitable resin. At least one heat pipe (9) for cooling the unit is set in the centre. The heat pipe forms at least one part of the winding of the transformer.

[0007] EP0498897 (B1) reveals an electrical wiring material that can use as cooling means for heating portions in electronic apparatuses and a transformer having a coil of one side also serving as the cooling means. The document discloses a material for electrical wirings provided with a cooling function. The material is characterized in that it comprises a slender hollow conductor in which an operating liquid is sealed. Preferably, pieces for electric connections are provided on the end parts or other parts of the hollow conductor. By such a configuration, when used for the wirings of electrical apparatuses, by the heat radiation due to the action of the operating liquid in the hollow conductor, there is no necessity to provide other cooling means in the electrical apparatuses, and the material for electrical wirings can contribute to the reduction of the size of the electrical apparatus. Also, this Ep patent relates to a transformer in which the material for electrical wirings is used for the coil on its low voltage side. Since the coil heated by the large current flowing through it dissipates the heat by itself, there is no necessity to provide other coiling means.

[0008] Moreover, since the transformer in accordance with the present invention is constituted as described above, due to a coil itself on a low voltage side in which a large current flow, the heat generated in the coil can be radiated. Consequently, no other cooling means is needed to the transformer or it may be enough by installing with extremely small capacity cooling means.

[0009] US6777835B1 discloses an electrical power cooling technique and particularly an apparatus for cooling a high power electrical transformer and electrical motors by using thermally conductive material interleaved between the turn layers of a high-power transformer and iron core laminates to provide a low resistant thermal path to ambient. The strips direct excess heat from within the interior to protrusions outside of the windings (and core) where forced air or thermally conductive potting compound extracts the heat. This technique provides for a significant reduction of weight and volume along with a substantial increase in the power density while operating at a modest elevated temperature above ambient. In an embodiment a transformer is made of material such as laminated iron, ferrite and other core materials and the transformer is formed of insulated copper windings wrapped around the core. Heat is dissipated through the core to a base plate, while thermally conductive strips are placed in preselected positions between the windings and are preferably of high modulus graphite laminate material, to conduct heat along its fibre orientation, which is unidirectional.

Disclosure of the invention

[0010] The invention provides an alternative structure of a compact magnetic power unit particularly adapted to be used as a transformer or inductor in the power industry and especially applicable in the electrical automobile field (mainly for hybrid and electrical vehicles) and comprising a magnetic core including at least one coil wound around the magnetic core and at least one cooling structure including a non-metallic thermally conductive element, such as the one disclosed in the cited US6777835B

[0011] According to this invention the non-metallic thermally conductive element is a heat pipe arranged inside (almost all the heat pipe is located within) a hole or inner cavity of the magnetic core and comprising at one of its ends a heat dissipation member.

[0012] In an embodiment, the heat pipe is made of a thermoplastic or ceramic material having magnetic, or non-magnetic, paramagnetic or diamagnetic properties and said heat dissipation member can be embodied by a plate.

[0013] Generally, the heat pipe is arranged coaxial with an axis (A-A) orthogonal to a plane containing at least a turn of said at least one coil, so that the heat pipe extending through the magnetic core (capturing the heat generated therein.

[0014] As per a preferred embodiment the heat pipe is a hollow pipe filled with a fluid having a low boiling point.

[0015] The compact magnetic power unit of this invention can be embodied in many ways being any of:

• a transformer comprising three coils wound in three respective orthogonal axes;
• a transformer comprising two coils wound in two respective orthogonal axes, a third orthogonal axis without coil or including a choke;
• a choke comprising three coils wound in three respective orthogonal axes or comprising two coils wound in two respective orthogonal axes;
• a transformer including three coils in each of the three-orthogonal axis,

or any combination of a transformer and choke distributed on three orthogonal axes magnetically coupled or uncoupled among them.

[0016] Other features of the invention appear from the following detailed description of some embodiments of the compact magnetic power unit regarding the accompanying drawings

Brief description of the drawings

[0017] In the attached drawings:

Fig.1 shows a partial exploded view of a compact magnetic power unit according to an embodiment of the present invention;

Fig. 2 shows an exploded view of the compact magnetic power unit of Fig. 1;

Fig. 3 shows schematically the arrangement of three coils wound around the magnetic core of the power unit of Fig. 1

Fig. 4 shows an exploded view of a compact magnetic power unit according to another embodiment of the present invention;

Fig. 5 shows a perspective sectional view of a compact magnetic power unit according to a still another particular embodiment of the present invention.

Detailed description of some embodiments

[0018] With respect to figure 1, a compact magnetic power unit 100, adapted to be used as a transformer or inductor in the electrical power industry and especially in the field of hybrid and electrical vehicles (involving among other DC/DC power transformer, and converters, DC/AC on board charger, or DC/DC power supply units), is shown. The compact magnetic power unit 100 comprises a magnetic core 10 which enables winding around it one or more orthogonal coils, and a cooling structure 50. The magnetic core 10 is provided with a through hole 30 for housing almost all a non-metallic thermally conductive element constituting the cooling structure 50. In particular, the non-metallic thermally conductive element is a heat pipe 51 configured to be arranged inside the magnetic core 10. Some embodiments may provide that the magnetic core 10 has a blind hole or in general a hole or inner cavity 30 inside of which a heat pipe 51 can be arranged.

[0019] The cooling structure 50 includes a heat dissipation member 52, preferably a heat dissipation plate, connected to the heat pipe 51 at one of its ends. The heat pipe 51 allows capturing the heat generated into the magnetic core 10 for carrying it to the dissipation plate 52. Thus, the compact magnetic power unit 100 provides a better volumetric performance (particularly 3D magnetic flux when three orthogonal windings are involved) and therefore can support density energy until a value of about 200 W/cm³. In this way, the compact magnetic power unit 100 can be realized with reduced dimensions without the risk of overheating that may be occur in some power application (e.g. battery charging in automotive field).

[0020] Preferably, the heat pipe 51 is made of a thermoplastic or ceramic material having magnetic, or non-magnetic, paramagnetic or diamagnetic properties. More preferably, the eat pipe 51 is a hollow pipe filled with a fluid having a low boiling point implementing a technique well known in the art.

[0021] The compact magnetic power unit 100 comprises at least one coil, wound around the magnetic core 10, not shown in figure 1 for a better clarity of the arrangement of hole 30 on the magnetic core 10. Depending on the number and on the arrangement of one or more orthogonal coils (see Fig. 3) wound around the magnetic core 10, the compact magnetic power unit 100 provides different working configurations that will be discussed with greater details in the following description.

[0022] The embodiment shown in figure 1 provides that the magnetic core 10 includes a first, a second and a third winding channel 2a, 2b, 2c, respectively arranged around a first, a second and a third intersecting axis A-A, B-B, C-C orthogonal to each other. Each winding channel 2a, 2b, 2c is intended for receiving at least one coil, having at least one turn, wound around the magnetic core 10. In this embodiment, the three axes are pairwise perpendicular and define a first, a second and a third plane in which the winding channels are located respectively. For example, the first winding channel 2a, that is arranged around the first axis A-A, is located in the first plane that is defined by the other two axis B-B and C-C (i.e. the first plane is the plane orthogonal to the first axis A-A and on which the axes B-B and C-C lie).

[0023] The three planes define eight octants, each including a protrusion defining a protruding spacer 20. The eight protruding spacers 20 are spaced to each other by the winding channels 2a, 2b, 2c.

[0024] With respect to figure 1, the heat pipe 51 is arranged coaxial with the axis A-A orthogonal to a plane containing at least a turn of the coil wound around the winding channel 2a.

[0025] For allowing a simple and reliable production of the magnetic core 10 shown in figure 1, the body of the magnetic core is preferably composed of at least two parts 11, 12 assembled together by means of an attachment. In this case, the magnetic core 10 is formed by a plurality of different partial magnetic cores 11, 12 made of a magnetic material selected among ferrite, ferromagnetic material, or a Polymer Bonded Soft Magnetic (PBSM) injectable material. The partial magnetic cores are assembled together (for example by an adhesive) forming a composed core 10 in a layered configuration (i.e. the partial magnetic cores are stacked to each other).

[0026] With respect to figure 2, the magnetic core 10 is preferably formed by three different partial magnetic cores comprising a central partial magnetic core 11 and two side partial magnetic cores 12, wherein each of the two side partial magnetic cores 12 includes four protruding spacers 20. The central partial magnetic core 11 is interposed between the two-side partial magnetic cores 12 and lacks of protruding spacers 20. In this embodiment, the two side partial magnetic cores 12 have a substantially flat surface configured to be attached to the central partial magnetic core 11 by means of an adhesive (not shown and having a thickness negligible with respect to the dimensions of the magnetic core 10).

[0027] Preferably, the composed core 10, when assembled, has a general geometric shape of a rectangular parallelepiped or a cube. In this case, as shown in figure 1 each protruding spacer 20 has a general geometric shape substantially cubic shape. An alternative embodiment (not shown) can provide that the composed core 10, when assembled, has a general geometric shape of a sphere. In this last case, each protruding spacer 20 has a general geometric shape comprising an external surface rounded.

[0028] Some embodiments can provide that the magnetic core 10 is formed by only two partial magnetic cores each having the protruding spacers 20 (for example two half partial magnetic cores having the same shape and configured to be assembled symmetrically), or by more than three partial magnetic cores. In this last case, the magnetic core 10 is preferably formed by two side partial magnetic cores 12, each including four protruding spacers 20, and a plurality of central partial magnetic cores 11 lacking of protruding spacers 20 stacked to each other.

[0029] As shown in figure 1 and 2, the core of the compact magnetic power unit 100 is preferably surrounded by flux closing magnetic covers 40 preferably made of a material selected among ferrite, ferromagnetic material, or a Polymer Bonded Soft Magnetic (PBSM) injectable material, more preferably the same material of which the composed magnetic core 10 is made. In this embodiment, the through hole 30 extends also through the flux closing magnetic covers 40, so that the dissipation pipe 51 can pass through the composed magnetic core 10 and the heat dissipation plate can be arranged externally to the flux closing magnetic covers 40.

[0030] In the case of a composed magnetic core 10 having a general geometric shape of a rectangular parallelepiped or a cube, the flux closing covers 40 are preferably constituted by three pairs of flux closing covers 40, arranged at the opposite sides of the magnetic core 10. Each cover 40 is in contact (for example attached by means of adhesive) with four protruding members 20 and is spaced from the central partial magnetic core 11.

[0031] Preferably, each flux closing cover 40 is in contact with other four flux closing covers 40 perpendiculars to it, through four perimeter faces 41. With respect to figure 1 and 2, the perimeter faces 41 are advantageously bevelled i.e. tapered towards the magnetic core 10 with an inclined coupling surface forming a truncated pyramid having preferably with a surface inclined of about 45°. In this way, in the case of magnetic core 10 having a general geometric shape of a cube (as shown in figure 1), covers 40 can be all realized with the same shape.

[0032] An alternative embodiment, not shown, can provide that the composed magnetic core 10 has a general geometric shape of a sphere. In this case, the flux closing covers 40 are constituted by at least two opposed spherical caps, and each flux closing cover is in contact (for example attached by means of adhesive) with four different protruding spacers 20.

[0033] Figure 4 shows three coils 70a, 70b, 70c wound around the three winding channels 2a, 2b, 2c of the composed magnetic core 10 shown in figure 1, respectively. In this embodiment, the magnetic power unit 100 provides a transformer comprising three coils 70a, 70b, 70c wound around the three-respective axis A-A, B-B, C-C orthogonal to each other, but as mentioned above, depending on the number and on the arrangement of one or more coils wound around the composed magnetic core 10, the magnetic power unit 100 may provide different device configurations.

[0034] In figure 4 the through hole 30 is not shown for a better clarity of the arrangement of the three coils 70a, 70b, 70c. It is intended that the turns of the coils 70b and 70c wound around the winding channels 2b and 2c are arranged for avoiding the hole 30 for allowing the passage of the heat dissipation pipe 51.

[0035] Some embodiments may provide that the magnetic power unit 100 is a transformer having two coils wound around two respective winding channels (i.e. arranged around two respective axes) and the third winding channel without coil. Furthermore, a third coil wound around the third winding channel may provide a choke for the transformer formed by the two coils wound around the other two winding channel.

[0036] Some embodiment may provide that the magnetic power unit 100 is a choke comprising three coils wound in the three-respective winding channel, or comprising two coils wound around two respective winding channels. With respect to figure 4, another embodiment of the compact magnetic power unit 100 according to the present invention is shown. Unlike the embodiment shown in figures 1 and 2, this embodiment provides that the two-side partial magnetic cores 12 have a substantially flat surface configured to be arranged to
ward the outside of the magnetic core 10 when it is assembled.

[0037] In this embodiment, the partial magnetic cores 11, 12 are preferably assembled together by means of a mechanical joint attachment using auxiliary elements 60a, 60b comprising preferably a pair of coupling members 60a, 60b each having a substantially C-shaped conformation. In particular, each coupling member 60a, 60b comprises a first wall 61 and two second walls 62 extending from two opposite sides of the first wall 61 towards an orthogonal direction with respect to the first wall. The ends of the two second walls 62 of a coupling member 60a, 60b are configured to snap with the first wall 61 of the other coupling member 60b, 60a.

[0038] In this embodiment, the central partial magnetic core 11 is surrounded by six walls of the auxiliary elements 60 (the first walls and second walls of the coupling members 60a, 60b). The first wall 61 of each coupling member 60a, 60b is provided with an opening 63, for passing the heat dissipation pipe 51 through the hole 30, and a sleeve 64 arranged around the opening 63. The end 65 of sleeves 64 are configured to snap with the flat surface of the side partial magnetic cores 12 when the composed magnetic core 10 is assembled.

[0039] Preferably, the walls 61, 62 of each coupling member 60a, 60b are provided with a plurality of notches configured to leave open a plurality of passages for allow a direct contact between the central partial magnetic core 10 and the protruding spacers 20 of the side partial magnetic cores 12.

[0040] More preferably, the coupling members 60a, 60b are conformed for providing eight passages to allow a direct contact between each of the eight corners of the central partial magnetic core 10 with each of the protruding spacers 20 of the side partial magnetic cores 12, respectively. In this last embodiment, each protruding spacer 20 is preferably provided with a seat having a shape complementary to the respective corner.

[0041] As shown in figure 4, the compact magnetic power unit 100 is preferably surrounded by flux closing magnetic covers 40 preferably made of a material selected among ferrite, ferromagnetic material, or a Polymer Bonded Soft Magnetic (PBSM) injectable material, more preferably the same material of which the composed magnetic core 10 is made.

[0042] In this embodiment, the flux closing covers 40 are preferably constituted by two pairs of flux closing covers 40, arranged at the opposite sides of the magnetic core 10 and orthogonally with respect to the side partial magnetic covers 12. Each cover 40 is in contact (for example attached by means of adhesive) with four protruding members 20 and is spaced from the central partial magnetic core 11.

[0043] With respect to figures 1, 2 and 4, each flux closing cover 40 includes preferably four notches 42, each notch 42 for providing winding connection windows when flux closing covers 40 are in contact with the protruding spacers 20.

[0044] With respect to figure 5, another embodiment of the compact magnetic power unit 100 according to the present invention is shown. Unlike the embodiment shown in figures 1-3, this embodiment provides that the magnetic core 10 is a single piece body. In this embodiment, the magnetic core 10 is preferably a pot shaped core, i.e. a core provided with an inner housing inside of which a coil can be wound.

[0045] With respect to figure 5, the magnetic core 10 has a substantially tubular shape inside of which a coil 70a is arranged around the axis A-A which is orthogonal to the plane defined by at least a turn of the coil 70a. The pot shaped magnetic core 10 has preferably a toroidal shape so that a hole or cavity 30 is defined at the centre of the toroid. In this embodiment, the heat pipe 51 is arranged inside the hole 30 coaxially with the axis A-A, and the plate 52 is arranged as a base for the toroidal magnetic core 10.

[0046] Preferably two coils 70b, 70c are wound around the magnetic core externally. The coils 70b, 70c are wound around the curvilinear axis p arranged into the inner housing of the pot shaped magnetic core 10. The curvilinear axis p lies on a plane orthogonal to the axis A-A.

[0047] The embodiment of figure 5 includes four coils 70a, 70b, 70c and 70d wound around the magnetic core 10. In this embodiment, the compact magnetic power unit 100 can provide a transformer comprising two coils 70b, 70c wound externally around the magnetic core 10 (around the curvilinear axis p) and a coil 70a wound internally within the housing of the pot shaped core 10 around the axis A-A, and a further winding 70d, but as mentioned above, depending on the number and on the arrangement of one or more coils wound around the composed magnetic core 10, the magnetic power unit 100 may provide different device configurations.

[0048] Two magnetic core 10 as per figure 5 can be assembled with their bases facing and sharing a central heat pipe (optionally with protruding heat dissipation fins) and external dissipation plates to provide a more complex unit involving several coils in orthogonal planes operating either as a transformer or simply inductor or as a choke related to the associated winding configuration.

[0049] For example, with respect to the embodiments shown in figures 1-4, the compact magnetic power unit 100 may be a transformer having two coils wound around two respective winding channels (i.e. arranged around two respective axes) and the third winding channel without coil. Furthermore, a third coil wound around the third winding channel may provide a choke for the transformer formed by the two coils wound around the other two winding channel.

[0050] Some embodiment may provide that the compact magnetic power unit 100 is a choke comprising three coils wound in the three-respective winding channel, or comprising two coils wound around two respective winding channels.

[0051] The heat pipe feature of this invention and its arrangement within the magnetic core along with the special structure of the magnetic core result in a compact magnetic unit with high electrical and magnetic performances highlighting among them the fact that it can support density energy until a value of about 200 W/cm³.

Claims

1. A compact magnetic power unit (100) adapted to be used as a transformer or inductor in the power industry and specially in the electrical automobile field and comprising a magnetic core (10) including at least one coil (70a, 70b, 70c) wound around the magnetic core (10) and at least one cooling structure (50) including a non-metallic thermally conductive element,
characterized in that said non-metallic thermally conductive element is a heat pipe (51) arranged inside a hole or inner cavity (30) of said magnetic core (10) and comprising at one of its ends a heat dissipation member (52).

2. The compact magnetic power unit (100) according to claim 1, wherein said heat pipe (51) is made in a thermoplastic or ceramic material having magnetic, or non-magnetic, paramagnetic or diamagnetic properties and said heat dissipation member (52) comprising a plate.

3. The compact magnetic power unit (100) according to claim 1 or 2, wherein the heat pipe (51) is arranged coaxial with an axis (A-A) orthogonal to a plane containing at least a turn of said at least one coil, so that the heat pipe (51) extending through the magnetic core (10) capturing the heat generated therein.

4. The compact magnetic power unit (100) according to any of the previous claims, wherein said heat pipe (51) is a hollow pipe filled with a fluid having a low boiling point.

5. The compact magnetic power unit (100) according to claim 1 to 4, wherein said magnetic core is a single piece body.

6. The compact magnetic power unit (100) according to claim 1 to 4, wherein said magnetic core (10) is a body composed of at least two parts (11, 12) assembled together through a mechanical joint attachment using auxiliary elements (60a, 60b).

7. The compact magnetic power unit (100) according to claim 1 to 4, wherein said core is a body composed of at least two parts (11, 12) assembled together through an adhesive.

8. The compact magnetic power unit (100) according to claim 1 to 4, wherein said core is a pot shaped core.

9. The compact magnetic power unit (100) according to claim 1 to 7, wherein said magnetic core (10) has a general geometric shape selected among a rectangular parallelepiped, cube or sphere.

10. The compact magnetic power unit (100) according to claim 1 to 7, or 9 wherein said magnetic core (10) further including a first, a second and a third winding channel (2a, 2b, 2c) respectively arranged around a first, a second and a third axis (A-A, B-B-, C-C) orthogonal to each other, each of said winding channels (2a, 2b, 2c) located in respectively orthogonal planes intended for receiving at least one coil (70a, 70b, 70c) wound around the magnetic core (10), each coil (70a, 70b, 70c) having at least one turn, wherein said first, second and third planes define eight octants, each including a protrusion defining a protruding spacer (20), said protruding spacers (20) being spaced to each other by said winding channels (2a, 2b, 2c).

11. The compact magnetic power unit (100) according to claim 11, wherein the magnetic power unit is surrounded by flux closing magnetic covers (40).

12. The compact magnetic power unit (100) according to claim 11, wherein said hole or inner cavity is a through hole (30) perpendicular to one of said first, second or third planes, and extends through said magnetic core (10) and through at least one of said flux closing magnetic covers (40).

13. The compact magnetic power unit (100) according to any of the claims 9-11 wherein the general geometric shape of the magnetic core (10) is a rectangular parallelepiped and the flux closing covers (40) are constituted by at least two pairs of flux closing covers (40), each cover (40) being parallel and spaced from one face of the rectangular parallelepiped and each pair of covers including two opposed members and each flux closing cover (40) is in contact with four different protruding spacers (20).

14. The compact magnetic power unit (100) according to any of the claims 11 or 12 wherein the general geometric shape of the magnetic core (10) is a sphere and the flux closing covers (40) are constituted by at least two opposed spherical caps, and each flux closing cover (40) is in contact with four different protruding spacers (20a).

15. The compact magnetic power unit (100) according to claim 1 being any of:

- a transformer comprising three coils wound in three respective orthogonal axes;

- a transformer comprising two coils wound in two respective orthogonal axes, a third axis without coil or including a choke;

- a choke comprising three coils wound in three respective orthogonal axes or comprising two coils wound in two respective axes;

- a transformer including three coils in each of the three-orthogonal axis,

or any combination of transformer and choke arranged or distributed along three-orthogonal axis and magnetically coupled or uncoupled among them.

16. The compact magnetic power unit (100) according to claim 10 wherein the magnetic core (10) and/or the flux closing covers (40) are made of a material selected among ferrite, ferromagnetic material, or a PBM injectable material.

Drawing