THERMAL CONDUCTIVE BOBBIN FOR A MAGNETIC POWER UNIT

Abstract

Thermal conductive bobbin, for a magnetic power unit, made of an injectable and polymerizable thermoplastic composition having a plastic polymer in an amount of between 5% and 15% by weight with respect to the total weight of the composition, an aluminium nanoparticles dispersion in mineral oil in an amount of between 25% and 55% by weight with respect to the total weight of the composition, silicon carbide microparticles between 20% and 45% by weight with respect to the total weight of the composition; and additives up to 10% by weight with respect to the total weight of the composition, and wherein the thermal conductive bobbin has a dielectric rigidity higher than 5 kV/mm.

Claims

1. A thermal conductive bobbin for a magnetic power unit, wherein the thermal conductive bobbin has a magnetic field closed around, generated with or without a core, and the thermal conductive bobbin is made of an injectable and polymerizable thermoplastic composition comprising: a plastic polymer in an amount of between 5% and 15% by weight with respect to the total weight of the composition; an aluminium nanoparticles dispersion in mineral oil in an amount of between 25% and 55% by weight with respect to the total weight of the composition; silicon carbide microparticles between 20% and 45% by weight with respect to the total weight of the composition; and additives up to 10% by weight with respect to the total weight of the composition, so that the thermal conductive bobbin has a dielectric rigidity higher than 5 kV/mm.

2. The thermal conductive bobbin according to claim 1, wherein the plastic polymer is selected from the group consisting of polybutylene terephthalate, polycaprolactam, poly(hexamethylene adipamide), polyethylene terephthalate, polyether ether ketone and polyimide.

3. The thermal conductive bobbin according to claim 1, wherein the additives are dispersants, lubricants, flame retardants or combinations thereof.

4. The thermal conductive bobbin according to claim 3, wherein the dispersant is a condensation product of polyethyleneimine and polycarbonylalkylenoxy.

5. The thermal conductive bobbin according to claim 3, wherein the lubricant is oil.

6. The thermal conductive bobbin according to claim 3, wherein the flame retardant is Aluminium Hydroxide.

7. The thermal conductive bobbin according to claim 1, wherein the aluminium nanoparticles have a D50 equal to or lower than 100 nm.

8. The thermal conductive bobbin according to claim 1, wherein the silicon carbide microparticles have a D50 equal to or lower than 10 μm.

9. An inductive unit comprising a thermal conductive bobbin and at least one magnetic core, the thermal conductive bobbin being made of an injectable and polymerizable thermoplastic composition comprising: a plastic polymer in an amount of between 5% and 15% by weight with respect to the total weight of the composition; an aluminium nanoparticles dispersion in mineral oil in an amount of between 25% and 55% by weight with respect to the total weight of the composition; silicon carbide microparticles between 20% and 45% by weight with respect to the total weight of the composition; and additives up to 10% by weight with respect to the total weight of the composition, so that the thermal conductive bobbin has a dielectric rigidity higher than 5 kV/mm.

10. The inductive unit according to claim 9, wherein the plastic polymer is selected from the group consisting of polybutylene terephthalate, polycaprolactam, poly(hexamethylene adipamide), polyethylene terephthalate, polyether ether ketone and polyimide.

11. The inductive unit according to claim 9, wherein the aluminium nanoparticles have a D50 equal to or lower than 100 nm; and/or the silicon carbide microparticles have a D50 equal to or lower than 10 μm.

12. The inductive unit according to claim 9, wherein the additives are: dispersants or dispersants made of a condensation product of polyethyleneimine and polycarbonylalkylenoxy; lubricants, or lubricant made of silicon oil; flame retardants or flame retardant made of Aluminium Hydroxide; or combinations thereof.

13. An inductive assembly including several inductive units, each inductive unit including a thermal conductive bobbin and at least one magnetic core, the inductive assembly constituting a transformer, each thermal conductive bobbin being made of an injectable and polymerizable thermoplastic composition comprising: a plastic polymer in an amount of between 5% and 15% by weight with respect to the total weight of the composition; an aluminium nanoparticles dispersion in mineral oil in an amount of between 25% and 55% by weight with respect to the total weight of the composition; silicon carbide microparticles between 20% and 45% by weight with respect to the total weight of the composition; and additives up to 10% by weight with respect to the total weight of the composition, so that the thermal conductive bobbin has a dielectric rigidity higher than 5 kV/mm.

14. The inductive assembly according to claim 13, wherein the plastic polymer is selected from the group consisting of polybutylene terephthalate, polycaprolactam, poly(hexamethylene adipamide), polyethylene terephthalate, polyether ether ketone and polyimide.

15. The inductive assembly according to claim 13, wherein the aluminium nanoparticles have a D50 equal to or lower than 100 nm.

16. The inductive assembly according to claim 13, wherein the silicon carbide microparticles have a D50 equal to or lower than 10 μm.

17. The inductive assembly according to claim 13, wherein the additives are: dispersants or dispersants made of a condensation product of polyethyleneimine and polycarbonylalkylenoxy; lubricants, or lubricant made of silicon oil; flame retardants or flame retardants made of Aluminium Hydroxide; or combinations thereof.

18. The inductive assembly according to claim 13, wherein the inductive assembly is configured to operate under a switching frequency of at least 400 KHz.

19. The inductive assembly according to claim 13, wherein the several inductive units are encased in a one-piece thermally conductive case made of aluminium with a number of housings, each housing containing at least one inductive unit.

20. The inductive assembly according to claim 19, wherein the case is filled with polyimide insulants having a thermal conductivity higher than 0.8 W/mk.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] The foregoing and other advantages and features will be more fully understood from the following detailed description of an embodiment with reference to the accompanying drawings, to be taken in an illustrative and non-limitative manner, in which:

[0036] FIG. 1 is an exploded perspective view of an inductive assembly including specifically two transformers and two chokes stored in a case defining two housings sealed by a thermal conductive resin and with an aluminium top cover.

[0037] FIG. 2 shows in a similar view another embodiment of an inductive assembly implementing the teaching of this invention.

[0038] FIG. 3 illustrates another embodiment of the invention in which the case includes three housings for a corresponding pair of transformers with a series resonant inductor as used in LLC technologies built using the explained bobbins.

[0039] FIG. 4 shows in perspective and in an exploded view another embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0040] As previously explained this invention proposes a thermoplastic material, injectable with glass transition temperatures above 200° C., based on 10-12% of polymer type PBT, PA6 PA66, PET, RPET, Peek or Poly-imide, a load of nanoparticles (<100 nm) of Alumina isolated in mineral oil between 30-50% by weight, Silicon Carbide (SiC) microparticles (<10 um) charge (25-40% by weight), and other steric dispersant additives, flame retardants, glass fiber charge, fluidizing agents, lubricants and colorants up to a maximum of 7% by weight. The material presents a high thermal conductivity superior to 1.8 W/° km, a high electrical resistivity (superior to 10 KOHM/mm).

[0041] The previous thermoplastic material withstands a high resistance to the induction of currents by magnetic field due to the high resistivity that its charges incorporate thanks to being isolated among themselves by organic steric dispersants, by the polymeric matrix and mineral oils.

[0042] The invention is particularly suitable for any bobbin (coil former) injected with this material to house a winding of conducting wire and on which a magnetic field with or without core is closed.

[0043] Any inductor or transformer can be made with this reel incorporating this material and especially those with a higher switching frequency such as those used in SiC switched systems at 400 KHz or higher as they require high thermal conductivity and high resistance to induction Eddy current losses.

[0044] The embodiments illustrated in the drawings show a transformer assembly with its resonant series inductor as used in LLC technologies built with these reels and materials. The cited transformer assembly exhibits a high-performance thermal bridge, elastic to avoid magnetostriction, with high thermal diffusivity and with thermal conductivity of at least 2 W/km based on a base of silicone polymers and natural fillers, especially with a third filler as claimed in EP3796342A1 (owned by PREMO).

[0045] FIG. 1 shows the different components of a transformer assembly according to the invention were the several inductive units are encased in a one-piece, thermally conductive made of pure aluminium, in the form of an injection moulded case 2 with vertical walls delimiting a number of housings each of them seized to contain at least one inductive unit.

[0046] Each inductive unit comprises a magnetic core which in this example is formed by two ferrite E-shaped con-figuration half-pieces 3 whose central branch is surrounded by a bobbin 5 configured in a material obtained by polymerization and cross-linking of a composition as previously detailed. In the illustrated embodiment a winding 4 is wound in the bobbin 5. Each transformer has associated aligned a choke with a bobbin 5, winding 4 and magnetic core 3. The case is filled with polyimide insulants 6 of thermal conductivity higher than 0.8 W/mk. Atop cover or lid 1 fixed by screws 7 closes the aluminium case 2.

[0047] FIG. 2 illustrates another embodiment of the invention where the ferrite core 3 of each of the transformer units as well as the bobbin 5 and windings 6 has a different shape. Plastic spacers 5 are used in the transformer units and the choke comprises a ferrite core bobbin 7 and winding 6. The case is filled with a thermal conductive resin 8 and silicone tube 11 connect terminals with each transformer unit through gromets 10.

[0048] FIG. 3 shows another embodiment where the case includes three housing for a corresponding power unit including a transformer and a choke.

[0049] Moreover, the disclosed power assemblies are specially designed to work with LLC converters based on Silicon Carbide semiconductors, this allowing the system to switch at higher frequencies (200 KHz to 800 KHz) in this case 200 KHz to 300 KHz and at higher voltages than Silicon Mosfets transistors (20 KHz to 150 KHz typo).