FR3103624A1 - electromagnetic induction device - Google Patents

Abstract

The invention relates to an electromagnetic induction device provided with a variable air gap provided with heat dissipation means. In particular, the device according to the present invention comprises a core at the level of which the variable air gap is housed. Said air gap also comprises first ferromagnetic plates intended to guide a magnetic flux capable of originating in the core and collectively presenting a saturation magnetic field lower than that of the core. The variable air gap according to the terms of the present invention further comprises lateral protuberances forming the heat dissipation means and which extend from lateral faces of the first plates. Figure for abstract: Figure 2 .

Description

ELECTROMAGNETIC INDUCTION DEVICE

The present invention belongs to the field of electronics and electricity. In particular, the present invention relates to a magnetic inductance with variable inductance and for which the magnetic and thermal losses are reduced with regard to the devices known from the state of the art.

The magnetic inductor according to the present invention is advantageously implemented in an AC/DC or DC/DC power converter, and in particular a DAB (“Dual Active Bridge”) converter.

PRIOR ART

Magnetic inductors are devices well known to those skilled in the art, and implemented in a number of applications.

A magnetic inductor generally comprises a core, made of a ferromagnetic material, and a winding formed around a section of the core. The core may also include an air gap. This device is characterized by a characteristic quantity, called the magnetizing inductance L, which depends on the ferromagnetic material, the geometry of the core (and its air gap), and the winding, in particular the number of turns forming this winding.

Some applications, especially electronic converters, may require a high magnetizing inductance value L for nominal operation and a low magnetizing inductance value for certain operating points.

This is particularly the case of topologies of resonant converters called LLC.

Indeed, the magnetizing inductance of the transformer of an LLC converter must be raised to the nominal operating voltage, in order to limit switching losses and guarantee good efficiency, but must be able to be greatly reduced in order to ensure continuity of power. delivered in the load, when the input voltage drops (cf. the case of a server power supply system having to ensure the backup of the data in the event of a power failure as described in the document [1] cited at the end of the description).

This problem can lead to sizing converters of this type with low inductance values to ensure the backup function to the detriment of efficiency.

In the case of DAB converter topologies, the inductance value called “series” because placed in series with the magnetizing inductance of the transformer determines the operating range of the converter.

The power transmitted is inversely proportional to the series inductance value L and to the phase difference between the input and output voltages set by the piloting.

In some cases, the series inductance function can be implemented by a separate component from the transformer. However, in other cases, the series inductance function is provided by the leakage inductance of the same transformer.

In these two cases, a single series inductance value restricts the operating range and proves to be less flexible for controlling the DAB converter as described in document [2] cited at the end of the description. In order to overcome these problems, it may be considered to implement a magnetic inductance with magnetizing inductance L or variable series according to the magnetic flux (and consequently to the current I flowing through the winding). More particularly, it may be required to have a magnetic inductor which has a high magnetizing L or series inductance at low current I and lower at high current I.

However, a magnetic inductance is generally sized to operate in a range of current I flowing in the winding lower than a saturation current I _sat for which the ferromagnetic core is not saturated.

In this field, as long as the current I is lower than the saturation current I _sat , the magnetizing inductance L remains independent of said current I. However, when the current I exceeds the value of the saturation current I _sat , a magnetic saturation of the core intervenes and causes a rapid decrease in its magnetic permeability and consequently in the magnetizing inductance L.

Thus, when a variability of the magnetizing inductance L is required during the operation of the magnetic inductance, different solutions can be considered. In general, these solutions propose to extend the field of operation of the magnetic inductor to a nonlinear regime preceding the complete saturation of the ferromagnetic material. For this purpose, it is therefore possible to consider a lower magnetic permeability and/or a resizing of the air gap.

As soon as one and/or the other of these two solutions is implemented, saturation occurs uniformly throughout the core for a value of the current I greater than the saturation current I _sat .

However, these solutions are not satisfactory.

Indeed, saturation of the entire core, when the inductor is subjected to a high frequency current I (typically greater than 10 kHz), can be a source of significant volumetric magnetic losses in the inductor, and in the whole of the component in which it is integrated.

Moreover, these losses can lead to heating of the core.

In addition, in the saturation regime, the magnetic flux lines, which are no longer confined in the core, are likely to disturb the components placed close to the magnetic inductance. These disturbances can in particular be the source of electromagnetic incompatibilities and/or losses by eddy currents.

It has therefore been possible to propose, in documents [3] to [7] cited at the end of the description, sizing of the core, and in particular of the air gap, making it possible to locate the saturation of the core at said air gap.

However, the proposed dimensions are not satisfactory.

Indeed, even if the saturation of the core remains localized in the vicinity of the air gap, the latter remains the seat of magnetic losses and overheating likely to disturb the operation of the whole component.

Moreover, these magnetic and heating losses limit the implementation of such magnetic inductors to currents I of high frequencies and in particular capable of reaching 500 kHz.

An object of the present invention is therefore to propose an electromagnetic induction device with a variable magnetizing inductance L and for which the magnetic losses and the heating are reduced with regard to the devices known from the state of the art.

Another object of the present invention is also to provide an electromagnetic induction device which can operate at higher frequencies than the devices known from the state of the art.

The objects of the present invention are, at least in part, achieved by an electromagnetic induction device comprising:
- a ferromagnetic core;
- at least one air gap, called variable air gap, and defining in the core a volume V, in which are arranged the main ferromagnetic plates, essentially parallel and arranged in a direction parallel to field lines capable of circulating in the core, the plates main plates having a cross-section configured so that all of said plates have a saturation magnetic field lower than that of the ferromagnetic core, the main plates also being provided with lateral protuberances intended to diffuse a heat likely to be produced within the main plates when the latter are traversed by a magnetic field greater than their saturation magnetic field, said lateral protrusions extending from lateral faces of said plates in a direction substantially orthogonal to said lateral faces.

According to one embodiment, the lateral protrusions interconnect the main plates two by two so as to form secondary plates perpendicular to said main plates.

According to one embodiment, the ferromagnetic core, the first plates and the protuberances are made of the same ferromagnetic material.

According to one embodiment, the main plates are all identical.

According to one embodiment, a vacant volume V _v of the volume V left vacant by the first plates and the protrusions is filled, at least in part, by a heat dissipation material which has a thermal conductivity greater than 10 W/m/K , advantageously the heat dissipation material comprises alumina.

According to one embodiment, the ferromagnetic core comprises a ferromagnetic material chosen from: a metal alloy of the FeX type where X comprises one of the elements chosen from Si, Al, Co, Ni, ferrite oxide of spinel structure of the A type (Fe ,B) ₂ O ₄ with A = (Mn, Ni) B=(Co, Cu, Al,..).

According to one embodiment, the ferromagnetic core comprises two planar ends, essentially parallel to each other, facing each other and a surface S, the two ends delimit the variable air gap, the main plates being arranged perpendicularly at the ends, advantageously the ferromagnetic core comprises a frame of polygonal shape, and even more advantageously of rectangular shape.

According to one embodiment, the main plates have a cross-section of a cross-sectional area S _t , the sum of the cross-sectional areas of all the main plates being less than the area S.

According to one embodiment, the ferromagnetic core comprises two bases each provided with two main faces, called respectively internal face and external face, essentially parallel, the bases each face each other according to their internal face, the variable air gap being formed in the one of the bases, the core further comprises a plurality of legs, essentially parallel to each other and which extend between the two internal faces, the plurality of legs comprises at least one main leg, at least one side leg and at least two legs leaks;

the device further comprises at least one primary winding and at least one secondary winding, each comprising a main section, wound around the main leg, and a trailing section, respectively referred to as primary trailing section and secondary trailing section, each wound on a different leaks leg.

According to one embodiment, the variable air gap being arranged between the two leakage legs, the primary plates being in the form of fins.

According to one embodiment, the fins are oriented in a direction defined by an axis joining the two trailing legs between which the air gap is arranged.

According to one embodiment, the recess opens onto the internal face of the base in question.

According to one embodiment, the recess opens onto the external face of the base in question.

According to one embodiment, the at least one main leg includes a single main leg, the at least two trailing legs include four trailing legs, wherein the primary trailing section includes two primary trailing sections such that the winding primary comprises in order one of the primary trailing sections, the main section, and the other primary trailing section, the primary trailing sections being each wrapped around a different trailing leg, and wherein the trailing section secondary comprises two secondary leakage sections such that the secondary winding comprises in order one of the secondary leakage sections, the main section, and the other secondary leakage section, the secondary leakage sections each being wound around a different leaks leg.

According to one embodiment, the at least one lateral leg comprises four lateral legs, the four lateral legs and the four trailing legs describing a circle centered on the main leg, and in which alternate, and in a regular manner, the side legs and the trailing legs, each primary trailing section being arranged diametrically opposite a secondary trailing section with respect to the main leg.

According to one embodiment, the at least one lateral leg comprises two lateral legs, the at least two trailing legs comprise four trailing legs, forming two groups of two trailing legs, referred to as the first group and second group respectively, the four trailing legs and the two side legs describing a circle centered on the main leg, and in which the side legs and the groups alternate regularly.

According to one embodiment, the at least one air gap comprising a first air gap and a second air gap arranged halfway between the trailing legs, respectively, of the first group and of the second group.

According to one embodiment, the primary leakage sections are each formed around, respectively, one and the other of the leakage legs (104) of the first group (106), and the secondary leakage sections are each formed around , respectively, of one or the other of the trailing legs (105) of the second group (107).

According to one embodiment, a groove is formed on one and the other of the internal faces, at a distance from and around each leak leg, the groove being interposed between the leak leg and the main leg.

Other characteristics and advantages will appear in the following description of an electromagnetic induction device according to the invention, given by way of non-limiting examples, with reference to the appended drawings in which:

is a perspective schematic representation of a variable air gap according to the present invention;

is a schematic representation in perspective of another configuration of a variable air gap according to the present invention;

is a representation of a ferromagnetic core capable of being implemented within the scope of the present invention;

is a graphical representation of the evolution of the inductance L (vertical axis, “H” unit) of the electromagnetic induction device as a function of an electric current I (horizontal axis, “A” unit) circulating the coil;

is a schematic representation of the electromagnetic induction device according to a first embodiment of the present invention;

are schematic representations of a half-core according to a side view (FIG. 6a) and a top view (FIG. 6b) capable of being implemented within the scope of the present invention;

is a schematic representation of the electromagnetic induction device according to a first embodiment of the present invention and implementing two half-cores as illustrated in FIGS. 6a and 6b;

is a schematic representation of the electromagnetic induction device according to a first variant of the second embodiment of the present invention;

is a schematic representation of a half-core in section, according to the internal face and according to a second variant of the second embodiment of the present invention;

is a perspective schematic representation of a half-core according to a second variant of the second embodiment of the present invention;

is a diagrammatic representation of a sectional half-core provided with the windings, according to the internal face and according to a second variant of the second embodiment of the present invention;

is a schematic representation of an air gap opening at the external face of a base in contact with a cold source.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

The present invention relates to an electromagnetic induction device provided with a variable air gap provided with heat dissipation means.

In particular, the device according to the present invention comprises a core at which the variable air gap is housed. Said air gap also comprises first ferromagnetic plates intended to guide a magnetic flux likely to originate in the core and intended to operate in a saturation regime for a magnetic flux value lower than the value required for the saturation of the core, the flux being conservative throughout the magnetic circuit.

The variable air gap according to the terms of the present invention further comprises lateral protuberances forming the heat dissipation means and which extend from the lateral faces of the first plates.

More particularly, the invention relates to an electromagnetic induction device 100 (FIGS. 1 to 3).

The electromagnetic induction device 100 can be a magnetic inductance of inductance L integrated in an AC/DC or DC/DC power transformer, and in particular a DAB converter.

The electromagnetic induction device 100 includes a ferromagnetic core 200 (shown in Figures 1, 2 and 3).

The ferromagnetic core 200 can comprise at least one ferromagnetic material chosen from: a metal alloy of the FeX type where X comprises one of the elements chosen from Si, Al, Co, Ni, a ferrite oxide of spinel structure of the A type (Fe, B) ₂ O ₄ with A = (Mn, Ni) B=(Co, Cu, Al,..).

The ferromagnetic core 200 is capable of being traversed by field lines induced by an electric current I flowing in at least one conductive coil 300 (or winding) formed around a section of the ferromagnetic core 200 and which extends along a main axis XX'.

By "main axis" is meant an axis of symmetry of the conductive coil.

The conductive coil 300 is in particular made of a winding of a conductive wire, for example a copper wire, around a section of the ferromagnetic core 200.

The ferromagnetic core 200 also comprises an air gap (“Air Gap” according to Anglo-Saxon terminology), and more particularly a variable air gap 400 (FIGS. 1 and 2).

The air gap 400 is in particular formed by a recess or an absence of material in the ferromagnetic core 400.

The recess or the absence of material results in a break in the continuity of the ferromagnetic material forming the ferromagnetic core 400.

The variable air gap 400 defines in the ferromagnetic core 200 a volume V corresponding to the volume of hollowed out or absent material.

Main plates 500, made of a ferromagnetic material, are arranged in the volume V defined by the variable air gap 400.

By "plate" is meant an element of generally flat shape and not very thick. In particular, a plate comprises two side faces 501, essentially parallel to each other and connected by a contour.

The main plates 500 are also essentially parallel to each other and arranged in a direction parallel to field lines capable of circulating in the ferromagnetic core 200.

According to the present invention, the orientation of a plate, and in particular of a main plate, is defined by the orientation of its side faces 501. In other words, said field lines are parallel to a direction of the planes formed by the side faces of the main plates 500.

The main plates 500 also have a surface cross-section S _t adapted so that all of said main plates 500 have a saturation magnetic field B _{sat 1} , called the first magnetic field B _sat1 , lower than that of the ferromagnetic core 200, called the second magnetic field B _sat2 .

By "transverse section" is meant a section along a section plane perpendicular to the field lines crossing the main plates.

The amplitude of the magnetic field B passing through the ferromagnetic core 200 depends on the electric current I flowing in the coil 300. In particular, the first magnetic field B _sat1 and the second magnetic field B _sat2 are reached when the electric current I flowing in the coil 300 is equal, respectively, to a first saturation current I _sat1 , and to a second saturation current I _sat2 .

Thus, the behavior of the electromagnetic induction device 100, and more particularly its magnetizing inductance L, will depend on the electric current I flowing in the coil 300.

In this regard, Figure 4 is a graphical representation of the different operating regimes of an electromagnetic induction device 100 whose main plates 500 are all identical.

“Identical main plates” means plates of the same shape, same dimensions and same material.

Such a device 100 has three operating regimes or stages "A", "B" and "C" associated with an electric current I flowing in the coil 300, respectively, lower than the first saturation current I _sat1 , comprised between the first current saturation current I _sat1 and the second saturation current I _sat2 , and greater than the second saturation current I _sat2 .

More particularly, the regime "A" corresponding to a linear regime for which the ferromagnetic core 200 and the main plates 500 are unsaturated. In this regime, the permeabilities of the ferromagnetic core 200 and of the main plates 500 are little or not dependent on the magnetic field circulating in the core so that the induction L is also essentially constant and equal to a first induction L ₁ .

Regime "B" is characterized by a drop in inductance L to a second induction L ₂ .

This drop is in particular due to saturation of the main plates 500 which, under the effect of a magnetic field greater than the first magnetic field B _sat1 , see their permeability decrease sharply to reach a value close to 1.

Finally, the regime “C” corresponds to a saturation regime of the ferromagnetic core 200 and of the main plates 500 caused by an electric current flowing in the coil 300 greater than the second saturation current I _sat2 . In this regime, the inductance L drops again to a value L ₃ .

According to the present invention, the main plates 500 are also provided with side protrusions 600 ferromagnetic.

By "protuberance" is meant organs protruding at the level of the surface on which they are arranged.

The lateral protuberances 600 are in particular intended to diffuse heat likely to be produced within the main plates 500 when the latter are traversed by a magnetic field greater than their saturation magnetic field B _sat1 .

The side protuberances 600 extend in particular from the side faces 501 of said main plates 500 in a direction essentially orthogonal to said side faces 501 (Figure 1 and 2).

The side protuberances 600 can have a rectangular, circular, square, triangular section.

The lateral protuberances 600 can interconnect the main plates 500 two by two so as to form secondary plates 700 perpendicular to said main plates 600 (FIG. 2).

In a particularly advantageous manner, the secondary plates 700 are dimensioned so as not to saturate when the magnetic field circulating in the core is lower than the second magnetic field B _sat2 . Thus, when the main plates 500 saturate, the secondary plates 700 limit the overflow of the magnetic flux around the air gap zone. In other words, the secondary plates 700 ensure the guiding of the magnetic flux in the air gap, and de facto limit any lateral radiation of the magnetic field.

Furthermore, the lateral protuberances can be limited to the volume V defined by the variable air gap.

Advantageously, the ferromagnetic core 200, the first plates 500 and the lateral protrusions 600 are made of the same ferromagnetic material.

Still advantageously, the vacant volume V _v of the volume V left vacant by the first plates 500 and the protrusions 600 can be filled, at least in part, by a heat dissipation material 601 (FIG. 5) which has a higher thermal conductivity at 10 W/m/K, advantageously the heat dissipation material comprises alumina.

The presence of the heat dissipation material makes it possible to assist the cooling by the side protrusions 600 by draining the heat produced in the air gap towards a heat sink.

According to a first embodiment of the electromagnetic induction device 100, the ferromagnetic core 200 comprises two planar ends 200a and 202b of surface S, essentially parallel to each other, facing one another.

The ends 200a and 200b delimit the variable air gap 400, and the main plates 500 are arranged perpendicular to the latter.

The main plates 500 have a cross section with a cross-sectional area S _t , the sum of the cross-sectional areas of all the main plates 500 being less than the area S.

The ferromagnetic core may comprise a frame of polygonal shape, and even more advantageously of rectangular shape.

For example, as illustrated in FIG. 5, the magnetic core 200 comprises five parallelepipedic sections 201-205 composed of ferromagnetic materials joined two by two by their ends in order to form a rectangular frame. Two sections 204 and 205 form one side of the rectangular frame and are spaced apart at their ends 200a and 200b by the air gap 400 (of spacing g).

The dimensioning principle of a device according to the present invention is presented below on the basis of the core forming a square frame of side l and illustrated in FIG. 5. This dimensioning principle is not however limited to this single configuration, and those skilled in the art can easily adapt it to other types of core geometries.

In this example, the primary plates 500, which are identical, connect the ends 200a and 200b which have a spacing g. The fraction of the end surface 200a and 200b covered by the sections of the primary plates is denoted f .

The reluctance R _e of the air gap structure provided only with primary plates made of a ferromagnetic material of permeability µ _s is then expressed as follows:
[Math 1]

As soon as N _p secondary plates are considered, the reluctance of the air gap structure is calculated simply by applying a reluctance network method to each of the constituents of the structure. The thickness of these plates, denoted e _p , is small compared to the spacing g ( e _p << g).

The secondary plates also comprise a ferromagnetic material of permeability µ _p and divide the air gap into several secondary air gaps placed in series.

The reluctance R _es of each secondary air gap is therefore expressed as follows:
[Math 2]

The total reluctance of the air gap structure comprising the primary and secondary plates is the sum of the N _p secondary reluctances separating the plates:
[Math 3]

These expressions make it possible to deduce the inductance L(µ _c , µ _s ) of the device illustrated in figure 5 and which is expressed as follows:
[Math 4]

This expression of the inductance is identical to that obtained with a constant air gap whose spacing g is weighted by the term F(µ _s , f) .

This term therefore makes it possible to modulate the air gap distance which intervenes in the value of the inductance without modifying the geometry of the magnetic circuit. For this, it is necessary to produce a variation of the permeability _µs of the primary plates as a function of the applied current.

The primary plates, which have a relatively small surface cross-section S _t with respect to the surface S, are traversed by a magnetic induction greater than that traversing the core according to the principle of conservation of the magnetic flux. Such a consideration makes it possible to produce locally, in particular at the level of the primary plates 500, a saturation effect.

The magnetic induction in the primary plates B _st corresponds to an amplification of the magnetic induction B _c in the ferromagnetic core. This amplification is a function of the surface fraction f and is given by the following relationship:
[Math 5]

When the current I flowing in the coil increases, the magnetic induction also increases. However, as soon as the current I flowing in the coil reaches the saturation current I _sat , the magnetic induction in the primary plates reaches the saturation value B _sat , while the ferromagnetic core remains in linear mode.

The value of the saturation current is in this respect given by the following relationship:
[Math 6]

For a current I greater than the saturation current I _sat , the permeability of the primary plates µ _s is equal to 1. In order to determine the amplitude of the inductance variation that can be reached by current control, nominal operation at low induction (I<<I _sat ), out of saturation, followed by high induction operation (I>>I _sat ) where saturation occurs in the primary plates (µ _s =1). The variation of inductance between these two limiting cases is given by:
[Math 7]

Figures 6a, 6b, and 7 propose another configuration of the ferromagnetic core in connection with the first embodiment of the electromagnetic induction device 100. In this other configuration, the ferromagnetic core comprises two half-cores 200 ₁ and 200 ₂ is of the ETD type (double E with cylindrical central leg), well known to those skilled in the art.

The dimensions of the ferromagnetic half-cores are given in relation to FIGS. 6a and 6b and listed in the following table:
[Table 1]

The two identical half-cores are mounted facing each other with an air gap provided at the level of a central column 207 (FIG. 7). The spacing g of the air gap is in this example equal to 5 mm.

The air gap structure comprises 5 primary plates (21.65 mm x 5 mm) 0.41 mm thick and 2 secondary plates (21.65 mm x 21.65 mm) 1 mm thick evenly spaced.

The permeability of the ferromagnetic material is 1500 and the saturation induction is 430 mT. The central column 207 is wound with a winding of 5 turns of conductive wire.

Under these conditions, the saturation current is 6 A. For a current lower than I _sat , the core inductance is 16 µH and decreases to 3 µH after saturation of the primary plates. The heat exchange surface developed by the secondary plates improves cooling by natural air convection and limits heating to 100°C in the structure.

The following description relates to a second embodiment of the electromagnetic induction device 100.

The electromagnetic induction device 100 corresponding to this second mode can in particular be implemented as a component of a power converter of the "Dual Active Bridge" (DAB) type, and essentially incorporates the elements described previously.

Figures 8 and 9-11 are in this respect schematic representations, in plan view, of a half-core 200 ₃ and 200 ₄ capable of being implemented according respectively to a first variant and a second variant of this second of achievement.

According to this second embodiment, the ferromagnetic core 200 comprises an assembly of the two half-cores 200 ₃ and 200 ₄ .

In this respect, the ferromagnetic core 200 comprises two bases 101 each provided with two main faces, called respectively internal face 101a and external face 101b, essentially parallel.

The bases each face each other according to their internal face 101a, and the variable air gap 400 is in one of the bases, more particularly in its volume.

The core further comprises a plurality of legs, essentially parallel to each other and which extend between the two internal faces 101a.

The plurality of legs includes at least one main leg 102, at least one side leg 103 and at least two trailing legs 104 and 105.

The device further comprises at least one primary winding 301 and at least one secondary winding 302.

Each of the primary 301 and secondary 302 windings comprises a main section, wound around the main leg 102, and a trailing section, respectively referred to as primary trailing section and secondary trailing section, each wound on a different trailing leg 104 and 105.

Advantageously, the variable air gap 400 being arranged between the two leak legs, and the primary plates are in the form of fins.

Still advantageously, the fins are oriented in a direction defined by an axis joining the two trailing legs between which the air gap is arranged.

Furthermore, the recess can lead to one and/or the other of the internal face and the external face of the base which comprises the air gap.

In this respect, FIG. 12 is a schematic representation of an air gap 400 opening out at the outer face 101b of a base 101 in contact with a cold source.

The ferromagnetic core may comprise a single main leg 102 and four trailing legs 104 and 105.

In this regard, the primary leakage section comprises two primary leakage sections so that the primary winding 301 comprises in order one of the primary leakage sections 301a, the main section 301b, and the other primary leakage section 301c, the primary leak sections each being wrapped around a different leak leg.

Equivalently, the secondary leakage section comprises two secondary leakage sections such that the secondary winding 302 comprises in order one of the secondary leakage sections 302a, the main section 302b, and the other secondary leakage section 302c, the secondary leak sections each being wrapped around a different leak leg.

According to the first variant (Figure 8), the at least one side leg 103 comprises four side legs 103.

More particularly, the four lateral legs 103 and the four trailing legs 104, 105 describe a circle centered on the main leg 102 and in which the lateral legs and the trailing legs alternate regularly. Each primary trailing section is also arranged diametrically opposite one of the secondary trailing sections with respect to the main leg.

The device thus described comprises a transformer function and a series inductance function.

The transformer function is ensured by the main sections 301b and 302b, respectively, of the primary winding 301 and of the secondary winding 302, surrounded around the main leg.

The series inductances created at the level of the primary and secondary windings are ensured by the primary leakage sections 301a and 301c and by the secondary leakage sections 302a and 302c.

Thus, a magnetic flux, called "transformer flux", created at the level of the main leg by the passage of a current in the primary winding follows a loop path successively crossing the base, the lateral legs, the other base, and crosses the main leg again.

Equivalently, a primary “leakage” flow follows a different contour connecting two primary circuit leakage legs and crossing the cylindrical base in its thickness along a line connecting the base of the two primary leakage legs. The secondary leak flow follows a similar contour described by the two secondary leak legs.

The implementation of the variable air gap between two primary leakage legs makes it possible to confer a variable leakage inductance character to the device.

Equivalently, the implementation of the variable air gap between two secondary leakage legs makes it possible to confer a variable leakage inductance character to the device.

According to the second variant (figure 9 to 11), the ferromagnetic core comprises two lateral legs 103, and four trailing legs 104 and 105.

The two trailing legs 104 and the two trailing legs 105 form two groups of two trailing legs, called respectively first group 106 and second group 107.

In addition, the four trailing legs and the two side legs describe a circle centered on the main leg, and in which the side legs and the groups alternate regularly.

Advantageously, the at least one air gap 400 comprises a first air gap 401 and a second air gap 402 arranged halfway between the trailing legs, respectively, of the first group 106 and the second group 107.

In particular, each of the primary trailing sections is formed around, respectively, one of the trailing legs and the other of the trailing legs of the first group.

Equivalently, each of the secondary trailing sections is formed around, respectively, one of the trailing legs and the other of the trailing legs of the second group 107.

According to this second variant, the proximity between the leak legs of the same group of leak legs allows more precise control of the leaks.

A flux barrier 800 can also be formed in the bases 101 so as to limit the magnetic flux between the trailing legs and the side legs. These flow barriers 800 may in particular comprise a recessed zone between each of the elements of the first group 106 and those of the second group 107 and the side legs.

The hollowed-out zone may in particular extend from the edge and along a radius of the base considered.

Finally, regardless of the variant considered, a groove can be formed on one or the other of the internal faces, at a distance from and around each trailing leg, and which is interposed between the trailing leg and the main leg.

The process for manufacturing the core according to the present invention may make use of an injection molding technique (“PIM” or “Powder Injection Molding” according to Anglo-Saxon terminology). This technique is particularly well suited for the mass production of parts with complex geometries.

Injection molding firstly involves a step of forming a masterbatch (“feedstock” according to Anglo-Saxon terminology).

The masterbatch comprises in particular a mixture of organic material (or polymeric binder) and inorganic powders (metallic or ceramic) intended to form the final part.

The masterbatch is injected into an injection molding machine, the technology of which is known to those skilled in the art. The injection molding machine makes it possible to melt the polymers injected with the powder in a cavity, and to give said powder the desired shape.

The masterbatch, thus shaped and molten, is subjected to cooling so as to solidify it and fix it in a shape imposed by the injection molding machine.

The part formed by the masterbatch is then removed from the mold and debinded in order to eliminate the organic matter.

The part can then be consolidated by sintering.

REFERENCES

[1] Jeong et al. , “ Analysis on Half-Bridge LLC Resonant Converter by Using Varaible Inductance for High Efficiency and Power Density Server Power Supply ”, 2017 IEEE Applied Power Electronics Conference and Exposition, March 26-30, 2017,

[2] Saeed et al. , “ Extended Operational Range of Dual-Active-Bridge Converters by using Variable Magnetic Devices” , 2019 IEEE Applied Power Electronics Conference and Exposition, March 17-21, 2019,

[3] US3603864,

[4] US5440225,

[5] US4728918,

[6] US2015/0109086,

[7] US2010/0085138.

Claims (18)

An electromagnetic induction device (100) comprising:
-a ferromagnetic core (200);
- at least one air gap, called variable air gap (400), and defining in the core a volume V, in which are arranged main ferromagnetic plates (500), essentially parallel and arranged in a direction parallel to field lines capable of circulating in the core, the main plates (500) having a cross section configured so that all of said plates have a lower saturation magnetic field than the ferromagnetic core (200), the main plates (500) also being provided with lateral protrusions (600) intended to diffuse heat likely to be produced within the main plates (500) when the latter are traversed by a magnetic field greater than their saturation magnetic field, said lateral protrusions (600) extending from side faces (501) of said plates in a direction substantially orthogonal to said side faces (501). Device according to Claim 1, in which the lateral protrusions (600) interconnect the main plates (500) two by two so as to form secondary plates (700) perpendicular to the said main plates (500). Device according to claim 1 or 2, wherein the ferromagnetic core (200), the main plates (500) and the side projections are made of the same ferromagnetic material. Device according to one of Claims 1 to 3, in which the main plates (500) are all identical. Device according to one of Claims 1 to 4, in which a vacant volume V _v of the volume V left vacant by the main plates (500) and the lateral protuberances is filled, at least in part, by a heat dissipation material which has a thermal conductivity greater than 10 W/m/K, advantageously the heat dissipation material comprises alumina. Device according to one of Claims 1 to 5, in which the ferromagnetic core (200) comprises a ferromagnetic material chosen from: a metal alloy of the FeX type where X comprises one of the elements chosen from Si, Al, Co, Ni, ferrite oxide with spinel structure of the A(Fe,B) ₂ O ₄ type with A = (Mn, Ni) B=(Co, Cu, Al, etc.). Device according to one of Claims 1 to 6, in which the ferromagnetic core (200) comprises two planar ends (200a, 200b), essentially parallel to each other, facing each other and a surface S, the two ends delimit the variable air gap (400), the main plates (500) being arranged perpendicular to the ends, advantageously the ferromagnetic core (200) comprises a frame of polygonal shape, and even more advantageously of rectangular shape. Device according to Claim 7, in which the main plates (500) have a cross-section of a cross-sectional area S _t , the sum of the cross-sectional areas of all the main plates (500) being less than the area S. Device according to one of Claims 1 to 6, in which the ferromagnetic core (200) comprises two bases (101) each provided with two main faces, called the internal face (101a) and external face (101b), respectively, essentially parallel, the bases (101) each face each other along their internal face (101a), the variable air gap (400) being formed in one of the bases, the core (200) further comprises a plurality of legs, essentially parallel to each other and which extend between the two internal faces, the plurality of legs comprises at least one main leg (102), at least one side leg (103) and at least two trailing legs (104, 105);
the device further comprises at least one primary winding (301) and at least one secondary winding (302), each comprising a main section (301b, 302b), wound around the main leg (102), and a trailing section, said respectively primary trailing section (301a, 301c) and secondary trailing section (302a, 302c) each wound on a different trailing leg. Device according to Claim 9, in which the variable air gap (400) being arranged between the two trailing legs, the primary plates being in the form of fins. Device according to Claim 10, in which the fins are oriented in a direction defined by an axis joining the two trailing legs between which the air gap is arranged. Device according to one of Claims 9 to 11, in which the recess opens onto the internal face (101a) of the base in question. Device according to one of Claims 9 to 12, in which the recess opens onto the external face (101b) of the base in question. Device according to one of Claims 9 to 13, in which the at least one main leg (102) comprises a single main leg (102), the at least two trailing legs comprise four trailing legs, in which the section of primary leakage comprises two primary leakage sections such that the primary winding comprises in order one of the primary leakage sections (301a), the main section (301b), and the other primary leakage section (301c), the sections primary leakage sections each being wound around a different leakage leg, and wherein the secondary leakage section comprises two secondary leakage sections such that the secondary winding comprises in order one of the secondary leakage sections (302a), the main section (302b), and the other secondary trailing section (302c), the secondary trailing sections each being wrapped around a different trailing leg. Device according to Claim 14, in which the at least one lateral leg comprises four lateral legs, the four lateral legs and the four trailing legs describing a circle centered on the main leg (102), and in which they alternate, and in a regular manner, the side legs and the trailing legs, each section being arranged diametrically opposite a secondary trailing section with respect to the main leg (102). Device according to Claim 14, in which the at least one lateral leg comprises two lateral legs, the at least two trailing legs comprise four trailing legs, forming two groups of two trailing legs, respectively called the first group (106) and second group (107), the four trailing legs and the two side legs describing a circle centered on the main leg (102), and in which the side legs and the groups (106, 107) alternate regularly . Device according to Claim 16, in which the at least one air gap comprising a first air gap (401) and a second air gap (402) arranged halfway between the trailing legs, respectively, of the first group (106) and of the second group (107). Device according to claim 17, in which the primary leakage sections are each formed around, respectively, one and the other of the leakage legs (104) of the first group (106), and the secondary leakage sections are each formed around, respectively, one or the other of the trailing legs (105) of the second group (107).