FR3131477A1 - Electrical machine incorporating phase change materials. - Google Patents

Abstract

The invention relates to an electric machine comprising a stator and a rotor driven in rotation by the stator, the stator comprising a frame from which extends at least one stator notch parallel to a first axis of rotation of the rotor, the electric machine comprising windings conductive elements extending concentrically in the at least one stator notch so as to form at each end of the stator, along the first axis of rotation of the rotor, a winding head, the electric machine comprising at least one shim notch in the stator notch so as to insulate the conductive elements from the winding, the electric machine comprising at least one heat sink arranged inside a stator notch between the conductive elements and/or in the notch spacer , the heat sink extending from the winding head of a first end of the stator along the first axis of rotation of the rotor to a winding head of a second end of the stator, the heat sink comprising a phase change material. Figure for the abstract: Fig. 1

Description

Electric machine integrating phase change materials.

The invention relates to cooling a heat-producing element. The invention finds application in the field of electrical machines and power electronics. Indeed, it is known that electrical elements as well as power electronics generate losses which result in the production of heat which must be evacuated. The evacuation of this heat, guaranteeing proper functioning of the elements mentioned above, therefore becomes a priority. The invention finds a particular application in the field of aeronautics where the trend is to increase the number of electrical equipment and therefore the on-board electrical power.

An aircraft propulsion engine comprises electrical machines comprising a rotor or rotating part and a stator or fixed part. Electric machines can be used either as a motor or a generator. The stator includes a magnetic circuit and an electrical circuit consisting of a set of windings composed of conductive wires.

In known manner, such electrical machines have transient operating phases encountered mainly during start-up or acceleration sequences of the aircraft engine or certain equipment included in the aircraft engine.

During these transient phases, the electrical machine thus heavily stressed dissipates a large quantity of heat which can be detrimental to it. In fact, the heat is mainly dissipated in the electrical circuits and/or on the permanent magnets if they are included in the electrical machine.

As said previously, electrical machines can then generate a lot of heat. In addition, the cooling necessary for the evacuation of this heat is limited by certain constraints. The bulk as well as the mass added by a possible cooling device are notably limited by the specificities of a vehicle carrying a high power density electric machine where cooling is generally limited to air. For example, for all-electric or hybrid aircraft, it is desirable to obtain a device capable of cooling the electrical elements with a low mass and compact.

In the field of electric aircraft with electric propulsion systems, several approaches have been taken.

Air cooling is the generally preferred cooling method for cooling electrical machines or assemblies of electrical machines and power electronics. Indeed, in a known manner, these electrical machines are equipped with a carcass with fins or cooling channels allowing convective exchange with a flow of air sweeping the carcass. The air circulates either thanks to a fan integrated exclusively for this purpose or thanks to the air induced by a propeller mounted upstream of the electric machine. However, this type of technology has the disadvantage of not allowing the specific power of the system to be improved due to the limits of air cooling and the limited quantity of calories to be evacuated with this type of cooling. The use of materials such as aluminum or copper, with high thermal conductivity, at the carcass level and air speeds guaranteeing forced convection is sometimes not enough.

In order to allow better cooling, it may be preferable to opt for forced cooling with a fluid, such as water or oil, allowing for fairly high exchange coefficients. However, the gain in mass on the motor and/or the power electronics is then significant due to the use of the bulky and heavy cooling system which requires an exchanger, pumps and a refrigerant fluid.

It is also suggested to use phase change materials as an alternative to coolant so as to store heat until a phase change (solid-liquid or liquid-gaseous) so as to "conduct" the heat to another refrigerant flow external to the system. This is particularly the case for patents EP 2523 314 B1 and US 2020/0076262 A1. However, these solutions require expensive modifications for implementation and require, for example, increasing the volume of the notch inside the stator. Consequently, the volume occupied by the electric machine and therefore its weight increases, which is not desirable. In addition, the phase change materials according to these documents do not exchange directly with the hot spots of the winding, which impairs the extraction of heat from these hot spots.

• qui présentent une puissance spécifique élevée,
• qui ne nécessitent qu’un refroidissement à air ou accessoirement forcé au travers d’une roue de ventilation ou d’une hélice portée(s) par l’arbre du moteur,
• qui est indépendant de tout dispositif de refroidissement déporté avec un fluide autre que le fluide de l’environnement dans lequel évolue le système embarquant le dispositif puissance,
• qui fonctionne en surcharge de manière ponctuelle ou sur un cycle intermittent avec des phases de charge ou de surcharge significative et des phases de repos ou de charge partielle ou minime.

The invention aims to overcome all or part of the problems cited above by proposing compact devices for electrical machines and power electronics:

• which have a high specific power,
• which only require air cooling or incidentally forced through a ventilation wheel or a propeller carried by the motor shaft,
• which is independent of any remote cooling device with a fluid other than the fluid of the environment in which the system embedding the power device operates,
• which operates in overload occasionally or on an intermittent cycle with phases of significant load or overload and phases of rest or partial or minimal load.

For this purpose, the subject of the invention is an electric machine comprising a stator and a rotor configured to be rotated by the stator, the stator comprising a carcass of which at least one stator notch extends parallel to a first axis of rotation of the rotor, the electric machine comprising windings of conductive elements extending concentrically in the at least one stator notch of the stator so as to form at each end of the stator, along the first axis of rotation of the rotor, a head of winding, the electric machine comprising at least one slot wedge arranged in the stator slot so as to physically isolate the conductive elements of the rotor winding, the electric machine comprising at least one heat sink arranged inside a stator slot between the conductive elements and/or in the slot wedge, the heat sink extending from the winding head of a first end of the stator along the first axis of rotation of the rotor to a head of winding of a second end of the stator, the heat sink comprising a phase change material.

According to one aspect of the invention, the phase change material is configured to undergo melting at a temperature greater than 100°C.

According to one aspect of the invention, the stator slot comprises a coil separator capable of ensuring electrical insulation between the conductive elements, the heat sink being included in the coil separator.

According to one aspect of the invention, the stator slot comprises an isthmus beyond the slot wedge along a second axis, perpendicular to the first axis, in the direction of the first axis of rotation of the rotor, the heat sink being included in the isthmus of the stator notch.

According to one aspect of the invention, the stator notch comprises a slot passing through the stator towards a medium external to the electrical machine along the second axis, the phase change material of the heat sink being included in the slot.

According to one aspect of the invention, the heat sink is a porous matrix.

According to one aspect of the invention, the winding of the conductive elements is encapsulated in a dielectric and thermally conductive insulating material.

According to one aspect of the invention, the phase change material is an aluminum-based material, a salt or a wax from the paraffin family.

According to one aspect of the invention, the electric machine comprises a thermal ring in contact with the stator, the thermal ring comprising cooling fins.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, description illustrated by the attached drawing in which:

represents a view along a plane perpendicular to an axis of rotation of a rotating electrical machine provided with at least one winding of conductive elements and a heat sink according to the invention;

represents an enlarged view of one end of the stator of the , a head for winding conductive elements and the heat sink according to the invention;

represents a schematic view of a notch of the stator according to the invention;

represents a schematic view of a first variant of the stator notch of the ;

represents a schematic view of a second variant of the stator notch of the ;

represents a schematic view of a third variant of the stator notch of the ;

represents a schematic view of a fourth variant of the stator notch of the ;

represents a schematic view of a second configuration of the stator notch;

represents a schematic view of a variant of the second configuration of the stator notch;

represents a schematic view of a third variant of the second configuration of the stator notch;

represents a schematic view of a stator of an electrical machine equipped with a heat exchanger;

For the sake of clarity, the same elements will carry the same references in the different figures.

In the following, the term "phase change material" refers to a material capable of changing its physical state within a given temperature range and which will absorb a large amount of thermal energy from its surrounding environment to change from the state solid to the liquid state or from the liquid state to the gaseous state and which restores part of the thermal energy when the material cools passing from the liquid state to the solid state or from the gaseous state in liquid state.

These phase change materials may be salts which may be composed of nitrate or hydroxide.

The transition from the solid phase to the liquid phase of the material takes place at a temperature above one hundred degrees Celsius up to a temperature of around 300°C.

There represents a stator 2 of an electrical machine 1 also comprising a rotor 3 configured to be rotated by the stator 2. It is possible to implement the invention with any other type of heat source, with or without a rotating part , whether this heat source is electrical or mechanical. Generally, an electrical machine capable of generating power is composed of a mobile part or rotor rotating around a first axis A1 and a fixed part or stator 2. During these phases of electrical power production in generator mode , or mechanical in motor mode, losses are generated in the form of heat which must be evacuated. The stator 2 comprises a carcass 21 of which extends at least one stator notch 20 parallel to the first axis A1 of rotation of the rotor. The stator notch 20 takes the form of an extrusion forming a hollow volume 200 in the stator 2. More precisely, the stator 2 comprises a set of stator notches 20 and teeth 22 juxtaposed with each other so that a tooth 22 is disposed between two stator notches 20 and a stator notch 20 is disposed between two teeth 22. The electric machine comprises a winding 4 of conductive elements extending concentrically in the at least one stator notch 20, around a tooth 22, of the stator 2 so as to generate at each end 24 of the stator 2, along the first axis A1 of rotation of the rotor, a winding head 42. Thus, each hollow volume 200 is filled with conductive elements of the winding 4 which wind around an adjacent tooth 22 forming the winding head 42 on a first end 24 of the stator 2 and on a second end 26 (represented in ) of stator 2.

The electric machine 1 also comprises at least one slot wedge 6. The slot wedge 6 arranged in the stator slot 20 so as to physically isolate and electrically protect the conductive elements of the winding 4 of the rotor 3.

In addition, the electric machine 1 comprises at least one heat sink 8 arranged inside a stator slot 20 between the winding conductive elements 4 and/or in the slot wedge 6. The heat sink 8 s 'extends from a winding head 42 of the winding heads 42 of the first end 24 of the stator 2 along the first axis A1 of rotation of the rotor 3 to the winding head 42 of the winding heads 42 of the second end 26 of the stator 2 along the first axis A1 of rotation of the rotor 3. More precisely, the heat sink 8 is positioned between two electrical conductors of winding 4 so as to be as close as possible to the heat source, in the vicinity of winding 4 The heat sink 8 comprises a phase change material.

Thus, the heat sink 8 allows the transfer of heat from the winding 4 to a heat dissipating carcass external to the electrical machine 1. To do this, the heat sink 8 comprising the phase change material is capable of storing large amounts of heat during a phase transition, i.e. melting, of the phase change material. Additionally, the phase change material is configured to melt at a temperature greater than 100°C and is therefore defined as melting temperature greater than 100°C. Phase change material is a material with high heat of fusion, which melts and solidifies at an appropriate transition temperature. At this appropriate transition temperature, the phase change material in the heat sink 8 continues to absorb heat with very little temperature increase until all of the phase change material melts or the quantity maximum heat produced by the winding 4 fades.

The heat sink 8 allows the accumulation of thermal energy during certain transient phases where a high intensity passes through the electrical conductors of the winding 4. The accumulation of thermal energy takes place at a stable temperature, for example at the melting temperature of the material of the heat sink 8. Apart from these transient phases of high energy dissipation, the material of the heat sink 8 returns thermal energy in particular towards the carcass 21 of the stator 2 in order to evacuate this energy towards the exterior of the electrical machine 1. By being located in direct contact with the electrical winding conductors 4 or in their immediate vicinity, the thermal transfer of the electrical winding conductors 4 towards the heat sink 8 takes place with a thermal inertia lower than the heat transfer of the entire electrical machine 1 to the outside. The presence of the heat sink 8 in the immediate vicinity or in contact with the electrical winding conductors 4 makes it possible to smooth out the heat emission peaks from the electrical winding conductors 4 while limiting the risks of temperature increase.

As an indicative example, the phase change material of the heat sink 8 is in the form of salts or in the form of organic or eutectic compounds or any material making it possible to store large quantities of energy in the material to be stored. phase change at the transition temperature, having solid-liquid phase change temperatures, adapted according to the constraints of use of the electrical machine, greater than a hundred degrees Celsius, typically between 100°C and 300°C, such as a material usually used for brazing, such as aluminum, zinc, a tin or lead-based material at low temperature, a salt or a wax from the paraffin family.

The heat sink 8 takes the form of a circular ring 81 whose radius is equivalent to a length between the first axis A1 of rotation of the rotor 3 and a bottom 202 of the stator notch 20. A first portion 82 of the ring circular 81 is thus embedded in the interstices forming the stator notches 20 while a second portion 84 of the circular ring 81 is in contact with the teeth 22 juxtaposed along the first axis A1 of rotation of the rotor 3. The first portion 82 is then extends from the first end 24 of the stator 2 along the first axis A1 of rotation of the rotor 3 to the second end 26 of the stator 2.

As stated previously, the heat sink 8 comprises a third portion 86 extending radially relative to the circular ring 81 in the direction of the first axis A1 of rotation of the rotor 3. More precisely, the third portion 86 of the heat sink 8 in phase change material extends from the first portion 82, inside the stator notch 20, towards the first axis A1 of rotation of the rotor 3, radially relative to the circular ring 81 and so as to be positioned between two windings 4 adjacent to each other. Thus, each third portion 86 is positioned, according to a plane perpendicular to the first axis A1 of rotation of the rotor 3, as shown in , between a first winding 41 of conductive elements and a second winding 43 of conductive elements. According to a preferred variant, the third portion 86 of phase change material is in direct contact with the two adjacent windings 4, that is to say the first winding 41 and the second winding 43, so as to optimize the exchange thermal coming from the first winding 41 and the second winding 42 and towards the heat sink 8, via the third portion 86.

In addition, the third portion 86 of phase change material of the heat sink 8 extends in the direction of the first axis A1 of rotation of the rotor 3 until it is in contact with the notch wedge 6.

The heat sink 8 may also include a fourth portion 88 extending inside the notch wedge 6 so as to increase the heat extraction capacity of the heat sink 8.

According to a variant, the third portion 86 of phase change material is distant from the notch wedge 6.

To maintain the phase change material in a given volume, it can be mixed in a porous matrix. Therefore, the heat sink 8 is a porous matrix. The phase change material can also be encapsulated in a flexible capsule whose walls have sufficient thermal conductivity to promote heat exchange between the winding 4 and the phase change material. The heat sink 8 is then a flexible capsule having these thermal characteristics.

There represents an enlarged view of the first end 24 of the stator 2 of the , at least one winding head 42 of conductive elements and the heat sink 8. However, as shown in , the heat sink 8 frames each winding head 42 via the second portion 84 of phase change material, the third portion 86 of phase change material 86 and the fourth portion 88 of change material phase allowing the heat coming from each winding head 42 to be evacuated.

The heat sink 8 therefore makes it possible to store the excess losses and therefore calories generated by a possible momentary and instantaneous overload coming from each winding 4 and each winding head 42. The heat sink 8 therefore avoids an elevation temperatures at the level of the winding 4 and the winding heads 42 which can, in the absence of the heat sink 8, risk damaging them or reducing their lifespan. The heat is then returned in the normal load and/or partial load phases.

Preferably, the second portion 84 of phase change material, the third portion 86 of phase change material and the fourth portion 88 of phase change material together describe a shape so as to frame the winding heads 42 like a kind of ring.

There represents a schematic view of a first winding configuration with a stator slot 20 comprising the first winding 41 of conductive elements, the second winding 43 of conductive elements, adjacent to each other and the heat sink 8. The first winding configuration can also be shown as a concentric winding. Indeed, the hollow volume 200 of the stator notch 20 is split, along a second axis A2 perpendicular to the first axis A1 into two volumes: a first volume 410 filled with the conductive elements of the first winding 41 and a second volume 430 filled with the elements conductors of the second winding 43. The first winding 41 is separated from the second winding 43 by a coil separator 44 ensuring electrical insulation between the conductive elements. In addition, the first winding 41 and the second winding 43 are, as stated previously, isolated from the rotor 3 via the notch block 6.

The conductive elements of the winding 4 can also be encapsulated in a dielectric and thermally conductive insulating material 7 filling the first and second volumes 410 and 430 left free by the conductive elements of the winding 4.

Thus, as stated previously, the first portion 82 of the heat sink 8 in phase change material is positioned against the bottom 202 of the stator notch 20. The third portion 86 of the heat sink 8 in phase change material is included in the coil separator 44 between the first winding 41 of conductive elements and the second winding 43 of conductive elements. In this way, the third portion 86 is closest to the greatest heat zone, between the conductive elements. Finally, the fourth portion 88 is arranged in the notch wedge 6, as shown in .

The heat sink 8 thus has the advantage of storing heat coming from the conductive elements of the first and second windings 41 and 43, via the first, third and fourth portions 82, 86 and 88, in particular during the phases transients and overload. This storage has the effect of introducing a new, slower temperature evolution time constant, thus delaying the moment when the conductive elements reach the maximum acceptable temperature and not inducing degradation of the conductive elements. If the transient phase is sufficiently short, the maximum temperature reached by the conductive elements of winding 4 is then lower. The degradation of insulators as well as components whose lifespan can deteriorate with temperature is thus avoided.

According to a variant represented in , the heat sink 8 can also be included in an isthmus 9 of the stator notch 20 beyond the notch wedge 6. In fact, the isthmus 9 represents a narrowed volume of the stator notch 20 by the widening of the adjacent teeth 22 beyond the notch wedge 6 along the second axis A2 towards the first axis A1 of rotation of the rotor 3. This configuration for introducing the heat sink 8 into the coil separator 44, in the notch wedge 6 and in the isthmus 9 thus has the advantage of increasing the thermal extraction capacity of the heat sink 8.

It can also be envisaged, according to a variant represented in , to introduce only the heat sink 8 against the bottom 202 of the stator slot 20, in the slot wedge 6 and in the isthmus 9 so as to favor the volume of conductive elements of the winding 4.

A slot 10 can also be envisaged, according to a variant shown in , crossing the stator 2 towards the external environment of the electric machine 1, along the second axis A2. This slot 10 has the advantage of increasing the volume available for melting the phase change material of the heat sink 8 and therefore of making it possible to extract more calories from the conductive elements of the winding 4. Indeed, the phase change material, passing from the solid state to the liquid state, occupies a larger volume. Therefore, the melting of the phase change material can be limited by the volume available in the coil separator 44, in the notch wedge 6 or even in the isthmus 9, due in particular to changes in pressure conditions in the heat sink 8. Therefore, the phase change material of the heat sink 8, passing from the solid state to the liquid state, can be included in the slot 10 and the heat sink 8 extends in this slot 10.

Figures 5a, 5b and 5c represent a schematic view of a second distributed winding configuration with a 20’ stator slot. Therefore, as for the concentric winding configuration, the hollow volume 200' of the stator notch 20' is split into a first volume 410' filled with the conductive elements of the first winding 41' and a second volume 430' filled with the conductive elements of the second winding 43'. However, unlike the concentric winding configuration, the hollow volume 200' is split along an axis perpendicular to the first axis A1 of rotation of the rotor 3 and to the second axis A2. Therefore, the coil separator 44', ensuring electrical insulation between the conductive elements, is also perpendicular to the first axis A1 of rotation of the rotor 3 and to the second axis A2. As with the concentric winding, the first winding 41' and the second winding 43' are isolated from the rotor 3 via the notch block 6'.

Thus, the represents a distributed winding configuration in which the heat sink 8 is included in the slot wedge 6'.

According to a variant of the distributed winding configuration, represented in , the heat sink 8 is included in the notch wedge 6' and in the isthmus 9'.

According to another variant of the distributed winding configuration, represented in , the heat sink 8 is included in the slot wedge 6', in the isthmus 9' and in the coil separator 44'.

In addition, the winding heads 42 of the conductive elements can also be encapsulated in the dielectric and thermally conductive insulating material 7, as shown in . The insulating material 7 thus comprises a first external portion 70 taking the form of a ring encompassing all the winding heads 42 of conductive elements and being placed against the first end 24 of the stator 2. A second external portion also taking the form of A ring encompassing all the winding heads 42 of conductive elements is also placed against the second end 26 of the stator 2.

In addition, the electric machine 1 may comprise a thermal ring 12 in contact with the stator 2. The thermal ring 12 comprises cooling fins 120 which extend radially relative to the first axis A1 of rotation of the rotor 3.

Thus, the heat captured by the heat sink 8 coming from the winding 4 and the conductive elements is transmitted to the thermal ring 12 so as to be evacuated by convection with a flow sweeping the cooling fins 120.

The invention therefore proposes a heat sink using a phase change material making it possible to attenuate the temperature at the level of the winding and the conductive elements and to delay the rise in temperature during overload phases introduced within the notch itself. stator, in the coil separator, in the wedge of the notch or even in the isthmus so as to be in the vicinity of the emitting heat source, namely the winding itself.

In order to ensure the location of the heat sink, the volume of the notch can possibly be adapted without significantly degrading the size and resulting mass of the rotating electrical machine.

Claims (9)

Electric machine (1) comprising a stator (2) and a rotor (3) configured to be rotated by the stator (2), the stator (2) comprising a carcass (21) from which extends at least one stator notch (20) parallel to a first axis (A1) of rotation of the rotor (3), the electric machine (1) comprising windings (4) of conductive elements extending concentrically in the at least one stator notch (20) of the stator (2) so as to form at each end (24, 26) of the stator (2), along the first axis (A1) of rotation of the rotor (3), a winding head (42), the electric machine (1) comprising at least one notch wedge (6) arranged in the stator notch (20) so as to physically isolate the conductive elements of the winding (4) of the rotor (3), the electric machine (1) comprising at least least one heat sink (8) arranged inside a stator slot (20) between the conductive elements and/or in the slot wedge (6), the heat sink (8) extending from the winding head (42) from a first end (24) of the stator (2) along the first axis (A1) of rotation of the rotor (3) to a winding head (42) from a second end ( 26) of the stator (2), the heat sink (8) comprising a phase change material. An electric machine (1) according to claim 1, wherein the phase change material is configured to undergo melting at a temperature above 100°C. Electric machine (1) according to one of claims 1 or 2, in which the stator notch (20) comprises a coil separator (44) capable of ensuring electrical insulation between the conductive elements, the heat sink (8 ) being included in the coil separator (44). Electric machine (1) according to one of claims 1 to 3, in which the stator notch (20) comprises an isthmus (9) beyond the notch wedge (6) along a second axis (A2), perpendicular to the first axis (A1), in the direction of the first axis (A1) of rotation of the rotor (3), the heat sink (8) being included in the isthmus (9) of the stator notch (20). Electric machine (1) according to one of claims 1 to 4, in which the stator notch (20) comprises a slot (10) passing through the stator (2) towards a medium external to the electric machine (1) along the second axis (A2), the phase change material of the heat sink (8) being included in the slot (10). Electric machine (1) according to one of claims 1 to 5, in which the heat sink (8) is a porous matrix. Electrical machine (1) according to one of claims 1 to 6, in which the winding (4) of the conductive elements is encapsulated in a dielectric and thermally conductive insulating material (7). Electric machine (1) according to one of claims 1 to 7, in which the phase change material is an aluminum-based material, a salt or a wax from the paraffin family. Electric machine (1) according to one of claims 1 to 8, comprising a thermal ring (12) in contact with the stator (2), the thermal ring (12) comprising cooling fins (120).