Rotating electrical machine with superconducting elements and cryogenic enclosures

Disclosed is a rotating electrical machine with axial air gap, comprising two rotors, each provided with superconducting axial magnetic flux barrier elements around an axis of rotation and having, between them, axial magnetic flux passage areas, at least one armature, comprising windings and a superconducting field coil surrounding the elements and the armature and capable of inducing an axial magnetic field. Each armature is positioned between two of the rotors. The superconducting elements of the rotors are coaxial with one another and also the flux passage areas. A first annular cryogenic enclosure encloses the field coil and a second cryogenic enclosure encloses the two rotors and the armature or only one rotor, with a third cryogenic enclosure around the other rotor without the armature.

The invention relates to a rotating electric machine.

A field of application of the invention relates to electricity generators and motors supplied with electricity, to equip means of transport, such as aircrafts for example airplanes or helicopters.

Rotating machines are known, comprising on their rotor, superconducting flux barrier pads inside an axial flux inductor coil, and one or two armature(s) during their operation as a generator. The rotation of the pads creates a modulation of the magnetic flux in the armature(s) between a minimum value created behind the pads and a maximum value created between the pads, thereby enabling to generate an electromotive force therein.

However, for applications requiring a large energy density, it is necessary to have a large difference between the maximum value and the minimum value of the magnetic flux in the armature, the modulation amplitude being directly proportional to the electromagnetic force created (Faraday's law).

Thus, in these known machines, it turns out that the minimum value of the magnetic flux in the armature is quite high.

The invention aims to obtain a rotating electric machine with superconducting elements, which allows reducing the minimum value of the magnetic flux in the armature while having a large maximum value of the magnetic flux in the armature.

To this end, a first subject matter of the invention is a rotating electric machine, comprising:

at least one rotor comprising a set of superconducting axial magnetic flux barrier elements distributed in a plane perpendicular to the axis of rotation in a tangential direction about the axis of rotation, said superconducting axial magnetic flux barrier elements being spaced by axial magnetic flux passage areas distributed in the tangential direction about the axis of rotation,

at least one armature, comprising armature windings distributed in the tangential direction about the axis of rotation,

at least one superconducting inductor coil surrounding the superconducting axial magnetic flux barrier elements and the at least one armature in the tangential direction about the axis of rotation,

the at least one superconducting inductor coil being able to induce an axial magnetic field directed along the axis of rotation,

the at least one rotor being rotatably mounted on the axis of rotation with respect to the armature and to the at least one inductor coil,

characterized in that the machine comprises as a rotor at least one first rotor and at least one second rotor,

the at least one first rotor and the at least one second rotor being spaced from each other along the axis of rotation,

the at least one armature being positioned between the at least one first rotor and the at least one second rotor,

the superconducting axial magnetic flux barrier elements of the at least one first rotor being coaxial at least partly with the superconducting axial magnetic flux barrier elements of the at least one second rotor,

the axial magnetic flux passage areas of the at least one first rotor being coaxial at least partly with the axial magnetic flux passage areas of the at least one second rotor.

Thanks to the invention, the modulation of the flux is improved by reducing the minimum value of the flux in the armature(s) and by increasing the difference between the maximum value of the flux and the minimum value of the flux in the armature(s).

According to an embodiment of the invention, the at least one second rotor comprises an armature on either side.

According to an embodiment of the invention, the rotating electric machine comprises N rotors comprising on either side of each of the rotors an armature, N being a natural number greater than or equal to 2.

According to an embodiment of the invention, the at least one armature comprises a rotor on either side.

According to an embodiment of the invention, the rotating electric machine comprises N armatures comprising on either side of each of the armatures a rotor, N being a natural integer greater than or equal to 2.

According to an embodiment of the invention, the superconducting axial magnetic flux barrier elements of the at least one first rotor are aligned along the axis of rotation with the superconducting axial magnetic flux barrier elements of the at least one second rotor, and the axial magnetic flux passage areas of the at least one first rotor are aligned along the axis of rotation with the axial magnetic flux passage areas of the at least one second rotor.

According to an embodiment of the invention, the armature windings comprise at least one superconducting armature winding.

According to an embodiment of the invention, the armature windings comprise at least one conductive winding.

According to an embodiment of the invention, the at least one superconducting inductor coil has an axial extent, which surrounds the plurality of the rotors and the at least one armature in the tangential direction about the axis of rotation.

According to an embodiment of the invention, the machine comprises a single superconducting inductor coil.

According to an embodiment of the invention, the rotating electric machine includes a cryogenic cooling enclosure, inside which the rotors, the at least one armature and the at least one superconducting field coil are placed.

According to an embodiment of the invention, the rotating electric machine comprises a first cryogenic cooling enclosure, which has an annular shape about the axis of rotation and which is delimited radially by a first external wall and by a second internal annular wall, the at least one superconducting inductor coil being located in the first cryogenic cooling enclosure between the first external wall and the second internal annular wall,

the machine comprising a second cryogenic cooling enclosure, which has a circular cylindrical shape about the axis of rotation and which is delimited radially by a third external wall located inside the second internal annular wall, the rotors and the at least one armature being located in the second cryogenic cooling enclosure.

According to an embodiment of the invention, the rotating electric machine comprises a first cryogenic cooling enclosure, which has an annular shape about the axis of rotation and which is delimited radially by a first external wall and by a second internal annular wall, the at least one superconducting inductor coil being located in the first cryogenic cooling enclosure between the first external wall and the second internal annular wall,

the machine comprising at least one second cryogenic cooling enclosure, which has a circular cylindrical shape about the axis of rotation and which is delimited radially by a third external wall located inside the second internal annular wall, the at least one first rotor being located in the second cryogenic cooling enclosure,

the machine comprising at least one third cryogenic cooling enclosure, which has a circular cylindrical shape about the axis of rotation, which is located axially at a distance from the second cryogenic cooling enclosure and which is delimited radially by a fourth external wall located inside the second internal annular wall, the at least one second rotor being located in the third cryogenic cooling enclosure,

the at least one armature being located between the second cryogenic cooling enclosure and the third cryogenic cooling enclosure.

According to an embodiment of the invention, at least one of the superconducting axial magnetic flux barrier elements comprises at least one full superconducting axial magnetic flux barrier pad.

According to an embodiment of the invention, at least one of the superconducting axial magnetic flux barrier elements comprises at least one superconducting axial magnetic flux barrier loop.

A second subject matter of the invention is an aircraft, comprising an electricity-consuming member or an electricity-generating member and a rotating electric machine as described above, which is connected to a circuit for connection to the electricity-consuming member or to the electricity-generating member to allow supplying it or providing it with electricity.

InFIGS.1,2and3, in a flux barrier electric machine1comprising superconducting axial magnetic flux barrier elements3, the modulation of the magnetic flux depends directly on the position of the shields that oppose the passage of the flux with respect to the windings7of the armature5(generator operation) or of the inductor (motor operation).

InFIGS.1,2and3, the rotating electric machine1is with axial flux and with flux barriers. The machine1comprises several rotors each generally designated by the reference2, which can be for example two or three rotors21,22and23inFIGS.1and2, or which can be other. The rotating electric machine1thus comprises one or several first rotor(s), designated by the reference21inFIGS.1,2and3, and one or several second rotor(s), designated by the reference22inFIG.1and by the references22and23inFIG.2. The terms “axial” and “coaxial” mean extending along the axis of rotation AX. The radial directions are located in planes perpendicular to the axis of rotation AX and start from the axis of rotation AX. The rotors2are secured to each other on a shaft or axis of rotation AX. Each rotor2comprises a set of superconducting axial magnetic flux barrier elements3, which are distributed in the tangential direction DC around the axis of rotation AX and which lie in a plane perpendicular to the axis of rotation AX. Between the superconducting axial magnetic flux barrier elements3of each rotor2,21,22,23are located axial magnetic flux passage areas4which are distributed in the tangential direction DC around the axis of rotation AX and which lie in the plane perpendicular to the axis of rotation AX. The rotors2,21,22,23are successively spaced from each other along the axis of rotation AX.

In an embodiment, each superconducting axial magnetic flux barrier element3of one of the rotors2(which can be for example the first rotor21) is coaxial at least partially with another superconducting axial magnetic flux barrier element3of the other rotor(s)2(which can be for example the second rotor(s)22,23). Thus, at least part of each superconducting axial magnetic flux barrier element3of one of the rotors2(which can be for example the first rotor21) is coaxial with at least part of another superconducting axial magnetic flux barrier element3of the other rotor(s)2(which can be for example the second rotor(s)22,23).

Each axial magnetic flux passage area4of one of the rotors2(which can be for example the first rotor21) is at least partially coaxial with another axial magnetic flux passage area4of the other rotor(s)2(which can be for example the second rotor(s)22,23). Thus, at least part of each axial magnetic flux passage area4of one of the rotors2(which can be for example the first rotor21) is coaxial with at least part of another axial magnetic flux passage area4of the other rotor(s)2(which can be for example the second rotor(s)22,23).

The machine1comprises one (or several) superconducting inductor coil(s)6, which is/are able to induce an axial magnetic field which is directed along the axis of rotation AX and which can be a DC magnetic field. For that purpose, the superconducting inductor coil6can comprise external electric terminals (not represented) serving to connect it to a DC electric voltage or to a DC current source, to produce the axial magnetic field. The superconducting inductor coil6is annular around the axis of rotation AX in the tangential direction DC and surrounds the superconducting axial magnetic flux barrier elements3of the rotors2and the armature(s)5. The superconducting inductor coil6creates an intense magnetic field B, thanks to high current densities circulating in this coil6, which can be for example 25 times greater than the current density of copper.

The machine1comprises one or several armature(s) (or stator(s)), which is/are each generally designated by the reference5, such as for example the armature(s)51and52. Each armature5comprises armature windings7which are distributed in the tangential direction DC around the axis of rotation AX.

The rotating electric machine1can operate in electricity-generating mode on the armature(s)5or in motor mode supplied with electricity on the armature(s)5.

According to one embodiment, each armature winding7can form, for example, a loop that does not surround the axis of rotation AX and comprises one or several conductor(s) forming a loop that does not surround the axis of rotation AX. This is illustrated by way of non-limiting example inFIG.11. Each auxiliary (geometric) direction70around which each armature winding7extends can be substantially parallel to the axis of rotation AX or have a component parallel to the axis of rotation AX. Thus, this auxiliary direction70of the winding (for example substantially parallel to the axis of rotation AX) is located at a first non-zero distance76from the axis of rotation AX. Thus, the conductor(s) of the loop formed by each armature winding7is/are located at a second distance77with respect to its auxiliary direction70, wherein this second distance is smaller than the first distance76and can be variable (as represented inFIG.11) or constant around its auxiliary direction70.

Each armature winding7can comprise other external electric terminals (not represented) used to connect it to an electric member, not represented. In the case where the rotating electric machine1operates in electricity-generating mode, each armature winding7allows sending to the electric receiving member the electric voltage (electromotive force) generated in this armature winding7by induction of the variable axial magnetic field moving in the tangential direction DC due to the rotation of the elements3of the rotors2around the axis of rotation AX. The electromotive force according to the Lenz-Faraday law is:

where ε is the electromagnetic force, Φ is the magnetic flux and t is the time. The elements3are brought closer with respect to the armature windings7along the axis AX to maximize the modulation of the flux and therefore the electromotive force generated in the armature windings7.

The rotors2are rotatably mounted on the axis of rotation AX with respect to the armature(s)5and to the inductor coil6, which are fixed to each other on a frame, not represented.

Each armature5is positioned between two of the rotors2in the direction along the axis of rotation AX.

In an embodiment represented inFIG.1, the single armature5is positioned between the first rotor21and the second rotor22.

In an embodiment represented inFIG.2, the first armature51is positioned between the first rotor21and the second rotor22, and the second armature52is positioned between the second rotor22and the other second rotor23.

In general, the machine1has a first number N of rotors2successively spaced from each other along the axis of rotation AX, where N is a prescribed natural integer, which is greater than or equal to 2 or 3, and a second number N-1 of armatures5positioned successively between the N rotors2along the axis of rotation AX. The embodiments corresponding to N≥3 are hereinafter referred to as machine1with several stacks of rotors2.

As represented inFIG.3, when the machine1is in generator operation, the superconducting inductor coil6generates a magnetic field B (as represented by the long arrows F1and the short arrows F2), which is directed along the axis of rotation AX in the interior space8it surrounds and in which the rotors2and the armature(s)5are located. Each superconducting axial magnetic flux barrier element3is configured to have a determined extent in the plane30perpendicular to the axis of rotation AX and create in this extent an obstacle (or shield) to the passage of the axial magnetic field B, as symbolized by the short arrows F2. For a temperature below their critical temperature (the critical temperature being for example below 100 K, or in particular below 50 K), the superconducting materials of the elements3, of the inductor coil6and possibly of the armature windings7have a zero resistivity, which allows DC currents to circulate without losses. For a temperature lower than their critical temperature, the superconducting materials of the elements3have a diamagnetic response during the rise of the magnetic field B, that is to say act as a magnetic field barrier similar to the Meissner effect observed under very low field.

This shield or this barrier to the passage of the axial magnetic field B results in a strong attenuation ATTB of the value of the magnetic field in front of and behind the element3along the axis AX, this attenuation ATT being all the greater (that is to say, the value of the magnetic field B being all the smaller) as moving from the external edge31of the element3to the center32of the element3behind the rear face33of the element3and in front of the front face34of the element3, as represented inFIG.4, showing the magnetic flux isolines around and in the element3and their value expressed in Tesla (T) with reference to the first scale ECH1of values.

In thisFIG.4, the superconducting pad forming the element3is circular cylindrical around the axis AX with a radius of 4 cm, is immersed in the constant axial magnetic field B of 3 T and has a critical current density of 1,000 A/mm2.FIG.4was obtained by calculation with a finite-element electromagnetic model (H-formulation). The majority of the current in the superconducting pads3develops on a thin thickness of penetration from their external surface. The penetration thickness depends on the intensity of the magnetic field in which the pad is immersed, as well as on its intrinsic electric properties. It can be noted that the penetration thickness is greater perpendicularly to the axis AX than along the axis AX. The thickness along the axis AX is proportional to the distance with respect to the center32of the pad. In general, the penetration thickness of the element3or of the pad3along the axis AX is relatively low, so as not to have degraded performances.

It can be seen inFIG.4that the value B1of the magnetic field in the vicinity of the external edge31of the element3is greater than the value B2of the magnetic field in the vicinity of the center32of the element3in the same plane perpendicular to the axis AX.

Similarly, this attenuation ATTB of the value of the magnetic field is all the lower (that is to say the value of the magnetic field is all the greater) as moving away from the element3parallel to the axis AX. It can indeed be seen inFIG.4that the value B3of the magnetic field far from the element3is greater than the value B4of the magnetic field at a distance closer to the element3in the same direction parallel to the axis AX.

On the other hand, the axial magnetic flux passage areas4allow values VB of the axial magnetic field B to pass, which are greater than those located in front of and behind the element3. It can indeed be seen inFIG.4that the value B5of the magnetic field transversely next to the element3is greater than the value B2of the magnetic field in the vicinity of the center32of the element3in front and behind it.

The rotation of the rotors2around the axis AX generates through the armature(s)5a magnetic flux, which varies depending on whether a superconducting axial magnetic flux barrier element3of the rotors2or an axial magnetic flux passage area4passes axially facing the armature(s)5.

In an embodiment represented inFIGS.1to3, each superconducting axial magnetic flux barrier element3of one of the rotors2(which can be for example the first rotor21) is aligned (that is to say is completely coaxial) along the axis of rotation AX with another superconducting axial magnetic flux barrier element3of the other rotor(s)2(which can be for example the second rotor(s)22,23), and each axial magnetic flux passage area4of one of the rotors2(which can be for example the first rotor21) is aligned (that is to say is completely coaxial) along the axis of rotation AX with another axial magnetic flux passage area4of the other rotor(s)2(which can be for example the second rotor(s)22,23).

Each axial magnetic flux barrier superconducting element3can have an extent limited to a first determined non-zero angular sector around the axis of rotation AX, and each axial magnetic flux passage area4can have an extent limited to a second determined non-zero angular sector around the axis of rotation AX. For example, the first determined angular sector can be equal to the second determined angular sector.

Each armature winding7can have an extent limited to a third determined non-zero angular sector around the axis of rotation AX. The third determined angular sector can be less than or equal to the first determined angular sector. The third determined angular sector can be less than or equal to the second determined angular sector. The number of armature windings7on each armature5can be greater than or equal to the sum of the number of superconducting axial magnetic flux barrier elements3and of the number of axial magnetic flux passage areas4of each rotor2, as represented inFIGS.1and2. Thus, in each rotational position of the rotors2around the axis of rotation AX, when some armature windings7are axially facing superconducting axial magnetic flux barrier elements3, other armature windings7are axially facing axial magnetic flux passage areas4. Thus, during the rotation of the rotors2around the axis of rotation AX, successively very low and then very high values of magnetic fluxes are obtained in each armature winding7.

FIG.5schematically represents a distribution calculated by the method of the finite elements for the value of the magnetic field, with reference to the second scale ECH2of values in Tesla (T), and this around two axially aligned superconducting axial magnetic flux barrier elements3, when an armature winding7is located between these two elements3and when a constant outer axial field is applied, and this without other elements3positioned along the axis of rotation AX, for a first example of a machine1according to the embodiment of the invention ofFIG.1, further having the following parameters: rated power of 50 kW, rated torque of 95 N.m, speed of rotation of 5,000 revolutions per minute, use temperature of 30 K, radius of the elements3of 40 mm, total weight of 20 kg, weight of each rotor of 4 kg.

FIG.6schematically represents a distribution calculated by the method of the finite elements for the value of the magnetic field, with reference to the third scale ECH3of values in Tesla (T), and this around two other axially aligned armature windings7′, when a superconducting axial magnetic flux barrier element3′ identical to the element3inFIG.5is located between these two armature windings7′ when a constant outer axial field identical to that ofFIG.5is applied, and this without other armature windings7′ and without other superconducting axial magnetic flux barrier element3′, according to a second comparative example not falling within the scope of the invention.

It can be seen inFIG.5that, although inFIG.5each superconducting axial magnetic flux barrier element3is axially further from the armature winding7than is each armature winding7′ with respect to the superconducting axial magnetic flux barrier element3′ inFIG.6, the value (minimum value) of the magnetic field at the center71,72of the front and rear faces of the armature winding7inFIG.5is lower (0.25 T) than the value (minimum value) of the magnetic field at the center71′,72′ of the front and rear faces of the armature coils7′ inFIG.6(0.45 T), turned towards the element3′. It can also be seen inFIG.5that the maximum value of the magnetic flux taken transversely next to the armature7(points73and74inFIG.5) is substantially identical to the maximum value of the magnetic flux next to the armatures7′ (points73′,73″,74′,74″) inFIG.6.

Thanks to the invention, a reduction of 44% in the minimum value of the magnetic flux in the armature7is therefore obtained while having a large maximum value of the magnetic flux in the armature. This allows an increase in the torque of the rotors7of 25%. Thanks to the invention, an increase in the modulation of the magnetic flux in the armature(s)7, and therefore an increase in the production of electricity in the armature(s)7are thus obtained.

the curve C1of the axial component Bz(expressed in T on the ordinate and calculated via the three-dimensional finite element electromagnetic model described above) of the magnetic induction generated by a machine1according to the first example aforementioned according to the invention at a point located at an average radius of the rotors2with respect to the axis AX (located axially facing the elements3of the rotors2and facing one of the armature windings7during the rotation of the rotors2) and at the center of the air gap between one of the rotors2and an armature5, as a function of the angular rotational position (expressed in radians) of the rotors2on the abscissa, as well as:

the curve C2of the axial component Bz(expressed in T on the ordinate and calculated via the three-dimensional finite element electromagnetic model described above) of the magnetic induction, generated by another machine according to the second comparative example aforementioned, not entering within the framework of the invention, whose single rotor is located axially between two single armatures according to the aforementioned comparative example, taken at a point located at an average radius of the rotor with respect to the axis AX (located axially facing superconducting axial flux barrier pads of the rotor2and facingone of the armature windings during the rotation of the rotor2) and at the center of the air gap between the rotor and one of the armatures, as a function of the angular rotational position (expressed in radians) of its rotor on the abscissa.

It can be seen inFIG.7that axially facing the superconducting axial magnetic flux barrier elements3, the magnetic flux is reduced by 95% between its maximum value and its minimum value on the curve C2for the comparative machine, whereas the magnetic flux is reduced by 99% between its maximum value and its minimum value on the curve C1for the machine according to the invention.

the curve C3of the axial component Bz(expressed in T on the ordinate and calculated via the three-dimensional finite element electromagnetic model described previously) of the magnetic induction generated by a machine1according to the aforementioned first example according to the invention at a point located at an average radius of the rotors2with respect to the axis A and on the turns of one of the armature windings7furthest from the elements3during the rotation of the rotors, as a function of the angular rotational position (expressed in radian) of the rotors2on the abscissa, as well as:

the curve C4of the axial component Bz(expressed in T on the ordinate and calculated via the three-dimensional finite element electromagnetic model described above) of the magnetic induction, generated by the aforementioned second comparative example of another comparative machine at one point located at an average radius of the rotors2with respect to the axis AX and on the turns of one of the armature windings7furthest from its elements, as a function of the angular rotational position (expressed in radians) of its rotor on the abscissa.

It can be seen inFIG.8that on the armature windings7, the magnetic flux varies between the maximum value of 1.4 T and the minimum value of 0.06 T on the curve C3for the machine according to the invention, i.e. a variation of 1.34 T which is 45% greater than the variation of 0.92 T between the maximum value of 1.26 T and the minimum value of 0.34 T on the curve C4for the comparative machine. Consequently, the invention allows increasing the shield effect by 45% and increasing the torque by 25% with respect to the comparative machine having a configuration according to the state of the art. This also results in an increase in the power of the machine1according to the invention, while making it possible to have an identical cryogenic cooling enclosure.

In one embodiment represented inFIGS.1to4, one or several or all of the superconducting axial magnetic flux barrier element(s)3comprise(s) or is/are formed of a full axial magnetic flux barrier pad made of superconducting material, whose extent is delimited by its external edge31. The full axial magnetic flux barrier pad3can be cylindrical around a direction parallel to the axis of rotation AX, for example circular cylindrical.

In another embodiment not represented, one or several or all of the superconducting axial magnetic flux barrier element(s)3comprise(s) or is/are formed of one or several axial magnetic flux barrier loop(s) made of superconducting material, whose extent is delimited by its external edge.

On each rotor2, the superconducting axial magnetic flux barrier elements3are fixed in through openings of an electrically insulating support9forming part of the rotor2. This support9is fixed to the axis of rotation AX and can be formed of a planar plate, for example circular around the axis AX. In one embodiment represented inFIGS.1and2, one or several or all of the axial magnetic flux passage area(s)4comprise(s) or is/are formed of part of the support9made of the electrically insulating material. In one embodiment represented inFIG.3, one or several or all of the axial magnetic flux passage area(s)4comprise(s) or is/are formed of another gaping opening in the support9.

In one embodiment represented inFIGS.1to17, one or several or all of the armature windings7comprise(s) or is/are formed of a superconducting winding (first case).

In another embodiment represented inFIGS.1to17, one or several or all of the armature winding(s)7comprise(s) or is/are formed of a conductive and not superconducting winding, which may be copper or the like (second case).

In one embodiment represented inFIGS.1to3,12,14and16, the superconducting inductor coil6has an axial extent L, which surrounds both the rotors2(and therefore also surrounds the superconducting axial magnetic flux barrier elements3), and the armature(s)5in the tangential direction DC around the axis of rotation AX. This further reduces the demagnetizing magnetic field and increases the level of induction. A single superconducting inductor coil6can be provided.

The superconducting axial magnetic flux barrier elements3can be cooled by a first cooling device, not represented, with circulation of cryogenic fluid, which can be for example helium, in particular in the embodiments ofFIGS.12to17, described below. The superconducting inductor coil6can be cooled by a second cooling device, not represented, with circulation of cryogenic fluid, which can be for example helium, in particular in the embodiments ofFIGS.12to17, described below. The cooling of the superconducting inductor coil6can be achieved by the same fluid circulating in series in the vicinity of the superconducting inductor coil6and of the superconducting axial magnetic flux barrier elements3of the rotors2, in particular in the embodiments ofFIGS.12to17, described below. When, in addition, the superconducting axial magnetic flux barrier elements3are superconducting pads, these superconducting elements3have a higher temperature tolerance than the superconducting coil6, and the fluid (helium) cools the superconducting inductor coil6before the superconducting pads3, in particular in the embodiments ofFIGS.12to17, described below and in the first and second cases described below. The rotors2can be placed inside a vacuum cryogenic enclosure, for example according to one of the embodiments described below with reference toFIGS.12to17. The vacuum allows ensuring the absence of exchanges of heat by convection between the surfaces of the enclosure and the rotors2, and therefore thermal insulation, in particular in the embodiments ofFIGS.12to17, described below.

The cryogenic cooling enclosures of the embodiments described below can contain the coolant fluid. This coolant fluid can be for example helium, or other. The cooling of the superconducting axial magnetic flux barrier elements3in rotation can be carried out by means of a rotating collector circulating the helium inside copper channels in contact with these elements3, in particular in the cryogenic cooling enclosure10of the embodiment ofFIGS.12and13, in the cryogenic cooling enclosure12of the embodiment ofFIGS.14and15, in the cryogenic cooling enclosure13of the embodiment ofFIGS.16and17and in the cryogenic cooling enclosure14of the embodiment ofFIGS.16and17, described below and in the fourth cryogenic cooling enclosure described below. The cryogenic cooling enclosures of the embodiments described below can operate at different temperatures from each other.

According to a first case of cooling, the cryogenic cooling enclosures10,11,12,13,14of the embodiments ofFIGS.12to17can be arranged and/or connected, from the point of view of the circulation of the coolant fluid, so that the coolant fluid first cools the superconducting inductor coil6, then the armature windings7of the armature5, and then the rotors2,21,22and/or23(superconducting axial magnetic flux barrier elements3), in the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7. The cooling order of the enclosures is from coldest to warmest, because the coolant fluid will heat up during cooling.

According to a second case of cooling, the cryogenic cooling enclosures10,11,12,13,14of the embodiments ofFIGS.12to17can be arranged and/or connected, from the point of view of the circulation of the coolant fluid, so that the coolant fluid first cools the superconducting inductor coil6, then the rotors2,21,22and/or23(superconducting axial magnetic flux barrier elements3), and then the armature windings7of the armature5, in the second case where the armature windings7are formed of conductive and not superconducting windings7. The cooling order of the enclosures is from coldest to warmest, because the coolant fluid will heat up during cooling.

In the second case, the armature windings7formed of conductive and not superconducting windings7of the armature5will typically operate at higher temperatures (possibly being on the order of 100 K) than in the first case of the armature windings7comprising one (or several) superconducting armature winding(s)7, which must be cooled below their critical temperature <100K, for example at a temperature that can be 70K or 50K). The comparison performed regarding the improvement in the torque for a configuration according to the second comparative example compared with a configuration according to the first example according to the invention is accompanied by an improvement in the machine power of the machine, which is proportional only for a completely superconducting machine. In this case, the size of the cryogenic enclosure remains relatively the same.

In one embodiment represented inFIGS.12and13, the machine1comprises a cryogenic cooling enclosure10, inside which the rotors2, the armature(s)5and the superconducting inductor coil6are placed, in the case where the armature windings7are also superconducting.

In one embodiment represented inFIGS.14and15, the superconducting inductor coil6is placed in a first cryogenic cooling enclosure11in the form of an annular bushing around the axis of rotation AX. The superconducting inductor coil6is located in a first housing space113of the enclosure13, located between a first external wall111of the first enclosure11and a second internal annular wall112of the first enclosure11, which delimit it radially. This first housing space113is separate from a second space114located radially inside the second internal annular wall11. In this second interior space114is placed a second cryogenic cooling enclosure12in which the rotors2and the armature(s)5are located in case the armature windings7are also superconducting. The second cryogenic cooling enclosure12has a circular cylindrical shape around the axis of rotation AX and is delimited radially by a third external wall121located inside the second internal annular wall112. The fact of having several enclosures allows more efficient cooling: each enclosure is cooled to the temperature required by the parts located inside the enclosures.

According to one embodiment, the first cryogenic cooling enclosure11of the embodiment ofFIGS.14and15comprises one (or several) first coolant fluid introduction inlet(s) connected to a source sending it the coolant fluid, and one (or several) first coolant fluid ejection outlet(s). The first coolant fluid ejection outlet or one (or several or all) of the first coolant fluid ejection outlet(s) is/are connected to one (or several) second coolant fluid introduction inlet(s) of the second cryogenic cooling enclosure12. The second cryogenic cooling enclosure12comprises one (or several) second coolant fluid ejection outlet(s).

The (or one or several or all of the) second coolant fluid introduction inlet(s) of the second cryogenic cooling enclosure12can be closer to the armature(s)5than to the rotors2,21,22and/or23, in the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7, in order to implement the first case of cooling mentioned above. The (or one or several or all of the) second coolant fluid ejection outlet(s) can be closer to the rotors2,21,22and/or23than to the armature(s)5, in the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7, in order to implement the first case of cooling mentioned above.

The (or one or several or all of the) second coolant fluid introduction inlet(s) of the second cryogenic cooling enclosure12can be closer to the rotors2,21,22and/or23than to the armature(s)5, in the second case where the armature windings7are formed of conductive and not superconducting windings7, in order to implement the second case of cooling mentioned above. The (or one or several or all of the) second coolant fluid ejection outlet(s) can be closer to the armature(s)5than to the rotors2,21,22and/or23, in the second case where the armature windings7are formed of conductive and not superconducting windings7, in order to implement the second case of cooling mentioned above.

In one embodiment represented inFIGS.16and17, the first enclosure11is similar to that of the embodiment described above with reference toFIGS.14and15. In the second interior space114is placed a second cryogenic cooling enclosure13in which the first rotor21is placed without the armature5, and a third cryogenic cooling enclosure14in which the second rotor22is placed without the armature5, in the second case where the armature windings7are not superconducting. The second cryogenic cooling enclosure13has a circular cylindrical shape around the axis of rotation AX and is delimited radially by a third external wall131located inside the second internal annular wall112. The third cryogenic cooling enclosure14has a circular cylindrical shape around the axis of rotation AX and is delimited radially by a fourth external wall141located inside the second internal annular wall112. The third cryogenic cooling enclosure14is distinct and located axially at a distance of the second cryogenic cooling enclosure13. In the second interior space114and between the second cryogenic cooling enclosure13and the third cryogenic cooling enclosure14is located the armature5. For example, a cryogenic enclosure13or14is provided around each rotor2of the machine1. The machine1can thus comprise N cryogenic cooling enclosures13,14in which the N rotors2are placed respectively. The armature windings7can be inserted between the external transverse surfaces of two different enclosures13and14, for example according to the embodiment described below with reference toFIG.11. In the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7, each armature5is placed in a fourth cryogenic cooling enclosure, which is located between the second cryogenic cooling enclosure13and the third cryogenic cooling enclosure14, which has a circular cylindrical shape around the axis of rotation AX and which is delimited radially by a fourth external wall located inside the second internal annular wall112. The fact of having several enclosures allows more efficient cooling: each enclosure is cooled to the temperature required by the parts located inside the enclosures.

According to one embodiment, the first cryogenic cooling enclosure11of the embodiment ofFIGS.16and17comprises one (or several) first coolant fluid introduction inlet(s) connected to a source sending it the coolant fluid, and one (or several) first coolant fluid ejection outlet(s). The second cryogenic cooling enclosure13comprises one (or several) second coolant fluid introduction inlet(s) and one (or several) second coolant fluid ejection outlet(s). The third cryogenic cooling enclosure14comprises one (or several) third coolant fluid introduction inlet(s) and one (or several) third coolant fluid ejection outlet(s). In the first case, the fourth cryogenic cooling enclosure comprises one (or several) fourth coolant fluid introduction inlet(s) and one (or several) fourth coolant fluid ejection outlet(s).

In the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7, in order to implement the first case of cooling mentioned above, the (or one or several or all of the) first coolant fluid ejection outlet(s) of the first cryogenic cooling enclosure11of the superconducting inductor coil6is/are connected to the (or one or several or all of the) fourth coolant fluid introduction inlet(s) of the fourth cryogenic cooling enclosure (armature5). The (or one or several or all of the) fourth coolant fluid ejection outlet(s) of the fourth cryogenic cooling enclosure (armature5) is/are connected to the (or several or all of the) second coolant fluid introduction inlet(s) of the second cryogenic cooling enclosure13and to the (or one or several or all of the) third coolant fluid introduction inlet(s) of the third cryogenic cooling enclosure14, in the first case where the armature windings7comprise one (or several) superconducting armature winding(s)7, in order to implement the first case of cooling mentioned above.

In the second case where the armature windings7are formed of conductive and not superconducting windings7, in order to implement the second case of cooling mentioned above, the (or one or several or all of the) first coolant fluid ejection outlet(s) is/are connected to the (or one or several or all of the) second coolant fluid introduction inlet(s) of the second cryogenic cooling enclosure13and to the (or one or several or all of the) third coolant fluid introduction inlet(s) of the third cryogenic cooling enclosure14. In the second case, forced air or liquid cooling devices can be envisaged to cool the armature windings7. For example, a crown on the external and/or internal radial peripheries of the armature windings7is well suited to a cooling device by circulation of a liquid in the second case.

In the embodiment ofFIG.11, the armature windings7of an armature5can be fixed on a cryostat cap35(for example made of ceramic) of the enclosure13and/or14in the form of a ring around the axis AX, one transverse face of which comprises notches36in which the armature windings7are respectively mounted. This system can in particular allow serving as a mechanical support for the coils in the absence of a magnetic yoke (iron-free machine). Channels and fins can be integrated into the cryostat cap34in order to improve the cooling.

The machine1according to the invention, and particularly the machine according to the embodiment described above with N≥3 rotors and N-1≥2 armatures with reference toFIG.2, called machine with several stacks of rotors2, is well suited to very high power machines with volume constraints (for example maximum external radius), or to fully superconducting topologies, as the armatures and rotors can all be placed inside a single cryogenic enclosure.

In the axial flux electric machine1, the addition of a stack according toFIG.2increases the power and also the mass. The mass power of the machine is increased. Indeed, the stack of rotors2leads to an increase in the length L of the inductor coil6(operation in generator mode). This lengthening of the coil6results in the reduction of the demagnetizing magnetic field Hd, which increases the level of the induction at the heart of the machine1and therefore its mass power.

The magnetic induction created by a solenoid S traversed by a current density J can be solved by an Amperian or Coulombian approach, with reference toFIG.9. The demagnetizing field is typically Coulombian, the magnetic surface charges are written:
σs(r)=μ0J(R2−R1) for 0<r<R1
σs(r)=μ0J(R2−r) forR1<r<R2
σs(r)=0 forr>R2

For a distribution of charges distributed over a surface Σ, the demagnetizing magnetic field Hdis given at a point M by:

where P is a point on the surface Σ. In the absence of an external magnetic field source, the total magnetic field vector H is simply written by:
H=Hd

Finally, the expression of the induction vector B is:
B=μ0(H+M)=μ0(Hd+M)

Vectorically, the demagnetizing magnetic field Hdis opposed to the magnetization M of the solenoid, which explains the demagnetizing nature. By increasing the length L of the superconducting coil6, the distance PM of the5expression above of the demagnetizing magnetic field Hdincreases and decreases the demagnetizing magnetic field Hd. Thus in view of the expression of B, the total induction increases and therefore the torque/power set of the machine also. A coefficient k can be used to represent the evolution of the induction as a function of the number of rotors2in the machine1according to the invention, such that:

where Bz1is the induction for an axial flux machine comprising a single rotor and a single armature and BzNthe induction of a machine1according to the invention comprising N rotors. The induction is proportional to this coefficient k. The increase in torque and power of the machine1is also proportional to this coefficient k.

FIG.10represents the evolution of the coefficient k (and therefore of the induction) as a function of the number (N-1) of stacks of rotors2. This curve C5was obtained by the interpolation of results obtained for calculations with finite elements of the machine1according to the invention comprising different numbers N-1 of stacks of rotors2. It can be seen that the coefficient k and the mass power of the machine1are doubled for N=3 (point P1on the curve C5) and more than tripled for N=9 (point P2on the curve C5). The curve C5has been determined as being for example of the form:
K=BzN/Bz1=A.(N.F)D−C

In the aforementioned example of the machine1according to the invention having the aforementioned parameters, A=9.03T−1.m−1, D=0.1372, C=5.15 and F=0.06 m. Of course, the coefficients A, D, C and F can be different for other values of the parameters of the machine1according to the invention.

The invention can be used for the electric machines1comprising flux barriers (full superconducting pads or short-circuited superconducting strips).

The technical field of use of the invention falls within the context of the electrification of aircrafts. Preparing for the installation of increasingly powerful electric systems for the electric or hybrid propulsion requires designing electric motors capable of competing, exceeding or improving the performance of the heat engines. The electric aircraft will require power densities of electric machines greater than 20 kW/kg. The use of superconducting materials represents a key tool to achieve these power densities. The invention can be used for electric machines comprising flux barriers3(full superconducting pads or short-circuited superconducting strips). The invention applies to entirely superconducting machines (superconducting armature3and inductor6) but also to partially superconducting machines (superconducting armature3or inductor6).

The rotating electric machine1can form part of an aircraft and have the at least two external electric terminals of the armature windings7which are connected to an electricity-consuming member or an electricity-generating member. This consuming or generating member can be located, for example, in one or several propulsion turbomachine(s) of the aircraft. In case the rotating electric machine1operates in electricity-generating mode, the rotating electric machine1can have the at least two external electric terminals of the armature windings7which are connected to an electricity-consuming member or to a connection circuit (which can be for example with controllable switching) itself connected by electric conductors to an electricity-consuming member, so that the electricity-generating rotating electric machine1can supply this consuming member with electricity. In case the rotating electric machine1operates in motor mode, the rotating electric machine1can have the at least two external electric terminals of the armature windings7which are connected to the electricity-generating member or to a connection circuit (which can be for example with controllable switching) itself connected by electric conductors to the electricity-generating member, so that the rotating electric machine1can be supplied with electricity by this generator member. Of course, the embodiments, characteristics, possibilities and examples described above can be combined with each other or selected independently of each other.