Electric machine with superconducting magnetic screens

Abstract

This flux-barrier electric machine comprises a stator including an annular inductor and an armature including at least one arrangement of electromagnetic coils, and a rotor (7) including superconducting pellets mounted radially inside the inductor, characterized in that it includes superconducting magnetic screens (13) in close proximity to at least one arrangement of electromagnetic coils. Figure for the abstract: Fig 5a

Description

Title of the invention: Electric machine with superconducting magnetic screens Technical field

[0001] The present invention relates to the reduction of leakage fluxes in electrical machines.

[0002] The present invention is applicable to superconducting or non-superconducting electrical machines, as well as axial, radial or transverse flux machines.

[0003] A particularly interesting application of the invention concerns turbo-machines intended for supplying aircraft on-board networks with electrical energy. Previous techniques

[0004] Propulsion systems for electric or hybrid aircraft require the use of electric motors capable of competing with, or even exceeding, the performance of thermal engines.

[0005] Electric machines intended for the propulsion of electric aircraft need to be capable of providing electrical power densities greater than approximately 20kW per kg.

[0006] In this context, the use of the most efficient machines possible is advantageous in order to achieve these power density levels.

[0007] The use of superconducting machines firstly makes it possible to obtain good efficiency.

[0008] Indeed, when they are cooled to a temperature below their critical temperature, superconducting materials have zero resistivity, which allows direct currents to flow without loss.

[0009] At this temperature, they also exhibit a diamagnetic response to any variation in the magnetic field. This behavior is analogous to that of a magnetic field barrier.

[0010] The absence of resistivity of superconducting materials at a temperature below their critical temperature therefore makes it possible to increase the current density circulating in the conductors.

[0011] Indeed, the absence of Joule effect losses in superconducting conductors makes it possible to avoid a linear increase in cooling requirements with the increase in the power of superconducting electric motors. It is nevertheless necessary to cool them to temperatures below the temperature criticality of the superconducting materials used, which is typically of the order of 100 Kelvin or even 150 Kelvin.

[0012] [Fig.l] shows an example of an embodiment of a superconducting electrical machine 1 with flux barriers and axial flux without magnetic core, also called ironless.

[0013] The electrical machine 1 comprises a stator 2 comprising an annular superconducting inductor 3 as well as one or more arrangements 5 of induced electromagnetic coils 6, the inductor 3 being coaxial with the arrangements 5 of electromagnetic coils 6.

[0014] The electrical machine also comprises a rotor 7 comprising superconducting pellets 8 arranged radially inside the annular inductor 3 and rotatable relative to the stator 2. The axis of rotation of the rotor corresponds to the axis of the axial flux of the electrical machine 1. The superconducting pellets 8 are cooled, for example with helium, nitrogen or hydrogen, and produce the variation of the magnetic field thanks to the diamagnetic response of the superconducting pellets 8. The superconducting pellets 8 have for example a circular shape or an annular section, the latter shape improving the power density of the electrical machine.

[0015] The example more particularly illustrated in [Fig.l] corresponds to an axial flux machine comprising a rotor 7 framed by two stators 2. In this case, a set of pellets 8 is framed on either side by an arrangement 5 of electromagnetic coils 6. As a variant, one could also have a stator framed by two rotors. In this variant, an arrangement 5 of electromagnetic coils is framed on either side by a set of superconducting pellets 8.

[0016] Such a machine can operate in generator or motor mode.

[0017] In a generator operating mode, the inductor 3 creates an intense magnetic field, the superconducting pellets 8 produce the variation of this magnetic field, in other words they modulate it, and the electromagnetic coils 6, here induced, are exposed to the variable magnetic field created by the rotation of the rotor 7: an electromotive force is generated according to Faraday's law.

[0018] In a motor operating mode, the inductor 3 creates an intense magnetic field, the superconducting pellets 8 are exposed to the variable magnetic field created by the electromagnetic coils 6, here inductors, which causes them to rotate.

[0019] In a conventional electrical machine, the magnetic flux is guided by ferromagnetic materials also called magnetic core, iron, or yoke. However, these materials are heavy and tend to saturate when the induction increases.

[0020] Thus, for an electrical machine without iron or whose iron is saturated, the magnetic flux is partially guided in the air, and significant leakage fluxes appear around the electromagnetic coils, harming the performance of the electrical machine.

[0021] [Fig. 2] schematically shows electromagnetic coils 6 comprising a useful surface 10 located in the center of the winding defining the contours 11 of each electromagnetic coil 6. A useful flux passes through the useful surface and participates in the normal operation of the electrical machine 1 while the leakage flux 12 propagates near the contours 11 of the electromagnetic coils 6. The leakage flux 12 thus does not participate in the generation of the torque of the electrical machine 1 and also impairs the performance of the electrical machine 1 by generating losses within the windings that it passes through. Statement of the invention

[0022] The present invention therefore aims to overcome the aforementioned drawbacks and to reduce leakage flows in the absence of iron in an electrical machine or in the event of saturation of the iron.

[0023] The present invention relates to an electrical machine with flux barriers comprising a stator comprising an annular inductor and an armature comprising at least one arrangement of electromagnetic coils, and a rotor comprising superconducting pellets mounted radially inside the inductor, the electrical machine comprising superconducting magnetic screens in proximity to the at least one arrangement of electromagnetic coils.

[0024] The magnetic screens thus arranged make it possible to reduce leakage fluxes and increase the maximum induction value of the air gap, which results in an increase in the electromotive force of the machine of up to 30%. In addition, alternating losses, also called AC losses, can be reduced by 15%.

[0025] Advantageously, the electrical machine operates with axial flux along the axis of rotation of the rotor, the at least one arrangement of electromagnetic coils being axially positioned on one side and / or the other of the rotor, leaving an air gap between the rotor and the at least one arrangement of electromagnetic coils, the at least one arrangement of electromagnetic coils comprising electromagnetic coils oriented along the axis of rotation of the rotor and arranged in an annular shape.

[0026] In a particular embodiment, the inductor is made of superconducting material.

[0027] Advantageously, the magnetic screens are made of ReBCO, preferably of YBCO, or of BSCCO, or of MgB2.

[0028] Advantageously, the magnetic screens are produced using processes of growth of seeds or stacks of superconducting ribbons.

[0029] Advantageously, the magnetic screens are positioned in the air gap between the rotor and the at least one arrangement of electromagnetic coils, and / or such that the at least one arrangement of electromagnetic coils is positioned between the rotor and the magnetic screens.

[0030] In one embodiment, the superconducting magnetic screens follow the shape of the contours of the electromagnetic coils so that the leakage fluxes located on the contour of each electromagnetic coil are reduced.

[0031] In another embodiment, the superconducting magnetic shields are a radial film strip extending along only a portion of the electromagnetic coils.

[0032] Advantageously, the electrical machine comprises a cooling enclosure comprising a cooling fluid at less than 150 Kelvin of the at least one arrangement of electromagnetic coils with the magnetic screens.

[0033] In one embodiment, the at least one arrangement of electromagnetic coils is bonded in contact with the magnetic shields in the cooling enclosure.

[0034] The invention also relates to a cooling enclosure comprising a cooling fluid at less than 150 Kelvin, as well as an arrangement of electromagnetic coils and superconducting magnetic screens in the vicinity of the at least one arrangement of electromagnetic coils.

[0035] The invention also relates to an aircraft comprising an electrical machine as defined above and / or a cooling enclosure as defined above. Brief description of the drawings

[0036] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0037] [Fig. 1] which has already been mentioned, illustrates schematically and in exploded view an electric machine with a flux barrier according to the state of the art;

[0038] [Fig.2] which has already been mentioned, schematically illustrates electro coils magnetic of an electric machine according to the state of the art;

[0039] [Fig.3] is a schematic view of an embodiment of magnetic screens of an electrical machine according to the invention;

[0040] [Fig.4] is a schematic view of a second embodiment of ma screens genetics of an electric machine according to the invention;

[0041] [Fig.5a]

[0042] and

[0043] [Fig.5b]

[0044] and

[0045] [Fig.5c] are schematic sectional views of different embodiments and positions of magnetic screens of an electrical machine according to the invention;

[0046] [Fig.6a]

[0047] and

[0048] [Fig.6b]

[0049] and

[0050] [Fig.6c]

[0051] and

[0052] [Fig.7a]

[0053] and

[0054] [Fig.7b]

[0055] and

[0056] [Fig.7c] are schematic sectional views of different embodiments of a cooling enclosure for an electrical machine according to the invention; and

[0057] [Fig.8] is an exemplary embodiment of a cooling enclosure of a cooling enclosure of an electrical machine according to the invention. Detailed description of at least one embodiment

[0058] [Fig. 3] schematically shows a view of an embodiment of superconducting magnetic screens 13.

[0059] These superconducting magnetic screens 13 can be positioned in a superconducting electrical machine 1 with flux barriers and axial flux without magnetic core according to [Fig.l].

[0060] In the embodiment illustrated in [Fig.l], the electrical machine 1 comprises, aligned on the same axis A and inside the inductor 3, two arrangements 5 of electromagnetic coils 6 arranged on either side of the rotor 7 comprising the superconducting pellets 8. The electromagnetic coils 6 are arranged radially so that the useful flux passing through their useful surface 10 is variable depending on the position of the superconducting pellets 8 of the rotor 7. A single arrangement 5 of electromagnetic coils 6 can also be used on one side or the other of the rotor 7. Alternatively, it would also be possible to have a stator framed by one or two rotors. In this alternative, an arrangement 5 of electromagnetic coils is framed on either side by a set of superconducting pellets 8.

[0061] An air gap 15 exists between each arrangement of electromagnetic coils 6 and the rotor 7.

[0062] In addition, the magnetic screens 13 are positioned near electro coils magnetic coils 6 as illustrated in [Fig.2]. The term "in proximity" means in particular that the magnetic screens 13 may be in direct contact with the electromagnetic coils 6 or at a close distance from said coils, for example at a distance less than ten times the distance of the air gap 15, in other words the distance between the electromagnetic coils and the pellets 8 of the rotor 7.

[0063] The magnetic screens 13 illustrated in [Fig. 3] comprise a central orifice 16 and are arranged facing the electromagnetic coils 6 so that each magnetic screen 13 is placed facing an electromagnetic coil 6 and completely covers the coil 6. Each central orifice 16 of magnetic screen 13 is of a size similar to that of the useful surface 10 of each electromagnetic coil 6.

[0064] The magnetic screens 13 follow the shape of the contours 11 of the electromagnetic coils 6 by acting as a screen in front of the contours 11 so that the leakage fluxes 12 located near the contours 11 are reduced thanks to the diamagnetic response of the magnetic screens 13 to the magnetic fluxes present in the electrical machine 1.

[0065] In particular, a magnetic screen 13 is trapezoidal in shape.

[0066] [Fig. 4] shows a second embodiment of magnetic screens 13. In this variant, the magnetic screens 13 may only partially cover the electromagnetic coils 6, for example in the case where a part such as the head T of an electromagnetic coil 6 is very little exposed to the magnetic field of the inductor 3 and does not need to be covered by a magnetic screen 13. The head T is for example the part located at the radial periphery of an arrangement 5 of electromagnetic coils 6. In this case, a magnetic screen 13 may be a radial film strip extending along a single part of the electromagnetic coils 6, for example along the long sides C.

[0067] The magnetic screens 13 are for example made of ReBCO (“Rare-earth barium copper oxide”), in particular of YBCO (“Yttrium barium copper oxide”). In another embodiment, the magnetic screens 13 are made of BSCCO (“Bismuth strontium calcium copper oxide”) or even of MgB2 (“Magnesium diboride”).

[0068] In a particular embodiment, the magnetic screens 13 are produced by a seed growth process. This process consists of forming a crystal by progressively adding material to the surface of a pre-existing seed.

[0069] In another embodiment, the magnetic screens 13 are produced by stacking superconducting ribbons, this type of process allowing better mechanical strength of the magnetic screens 13.

[0070] For example, the magnetic screens 13 have a thickness of 0.5 millimeters to 1 centimeter. The thickness to be achieved for a magnetic screen 13 depends on its temperature. operating temperature as well as the amplitude of the magnetic field to which the magnetic screen 13 faces.

[0071] Diagrammatically shown in Figures 5a, 5b and 5c are portions of axial sections of the different possible positions of the magnetic screens 13 in the electrical machine 1. The magnetic screens 13 are positioned relative to the rotor 7 and to an arrangement 5 of electromagnetic coils 6. In an embodiment comprising two arrangements 5 of electromagnetic coils 6 on either side of the rotor 7 as illustrated in [Fig.l], the magnetic screens 13 will be arranged in the same way symmetrically relative to the rotor 7.

[0072] [Fig.5a] illustrates an embodiment in which the magnetic screens 13 are positioned in the air gap 15 between the rotor 7 and an arrangement 5 of electromagnetic coils 6.

[0073] [Fig.5b] illustrates another embodiment in which the magnetic shields 13 are positioned at the axial end of the electrical machine 1 so that an arrangement 5 of electromagnetic coils 6 is positioned between the rotor 7 and the magnetic shields 13.

[0074] [Fig. 5c] illustrates a final embodiment in which the magnetic screens 13 meet the conditions of FIGS. 5a and 5b. In particular, magnetic screens 13 are positioned on either side of the arrangements 5 of electromagnetic coils 6.

[0075] Superconducting materials require cooling to cryogenic temperatures to utilize the superconducting effects of the material. Cryogenic temperatures are in the order of less than 150° Kelvin. In addition, electromagnetic coils also require cooling.

[0076] However, the inductor 3, the armature represented by the electromagnetic coils 6, the superconducting pellets 8, and the magnetic screens 13 do not necessarily operate at the same temperatures. Sealing systems are therefore deployed between the different elements.

[0077] In particular, the electrical machine 1 comprises a sealed cooling enclosure 17 making it possible to contain an arrangement 5 of electromagnetic coils 6 with the magnetic screens 13 associated with the electromagnetic coils 6 to reduce the leakage fluxes 12.

[0078] Several cooling enclosures 17 are used when the electrical machine 1 comprises several arrangements 5 of electromagnetic coils 6. For example, for two arrangements 5 of electromagnetic coils 6, the electrical machine 1 comprises two cooling enclosures 17 each containing an arrangement 5 of electromagnetic coils 6 and the corresponding magnetic screens 13.

[0079] The cooling enclosure 17 comprises a cooling fluid 18 at least of 150° Kelvin. The cooling fluid 18 is for example helium, hydrogen or nitrogen.

[0080] Figures 6a, 6b and 6c schematically show different embodiments and arrangements of magnetic screens 13 and electromagnetic coils 6 in the cooling enclosure 17 in the case where the magnetic screens 13 are in the air gap 15 between the rotor 7 and the electromagnetic coils 6.

[0081] The cooling enclosure 17 comprises a support 20, a cover 21, a cooling fluid 18, electromagnetic coils 6, in particular an arrangement 5 of electromagnetic coils 6 and magnetic screens 13.

[0082] The support 20 and the cover 21 form the wall and delimit the volume of the cooling enclosure 17, the sealing of which is ensured by O-rings 22. The cooling enclosure 17 further comprises at least one fluid inlet and at least one fluid outlet allowing the cooling fluid 18 to circulate in the cooling enclosure 17 from an external source.

[0083] [Fig.6a] illustrates an embodiment in which the magnetic screens 13 are axially bonded to the electromagnetic coils 6 and in which the magnetic screens 13 are bonded to the support 20, in particular bonded in the bottom 23 of the support 20. The bonding of the magnetic screens 13 to the support 20 makes it possible in particular to stiffen the wall of the cooling enclosure 17 and thus to improve the mechanical strength of the cooling enclosure 17. Indeed, the air gap 15 of the electrical machine 1 being minimized for better performance, and the support 20 passing at the level of the air gap 15, the support 20 is quite thin, of the order of a few millimeters.

[0084] In this embodiment, the electromagnetic coils 6 are glued to the magnetic screens 13 if their operating temperature is equal to or lower than that of the magnetic screens 13. The cooling fluid 18 is therefore located between the electromagnetic coils 6 and the cover 21, at one of the axial ends of the electrical machine 1.

[0085] [Fig.6b] illustrates an embodiment in which the magnetic screens 13 are glued to the bottom 23 of the support 20, making it possible to stiffen the wall of the cooling enclosure 17 and thus improve the mechanical strength of the cooling enclosure 17. In this embodiment, the electromagnetic coils 6 are surrounded by cooling fluid 18. This embodiment is advantageous if the electromagnetic coils 6 operate at temperatures higher than those of the magnetic screens 13. The cooling fluid 18 is therefore located between the electromagnetic coils 6 and the cover 21, as well as between the electromagnetic coils 6 and the magnetic screens 13 in order to cool the magnetic screens 13.

[0086] In this embodiment, the cooling enclosure 17 comprises shims 25 so as to ensure the correct positioning of the electromagnetic coils 6.

[0087] [Fig.6c] illustrates a variant of the embodiment illustrated in [Fig.6b] in which the magnetic screens 13 are glued to the bottom 23 of the support 20, making it possible to stiffen the wall of the cooling enclosure 17 and thus improve the mechanical strength of the cooling enclosure 17. In this variant, the electromagnetic coils 6 are in contact with the cover 21, for example glued to the cover 21. The cooling fluid 18 is therefore located between the electromagnetic coils 6 and the magnetic screens 13 in order to cool the magnetic screens 13 and the electromagnetic coils 6.

[0088] In this variant, the shims 25 are not necessary if the electromagnetic coils 6 are glued to the cover 21 and the magnetic screens 13 are glued to the support 20. This variant also makes it possible to stiffen the cover 21 and to avoid losses of sealing.

[0089] Figures 7a, 7b and 7c schematically show different embodiments and arrangements of magnetic screens 13 and electromagnetic coils 6 in the cooling enclosure 17 in the case where the arrangement 5 of electromagnetic coils 6 is positioned between the rotor 7 and the magnetic screens 13.

[0090] The cooling enclosure 17 comprises a support 20, a cover 21, a cooling fluid 18, electromagnetic coils 6 and magnetic screens 13.

[0091] The support 20 and the cover 21 form the wall of the cooling enclosure 17, the sealing of which is ensured by O-rings 22.

[0092] [Fig.7a] illustrates an embodiment in which the electromagnetic coils 6 are axially glued to the bottom 23 of the support 20 and in which the magnetic screens 13 are glued to the electromagnetic coils 6. The gluing of the electromagnetic coils 6 to the support 20 makes it possible in particular to stiffen the wall of the cooling enclosure 17 and thus to improve the mechanical strength of the cooling enclosure 17. Indeed, the air gap 15 of the electrical machine 1 being minimized for better performance, and the support 20 passing at the level of the air gap 15, the support 20 is quite thin, of the order of a few millimeters.

[0093] In this embodiment, the electromagnetic coils 6 are glued to the magnetic screens 13 if their operating temperature is equal to or lower than that of the magnetic screens 13. The cooling fluid 18 is therefore located between the magnetic screens 13 and the cover 21, at one of the axial ends of the electrical machine 1.

[0094] [Fig.7b] illustrates an embodiment in which the electromagnetic coils 6 are glued to the bottom 23 of the support 20, making it possible to stiffen the wall of the cooling enclosure 17 and thus improve the mechanical strength of the cooling enclosure 17. In this embodiment, the magnetic screens 13 are surrounded by cooling fluid 18. This embodiment is advantageous if the electromagnetic coils 6 operate at temperatures higher than those of the magnetic screens 13. The cooling fluid 18 is therefore located between the magnetic screens 13 and the cover 21, as well as between the electromagnetic coils 6 and the magnetic screens 13 in order to cool the magnetic screens 13 and the electromagnetic coils 6.

[0095] In this embodiment, the cooling enclosure 17 comprises shims 25 so as to guarantee the correct positioning of the magnetic screens 13.

[0096] [Fig.7c] illustrates a variant of the embodiment illustrated in [Fig.7b] in which the electromagnetic coils 6 are glued to the bottom 23 of the support 20, making it possible to stiffen the wall of the cooling enclosure 17 and thus improve the mechanical strength of the cooling enclosure 17. In this variant, the magnetic screens 13 are in contact with the cover 21, for example glued to the cover 21. The cooling fluid 18 is therefore located between the electromagnetic coils 6 and the magnetic screens 13 in order to cool the magnetic screens 13 and the electromagnetic coils 6.

[0097] In this variant, the shims 25 are not necessary if the magnetic screens 13 are glued to the cover 21 and the electromagnetic coils 6 are glued to the support 20. This variant also makes it possible to stiffen the cover 21 and to avoid losses of sealing.

[0098] The embodiments illustrated in figures 6a, b, c and 7a, b, c are compatible when magnetic screens 13 are placed on either side of an arrangement 5 of electromagnetic coils 6 according to [Fig.5c].

[0099] [Fig. 8] shows an exemplary embodiment of a cylindrical cooling enclosure 17. This embodiment is compatible with the previous embodiments. The cooling enclosure 17 comprises a support 20 and a cover 21 which can be secured by a fixing system, for example a set of screws 26. The support 20 comprises housings 27 intended to receive electromagnetic coils 6 and magnetic screens 13. The cover 21 comprises a fluid inlet 28 and outlet 29 for circulating the cooling fluid 18 in the cooling enclosure 17 from an external source (not shown). Alternatively, the fluid inlet 28 and outlet 29 are positioned on the support 20. In a second alternative, the fluid inlet 28 and outlet 29 are positioned on the radial periphery 30 of the cooling enclosure 17.

[0100] The cooling enclosure 17 also comprises an internal anti-recirculation wall 31 positioned so that the cooling fluid 18 passes through the entire volume of the cooling enclosure 17 between the inlet 28 and the outlet 29 of the cooling enclosure 17 without exiting directly after its inlet. The wall internal 31 is for example located in the cover 21 or in the support 20.

Claims

Claims

1. Electrical machine with flux barriers comprising a stator (2) comprising an annular inductor (3) and an armature comprising at least one arrangement (5) of electromagnetic coils (6), and a rotor (7) comprising superconducting pellets (8) mounted radially inside the inductor (3), characterized in that it further comprises superconducting magnetic screens (13) in the vicinity of the at least one arrangement (5) of electromagnetic coils (6).

2. Electrical machine according to claim 1, characterized in that it operates with axial flux along the axis of rotation of the rotor, the at least one arrangement (5) of electromagnetic coils (6) being axially positioned on one side and / or the other of the rotor (7), leaving an air gap (15) between the rotor (7) and the at least one arrangement (5) of electromagnetic coils (6), the at least one arrangement (5) of electromagnetic coils (6) comprising electromagnetic coils (6) oriented along the axis of rotation of the rotor (7) and arranged in an annular shape.

3. Electrical machine according to one of claims 1 and 2, in which the inductor (3) is made of superconducting material.

4. Electrical machine according to any one of claims 1 to 3, in which the magnetic screens (13) are made of ReBCO, preferably of YBCO, or of BSCCO, or of MgB2.

5. An electrical machine according to any one of claims 1 to 4, wherein the magnetic screens (13) are made from seed growth processes or stacks of superconducting ribbons.

6. An electrical machine according to any one of claims 2 to 5, wherein the magnetic shields (13) are positioned in the air gap (15) between the rotor (7) and the at least one arrangement (5) of electromagnetic coils (6), and / or such that the at least one arrangement (5) of electromagnetic coils (6) is positioned between the rotor (7) and the magnetic shields (13).

7. An electrical machine according to any one of claims 1 to 6, wherein the superconducting magnetic screens (13) follow the shape of the contours (11) of the electromagnetic coils (6) so that the leakage fluxes (12) located on the contour (11) of each electromagnetic coil (6) are reduced.

8. An electrical machine according to any one of claims 1 to 6, wherein the superconducting magnetic screens (13) are a radial film strip extending along a single portion (C) of the electromagnetic coils (6).

9. An electrical machine according to any one of claims 1 to 8, comprising a cooling enclosure (17) comprising a cooling fluid (18) at less than 150 Kelvin of the at least one arrangement (5) of electromagnetic coils (6) with the magnetic screens (13).

10. An electrical machine according to claim 9, wherein the at least one arrangement (5) of electromagnetic coils (6) is bonded in contact with the magnetic screens (13) in the cooling enclosure (17).

11. Cooling enclosure comprising a cooling fluid (18) at less than 150 Kelvin, characterized in that it comprises an arrangement (5) of electromagnetic coils (6) and superconducting magnetic screens (13) in proximity to the at least one arrangement (5) of electromagnetic coils (6).

12. Aircraft characterized in that it comprises an electrical machine according to any one of claims 1 to 10 and / or a cooling enclosure (17) according to claim 11.

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