Homopolar electric machine, particularly for aircraft turbomachinery

Abstract

The present invention relates, according to one aspect, to a homopolar electrical machine (10), configured to drive a rotating element (5) about an axis of rotation (X) of the electrical machine (10) or to generate electrical energy from the mechanical energy transmitted by said rotating element (5), the axis of rotation (X) of the electrical machine (10) defining an axial direction, the electrical machine (10) comprising: A stator (1) disposed about the axis of rotation (X) of the electrical machine (10), comprising a first face (6) substantially cylindrical whose axis of revolution coincides with the axis of rotation (X) of the electrical machine (10) and two second faces (7, 7') disposed in planes substantially normal to the axis of rotation (X) of the electrical machine (10), the first and second faces delimiting an internal zone of the stator about the axis of rotation (X), A rotor (2), received in the internal zone of the stator (1),and defining between the rotor (2) and each second face (7, 7') of the stator (1) an air gap (8), an excitation coil (4) of the rotor (2), fixed relative to the stator (1) and arranged around the rotor (2), the excitation coil (4) being supplied by a direct electric current, the excitation coil (4) being configured to generate a magnetic flux in the rotor (2) by magnetic induction, a stator winding (3, 3') being arranged on at least one of the second faces (7, 7'), the rotor being configured to generate a substantially unidirectional magnetic flux oriented along the axial direction in the air gap (8). Figure for the abstract: Fig. 1,

Description

Title of the invention: Homopolar electric machine, in particular for aircraft turbomachine FIELD OF THE INVENTION

[0001] The invention relates generally to the field of electrical machines, and more particularly to homopolar type machines.

[0002] It finds advantageous application in the field of aeronautics, in particular for aircraft turbomachines. STATE OF THE ART

[0003] Electrical machines allow mechanical energy to be converted into electrical energy, or vice versa. This process being reversible, an electrical machine can operate in one direction of conversion from mechanical energy to electrical energy, or in the opposite direction of conversion from electrical energy to mechanical energy.

[0004] In the field of aeronautics, we speak of a "generator" for an electrical machine operating in order to generate electrical energy from mechanical energy. Such machines make it possible in particular to generate electrical energy from the mechanical energy provided by the rotation of the shaft of a turbomachine such as a gas turbine. This makes it possible, for example, to supply electrical energy to a network operating in alternating current which supplies the so-called primary organs of an aircraft, including equipment linked to navigation, flight and propulsion controls, etc. It is known to integrate generators into a device called a "variable frequency generator" (VFG) which allows the supply of the electrical network with a variable frequency which depends on the speed of the turbomachine.

[0005] Permanent magnet electric machines (PMGs) are known, the rotor of which comprises permanent magnets generating a magnetic flux in the air gap with a stator winding arranged on the stator. These machines can achieve high mechanical torques and have the advantage of having low rotor losses. However, permanent magnets are made of rare earths, which are expensive and whose use is growing rapidly, so their cost is likely to increase sharply in the future. In addition, since the magnetization of permanent magnets is not controllable, it is difficult to de-excite such an electric machine, which is problematic in the event of a failure of the turbomachine. Finally, this type of electric machine cannot exceed a certain rotational speed, beyond which there is a risk of damaging the magnets. permanent rotor.

[0006] Another type of electrical machine known from the state of the art is the brush machine. In this type of machine, graphite brushes allow the transmission of a current to the rotor, formed by an electromagnet. The maintenance cost of such machines is high due to the wear of the brushes. In addition, the rotation speeds achieved by these machines are not satisfactory for aeronautical applications.

[0007] More recently, a solution has been proposed in the aeronautical field, namely a so-called "three-stage" generator topology. For an example of an application of this type of generator, one can advantageously refer to patent application WO2019 / 229390. This type of generator has a main stage where most of the electromechanical conversion takes place, an excitation stage where a brushless and ringless excitation system (in English brushless) comprising an excitation coil powered by direct current allows the excitation of the rotor, and a permanent magnet stage (PMG stage), which generates the electrical energy necessary for the coil of the excitation system. This topology has several advantages: self-powering - the excitation stage being powered by the PMG stage; simple regulation and ease of de-excitation in the event of a fault.Furthermore, three-stage generators are commonly used in the aeronautical field and represent a proven topology, with predictable behavior.

[0008] However, three-stage generators are bulky and represent a significant portion of the on-board mass of the turbomachine, which is in itself a major drawback due to the increase in specific fuel consumption that this can cause. In addition, this significant weight limits the angular speed that the generator can achieve, so that a reducer is necessary between the shaft of the turbomachine and the generator, adding more weight and volume to the turbomachine.

[0009] Another disadvantage of three-stage generators is their complexity. Indeed, the different stages require separate power supplies (alternating current for the main stage and the PMG stage; direct current for the excitation stage) thus requiring the use of a rectifier between the excitation and main stages, with its own weight and volume. Also, each stage - as well as the connections between them - represents an additional point of failure which can compromise the reliability of the generator and increase the maintenance costs of the turbomachine.

[0010] Patent FR 3 080 231 presents a homopolar flux electric machine comprising neither permanent magnets nor brushes. This machine has a simplified structure compared to three-stage machines. However, this machine does not allow the desired angular speeds to be reached, and in particular requires the use of an intermediate reducer between its shaft and that of the turbomachine. Statement of the invention

[0011] An aim of the present invention is to remedy the drawbacks presented above, by proposing an electrical machine capable of reaching particularly high speeds, allowing, when operating in generator mode, to provide higher electrical power than the machines known from the state of the art.

[0012] Another object of the invention is to provide an electrical machine whose structure is simplified and which has both robustness and reliability satisfactory for aeronautical applications.

[0013] Another aim of the invention is to reduce the contribution to the on-board mass, and therefore to the specific fuel consumption, of such an electrical machine used as a generator in a turbomachine.

[0014] There is thus proposed, according to a first aspect of the invention, a homopolar electrical machine, configured to drive a rotary element in rotation around an axis of rotation X of the electrical machine or to generate electrical energy from the mechanical energy transmitted by said rotary element, the axis of rotation X of the electrical machine defining an axial direction, the electrical machine comprising: A stator arranged around the axis of rotation X of the electrical machine, comprising a first substantially cylindrical face whose axis of revolution coincides with the axis of rotation X of the electrical machine and two second faces arranged along planes substantially normal to the axis of rotation X of the electrical machine, the first and second faces delimiting an interior zone of the stator around the axis of rotation X, A rotor, received in the interior zone of the stator, and defining an air gap between the rotor and each second face of the stator, A rotor excitation coil, fixed relative to the stator and arranged around the rotor, the excitation coil being powered by a direct electric current, the excitation coil being configured to generate a magnetic flux in the rotor by magnetic induction, a stator winding being arranged on at least one of the second faces, the rotor being configured to generate a substantially unidirectional magnetic flux oriented in the axial direction in the air gap.

[0015] According to one embodiment, the second face on which the stator winding is arranged comprises teeth and notches, the stator winding being wound around at least one tooth passing through at least one notch.

[0016] According to one embodiment, two separate stator windings are arranged respectively on each of the second faces.

[0017] According to one embodiment, the electrical machine further comprises a cooling system configured to cool the excitation coil.

[0018] According to one embodiment, the rotor comprises at least two North poles and two South poles, the North poles and the South poles projecting from an intermediate part of the rotor in the axial direction.

[0019] Another aspect of the invention relates to a turbomachine comprising an electrical machine as defined above, the rotary element being a shaft of the turbomachine, the electrical machine being mechanically connected to the rotary element so as to be able to convert mechanical energy supplied by the rotation of the rotary element into electrical energy.

[0020] Another aspect of the invention relates to an aircraft comprising a turbomachine as defined in the preceding paragraph.

[0021] Another aspect of the invention relates to a method of using in generator mode an electrical machine as defined above, comprising the excitation of the rotor by the excitation coil so as to polarize it, and the transmission to the rotor of a mechanical torque by the rotating element so as to cause the rotor to rotate, then the magnetic induction of at least one of the stator windings by the polarized rotor.

[0022] According to one implementation, the method comprises: • in nominal operation of the electrical machine, an electromagnetic induction of the two stator windings by the rotor, • in degraded operation of the electrical machine, electromagnetic induction of only one of the two stator windings by the rotor.

[0023] According to one implementation, the method comprises electromagnetic induction of the two stator windings, such that the magnetic field generated by one of the two stator windings attenuates space harmonics of the magnetic field generated by the other of the two stator windings.

[0024] Thus, the proposed electrical machine does not comprise any sensitive rotating parts and has a rotor topology that is symmetrical along a plane orthogonal to the axial direction. It can therefore achieve higher rotational speeds than the machines of the prior art, and generate more electrical power when used in generator mode, while being lighter and more compact than the multi-stage machines used as generators for aeronautical applications. In addition, when connected to a high-speed rotating element, the machine according to the invention makes it possible to dispense with the use of a reducer between its rotor and this rotating element.

[0025] It is hereby emphasized that the invention falls within the framework of the environmental policy- national of the Applicant, which has been working for several years now to make a strong contribution to the fight against climate change and significantly improve the environmental performance of aircraft.

[0026] The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-consuming, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0027] Its ongoing research and development work focuses on new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels. DESCRIPTION OF FIGURES

[0028] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0029] [Fig.l] schematically illustrates an electric machine according to one embodiment of the invention;

[0030] [Fig.2] schematically illustrates a coupling between an electric machine according to one embodiment of the invention and a rotating element, such as in particular a turbomachine shaft;

[0031] [Fig.3] schematically illustrates a rotor of an electric machine according to an embodiment of the invention;

[0032] [Fig.4a] illustrates the magnetic flux in a radial flux electric machine.

[0033] [Fig.4b] illustrates the magnetic flux in an axial flux electric machine according to an embodiment of the invention.

[0034] [Fig.5] schematically illustrates a turbomachine equipped with an electric machine according to one embodiment of the invention.

[0035] [Fig.6] schematically illustrates an aircraft comprising a turbomachine equipped with an electric machine according to one embodiment of the invention.

[0036] [Fig.7] illustrates an implementation of a method for using an electrical machine in generator mode according to an embodiment of the invention.

[0037] Throughout the figures, similar elements bear identical references.

[0038] DETAILED DESCRIPTION OF EMBODIMENTS AND IMPLEMENTATION OF THE INVENTION

[0039] With reference to [Fig.l], there is shown an electrical machine 10 comprising, conventional manner, a stator 1 and a rotor 2. The machine 10 is arranged around a main axis X defining an axial direction, and along which a shaft 15 of the rotor 2 extends. A radial direction is further defined as being any direction perpendicular to the axial direction and passing through the main axis X, and an orthoradial or circumferential direction as being a direction perpendicular to a radial direction and not passing through the main axis X. In operation of the machine 10, the stator 1 remains fixed while the rotor 2 rotates around the main axis X. As illustrated in [Fig.2], the electrical machine 10 is connected directly or indirectly via its shaft 15 to a rotating element 5, which may in particular be a shaft of a turbomachine 23.When the electrical machine 10 operates in generator mode, the rotor 2 is driven by its shaft 15, itself driven in rotation by a movement of the rotating element 5, and generates from this mechanical energy an electrical energy, a current being induced in a stator winding 3, 3' which is electromagnetically induced by the moving rotor 2. On the other hand, when the electrical machine 10 operates in motor mode, a current is imparted to the stator winding 3, 3' and allows the induction of the rotor 2, causing it to start rotating and thus generating, via the shaft 15 of the rotor, a mechanical energy in the rotating element 5.

[0040] The stator 1 comprises a first face 6 of cylindrical shape, having the main axis X as its axis of revolution. The stator 1 further comprises two second faces 7, 7' on either side of the first face 6 in the axial direction, each second face comprising a ring 16, 16', arranged directly in the axial extension of the first face 6, as well as a plurality of teeth 9 extending radially from the ring 16, 16' in the direction of the main axis X and separated from each other by notches 11. The first and second faces 6, 7, 7' define between them an inner zone of the stator 1 in which the rotor 2 is received so as to be able to rotate around the shaft 15, that is to say that a spacing exists between the rotor 2 and an inner side of the faces 6, 7, 7' of the stator 1.

[0041] In a circumferential spacing arranged between the rotor 2 and the inner side of the first face 6 of the stator 1 is arranged an excitation coil 4, fixed relative to the stator 1 and having a radial spacing with the rotor 2, so as to allow the rotation of the latter around the main axis X. The excitation coil 4 has an annular shape and is formed of a wound conductive wire. It is powered by a direct current generator, the value of which can be adjustable. The excitation coil 4 allows, when the machine 10 is operating in motor mode, the magnetic polarization of the rotor 2. A magnetic flux is generated in the rotor, as shown in broken arrows in [Fig. 3]. The rotor 2 is divided into two halves by a radial plane P. An outer part 26 of the first half of the rotor 2, that is to say arranged at the opposite of the first half with respect to the radial plane P, behaves as North magnetic poles while an external part 27 of the second half of the rotor 2 behaves as South magnetic poles. The rotor is therefore homopolar, all the poles arranged on a respective side of the radial plane P having the same polarity which does not vary over time.

[0042] According to one embodiment, the electrical machine 10 comprises a cooling system, configured to cool the excitation coil 4.

[0043] The length of the teeth 9 of the second faces 7, 7' of the stator is chosen so as to allow the excitation coil 4 to be housed in the inner zone of the stator 1, the stator windings 3, 3' as well as current leads connected to said windings. Furthermore, the teeth 9 must be long enough to allow the passage of a sufficient magnetic flux relative to the mechanical torque of the machine 10, without magnetic saturation occurring in the stator 1. Finally, the teeth 9 create a thermal interface between the excitation coil 4 and the rest of the machine 10, so that their length must be limited so as not to exceed the capacity of the cooling system. The length of the teeth 9 must also be limited so as not to induce excessive iron losses.

[0044] The rotor 2 is made up of a single solid piece.

[0045] According to one embodiment, illustrated by [Fig. 3], each external part 26, 27 has a crenellated shape, so that the rotor 2 comprises at least two North poles 12 and two South poles 13 projecting in the axial direction, the poles being formed respectively by the crenellations of the external parts 26 and 27. The rotor also has an intermediate part 14, arranged between the North poles 12 and the South poles 13, the excitation coil 4 extending at the same level as the intermediate part 14 in the axial direction. This prevents the excitation coil 4 itself from being affected by the polarization that it creates in the rotor 2, during the rotation of the North 12 and South 13 poles. The rotor has symmetry along the radial plane P. Here, "symmetry" means that the North and South poles have the same dimensions, and that the parts located on either side of the radial plane P have the same circumference.The North 12 and South 13 poles are not, however, necessarily located opposite each other along the radial plane P.

[0046] The use of an excitation coil 4 makes it possible to dispense with the use of permanent magnets, the rotor being polarized by the excitation coil 4. This characteristic of the machine 10, in combination with the monobloc and symmetrical nature of the rotor 2 as described above, means that said machine 10 has no sensitive rotating parts. The rotor 2 can therefore reach high rotation speeds, higher than electrical machines according to the state of the art, and similar to that of a turbomachine shaft in operation. Also, during a function operation of the machine 10 in generator mode, the rotor 2 can withstand mechanical torques transmitted by its shaft 15 higher than electrical machines according to the state of the art. In addition, the excitation coil 4 also makes it possible to de-excite the rotor - for example in the event of a fire starting in the machine 10 caused in particular by a short circuit in the stator winding 3, 3', by cutting off the power supply to the coil, which is impossible in the case of a rotor with permanent magnets. This results in an electrical machine with increased operational safety.

[0047] The second faces 7, 7' of the stator 1 are configured to individually accommodate a stator winding 3, 3'. The stator windings 3, 3' are wound around the teeth 9 passing through the notches 11 arranged between them. It may be provided that a single winding is arranged on a second face 7, 7' of the stator 1, or that each second face 7, 7' accommodates a winding 3, 3' respectively. The poles 12, 13 of the rotor and the stator winding 3, 3' define between them an air gap 8, which varies according to the circumferential position of the projecting poles 12, 13 over time. Thus, with reference to [Fig. 4a], in radial flux machines, such as that presented in patent FR 3 080 231, the air gap 8 between the rotor and the stator winding is arranged in the axial direction and has a cylindrical shape, whereas, with reference to [Fig.4b], the axial flux electrical machine 10 has an air gap 8 between the rotor and each second face 7, 7' on which is arranged a stator winding 3, 3' which has a discoid shape and which is included in a plane orthogonal to the axial direction. It is thus possible to increase the surface area of ​​the air gap 8 without however increasing the length of the axial flux machine 10, and therefore, for an equal machine diameter, generate the same electromagnetic torque as a radial flux machine, while having a reduced machine length - so as to reduce the mass and size of the machine 10.

[0048] The electrical machine 10 has, at its air gap 8, a substantially unidirectional axial magnetic flux path, whereas transverse flux machines have a three-dimensional magnetic flux, and therefore a more complex and more unpredictable operation.

[0049] In the salient pole embodiment, the teeth 9 of the stator 1 are subjected to a magnetic field which varies as a function of time. This variable magnetic field depends on the circumference of the rotor over which the poles extend, or, equivalently, on the circumference of the portions of the rotor not comprising salient poles. Thus, by varying the number of poles and their circumferential dimension, it is possible to modify the magnetic field seen by the teeth 9, as well as modify the magnetic saturation of the teeth. This also makes it possible, when necessary, to act on the space harmonics of the electrical machine 10. The thickness of the poles e, defined as their dimension in the axial direction, has no direct impact on the voltage induced in the rotor 2, but has an effect on the performance of the electrical machine 10: increasing this thickness limits magnetic leakage by channeling the flux, so that a greater proportion of the magnetic flux is effectively used for the induction of the stator winding 3, 3' or of the rotor 2, but also has the consequence of increasing the iron losses in the rotor. Finally, increasing the thickness e of the poles of the rotor 2 can influence the efficiency of the cooling system, an increase in the thickness e of the poles allowing a distance between the intermediate part 14 and the second faces 7, 7' of the stator, thus allowing better cooling of the electrical machine 10.

[0050] The electrical machine 10 may be manufactured according to methods known to those skilled in the art. With regard to the stator 1, it may in particular be manufactured by stacking magnetic sheets, by injecting iron powder or by machining a solid magnetic material. Other methods suitable for the manufacture of stators of electrical machines may be used.

[0051] The rotary element 5 may in particular be a shaft of a turbomachine to which the shaft 15 of the rotor 2 is mechanically connected. The electrical machine 10 used in generator mode can then convert mechanical energy provided by the rotation of the turbomachine shaft into electrical energy. The shaft 15 of the rotor 2 may be directly connected to the shaft 5 of the turbomachine, so as to have the same rotation speed as the latter. Alternatively, a reducer may be arranged between the shaft 15 of the rotor 2 and the shaft 5 of the turbomachine, thus allowing the shaft 15 of the rotor to rotate less quickly than that of the shaft 5 of the turbomachine. The fact of being able to do without a reducer is a direct consequence of the symmetrical shape of the rotor 2 as well as the absence of permanent magnets to polarize the rotor 2, which allow the rotation of the rotor 2 at speeds similar to that of a turbomachine shaft in operation.The absence of a reducer makes it possible to give the electric machine 10 a lower mass and volume.

[0052] [Fig. 5] shows a turbomachine 23 which may comprise a fan section 19, and comprising a compression section 20, a combustion section 21 and a turbine section 22. The turbomachine 23 further comprises an electrical machine of the type of the electrical machine 10 which has just been described. The rotating element 5 is a shaft of said turbomachine, the shaft 15 of the electrical machine 10 being mechanically connected to the rotating element 5 so as to be able to convert mechanical energy supplied by the rotation of the rotating element 5 into electrical energy.

[0053] [Fig.6] represents an aircraft 24 comprising such a turbomachine 23.

[0054] A method of using 100, in generator mode, the electric machine 10 is described below.

[0055] The method, illustrated in [Fig.7], comprises the magnetic excitation 101 of the rotor 2 so as to polarize it by the excitation coil 4 and the transmission 102 to the rotor 2 of a mechanical torque by the rotary element 5, so as to cause the rotor 2 to rotate, then the magnetic induction 103 of one or both stator winding(s) 3, 3' by the polarized rotor 2.

[0056] Having two separate stator windings 3, 3' makes it possible to provide several separate operating modes for the electrical machine 10. Indeed, the distance between the two windings, separated by the rotor 2 as well as by the air gap 8 on each side of the rotor 2, allows complete magnetic segregation of the two stator windings 3, 3'. According to a first implementation, only one of the second faces 7, 7' of the stator accommodates a stator winding 3, 3'. According to a second implementation, each second face 7, 7' accommodates a respective stator winding 3, 3', and the method can comprise either the electromagnetic induction of the two windings 3, 3' in a so-called "nominal" operating mode of the electrical machine 10, or the induction of only one of the two windings 3, 3' in a so-called "degraded" operating mode of the electrical machine 10.Thus, the electrical machine is capable of operating even when one of the two stator windings 3, 3' is not operating. A third operating mode may also be provided, in which the two stator windings 3, 3' are induced with different electric currents, one of the two stator windings being induced with the same current intensity as that corresponding to the nominal operating mode, the other stator winding being induced with a reduced current intensity.

[0057] According to an alternative implementation of the method, the two stator windings 3, 3' are electromagnetically induced by the rotor 2, so that the power supply on one of the two windings is configured to generate a magnetic field which allows the attenuation of space harmonics of the magnetic field generated by the other of the two stator windings 3, 3'.

Claims

Claims

1. Homopolar electrical machine (10), configured to rotate a rotary element (5) around an axis of rotation (X) of the electrical machine (10) or to generate electrical energy from the mechanical energy transmitted by said rotary element (5), the axis of rotation (X) of the electrical machine (10) defining an axial direction, the electrical machine (10) comprising: - A stator (1) arranged around the axis of rotation (X) of the electrical machine (10), comprising a first substantially cylindrical face (6) whose axis of revolution coincides with the axis of rotation (X) of the electrical machine (10) and two second faces (7, 7') arranged along planes substantially normal to the axis of rotation (X) of the electrical machine (10), the first and second faces delimiting an inner zone of the stator around the axis of rotation (X), - A rotor (2), received in the inner zone of the stator (1),and defining between the rotor (2) and each second face (7, 7') of the stator (1) an air gap (8), - An excitation coil (4) of the rotor (2), fixed relative to the stator (1) and arranged around the rotor (2), the excitation coil (4) being powered by a direct electric current, the excitation coil (4) being configured to generate a magnetic flux in the rotor (2) by magnetic induction, characterized in that a stator winding (3, 3') is arranged on at least one of the second faces (7, 7'), the rotor being configured to generate a substantially unidirectional magnetic flux oriented in the axial direction in the air gap (8).,

2. Electrical machine according to claim 1, the second face (7, 7') on which the stator winding (3, 3') is arranged comprising teeth (9) and notches (11), the stator winding (3, 3') being wound around at least one tooth (9) passing through at least one notch (11).

3. Electrical machine according to any one of the preceding claims, two separate stator windings (3, 3') being arranged respectively on each of the second faces (7, 7').

4. An electrical machine according to any preceding claim, further comprising a cooling system configured to cool the excitation coil (4).

5. An electrical machine according to any one of claims 1 to 4, the rotor (2) comprising at least two North poles (12) and two South poles (13), the North poles and the South poles projecting from an intermediate portion (14) of the rotor (2) in the axial direction.

6. A turbomachine (23) comprising an electrical machine (10) according to any one of claims 1 to 5, the rotating element (5) being a shaft of the turbomachine, the electrical machine being mechanically connected to the rotating element (5) so as to be able to convert mechanical energy supplied by the rotation of the rotating element (5) into electrical energy.

7.

8. Aircraft (24) comprising a turbomachine according to claim 6. Method of using in generator mode an electric machine according to one of claims 1 to 5, comprising the excitation of the rotor (2) by the excitation coil (4) so ​​as to polarize it, and the transmission to the rotor (2) of a mechanical torque by the rotating element (5) so as to cause the rotor (2) to rotate, then the magnetic induction of at least one of the stator windings (3, 3') by the polarized rotor (2).

9. Method of using an electrical machine according to claim 8, comprising: • in nominal operation of the electrical machine, an electromagnetic induction of the two stator windings (3, 3') by the rotor (2), • in degraded operation of the electrical machine, an electromagnetic induction of only one of the two stator windings (3, 3') by the rotor (2).

10. A method of using an electrical machine according to claim 9, comprising electromagnetic induction of the two stator windings (3, 3'), such that the magnetic field generated by one of the two stator windings (3, 3') attenuates space harmonics of the magnetic field generated by the other of the two stator windings (3, 3').

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