Annular stator of an electrical machine and associated electrical machine

Abstract

Annular stator of an electrical machine and associated electrical machine. An annular stator (10, 10', 10'') of an electrical machine comprising an annular base (11), teeth (12) and slots (13), each slot (13) having a radial inlet opening (14) extending between a first axial end (102) and a second axial end (104) of the stator (10, 10', 10'') and having an inlet opening width (Li, L102, L104) measured along the circumferential direction (DC) between the second radial ends (124) of the two adjacent teeth (12) delimiting the slot (13), the width (Li, L102, L104) of the inlet opening (14) varying along the axial direction (DA), at least one width (Li) of the inlet opening (14) measured at a different location from the first and second axial ends (102, 104) of the stator (10, 10', 10'') being smaller than the widths (L102,L104) of inlet opening (14) measured at the first axial end (102) and at the second axial end (104) of the stator (10, 10', 10''). Figure for the abbreviation: Fig. 4,

Description

Title of the invention: Annular stator of an electrical machine and associated electrical machine Technical field

[0001] The field of the invention is that of electrical machines, and refers more particularly to electrical machines with an annular stator adapted to reduce mechanical torque ripples and the detent torque at the output of the electrical machine. Prior art

[0002] Permanent magnet AC electric machines have a variety of applications, such as wind turbine generators, electric vehicle motors, household appliances, pumps and compressors, and general drives.

[0003] Unless special design or control techniques are used, these machines tend to have high levels of hang-up torque, or cogging torque, and torque ripple, which leads to the generation of acoustic vibrations and noise.

[0004] Cogging torque is the torque due to the interaction between the permanent magnets of the rotor and the slots of the stator of a permanent magnet machine. It is also known as detent torque or current-free torque. This torque depends on the position of the rotor and its periodicity per revolution depends on the number of magnetic poles and the number of stator teeth. Cogging torque is an undesirable component for the operation of such an electric machine motor. It is particularly noticeable at low speeds, with jerking symptoms. Cogging torque generates ripple torque as well as speed ripple. However, at high speeds, the moment of inertia of the motor filters out the effect of cogging torque.

[0005] Cogging torque occurs in the unpowered state of a conventional motor when the attraction between the rotor's permanent magnets and the steel teeth of the stator laminations creates a "jumping" motion during rotation.

[0006] Torque ripple occurs in the energized state of a motor. This phenomenon is due to variations in electromagnetic fields during the interaction between the rotor and the stator.

[0007] Conventional motors, sometimes called slotted motors, have laminations that are stacked on top of each other forming a lamination pack, with copper windings inserted into these slots. The part of the stator closest to the rotor is called the tooth. It focuses the electromagnetic flux towards the rotor magnets, thus concentrating the energy better than a slotless design.

[0008] Compared to a slotless motor, conventional motors offer a good balance between output torque, motor constant, efficiency, and manufacturability. For their size, conventional brushless motors have a high motor constant with high efficiency and high acceleration speeds with low inertia. This allows a conventional motor to have less armature reaction at high current, less torque ripple, and higher continuous torque at low speeds.

[0009] Conventional motors with a high number of poles can be problematic in some respects. They are generally less efficient and have lower torque at high speeds. But the biggest problem with conventional motors is the presence of cogging torque.

[0010] Conventional motors, with their higher torque per volume, efficiency and output, are better suited to low-speed systems. They are also distinguished by their manufacturability. It is known to adjust the number of slots and the number of poles to minimize cogging torque.

[0011] There are several other design options and measures to minimize the impact of cogging torque. They can reduce motor efficiency, but depending on the system design, they may not be necessary: ​​pole spacing (magnet width), magnet shaping, slot opening and tooth tip design, magnet assembly tilt.

[0012] In systems requiring smooth operation, high acceleration speeds, and high constant torque, conventional brushless motors remain the first choice. When the load is light, a slotless motor can be a good alternative. However, they do not have all the performance required for aggressive, higher-torque applications. Conventional brushless motors can produce higher peak torque, while slotless motors do not perform as well in these medium- to high-torque applications.

[0013] Many studies published in the literature attempt to minimize cogging torque and torque ripple in permanent magnet machines. The main techniques used for this purpose rely on adjustments in the electronic control of the machine or on design techniques modifying the geometry of a conventional electric machine.

[0014] Regarding the techniques based on the mechanical design of the electrical machine, these can be generically classified between modifications made to the stator topology, modifications made to the air gap topology and modifications made to the rotor topology.

[0015] [Fig. 1] schematically presents a perspective view of an example of an annular stator 1 according to the state of the art, the annular stator 1 defining an axial direction DA, a radial direction DR, and a circumferential direction Dc. [Fig. 2] shows a portion of another example of an annular stator according to the state of the art, and [Fig. 3] presents a sectional view of [Fig. 2] along a section plane orthogonal to the axial direction DA of the annular stator 1.

[0016] As illustrated in Figures 1 and 2, the annular stator 1 comprises an annular base 2 from which teeth 3 project radially having a first radial end 4 secured to the annular base 2 of the stator 1 and a second radial end 5 which is free. The stator 1 also comprises notches 6 each formed by the space separating two adjacent teeth 3 and an inlet opening 7 of notch 6, the inlet opening 7 of notch 6 being defined by the space, in the circumferential direction Dc, separating the second ends 5 of two adjacent teeth 3.

[0017] Usually, the way to manufacture the stator of an AC electric machine is to punch or cut by another mechanism (e.g. laser) a rolled sheet which is then stacked and joined or stiffened by a process of welding, stapling, gluing, pressing, etc. In the typical forming procedure, the notch, corner and notch opening regions are obtained from the same operation. Statement of the invention

[0018] The invention aims to propose an architecture and a design of an electric machine making it possible to combine the best compromise between the ripple torque and the cogging torque, with a simple implementation process in terms of manufacturing and assembly.

[0019] This object is achieved by means of an annular stator of an electrical machine, the stator comprising an annular base, teeth and notches. The annular base defines an axial direction, a radial direction and a circumferential direction. Each of the teeth extends radially projecting from the annular base between a first radial end secured to the annular base and a second radial end which is free. Each notch extends in the circumferential direction between two adjacent teeth and has a radial inlet opening extending axially between a first axial end of the stator and a second axial end of the stator and has an inlet opening width measured in the circumferential direction between the second radial ends of the two adjacent teeth delimiting the notch.

[0020] According to a general characteristic of the invention, the entry opening width of each notch varies along the axial direction, at least one opening width inlet width measured at a location different from the first and second axial ends of the stator being smaller than the inlet opening widths measured at the first axial end and the second axial end of the stator.

[0021] This solution allows a significant reduction in cogging torque and ripple torque with the advantage of keeping a simple winding, which is simpler than alternative solutions with a slot tilt.

[0022] Modifying the opening of the stator slots in the axial direction of the electric machine so that the variation in the width of the input opening does not follow a straight curve, makes it possible to minimize both the cogging torque and the torque ripple.

[0023] This technique aims to modify the torque waveforms of the machine both when no current flows through the stator (no-load operation) and when the machine operates with currents flowing in the stator (load operation).

[0024] The proposed technique has the secondary objective of facilitating the winding of the machine compared to other cogging reduction techniques consisting of modifying the stator, such as: offset slot openings, dissimilar slot openings or slots along the periphery of the stator, etc.

[0025] Preferably, the variation of the width of the inlet opening of each notch along the axial direction is non-linear.

[0026] In a first embodiment of the stator according to the invention, the smallest width of the inlet opening of each notch is measured in the middle of the axial length of the stator.

[0027] In a second embodiment of the stator according to the invention, the variation in the width of the inlet opening of each notch along the axial direction may be discontinuous, with at least three notch portions with different widths.

[0028] In a third embodiment of the stator according to the invention, the variation of the width of the inlet opening of each notch along the axial direction can be continuous.

[0029] In a fourth embodiment of the stator according to the invention, the teeth can extend radially outwards to form an internal stator.

[0030] In one variant, the teeth may extend radially inward to form an outer stator.

[0031] In another aspect, there is provided an electrical machine comprising an annular stator as defined above.

[0032] Preferably, the electric machine is a linear electric machine with permanent magnets. Brief description of the drawings

[0033] [Fig.l] [Fig.l], already described, schematically illustrates a perspective view of an example of an annular stator according to the state of the art.

[0034] [Fig.2] [Fig.2], already described, illustrates a portion of another example of stator annular according to the state of the art.

[0035] [Fig.3] [Fig.3], already described, shows a sectional view of [Fig.2] according to a plane cut orthogonal to the axial direction of the annular stator.

[0036] [Fig.4] [Fig.4] illustrates a perspective view of a stator of a machine electric according to a first embodiment of the invention.

[0037] [Fig.5] [Fig.5] illustrates a perspective view of said stator according to a second embodiment of the invention.

[0038] [Fig.6] [Fig.6] illustrates a sectional view of two notches in the stator of [Fig.4] or [Fig.5].

[0039] [Fig.7] [Fig.7] illustrates a perspective view of said stator according to a third embodiment of the invention. Description of the embodiments

[0040] In [Fig.4] is schematically illustrated a perspective view of a stator 10 of an electrical machine according to a first embodiment of the invention.

[0041] The annular-shaped stator 10 comprises an annular base 11, teeth 12 and notches 13. The annular base 11 defines an axial direction DA, a radial direction Dr and a circumferential direction Dc. The stator 10 extends axially between a first axial end 102 and a second axial end 104.

[0042] Along the axial direction DA, each tooth 12 extends parallel to the axial direction DA between the first axial end 102 of the stator 10 and the second axial end 104 of the stator 10.

[0043] In the radial direction DR, each tooth 12 projects outwardly from the annular base 11. The stator 10 thus forms an internal stator. In the radial direction DR, each tooth 12 of the stator 10 has a first radial end 122 which is integral with the annular base 11 and a second radial end 124 which is free.

[0044] Each notch 13 is formed by the free space separating two adjacent teeth 12 in the circumferential direction Dc. Each notch 13 thus extends in the axial direction DA between the first axial end 102 of the stator 10 and the second axial end 104 of the stator 10. Each notch 13 further comprises a radial inlet opening 14 formed between the second radial ends 124 of the two adjacent teeth 12 delimiting the notch 13. In the radial direction DR, each notch 13 thus extends between the annular base 11 and its inlet opening 14.

[0045] Each inlet opening 14 extends axially between the first axial end 102 of the stator 10 and the second axial end 104 of the stator 10.

[0046] The inlet opening 14 of each notch has a width which is measured in the circumferential direction Dc between the second radial ends 124 of the two adjacent teeth 12 delimiting the notch 13. This width is denoted L in FIGS. 4 to 7 and it varies along the axial direction DA. In the figures, to differentiate the different values ​​of width L of the inlet opening 14, an index is added to the reference L. Thus, in [Fig. 4], we have the reference L102 which corresponds to the width of the inlet opening 14 measured at the first axial end 102 of the stator 10, the reference L104 which corresponds to the width of the inlet opening 14 measured at the second axial end 104 of the stator 10, and the reference L; which corresponds to the inlet opening width 14 measured at the middle of the axial length of the stator 10,

[0047] In the first embodiment of the invention illustrated in [Fig. 4], the width L; of the inlet opening 14 axially in the middle of the stator 10 is smaller than the width L102 of the inlet opening 14 measured at the first axial end 102 of the stator 10 and than the width L104 of the inlet opening 14 measured at the second axial end 104 of the stator 10.

[0048] In the first embodiment illustrated in [Fig.4], the width L of the inlet opening 14 varies non-linearly between the first axial end 102 of the stator 10 and the second axial end 104 of the stator 10, and continuously.

[0049] In [Fig.5] is schematically illustrated a perspective view of a stator 10' of an electrical machine according to a second embodiment of the invention.

[0050] The stator 10' according to the second embodiment illustrated in [Fig.5] differs from the stator 10 of the first embodiment illustrated in [Fig.4] in that the stator 10' is an external stator with teeth 12 extending radially inwardly.

[0051] In [Fig.6] is shown schematically a sectional view of two notches 13 of a stator 10 of [Fig.4] or of the stator 10' of [Fig.5].

[0052] The section plane comprises the axial direction DA and the radial direction DR.

[0053] In [Fig.7] is schematically illustrated a perspective view of a 10” stator of an electric machine according to a third embodiment of the invention.

[0054] The stator 10” according to the third embodiment illustrated in [Fig.7] differs from the stator 10 of the first embodiment illustrated in [Fig.4] in that the width L of the inlet opening 14 of the notches 13 varies discontinuously.

[0055] In this third embodiment, each tooth 12 comprises five portions with different thicknesses. Consequently, each notch 13 comprises five portions with different widths L.

[0056] Each tooth 12 has a first axial portion 21, a second axial portion 22, a third axial portion 23, a fourth axial portion 24 and a fifth axial portion 25. The first axial portion 21 extends axially between the first axial end 102 of the stator 10” and the second axial portion 22. The second axial portion 22 extends axially between the first axial portion 21 and the third axial portion 23, the third axial portion 23 extends axially between the second axial portion 22 and the fourth axial portion 24. The fourth axial portion 24 extends axially between the third axial portion 23 and the fifth axial portion 25. And the fifth axial portion 25 extends axially between the fourth axial portion 24 and the second axial end 104 of the stator 10”.

[0057] For each tooth 12, the first axial portion 21 and the fifth axial portion 25 have the same first thickness Ei measured along the circumferential direction Dc, and the second axial portion 22 and the fourth axial portion 24 have the same second thickness E2 measured along the circumferential direction Dc. The third axial portion 23 has a third thickness E3 along the circumferential direction Dc greater than the second thickness E2 and the first thickness Eb, the second thickness E2 being greater than the first thickness Eh.

[0058] Thus, along the axial direction between the first axial end 102 of the stator 10” and the second axial end 104 of the stator 10”, each notch 13 has a first inlet opening portion 31 with a first width Lb, a second inlet opening portion 32 with a second width L2, a third inlet opening portion 33 with a third width L3, a fourth inlet opening portion 34 with a fourth width L4, and a fifth inlet opening portion with a fifth width L5. The first width Li and the fifth width L5 are equal. The second width L2 and the fourth width L4 are equal. The third width L3 is greater than the other widths Lh L2, L4 and L5., the second and fourth widths L2 and L4 are greater than the first and fifth widths Li and L5. The first width Li corresponds to the width Li02 measured at the first axial end 102 of the stator 10”.And the fifth width L5 corresponds to the width Li04 measured at the second axial end 104 of the stator 10”. Thus, the width Li02 measured at the first end 102 of the stator 10” and the width L i04 measured at the second end 104 of the stator 10” are equal.

[0059] On the other hand, the third width L3 corresponds to the width L; measured axially in the middle of the stator 10”.

Claims

Claims

1. Annular stator (10, 10', 10”) of an electrical machine, the stator (10, 10', 10”) comprising an annular base (11), teeth (12) and notches (13), the annular base (11) defining an axial direction (D a), a radial direction (DR) and a circumferential direction (Dc), each of the teeth (12) extending radially projecting from the base (11) between a first radial end (122) integral with the base (11) and a second radial end (124) which is free, each notch (13) extending in the circumferential direction (Dc) between two adjacent teeth (12) and comprising a radial inlet opening (14) extending axially between a first axial end (102) of the stator (10, 10', 10”) and a second axial end (104) of the stator (10, 10', 10”), each notch (13) having an inlet opening width (L;, L102, L104) measured along the circumferential direction (Dc) between the second radial ends (124) of the two adjacent teeth (12) delimiting the notch (13), characterized in that the width (L;, Li02, L104) of the inlet opening (14) of each notch (13) varies along the axial direction (DA), at least one width (L;) of the inlet opening (14) measured at a location different from the first and second axial ends (102, 104) of the stator (10, 10', 10”) being smaller than the widths (Li02, L104) of the inlet opening (14) measured at the first axial end (102) and at the second axial end (104) of the stator (10, 10', 10”).;

2. Annular stator (10, 10', 10”) according to claim 1, wherein the variation of the width (L;, Li02, L104) of the inlet opening (14) of each notch (13) along the axial direction (DA) is non-linear.

3. Annular stator (10, 10', 10”) according to one of claims 1 or 2, wherein the smallest width (L;) of the inlet opening (14) of each notch (13) is measured at the middle of the axial length of the stator (10, 10').

4. Annular stator (10”) according to one of claims 1 to 3, wherein the variation in the width (L;, Li02, L104) of the inlet opening (14) of each notch (13) along the axial direction (DA) is discontinuous, with at least three notch portions with different widths.

5. Annular stator (10, 10') according to one of claims 1 to 3, wherein the variation of the width (L;, L102, L104) of the inlet opening (14) of each notch (13) along the axial direction (DA) is continue.

6. Annular stator (10, 10”) according to one of claims 1 to 5, in which the teeth (12) extend radially outwards.

7. Annular stator (10') according to one of claims 1 to 5, in which the teeth (12) extend radially inwards.

8. Electrical machine comprising a stator (10) according to one of claims 1 to 7.

9. An electric machine according to claim 8, wherein the electric machine is a linear permanent magnet electric machine.

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