Electrical machine having a segmented stator or rotor

Field of invention

The present invention relates to an electrical machine having a stator or a rotor with a segmented geometry, i.e. a stator or a rotor including a plurality of stator segments circum ferentially joined together.

Art Background

In large electrical machines, segmentation of the stator and/or the rotor structure is required to ease manufacturing and transportation. This is particularly required for stators or rotors where a winding is provided. The integral slot dis tributed winding and fractional slot concentrated winding are two options to realize a stator or rotor structure. The inte gral slot distributed winding suffers from large torque rip ple and the fractional slot distributed winding suffers from large rotor eddy current loss. With the purpose of achieving small torque ripple and rotor loss simultaneously, the frac tional slot machine with 2-slot-pitch winding may be a poten tial solution. However, due to the overlapping winding struc ture, the stator of the conventional 2-slot-pitch winding cannot be segmented, which prevents its application in large electrical machines.

Summary of the invention

Scope of the present invention is to provide a new segment design, for achieving the advantages above described, i.e. a segmented structure with smaller torque ripple and rotor loss in comparison with the segments designs of the prior art. This scope is met by the subject matter according to the in dependent claim. Advantageous embodiments of the present in vention are described by the dependent claims.

According to the invention, it is provided a segment for the stator or the rotor of an electrical machine including a seg ment body circumferentially extending about a longitudinal axis of the stator segment between two circumferential ends. The segment body includes:

- two end teeth at the two circumferential ends respec tively, each end tooth having a first circumferential exten sion,

- a plurality of N intermediate teeth protruding accord ing to a radial direction orthogonal to the longitudinal axis from a yoke of the segment body to respective tooth radial ends, the plurality of intermediate teeth being circumferen tially distributed between the two end teeth, each of the plurality N intermediate teeth having a second circumferen tial extension greater than the first circumferential exten sion, N being an integer greater than 1,

- a plurality of N+l slots circumferentially distributed between the two end teeth, each pair of circumferentially ad jacent intermediate teeth having a slot interposed there between, a slot being provided between each end tooth and a respective circumferentially adjacent intermediate tooth.

The segment further includes:

- at least one 2-pitch coil, the 2-pitch coils being in the number of N-l and extending between an i-th slot and a (i+2)-th slot, the slots being progressively counted from one to the other of the two circumferential ends, i being an in teger between 1 and N-l.

The above described segment may be advantageously integrated in a segmented stator or rotor of an electrical machine, ei- ther generator or motor. For example, the above described segment may be advantageously integrated in the stator of an electrical generator for a wind turbine.

According to the above described segment design of the pre sent invention, a spatial distribution of the magnetomotive force (MMF) may be achieved which contains very low subhar monics, which leads to extremely low rotor eddy current loss in the machine. The fractional slot design of the invention achieves a significant reduction of the torque ripple in com parison with the prior art. The end coils of each segment are physically protected by the circumferential end teeth, which makes it convenient for manufacture, transport and assembly.

According to embodiments of the invention, each slot includes a bottom portion adjacent to the yoke and a top portion radi ally opposed to the bottom portion, the at least one 2-pitch coil extends between a top portion of the i-th slot and a bottom portion of the (i+2)-th slot or between a bottom top portion of the i-th slot and a top portion of the (i+2)-th slot. This permits to achieve a double layer winding where torque ripple and rotor loss may be significantly reduced in comparison with conventional fractional slot winding schemes and conventional integral slot winding schemes.

According to embodiments of the invention, the segment fur ther includes at least one 1-pitch coil between two circum ferentially adjacent slots of said plurality of N+l slots, said at least one 1-pitch coil being adjacent to one end tooth. In particular, the at least one 1-pitch coil may ex tend between two respective top portions or two respective bottom portions of the two circumferentially adjacent slots of said plurality of N+l slots. In such embodiments each slot houses two coils according to a double layer scheme, i.e. one on the top radial portion and the other on the bottom radial portion. At the circumferential ends each slot may house one 2-pitch coil and one 1-pitch coil. Alternatively, at the cir cumferential ends each slot may house only one 2-pitch coil, at the bottom portion or at the top portion, i.e. at the cir cumferential ends each slot may be half filled, while each slot between the slots at the circumferential ends houses two 2-pitch coils.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodi ment but to which the invention is not limited.

Brief Description of the Drawing

Figure 1 shows a schematic section of a wind turbine includ ing an electrical generator with a stator geometry according to the present invention.

Figure 2 shows a cross section of an electrical generator in accordance with a first embodiment of the present invention.

Figure 3 shows a cross section of an electrical generator in accordance with a second embodiment of the present invention.

Detailed Description

The illustrations in the drawings are schematic. It is noted that in different figures, similar or identical elements are provided with the same reference signs.

Figure 1 shows a wind turbine 1 according to the invention. The wind turbine 1 comprises a tower 2, which is mounted on a non-depicted foundation. A nacelle 3 is arranged on top of the tower 2. The wind turbine 1 further comprises a wind ro tor 5 having two, three or more blades 4 (in the perspective of Figure 1 only two blades 4 are visible). The wind rotor 5 is rotatable around a rotational axis Y. When not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotational axis Y. The blades 4 extend radially with respect to the rotational axis Y. The wind turbine 1 comprises a concentrated winding electrical generator 10. The wind rotor 5 is rotationally coupled with the electrical generator 10 by means of a rotat able main shaft 9. According to other possible embodiments of the present invention (not represented in the attached fig ures), the wind rotor 5 is rotationally coupled directly with the electrical generator 10 (direct-drive generator configu ration) . A schematically depicted bearing assembly 8 is pro vided in order to hold in place the rotor 5. The rotatable main shaft 9 extends along the rotational axis Y. The perma nent magnet electrical generator 10 includes a stator 11 and a rotor 12. The rotor 12 is radially external to the stator 11 and is rotatable with respect to the stator 11 about the rotational axis Y. According to other embodiments of the pre sent invention (not shown) the rotor is radially internal to the stator. According to other possible embodiments of the present invention (not represented in the attached figures), the present invention can be applied to any electrical gener ator or motor which has concentrated winding topology, for example geared drivetrains or electrical machine of the syn chronous or asynchronous types.

According to other possible embodiments of the present inven tion (not represented in the attached figures), the present invention can be applied to any electrical generator or motor which has a fractional slot concentrated winding.

Figure 2 shows a schematic view of a cross section, orthogo nal to the rotational axis Y, of a first embodiment of the electrical generator 10 with radially internal stator 11 and the radial external rotor 12. The electrical generator 10 in cludes a circumferential air gap 19, radially interposed be tween the stator 11 and the rotor 12. The rotor 12 includes plurality of circumferentially distributed permanent magnets 33. The circumferential air gap 19 is radially interposed be tween the permanent magnets 33 and the stator 11. The stator 11 includes a plurality of circumferential segments 100 (six segments 100 in the embodiment of figure 2, each segment 100 having an angular extension about the longitudinal axis Y of 60°), which are circumferentially joined together. According to other possible embodiments of the present invention (not represented in the attached figures), the present invention and the description which follows is applied to a rotor of an electrical machine.

Each segment 100 includes a segment body 22 circumferentially extending about the longitudinal axis Y between a first cir cumferential end 23a and a second circumferential 23b. In the exemplary representation of figure 2 each segment span clock wise between the respective first circumferential end 23a and the respective a second circumferential 23b. The segment body 22 includes a yoke 13, from which a plurality of teeth 15a, 15b, 16 and a plurality of slots 17 radially protrudes. The teeth 15a, 15b, 16 and the plurality of slots 17 are circum ferentially distributed as follows.

A first end tooth 15a is provided at the first circumferen tial end 23a and a second end tooth 15b is provided at the second circumferential ends 23b. Each end tooth has a first circumferential extension or thickness tl. The plurality of circumferential segments 100 are joined together by joining together the first end tooth 15a of one segment 100 with the second end tooth 15b of another segment 100. Any means of joining may be used. A plurality of N (N=12 in the embodiment of figure 2) intermediate teeth 16 protrude according to a radial direction orthogonal to the longitudinal axis Y from the yoke 13 to respective tooth radial ends 36. The plurality of intermediate teeth 16 are circumferentially distributed between the two end teeth 15a, 15b. Each of the plurality of N intermediate teeth 16 having a second circumferential ex tension or thickness t2 greater than the first circumferen- tial extension tl. According to possible embodiment of the present invention, t2 may equal to two times of tl. A plural ity of N+l slots 17 (i.e. thirteen slots in the embodiment of figure 2) are circumferentially distributed between the two end teeth 15a, 15b. Each pair of circumferentially adjacent intermediate teeth 16 has a slot 17 interposed therebetween.

A slot 17 is also provided between each end tooth 15a, 15b and a respective circumferentially adjacent intermediate tooth 16. The segment 100 further includes plurality of N-l 2-pitch coils 30 (i.e. eleven 2-pitch coils in the embodiment of figure 2). Each 2-pitch coil 30 is wound between an i-th slot and a (i+2)-th slot, i being an integer ranging between 1 and N-l (i.e. i=l,2,...,ll in the embodiment of figure 2).

The coils 30 are wound according to a fractional slot winding scheme. Considering the slots being progressively counted from the first circumferential end 23a to the second circum ferential end 23b, a first 2-pitch coil 30 is wound between the first slot and the third slot, a second 2-pitch coil 30 is wound between the second slot and the forth slot and so on up to the eleventh 2-pitch coil 30 that is wound between the eleventh slot and the thirteen and last slot.

Each slot 17 extends radially so that it includes a bottom portion 17a adjacent to the yoke 13 and a top portion 17b ra dially opposed to the bottom portion 17a. In the embodiment of figure 2, the 2-pitch coils 30 extends between a top por tion of the i-th slot and a bottom portion of the (i+2)-th slot. According to other embodiments of the invention (not shown) the 2-pitch coils 30 extends between a bottom portion of the i-th slot and a top portion of the (i+2)-th slot. Ac cording to other embodiments of the invention (not shown) the 2-pitch coils 30 extends between a bottom portion of the i-th slot and a bottom portion of the (i+2)-th slot. According to other embodiments of the invention (not shown) the 2-pitch coils 30 extends between a top portion of the i-th slot and a top portion of the (i+2)-th slot. The above described winding is a double-layer winding, where each slot 17 may include one coil at the bottom portion 17a and one coil at the top por tion 17b.

Each segment 100 further includes a first 1-pitch coil 31 ad jacent to the first end tooth 15a and a second 1-pitch coil 31 adjacent to the second end tooth 15b. According to above considered slot counting, the first 1-pitch coil 31 is wound between the first slot and the second slot and the second slot is wound between the last ((N+l)-th) slot and the previ ous next to last (N-th) slot. In the embodiment of figure 2, the first 1-pitch coil 31 is wound between two respective bottom portions 17a of the first slot and the second slot. According to other embodiments of the invention (not shown), the first 1-pitch coil 31 is wound between two respective top portions 17b of the first slot and the second slot. The 1- pitch coil 31 may be wound between the portions of slots left free from the 2-pitch coil 30. Similarly, in the embodiment of figure 2, the second 1-pitch coil 31 is wound between two respective top portions 17b of the last ((N+l)-th) slot and the previous next to last (N-th) slot. Alternatively, the second 1-pitch coil 31 may be wound between two respective bottom portions 17a of the last ((N+l)-th) slot and the pre vious next to last (N-th) slot. In the embodiment of figure 2, each of the thirteen slots 17 includes two 2-pitch coils 30 or one 2-pitch coil 30 and one 1-pitch coil 31. Namely, the first two slots and the last two slots includes one 2- pitch coil 30 and one 1-pitch coil 31.

Compared with the conventional 2-slot-pitch winding with its tooth number equal to the total number of the intermediate teeth 16, the present invention has a greater number of the permanent magnets 33 on the rotor 12. The increased permanent magnet 33 number i may be any integer greater than 1, i.e. i may be 2,3....etc.

Figure 3 shows a schematic view of a cross section, orthogo nal to the rotational axis Y, of a second embodiment of the electrical generator 10. This second embodiment differenti- ates itself from the first one in that the stator 11 includes three circumferential segments 100, each segment 100 having an angular extension about the longitudinal axis Y of 120°, in that N= 25 and in that only 2-pitch coils 30 are wound on the teeth (no 1-pitch coils is present). Consequently, the first two slots and the last two slots includes only one 2- pitch coil 30 and are therefore only half filled.

According to other embodiments of the present invention (not shown) the stator 11 (or the rotor 12) may include any plu rality of segments 100, i.e. two or more segments.

According to other embodiments of the present invention (not shown) the number N of intermediate teeth 16 may be any inte- ger greater than 2, i.e. N may be 2,3....etc. In the smallest possible version of a segment 100, i.e. with N=2, the segment 100 includes the first end tooth 15a, the second end tooth 15b, two intermediate teeth 16, three slots 17 and one 2- pitch coil 30 extending between the first and the third (last) slot. Two 1-pitch coils respectively between the first and the second slot and between the second and the third slot may be optionally present.