Patent Description:
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 distributed winding and fractional slot concentrated winding are two options to realize a stator or rotor structure. The integral slot distributed winding suffers from large torque ripple 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 fractional slot machine with <NUM>-slot-pitch winding may be a potential solution. However, due to the overlapping winding structure, the stator of the conventional <NUM>-slot-pitch winding cannot be segmented, which prevents its application in large electrical machines.

<CIT> discloses a structure for a modular motor stator and end part overlapping fractional slot windings of the modular motor stator.

<CIT> discloses:Segment for the stator or the rotor of an electrical machine including a segment body circumferentially extending about a longitudinal axis of the stator segment or rotor segment between two circumferential ends, the segment body including:.

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 independent claim.

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

The above described segment may be advantageously integrated in a segmented stator or rotor of an electrical machine, either 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 present invention, a spatial distribution of the magnetomotive force (MMF) may be achieved which contains very low subharmonics, 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 comparison 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 the invention, each slot includes a bottom portion adjacent to the yoke and a top portion radially opposed to the bottom portion, the <NUM>-pitch coils extending between a top portion of the i-th slot and a bottom portion of the (i+<NUM>)-th slot or between a bottom portion of the i-th slot and a top portion of the (i+<NUM>)-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 the invention, the segment further includes a plurality of <NUM>-pitch coils between two circumferentially adjacent slots of said plurality of N+<NUM> slots, one said <NUM>-pitch coil being adjacent to the first end tooth, a second <NUM>-pitch coil being adjacent to the second end tooth. In particular,
the at least one <NUM>-pitch coil may extend between two respective top portions or two respective bottom portions of the two circumferentially adjacent slots of said plurality of N+<NUM> 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 <NUM>-pitch coil and one <NUM>-pitch coil. Alternatively, at the circumferential ends each slot may house only one <NUM>-pitch coil, at the bottom portion or at the top portion, i.e. at the circumferential ends each slot may be half filled, while each slot between the slots at the circumferential ends houses two <NUM>-pitch.

Still further, according to the invention, the segment body includes a fractional slot winding including said <NUM>-pitch coils.

The invention will be described in more detail hereinafter with reference to examples of embodiment.

<FIG> shows a wind turbine <NUM> according to the invention. The wind turbine <NUM> comprises a tower <NUM>, which is mounted on a non-depicted foundation. A nacelle <NUM> is arranged on top of the tower <NUM>. The wind turbine <NUM> further comprises a wind rotor <NUM> having two, three or more blades <NUM> (in the perspective of <FIG> only two blades <NUM> are visible). The wind rotor <NUM> 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 <NUM> extend radially with respect to the rotational axis Y. The wind turbine <NUM> comprises a concentrated winding electrical generator <NUM>. The wind rotor <NUM> is rotationally coupled with the electrical generator <NUM> by means of a rotatable main shaft <NUM>. According to other possible embodiments of the present invention (not represented in the attached figures), the wind rotor <NUM> is rotationally coupled directly with the electrical generator <NUM> (direct-drive generator configuration). A schematically depicted bearing assembly <NUM> is provided in order to hold in place the rotor <NUM>. The rotatable main shaft <NUM> extends along the rotational axis Y. The permanent magnet electrical generator <NUM> includes a stator <NUM> and a rotor <NUM>. The rotor <NUM> is radially external to the stator <NUM> and is rotatable with respect to the stator <NUM> about the rotational axis Y. According to other embodiments of the present 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 generator or motor which has concentrated winding topology, for example geared drivetrains or electrical machine of the synchronous or asynchronous types.

According to other possible embodiments of the present invention (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.

<FIG> shows a schematic view of a cross section, orthogonal to the rotational axis Y, of a first embodiment of the electrical generator <NUM> with radially internal stator <NUM> and the radial external rotor <NUM>. The electrical generator <NUM> includes a circumferential air gap <NUM>, radially interposed between the stator <NUM> and the rotor <NUM>. The rotor <NUM> includes plurality of circumferentially distributed permanent magnets <NUM>. The circumferential air gap <NUM> is radially interposed between the permanent magnets <NUM> and the stator <NUM>. The stator <NUM> includes a plurality of circumferential segments <NUM> (six segments <NUM> in the embodiment of <FIG>, each segment <NUM> having an angular extension about the longitudinal axis Y of <NUM>°), 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 <NUM> includes a segment body <NUM> circumferentially extending about the longitudinal axis Y between a first circumferential end 23a and a second circumferential 23b. In the exemplary representation of <FIG> each segment span clockwise between the respective first circumferential end 23a and the respective a second circumferential 23b. The segment body <NUM> includes a yoke <NUM>, from which a plurality of teeth 15a, 15b, <NUM> and a plurality of slots <NUM> radially protrudes. The teeth 15a, 15b, <NUM> and the plurality of slots <NUM> are circumferentially distributed as follows.

A first end tooth 15a is provided at the first circumferential 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 t1. The plurality of circumferential segments <NUM> are joined together by joining together the first end tooth 15a of one segment <NUM> with the second end tooth 15b of another segment <NUM>. Any means of joining may be used. A plurality of N (N=<NUM> in the embodiment of <FIG>) intermediate teeth <NUM> protrude according to a radial direction orthogonal to the longitudinal axis Y from the yoke <NUM> to respective tooth radial ends <NUM>. The plurality of intermediate teeth <NUM> are circumferentially distributed between the two end teeth 15a, 15b. Each of the plurality of N intermediate teeth <NUM> having a second circumferential extension or thickness t2 greater than the first circumferential extension t1. According to possible embodiment of the present invention, t2 may equal to two times of t1. A plurality of N+<NUM> slots <NUM> (i.e. thirteen slots in the embodiment of <FIG>) are circumferentially distributed between the two end teeth 15a, 15b. Each pair of circumferentially adjacent intermediate teeth <NUM> has a slot <NUM> interposed therebetween. A slot <NUM> is also provided between each end tooth 15a, 15b and a respective circumferentially adjacent intermediate tooth <NUM>. The segment <NUM> further includes plurality of N-<NUM><NUM>-pitch coils <NUM> (i.e. eleven <NUM>-pitch coils in the embodiment of <FIG>). Each <NUM>-pitch coil <NUM> is wound between an i-th slot and a (i+<NUM>)-th slot, i being an integer ranging between <NUM> and N-<NUM> (i.e. i=<NUM>,<NUM>,. ,<NUM> in the embodiment of <FIG>). The coils <NUM> are wound according to a fractional slot winding scheme. Considering the slots being progressively counted from the first circumferential end 23a to the second circumferential end 23b, a first <NUM>-pitch coil <NUM> is wound between the first slot and the third slot, a second <NUM>-pitch coil <NUM> is wound between the second slot and the forth slot and so on up to the eleventh <NUM>-pitch coil <NUM> that is wound between the eleventh slot and the thirteenth and last slot.

Each slot <NUM> extends radially so that it includes a bottom portion 17a adjacent to the yoke <NUM> and a top portion 17b radially opposed to the bottom portion 17a. In the embodiment of <FIG>, the <NUM>-pitch coils <NUM> extends between a top portion of the i-th slot and a bottom portion of the (i+<NUM>)-th slot. According to other embodiments of the invention (not shown) the <NUM>-pitch coils <NUM> extends between a bottom portion of the i-th slot and a top portion of the (i+<NUM>)-th slot. According to other embodiments of the invention (not shown) the <NUM>-pitch coils <NUM> extends between a bottom portion of the i-th slot and a bottom portion of the (i+<NUM>)-th slot. According to other embodiments of the invention (not shown) the <NUM>-pitch coils <NUM> extends between a top portion of the i-th slot and a top portion of the (i+<NUM>)-th slot. The above described winding is a double-layer winding, where each slot <NUM> may include one coil at the bottom portion 17a and one coil at the top portion 17b.

According to the invention, each segment <NUM> further includes a first <NUM>-pitch coil <NUM> adjacent to the first end tooth 15a and a second <NUM>-pitch coil <NUM> adjacent to the second end tooth 15b. According to above considered slot counting, the first <NUM>-pitch coil <NUM> is wound between the first slot and the second slot and the second slot is wound between the last ((N+<NUM>)-th) slot and the previous next to last (N-th) slot. In the embodiment of <FIG>, the first <NUM>-pitch coil <NUM> 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 <NUM>-pitch coil <NUM> is wound between two respective top portions 17b of the first slot and the second slot. The <NUM>-pitch coil <NUM> may be wound between the portions of slots left free from the <NUM>-pitch coil <NUM>. Similarly, in the embodiment of <FIG>, the second <NUM>-pitch coil <NUM> is wound between two respective top portions 17b of the last ((N+<NUM>)-th) slot and the previous next to last (N-th) slot. Alternatively, the second <NUM>-pitch coil <NUM> may be wound between two respective bottom portions 17a of the last ((N+<NUM>)-th) slot and the previous next to last (N-th) slot. In the embodiment of <FIG>, each of the thirteen slots <NUM> includes two <NUM>-pitch coils <NUM> or one <NUM>-pitch coil <NUM> and one <NUM>-pitch coil <NUM>. Namely, the first two slots and the last two slots includes one <NUM>-pitch coil <NUM> and one <NUM>-pitch coil <NUM>. Compared with the conventional <NUM>-slot-pitch winding with its tooth number equal to the total number of the intermediate teeth <NUM>, the present invention has a greater number of the permanent magnets <NUM> on the rotor <NUM>. The increased permanent magnet <NUM> number i may be any integer greater than <NUM>, i.e. i may be <NUM>,<NUM>.

<FIG> shows a schematic view of a cross section, orthogonal to the rotational axis Y, of a second embodiment of the electrical generator <NUM>. This second embodiment differentiates itself from the first one in that the stator <NUM> includes three circumferential segments <NUM>, each segment <NUM> having an angular extension about the longitudinal axis Y of <NUM>°, in that N= <NUM> and in that only <NUM>-pitch coils <NUM> are wound on the teeth (no <NUM>-pitch coils is present). Consequently, the first two slots and the last two slots includes only one <NUM>-pitch coil <NUM> and are therefore only half filled.

Claim 1:
Segment (<NUM>) for the stator (<NUM>) or the rotor (<NUM>) of an electrical machine (<NUM>) including a segment body (<NUM>) circumferentially extending about a longitudinal axis (Y) of the stator segment or rotor segment (<NUM>) between two circumferential ends (23a, 23b), the segment body (<NUM>) including:
- two end teeth (15a, 15b) at the two circumferential ends (23a, 23b) respectively, each end tooth having a first circumferential extension (t1),
- a plurality of N intermediate teeth (<NUM>) protruding according to a radial direction orthogonal to the longitudinal axis (Y) from a yoke (<NUM>) of the segment body (<NUM>) to respective tooth radial ends (<NUM>), the plurality of intermediate teeth (<NUM>) being circumferentially distributed between the two end teeth (15a, 15b), each of the plurality of N intermediate teeth (<NUM>) having a second circumferential extension (t2) greater than the first circumferential extension (t1), N being an integer greater than <NUM>,
- a plurality of N+<NUM> slots (<NUM>) circumferentially distributed between the two end teeth (15a, 15b), each pair of circumferentially adjacent intermediate teeth (<NUM>) having a slot (<NUM>) interposed therebetween, a slot (<NUM>) being provided between each end tooth (15a, 15b) and a respective circumferentially adjacent intermediate tooth (<NUM>),
wherein the segment (<NUM>) includes:
- a plurality of <NUM>-pitch coils (<NUM>), the <NUM>-pitch coils (<NUM>) being in the number of N-<NUM> and extending between an i-th slot and a (i+<NUM>)-th slot, the slots being progressively counted from one to the other of the two circumferential ends (23a, 23b), i being an integer between <NUM> and N-<NUM>,
- a plurality of <NUM>-pitch coils (<NUM>) between two circumferentially adjacent slots (<NUM>) of said plurality of N+<NUM> slots (<NUM>), one said <NUM>-pitch coil (<NUM>) being adjacent to the first end tooth (15a), a second <NUM>-pitch coil being adjacent to the second end tooth (15b)
- a fractional slot winding (<NUM>, <NUM>) including said <NUM>-pitch coils (<NUM>) and, optionally, said <NUM>-pitch coils (<NUM>),
wherein each slot (<NUM>) includes a bottom portion (17a) adjacent to the yoke (<NUM>) and a top portion (17b) radially opposed to the bottom portion (17a), the <NUM>-pitch coils (<NUM>) extending between a top portion of the i-th slot and a bottom portion of the (i+<NUM>)-th slot or between a bottom portion of the i-th slot and a top portion of the (i+<NUM>)-th slot.