Concentrated winding layout for a stator of an electrical AC machine

Field of invention

The present invention relates to a concentrated winding lay out for a stator of an electrical AC machine. Particularly, but not exclusively the present invention may relate to a concentrated winding layout for a stator of a generator of a wind turbine. The present invention further relates to a man ufacturing method for manufacturing an electrical AC machine including a concentrated winding layout in the stator of the electrical AC machine.

Art Background

Designing poly-phase AC electric machines with a winding lay out having two or more coils per slot requires particular at tention in providing an effective electrical insulation sys tem.

Firstly, the machine stator magnet-winding shall be insulated from the stator by an insulation part, commonly annotated ground-wall or main-wall insulation. If the machine is de signed for a single-layer (i.e. one coil per slot) winding layout, then main-wall insulation is sufficient - given that the magnet wires/strands are turn-turn insulated.

If the machine is designed with two (double-layer winding layout) or more coil per slot, then it could be needed to add phase separators inside each slot to insulate each phase from one another. The dimensions, in particular the thickness, of the phase separators depends on the maximum voltage differ ence between the coils belonging to different phases, which are housed next to each other in the same slot and which need therefore to be separated by the phase separator. The above described problem is particularly relevant in poly phase AC electric machines having more than three phases. For larger machines such as some generators for offshore wind turbines, the generator windings can be split up in two three phase system (six-phase AC electric machines) , fed from two independently voltage converters each producing three-phase sinusoidal waveforms.

The two three phase systems may be typically provided in se ries to each other and electrically separated by a phase an gle of 30° or 60° (any other phase angle shift is possible) . Shifting one of the converter systems to produce angle dif ference from the two presents the opportunity to reduce torque ripple. This method also gives great flexibility in combining the winding configuration of the machine to mini mize voltage stresses.

However, in the known poly-phase AC electric machines with concentrated winding layout the voltage difference between phases housed in the same slot is not optimized. Maximum voltage difference may exceed a nominal voltage of the elec tric machine. This requires the insertion of thick phase sep arators .

Therefore, in the technical field of poly-phase AC electric machines there is still the need to reduce or eventually eliminate the voltage difference between phases housed in the same slot of the stator, thus also reducing the thickness of the phase separator or eventually eliminating the phase sepa rator .

Smaller phase separators yield to higher slot/copper fill- factors and thereby decrease winding resistance which lowers power dissipation throughout the whole stator.

Summary of the Invention

The above described need may be met by the subject matter ac cording to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims . According to a first aspect of the present invention an elec trical AC machine is provided, which comprises:

a stator having a plurality of teeth alternating with a plurality of slots in a circumferential direction,

a concentrated winding layout comprising a plurality of coils wound on the plurality of teeth and belonging to at least six phases, each slot of the plurality of slots housing at least two coils of said plurality of coils, each phase of the at least six phases comprising a first coil and a second coil, the second coil of one phase being wound in opposite direction with respect to the respective first coil of the same phase,

a plurality of interconnections connecting the first and sec ond coil of each phase, the interconnections being parallel to each other.

According to a second aspect of the present invention a meth od of manufacturing an electrical AC machine is provided, which comprises:

providing a stator having a plurality of teeth alternat ing with a plurality of slots in a circumferential direction, arranging a concentrated winding layout comprising a plurality of coils wound on the plurality of teeth and be longing to at least six phases, each slot of the plurality of slots housing at least two coils of said plurality of coils, each phase of the at least six phases comprising a first coil and a second coil, the second coil of one phase being wound in opposite direction with respect to the respective first coil of the same phase,

arranging a plurality of interconnections for connecting the first and second coil of each phase, the interconnections being parallel to each other.

In the concentrated winding layout of the present invention the interconnections have all the same length and any cross ing between conductors which constitutes the winding layout is avoided. The electrical AC machine of the present invention may be in particular a permanent magnet synchronous electrical machine. The electrical machine may be or comprise a motor or a gener ator, in particular a generator included in a wind turbine.

According to embodiments of the present invention, each of the plurality of slots extends radially from a slot top to a slot bottom, each of the interconnections extending between the slot top of one slot to the slot bottom of another slot. Each of the interconnections may extend between two respec tive slots of a first set of slots alternating in the circum ferential direction with a second set of slots, which houses coils not connected by any interconnection.

According to embodiments of the present invention, the con centrated winding layout comprises at least a first set of coils and a second set of coils, respectively corresponding to a first set of three phases and to a second set of three phases of the concentrated winding layout.

In such embodiments, each of the interconnections may extend through six respective teeth and five respective slots.

In such embodiments, the first set of coils is electrically connected in series to the second set of coils. The first set of coils and the second set of coils may electrically sepa rated by a phase angle of 30° or of 60°.

The present invention may be adapted also to a concentrated winding layout having more than six phases.

According to embodiments of the present invention, the first set of coils are wound on a respective first set of teeth and the second set of coils are wound on a respective second set of teeth alternating with the first set of teeth in the cir cumferential direction.

In particular, according to an embodiment of the present in vention, each of the first set of coils wound on the first set of teeth and each of the second set of coils wound on the second set of teeth may comprise, along the circumferential direction, the following arrangement:

- a first coil of a first phase,

- a first coil of a second phase,

- a first coil of a third phase,

- a second coil of the first phase connected to the first coil of the first phase through a first interconnection,

- a second coil of the second phase connected to the first coil of the second phase through a second interconnection,

- a second coil of the third phase connected to the first coil of the third phase through a third interconnection.

Each coil of the plurality of coils may wound on a respective tooth of the plurality teeth between a phase input or a neu tral output and one interconnection of the plurality of in terconnections .

According to embodiments of the present invention, in each of the first set of coils and of the second set of coils, the first coil of the first phase, the first coil of the second phase and the first coil of the third phase are wound in the same direction. Instead, the second coil of the first phase, the second coil of the second phase and the second coil of the third phase may be all wound in the opposite direction with respect to the first coils.

Considering the above scheme, the first set of coils and the second set of coils may be wound in opposite direction, i.e. the first coils of the first set of coils are wound in the opposite direction of the first coils of the second set of coils and the second coils of the first set of coils are wound in the opposite direction of the second coils of the second set of coils.

Embodiments of the present invention are now described with reference to the accompanying drawings. The invention is not restricted to the illustrated or described embodiments. Brief Description of the Drawings

Fig. 1 shows a schematic section of a wind turbine including an electrical AC machine according to the present invention;

Fig. 2 shows a schematic diagram of a 6-phase concentrated winding layout according to the present invention;

Fig. 3 shows a voltage vector diagram of the concentrated winding layout of Fig. 2;

Fig. 4 schematically shows a physical arrangement of the of the concentrated winding layout of Figs. 2 and 3;

Fig. 5 shows a slot of a stator of an electrical AC machine according to 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 rotor 5 having at least one blade 4 (in the embodiment of Figure 1, the wind rotor comprises three blades 4, of which only two blades 4 are visible) . The wind rotor 5 is rotatable around a rota tional axis Y.

The blades 4 extend substantially radially with respect to the rotational axis Y.

The wind turbine 1 comprises an electric generator 11, in cluding a stator 20 and a rotor 30. The rotor 30 is rotatable with respect to the stator 20 about the rotational axis Y. The wind rotor 5 is rotationally coupled with the electric generator 11 either directly, e.g. direct drive or by means of a rotatable main shaft 9 and/or through a gear box (not shown in Figure 1) . A schematically depicted bearing assembly 8 is provided in order to hold in place the main shaft 9 and the rotor 5. The rotatable main shaft 9 extends along the ro tational axis Y.

As shown in Figure 4 the stator 20 has a plurality of teeth 101, 102, 103, 104 , 105, 106, 107, 108, 109, 110, 111, 112 alternating with a plurality of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in a circumferential direction X of the stator 20, circumferentially orientated with respect to the rota tional axis Y.

Each of the plurality of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 extends along a radial direction R, i.e. orthogonally to the the rotational axis Y, from a respective slot bottom lb, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, lib, 12b to a re spective slot top la, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, 10a,

11a, 12a.

According to the present invention the electric generator 11 includes a concentrated winding layout 100 comprising a plu rality of coils 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 wound on the plurality teeth 101, 102, 103,

104, 105, 106, 107, 108, 109, 110, 111, 112 and belonging to at least six phases Al, A2, Bl, B2, Cl, C2, each slot 1, 2,

3, 4, 5, 6, 7, 8, 9, 10, 11, 12 housing at least two coils, each phase Al, A2, Bl, B2, Cl, C2 comprising a first coil 201, 202, 203, 204, 205, 206 and a second coil 207, 208, 209, 210, 211, 212, the second coil 207, 208, 209, 210, 211, 212 of one phase being wound in opposite direction with respect to the respective first coil 201, 202, 203, 204, 205, 206 of the same phase. The concentrated winding layout 100 further comprises a plurality of interconnections 301, 302, 303, 304, 305, 306 connecting the first and second coil of each phase, the interconnections 301, 302, 303, 304, 305, 306 being par allel to each other. The coils 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 and the interconnections 301, 302, 303, 304, 305,

306 carry respective insulations on the respective surfaces.

Figure 2 schematically shows for each phase Al, A2, Bl, B2, Cl, C2 the respective first coil 201, 202, 203, 204, 205, 206 and second coil 207, 208, 209, 210, 211, 212 as detailed in the following. Each interconnection 301, 302, 303, 304, 305, 306 is schematically represented by a point.

Figure 3 schematically shows the correspondent voltage vector diagram. The first set of coils 201, 203, 205, 207, 209, 211 are electrically separated from the second set of coils 202, 204, 206, 208, 210, 212 by a phase angle a of 30°.

According to other embodiments of the present invention (not shown) , the phase angle may have any other value, for exam ple 60°.

In the embodiment of the attached Figures 2 to 4, the concen trated winding layout 100 comprises a first set of coils 201,

203, 205, 207, 209, 211 and a second set of coils 202, 204, 206, 208, 210, 212, respectively corresponding to a first set of three phases Al, Bl, Cl and to a second set of three phas es A2, B2, C2. Each first set of coils 201, 203, 205, 207,

209, 211 and of the second set of coils 202, 204, 206, 208,

210, 212 correspond to a respective three-phase system. The first set of coils 201, 203, 205, 207, 209, 211 is connected through three respective interconnections 301, 302, 303. The second set of coils 202, 204, 206, 208, 210, 212 is connected through three other respective interconnections 304, 305,

306.

According to other embodiments of the present invention (not shown) , the concentrated winding layout may include a differ ent number of phases, for example more than two three-phase systems .

The first set of coils 201, 203, 205, 207, 209, 211 is elec trically connected in series to the second set of coils 202,

204, 206, 208, 210, 212. With reference to representation of the winding layout 100 in Figure 4 , the first set of coils 201, 203, 205, 207, 209, 211 are wound on a respective first set of teeth 101, 103, 105, 107, 109, 111 and the second set of coils 202, 204, 206, 208, 210, 212 are wound on a respective second set of teeth 102,

104, 106, 108, 110, 112 alternating with the first set of teeth 101, 103, 105, 107, 109, 111 in the circumferential di rection X.

The first set of coils 201, 203, 205, 207, 209, 211 compris es, along the circumferential direction X:

- a first coil 201 of a first phase Al,

- a first coil 203 of a second phase Bl,

- a first coil 205 of a third phase Cl,

- a second coil 207 of the first phase Al connected to the first coil 201 of the first phase Al through a first inter connection 301,

- a second coil 209 of the second phase Bl connected to the first coil 203 of the second phase Bl through a second inter connection 302,

- a second coil 211 of the third phase Cl connected to the first coil 205 of the third phase Cl through a third inter connection 303.

The first coils 201, 203, 205 are wound according to a first direction, while the second coils 207, 209, 211 are wound ac cording to a second direction, opposite to the first direc tion .

According to embodiments of the present invention, the first coils 201, 203, 205 are wound clockwise, while the second coils 207, 209, 211 are wound anticlockwise.

According to other embodiments of the present invention, the first coils 201, 203, 205 are wound anticlockwise, while the second coils 207, 209, 211 are wound clockwise.

More particularly:

- the first coil 201 of the first phase Al is wound in the first direction on a first tooth 101 of the first set of teeth 101, 103, 105, 107, 109, 111; - the first coil 203 of the second phase B1 is wound in the first direction on a second tooth 103 of the first set of teeth 101, 103, 105, 107, 109, 111,

- the first coil 205 of the third phase Cl is wound in the first direction on a third tooth 105 of the first set of teeth 101, 103, 105, 107, 109, 111,

- the second coil 207 of the first phase A1 is wound in the second direction on a fourth tooth 107 of the first set of teeth 101, 103, 105, 107, 109, 111,

- the second coil 209 of the second phase B1 is wound in the second direction on a fifth tooth 109 of the first set of teeth 101, 103, 105, 107, 109, 111,

- the second coil 211 of the third phase Cl is wound in the second direction on a sixth tooth 111 of the first set of teeth 101, 103, 105, 107, 109, 111.

In figure 4 the slots 1 - 12 can be identified as a series of slots oriented according to the circumferential direction X from a first slot 1 to a twelfth slot 12.

The first set of coil 201, 203, 205, 207, 209, 211 is con nected in the slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in such a way that :

- the first coil 201 of the first phase A1 is wound between an input 401 of the first phase Al, at the slot bottom lb of the first slot 1, and the first interconnection 301, at the slot top 12a of the twelfth slot 12 (the twelfth slot 12 be ing adjacent to the first slot 1 in the opposite direction with respect to the circumferential direction X) ;

- the first coil 203 of the second phase B1 is wound between the second interconnection 302, at the slot top 2a of the second slot 2, and a neutral output N, at the slot bottom 3b of the third slot 3,

- the first coil 205 of the third phase Cl is wound between the third interconnection 303, at the slot top 4a of the fourth slot 4, and an input 403 of the third phase Cl, at the slot bottom 5b of the fifth slot 5,

- the second coil 207 of the first phase Al is wound between a neutral output N, at the slot top 7a of the seventh slot 7, and the first interconnection 301, at the slot bottom 6b of the sixth slot 6,

- the second coil 209 of the second phase B1 is wound between an input 402 of the second phase Bl, at the slot top 9a of the ninth slot 9, and the second interconnection 302, at the slot bottom 8b of the eighth slot 8,

- the second coil 211 of the third phase Cl is wound between a neutral output N, at the slot top 11a of the eleventh slot 11, and the third interconnection 303, at the slot bottom 10b of the tenth slot 10.

The second set of coils 202, 204, 206, 208, 210, 212 compris es, along the circumferential direction X:

- a first coil 202 of a first phase A2,

- a first coil 204 of a second phase B2,

- a first coil 206 of a third phase C2,

- a second coil 208 of the first phase A2 connected to the first coil 202 of the first phase A2 through a fourth inter connection 304,

- a second coil 210 of the second phase B2 connected to the first coil 204 of the second phase B2 through a fifth inter connection 305,

- a second coil 212 of the third phase C2 connected to the first coil 206 of the third phase C2 through a sixth inter connection 306.

The first coils 202, 204, 206 are wound according to the sec ond direction, while the second coils 208, 210, 212 are wound according to the first direction.

More particularly:

- the first coil 202 of the first phase A2 is wound in the second direction on a first tooth 102 of the second set of teeth 102, 104, 106, 108, 110, 112;

- the first coil 204 of the second phase B2 is wound in the second direction on a second tooth 104 of the second set of teeth 102, 104, 106, 108, 110, 112,

- the first coil 206 of the third phase C2 is wound in the second direction on a third tooth 106 of the second set of teeth 102, 104, 106, 108, 110, 112, - the second coil 208 of the first phase A2 is wound in the first direction on a fourth tooth 108 of the second set of teeth 102, 104, 106, 108, 110, 112,

- the second coil 210 of the second phase B2 is wound in the first direction on a fifth tooth 110 of the second set of teeth 102, 104, 106, 108, 110, 112,

- the second coil 212 of the third phase C2 is wound in the first direction on a sixth tooth 112 of the second set of teeth 102, 104, 106, 108, 110, 112.

The second set of coil 202, 204, 206, 208, 210, 212 is con nected in the slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in such a way that :

- the first coil 202 of the first phase A2 is wound between an input 402 of the first phase A2, at the slot bottom lb of the first slot 1, and the fourth interconnection 304, at the slot top 2a of the second slot 2;

- the first coil 204 of the second phase B2 is wound between the fifth interconnection 305, at the slot top 4a of the fourth slot 4, and a neutral output N, at the slot bottom 3b of the third slot 3,

- the first coil 206 of the third phase C2 is wound between the sixth interconnection 306, at the slot top 6a of the sixth slot 6, and an input 406 of the third phase C2, at the slot bottom 5b of the fifth slot 5,

- the second coil 208 of the first phase A2 is wound between a neutral output N, at the slot top 7a of the seventh slot 7, and the fourth interconnection 304, at the slot bottom 8b of the eighth slot 8,

- the second coil 210 of the second phase B2 is wound between an input 405 of the second phase B2, at the slot top 9a of the ninth slot 9, and the fifth interconnection 305, at the slot bottom 10b of the tenth slot 10,

- the second coil 212 of the third phase C2 is wound between a neutral output N, at the slot top 11a of the eleventh slot 11, and the sixth interconnection 306, at the slot bottom 12b of the seventh slot 12. In both the first set of coils 201, 203, 205, 207, 209, 211 and the second set of coil 202, 204, 206, 208, 210, 212, - each of the interconnections 301, 302, 303, 304, 305, 306 ex tends between the slot top 12a, 2a, 4a, 6a of one slot 12, 2, 4, 6 to the slot bottom 6b, 8b, 10b, 12b of another slot 6,

8, 10, 12.. This assures that the interconnections 301, 302, 303, 304, 305, 306 are parallel to each other and have the same length.

Each of the interconnections 301, 302, 303, 304, 305, 306 ex tends through six respective teeth and five respective slots, i.e. each of the interconnections 301, 302, 303, 304, 305,

306 connects two slots which are separated to each other by six respective teeth and five respective slots.

In the winding layout 100 above described, the plurality of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 can be considered divided into comprises a first set of slots 2, 4, 6, 8, 10,

12 and a second set of slots 1, 3, 5, 7, 9, 11 alternating with the first set of slots 2, 4, 6, 8, 10, 12 in the circum ferential direction X, each of the interconnections 301, 302, 303, 304, 305, 306 extending between two respective slots of the first set of slots 2, 4, 6, 8, 10, 12. The second set of slots 1, 3, 5, 7, 9, 11 houses the inputs 401, 402, 403, 404, 405, 406 of the phases Al, A2, Bl, B2, Cl, C2 and the neutral outputs N.

The above described winding layout 100 can be repeated N times (N being an integer or a fraction) upstream the first tooth 101 of the first set of teeth 101, 103, 105, 107, 109, 111 or downstream the twelfth slot 12

"Upstream" and "downstream" are referred to the circumferen tial direction X.

With reference to Figure 5, a slot 501 (corresponding to any of the slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 of Figure 4) between two teeth 502 and 503 is shown. The slot 501 hous es two adjacent phases 504, 505. A wall insulator 506 is pro vided between each of the phases 504, 505 and the walls of the teeth 502 and 503. A phase separator 507 oriented radial- ly separates the phases 504, 505 from one another. According to the present invention the thickness of the phase separator 507 can be minimized, as a consequence of the reduction of the voltage difference between the phases 504, 505.

Eventually, according to possible embodiment of the present invention, the phase separator 507 is not present the voltage difference between the phases 504, 505 being reduced to a minimum or null value. In such cases the insulation on the surface of the coils of each phase 504, 505 is enough to pro- vide an effective insulation between the phases 504, 505.