Concentrated winding arrangement for ac machine stator and method

Abstract

An AC electric machine (31) comprising: a stator (20) having a plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) and a plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) distributed along a circumferential direction (X); a rotor (30) rotatable in opposition to the stator (20); a concentrated winding layout (100) comprising a plurality of coils (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) wound respectively on the plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) and belonging to at least six phases (A1, A2, B1, B2, C1, C2), the coils being wound so that, when considering three adjacent coils, the middle coil is interposed between one coil wound in the same direction of the middle coil and another coil wound in the opposite direction of the middle coil, wherein the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) comprises a first odd / even slots set (1, 3, 5, 7, 9, 11) and a second even / odd slots set (2, 4, 6, 8, 10, 12), each coil (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) in the first slots set (1, 3, 5, 7, 9, 11) being connected to an input conductor (401, 402, 403, 404, 405, 406) or to a neutral conductor (N1, N2) of one phase (A1, A2, B1, B2, C1, C2), each interconnection (301, 302, 303, 304, 305, 306) extending between two respective slots of the second slots set (2, 4, 6, 8, 10, 12).

Description

TECHNICAL FIELD

[0001] The present invention relates to a concentrated winding layout for an AC machine stator. In particular, but not exclusively, the present invention can relate to a concentrated winding layout for a wind turbine generator stator. The present invention further relates to a manufacturing method for manufacturing an AC machine comprising a concentrated winding layout in an AC machine stator. BACKGROUND

[0002] Designing a multi-phase AC machine with a winding layout having two or more coils per slot requires special attention to provide an efficient electrical insulation system.

[0003] First of all, the machine stator magnetic winding shall be insulated from the stator by an insulation member, usually noted as ground wall or main wall insulation. If the machine is designed for a single layer (i.e. one coil per slot) winding layout, then the main wall insulation is sufficient - provided that the magnetic wire / strand is turn-to-turn insulated. If the machine is designed with two (double layer winding layout) or more coils per slot, then it can be necessary to add a phase separator inside each slot to insulate each phase from each other. The size, in particular the thickness, of the phase separator depends on the maximum voltage difference between the coils belonging to different phases, which are housed next to each other in the same slot, and which therefore need to be separated by the phase separator.

[0004] The problem described above is particularly relevant in multi-phase AC machines having more than three phases. For larger machines, such as some generators of offshore wind turbines, the generator winding can be split into two three-phase systems (six-phase AC machine), fed from two independent voltage converters, each generating a three-phase sinusoidal waveform. The two three-phase systems can usually be provided in series to each other and electrically separated by a phase angle of 30° or 60° (any other phase angle shift is possible). Shifting one of the converter systems to generate an angle difference between the two converter systems presents an opportunity to reduce torque pulsation. This approach also gives a lot of flexibility in combining the winding configuration of the machine to minimize voltage stress.

[0005] However, in known multi-phase AC machines having a concentrated winding layout, the voltage difference between the phases housed in the same slot can be improved. SUMMARY

[0006] The above described needs can be met by the subject-matter according to the independent claims. The dependent claims describe advantageous embodiments of the present invention.

[0007] According to a first aspect of the present invention, there is provided an AC machine comprising:

[0008] a stator having a plurality of teeth distributed along a circumferential direction from a first tooth to a last tooth and a plurality of slots alternating with the plurality of teeth in the circumferential direction;

[0009] a rotor rotatable with respect to the stator around an axis of rotation, the direction of rotation of the rotor being opposite to the circumferential direction;

[0010] a concentrated winding layout comprising a plurality of coils wound on the plurality of teeth respectively and belonging to at least six phases, said coils being wound such that, when considering three adjacent coils, the middle coil is inserted between one coil wound in the same direction as the middle coil and another coil wound in the opposite direction of the middle coil,

[0011] each slot of the plurality of slots accommodating at least two coils of said plurality of coils, each phase of said at least six phases comprising a first coil and a second coil, the second coil of one phase being wound in the opposite direction with respect to the corresponding first coil of the same phase,

[0012] a plurality of interconnections connecting the first and second coils of each phase,

[0013] wherein said plurality of slots comprises a first set of slots and a second set of slots alternating with the first set of slots in the circumferential direction, each coil of the first set of slots being connected to an input conductor or a neutral conductor of one phase, each interconnection extending between two respective slots of the second set of slots.

[0014] According to a second aspect of the invention, there is provided a method of manufacturing an AC electric machine as described above.

[0015] According to the invention, the thickness of the phase separator between two coils in the same slot can be minimized due to the reduction of the voltage difference between the corresponding phases, which is experienced when using the winding layout described above. Eventually, according to possible embodiments of the invention, such phase separator can be absent, the voltage difference being reduced to a minimum or to zero.

[0016] The AC electric machine of the invention can be a permanent magnet synchronous electric machine. The electric machine can be or comprise an electric motor or a generator, in particular a generator comprised in a wind turbine.

[0017] According to embodiments of the invention, the concentrated winding layout comprises at least a first set of coils and a second set of coils, corresponding respectively to a first set of three phases and a second set of three phases of the concentrated winding layout. 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 can be electrically separated by a phase angle of 30° or 60°. The invention can also be adapted to a concentrated winding layout having more than six phases.

[0018] Embodiments of the present application will now be described with reference to the accompanying drawings. The present application is not limited to the embodiments illustrated or described. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A schematic cross-section of a wind turbine comprising an AC machine according to the present application is shown;

[0020] Figure 2 A schematic diagram of a 6-phase concentrated winding layout according to the present application is shown;

[0021] Figure 3 A voltage vector diagram of the concentrated winding layout of Figure 2 is shown;

[0022] Figure 4 A schematic arrangement of the concentrated winding layout of Figure 2 and Figure 3 is shown;

[0023] Figure 5 A first embodiment of the connection arrangement of the concentrated winding layout of Figure 4 is shown;

[0024] Figure 6 A schematic physical arrangement of the connection arrangement of Figure 5 is shown;

[0025] Figure 7 A second embodiment of the connection arrangement of the concentrated winding layout of Figure 4 is shown;

[0026] Figure 8 A schematic physical arrangement of the connection arrangement of Figure 7 is shown;

[0027] Figure 9 A third embodiment of the connection arrangement of the concentrated winding layout of Figure 4 is shown;

[0028] Figure 10 A schematic physical arrangement of the connection arrangement of Figure 9 is shown;

[0029] Figure 11 A slot of an AC machine stator according to the present application is shown. DETAILED DESCRIPTION

[0030] 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.

[0031] Figure 1A wind turbine 21 according to the present invention is shown. The wind turbine 21 includes a tower 32 mounted on a foundation (not depicted). A nacelle 33 is arranged on top of the tower 32. The wind turbine 21 further includes a wind turbine rotor 35 having at least one blade 34. Figure 1 In one embodiment, the wind turbine rotor includes three blades 34, of which only two blades 34 are visible. The wind turbine rotor 35 is rotatable about an axis of rotation Y. The blades 34 extend generally radially relative to the axis of rotation Y. The wind turbine 21 includes a generator 31, which includes a stator 20 and a rotor 30. The rotor 30 is rotatable relative to the stator 20 about the axis of rotation Y. The wind turbine rotor 35 is either directly (e.g., directly driven) or by means of a rotatable main shaft 39 and / or through a gearbox ( Figure 1 (Not shown) is rotatably coupled to generator 31. A schematically depicted bearing assembly 38 is provided to hold the main shaft 39 and rotor 35 in place. The rotatable main shaft 9 extends along the axis of rotation Y.

[0032] like Figures 5 to 10As shown in the middle, the stator 20 has a plurality of teeth 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112 which alternate with a plurality of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in the circumferential direction X of the stator 20, the circumferential direction X of the stator 20 being in circumferential orientation with respect to the rotation axis Y. The rotation direction V of the rotor 30 is opposite to the circumferential direction X. Each of the plurality of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 extends from a respective slot bottom 1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, 11b, 12b to a respective slot top 1a, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, 10a, 11a, 12a along a radial direction R, i.e. orthogonal to the rotation axis Y. According to the present application, the electric generator 31 comprises a concentrated winding layout 100 comprising a plurality of coils 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 wound on the plurality of 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. When considering three adjacent coils along the circumferential direction X, the coils are wound so that the middle coil, which is interposed between the other two adjacent coils, is wound in a first direction (clockwise or counterclockwise), while one of the other two coils is wound in the same direction (clockwise or counterclockwise) of the middle coil and the other coil is wound in the opposite direction (counterclockwise or counterclockwise) of the middle coil. Each slot 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 houses at least two coils, each phase Al, A2, Bl, B2, Cl, C2 comprises 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 the opposite direction with respect to the respective first coil 201, 202, 203, 204, 205, 206. A plurality of interconnections 301, 302, 303, 304, 305, 306 is provided for connecting the first and second coils of each phase. The plurality of slots comprises a first set of slots 1, 3, 5, 7, 9, 11 and a second set of slots 2, 4, 6, 8, 10, 12 which alternate with the first set of slots 2, 4, 6, 8, 10, 12 in the circumferential direction X.In the embodiment of the figures, the first slot set 1, 3, 5, 7, 9, 11 coincides with the odd slots (first, third, fifth, seventh, ninth and eleventh) and the second slot set 2, 4, 6, 8, 10, 12 coincides with the even slots (second, fourth, sixth, eighth, tenth and twelfth). Each coil 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 of the first slot set 1, 3, 5, 7, 9, 11 is connected to an input conductor 401, 402, 403, 404, 405, 406 or neutral conductor N1, N2 of one phase A1, A2, B1, B2, C1, C2. Each interconnection 301, 302, 303, 304, 305, 306 extends between two respective slots of the second slot set 2, 4, 6, 8, 10, 12.

[0033] The coils 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 and the interconnections 301, 302, 303, 304, 305, 306 can carry respective insulation on the respective surfaces.

[0034] Figure 2 The respective first coil 201, 202, 203, 204, 205, 206 and second coil 207, 208, 209, 210, 211, 212 of each phase A1, A2, B1, B2, C1, C2 is schematically shown. Each interconnection 301, 302, 303, 304, 305, 306 is schematically represented by a dot.

[0035] Figure 3 The corresponding voltage vector diagram is schematically shown. The first coil set 201, 203, 205, 207, 209, 211 is electrically separated from the second coil set 202, 204, 206, 208, 210, 212 by a phase angle a of 30°. According to other embodiments (not shown) of the invention, the phase angle a can have any other value, for example 60°.

[0036] Figure 4 A schematic arrangement of the concentrated winding layout 100 is shown as seen from the radial top of the tooth (radial direction perpendicular to the plane of the drawing) Figure 4corresponding to a first set of three phases Al, Bl, Cl and a second set of three phases A2, B2, C2. Each first coil set 201, 203, 205, 207, 209, 211 and each second coil set 202, 204, 206, 208, 210, 212 corresponds to a respective three-phase system. The first coil set 201, 203, 205, 207, 209, 211 is connected by three respective interconnections 301, 302, 303. The second coil set 202, 204, 206, 208, 210, 212 is connected by three other respective interconnections 304, 305, 306. According to other embodiments of the application (not shown), the concentrated winding layout can comprise a different number of phases, for example more than two three-phase systems. The first coil set 201, 203, 205, 207, 209, 211 is electrically connected in series to the second coil set 202, 204, 206, 208, 210, 212. The coils 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212 are wound around the teeth 106, 105, 102, 101, 110, 109, 112, 111, 108, 107, 104, 105, respectively. In the view of Figure 1, the coils 201, 203, 205, 208, 210, 212, i.e. the first three coils of the first coil set and the last three coils of the second coil set, are wound counterclockwise, while the other coils 202, 204, 206, 207, 209, 211, i.e. the first three coils of the second coil set and the last three coils of the first coil set, are wound clockwise. According to other embodiments of the application (not shown), the coils 201, 203, 205, 208, 210, 212 can be wound clockwise, while the other coils 202, 204, 206, 207, 209, 211 can be wound counterclockwise. Figure 4 In the view of Figure 1, the coils 201, 203, 205, 208, 210, 212, i.e. the first three coils of the first coil set and the last three coils of the second coil set, are wound counterclockwise, while the other coils 202, 204, 206, 207, 209, 211, i.e. the first three coils of the second coil set and the last three coils of the first coil set, are wound clockwise. According to other embodiments of the application (not shown), the coils 201, 203, 205, 208, 210, 212 can be wound clockwise, while the other coils 202, 204, 206, 207, 209, 211 can be wound counterclockwise.

[0037] The first coil set 201, 203, 205, 207, 209, 211 comprises:

[0038] - a first coil 201 of the first phase Al,

[0039] - a first coil 203 of the second phase Bl,

[0040] - a first coil 205 of the third phase Cl,

[0041] - a second coil 207 of the first phase Al connected to the first coil 201 of the first phase Al by the first interconnection 301,

[0042] - a second coil 209 of the second phase B1 connected to the first coil 203 of the second phase B1 by a second interconnection 302,

[0043] - a third coil 211 of the third phase C1 connected to the first coil 205 of the third phase C1 by a third interconnection 303.

[0044] The first set of coils 201, 203, 205, 207, 209, 211 is connected in the slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in such a way that:

[0045] - the first coil 201 of the first phase A1 is wound between the input conductor 401 of the first phase A1 and the first interconnection 301,

[0046] - the first coil 203 of the second phase B1 is wound between the second interconnection 302 and the input conductor 402 of the second phase B1,

[0047] - the first coil 205 of the third phase C1 is wound between the third interconnection 303 and the input conductor 403 of the third phase C1,

[0048] - the second coil 207 of the first phase A1 is wound between the first neutral output conductor N1 and the first interconnection 301,

[0049] - the second coil 209 of the second phase B1 is wound between the first neutral output conductor N1 and the second interconnection 302,

[0050] - the second coil 211 of the third phase C1 is wound between the first neutral output conductor N1 and the third interconnection 303.

[0051] The second set of coils 202, 204, 206, 208, 210, 212 comprises:

[0052] - a first coil 202 of the first phase A2,

[0053] - a first coil 204 of the second phase B2,

[0054] - a first coil 206 of the third phase C2,

[0055] - a second coil 208 of the first phase A2 connected to the first coil 202 of the first phase A2 by a fourth interconnection 304,

[0056] - a second coil 210 of the second phase B2 connected to the first coil 204 of the second phase B2 by a fifth interconnection 305,

[0057] - the second coil 212 of the third phase C2 is connected to the first coil 206 of the third phase C2 by the sixth interconnection 306.

[0058] The second coil sets 202, 204, 206, 208, 210, 212 are connected in the slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 in such a way that:

[0059] - the first coil 202 of the first phase A2 is wound between the input conductor 404 of the first phase A2 and the fourth interconnection 304,

[0060] - the first coil 204 of the second phase B2 is wound between the fifth interconnection 305 and the input conductor 405 of the second phase B2,

[0061] - the first coil 206 of the third phase C2 is wound between the sixth interconnection 306 and the input conductor 406 of the third phase C2,

[0062] - the second coil 208 of the first phase A2 is wound between the second neutral output conductor N2 and the fourth interconnection 304,

[0063] - the second coil 210 of the second phase B2 is wound between the second neutral output conductor N2 and the fifth interconnection 305,

[0064] - the second coil 212 of the third phase C2 is wound between the second neutral output conductor N2 and the sixth interconnection 306.

[0065] In the first embodiment of the Figure 5 and Figure 6 the connections to the first and second neutral output conductors N1, N2 and to the input conductors 401, 402, 403, 404, 405, 406 are provided at the respective slot bottoms 1b, 3b, 5b, 7b, 9b, 1 lb. In particular (see Fig. 2): Figure 5 ) :

[0066] - at the slot bottom 1b of the first slot 1, between the first and second teeth 101, 102, a connection to the input conductors 402, 405 of the second phases B1, B2 is provided,

[0067] - at the slot bottom 3b of the third slot 3, between the third and fourth teeth 103, 104, a connection to the first and second neutral output conductors N1, N2 is provided,

[0068] - at the slot bottom 5b of the fifth slot 5, between the fifth and sixth teeth 105, 106, a connection to the input conductors 401, 404 of the first phases A1, A2 is provided,

[0069] - in the slot bottom 7b of the seventh slot 7, between the seventh and eighth teeth 107, 108, connections are provided to the first and second neutral output conductors N1, N2,

[0070] - in the slot bottom 9b of the ninth slot 9, between the ninth and tenth teeth 109, 110, connections are provided to the input conductors 403, 406 of the third phase C1, C2,

[0071] - in the slot bottom 11b of the eleventh slot 11, between the eleventh and twelfth teeth 111, 112, connections are provided to the first and second neutral output conductors N1, N2.

[0072] Thus, connections are provided to the interconnections 301, 302, 303, 304, 305, 306 at the slot tops 2a, 4a, 6a, 8a, 10a, 12a of the other slots 2, 4, 6, 8, 10, 12, not including the connections to the first and second neutral output conductors N1, N2 and the input conductors 401, 402, 403, 404, 405, 406 Figure 6 ).

[0073] In Figure 7 and Figure 8 a second embodiment, the connections to the first and second neutral output conductors N1, N2, the input conductors 401, 402, 403, 404, 405, 406 and the interconnections 301, 302, 303, 304, 305, 306 are provided according to:

[0074] - in the slot top 1a of the first slot 1, connections are provided to the input conductors 402, 405 of the second phase B1, B2,

[0075] - in the slot bottom 2b of the second slot 2, connections are provided to the second and sixth interconnections 302, 306,

[0076] - in the slot top 3a of the third slot 3, connections are provided to the first and second neutral output conductors N1, N2,

[0077] - in the slot bottom 4b of the fourth slot 4, connections are provided to the third and fourth interconnections 303, 304,

[0078] - in the slot top 5a of the fifth slot 5, connections are provided to the input conductors 401, 404 of the first phase A1, A2,

[0079] - in the slot bottom 6b of the sixth slot 6, connections are provided to the first and fifth interconnections 301, 305,

[0080] - in the seventh slot 7, connections are provided to the first and second neutral output conductors N1, N2, respectively in the slot bottom 7b and the slot top 7a,

[0081] - in the slot top 8a of the eighth slot 8, connections to the second and sixth interconnections 302, 306 are provided,

[0082] - in the slot bottom 9b of the ninth slot 9, connections to the input conductors 403, 406 of the third phase C1, C2 are provided,

[0083] - in the slot top 10a of the tenth slot 10, connections to the third and fourth interconnections 303, 304 are provided,

[0084] - in the eleventh slot 11, connections to the first and second neutral output conductors N1, N2 are provided in the slot top 11a and the slot bottom 11b, respectively,

[0085] - in the slot bottom 12b of the twelfth slot 12, connections to the first and fifth interconnections 301, 305 are provided.

[0086] In a third embodiment of the Figure 9 and Figure 10 the connections to the first and second neutral output conductors N1, N2, to the input conductors 401, 402, 403, 404, 405, 406 and to the interconnections 301, 302, 303, 304, 305, 306 are provided according to:

[0087] - in the slot top 1a of the first slot 1, connections to the input conductors 402, 405 of the second phase B1, B2 are provided,

[0088] - in the slot bottom 2b of the second slot 2, connections to the second and sixth interconnections 302, 306 are provided,

[0089] - in the slot top 3a of the third slot 3, connections to the first and second neutral output conductors N1, N2 are provided,

[0090] - in the slot bottom 4b of the fourth slot 4, connections to the third and fourth interconnections 303, 304 are provided,

[0091] - in the slot top 5a of the fifth slot 5, connections to the input conductors 401, 404 of the first phase A1, A2 are provided,

[0092] - in the sixth slot 6, connections to the first and fifth interconnections 301, 305 are provided in the slot bottom 6b and the slot top 6a, respectively,

[0093] - in the slot bottom 7b of the seventh slot 7, connections to the first and second neutral output conductors N1, N2 are provided,

[0094] - in the slot top 8a of the eighth slot 8, connections to the second and sixth interconnections 302, 306 are provided,

[0095] - At the bottom 9b of slot 9, a connection is provided for the input conductors 403 and 406 of the third phases C1 and C2.

[0096] - At the top 10a of the tenth slot 10, a connection is provided with the third and fourth interconnects 303, 304.

[0097] - At the bottom 11b of the eleventh slot 11, a connection is provided for the first and second neutral output conductors N1 and N2.

[0098] - In the twelfth slot 12, connections to the first and fifth interconnects 301, 305 are provided at the top 12a and bottom 12b of the slot, respectively.

[0099] In the third embodiment, interconnects 301, 302, 303, 304, 305, and 306 are parallel to each other. Figure 10 That is, each interconnect 301, 302, 303, 304, 305, 306 extends between the top and bottom of the corresponding slot.

[0100] Reference Figure 11 The groove 501 between the two teeth 502 and 503 is shown (corresponding to...). Figure 4 (Any of slots 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12). Slot 501 accommodates two adjacent phases 504, 505. Wall insulator 506 is provided between the walls of each phase 504, 505 and teeth 502 and 503. A radially oriented phase separator 507 separates phases 504, 505 from each other. According to the invention, the thickness of the phase separator 507 can be minimized due to the reduction in the voltage difference between phases 504, 505. Ultimately, according to a possible embodiment of the invention, the phase separator 507 is absent, and the voltage difference between phases 504, 505 is reduced to a minimum or zero value. In such a case, the insulation on the coil surface of each phase 504, 505 is sufficient to provide effective insulation between phases 504, 505.

Claims

1. An AC electric machine (31) comprising: - a stator (20) having a plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) distributed along a circumferential direction (X) from a first tooth (101) to a last tooth (112) and a plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) alternating with said plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) in the circumferential direction (X), - a rotor (30) rotatable with respect to the stator (20) around an axis of rotation (Y) in a direction of rotation opposite to the circumferential direction (X), - a concentrated winding layout (100) comprising a plurality of coils (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) belonging to at least six phases (Al, A2, Bl, B2, Cl, C2) wound respectively on said plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) and wound so that, when considering three adjacent coils, the middle coil is interposed between one coil wound in the same direction of the middle coil and another coil wound in the opposite direction of the middle coil, - each slot of said plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) housing at least two coils of said plurality of coils (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212), each phase (Al, A2, Bl, B2, Cl, C2) of said at least six phases 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 the opposite direction with respect to the corresponding first coil (201, 202, 203, 204, 205, 206) of the same phase, - a plurality of interconnections (301, 302, 303, 304, 305, 306) each having a first end and a second end connecting respectively the first and the second coils of each phase, wherein the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) comprises a first set of slots (1, 3, 5, 7, 9, 11) and a second set of slots (2, 4, 6, 8, 10, 12) alternating in a circumferential direction (X) with the first set of slots (2, 4, 6, 8, 10, 12), each coil (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) in the first set of slots (1, 3, 5, 7, 9, 11) is connected to an input conductor (401, 402, 403, 404, 405, 406) or a neutral conductor (N1, N2) of one phase (A1, A2, B1, B2, C1, C2), each interconnection (301, 302, 303, 304, 305, 306) extends between two respective slots of the second set of slots (2, 4, 6, 8, 10, 12), wherein each of the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) extends radially from a slot top (1a, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, 10a, 11a, 12a) to a slot bottom (1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, 11b, 12b), at the slot bottom (1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, 11b, 12b) providing each connection between the input conductors (401, 402, 403, 404, 405, 406) and the neutral conductors (N1, N2), wherein for each phase of the at least six phases: a first end of the interconnection is connected to a first coil at a slot top or a slot bottom of a first slot adjacent to a tooth on which the first coil is wound, and a second end of the interconnection is connected to a second coil at a slot top or a slot bottom of a second slot adjacent to a tooth on which the second coil is wound.

2. The AC electric machine (31) of claim 1, wherein the concentrated winding layout (100) comprises at least a first set of coils (201, 203, 205, 207, 209, 211) and a second set of coils (202, 204, 206, 208, 210, 212) corresponding to a first set of three phases (A1, B1, C1) and a second set of three phases (A2, B2, C2) of the concentrated winding layout (100), respectively.

3. The AC electric machine (31) of claim 1 or 2, wherein the first set of slots (1, 3, 5, 7, 9, 11) comprises a first subset of slots (1, 5, 9) and a second subset of slots (3, 7, 11) alternating with the first subset of slots (1, 5, 9), the coils (201, 202, 205, 206, 209, 210) in the first subset of slots (1, 5, 9) being connected to the input conductors (401, 402, 403, 404, 405, 406) and the coils (203, 204, 207, 208, 211, 212) in the second subset of slots (3, 7, 11) being connected to the neutral conductors.

4. The AC electric machine (31) of claim 3, wherein the two coils (201, 202, 205, 206, 209, 210) in each slot of the first subset of slots (1, 5, 9) are connected to an input conductor (401, 402, 403, 404, 405, 406) of a first three-phase set (Al, Bl, Cl) and an input conductor (401, 402, 403, 404, 405, 406) of a second three-phase set (A2, B2, C2), respectively.

5. The AC electric machine (31) of any one of claims 3 to 4, wherein each interconnection (301, 302, 303, 304, 305, 306) extends between a top (12a, 2a, 4a, 6a) of one slot (12, 2, 4, 6) to a bottom (6b, 8b, 10b, 12b) of another slot (6, 8, 10, 12).

6. The AC electric machine (31) of any one of claims 2 to 5, wherein the first set of coils (201, 203, 205, 207, 209, 211) is electrically connected in series to the second set of coils (202, 204, 206, 208, 210, 212).

7. The AC electric machine (31) of claim 6, wherein the first set of coils (201, 203, 205, 207, 209, 211) and the second set of coils (202, 204, 206, 208, 210, 212) are electrically separated by a phase angle (a) of 30° or 60°.

8. A wind turbine (21) comprising an AC electric machine (31) according to any one of the preceding claims.

9. A method of manufacturing an AC electric machine (31), comprising: providing a stator (20) having a plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) distributed along a circumferential direction (X) from a first tooth (101) to a last tooth (112) and a plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) alternating with the plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) in the circumferential direction (X), A rotor (30) is provided, which is rotatable with respect to a stator (20) about an axis of rotation (Y), the direction of rotation of the rotor (30) being opposite to the circumferential direction (X), a concentrated winding layout (100) is arranged, comprising a plurality of coils (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) wound on the plurality of teeth (101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112) respectively and belonging to at least six phases (A1, A2, B1, B2, C1, C2), the coils being wound so that, when considering three adjacent coils, the intermediate coil is interposed between one coil wound in the same direction of the intermediate coil and another coil wound in the opposite direction of the intermediate coil, each slot of the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) housing at least two coils of the plurality of coils (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212), each phase (A1, A2, B1, B2, C1, C2) of the at least six phases 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 the opposite direction with respect to the corresponding first coil (201, 202, 203, 204, 205, 206) of the same phase, a plurality of interconnections (301, 302, 303, 304, 305, 306) is arranged, each interconnection having a first end and a second end connecting the first and second coils of each phase respectively, wherein the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) comprises a first set of slots (1, 3, 5, 7, 9, 11) and a second set of slots (2, 4, 6, 8, 10, 12) alternating in a circumferential direction (X) with the first set of slots (2, 4, 6, 8, 10, 12), each coil (201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212) in the first set of slots (1, 3, 5, 7, 9, 11) is connected to an input conductor (401, 402, 403, 404, 405, 406) or a neutral conductor (N1, N2) of one phase (A1, A2, B1, B2, C1, C2), each interconnection (301, 302, 303, 304, 305, 306) extends between two respective slots of the second set of slots (2, 4, 6, 8, 10, 12), wherein each of the plurality of slots (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) extends radially from a slot top (1a, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, 10a, 11a, 12a) to a slot bottom (1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, 11b, 12b), at the slot bottom (1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b, 10b, 11b, 12b) providing each connection between the input conductors (401, 402, 403, 404, 405, 406) and the neutral conductors (N1, N2), wherein for each phase of the at least six phases: a first end of the interconnection is connected to a first coil at a slot top or a slot bottom of a first slot adjacent to a tooth on which the first coil is wound, and a second end of the interconnection is connected to a second coil at a slot top or a slot bottom of a second slot adjacent to a tooth on which the second coil is wound.

10. The method according to the preceding claim 9, wherein the concentrated winding layout (100) comprises at least a first set of coils (201, 203, 205, 207, 209, 211) and a second set of coils (202, 204, 206, 208, 210, 212) electrically connected in series with the first set of coils (201, 203, 205, 207, 209, 211), respectively corresponding to a first set of three phases (A1, B1, C1) and a second set of three phases (A2, B2, C2) of the concentrated winding layout (100), the first set of coils (201, 203, 205, 207, 209, 211) and the second set of coils (202, 204, 206, 208, 210, 212) being electrically separated by a phase angle (a) of 30° or 60°.

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