Distributed double litz wire winding in open slots

Abstract

An electric machine comprising a stator having a plurality of open slots accommodating a double layer distributed winding having conductors transposed in the end winding region. The conductors are Litz wire conductors and the end winding portions of the conductors are not twisted or rotated about the axis of the conductors.

Description

[0001] The invention relates to an electric machine with a double-layer distributed winding according to the preamble of claim 1 .

[0002] More particularly, it relates to an electric machine having a double-layer distributed winding disposed in open slots. Background Art

[0003] When designing an electric machine, it is desirable to have a slot design in which the electrical losses in the conductors are as low as possible and at the same time there is some path with low thermal resistance for heat transfer from all the conductors in the slot to the stator core. These two goals are often in conflict with each other.

[0004] This contradiction is even more serious for machines with open slots operating at frequencies above 50 Hz, since the high frequency pulsed magnetic field generates additional losses in the conductor through the slot openings.

[0005] In order to achieve low thermal resistance to heat flow from the slots, especially from the central part of the slot area, the slot filling factor (SFF) of the winding should be as high as possible. This means that as much area as possible in the slot area is occupied by copper or other conductive material, and as little area as possible is occupied by insulating material. Copper is a good conductor of heat, while insulating material is a poor conductor of heat.

[0006] The conventional way to achieve high SFF is to use solid profiled conductors with a rectangular cross section. This allows SFFs of up to 80-85%. However, the challenge with solid profiled conductors is the uneven current distribution in the individual conductors and in the slot area, especially when the machine is fed with high frequencies, and due to the pulsed magnetic field, especially at the slot openings, resulting in higher electrical losses than is typical for low frequencies and machines with closed or semi-closed slots. The causes of the uneven current distribution are the well-known skin effect and proximity effect.

[0007] To reduce the skin effect and the proximity effect, two measures are known and widely used: reducing the cross-sectional area of ​​the conductor, first reducing its height, and then using transposition of the conductor, the latter meaning that the conductor changes its position in the slot after passing the end winding area.

[0008] For example, in US7759834 B2, a solid profiled conductor is used, wherein the conductor height is low, and for a toothed coil, such as Figure 1a As shown, the position of the conductor changes after passing the end winding area. This solution can provide high SFF values, but at the same time the production costs are high, because several conductors of different lengths will have to be available for each machine design, and the solid conductors must be bent, which is not easy in practice.

[0009] Typically, the need for transposition leads to twisting or turning the conductors in the end winding region, which is achieved in so-called hairpin windings or diamond windings. Examples can be found in US2014015348 A1 and US6894417 B2. The latter solution is as follows Figure 1b This approach will result in longer end windings, resulting in higher losses and increased machine length. In addition, twisting the conductors negatively affects the insulation of the conductors, increasing the likelihood of electrical failure.

[0010] Another known solution is to use stranded wires, for example as in US8946965 B2. Figure 1c However, this requires turning the conductor strands in the end winding region, which complicates manufacturing.

[0011] A more well-known approach to solving the problem is to use a Roebel rod. In WO2009000837 A2, each coil side includes a plurality of mutually transposed strands, so that the coil side defines a Roebel rod ( Figure 1d ). In each slot length, the strands are transposed 180 degrees. The coil is a so-called diamond coil. This solution helps to reduce power losses, however, Roebel bars are expensive to manufacture and do not offer high SFF.

[0012] In order to reduce the electrical losses caused by the skin and proximity effects, litz wire can be used. Litz wire has been known in the field of electric machines for many years, but its application is reserved for high-end applications characterized by very high frequencies. The SFF that can be achieved with litz wire can reach 60-65%, which together with the relatively high price has always been considered a disadvantage of this type of conductor and has limited its application in the above-mentioned fields.

[0013] In summary, it is well known that transposition is desirable in most types of windings and hairpin (turned or twisted) end windings are often used to achieve transposition. It is also common practice to use stranded and solid formed conductors in distributed windings.

[0014] But there is still a need for better machine designs, especially for machines operating at increased frequencies. These improvements should lead to better manufacturability, higher efficiency and higher reliability.

[0015] Since it takes many hours to complete the insertion of the windings into the stator for a machine with semi-closed slots, better manufacturability is achieved by using open slots.

[0016] Higher efficiency can be achieved by reducing electrical losses due to skin effect and proximity effect.

[0017] Higher reliability can be achieved by avoiding turning and twisting the conductors, thereby reducing the impact on the conductor insulation and the risk of failure.

[0018] Purpose

[0019] The main object of the present invention is to provide an electric machine that partially or fully solves the above-mentioned drawbacks and disadvantages of prior art solutions.

[0020] Another object of the present invention is to provide an electric machine having improved manufacturability by reducing the time required to insert the windings into the stator.

[0021] The object of the present invention is to provide an electric machine whose efficiency is increased by reducing electrical losses.

[0022] The object of the present invention is to provide an electric machine with higher reliability by avoiding rotation and twisting of the conductors, thereby reducing the impact on the insulation of the conductors and the risk of failure.

[0023] Other objects appear from the following description, claims and drawings. Summary of the invention

[0024] The electric machine according to the invention is disclosed in claim 1. Preferred features of the electric machine according to the invention are disclosed in the dependent claims.

[0025] The present invention relates to improvements in electric machines, and more particularly to improvements in the arrangement of windings in stators of electric machines.

[0026] The present invention is based on exploiting the inherent characteristics / properties of Litz wire. Firstly, the winding design according to the present invention exploits the inherent transposition of the fine strands within the Litz wire and thereby avoids the need to twist the strands in the end winding region. Secondly, the mechanical flexibility of the Litz wire allows the end windings to be short and compact without compromising reliability.

[0027] When designing motors using profiled solid conductors, designers aim for a high SFF (slot filling factor) to have smaller slots. However, relatively high losses due to skin effect and proximity effect limit the extent to which the slot area can be reduced, as effective heat dissipation requires a larger slot circumference.

[0028] According to the invention, a lower SFF is accepted due to easier heat dissipation due to better current distribution and lower electrical losses in the slot by applying Litz wire. This alternative approach results in a slot size comparable to conventional designs.

[0029] Therefore, in the present invention, the coils are made of profiled Litz wire and formed before being placed in the open slots of the stator. With the coil sides of each coil positioned one above the other along the slot height, the coils belonging to different phases form an overlapping structure similar to that in conventional distributed windings.

[0030] The result is compact and short end windings. An additional benefit is higher reliability as there is no conductor twisting. It is also easy to provide phase-to-phase insulation between the end windings to prevent phase-to-phase short circuits.

[0031] For example, the price of Litz wire is not too high compared to bent solid conductors manufactured in different lengths, or compared to Roebel bars, so the cost of a motor with higher efficiency due to reduced losses is not too high.

[0032] According to the invention, the stator accordingly has a plurality of slots extending in the transverse direction of the stator, wherein the slots are open and in which the coils according to the invention are arranged. The coils according to the invention comprise a first coil side and a second coil side, the first coil side and the second coil side comprising several Litz wire conductors as described above positioned in-line one after the other along the slot height, wherein an end winding region connects the first coil side and the second coil side outside the slot.

[0033] According to the invention, the number of conductors in the coil side can be arbitrary - two or more.

[0034] According to the present invention, the first coil side and the second coil side of each coil are arranged in separate non-adjacent slots, wherein the first coil side of each coil is arranged in a slot closer to the bottom of the slot, and the second coil side of each coil is arranged in a non-adjacent slot closer to the opening of the slot.

[0035] According to the invention, some or all of the conductors are transposed in the end winding region of each coil, thereby changing their vertical position on the coil side. The end winding section of the Litz wire conductor is not twisted or turned around the axis of the conductor. Depending on the number of conductors, there are different possible arrangements of the conductors on the first coil side and the second coil side, which will be explained in detail in the following example description.

[0036] As described above, when two coil sides from two different coils of two different phases fall into the same slot, the coil sides are positioned one above the other along the slot height, thereby forming a double-layer structure.

[0037] According to an embodiment of the invention, the conductor is preformed to have a substantially square or rectangular form.

[0038] In another embodiment of the invention, the opening of the open slot is covered by a magnetic, semi-magnetic or non-magnetic slot wedge.

[0039] Further preferred features and advantageous details of the invention will be disclosed in the following exemplary description, in the claims and in the drawings.

[0040] Example

[0041] The present invention will be described in more detail below with reference to the accompanying drawings, in which:

[0042] Figure 1a-1d The winding design of the prior art is shown,

[0043] Figure 2a-2d shows the transposition of turns of the same coil in the slots,

[0044] Figure 3a-Figure 3b The turns and end windings of the two coils are shown,

[0045] Figure 4a-4d A schematic diagram showing one of the coils, and

[0046] Figure 5 3D view showing the end winding insertion in the slots of the stator.

[0047] Reference is first made to presenting four prior art winding designs that the present invention seeks to improve as discussed above. Figure 1a-1d .

[0048] Reference is now made to the schematic diagram showing the principle of the winding design of the stator of the electric machine according to the invention. Figure 2a-2d According to the invention, the stator is formed by a stator armature 100 provided with a plurality of open slots 110 extending in a transverse direction of the stator armature 100 (eg an iron core or the like), wherein the open slots 110 exhibit a bottom 111 at one end and an opening 112 at the other end.

[0049] exist Figure 2a An embodiment is shown in FIG. Figure 4a-4d The coil 10 shown in detail in FIG. 1 comprises a first coil side 11 and a second coil side 12 arranged in separate non-adjacent open slots 110 of a stator armature 100. The first coil side 11 and the second coil side 12 are respectively composed of a plurality of conductors 20A-20D positioned one after another in a straight line along the height of the slot 110, wherein the end winding region 30 (see FIG. 1 ) is formed by a plurality of conductors 20A-20D arranged in a straight line along the height of the slot 110. Figure 2b-Figure 2c ) connects the first coil side 11 and the second coil side 12 outside the slot 110. According to the present invention, the conductors 20A-20D are Litz wire conductors. According to an embodiment of the present invention, the Litz wire conductors are preformed to have a substantially square or rectangular form, wherein the width corresponds to the width of the open slot 110.

[0050] When passing through the end winding region 30 (such as Figure 2b-Figure 2c When the conductors 20A-20D are partially or completely displaced along the slot 110 height to change their positions in the first coil side 11 and the second coil side 12. Figure 2b , it is shown how the conductors 20B and 20C change positions in the first coil side 11 and the second coil side 12:

[0051] The conductor 20C which is next closest to the slot opening 112 in the first coil side 11 is transposed in the end winding region 30 to be next closest to the slot bottom 111 in the second coil side 12.

[0052] The conductor 20B that is next closest to the slot bottom 111 in the first coil side 11 is transposed in the end winding region 30 to be next closest to the slot opening 112 in the second coil side 12 .

[0053] Figure 2b The two conductors 20B and 20C are shown transposed in the end winding region 30, and Figure 2c The transposition of all conductors 20A-20D in the end winding region 30 is shown.

[0054] Reference is now made to the diagram showing how the conductor 20A is transposed. Figure 2d The conductor 20A closest to the slot bottom 111 in the first coil side 11 is transposed along the coil height in the end winding region 30 to be closest to the slot opening 112 in the second coil side 12. This conductor 20A has the longest end winding section.

[0055] Furthermore, in the illustrated embodiment, the conductor 20B that is next closest to the slot bottom 111 in the first coil side 11 is transposed along the coil height in the end winding region 30 to be next closest to the slot opening 112 in the second coil side 12, and the conductor 20C that is next closest to the slot opening 112 in the first coil side 11 is transposed along the coil height in the end winding region 30 to be next closest to the slot bottom 111 in the second coil side 12.

[0056] The conductor 20D closest to the slot opening 112 in the first coil side 11 is transposed along the coil height in the end winding region 30 to be closest to the slot bottom 111 in the second coil side 12 .

[0057] Therefore, the order of the conductors 20A- 20D is reversed in the second coil side 12 relative to the first coil side 11 .

[0058] According to the present invention, none of the conductors 20A-20D twists or rotates about the axis of the conductors 20A-20D.

[0059] Reference now Figure 3a , which shows how two coils (solid lines indicate conductors 20A-20D of the first coil, dashed lines indicate conductors 20E-20H of the second coil) are arranged one after another in the slot 110. A first coil with a first coil side 11 and a second coil side 12 as described above and a second coil with a first coil side 11 and a second coil side 12 are shown, wherein, similar to the first coil, the first coil side 11 and the second coil side 12 each include several conductors 20E-20H positioned one after another in a straight line along the height of the slot 110.

[0060] Reference now Figure 3b In the present invention, when the first coil side 11 and the second coil side 12 of different coils 10a-10n from different phases fall into the same slot 110, the corresponding first coil side 11 or second coil side 12 of the different coils 10a-10n are positioned one above the other along the height of the slot 110, thereby forming a double-layer structure. Figure 3b , this situation is shown for coils 10d and 10n, wherein the first coil side 11 of coil 10d and the second coil side 12 of coil 10n fall into the same slot 110, wherein coil side 11 is positioned closest to the bottom 111 of the slot 110 and coil side 12 is positioned closest to the opening 112.

[0061] The order of connecting the coils according to the present invention provides a double-layer distributed winding in the stator armature 100. Figure 3b It can be seen that this results in a very compact end winding 30 .

[0062] Referring now to the details showing the appearance of the coil 10 according to the present invention Figure 4a-4d .

[0063] exist Figure 4a , a 3D view of the coil 10 is shown, Figure 4b The coil 10 is shown in a tangential view, Figure 4c An axial view is shown from the end winding 30 side, and Figure 4d The coil 10 according to the invention is shown from a top view.

[0064] Referring now to the 3D view of the end winding region 30 presented in FIG. Figure 5 , thereby showing the compact structure of the end winding 30 achieved by the flexibility of the end winding made of Litz wire. It should be noted that the solution without hairpin end windings or twists in the end winding area 30 is only possible due to the flexibility of the Litz wire.

[0065] Change Example

[0066] This type of winding may be applied in AC machines such as, for example, synchronous and induction machines.

[0067] In some embodiments, there may be a wedge covering the opening of the open slot. The wedge may be non-magnetic, semi-magnetic, or magnetic.

[0068] The number of conductors in the coil side can be any number - two or more. For example, when the number of conductors in the coil side is 3, the transposition is performed as follows:

[0069] a first conductor positioned closest to the slot bottom in the first coil side is transposed along the coil height in the end winding region to a position closest to the slot opening in the second coil side,

[0070] the second conductor positioned closest to the slot opening in the first coil side is transposed along the coil height in the end winding region to a position closest to the slot bottom in the second coil side,

[0071] At the same time, the third conductor located between the first conductor and the second conductor is not transposed.

[0072] For other numbers of conductors, the transposition is performed according to the same principle.

[0073] Reference numerals

[0074] 10 - Coil

[0075] 10a-10n - Coil #1 to Coil #n

[0076] 11-First coil side

[0077] 12-Second coil side

[0078] 20A - Conductor #1 in Coil #1

[0079] 20B - Conductor #2 in Coil #1

[0080] 20C - Conductor #3 in Coil #1

[0081] 20D - Conductor #4 in Coil #1

[0082] 20E - Conductor #1 in Coil #2

[0083] 20F - Conductor #2 in Coil #2

[0084] 20G - Conductor #3 in Coil #2

[0085] 20H - Conductor #4 in Coil #2

[0086] 30 - End winding

[0087] 100-Stator armature

[0088] 110 - Open slots in stator armature

[0089] 111 - bottom of slot 110

[0090] 112 - opening of slot 110

Claims

1. An electric machine, comprising a stator formed by a stator armature (100), wherein the stator armature (100) is provided with a plurality of slots (110) extending in a transverse direction of the stator armature (100), in, The slot (110) is open and a coil (10, 10a-n) is arranged in the slot (110), the coil (10, 10a-n) comprising a first coil side (11) and a second coil side (12), the first coil side (11) and the second coil side (12) comprising a plurality of conductors positioned one behind the other in a straight line along the height of the slot (110), wherein an end winding region (30) connects the first coil side (11) and the second coil side (12) outside the slot (110), wherein the first coil side (11) and the second coil side (12) of each coil (10, 10a-n) are arranged in separate non-adjacent slots (110), wherein a first coil side (11) of each coil (10, 10a-n) is arranged in one of the slots (110) closer to a bottom (111) of the slot (110), and a second coil side (12) of each coil (10, 10a-n) is arranged in a non-adjacent slot (110) closer to an opening (112) of the slot (110), and wherein part or all of the conductors are transposed at the end winding region (30) of each coil (10, 10a-n) so as to change the vertical position of the part or all of the conductors in the first coil side and the second coil side, wherein the conductors of each coil (10, 10a-n) are Litz wire conductors, It is characterized in that The end winding portions of the conductors are not twisted or rotated around the axis of the conductors, and wherein the end winding portion of the first conductor in the end winding area (30) is arranged axially closest to the effective length section of the coil (10, 10a-n), and wherein the end winding portions of the remaining conductors of each coil (10, 10a-n) are sequentially arranged beside the end winding portion of the first conductor, but axially outside the effective length section of the coil (10, 10a-n) and farther from the effective length section of the coil (10, 10a-n) than the first conductor.

2. The motor according to claim 1, wherein: When the first coil side and the second coil side of different coils (10, 10a-n) from different phases fall into the same slot (110), the first coil side and the second coil side are positioned one above the other along the slot (110) height, thereby forming a double-layer structure.

3. The motor according to claim 1, wherein: The conductor is preformed to have a substantially square or rectangular form.

4. The motor according to claim 1, wherein: The opening (112) of the open slot (110) is covered with a magnetic, semi-magnetic or non-magnetic slot wedge.

5. The motor according to claim 1, wherein: The number of conductors in each of the first coil side and the second coil side is four, and A first conductor closest to a slot bottom (111) in a first coil side (11) is transposed along the coil (10, 10a-n) height in an end winding region (30) to be closest to a slot opening (112) in a second coil side (12), A second conductor next closest to the slot bottom (111) in the first coil side (11) is transposed along the coil (10, 10a-n) height in the end winding region (30) to next closest to the slot opening (112) in the second coil side (12), A third conductor next closest to the slot opening (112) in the first coil side (11) is transposed along the coil (10, 10a-n) height in the end winding region (30) to next closest to the slot bottom (111) in the second coil side (12), A fourth conductor in a slot opening (112) closest to the first coil side (11) is transposed along the coil (10, 10a-n) height in the end winding region (30) to be closest to a slot bottom (111) in the second coil side (12).

6. The motor according to claim 1, wherein: The number of conductors in each of the first coil side and the second coil side is three, and A first conductor positioned closest to a slot bottom (111) in a first coil side (11) is transposed along the coil (10, 10a-n) height in an end winding region (30) to a position closest to a slot opening (112) in a second coil side (12), a second conductor positioned closest to a slot opening (112) in the first coil side (11) is transposed along the coil (10, 10a-n) height in the end winding region (30) to a position closest to a slot bottom (111) in the second coil side (12), At the same time, the third conductor located between the first conductor and the second conductor is not transposed.

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