CH715403A2 - Winding for electric machines. - Google Patents

Abstract

The subject of the invention is a rotary electric machine comprising a rotor and a stator separated by an air gap; said stator comprising a winding with a plurality of coils (40), each coil comprising at least one electrically conductive wire (400), in which at least one of said coils (40) has a cross section with a thickness (b) measured radially from the internal side (401) of the coil to the external side (402) of the coil, and a width (a) measured substantially perpendicular to the length of the wire and substantially parallel to the external side (402) of the coil (40), wherein said thickness (b) is variable along the coil and wherein said width (a) is variable along the coil.

Description

Field of the invention

The present invention relates to an electric machine, such as an electric motor or generator, with an improved winding.

Description of the prior art

[0002] Electric machines are defined as devices capable of transforming energy from one form to another when at least one of them is electric. In particular, when electrical energy is transformed into mechanical energy, electrical machines are classified as rotary or linear motors. And when mechanical energy is transformed into electrical energy, electrical machines are classified as rotary or linear generators. In this document, the term electric machines designates both motors and generators, rotary or linear.

[0003] Motors and generators vary from a few millimeters in diameter to several meters in length. The length of linear motors varies from a few millimeters to several kilometers, for example in the case of rail transport.

[0004] In motors and generators, a form of transient energy is involved: magnetic energy. Magnetic fluxes in machines are due to electric currents flowing in the windings. Windings are therefore an essential component of electrical machines.

[0005] Electrical machines consist of a fixed part, the stator, and a moving part, the rotor. The air space between a stator and a rotor is an air gap. The windings can be placed on the stator and / or the rotor, or between the two. They consist of one or more coils. The coils consist of turns connected in series. The material used for the turns has low electrical resistivity to reduce Joule losses.

[0006] According to an example of an electric motor, brushless direct current motors 1 are already known. As shown in the sectional view of FIG. 1, they generally include a rotor 2 with a shaft 20 and a housing 21 to protect the permanent magnet 22 of the rotor from corrosion and / or to support mechanical forces due to rotation. The rotor is assumed to be axially centered in a stator 6. The stator has a winding 4 in the form of a hollow cylinder and comprising a plurality of coils 40. Applying an alternating current to the coils 40 creates a rotating magnetic field to rotate. the rotor. The present invention relates to an improvement in the windings of these motors and other electrical machines.

[0007] US 7,893,587 B2 (Electromag et al.) Describes such a brushless direct current motor where the stator winding is in the form of a hollow cylinder and composed of a plurality of single rhombic flat wire coils.

[0008] FIG. 2 illustrates an example of winding 4 for the stator of a three-phase motor with 6 coils 40 without slot. Slitless windings, also called self-supporting windings, are commonly used in small high and very high speed brushless DC electric machines. Unlike slit windings which are forced to follow the direction of the slits, slit windings can be arranged freely in the air gap.

[0009] Each of the 6 coils of this example has a rhombic shape with two outer corners 41 on the lateral sides 43 of the winding, and two inner corners 42 between these sides. A "wedge" designates a part of the spool where the wire changes direction; corners can be rounded. The coils are entangled and overlap in two layers.

The 2 coils per phase can be connected in series or in parallel and the 3 phases connected in delta or star.

[0011] A 4-pole rotor is also possible.

[0012] Despite many advantages, the winding of FIG. 2 has some limitations. The fill factor is limited because the turns have a constant width and thickness and therefore the spaces between the coils cannot be filled which would increase the fill factor of the copper and therefore the torque produced. In particular, there is a gap between the inner corners of successive coils, in the central region where the radial induction field created by the magnet is maximum. The distance between the coils is given by the bending radius of the coil.

[0013] In order to reduce this difference, it has been suggested to use a winding for a rotating electrical machine comprising conductors on a printed circuit (PCB) of variable width. WO 2014/207 174 A3 (Catholic University of Louvain) describes such a winding where the shape of the conductors on the PCB has a variable width in order to increase performance.

Brief summary of the invention

An object of the present invention is to provide an electric machine with a new winding which increases performance, and more particularly the motor constant connecting the torque created to the copper losses.

[0015] According to one aspect of the invention, these goals are achieved by changing the width and thickness of the coils.

[0016] The use of a coil of varying width and thickness gives more freedom to optimize the magnetic field created by the coils or the back-electromotive force induced in the coils.

[0017] According to the invention, these objects are also achieved by means of a rotary electric machine comprising a rotor and a stator separated by an air gap; said stator comprising a winding with a plurality of coils, each coil comprising at least one electrically conductive wire, wherein at least one of said spools has a cross section with a thickness measured radially from the inner side of the spool to the outer side of the spool, and a width measured substantially perpendicular to the length of the yarn and substantially parallel to the outer side of the spool. coil, wherein said thickness is variable along the coil and wherein said width (a) is variable along the coil.

Consequently, the shape of the coils can vary in the 3 dimensions; both the width and the thickness of the coils can vary at the same time. This results in greater flexibility in designing a coil with an efficient shape.

The area of the cross section of the coil can be substantially constant.

The area of the cross section of the coil can be substantially variable.

It can be demonstrated, using Laplace forces, that the torque produced by a motor is maximum when the current flows in the axial direction. The same goes for the electromotive force induced in a generator. In other words, the wire should be straight in the axial direction.

[0022] The outer corners of the coil on the lateral sides of the coil are called "coil terminations". Winding terminations are necessary to close electrical circuits, but do not contribute to the useful magnetic potential. Indeed, they are generally located where the magnetic field at the air gap is weakest. Therefore, the contribution of the winding terminations to the torque produced (for a motor) or to the back-electromotive force (against EMF, for a generator) is low. In addition, the winding terminations increase the resistance of the coil.

[0023] In order to avoid or limit these problems, in one embodiment, the winding has two side faces. Each coil has a shape corresponding substantially to the projection of a polygon, for example an octagon, against a cylinder, in which said shape comprises two outer corners, comprising an outer corner at each of the lateral sides of said stator, and two inner corners between said lateral sides. The thickness of the coil is greater at the outside corners than at the inside corners.

[0024] This increase in thickness reduces the resistance of the coil at the winding terminations.

[0025] In one embodiment, the width of the coil is smaller at the exterior angles than at the interior angles. This reduces the amount of the magnetic field produced at the winding terminations, whose torque contribution is limited anyway.

[0026] In one embodiment, the shape of each coil substantially corresponds to the projection of an octagon against a virtual cylinder. As a result, the portion of the wire between the two lateral sides of the winding is straight in the axial direction. This straight portion preferably represents at least 20% of the dimension of the winding between the two lateral sides, for example about 30%.

The wire composing the coils can be of rectangular section, which allows to obtain a better fill factor than a winding of circular section and better thermal conductivity.

[0028] The coils are preferably entangled and superimposed on two layers.

[0029] The winding can be used for a machine with a structure without a slot.

[0030] The winding can be used for a machine with a slit structure.

The coils and / or son of variable thickness can be manufactured by variable speed extrusion; 3D printing; Selective Laser Melting (SLM), Wire Cutting Electric Discharge (EDM) Machining, etc.

[0032] The coils preferably overlap in a nested manner, so as to form a hollow cylinder.

[0033] In one embodiment, the width of said wire varies along the length of said wire.

[0034] In one embodiment, the thickness of said wire varies along the length of said wire.

[0035] In one embodiment, the proportions and / or the shape of the cross section of said wire vary along the length of said wire.

The machine can be a brushless and slotless synchronous DC machine

The wire can be extruded or 3D printed.

Brief description of the drawings

[0038] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which: FIG. 1 illustrates a cross section of a brushless direct current machine containing a slitless winding. Fig. 2 illustrates a three-phase winding with 6 coils, without slot, manufactured with coils of constant section. Fig. 3 illustrates a three-phase, 6-coil, slotless winding fabricated with coils of non-constant width and constant thickness in cross-section. Figs. 4A - 4B show a three-phase, 6-coil, slotless winding manufactured with coils of non-constant width and thickness in cross-section. Fig. 5 illustrates a portion of a coil. Fig. 6 illustrates a portion of a wire. Figs. 7A and 7B illustrate a comparison of two concentrated windings with a constant coil section (7A) and a non-constant coil section (7B) and with B <A and E> D

Detailed description of possible embodiments of the invention

There are several ways to compare motors and generators. However, one of the most popular used by engine designers and manufacturers is the motor constant defined as follows

where Tem is the electromagnetic torque produced by the motor, Pcoils are the power losses of the coil, R is the phase resistance, I is the phase current and KT is the torque constant. It is given for a certain temperature and without saturation in the magnetic circuit. Motor constant is also used to compare generators because the back electromotive force EFM is proportional to the torque constant.

[0040] The motor constant expresses the torque efficiency, that is, it relates the torque produced by the motor and the corresponding losses in the winding to produce it. This ratio does not depend on the current and the number of turns (for a constant fill factor). It is also independent of the winding configuration (connected in delta or star). In addition, the knowledge acquired from this unique constant allows us to optimize the resistance of the winding and therefore the shape of the winding.

[0041] Given the winding of FIG. 2, the motor constant Km can be expressed in terms of the torque constant of a coil KT ́ and the resistance R ́ of a coil and is

[0042] It does not depend on the configuration of the winding (in series or in parallel and connected in delta or star).

[0043] The coil torque produced by the interaction of the magnetic flux density of the permanent magnet and the coil current can be calculated using Laplace forces. Only the current flowing in the axial direction and the radial induction field contribute to a torque.

[0044] In order to have an accurate evaluation of the torque and to consider the final effect of the rotor during the optimization process, the radial induction field on the planes of the upper and lower layers is extracted by the EMF electromotive force. Therefore, each layer winding is individually optimized to achieve better overall performance.

[0045] By placing the coil on the interpolar (axial) axis, the maximum torque is obtained. Thus, assuming the currents are sinusoidal, the torque constant KT ́ for a coil can be evaluated in cylindrical coordinates by

where Bδrest the radial induction field. Likewise, the resistance R 'of a coil is calculated by integration along the wire, taking into account possible variations in the cross section.

This leads to:

where ρ is the resistivity of the coil and w and h are the width and thickness of the wire, respectively. The torque constant KT 'depends on the induction field at the air gap, which depends on the magnet and the magnetic circuit, but also on the path of the coil. The resistance of the coil R ́ depends only on the material, the length and the section of the coil. Therefore, motor constant is a very suitable choice for winding optimization.

[0047] Instead of optimizing each turn of the coil, only the outermost turn is considered a variable. This results in a decrease in the number of optimization variables, a reduction in the complexity of the stresses between the wires (for example, no overlap) and a shorter computation time.

[0048] As we have already stated, one problem with 2-layer entangled windings with a constant wire width is that they cannot always fill all the available space in the width direction; there remains a space between the interior corners of the successive coils.

[0049] In order to solve or alleviate this problem, a winding is therefore generated with a non-constant wire width to fill the available space.

[0050] The result can be seen in FIG. 3. Increasing the width of the wire decreased the resistance of the spool by 7.6% compared to a winding generated with a wire having a constant width, but the torque constant of a spool also decreased slightly. This is because the coils take up additional space where the radial induction field is weaker, especially at the winding terminations (outside angles). Finally, the motor constant is increased by 2.6% compared to a similar motor optimized with a constant width wire.

[0051] As we have already mentioned, the winding terminations produce virtually no useful torque (the radial induction field is very weak at their location) while they increase the resistance of the coil. Thus, according to one aspect of the invention, the width of the winding terminations is reduced in the axial direction.

[0052] This reduction in thickness makes it possible to reduce the length of the winding terminations. Since winding terminations are shortened, the gain on axial length is reported to extend the central part of the spool. We thus obtain the non-trivial octagon-shaped winding of fig. 4A, 4B, comprising a straight axial portion 45 between the two lateral sides 43.

[0053] The resistance of a coil is increased but, on the other hand, the torque constant of a coil is increased even more significantly. As for the motor constant, the increase is a third. This shows that shortening the winding terminations also increases the fill factor at the location of the winding terminations.

The shape of the coils and / or the shape of the wire can vary in the 3 dimensions; both the width and the thickness of the coils can vary at the same time.

[0055] The thickness of the wire of the winding terminations can be increased to compensate for the reduction in its width. For example, the thickness of the wire at the outer corners (winding terminations) has been doubled compared to the thickness at the inner corners. Therefore, the torque constant remains the same but the resistance decreases, which increases the motor constant even more.

[0056] FIG. 5 shows a portion of a spool 40, including a cross section 44. The spool comprises a plurality of turns of the wire 400. The width of the spool is indicated by the reference letter a while the thickness of the spool is. indicated by the reference letter b.

The area, and / or the shape, and / or the proportion of the cross section 44 varies between the inner corners 42 and the outer corners 41 of the coil. This variation can be achieved in different ways. In one example, this variation is achieved by varying the area, and / or the shape, and / or the proportion of the cross section 403 of the wire 400 (Fig. 6) between the inside corners and the outside corners. In another example, this variation is obtained by a different arrangement of the different portions of the wire at the inside corners and at the outside corners; for example, the cross section 44 can be obtained with a matrix of wire portions having a different number of rows and columns at the inner corners compared to the outer corners, the number of portions remaining the same. It is also possible to vary both the area, the shape and / or the proportion of the different portions of the wire, as well as their arrangement between the outside and inside corners.

[0058] The non-constant section wires can be manufactured by extruding a metal wire at variable speed and / or by additive manufacturing methods.

[0059] Improved windings with coils and / or wires of varying width and thickness can also be used in split parts of electrical machines.

[0060] Concentrated windings are defined as windings around salient poles or windings in which the sides of the coil occupy only one slot 60 per pole. They can be placed on both stator 6 and rotor. Fig. 7 shows the difference between a constant section and a non-constant section of a winding concentrated around a tooth 61. In both cases, the section of the coil 40 is identical and constant (width A and thickness D) in the slots. of the stator 60. The winding terminations 41 are offset from the stator surface by a length of C. Only one side of the winding terminations and only the outer dimension of a single coil 40 are shown.

[0061] In FIG. 7A, the section of winding terminations of 41 remains unchanged. But in the case of fig. 7B, the cross-sectional area, or their shape / proportions, changes at the windings 41 terminations. The width becomes B with B <A and the thickness becomes E with E> D. Hence, either the axial length of the stator can be increased, resulting in better torque or constant back EMF; or the offset of the C winding terminations can be reduced, reducing the resistance of the coil and increasing the power density (the volume of the machine decreases). The foregoing considerations also apply to slot rotors.

[0062] In the event that it is not possible to increase the thickness of the coil at the location of the winding terminations, one can also consider changing only the width of the coil. On the one hand, the resistance of the coil would increase, but on the other hand, the torque or the constant of the counter-electromotive force would increase.

[0063] Improved windings with coils and / or wires of varying width and thickness can also be used in linear motors or generators.

Claims (10)

1. A rotary electric machine (1) comprising a rotor (2) and a stator (4, 6) separated by an air gap (3); said stator (4, 6) comprising a winding (4) with a plurality of coils (40), each coil comprising at least one electrically conductive wire (400), wherein at least one of said coils (40) has a cross section with a thickness (b) measured radially from the inner side (401) of the coil to the outer side (402) of the coil, and a width (a) measured substantially perpendicular to the length of the wire and substantially parallel to the outer side (402) of the coil (40), wherein said thickness (b) is variable along the coil and wherein said width (a) is variable along the coil. 2. The machine according to claim 1, wherein the cross section (403) of said wire (400) varies along the length of said wire. 3. The machine according to claim 1 or 2, wherein the surface of the cross section (44) of said coil is substantially constant. 4. The machine according to one of claims 1 to 3, in which said winding (4) comprises two lateral sides (43), in which each coil (40) has a shape corresponding substantially to the projection of a polygon against a cylinder, wherein said shape comprises two outer corners (41), comprising an outer corner on each of the lateral sides (43) of said stator, and two inner corners (42) between said lateral sides, and wherein the thickness (b) of said coil (40) is equal to or greater at the outside corners (41) than at the inside corners (42). 5. The machine according to claim 4, wherein the width (a) of said coil is less than the outer corners (41) than the inner corners (42). 6. The machine according to one of claims 1 to 5, wherein said coils (40) overlap in a nested manner, to form a hollow cylinder. 7. The machine according to one of claims 1 to 6, wherein said wire (400) has a rectangular section. 8. The machine according to one of claims 1 to 7, wherein the width (c) and / or the thickness and / or the proportions and / or the shape of the cross section of said wire (400) varies (s) along the length of said wire. 9. The machine according to claim 8, wherein the surface of said wire (400) is substantially constant over the length of said wire. 10. The machine according to one of claims 1 to 9, said film (400) or said reel being printed in 3D.